THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID

THE PHYSIOLOGY^*-

OF THE

DOMESTIC ANIMALS

A TEXT-BOOK FOR VETERINARY AND MEDICAL STUDENTS
AND PRACTITIONERS.

BY

ROBERT MEADE SMITH, A.M., M.D.,

PROFESSOR OF COMPARATIVE PHYSIOLOGY IN THE UNIVERSITY OF PENNSYLVANIA

FELLOW OF THE - COLLEGE OF PHYSICIANS AND . ACADEMY OF THE

NATURAL SCIENCES, PHILADELPHIA; OF THE AMERICAN

PHYSIOLOGICAL SOCIETY; OF THE AMERICAN SOCIETY

OF NATURALISTS; ASSOCIE ETRANGER DE LA

SOCIETE FRANCAISE D' HYGIENE, ETC.

WITH OVER 400 ILLUSTRATIONS.

PHILADELPHIA AND LONDON :

F. A. DAVIS, PUBLISHER

1890.

Entered according to Act of Congress, in the year 1889, by

F. A. DAVIS,

In the Office of the Librarian of Congress, at Washington, D. C., U. S.
All rights reserved.

Philadelphia:

The Medical Bulletin Printing House,
1231 Filbert Street.

TO MY FRIEND AND TEACHER,

CARL LUDWIG,

IN

HUMBLE RECOGNITION OF THE MANY FAVORS
CONFERRED ON THE AUTHOR.

M351840

PREFACE.

IN lecturing in the Veterinary Department of the Univer-
sity of Pennsylvania the author has found it a serious disad-
vantage that the students are compelled to rely solely on
the notes that they may be able to take during the lectures.
While French students have access to the encyclopaedic work
of Colin, and those familiar with the German language to the
admirable works of Schmidt-Miilheim, Bruckmiiller, Munk,
Ellenberger, Ghirlt, Thanhoffer, Miiller, and others, English-
speaking students have absolutely no work to which they
can turn to obtain any application of the laws of physiology
to* the functions of the domestic animals. Commenced
originally as outline notes for the author's own use in
lecturing, this work has been published at the request of his
students, in the hope that it may supply them with an
exponent of the laws of modern physiology applied, as far
as possible, to the functions of the domestic animals, and
that a recognition of its shortcomings may stimulate inves-
tigation of this much-neglected branch of physiology.

It is surprising, in view of the ceaseless activity of
physiological students throughout all the world, that more
attention has not been devoted to the application of improved
methods of research to the study of the functions of animals
so important in the domestic economy. Unfortunately,
investigators in this domain may almost be counted on the
fingers, and the field which is yet untouched is almost
unbounded. The author, therefore, has been compelled to
assume that in many cases the laws of the physiology of
man, which, to be sure, have been deduced from experiments

(v)

vi PREFACE.

on animals, are applicable to the vital processes of the
domestic animals.

Modern physiology rests on the application through
experimental research of the laws of physics and chemistry.
The fundamental principles of these sciences in their relation
to biology have been, therefore, discussed somewhat at
length. Experience has taught that a comprehension of the
laws of life in the higher mammals is best attained after a
familiarization with the vital operation of lower forms. The
first part of this book, therefore, deals with the general laws
of life, while in the second part these principles are applied
to the study of the vital operations in the domestic animals,
the study of each function being introduced by a sketch of
the mode of development of the mechanism by which that
function, in passing from lower to higher forms, is accom-
plished.

As far as possible the author has acknowledged in the
text his indebtedness to various authorities for the matter
or manner of his subject, though references to publications,
as tending to confuse the student, have been omitted.

For illustrations the author is indebted to the liberality
of the publisher, Mr. Davis, and to Messrs. Blakiston and
H. C. Lea & Co., of Philadelphia ; Appleton, Win. Wood & Co.,
and Macmillan, of New York; Ferdinand Enke, Stuttgart;
Engelmann and F. C. W. Vogel, Leipsic ; Paul Parey, Berlin ;
W. Braumiiller, Vienna; Carl Winter, Heidelberg; Hachette &
Cie, Bailliere & Fils, Asselin & Cie, Paris; Simpkin, Marshall
& Co., London; Moritz Perles, Vienna, and Hirschwald, Berlin.

ROBERT MEADE SMITH.

PHILADELPHIA:

332 SOUTH TWENTY-FIRST STREET,
January 3, 1889.

TABLE OF CONTENTS.

PAGK

INTRODUCTION, 1

PART I.

GENERAL PHYSIOLOGY.
THE PHYSIOLOGY OF ANIMAL CELLS.

SECTION I.

THE STRUCTURE OF ORGANIZED BODIES.

I. THE GENERAL PROPERTIES OF CELLS, . . . . .12

II. THE ORIGIN OF CELLS, . .14

III. THE MODIFICATION IN THE FORM OF CELLS, .... 26
IT. THE DEVELOPMENT OF TISSUES AND ORGANS, . . , 31

SECTION II.

CELLULAR PHYSICS.

I. THE PHYSICAL PROCESSES IN CELLS, . . . ... 37

1. Cohesion, 38 ; 2. Adhesion, 40 ; 3. Capillarity, 40 ; 4. Solution, 43 ;
5. Imbibition, 44 ; 6. Filtration, 48 ; 7. Diffusion of Liquids, 49 ;
8. Osmosis, 51; 9. Diffusion of Gases, 56 ; 10. Absorption of Gases,
58.

II. THE PHYSICAL PROPERTIES OF THE TISSUES, . . . .61

1. Cohesion, 62 ; 2. Elasticity, 65 ; 3. Optical Characteristics, 68 ; 4.
Electrical Phenomena, 70.

III. MECHANICAL MOVEMENTS IN CELLS, .70

1. Motion Produced by Imbibition in Cells, 70 ; 2. Protoplasmic Move-
ments, 72 ; (1) Movements in Protoplasmic Contents of Cells,
73 ; (2) Ciliary Movement, 77 ; (3) Movement in Specialized
Contractile Tissues, 81.

GENERAL CONDITIONS GOVERNING PROTOPLASMIC MOVEMENT, . » 82
1. Temperature, 82; 2. Degree of Imbibition, 82; 3. The Supply of
Oxygen, 83; 4. Various Chemical and Physical Agents, 84.

(vii)

Vlll TABLE OF CONTENTS,

SECTION III.

CELLULAK CHEMISTRY.

I- PAGE

THE CHEMICAL CONSTITUENTS OF ORGANIZED BODIES, ... 85

A. NITROGENOUS ORGANIC CEL£-CONSTITUENTS — PROTEIDS AND THEIR

DERIVATIVES, 88

Class I. Albumens, 92; (1) Serum-Albumen, 92; (2) Egg Albumen,
93; (3) Vegetable Albumens, 93.

Class II. Globulins, 96 ; (1) Vitellin, 97; (2) Myosin, 97 ; (3) Para-
globulin, 97 ; (4) Fibrinogen, 97; (5) Globulin or Crystallin, 97.

Class III. Fibrins, 98.

Class IV. Derived Albuminates, 98 ; (1) Acid Albumen, 98; (2)
Alkali Albumen, 101.

Class V. Coagulated Proteids, 102.

Class VI. Amyloid Substance or Lardacein, 102.

Class VII. Peptones, 103.

ALBUMINOIDS, . . . . . 104

1. Mucin, 104; 2. Collagenous Albuminoids, 105; (a) Collagen, 106;
(b) Gelatin, 106 ; (c) Chondrogen, 107 ; (d) Chondrin, 107 ; 3.
Elastin, 108 ; 4. Keratin, 109.

DECOMPOSITION OF ALBUMINOUS BODIES, . . *" . . .109
FERMENTS, '- V ' • • • • HO

B. NON-NlTROGENOUS ORGANIC CELL-CONSTITUENTS, . . . . 112

I. CARBOHYDRATES, - . .. . .112

(a) Starches, 112; (1) Starch, 113; (2) Cellulose, 115; (3) Dextrin,
116 ; (4) Glycogen, 116 ; (5) Inulin, 116.

(5) Glucoses, 117; (1) Grape-Sugar, 117; (2) Laevulose, 118; (3)
Inosite, 118.

(c) Saccharoses, 119 ; (1) Cane-Sugar, 119 ; (2) Maltose, 120; (3) Lac-
tose, 120 ; (4) Arabin, 120.

II. HYDROCARBONS OR FATS, 120

C. INORGANIC CELL-CONSTITUENTS, 123

1. Water, 124 ; 2. Sodium Chloride, 128 ; 3. Potassium Chloride, 129 ;
4. Sodium and Potassium Carbonates, 129; 5. Calcium Carbonate,
130; 6. Magnesium Carbonate, 130 ; 7. Alkaline Phosphates, 130 ;
8. Calcium Phosphate, 133 ; 9. Magnesium Phosphate, 134 ; 10.
Sodium and Potassium Sulphates, 135 ; 11. Hydrochloric Acid,
135.

II.

THE CHEMICAL PROCESSES IN CELLS, 136

1. The Vegetable Cell, 137 ; 2. The Animal Cell, 142 ; 3. Fermenta-
tions, 145 ; 4. The Consumption and Development of Force in
Cells, 147.

TABLE OF CONTENTS. IX

PART II.
SPECIAL PHYSIOLOGY.

BOOK FIRST.
THE NUTRITIVE FUNCTIONS.

SECTION I.

FOODS. PAGE

I. VEGETABLE FOODS, 161

1, The Cereals, 163 ; 2. The Leguminous Plants, 173 ; 3. Bulbs and
Roots, 174 ; 4. Grasses, 175.

II. ANIMAL FOODS, ... V 188

1. Milk, 188 ; 2. Meat, 188.

III. INORGANIC FOODS, . ..191

1. Water, 191 ; 2. Nutritive Salts, 192.

IV. THE DIET OF ANIMALS, *-./-, 193

SECTION II.

DIGESTION.
I. GENERAL CHARACTERISTICS OP THE DIGESTIVE APPARATUS, . 203

IT. PREHENSION OF FOOD, • . • .226

1. Prehension of Solids, 226 ; 2. Prehension of Liquids, 236.

III. MASTICATION, . 238

1. Movements of the Jaws, 241 ; 2. Action of the Teeth in Mastica-
tion, 245 ; 3. Determination of Age by the Teeth, 255 ; 4. Action
of Tongue, Lips, and Cheeks, 264.

IV. DIGESTION IN THE MOUTH, . . . .."•.. . , . 268

The Salivary Secretion, 268 ; 1. The Parotid Secretion, 274; 2. The
Submaxillary Secretion, 279 ; 3. The Sublingual Secretion, 283 ;
4. General Characters of the Salivary Secretion, 284; 5. The
Quantity of Saliva, 286 ; 6. The Physiological Role of the Saliva,
287 ; 7. The Mechanism of Salivary Secretion, 293.

!»•«••_»(

V. DEGLUTITION, 307

VI. RUMINATION, . . . 316

VII. VOMITING, ^ 331

X TABLE OF CONTENTS.

PAGE

VIII. GASTRIC DIGESTION, 337

1. Chemistry of the Gastric Juice, 342 ; (a} Pepsin, 346 ; (5) Milk-
Curdling Ferment, 347 ; (c) The Acid of Gastric Juice, 349 ; 2.
The Action of Gastric Juice on the Food, 351 ; 3. The Secretion of
Gastric Juice, 356 ; 4. Gastric Digestion in Carnivora, 360 ; 5.
Gastric Digestion in Omnivora, 363 ; 6. Gastric Digestion in Soli-
pecles, 368 ; 7. Gastric Digestion in Ruminants, 374 ; 8. Gastric
Digestion in Birds, 379,

IX. DIGESTION IN THE SMALL INTESTINE, 382

I. Bile, 382 ; 1. The Chemical Characteristics of the Bile, 383 ; (a)

Mucin, 384; (6) The Bile Acids, 384; (c) The Coloring Matters of
the Bile, 387 ; (d) Cholesterin, 389 ; O) The Inorganic Constitu-
ents of the Bile, 390 ; 2. The Secretion of the Bile, 391 ; 3. The
Physiological Action of the Bile, 393.

II. The Pancreatic Secretion, 396 ; 1. The Chemical Composition of

the Pancreatic Juice, 402; The Pancreatic Ferments, 404 ; 2. The
Action of the Pancreatic Juice on Food-Stuffs, 405 ; (a) Action
on Carbohydrates, 406 ; (&) Action on Fats, 406 ; (c) Action on
Proteids, 408 ; 3. The Secretion of Pancreatic Juice, 412.

III. The Intestinal Juice, 416.

IV. Fermentative Processes in the Small Intestine, 418.
V. Intestinal Digestion in Different Animals, 419.

X. DIGESTION IN THE LARGE INTESTINE, . . , i .. 423

1. The Functions of the Caecum, 423 ; 2. The Functions of the
Colon, 429.

XI. THE COMPARATIVE DIGESTIBILITY OF DIFFERENT FOOD-STUFFS, 432
XII. THE COMPOSITION OF FAECES, . . , . . . . 445

XIII. THE MOVEMENTS OF THE INTESTINES, ..... 448

XIV. DEFECATION, . .'451

SECTION III.
ABSORPTION, . 453

1. Venous Absorption, 453 ; 2. Absorption by the Lymphatics, 456.

SECTION IV.
THE CHYLE, . ' 459

SECTION V.
THE LYMPH, .....;. 463

TABLE OF CONTENTS. JO.

SECTION VI. PAGE

THE BLOOD, .• 469

1. The Red Blood-Corpuscles, 471 ; 2. The White Blood-Corpuscles,
479 ; 3. Blood-Plasma and Blood Coagulation, 483 ; 4. The Blood-
Serum, 489.

SECTION VII.

THE CIRCULATION OF THE BLOOD, 491

1. General View of the Organs of Circulation, 491 ; 2. The Action
of the Heart, 499 ; 3. The Hydraulic Principles of the Circula-
tion, 516 ; 4. The Circulation in the Arteries, 523 ; Blood Pres-
sure, 525 ; Velocity of the Blood, 530 ; The Pulse, 533 ; 5. The
Circulation in the Capillaries, 536 ; 6. The Circulation in the
Veins, 539 ; 7. The Influence of the Nervous System on the
Heart, 540 ; The Inhibitory Nerves of the Heart, 549 ; The Ac-
celerator Nerves of the Heart, 551 ; 8. The Influence of the
Nervous System on the Arteries, 552.

SECTION VIII.

RESPIRATION, . ... 561

1. General View of the Organs of Respiration, 562 ;. 2. The Mechani-
cal Processes of Respiration, 574 ; 3. The Rhythm of Respiration,
579; 4. The Chemical Phenomena of Respiration,. 587 ; 5. The
Nervous Mechanism of Respiration, 598 ; 6. The Influence of
Respiration on the Circulation, 605.

SECTION IX.
THE MAMMARY SECRETION, 609

1. The Physical and Chemical Properties of Milk, 610 ; 2. Casein and
Milk Coagulation, 614 ; 3. Milk-Sugar, 616 ; 4. Fat and Cream,
617 ; 5. The Inorganic Constituents of Milk, 619 ; 6. Variations
in the Quantity and Composition of Milk, 619 ; 7. The Secretion
of Milk, 624 ; 8. Milk Analysis and Inspection, 631.

SECTION X.
THE RENAL SECRETION, x 635

1. The Physical and Chemical Properties of Urine, 635 ; 2. The
Mechanism of Renal Secretion, 640 ; 3. The Mechanism of Mic-
turition, 648.

SECTION XL
THE CUTANEOUS FUNCTIONS, 651

1. The Sweat Secretion, 652 ; 2. The Sebaceous Secretion of the -Skin,
655 ; 3. Cutaneous Absorption, 656 ; 4. Cutaneous Respiration,
656 ; 5. The Lachrymal Secretion, 658.

Xll TABLE OF CONTENTS.

SECTION XII, PAGE

NUTRITION, 659

I. THE FATE or THE ALBUMINOUS FOOD-CONSTITUENTS, . . 660
II. THE FATE OF THE FATTY FOOD-CONSTITUENTS, . . .664

III. THE FATE OF THE CARBOHYDRATE FOOD-CONSTITUENTS, . . 666

IV. THE STATISTICS OF NUTRITION, . ; . . . . .672

1. Tissue Changes in Starvation, 674 ; 2. The Nutritive Processes in
Feeding, 680; (a) Feeding with Meat, 680; (6) Feeding with
Fat, 682 ; (c) Feeding with Carbohydrates, 683.

V. THE FOOD REQUIRED BY THE HERBIVORA UNDER DIFFERENT

CONDITIONS, . . . . ••;• . .-.•-. . ... 684
VI. HUNGER AND THIRST, . . . * . ' . . . 692

SECTION XIII.
ANIMAL HEAT, . . . . ". ^ - - ~ .- ^ ^ ^ ^ 693

BOOK SECOND.
THE ANIMAL FUNCTIONS.

SECTION I.
THE PHYSIOLOGY OF MOVEMENT, . . . .. . .701

1. The Contractile Tissues, 701 ; (a) Chemical Composition of Muscle,
704 ; (&) Muscular Irritability, 709 ; (c) The Phenomena of Mus-
cular Contraction, 710 ; (d) The Electrical Phenomena in Muscle,
721 ; 2. The Applications of Muscular Contractility, 722 ; 3. Ani-
mal Locomotion, 731; 4. The Gaits of the Horse, 739 ; (a) The
Walk, 744; (5) The Amble, 746; (c) The Trot, 748; (d) The
Gallop, 749 ; 5. Other Movements in the Horse, 750 ; (a) Rearing,
750 ; (&) Kicking, 753 ; (c) Lying Down and Rising Up, 754 ;
(d) Walking Backward, 754 ; (e) Swimming, 755 ; 6. Special Mus-
cular Mechanisms — The Voice, 757.

SECTION II.

THE PHYSIOLOGY OF THE NERVOUS SYSTEM, . . . . .765

I. THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF NERVOUS

TISSUES, . . 774

II. NERVOUS IRRITABILITY, . . » 776

III. THE ELECTRICAL PHENOMENA IN NERVES, . . . .779

IV. GENERAL PHYSIOLOGY OF THE NERVE-CENTRES, . . . 781
1. Reflex Action, 782 ;• 2. Automatism, 784 ; 3. Inhibition, 785 ; 4.

Augmentation, 785 ; 5. Co-ordination, 785.

TABLE OF CONTENTS. xiii

PAGE

Y. THE FUNCTIONS OF THE SPINAL CORD, 786

(a) The Spinal Cord as a Collection of Nerve-Centres, 789 ; (&) The
Spinal Cord as an Organ of Conduction, 795.

VI. THE FUNCTIONS OF THE BRAIN, 803

1. The Medulla Oblongata, 810 ; 2. The Course of the Fibres of the
Medulla Oblongata, 818 ; 3. The Pons Yarolii, 821 ; 4. The Cere-
bral Peduncles, 821 ; 5. The Corpora Quadrigemina, 822 ; 6. The
Functions of the Basal Ganglia, 822; 7. The Functions of the
Cerebral Lobes, 823 ; 8. The Functions of the Cerebellum, 825.

VII. THE CRANIAL NERVES, 832

VIII. THE SYMPATHETIC NERVOUS SYSTEM, . . . . 835

IX. GENERAL AND SPECIAL SENSIBILITY, . . . . .837

A. THE SENSE OF SMELL, 841

B. THE SENSE OF SIGHT, .846

1. The Dioptric Mechanisms of the Eye, 851; 2. Visual Sensations, 864.

C. THE SENSE OF HEARING, 875

D. THE SENSE OF TASTE, .893

E. THE SENSE OF TOUCH,. . . . . . . . . 897

PART III.

THE REPRODUCTIVE FUNCTIONS, .901

SECTION I.
THE REPRODUCTIVE PROCESSES, 903

1. The Reproductive Tissues of the Female, 908 ; 2. The Reproduc-
tive Tissues of the Male, 913.

INTRODUCTION.

PHYSIOLOGY treats of the functions or actions of living beings.

When these actions or functions occur in a disturbed or irregular
manner, they constitute disease, or abnormal life, and become the subject
of abnormal physiology or pathology. Normal physiology is the basis of
pathology, and a knowledge of the one must precede the intelligent study
of the other: just as an acquaintance with the functions of the com-
ponent parts of a machine must precede the recognition of disordered
movement and the provision of means of repair.

Since the functions of the animal body are resident in the various
tissues and organs of the body, an acquaintance with the forms and
structure of those organs and tissues must precede the study of their
functions. The study of anatomy and histology, or microscopic anat-
omy, must therefore precede the study of physiology.

GENERAL PHYSIOLOGY treats of the functions of organized beings in
an abstract manner, — that which regards the general laws of life, whether
seen in the animal or vegetable world. Although for the purposes of
practical life physiology is divided into several provinces, yet the knowl-
edge of general physiology is essential even to special students, since
the relation between the different forms of life is very close.

VEGETABLE PHYSIOLOGY is concerned solely with the consideration
of the vital actions or functions of plants.

COMPARATIVE PHYSIOLOGY treats of the functions of animals below
man, with a consideration of the means by which different functions are
accomplished by different animal forms.

SPECIAL PHYSIOLOGY is confined to the consideration of the vital
phenomena of a single species, single genus, or it may deal with the
consideration of a special function. In this book special physiology
will refer mainly to the study of the vital phenomena of the domestic
animals.

HUMAN PHYSIOLOGY treats exclusively of the vital phenomena of
man. But, while this branch of physiology is of greater importance to
the physician than the other divisions, in consequence of its relations
to human pathology and therapeutics, it should not be made the exclu-
sive subject of study; for the physiology of man cannot be properly
understood without a previous acquaintance with the vital phenomena of

2 INTRODUCTION.

the lower animals and plants. For the veterinary physician the study
of life in the domestic animals must be of the greatest importance.

Every living body is organized, — that is. composed of instruments
or organs each one of which is destined to fulfill some special office in
the organism called its function, the sum of which functions constitute
the life of the individual. Other bodies met with in nature, and not so
constituted, are called unorganized, or inorganic, e.g., the mineral.

DISTINCTIONS BETWEEN ORGANIZED AND UNORGANIZED BODIES. — Organ-
ized and unorganized bodies have few or no correlative points, but stand
opposed to each other in almost every characteristic trait.

Unorganized matter is only subject to the forces whose generality
of action constitutes physical and chemical laws. Organized matter is
also controlled to a certain extent by the same laws, and, although there
are a great many actions manifested by living bodies which are not
readily explicable by the ordinary physical laws, and for which the term
" vital phenomena" is conveniently employed, it does not by any means
follow that we have here to deal with any entirely distinct series of laws.
The attempt to reduce the so-called vital phenomena to physical and
chemical laws has already succeeded in demonstrating the dependence, on
physical and chemical principles, of many functions previously regarded
as purely vital in nature, and the hope may be reasonably held for con-
tinued progress in this direction. The sciences of physics and chemistry
are therefore the foundation-stones of modern physiology.

Nevertheless, organized and unorganized matter differ to such an
extent that their consideration forms entirely distinct branches of study.
The forms, the forces, and the laws of unorganized matter are the sub-
jects embraced by physics and chemistry. The forms and forces of
living organized matter are the objects of physiological science, or
biology.

Organic bodies differ from inorganic —

1. In their Origin. — The former spring from a parent, or from
previously-existing living matter, either by splitting, budding, seeds, or
eggs. The latter have no such origin, but ma}^ arise from the combina-
tion, under the influence of chemical affinity, of the elements which com-
pose them. Spontaneous generation, though claimed by some, has not
been satisfactorily established.

2. In their Form. — Organized bodies are usually determinate in
their form, rounded in their outline, and, in their simplest expression,
either spherical or spheroidal in shape. Unorganized bodies, on the
other hand, are irregular in their outline (amorphous), or, if determinate
in form, are bounded by plane surfaces and straight lines.

3. Duration of Existence. — Organized bodies have a definite time
to live, pass through distinct stages of development and growth, and ulti-

INTEODUCTION. 6

mately die. But the inorganic body may continue to exist until some
disrupting force separates the inorganic elements of which it is com-
posed, and enables them to form new combinations ; but so long as
uninfluenced by such an agency it may remain unchanged for an indefi-
nite period.

4. Size. — Organized bodies have a definite limit to which they may
attain, varying, however, among individuals of the same species. And
vhen they exceed the average size of the species it is not by the
increased size of the individual, but b}^ the continued production of new
individuals or a repletion of parts already existing. The unorganized
body, on the other hand, is as indeterminate in size as in duration, con-
tinuing to grow so long as fresh particles are brought together.

5. Chemical Constitution. — Of the sixty-five simple elements found
in nature but about twenty enter into the composition of organized bodies,
and of these but four are to be regarded as essential, viz., C.O.H.N.,
of which at least two are found in every organic compound. The remain-
ing elements are called incidental. Unorganized bodies may be simple in
their composition, or binary, ternary, quaternary, or higher ; but binary
is the most usual combination.

The molecular constitution of the organic body is also different
from the inorganic in being much more complex, both in the number of
elements which it contains and the number of atoms, or combining
equivalents of those atoms, which exist in a combining equivalent of
the compound. Thus, albumen, which forms an important constituent
of nearly all organized bodies, may be represented as C^oHagaNggO.;,^
(Schutzenberger), while ammonium carbonate, an inorganic compound
containing the same elements, with the exception of sulphur, may be
written as follows: (NH4)SCOS-J-H30.

From the large number of elements which enter into the composition
of organic bodies, and the large number of atoms constituting an organic
molecule, arises the great tendency to decomposition by which they are
characterized ; for, " the greater the number of atoms of an element
which enters into the formation of a molecule of a compound, the less
is the stability of that compound."

Inorganic compounds are therefore stable ; organic bodies, unstable.

It was formerly supposed that organic compounds could only be
formed under the influence of vitality, and that they could be decom-
posed by the chemist, but not recomposed. But this has been shown to
be an error, some of the organic acids, alcohols, organic coloring matters,
and some of the secondary organic components, such as uric acid and
urea, having been synthetically prepared by the chemist. It is thought,
therefore, not to be impossible that some of the higher organic com-
pounds, such as albumen, may ultimately be also made in the same

4: INTRODUCTION.

manner, though thus far all attempts in this direction have been unavail-
ing. All those compounds which have as yet been made by synthesis
are allied to those which result from a long-continued series of chemical
changes in the organism, produced by the action of oxygen upon prod-
ucts of disintegration.

6. In their Mode of Growth. — Organized bodies grow by assimila-
tion,—the internal deposit of materials by which the unlike become the
like. Unorganized bodies grow, or increase in size, by external deposit
or accretion. The organized body is dying from the moment of its birth,
and requires new materials to repair those losses and for the increase in
size. The unorganized body, as the crystal or the stalactite, continues
to increase in size so long as fresh particles are deposited upon it.
Every part of an inorganic body is therefore alike and independent of
the rest, and exhibits the same properties as the whole. The organized
body, on the contrary, is made up of a number of dissimilar parts, each
of which is more or less dependent upon the others, and each of which
requires different materials for its growth and reparation. In the unor-
ganized body a small portion serves to determine by anatysis the consti-
tution of the whole ; in other words, it is homogeneous. In the organ-
ized body each part is more or less dependent on the remainder, and
differs from it in chemical composition ; in other words, it is hetero-
geneous. Organic compounds, moreover, from the large quantity of
fluid they contain, are usually soft and ductile, while the inorganic body
is hard, rigid, and inflexible, and when once the affinities of its chemical
elements are satisfied it remains an inert mass. Within the organized
living body all is change. Death and repair are ever taking place. From
the commencement of its existence its growth, its progress toward
maturity, its decline, decay, and death are all made up of an incessant
series of changes. It is the constant round of these actions which con-
stitutes life ; their study is the subject of physiology.

It is thus seen that organized are distinguished from unorganized
bodies by three cardinal characteristics : 1. Tlie law of nutrition, the
most fundamental of all vital laws ; since in virtue of it the organism
continues to exist as an active being, and increases from infancy to
maturity. 2. The law of development, or differentiation, which causes
the organism to pass through the definite cycles of change constituting
what we call ages, and leading inevitably to the final changes which we
call death. 3. The law of reproduction, another aspect of the first law,
in virtue of which the organism gives origin to similar organisms from
one generation to another.

In no example of inorganic matter can any of these characteristics
be found. When inorganic bodies are said to grow, their growth is a
process of mere aggregation, one part adhering to another similar part.

INTRODUCTION. 5

The growth arises from no internal necessity, as in organic bodies. The
bulk is not increased by a process of assimilation which converts the
unlike into the like. Minerals do not feed ; they cohere. Nor have they
any power of development. They pass through no definite cycles of
change ; they have no stages of growth, no ages, no power of repro-
duction.

The constant round of actions, therefore, in the organized structure
called life, in them is wanting. They occupy space, but have neither
birth nor death.

DISTINCTION BETWEEN PLANTS AND ANIMALS. — Organized bodies are
divided into two classes, — animals and vegetables, — constituting two sep-
arate kingdoms, which, though capable of ready recognition when studied
in their higher members, seem almost to overlap in their lowest expres-
sion. Hence, while the differences between the higher animals and higher
plants are so striking as not to need mention, when we examine the lowest
forms of life the greatest difficulty will sometimes be met with in the
attempt to decide whether the organism is an animal or a vegetable. For
when the protozoa, or lowest animals, are compared with the protophyta,
or lowest plants, all the differences which are so striking between the
higher animals and plants are completely wanting ; yet the protozoa are
as truly animal as are the vertebrata, and the protophyta just as surely
plants. Consequently the definition of an animal or a plant, to be of any
scientific value, must include the lowest as well as the highest forms.

We found, in our comparison of organic and inorganic matter, that
differences in form could be clearly made out. The external charac-
teristics of plants and animals are, however, inadequate to distinguish
them. Many animal forms, such as the hydrozoa, are essentially plant-
like in their external form, growing from fixed points and even repro-
ducing themselves by " budding," — a process almost universally holding
in the vegetable kingdom. So also the well-known coral polyps and the
sponge closely resemble plants in external configuration, and, though
undoubtedly animals, were long placed by naturalists in the vegetable
kingdom.

Then, on the other hand, many plants, examined in respect to their
external form alone, would often be confounded with animals. Thus,
the germs of many algae, the ciliated zoospores, are scarcel}* to be dis-
tinguished from infusorial animalcules.

It was at one time thought that the power of motion was a proof
of animality ; but many of the lowest plants, such as volvox and the
diatoms, possess the power of motion, of changing their location, the
instruments being the same as in many animals, viz., cilia. Nor is the
power of moving in response to an irritant peculiar to animal life :
witness the Mimosa pudica, the sensitive plant, which closes its leaflets

6 INTRODUCTION.

on irritation ; the Dionsea muscipula, the Venus' Fly-Trap, the extremities
of whose leaves have the power of closing on insects or other bodies
brought into contact with them. Plants are also possessed of internal
motion: witness the circulation of the sap and the circulatory motions
in the interior of many vegetable cells. They also turn spontaneously
to the light and extend their rootlets to the most nutritive soil.

Again, all animals are not possessed of the power of motion.
Sponges, coral polyps, hydroid zoophytes, sea-mats, etc., are entirely
destitute of locomotive power, and spend their entire existence rooted
fast to some immovable object. Hence, the possession of motor power
is not characteristic of animal life, and its absence does not prove the
organism to be a vegetable.

Chemical analysis helps us but little more in the attempt to dis-
tinguish animals from vegetables. Carbon and nitrogen compounds form
a large proportion of the constituents of each, and a large number of
complex combinations found in animal tissues are represented by entirely
similar compounds in vegetable matter. There is therefore no one chemi-
cal compound whose presence is characteristic of animality or vegetable
nature; for u cellulose," the substance out of which wood-fibre and .the
walls of plant-cells are formed, has been ascertained to form the greater
part of the external coverings of certain molluscous animals (ascidians).
So also chlorophyll, the green coloring matter of plants, is the cause of
the green color of many infusorial animalcules and of Hydra viridis,
while starch has been found in the ventricles of the brain of animals,
and is represented by glycogen, a body closely analogous to starch and
manufactured by the animal economy. Such examples, therefore, show
that chemical examination can give us no definite aid in separating plants
and animals.

The microscope is also powerless to give us an infallible rule which
will enable us to distinguish animal from vegetable tissue. In other
words, plants and animals are built up on the same general plan ; their
intimate structure closely coincides. Both originate in cells, consisting,
in their typical form, of a cell-wall, cell-contents, or protoplasm, — nucleus
and nucleolus,— and in both the parent cell undergoes subdivision and
results in the birth, growth, and development of myriads of other cells,
constituting the tissue of the plant or animal, and differing no more from
each other than almost any mature animal or vegetable cell does from
the germ from which it originated.

Nor is the possession of a digestive cavity, mouth, or alimentary
tube characteristic of animals ; for there are vegetables which possess a
stomach, as the Nepenthes, or Pitcher-Plant, which has a cavity cor-
responding to a stomach, in which digestive fluids are poured out, and
in which digestion and absorption take place. On the other hand, many

INTRODUCTION. 7

animals among the protozoa, such as the amoeba, have no stomach, the
general surface serving not only for the purpose of digestion, but also
for absorption, an extemporaneous stomach being formed by wrapping a
part of the external general body surface around the substance to be
digested.

So also in the tape-worms and other parasitic forms of animal life,
there is an entire absence of any special aperture for the entrance of
nutritive matter, such organisms living by the simple imbibition of
nutritive matter in solution.

When, however, we examine into the nature and mode of assimila-
tion of food, the nutritive processes occurring in the interior of the
organism, and the results of the conversion and assimilation of food,
then only have we any reliable scientific data for distinguishing animals
from plants. In the first place, the food of animals differs from that of
plants in its nature. Animals require organic food ; plants live on inor-
ganic or mineral matter. The nutritive processes in the two kingdoms
are also diametrically opposed : the plant absorbs water, ammonia, carbon
dioxide and certain salts, and out of these manufactures the albuminoids,
carbohydrates and hydrocarbons found in vegetable tissue. The
animal feeds on these complex vegetable compounds, — and this holds
whether the animal be herbivorous or carnivorous, — and returns to the
soil and atmosphere the inorganic matter from which they were manu-
factured by the plant; and in the same form, i.e., carbon dioxide, water,
ammonia, and certain salts. The plant therefore converts simple inor-
ganic compounds into complex organic compounds, while the animal
reduces complex organic matter to its simple inorganic constituents.

A further point of distinction between animals and vegetables, and
one closely connected with the nutritive processes, is their behavior to
the atmosphere. The animal requires for the processes of reduction
already mentioned as constituting its mode of nutrition a constant supply
of ox}-gen, which is withdrawn from the atmosphere and returned to it
in the form of CO,, representing one of the end products of oxidation
of the carbon of its tissues and food. Plants, on the other hand, absorb
CO,, and under the influence of sunlight, by the action of their chloro-
phyll, break up this CO,, fix the carbon in their tissues, and set free
ox}-gen into the air. The plant thus absorbs what the animal excretes,
and the animal absorbs what the plant excretes. We thus see that
animals and plants offer striking points of contrast as to the character
of their food and the nature of their nutritive processes, and, although
there are several apparent exceptions to the general outline here given,
their consideration may be deferred to the chapters on the Chemical
Processes in Cells.

We have found now that all objects in nature must be either organic

8 INTRODUCTION.

or inorganic, and we have considered the means by which these bodies
may be separated: we, therefore, here leave the inorganic world (the
domain of physics, chemistry, mineralog}r, etc.), to confine our studies
to the animal kingdom. But here, from the fact that there was great
difficulty in separating the lower forms of animal from vegetable life, it
must be recognized that animals and plants possess many vital functions
in common ; and as the simplest expression of these functions must be in
the simplest organisms, the study of those functions may best commence
in the simple, uncellular organisms, whether animal or vegetable.
General physiology will thus deal with the Animal Cell : its form, origin,
modifications, constitution, and the various chemical and physical proc-
esses concerned in its nutrition, growth, development and reproduction.

It will, then, be shown that the higher animals are mere associations
of such simple organisms, in which the modification in the characters
of the various constituent cells leads to a division of labor. In other
words, development of tissues leads to a specialization of function, and
Special Physiology will deal with the study of the development of func-
tion, especially as seen in our domestic animals. The functions of animals
are divided into the Vegetative Functions, the Animal Functions, — or
the functions of relation, — and the Reproductive Functions.

The Yegetative Functions include everything which relates to the
nutrition of the animal in its widest sense. As the blood in higher
animals is the organ of nutrition, under this head are included (1st)
the additions to the blood, — therefore, the description and modes of
prehension of Food ; Digestion, or the preparation of food for absorption ;
and Absorption, or the means by which nutritive and other matters enter
the blood. The Blood will, then, be considered as a tissue of nutrition
<or as a carrier to and from the various organs of the body by means of
its Circulation. As a boundary between the additions and (2d) the losses
to the blood Respiration will demand attention, while under the latter
head come the functions of Secretion and Excretion. The means by
which the identit}^ of the individual is preserved concludes the subject
of Nutrition and deals with the nutritive value of different foods and
their combinations, the adaptment of foods to the different demands on
the animal economy, and the subject of Animal Heat. The Animal Func-
tions, or those by which the body is brought into relation with the
external world by means of sensation, power of movement, consciousness,
and volition, include the study of the Muscular and Nervous Systems,
while finally the Reproductive Functions lead to the preservation of the
species, and include the subjects of Generation and Development, or
Embryology.

PART I.

GENERAL PHYSIOLOGY.

THE PHYSIOLOGY OF ANIMAL CELLS.

(9)

SECTION I.
THE STRUCTURE OF ORGANIZED BODIES.

CHEMICAL ANALYSIS has shown that all organized bodies are capable
of resolution into simple chemical elements which in themselves do not
differ from the elements out of which all matter is composed : in other
words, that the simple elements of which organized bodies are built up
are universally distributed throughout nature, and that no one element
is peculiar to organized matter. The characteristic of organized bodies
is, therefore, not to be found in any peculiarity of the matter of which
they are composed, but in the manner in which the atoms composing
that matter are grouped. In an inorganic body we are accustomed to
attribute its chemical properties to the nature, number, and mode of
association of its constituent elements, while its physical properties are
attributable to the mode of arrangement of its molecules.

Anatysis of organized bodies shows that in them we have certain
elements constantly present in certain definite proportions: it is there-
fore warrantable to assume that the chemical properties of organized
bodies are, as in the case of inorganic matter, due to the number, nature,
and mode of association of their elements. Further, we find in all
organized living bodies a certain identity of physical properties : it is
therefore warrantable to assume that the physical processes seen in
organized bodies are dependent on the mode of arrangement of their
constituent molecules. The elements constantly associated in living
matter are carbon, nitrogen, oxygen, hydrogen, and sulphur, forming a
complex combination, to which the term protoplasm has been applied.
This matter, protoplasm, whether found in the tissues of the highest
animals or plants, or in the lowest unicellular members of either kingdom,
has always the same composition and is always possessed of nearly the
same attributes ; with the restriction that we have already referred to as
to the difference in functions possessed by animals and plants, — differences
which will probably in the future be cleared up, and found not to be in
contradiction to the statement that protoplasm is the universal basis of
organization.

All organized bodies are built up of associations of masses of proto-
plasm, which from their appearance are termed cells, or, from the func-
tions which they fulfill, elementary organisms: and as the physical
properties of inorganic matter are dependent on the arrangement of

12 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

their molecules, so the physiological peculiarities of organized bodies
are dependent on their cellular structure.

Physiology is therefore the study of the properties of cells. Cells
possess the properties of Nutrition, Reproduction, Growth, Develop-
ment, and in many cases their contents are capable of Motion and mani-
festing Irritability.

I. THE GENERAL PROPERTIES OF CELLS.

Microscopic examination teaches that every living object, from man
down to the smallest animalcule invisible to the naked eye, — from the
largest tree down to the most microscopic plant, — is built up on the
same general plan. In each the same element of organization is found,
and every living form is built up of associations of these microscopic
units, each of which, even in the most complex forms of life, may be
regarded as separate individual organisms.*

For even in complex organisms cells to a certain extent carry on a
separate and independent existence. We see
separate cells originate separately, grow, repro-
duce themselves, become diseased and die
without the entire organism as a whole taking
any part in these different stages of existence
of its component parts. The individual life of
each separate cell is recognized in the different
activities of different cells : the activity of the
FIG i— TYPICAL ANIMAL organism is the result of the, sum of these
(m£nV) °VUM °F separate existences.

In tlieir typical form both animal and
vegetable cells consist of closed vesicles, with

homogeneous or striated walls, a viscid albuminous contents, termed
protoplasm, containing an aggregation of granules called -a nucleus,
within which again is a still denser formation called a nucleolus. The
cell-contents is frequently vacuolated, i.e., contains minute cavities filled
with a clear fluid.

The contents of the cells, which we shall find to be functionally the
most important, is called protoplasm. It is a transparent mass in which
numerous granules are suspended, and which possesses in all young cells
(the property of contractility. It is often seen to be reticulated. In
older cells the quantity of fluid diminishes and the cells become firmer
and drier, while vacuoles often form and contain fluid. This change in
.the physical properties of cells is often associated with a visible change
in their chemical nature, — thus, with a deposit of coloring matter, starch

* Such units of organization are termed cells, from the resemblance which micro-
scopic sections of young tissues, whether plant or animal, bear to a honey-comb.

THE GENERAL PEOPEKTIES OF CELLS. ; 13.

granules, fat globules, or granular matter. All substances which coagu-
late proteids have the same effect on protoplasm. The vital properties
of protoplasm will be studied later.

A membrane is usually present in all mature cells, though always
absent in embryonic forms. It may therefore be assumed that the mem-
brane results from a condensation of the outer layers of the cell-contents.
The membrane is apparently homogeneous, or may be porous.

The nucleus, the size of which is generally in proportion to that of
the cell, and which is usually oval or spherical, is never absent in early
forms of active cells, though it may disappear when the cell reaches
maturity. In its mature stage it is generally reticulated, — that is, com-
posed of an investing cuticle within which the contents are arranged in
the form of a fibrillar net-work. The presence of a nucleus, which is
often difficult of recognition on account of its minute size, may be
demonstrated through the action of certain reagents, especially dilute
acids and staining fluids. Dilute acids render the protoplasm of cells
transparent without affecting the nucleus, which consequently becomes
more prominent; while staining fluids, such as carmine, haematoxylin,
and the anilin dyes, color the nucleus deeper in tint than the cell-contents.
The nucleus appears to be especially important in the reproductive func-
tions of cells, since when cells multiply by division the division always
commences in the nucleus.

The nucleolus is simpty a closer aggregation of the granules which
constitute the nucleus, and is very frequently absent.

Both cell-wall and nucleus may be absent from the lowest elementary
organisms.

As our conception of the structure of the higher animals and plants
is an association of elementary organisms invariably taking origin from
a single cell, our definition of such a simple organism or cell must be
modified so as to apply to the description of the simplest conceivable
organism capable of carrying on an independent existence. And as we
have seen that of the constituents of a typical cell but one, the cell-con-
tents, or protoplasm, is essential ; and as we know that there are
organisms capable of carrying on an independent existence in whom
neither cell-wall, nucleus, or nucleolus is to be detected, a cell may be
defined as a more or less homogeneous mass of organized material, —
protoplasm, — possessing development, growth, reproduction, nutrition,
and automatism.

The best known of such undifferentiated forms of cell life is the
amoeba, — one of the simplest examples of an animal organism.

In its lowest form the amoeba (Protamoeba primitiva, Haeckel) con-
sists of a mass of jelly-like, structureless, albuminoid substance (proto-
plasm), which, so far as its chemical composition and general attributes

14 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

are concerned, cannot be distinguished from the contents of all active
forms of cells (Fig. 2).

The amoeba is capable of spontaneous motion, both as regards
change of external form and of progressing from place to place.
Motions may also be evoked by various stimuli ; hence, free protoplasm,
in common with muscular fibre and ciliated organisms, is contractile.
The peculiarity of protoplasmic motion, as seen in the amoeba, is that
motion does not occur around a fixed point, but rather is a flowing
motion, such as might occur in the particles of a fluid. Thus, in an
amoeba the changes in form and location are effected through the thrust-
ing out of lobe-like prolongations of the periphery (pseudopodia), and
their subsequent withdrawal or the flowing into these extensions of the
remainder of the body.

Occasionally one or more of these pseudopodia become gradually
more and more constricted, until, finally, a portion becomes entirely

separated from the original
mass, increases in size, and
itself possesses all the proper-
ties of the parent stock; hence,
protoplasm is reproductive,
and possesses the power of
growth. Moreover, the move-
ments of an amo3ba are not

FIG. 2. -A NON-NUCLEATED CELL, THE PROT- necessarily the consequences
AMCEBAPRIMITIVA, AFTER HAECKEL. (Wundt.) of externai stimuli, but may

A, original condition ; B, commencement of reproduction by fission : , 0 . .

C, after complete separatum. be Self-Originating ; llCHCC,

protoplasm is also automatic.

If watched for some time, an amoeba will often be seen to take into
its interior, by flowing around them, small vegetable organisms, of which
portions are dissolved and converted into the substance of its body,
while the undigested remainder is extruded ; therefore, protoplasm, even
in the absence of all digestive organs, possesses the power of nutrition.

The amoeba requires for its existence an atmosphere of ox3rgen,
which is absorbed, and which it again partly exhales as carbon dioxide.
Protoplasm is therefore respiratory.

II. ORIGIN OF CELLS.

We iiave seen that in the amoeba a simple mass of undifferentiated
protoplasm possesses the powers of reproduction, contractility, respira-
tion, irritabilit}^ nutrition, and automatism. Every form of life com-
mences its existence in the form of just such a simple mass of proto-
plasm. Starting with the ovum, and ending with the nucleated elements
found in the organs and tissues of the embryo and adult; there is one

OKIGIN OF CELLS. 15

uninterrupted series of generations of cells, each cell becoming so modi-
fied as to specialize certain functions which are together possessed by all
forms of undifferentiated protoplasm. Thus, in the higher forms certain
cells will be found to have become so modified as to have the function of
reproduction especially developed ; they will therefore constitute the
reproductive tissues. In other cells the nutritive functions will become
most prominent ; they will therefore form part of the tissues whose
function is to preserve the nutritive balance of the organism. Specializa-
tion of function is therefore the explanation of the development of
tissues; the result is a plr^siological division of labor. We will have to
return to this subject again.

The germ of every animal and vegetable organism is a cell which
owes its existence to some similar, previously-existing cell. Neglecting
the origin and development of cells in the vegetable kingdom, every
cell which forms part of the organs or tissues of all forms of animal
life originated in and developed from a germ-cell or ovum.

The ovum of man and other mammals is
a minute mass of protoplasm, corresponding in
its general appearance with the description of a
typical cell. The protoplasm, or cell-contents,
is surrounded by a delicate, striated membrane,
the Zona radiata, or vitelline membrane. Within
the cell-contents, in addition to numerous minute
particles, — the so-called yelk- globules, — is a
collection of denser particles of protoplasm, FIG. 3.— TYPICAL ANIMAL
—the nucleus, or germinal vesicle, and within uS?"cx£jJ) °VUM OF
that, again, one or more still more solid masses, A»
— the nucleoli, or germinal spots.

The cell-contents is identical in nature and properties with the sub-
stance of the amoaba, and before and immediately after fertilization may
even be the seat of spontaneous movements of contraction and expan-
sion. When mature, its diameter in the domestic animals and man varies
from the ^J^ to the T^ of an inch (0.18-0.2 mm.).

Fertilization leads to a cleavage of the protoplasm into two parts,
the nucleus being first divided, so that two new elements originate from
the ovum, each consisting of protoplasm and each containing a nucleus.
Each of the two new cells thus formed again subdivide into four, these
into eight, and so on through many generations, until a large number of
new cells, the so-called "mulberry mass," results from the subdivision of
the original parent cell.

According to Schleiden and Schwann, the founders of the cell doc-
trine, organic forms of life may originate in one of two wa}rs, — either by
the aggregation of granules in a previously-existing homogeneous fluid

16

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

FIG. 4.— BLOOD-CORPUSCLES
IN DIFFERENT STAGES OF
DEVELOPMENT, SHOWING
REPRODUCTION BY FIS-
SION. (Ranke.)

(the blastema), forming the so-called "free cell-formation," or by the
subdivision of a previously-existing cell, — the " endogenous cell-forma-
tion."

According to the first of these views, which may be compared to the
formation of crystals in a saline solution, granules first develop in a fluid

which contains all the. chemical constituents of
the organism, forming the nucleolus of the
future cell. Around this other granules are
gradually deposited until the nucleus is formed,
and the cell-contents and membrane gradually
consolidate around this. The first objection
to this theory, which, it is seen, implies spon-
taneous generation, lies in the fact that no one-
has ever been able to demonstrate such a cell-
formation or to discover the so-called cyto-
blasts. It was then shown that all the cells of
the embryo originate in the segmentation

spheres of the ovum, and the falsity of this doctrine of free cell-
formation is further proved from analogy by the manner in which the
connective-tissue cells take part in the development of pathological new
formations. There is now no more firmly-established dictum in plrysi-
ology than the statement that every cell originates from a previously-
existing cell. (Omnis cellula e cellula.)

The other view, which was also to a certain extent advocated by
Schwann, as to the origin of cells by sub-
division of a parent cell, is exemplified in
the mode of reproduction of many of the
lower forms of life. Cells may reproduce
themselves by simple division of the parent
cell or by endogenous division.

Cell reproduction always starts in the
nucleus. In simple division the nucleus first
becomes marked with a furrow, which gradt
ually deepens until the nucleus is divided
into two. The protoplasm of the cells is
then modified in the same way, until two new
cells are formed by the division of the

parent cell. This process may be followed in the reproduction of
the nucleated red blood-corpuscles of the embryo of the chick and
even in mammals (Fig. 4). A modification of this form of cell
reproduction is sometimes described as " budding." This process also
starts with the nucleus. A number of nuclei are first formed by the
subdivision of the nucleus ; these gradually separate; the protoplasm

FIG. 5.— GEMMATION. A BUD-
DING GERM-CELL OF GOR-

DIUS, AFTER MEISSNER.

(Wundt.)

ORIGIN OF CELLS. 17

collects around them so as to form projections from the periphery of the
cell, which become more and more constricted until they finally separate
(Fig. 5). During division the nuclear membrane disappears, and the
nucleus usually divides before the cell-protoplasm, but not directly, by
simple cleavage, as was formerly supposed, but indirectly, by karyo-
kitiesis (from movement of nuclear fibrils). This is an exceedingly com-
plicated process. Its different stages may be divided about as follows : —

1. The nuclear fibrils become very distinct, while the nuclear mem-
brane disappears and the fibrils of the nuclear net-work become twisted
and bent into a more or less dense convolution, while the entire nucleus
•enlarges.

2. The fibrils unravel into loops arranged around the centre as a
wreath or rosette.

3. The peripheral points of the loops become broken and a star-
shaped figure of single loops is obtained. This is termed the aster, or
star.

4. The loops separate into two groups or new centres. This is the
diaster, or double star.

5. The two groups of threads become farther apart, as if attracted
by opposite poles, but still remain connected by fine pole-threads, which
represent the interstitial nuclear substance. In this stage the figure
resembles a spindle.

6. The connection between the two sets of threads is broken.

7. The threads of each set become convoluted.

8. A membrane forms for each set, and thus new daughter nuclei
result. (See Fig. 6.)

The cell-protoplasm may commence to divide at any stage between
the one when the threads aggregate around the two centres and the one
when two distinct nuclei are present ; or the division of the nucleus may
be followed by division of the cell, so giving a cell with two nuclei. It
is not proved that this is the universal mode of divisions of nuclei,
though it has been observed in all kinds of cells in the embryo, and to a
limited degree in the adult. On the contrary, it is probable that amoeboid
cells divide by the direct method and that other nuclei may also undergo
direct division, or Remak's division, by simple cleavage, though all the
cases in which constriction of nuclei is observed need not be cases of
commencing division, as the change in- shape may be due to pressure of
cell-protoplasm, or to nuclear contractions. (Klein).

The second form of cell-formation is termed by Kolliker " endoge-
nous cell-formation," and consists in the formation of cells within the
membrane of the parent cell, which ultimately bursts and discharges its
progeny of j^oung cells. The division of the mammalian ovum, the
growth of cartilage, and many pathological cell-formations are types of

2

18

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

this mode of cell reproduction. The latter example furnishes many
instances in which a number of cells with entirety different attributes
from the parent cell develop in the interior of a cell, such as the develop-

FIG. 6.— KARYOKINESIS. (Klein.}

A, ordinary nucleus of a columnar epithelial cell ; B, C, the same nucleus in the stage of convolution :
D, the wreath, or rosette form ; E, the aster, or single star ; F, a nuclear spindle from the Descemet's
endothelium of the frog's cornea ; G, H, I, the diaster ; K, two daughter nuclei.

ment of pus-corpuscles in the interior of different tissue-cells in inflam-
mation (Fig. 7).

The best object for the study of cell reproduction by division, and

the one of most interest tor us, is
found in the fertilized ovum of
mammals.

As the ovum approaches maturity,
even before impregnation takes place,
the germinal vesicle becomes obscure
and more and more irregular in out-
line, its membrane and reticulum
disappear, and the germinal spot is
broken up. What remains of the
germinal vesicle becomes converted
into a striated, spindle-shaped body,
which moves to the surface of the
ovum, to there undergo division into
two parts. One part becomes ex-
truded from the ovum to form what
is known to embryologists as the polar cell, and is soon followed by a
second similar cell, while the portion of the spindle remaining within
the ovum forms a new nucleus, the female pronucleus, from which, in
conjunction with the male elements, the future embryo is developed.

FIG. 7.— THE FORMATION OP PUS-COR-
PUSCLES IN THE INTERIOR OF EPITHE-
LIAL CELLS, SHOWING ENDOGENOUS
CELL-FORMATION. (Ranke.)

A, single cylindrical cell from the human bile-duct :
B, a similar cell containing two, C containing four, and
D numerous pus-cells: E, isolated pus-corpuscles;
F, a ciliated epithelial cell from the human respiratory
tract, containing a single pus-corpuscle : and G, a pave-
ment epithelial cell from the urinary bladder of man,
containing numerous pus-corpuscles.

OKIGIN OF CELLS.

19

111 the unimpregiiated ovule spontaneous contractions are generally
seen in the protoplasmic cell-contents. When the egg becomes fertilized
these contractions become so modified as to cause the germinal vesicle
(or the bod}r resulting from the union of the male and female pronuclei),
and then the cell-contents to split into two parts contained within the
cell-membrane, which takes no part in this division. These segmentation
spheres, as already mentioned, continue to subdivide until an immense
number of minute, nucleated, membraneless cells are contained within the
vitelline membrane (forming the so-called mulberry mass).

From these elements, which become progressively smaller as cleavage
goes on, all the tissues of the embryo are formed. At first the}T all
possess mobilit}T (amoeboid movements), showing their analogy to the
simple amoaba, but. at birth this property is only retained by certain cells.
Like amrebse, they also grow in size and divide into new individuals.

At first all the cells resulting from the segmentation of the ovum
are exactly alike : they then undergo certain modifications in arrange-

123 A-

FIG. 8.— OVA OF THE DOG FROM THE FALLOPIAN TUBE, SURROUNDED BY THE
ZONA PELLUCIDA, IN WHICH ARE FOUND NUMEROUS SPERMATOZOA, AFTER
BISCIIOFF. (Rank<>.}
1, ovum with two segmentation spheres, the Zona pellucida being surrounded by the Membrana gran-

ulosa ; 2, ovum with four segmentation spheres ; 3, ovum with eight segmentation spheres ; 4, ovum with

innumerable segmentation spheres, forming the mulberry mass.

ment and form, different in different classes of animals, from which the
different tissues of the embryo are developed.

The ova of animals are divided into two classes, — those in which the
entire yelk is concerned in the production of the embryo, and those in
^Yhich a part only serves for this purpose, — while the remainder of the cell-
contents is drawn upon for the nutritive needs of the embr3ro. The first
of these which undergoes total segmentation is termed a holoblastic egg;
the second undergoes only partial segmentation, and is termed a mero-
blastic egg. The ovum of mammals serves for a type of the former
class ; the ovum of birds is typical of the second class. As already
mentioned, the mammalian ovum represents a typical cell; the ovum of
the bird differs in many points. Beneath the yelk-membrane is a layer
of minute flattened cells, which gradually disappear during the maturing
of the egg ; while the yelk consists of two parts, one serving for the
development of the embryo, the other for its nutrition. The part from

20 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

which the embryo is formed is a small, white disk lying directly beneath
the vitelline membrane and termed the tread, the blastoderm or cicatricula.
In the hen's egg this disk is about four millimeters in diameter, and is
always found in the upper surface of the yelk. If a hen's egg is hard-
ened by boiling, and then cut in two by a vertical section so as to bisect
the yelk, the latter will be found not to be perfectly homogeneous. The
yelk is clothed externally by a thin layer of different material, which at
the edge of the blastoderm passes beneath it and becomes thicker so as
to form a bed on which the blastoderm rests, to become connected by a
narrow neck with a mass of similar matter occupying the centre of the

WY
W.Y. W

N.P.
B.L.

Y.V

CH.L

CH.L.

W.

VT.

FIG. 9.— DIAGRAMMATIC SECTION OF AN UNINCUBATEB FOWL'S EGG, AFTER
ALLEN THOMPSON. (Foster and Balf our.)

BLi, blastoderm ; WY, white yelk — this consists of a central, flask-shaped mass and a number of
layers arranged concentrically around this; YY, yellow yelk; VT, vitelline membrane; X, layer of
more fluid albumen immediately surrounding the yelk ; W, albumen, consisting of alternate denser and
more fluid layers ; CHL, chalazae ; ACH, air-chamber at the broad end of the egg— this chamber is
merely a space left between the two layers of the shell-membrane ; ISM, internal layer of shell-membrane :
SM, external layer of shell-membrane ; S, shell ; NP, nucleus of Pander.

yelk, which nearly always remains partially fluid in the hard-boiled egg.
Within the yelk again are several concentric layers of this white yelk,
separated from each other b}^ la}Ters of yellow }relk. The 3Tellow yelk is
composed of comparatively large, unnucleated cells filled with highly
refractive granules, and containing vitellin, lecithin, and various fatty
bodies. The cells which form the white yelk are much smaller, are
nucleated, and often a large cell will be seen to contain numerous similar
but smaller cells.

When the egg is laid by the hen it has already undergone changes
which result from fertilization. We will first describe the characters of

ORIGIN OF CELLS.

21

the blastoderm when the egg is first laid, and then the changes which
have preceded it.

The blastoderm of an unincubated fertilized egg may be recognized
by the naked eye, when viewed from above, to consist of two parts: an
opaque, white circumference, the area opaca, and a central transparent
portion, the area pellucida. In the unfertilized egg these divisions are
not marked. They are due simply to the way the blastoderm, which is
itself entirely transparent, rests on the white yelk. The opaque, circular
ring is where the blastoderm is directly in contact with the white yelk,
while the central clear portion is due to the fact that the blastoderm is
separated from the yelk by a layer of liquid. The white spot often seen
in the centre of the blastoderm is the central column of white yelk
shining through the transparent membrane (Nucleus of Pander).

When the blastoderm is hardened and cut into vertical sections, it
is found to be composed of two layers of cells : the upper, small, nucle-
ated, C3"lindrical cells adhering closely together in a single la3Ter and

FIG. 10.— SECTION OF AN UNINCUBATED BT-ASTODERM OF CHICK. (Klein.)

A, cells forming the ectoderm ; B, cells forming the endodenn ; C, large, formative cells : F, segmen-
tation cavity.

resting on the white 3Telk ; the lower, an irregular net-work of larger cells
which are not nucleated, apparently, but which contain numerous highly
refractive granules. These are probably identical with the white-yelk
spheres already referred to, and are spoken of as formative cells.

The processes which in the hen's bod}r result in the formation of
such an egg are about as follow :

In the capsule of the ovary the yelk alone constitutes the egg. It
then, just before bursting its capsule, consists of a minute, yellowish,
ellipsoidal, cellular body, with a delicate membrane, the vitelline mem-
brane, immediately below which in a granular cell-contents, the yelk, lies
a lenticular, mass of protoplasm, the germinal disk; within this again is
a nucleus, the germinal vesicle, containing a nucleolus, or germinal spot.

When the ovum becomes mature the ovarian capsule bursts, and
the ovum (representing the yelk of the egg as laid) escapes into the
oviduct, undergoes impregnation by the spermatozoa found in the upper
portion of the oviduct, and has deposited around it the accessory

22 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

portions of the egg through secretions from the walls of the oviduct.
Thus, the layer of albumen surrounding the yelk is first deposited in
the passage of the ovum through the second, tubular portion of the
oviduct, the chalazse (see Fig. 9), or twisted, denser portions of the
albumen, being due to the rotatory motion of the egg against the spiral
ridges of the oviduct. The shell-membrane is formed by the organiza-
tion of the most external layers of albumen, and the shell is formed in
the third portion of the oviduct, or the uterus. The walls of this
portion of the tube secrete a viscid fluid which surrounds the egg, and in
which inorganic particles are deposited. The egg remains in the uterus
for from twelve to eighteen hours, and is then expelled through the
cloaca, narrow end downward, by its muscular contractions.

1 2 3

FIG. 11.— SURFACE VIEW OF THE EARLY STAGES OF SEGMENTATION IN A

Fowi/s EGG, AFTER COSTE. (Foster and Balfour.)

1 represents the earliest stage. The first furrow, B, has begun to make its appearance in the centre
of the germinal disk, whose periphery is marked by the line A. In 2 the first furrow is completed across
the disk, and a second similar furrow at nearly right angles to the first has appeared. The disk thus
becomes divided somewhat irregularly into quadrants by four (half) furrows. In a later stage, 3, the
meridian furrows, B, have increased in number, from four, as in B, to nine, and cross-furrows have also
made their appearance. The disk is thus cut up into small central, C, and larger. D, peripheral segments.
Several new cross-furrows are seen just beginning, as ex. gr., close to the end of the line of reference, D.

About the time the shell is being formed, provided impregnation
has taken place, changes occur in the blastoderm, which, though analo-
gous to the process of segmentation already mentioned as taking place
in the mammalian ovum, yet differs from it. The germinal vesicle first
disappears, and a furrow is then seen to run across the germinal disk,
dividing it into two halves. This furrow is then met by a second run-
ning at right angles to the first ; this is then crossed by another, and
division of the segments proceeds rapidly by furrows running in all
•directions until the germinal mass is cut up into an immense number of
minute masses of protoplasm, smaller toward the centre than at the
periphery of the disk.

The furrows thus formed are not merely superficial, but extend
through the entire thickness of the germinal disk: hence the germinal
disk is cut up into minute masses of protoplasm. In other words, a

ORIGIN OF CELLS.

23

large number of cells has resulted from the segmentation of the parent
cell.

These cells arrange themselves into an upper layer, with their long

FIG. 12.— SURFACE VIKW OF THE GERMINAL DISK OF A HEN'S EGG DURING
THE LATER STAGES OF SEGMENTATION. (Foster and Bal four.)

At C, in the centre of the disk, the segmentation masses are very small and numerous ; at B, nearer
the edge, they are larger and fewer; while those at the extreme margin, A, are largest and fewest of all.
It will be noticed that the radiating furrows marking off the segments, A, do not reach to the extreme
margin, E, of the disk.

The drawing is complete in one quadrant only. It will, of course, be understood that the whole circle
should be filled up in a precisely similar manner.

axes vertical, their nuclei become distinct, while the lower cells remain
large and granular and irregularl}' placed, forming in this way the unin-
ciibated blastoderm already described. (See Fig. 10.)

FIG. 13.— SECTION OF THE GERMINAL DISK OF A FOWL'S EGG DURING THE
LATER STAGES OF SEGMENTATION. (Foster and Bal/our.)

This section, which represents rather more than half the breadth of the blastoderm (the middle line
being shown at C), shows that the upper and central parts of the disk segment faster than those below and
toward the periphery. At the periphery the segments are still very large. One of the larger segments is
shown at A. In the majority of segments a nucleus can be seen ; and it seems probable that a nucleus is
present in them all. Most of the segments are filled with highly refracting spherules, but these are more
numerous in some cells (especially the larger cells near the yelk) than in others. In the central part of
the blastoderm the upper cells have commenced to form a distinct layer. No segmentation-cavity is present.

A, large peripheral cell ; B, larger cells of the lower parts of the blastoderm ; C, middle line of blasto-
derm; E, edge of the blastoderm adjoining the white yelk; W, white yelk.

As a result of incubation a third layer of cells makes its appearance
between the two layers of the blastoderm just described, forming an
upper, a middle, and a lower Ia3*er, or the epiblast, the mesoblast, and the

24 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

hypoblast (Fig. 14). From these three layers of cells the embryo is
developed.

Leaving at this point the changes which occur in the egg of the bird,
we have now to follow the analogous changes in the mammalian ovum.

We have already seen that in the mammalian ovum one of the first
evidences of impregnation is the division of the protoplasm of the ovum
progressively into smaller and smaller segmentation spheres, until the
cell-membrane becomes filled with an immense number of minute masses
of protoplasm. The general character of this process in its earlier stages
is probably identical in all the mammalia. The ovum of the rabbit has
been most studied, and the sketch here given is based mainly on Balfour's
summary of the early stages of development in the rabbit's ovum.

The ovum first divides into two nearly equal spheres, of which one

BD

BD, BD. MC.

FIG. 14.— SECTION OF A BLASTODERM OF CHICK, AT RIGHT ANGLES TO THE
LONG Axis OF THE EMBRYO, AFTER EIGHT HOURS' INCUBATION, ABOUT
MIDWAY BETWEEN FRONT AND HIND ENDS. (Foster and Balfvur.)

A, epiblast; B, mesoblast; C, hypoblast: PR, primitive groove; F, fold in the blastoderm produced
accidentally ; MC. mesoblast-cell,— the line points to one of the peripheral mesoblast-cells lying between
epiblast and hypoblast; BD, formative cells.

The section shows: (1) the thickening of the mesoblast under the primitive groove, PR, even when it
is hardly present at the sides of the groove : (2) the hypoblast, C, early formed as a single layer of spindle-
shaped cells ; (3) the so-called segmentation cavity, in which coagulated albumen is present. On the
floor of this are the large formative cells, BD.

is slightly larger and more transparent than the other. The larger sphere
and its products will be spoken of as the epiblastic spheres ; the smaller
one and its products as the hypoblastic spheres. Both these original
spheres soon divide into two, and each of these into two more, thus
making eight. At first these spheres are spherical, and arranged in two
layers formed of four epiblastic and four hypoblastic spheres. Soonr
however, one of the hypoblastic spheres passes into the centre, and the
whole ovum becomes spherical again.

In the next stage each of the four epiblastic spheres divides into
two, followed b}r the division of the hypoblastic spheres into two. The
ovum is then made up of sixteen different spheres, nearly of the same
size. Of the eight hypoblastic spheres four soon pass to the centre, and are
surrounded by the eight epiblastic spheres, arranged in the form of a cup.
Division of both sets of spheres now continues, the epiblastic layer con-

ORIGIN OF CELLS. 25

tinning to surround the central kypoblastic spheres, both sets continuing
to subdivide, until finally the ovum consists of an almost solid mass of
hypoblastic spheres surrounded by a layer of epiblastic cells.

When the process of segmentation is complete the epiblastic cells
are clear and have an irregularly cubical form, while the hypoblastic
cells are polygonal and granular and somewhat larger than the epi-
blastic cells.

The blastodermic vesicle next forms. This results from the forma-
tion of a narrow cavity between the epiblast and h}Tpoblast, which
increases in size until it entirely separates these two layers, except at the
point where the blastoderm was last in forming (the blastopore). As
the cavity increases in size the ovum also enlarges, so that soon it exists
in the form of a large vesicle, formed of a thin wall of a single layer of

EP

FIG. 15.— OPTICAL, SECTIONS OP A RABBIT'S OVUM AT Two STAGES CLOSELY
FOLLOWING UPON THE SEGMENTATION, AFTER E. VAN BENEDEN.
(Half our.')

EP, epiblast; HY, primary hypoblast ; BP, Van Beneden's blastopore. The shading of the epiblast
and hypoblast is diagrammatic.

cells, — the epiblastic cells,— with a large cavity, the hypoblastic cells
forming a small, ventricular mass attached to the inner side of the epi-
blastic cells (Fig. 16). The ovum of the rabbit has now increased in
size from 0.09 mm., its size at the close of segmentation, to about 0.28
mm. It is inclosed by the vitelline membrane and a mucous layer
deposited by the walls of the Fallopian tube.

As the vesicle continues to enlarge, the hypoblastic cells spread out
beneath the epiblast, though remaining thicker in the centre than at the
edges, where the cells still possess the power of amoeboid movement.
The central, thicker portion, which is the commencement of the embryonic
area, forms an opaque, circular spot on the blastoderm.

The primitive hypoblast now becomes divided into two layers, the
lower continuous with the peripheral hypoblast and formed of flattened
cells, while the upper is formed of small, rounded elements, — the meso-

26

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

blast. The superficial epiblast, again, is formed of flattened cells, which
soon become columnar and appear to unite with the rounded elements
below, except at the lower part of the embryonic area. Here the blasto-

FIG. 16.— RABBIT'S OVUM BETWEEN SEVENTY TO NINETY HOURS AFTER
IMPREGNATION, AFTER E. .VAN BENEDEN. (Sal/our.)

BV, cavity of blastodermic vesicle (yelk-sac) ; EP, epiblast ; H Y, hypoblast ; ZP, mucous envelope
(Zona pellucida).

derm, as in the chick, is constituted by three layers, — the epiblast, the
mesoblast, and the hypoblast.

P.R,

EP.

M

HY.

FIG. 17.— SECTION THROUGH THE OVAL BLASTODERM OF A RABBIT IN THE
SEVENTH DAY, THROUGH THE FRONT PART OF THE PRIMITIVE STREAK.
(Balfour.)

EP, epiblast; M, mesoblast; HY, hypoblast; PR, primitive streak.

The subsequent changes in the development of the blastoderm form
the subject of Embryology, and for their consideration the reader is
referred to text-books on anatomy.

III. THE MODIFICATION IN THE FOKM OF CELLS.

We have seen that originally all the cells formed by cleavage in the
egg are absolutely alike. Like the original egg, they are typical cells,
consisting of a cell-membrane inclosing finely granular protoplasm, in
which a nucleus and nucleolus may be recognized. They only differ from

MODIFICATION IN THE FOKM OF CELLS.

27

the original cell in size and in as
vet unmarked individual char-
acteristics which in the speciali-
zation of function of the organ-
ism will cause them finally, for
the: most part, to lose all mor-
phological resemblance to the
parent cell.

These differences in cells
produced in the development of
the organism are very numer-
ous.

First, as regards their size,
we find cells varying from the red
blood-cell -g-g1^ to the large
ganglion-cell, ^<y of an inch
(Figs. 18 and 19).

In nearly all instances where
a collection of cells develop into
an organ or tissue the original
spherical form is lost, often
merely from mutual pressure and
from alteration in the cell-con-
tents, by which the most varied
forms are produced. Thus,
instead of the spherical form,
cells may take on an oval, elon-
gated shape (Fig. 20), or may be
cylindrical (Fig. 21), or again
from mutual pressure may form
regular hexagons. Others may
have long, thread-like attach-
ments developed, as in the sperm-
cells (Fig. 22), or even a number
of such prolongations, which as
long as the cell is alive continue
in active movement (ciliated
cells). (See Fig. '21.)

Often the nucleus deviates
from its spherical form, and may
become oval or, irregular in out-
line,, or, as in certain cells of
the marrow of bone and in

FIG. 18.— RED AND WHITE BLOOD-CORPUSCLES,
ENLARGED Six HUNDRED DIAMETERS.

(Ellenberger.)

A, surface view of red corpuscles ; B, profile view ; C, rou-
leaux of red corpuscles ; D, central depression in red corpuscles :
E, crenated red corpuscles ; F, small, and G, large white cor-
puscles.

FIG. 19. — AN ISOLATED GANGLION-CELL OF
THE ANTERIOR HORN OF THE HUMAN
SPINAL CORD, AFTER GERLACH. (Klein.)

A, axis-cylinder ; B, pigment. The branched processes of
the ganglion-cell break up into the fine nerve net-work shown
in the upper part of the figure.

28

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

FIG. 20.— NON-STRIATED MUSCULAR FIBRES, ISOLATED. (Klein.)

The cross-markings indicate corrugations of the elastic sheath of the individual fibres.

FIG. 21.— VARIOUS KINDS OF EPITHELIAL CELLS. (Klein.)

A, columnar cells of intestine ; B, polyhedral cells of the conjunctiva : C, ciliated conical cells of the
trachea : D, ciliated cell of frog's mouth ; E, inverted conical cell of trachea ; F, squamous cell of
the cavity of the mouth, seen from its broad surface ; G, squamous cell, seen edgeways.

FIG. 22.— VARIOUS KINDS OF SPERMATOZOA. (Klein.)

A, spermatozoon of guinea-pig not yet matured ; B, the same seen sideways, the head being flattened
from side to side ; C, a spermatozoon of the horse ; D, a spermatozoon of the newt.

MODIFICATION IN THE FORM OF CELLS.

29

striped muscle, may undergo reduplication without division of the
cell (Fig. 23).

The cell-contents, or protoplasm, particularly as regards its granular
constituents, may undergo the greatest variation. Often true crystalline

FIG. 23.— BONE-CORPUSCLES, WITH THEIR PROLONGATIONS, AFTER ROLLETT.

(Flint.)

formations are included in the cell-contents ; or vacuoles may form in
which different fluids, sometimes watery, sometimes fatty, may collect, to
again disappear in later stages of the life of the cell.

FIG. 24.— DIAGRAM OF DIFFERENT FORMS OF CARTILAGE. (Ellenberger.)

A, hyaline ; B, fibro-cartilage ; C, elastic cartilage ; D, secondary cartilaginous capsule, containing
the primary capsule.

Another modification in the form of cells consists in the alteration
of the border laj-ers of protoplasm, so that the cell is surrounded by a
more or less chemically or morphologically different area, or intercellular

30

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

substance, which may present the greatest variety as to quantity. The
cell-membrane and so-called cell-capsule belong to these forms of proto-
plasmic modification. In cartilage and loose connective tissue this
intercellular substance exists in such amount that the still actively
moving protoplasmic cells appear to be forced apart by it. (See Fig. 24.)
Since the more active vital movements can only originate in the
semi-fluid protoplasm of cells, it is evident that the more or less rigid
intercellular substance could only take a slight part in organic processes
if there were not some means by which it could be brought into close

FIG. 25.— NERVE-FIBRES. (Thanhoffcr.)

1, a, tnedullated nerve-fibre: b. non-medullated nerve-fibre from the sympathetic of the ox (after
Schultze) ; 2, non-medullated nerve-fibre from Jacobson's organ in the sheep (after Schnltze) ; 3, nerve-
fibres with Ranvier's nodes (R), from the sciatic of the frog: 4, funnel-shaped arrangement of medulla
from sciatic of frog, treated with osmic acid ; 5, nerve-fibre from frog, with axis-cylinder (t) and so-called
horny mesh-work; 6, diagram of medullated nerve-fibre: n, neurilemma; v, medullary sheath : t, axis-
cylinder.

association with the active vital processes constantly occurring in the
interior of cells. Consequent!}' we find the entire intercellular substance
pierced of a mesh-work of fine canals, through which the cells send
prolongations of their outer layer, which, after numerous subdivisions,
serve to connect neighboring cells.

By means of these juice-canals interchange between the contents of
the various cells is possible and the intercellular substance receives its
necessary supply of nourishment, while the connection of cell with cell
is an illustration of the loss of individuality of cell-life. Often we find

DEVELOPMENT OF TISSUES AND OKGANS. 31

cells connected by branching prolongations : in other cases the exten-
sions of the cells — which, to be sure, have a very different function and
structure from those alreacty alluded to, but which, nevertheless, serve as
connections between cells — so overbalance the cells in extent and number
that the latter often appear only as rounded swellings in the extensions
(e.g., in the nerves). (See Figs. 25 and 26.)

FIQ. 26.— NERVOUS GANGLIONIC CEL.L AND BRANCHING FIBRES, AFTER
KRAUSE. (Thanhoffer.)

xt, cell body; m, nucleus; me, nucleolus; pn, protoplasmic prolongations; tf, axis-cylinder fibres;
tn, axis-cylinder prolongations.

IV. THE DEVELOPMENT OF TISSUES AND ORGANS.

The final result of the metamorphosis of cells is the formation of
tissues out of which the various organs of the body are built up.

32 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The development of tissue starts in the earliest stages of develop-
ment of the egg.

We have seen already that, as a result of fecundation, the egg divides
into a number of minute segmentation spheres which at first form a
solid, mulberry -like mass, and we have now to consider the changes
occurring in the mass of simple, undifferentiated cells which result in the
development of the tissues and organs of the completed organism.

In their early stages, as in the amoeba, each of these cells possesses
the powers of development, reproduction, growth, assimilation, respira-
tion, and contractility. As the organism passes to a higher stage we
find that many of these cells lose these general properties possessed in
their entirety by undifferentiated protoplasm, while certain of them are
put aside to carry on specific individual functions. Thus, in the young
embryo, as in the amoeba, all the cells possess the power of contractilit}' ;
as the organism develops, this property becomes restricted to cells form-
ing constituents of certain tissues, the contractile tissues, or the muscular
system. The amoeba, which we have already seen maj^ be regarded as
representing one of the units of which the higher organisms are built up,
possesses the power of irritability and automatism. In higher forms
this property of undifferentiated protoplasm is restricted to a single
tissue, the nervous system. The amoeba has no part specialized for the
various processes of nutrition; any part of its substance may take in
nutritive matter, may digest out the portions capable of supplying its
nutritive needs, may remove the undigestible residue : any portion of
the amoeba is capable of carrying on the metabolic processes by which
the matter absorbed as food is converted into protoplasm like itself, and
any portion is capable of absorbing the gases necessary for these com-
plex chemical processes and of getting rid of the effete products of its
nutritive processes. In the higher organisms certain cells are set aside
to form the organs concerned in the prehension of food ; others have for
their sole function the secretion of solvent juices which will digest out
the nutritive matters of the food ; others are the carriers of the matters
absorbed to remote corners of the organisms ; and the sole business of
certain other cells is to get rid of the useless matter and the products
of the waste of the economy. In the amoeba any portion may divide off
from the parent stock and so originate a new individual; in the higher
animals certain tissues or collections of cells have for their sole office
the reproduction of cells which shall constitute the starting point of a
new organism. In the amoeba, therefore, specialization of function has
not commenced ; each minute particle of the protoplasm which constitutes
it is capable of carrying on all the vital functions. In the higher organ-
isms, however, the elementary organisms of which they are built up are
so arranged that there may be a division of labor. These collections of

DEVELOPMENT OF TISSUES AND OEGANS. 33

cells, marked by a more or less exclusiveness of function, are termed
tissues. It must not be overlooked, however, that, though certain func-
tions are accentuated in individual tissues, they all possess remnants of
all the functions originally seen in undifferentiated protoplasm. Thus,
maii}^ besides the muscular tissues possess the power of contractility :
it is not the nervous system alone which retains the property of
responding to irritants. All the tissues are capable of reproducing them-
selves in part, and all possess the power of carrying on their own
nutritive processes if suitable food is supplied to them.

We have seen that fecundation of the ovum leads to the develop-
ment of an immense number of new cells, and we have referred to the
modifications in form to which these segmentative spheres may be
subjected.

Tissues are formed from these segmentative spheres in three different
ways (Wundt) : —

1. Through formation of layers of cells.

2. Through union of cells.

3. Through excretions by cells.

Often all of these methods are united in the formation of a compound
tissue which is functionally active as a unit. Such a tissue is called an
organ. The classification of tissues is based on anatomical grounds; of
organs, on ph}'siological grounds.

1. To the first group belong the epitheliums. In most of these the
only modifications which occur in the form of the cells are due to
mutual pressure from close contact. Such cells are therefore polygonal
or flattened, or, when growth is most marked in one axis, cylindrical.
The epitheliums, in series of layers or in single rows, cover the external
surfaces of the body as well as the coatings of the digestive, urinary,
genital and respiratory tracts which communicate with it, the ducts of
glands, and the closed serous sacs. In the latter localitj^ they are called
endothelia, in the former epithelia. The hair and nails are modifications
of these tissues formed of small elongated cells grown together into
almost homogeneous tissues. The terminal portions of the organs of
special sense are also epithelial in nature.

Epithelial cells are connected by a thin layer of an albuminous
cement substance, which during life is in a semi-fluid condition.
The shape of the cell may be columnar or squamous. Spindle-shaped and
club-shaped cells, as well as goblet cells, ciliated cells, epidermic cells,
and prickle cells, are all modifications of these shapes. Endothelial cells
are always of the squamous variety, arranged in single layers of flattened,
transparent cells with oval nuclei. When their form approaches the
columnar, as occasionally is the case in certain serous membranes, they
are then in an active state of division, are called germinating cells, and

3

34 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the small spherical lymphoid cells which result are carried to the circu-
lation to become white blood-corpuscles.

Glandular tissue is also epithelial in nature. Cells are the essential
secreting organs of glands, though numerous other tissues enter into
their composition. Such cells are usually rounded or polygonal, and are
soft in consistence. Frequently the cells rapidly partially break down
and are carried off as constituents of the secretion, as colostrum cells,
or mucoid corpuscles (moulting); or the destruction of the cell form may
be complete and the constituents of the cell enter the secretion in the
form of a solution.

Muscular tissue forms the third of the group. In the muscles the
muscular cells are always closely associated with connective tissue.
Such cells may be of two different kinds, different in structure and in
function, — the striped and unstriped cells. Muscle-cells are contractile,
like amoeboid cells, but contractility is only possible in one definite direc-
tion, that of their long axis ; muscles, therefore, become shorter and
thicker during contraction.

2. To the second group of tissues formed by union of cells belong
two tissues in which, in their development, the cells have become greatly
elongated, and after absorption of the cell-wall become converted into
fibres or tubes ; these are the nerves and capillaries.

In the nervous tissues certain cells retain their primitive character,
the nerve-cells, and only nerve-fibres properly belong to this group of
tissues. Nevertheless the nerve-cells are in continuity with the nerve-
fibres.

The capillaries in a similar manner originate from the arrangement
of nucleated, spindle-shaped cells in rows, which become hollowed out
through the formation of vaeuoles. The formative cells manifest a ten-'
dency to send out sprouts which connect with other forming or mature
capillaries by which the net-work of capillaries is formed. Lymphatic
capillaries are developed in the same way as the blood-vessels.

3. Tissues formed by excretions from cells, forming the third group,
may also be called intercellular tissues. Connective tissue is a type of
this class. Connective tissues serve to bind together all the organs of
the body ; they exist in various forms, which are to a certain extent
mutual!}' convertible ; they all yield allied chemical products.

Connective tissue originates in spherical cells, with very soft proto-
plasmic nucleated contents, which ultimately may form a perfectly homo-
geneous, laminated, or fibrous intercellular substance.

The cells themselves may exist in various different forms, either as
tendon-cells, when they are flattened, oblong masses of protoplasm
arranged in rows, with round nuclei lying in bundles of fibrils of white
connective tissue ; as branched cells, found in the cornea, serous mem-

DEVELOPMENT OF TISSUES AND ORGANS. 35

branes, and subcutaneous tissues, which, under certain conditions, pre-
serve their power of movement ; as pigment-cells, which are branched
cells filled, with the exception of their nucleus, with granules • as fat-
cells, in which the protoplasmic cell-contents are replaced by a drop of
oil, which forces the flattened nucleus against the cell-membrane; and as
migratory cells, which are formed in the spaces of fibrous tissue, and
which possess the power of amoeboid movement.

The form of connective tissue in which least change is produced in
development is the so-called mucoid or gelatinous tissue. In some
of the invertebrates, as in mollusks, this tissue forms the greater part of
the bod}\ It consists of a soft, semi-fluid, intercellular substance, in which
numerous granules and broken down membraneless cells are suspended.
Many of these cells possess the power of amoeboid movement.

From this tissue in vertebrates the fibrillar connective tissue is de-
veloped by the condensation of this intercellular substance into bundles
of fibres, held together by an albuminous cement substance, in which
the forms of the cells become much changed, becoming flattened and
elongated by mutual pressure until the diameter of the cell is not greater
than that of the nucleus.

The elastic tissues are formed out of the fibrillar connective tissues,
which become so modified chemically as to yield elastin and not gelatin.
The fibres of elastic tissue are bright j'ellow in color, usually anastomose,
and are sometimes straight, but more often coiled up in bundles.

The different "forms of development of connective tissue, especially
of the intercellular substance, depend upon its different chemical meta-
morphoses. Thus, the gelatinous tissues owe their properties to a semi-
fluid albuminous booty, the connective tissue proper to gelatin-forming
bodies, cartilage or chondrin, and the elastic tissues to elastin, etc.

Bone is characterized by the deposit of inorganic compounds in its
intercellular substance. This hardened tissue then incloses the partially
broken down cells, which form the lacunae or bone-corpuscles, in which
the thickened membrane and nucleus are often visible, though they dis-
appear in old bones and their place is then taken \)y serous fluids, etc.

The bones are also rich in vessels which traverse the Haversian
canals.

As the deposit of salts occurs partly from these and partly from
the external membrane, the bones become laminated in structure, some
layers being parallel- with the canals, others with the exterior.

Cartilage is characterized by a sparse intercellular substance which
yields chondrin, and by large cells which are often the seat of endoge-
nous multiplication. As in bone, so in cartilage, the intercellular sub-
stance becomes arranged in the form of capsules around the cells, and
may either remain homogeneous (hyaline) or become fibrillar (fibrp-

36 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

cartilage or elastic cartilage, in which a dense net-work of elastic fibres
occupies the intercellular matrix). Most cartilages, except on articulating
surfaces, are covered by a fibrous membrane, the perichondrium, supplied
with blood-vessels, lymphatics, and nerves.

Bone is surrounded by a fibrous membrane, the periosteum, with an
inner layer of oblong nucleated cells, which, from the fact that the bone
is developed from them, are termed osteoblasts. Similar cells are also
found in the marrow of bones.

The organs of the animal body are always composed of several
tissues; they may be of three classes, in each one of which some one
tissue is especially prominent in function : —

1. Organs whose chief function depends upon tissues of the first
class (cells without intercellular substance).

a. Glands, which always in addition to the epithelium contain nerves
and blood-vessels. The epithelium is the essential part of glands, skin,
mucous and serous membranes.

/;. Muscles. In these are found muscle-cells as the functionally
prominent tissues, though associated with them are connective tissue,
blood-vessels, and nerves.

2. Organs whose chief function is manifested through tissues of the
second class.

a. Compound vessels, arteries, veins, and rvmph-vess-els. Although
the capillaries are formed by union of cells, in larger trunks this mode
of formation only applies to the endothelium, on which the other tissues
— elastic tissue, connective tissue, and pale muscular fibres — subsequently
develop in layers.

b. The organs of the nervous system. Nerve-cells and nerve-fibres,
formed by union end to end of cells, here form the essential tissues,
though blood-vessels and connective tissue are associated with them.

3. Organs whose function is due to intercellular substance. The bony
skeleton is the only representative of this group, and the modification
of connective tissue known as bone, or its antecedent cartilage, is the
characteristic tissue; as secondary tissues, connective tissue and blood-
vessels and nerves, representatives of the second class, are also met with.

For the mode of development of the compound organs in the
embryo the reader must be referred to text-books on anatomy or
embryology.

SECTION II.
CELLULAR PHYSICS.

I. THE PHYSICAL PEOCESSES IN CELLS.

As the tissues and organs of the animal body originate in ceils, we
should expect that the functions of the higher organisms, which we know
to be identical with those of the most elementary forms of life, would to
a certain extent be accomplished by the same general processes. We
have already divided the functions of animal life into the vegetative, or
nutritive, functions and the functions of relation, and have called atten-
tion to the attempt which has been made to reduce the working of these
processes to physical and chemical laws. Although in many points this
endeavor fails, the operation of the ordinary physical and chemical laws
serves to explain many of the complex phenomena of animal life. This
is especially seen in the maintenance of the nutrition of the organism.

That cells may retain a nutritive balance it is requisite, in the first
place, that they be .supplied with a proper pabulum, which must pass
from the exterior to the interior of the cells. We have found that the
typical cell is surrounded by a homogeneous or striated membrane,
which, like all other organic tissues, contains a large amount of water
closely associated with the ultimate molecules of which that membrane
is made up. Hence, the cell-membrane may be regarded as a porous
partition whose pores are filled with water, and which separates the
cell-contents from the surrounding media. These media may be either
gaseous, as the atmosphere ; fluid, like the lymph and blood in higher
animal forms, or water in aquatic forms of life; or semi-fluid, like the
more or less solid intercellular substance.

This passage of nutriment from the exterior to the interior of cells
is mainly accomplished b}^ purely physical means, not only in simple
unicellular organisms but also in higher forms of life, where digestion,
or the preparation of food for absorption, has for its object the reduc-
tion of food into such forms that the operation of the physical laws of
imbibition, capillarity, filtration, diffusion, and osmosis, aided perhaps
by chemical affinity, will be sufficient to enable the nutritive matters to
pass to the interior of cells.

When once in the interior of the cells the raw food-products must
be transformed into protoplasm similar to that of which the cell-contents

(37)

38 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

is composed. This is a purely chemical process, is accompanied by the
liberation of force, and requires for its performance the free access of
oxygen. Gases, also, must therefore pass from the exterior to the
interior, — a process which the laws of absorption and diffusion of gases
are quite sufficient to explain. Again, the chemical processes concerned
in the assimilation of food result in the formation of carbon dioxide,
urea, kreatin, and other crystalline bodies which are no longer of use
and which must be removed ; or the cell activity may take on the form
of a secretion, — that is, the cell-protoplasm ma}7, from the matter sup-
plied to it, manufacture certain substances which in the higher organisms
have to be used elsewhere. In either case the products of the proto-
plasmic operations must be removed. Here, also, physical laws are all
sufficient. Gases are removed under the laws of gaseous diffusion and
absorption. All ciystallized products are eliminated by equally
simple means. The absorption of fluid by the cell-contents through imbi-
bition leads to increase of volume, and hence to increased pressure on the
cell-membrane. Filtration thus comes into operation. Or, if the pres-
sures within and without the cell are equal, interchange of matters in
solution may take place through diffusion and osmosis. All these proc-
esses may occur equally well in membraneless cells ; for, in all cases, to
permit interchange the dividing membrane must be capable of absorbing
the fluids or solutions with which it is in contact. The conditions, then,
are analogous to those of a body containing fluid by imbibition in con-
tact with another fluid.

We have now to consider some of the physical processes concerned
in these operations. The chemical processes will subsequently receive
attention.

The explanation of the physical processes in cells is to be found in
the molecular forces which fluid molecules exert on each other and on
solids with which they may be in contact.

1. COHESION is the force which binds together adjacent molecules of
the same nature ; for example, two molecules of water or two molecules
of iron. This attractive force is strongly exerted in solids, less so in
liquid, and is absent in gases. It is measured by the force which is
required to tear a body asunder. The closer the molecules of a body
are together, the greater their cohesive force.

Cohesion varies inversely with the square of the distance which
separates the molecules ; anything, therefore, which drives the molecules
apart will tend to weaken their cohesive force. When bodies are heated
the expansion which they undergo is due to the separation of their mole-
cules. Hence, when solids are heated their molecules are further and
further separated until finally their cohesive force is balanced by the
repulsive force, and the bodies«pass from a solid to a liquid state. This

PHYSICAL PEOCESSES IN CELLS. 39

occurs in all cases, provided the heat to which they are subjected does
not cause them to undergo chemical change. If a body which has been
fused by heat has its temperature still further raised its molecules
become so much further separated that the force of cohesion is not
sufficient to keep them in contact, and the body then becomes vaporized.

In liquids the force of cohesion is not great ; hence their molecules
are readily displaced and a mass of liquid assumes the shape of the vessel
which contains it ; in other words, the force of gravity overcomes the
force of cohesion. Cohesive force is, nevertheless, present in liquids, and
may be demonstrated by the difficulty with which a plate of glass placed
horizontally in contact with the surface of water is removed vertically
upward. This difficulty is due to the fact that the adhesion of the glass
to the water being greater than the cohesion of the water, the molecules
of water must be violently separated to permit of the removal of the
glass.

The spheroidal form assumed by small masses of liquid, as in a drop
of dew, a globule of mercury, is due to the working of the force of cohe-
sion of the molecules of the liquid. In a small drop of mercury placed
on a surface for which it has no adhesion, as wood or glass, the sum of
the mutual attractions of all its molecules being greater than the force
of gravity acting on them, the globule assumes the spherical form. If,
however, the drop of mercury is large, then the force of gravity increas-
ing with the mass of the body becomes greater than its cohesion and the
drop becomes flattened.

The molecules of all liquids attracting each other, it is evident that
the molecules in the free surface of a liquid will be attracted by and will
attract those below them, but will exert or will be subjected to no exter-
nal attraction. At the surface of liquids, therefore, there is always an
inward attraction, which is called surface tension. Of course, in these
considerations external accidental pressures and attractions to which the
liquid may be subjected are neglected.

The surface tension of liquids is well illustrated by blowing a soap-
bubble on the end of a glass tube ; as long as the other end of the tube
remains closed the elastic tension of the air in the bubble balances the sur-
face tension of the soap-film, but when the end of the glass tube is opened
the tension of the film leads to the contraction and final disappearance
of the bubble. So also insects can move on the surface of water without
sinking, for the water, not being able to wet their feet, forms a depression,
and the elastic reaction of the surface supports them. The case is simi-
lar when a sewing-needle is floated on water ; as the needle is coated
with a thin film of oil the water does not adhere to it, the surface becomes
depressed, and its increased tension serves to support the weight. Wash-
ing the needle first in alcohol, ether, or potash causes it at once to sink.

40

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The importance of these facts will be seen in the explanation of
capillary phenomena.

2. ADHESION is the molecular attraction exerted between the surfaces
of bodies in. contact ; it may be manifested between solids (as between
two freshly-cut surfaces of a leaden bullet, or two pieces of plate-glass),
between solids and liquids (as when a drop remains clinging to a glass
rod which has been dipped in water), and between solids and gases (as
shown by the bubbles of air which adhere to a glass or metal plate when
immersed in water).

The adhesion of liquids to solids, which alone of the above will
receive attention at present, is greater than the cohesion of liquids, as
already mentioned. Thus, when a drop of water is placed on a glass
surface it does not assume the spheroidal form, but becomes flattened
out, showing that the adhesion of the water to the glass is greater than
the cohesion of the water. If, however, the glass plate be greasy, then
the drop of water will exert no adhesion to the glass and will remain
spheroidal. This adhesion of liquids to solids is not universal, but

.FIG. 27. FIG. 28. FIG. 29. FIG. 30.

CAPILLARY PHENOMENA. (Ganot.)

depends on the nature of both the solid and the liquid. Certain liquids
are capable of adhering to, or wetting, certain solids and not others ; and
a solid to which one liquid will adhere will be inert, or even repulsive to
another. These facts also are of importance in the explanation of
capillarity.

3. CAPILLARITY. — When a solid body is placed in contact with a liquid
the phenomena (attraction or repulsion) which result are termed capillary
phenomena from the fact that they are best seen when capillary tubes
(capillus, a hair) are immersed in liquids.

As already stated, water is capable of adhering to glass. When a
glass rod is dipped into water, the water is raised up against the sides
of the rod to form a concave surface above the level of the water, as if
no longer subject to the laws of gravity (Fig. 27). If, on the other
hand, a glass rod be dipped into mercury, which does not adhere to
it, the mercury is depressed around the rod, forming a convex surface
below the level of the surrounding fluid (Fig. 28). If glass tubes
with narrow bore are immersed in water and mercury, in the former

PHYSICAL PKOCESSES IN CELLS.

41

the water will rise within the tube considerably above the level of
the water outside, and the surface of the water in the tube will be
concave (concave meniscus); while the mercury will be depressed in
the glass tube below the level of the mercury on the outside and the
surface of the mercury within the tube will be convex (convex meniscus)
(Figs. 29 and 30). If any two bodies, such as two glass plates, are
immersed sufficiently near to each other in a liquid, the liquid will
rise or be depressed between them, according as the liquid has or
has not any adhesion to the plates (Fig. 31), the degree of elevation or
depression being one-half what it would be if a tube of glass whose
diameter equals the distance between the two plates were immersed in the
same liquids. If a drop of water be placed in a conical glass tube of
small angle and horizontal axis, each end of the drop will have a concave
meniscus and it will move from the large to the small end of the tube :
if the liquid be mercury, each end will have a coiiA*ex meniscus and it
will move in the reverse direction (Figs. 32 and 33).

In the explanation of capillary phenomena
two causes deserve attention : first, the cause of
the curvature of the surface, and, second, the cause
of the ascent or depression of the liquid within
the tube.

FIG. 31.

FIG. 32.

FIG. 33.

The form of the surface of a liquid in contact with a solid depends
on the relation between the attraction exerted by the solid on the liquid
and the mutual attractions of the molecules of the liquid. Any molecule
of a liquid in which a solid is immersed is acted on by three forces : 1st,
gravity; 2d, the attractive force of the solid for the liquid molecule ; and
3d, the cohesive attractions of the other molecules of the fluid.

According to the relative intensities of these forces their resultant
may occupy one of three positions : —

First. — If the attraction of the solid balances the cohesive attrac-
tion of the fluid, the resultant of these two forces will coincide with the
force of gravity and the surface of the fluid will be horizontal; for to
be in equilibrium the surface of a liquid must be at right angles to the
direction of the resultant of all the forces acting on that liquid
(Fig. 34).

Second. — If the attractive force of the solid for the fluid increases,
or if the cohesive force of the liquid diminishes, the resultant will fall
outside of the line of gravity or between the line of attraction of the

42

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

solid and the line of gravit.y, and the surface of the liquid being at right
angles to that resultant will be concave (Fig. 35).

Third. — If the attraction of the solid for the liquid decreases, or
the cohesive attraction of the liquid increases, the resultant will fall to
the other side of the line of gravity, or between the line of cohesive
force of the liquid and the line of gravity, and the surface of the liquid,
being perpendicular to that resultant, will be convex (Fig. 38).

FIG. 34.

FIG. 35.

FIG.

DIAGRAMS ILLUSTRATING CAUSE OF CURVATURE OF LIQUID SURFACES IN
CONTACT WITH SOLIDS. (Ganot.)

The molecule m is acted on by gravity, in the vertical line m P : is attracted by the plate n. in the line
n m, and by the liquid F, in the line m F. The direction of the resultant m R will depend upon the relative
intensities of these forces. If n m and m F balance, the resultant is vertical, m R (Fig. 34), and the surface
is horizontal. If n m increases, or m F decreases, the resultant R is within the angle n m P, and the surface
is concave (Fig. 35). If m F increases, or n m decreases, the resultant R is within the angle I'm F, and the
surface is convex, for the surface of a liquid is always perpendicular to the resultant of forces acting on
its molecules (Fig. 36).

The ascent or descent of liquid within a capillary tube is dependent
on the manner in which the curvature of the surface modifies the prin-
ciples of hydrostatic equilibrium.

When a tube of large calibre is immersed in a vessel containing
liquid the conditions of equilibrium are the same as in two communicating
vessels containing the same fluid. Equilibrium is only possible when the

surface of the liquid in both vessels is
on the same horizontal plane. For, take
any molecule in the plane MN (Fig. 37).
It will be subjected to a downward pres-
sure equal to the weight of a column of
the same fluid, the height of which is equal
to the distance of that molecule from the
surface of the fluid within the tube. It
will also be subjected to an upward pres-
sure which is equal to the weight of a
column of liquid whose height is equal to
the distance of that plane from the surface

of the liquid without the tube. These weights are, however, equal.
Therefore every molecule in the plane MN will be subjected to equal and
contrary pressures, and will consequently be in equilibrium.

Suppose, however, the tube have a diameter less than one millimeter.
The concave surfaces produced by the adhesion of the fluid to the

FIG. 37.— DIAGRAM ILLUSTRATING
LIQUID PRESSURES.

PHYSICAL PROCESSES IN CELLS. 43

walls of the tube will then intersect, and the surface of the fluid within
the tube will be a concave meniscus. In other words, every portion of
the surface of the liquid within the tube will be under the attractive influ-
ence of the walls of the tube. A certain portion of the fluid within the
tube will so be held up by adhesion to the tube, and will hence exert
no downward pressure. As a consequence the downward pressure within
the tube will be less than the upward pressure of a column of fluid of
the same height without the tube. Any molecule on any plane below
the surface of the fluid in the tube would so be subjected to two
unequal pressures, a greater upward pressure and a lesser downward
pressure ; the column of liquid will therefore rise within the tube until
these two pressures are equal.

When, however, the force of cohesion of the liquid is greater than
that of adhesion to the walls of the tube, as already explained, the sur-
face becomes convex and the surface tension is increased. Since the
molecular forces are greater than gravity, the downward pressure in the
tube is greater than the upward pressure to which any plane is subjected
by the weight of the liquid outside of the tube. The fluid then is de-
pressed in the tube until these two pressures are equal.

Capillarit}- partly explains the ascent of the sap in trees, the ascent,
of oil in a lamp-wick, to a certain extent the movement of the blood and
lymph in the capillaries, but more especially the entrance of fluid into
porous bodies, — a fact of the greatest importance as underlying the expla-
nation of imbibition, filtration, and osmosis.

4. SOLUTION. — That a substance may enter the interior of cells it
must, as a rule, be in a state of solution; though we shall find, when we
study the process of absorption, that there are several exceptions to this
statement.

The process of solution of solids in fluids is of very general occur-
rence in cell life. Almost all food-stuffs are solid, and to be of nutritive
value must first be reduced to the form of a solution ; even the con-
sumption of organic matter in the vital processes of a cell results in the
formation of a watery solution, as in the formation of urine, sweat, and
the various secretions.

When a solid dissolves in a liquid, the cohesion of the molecules
of the solid is broken by their adhesion for the molecules of the liquid.
When, therefore, the attraction of the liquid for the solid is greater
than the cohesion of the solid, the latter is said to be soluble and its
molecules separate. The limit of solubility is reached when the attrac-
tions of adhesion and cohesion are balanced.

Anything that reduces the cohesion of a solid favors its solution;
thus, heat accelerates solution by separating solid molecules through
the expansion which it produces, and, by increasing the distance between

44 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the molecules, thereby weakens their cohesive force. Pulverizing, by
mechanically separating the molecules to a certain extent, also assists
solution.

Heat is always essential to the conversion of a solid into a solution.
Ordinarily the heat is abstracted from the surrounding media, and is
rendered latent in the solution, thus explaining the mode of action of
freezing mixtures. The amount of heat so rendered latent in forming a
solution is nearly always equivalent to the amount required to melt the
body.

In certain cases, however, instead of the temperature being lowered
in the process of solution, it actually rises, as when caustic potash is dis-
solved in water. This depends upon the fact that two contrary proc-
esses are going on at the same time ; the solution, which tends always
to produce a reduction of temperature, and the chemical union of the
potash with the water, which, like many other chemical processes, tends to
cause an increase of temperature. Consequently, as one or the other of
these processes predominates the temperature will fall or rise ; or, if the
two balance, will remain unchanged.

Solubility varies greatly in different bodies and in different liquids.
Some solids are soluble only in hot media, and are deposited on cool-
ing ; others only in cold liquids, and are thrown out of solution when
the temperature of the liquid is raised. As a rule, bodies dissolve in
liquids which have similar properties ; thus crystalline bodies are soluble
in water, fats in oil, metals in mercury, and resins in alcohol.

u When two or more salts are dissolved in water without chemical
action on each other, three conditions result : 1st. The quantity of each
salt held in solution is less than when it alone is present, though the
combined quantity is greater than when only one salt is used. 2d. The
quantity of each is as great as when one only is used ; then the total
quantity dissolved is the sum of that taken up in each single solution.
3d. The quantity dissolved is greater than when one alone is used,
the addition of the second salt in this case increasing the solubility of
the first, and often the first increasing also the solubility of the second"
(Draper).

When the cohesion of the solid and its adhesion for the liquid mole-
cules balance, the solution is then said to be saturated. In the case of
certain fluids, like alcohol and water, there is no limit to solubility ; their
molecules will freely mingle with each other, and the resulting liquid is
said to be a mixture, or an emulsion. On the other hand, two liquids
may offer an example of true solution, one being only capable of passing
to a certain degree between the molecules of the other, as in the case of
volatile oils and water, where the limit of solubility is readily reached.

5. IMBIBITION. — Every porous solid may be considered as formed of

PHYSICAL PKOCESSES IN CELLS. 45

a collection of capillary tubes. When such a solid (e.g., a piece of chalk)
is immersed in a fluid which is capable of wetting it, the fluid will enter
into the pores of the solid through capillarity, and will remain even after
the body is removed from the fluid. The solid is then said to have
absorbed fluid by imbibition. Organic bodies also are capable of absorb-
ing fluid by imbibition, but the process is somewhat different from that
of the inorganic porous body.

Every organic bod}^, no matter what its consistency, contains always
a large amount of water in its composition, to which fluid, as we shall
find later, many of the physical properties of the tissues are due. When
inorganic bodies contain fluid, that fluid is held in one of two ways, —
either chemically united with the body, as in hydrates, or as water of
crystallization ; or mechanically in the pores of the solid. Organic bodies
occupy a mean between these two. The water in their composition is
not in a form of chemical combination, nor is it held mechanicalty in
pores, as in the porous inorganic body, though the conditions are some-
what similar to the latter case. That there is a difference, however, is
proved by the different effects of the abstraction of water from organic
and porous inorganic bodies. The physical characters of porous, inor-
ganic solids, such as baked clay, are not seriously altered by the removal
of water contained in their pores. The abstraction of water from semi-
solid organic bodies, on the other hand, entirely changes their physical
and physiological properties. A piece of connective tissue in its fresh
condition is soft, white and glistening, flexible, extensible and elastic.
When the water which it contains is removed by drying, it shrivels up,
becomes rigid, yellowish in color, brittle, and loses weight. If it be then
immersed in water its previous characters will be restored. This differ-
ence in the manner in which the water entering into the composition of
organic and inorganic bodies is held is explained by the assumption that
in the porous inorganic body the water occupies comparatively large
spaces between particles of solid, while in the organic body the water
surrounds the ultimate molecules of the body. Organic tissues, ma}'
therefore be defined as bodies whose intermolecular spaces are filled
with fluid.

As the fluids are held in a different manner in inorganic and organic
bodies, it is natural to find that the way in which the fluid is absorbed
differs in the two cases.

When a dry, porous, inorganic body, such as a piece of chalk, is
thrown into wrater, the water enters the pores of the chalk by capillarity
and displaces the air which was contained in its pores. It increases in
weight by the addition of the weight of the absorbed water, but does
not increase in volume. When a dry organic body, such as a piece of
gelatin, is thrown into water no air is displaced, and yet many times

46 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

its own volume of water may be absorbed. The gelatin must therefore
increase in volume. The fluid in organic imbibition passes into the inter-
molecular spaces and separates the molecules. That an organic body may
imbibe fluid it is consequently necessarj^ that its molecules be freely
movable.

The power of imbibition possessed by the organic tissues is espe-
cially due to their albuminoid constituents. Protoplasm is, therefore,
above all capable of imbibition, and the rapid formation or disappear-
ance of vacuoles in protoplasmic cells may be due to rapid changes in
imbibition.

Every organic substance has a limit be}rond which imbibition is
impossible. This limit is lower when the water contains solids in solu-
tion, provided the solids are not chemically acted on by the tissues, from
the fact that imbibed water is held with greater tenacity by the tissues
than are the substances held in solution in the water. Thus, when a
tissue saturated with a salt solution is subjected to pressure, the solution
first pressed out is more concentrated than that which is forced out when
the pressure is subsequently increased ; and in general the fluids lose in
concentration in imbibition. Organic tissues therefore absorb water with
greater readiness than saline solutions. The importance of this fact will
be seen in the explanation of osmosis.

The extent of imbibition depends, therefore, on the membrane and
the nature of the fluid with which it is in contact. Thus it has been
found by Liebig that one hundred parts of ox-bladder absorb, of —

Water, 268 volumes.

Salt solution (1.204 sp. gr.), . . . .133
Alcohol (84 per cent.), . . . . .38 "
Marrow oil, . . . . . 17 - "

Membrane, therefore, has less affinity for a salt solution than for
water. This may also be shown by soaking a bladder in water, wiping
it dry, and then sprinkling it with common salt. The salt comes in
contact with some of the water in the bladder, dissolves, and forms a
salt solution. But as the membrane can contain less salt solution than
water, some of the solution is expelled and the bladder shrivels up.
So also a moistened bladder thrown into alcohol shrivels up, because
the alcohol mixes with the water in the bladder ; and as the bladder,
as shown above, can only absorb one-seventh as much alcohol as
water, the solution is driven out. This is the explanation -of the use
of alcohol and various saline solutions for hardening tissues for making
microscopic sections.

In the nutrition of animal cells the process of imbibition is an
important factor. Every substance which is soluble in water is capable
of being appropriated by the protoplasm and maj^, through imbibition,

PHYSICAL PEOCESSES IN CELLS. 47

obtain access to the interior of cells, to there undergo the transformations
which the needs of the economy necessitate. In cells which possess a
closed membrane, capillarity may also be concerned ; for there is reason
to suppose that the striated appearance which is seen on examining most
cell-membranes with a high power under the microscope is in reality due
to the presence of minute apertures, or canaliculi. Fluid will therefore
enter the pores in the membranes of cells, and so obtain access to the
protoplasmic cell-contents. The passage of fluids, however, through the
cell-membrane is not necessarily dependent on capillarity. For the
cell-membrane, like other organic tissues, is capable of absorbing water
by imbibition in the same way in which water is absorbed b}T gelatin, i.e,
by entering into its intermolecular spaces. The state of affairs is thus
similar to the conditions described in the experiment with the bladder
and salt. We have an organic tissue soaked with a fluid in contact with
a substance (protoplasm) having an affinity for that fluid greater than
the affinit}^ of the membrane for the fluid; the fluid, therefore, leaves
the cell-membrane to enter the protoplasm by organic imbibition.

The affinity of protoplasm for water is never satisfied during life :
or, in other words, the maximum amount of water capable of being
absorbed by cell-contents is never reached. Cells will, therefore, always
absorb fluid when brought into contact with it, and by so doing will
tend to increase in volume. As, however, the extensibility of cell-
membranes is in most cases very limited, the increase in volume of the
cell-contents will tend to cause filtration of the fluid contained in the
meshes of the protoplasm back through the cell-membrane to the
exterior.

These facts which we have learned in reference to the imbibition of
fluids by organic tissues give but an imperfect idea of the processes of
imbibition which take place in living cells. Many fluids which are
absorbed by dead tissues are perfectly indifferent to living cells, and
there can be no doubt but that imbibition in living tissues is largely
governed by the nature of the chemical affinities caused by the chemical
processes continually taking place in the interior of active cells. Thus,
living tissues (muscles) are incapable of absorbing dilute solutions of
sodium salts ; the same tissues when dead will absorb it in large amounts.
Potassium salts, on the other hand, are rapidly absorbed by the same
tissue and almost instantly cause its death, though even in this case the
power of imbibition for the potassium salt is greatly increased after
death. Again, we shall find that the prolonged activity of many tis-
sues, especially the muscles, is manifested in the production of an acid
reaction in the cell-contents; under such circumstances, sodium solutions,
which are indifferent to these tissues at rest, will now be absorbed by
them.

48 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The following figures represent the behavior of the muscular tissue
to solutions of different salts (Ranke) : —

MAXIMUM IMBIBITION.

1 PER CENT. Na'Cl. 1 PER CENT. K Cl.

Living, resting muscle, . 0 Positive, but not capable of

estimation, as the muscle
instantly died.

Living, tetanized muscle, . 13 Positive : not to be estimated,

for the same reason as above.
Dead muscle, . . .35 136 per cent.

Perfectly analogous observations have also been made in the case of
the nervous tissues.

It would, therefore, appear that living tissues only absorb by
imbibition when their vital forces are diminished in energy. In the
organism the cells are continually bathed in a fluid which contains the
matters necessary for the nutrition of the cells. If the cells have been
at rest their nutritive equilibrium lias not been disturbed and imbibition
does not take place. If, however, they are exhausted by previous
activity, imbibition is then inaugurated, nutritive substances enter, the
results of cell activity are extruded (acids, etc.), nutritive equilibrium is
restored, and imbibition not only ceases, but from the increased volume
of the cell-contents pressure is produced on the cell-membrane and the
excess of fluid is forced through again to the exterior b}T filtration.
Consequently cells which are most weakened by prolonged activity are
the cells which carry ont as a direct result of the chemical affinities
created by that activity, the most active imbibition. By these peculi-
arities in the conditions which govern imbibition in living cells is to be
explained the peculiar distribution of the inorganic salts in the animal
bod}T, — sodium in the fluids, potassium in the solid organs of the body.
For, as we know, sodium solutions are indifferent fluids and are not
absorbed by the tissues unless they have undergone some depression in
energy, while potassium salts in solution are rapidly absorbed and lead
to the death, the drowning out of protoplasm.

6. FILTRATION OR TRANSUDATION is the passage of fluid through a
membrane dependent upon inequality of hydrostatic pressures ; but that
a fluid should so pass it is essential that the membrane be capable of
absorbing the fluid by imbibition.

The greater the affinit}^ of the fluid for the membrane (see Imbibition}
the more rapidly will the fluid under a moderate pressure pass through
the membrane: thus water, or even a saline solution, will filter more
rapidly than oil. Filtration will occur more rapidly through a thin than
a thick membrane.

The rapidity of filtration is, further, in direct proportion to the pres-
sure which the fluid exerts on the membrane, and increases with increas-

PHYSICAL PROCESSES IN CELLS. 49

ing temperature. Solutions of different salts pass almost unaltered
through membranes, though the filtrate, from the fact that the membrane
keeps back some of the water of solution, may be more concentrated.
The reverse is true in the filtration of colloids (bodies like glue) ; there
the filtrate contains a smaller percentage of the colloid than the original
fluid, — from the fact that the membrane allows more water to pass than
gum, albumen, etc.

This explains the fact that colloid bodies, perhaps on account of
the great size of their molecules, are with great difficulty removed from
the pores of animal and vegetable tissues, especially since it has been
found that if the fluid which contains colloids in solution also contains
crystalloids, less colloid will filter through than if the crystalloids had
been absent, and the filtrate is richer in crystalloids than the fluid in the
filter. Crystalloids, therefore, hinder the filtration of colloids ; and as
protoplasm is always associated with certain saline bodies, the latter
prevent the loss of the albuminoids of the cell-contents.

Many of the phenomena of filtration may be explained under the
working of the laws of capillarity, especially when the filter is an inorganic,
porous solid. When, however, it is an organic membrane, as of course
is always the case in the animal or vegetable cell, there the laws of imbi-
bition are of prime importance.

Cell life furnishes many examples of the process of filtration. When
the cell-contents increase in bulk through imbibition the pressure on the
interior of the cell-membrane is greater than on the exterior; substances
in solution within the cell may then pass through the cell-membrane.
The formation of the saline constituents of the various secretions is
probably accomplished in this way. When the flow of blood is obstructed
in a vein the pressure back of the obstruction becomes greatly increased,
and the water and saline constituents of the blood pass through the
walls of the vessel. In this way O3dema and dropsies are produced. In the
liver, so long as the pressure in the bile-ducts is low, the bile filters from
the liver-cells into the bile-ducts. But if the flow of bile is interfered
with so as to make only a slight resistance in the bile-ducts, the bile then
filters into the hepatic parenchyma, from there into the lymphatics, by
which it is carried throughout the body, and jaundice is produced.

When the renal secretion comes under consideration it will be found
that the process of filtration there fills a very important role.

When fluids pass from the interior to the exterior of cells, or the
reverse, they usually come into contact with other fluids. Under certain
circumstances these fluids will mix ; under others mixing will not occur.
Those conditions now demand consideration.

7. DIFFUSION OF LIQUIDS. — The molecules of liquids, as has been
already seen, are held together by a force of attraction, or cohesion ; the

4

50 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

molecules of liquids are also capable of exerting an attractive force on
solids, or adhesion. In addition to these two modes of manifestation
of molecular force, molecules of liquids are capable of attracting mole-
cules of other liquids. If in two different liquids brought into contact
the cohesive force between the molecules of each liquid is greater than
the attractive force between the molecules of the different liquids, the
liquids remain separate and apart, and are said not to be miscible.
Water and oil furnish examples of such liquids.

If, however, the attraction between the molecules of the different
liquids is greater than the cohesive force of either, then the liquids will
mix, even against gravity, until the mixture becomes uniform. Such a
process of mixing is called diffusion of liquids. It follows, therefore,
that whenever two chemically indifferent fluids are brought into contact
with one another the}^ mix, even without any disturbing cause, until a
perfectly uniform mixture results.

Diffusion may be illustrated by filling a small bottle with some saline
solution and then placing it in a large jar, which is then carefully filled
with distilled water, so poured in as to cover the mouth of the small jar
which contains the saline solution, at the same time avoiding any mixing
of the fluids by movement.

If a small portion of the water in the large jar is then drawn off
carefully from time to time with a pipette, it will be found that the
water will contain a gradually increasing quantity of the salt, until
finally the jar will be filled with a perfectly uniform saline solution.

From such experiments it has been found that the rapidity of dif-
fusion increases with the extent of surfaces in contact, with the tempera-
ture, and with the difference in concentration of the two fluids ; it is,
therefore, more rapid at the beginning of the experiment, when the outer
jar contains distilled water, than later, when it contains a saline solution.
The rapidity of diffusion also varies with the chemical nature of the
solutions ; thus, potassium salts diffuse much more readily than sodium
salts, — a point which we shall later see is of great importance. Acids dif-
fuse very rapidly; alkaline salts and sugar slower, and colloids, perhaps
from the fact that they cannot form true solutions, scarcely at all, though
colloids in solutions with crystalloids do not interfere with the diffusion
of the latter ; while, when two salts undergo diffusion together, the least
diffusible salt diffuses more rapidly than it would alone.

In the different animal tissues, in addition to the intermolecular
spaces filled with fluid, we have also larger spaces, or sensible pores,
which contain fluids, and which form a system of more or less fine canals
traversing the different parts of the body (lymph-spaces, lymph- and
blood-capillaries). Therefore every internal part of the animal body is
continually bathed in liquid into which fluids leaving the cells are

PHYSICAL PROCESSES IN CELLS. 51

capable of diffusion. In most cases, however, these fluids are in con-
stant motion, and the purely physical phenomena of diffusion are of
little importance, particularly when the extreme slowness of ordinary
diffusion is remembered. As the composition of the fluids of the body
is continually changing, diffusion, greatly aided by the motion of the
fluids, will, nevertheless, serve to maintain a certain degree of constancy
of composition.

It has been already shown that when watery solutions are found on
different sides of a membranous partition, as in the case of the cell-con-
tents of two neighboring cells whose contents are more or less fluid, the
membrane does not serve to keep the fluids apart. For, the membrane
being capable of absorbing liquids by imbibition, the liquids fill the
intermolecular spaces of the membrane, and so come in contact with each
other; the phenomena of diffusion then commence, though the process is
very greatly modified by the behavior of the intervening membrane. As
already mentioned, diffusion, with the exception of the part it plays in
distributing fluids uniformly through the interior of cells, fills quite a
secondary role in the physical processes of the animal economy. Dif-
fusion as modified by the passage of liquids through an animal membrane
occupies a much higher position in point of importance.

8. OSMOSIS. — When two liquids capable of mixing are separated by a
membrane which possesses the power of imbibing these liquids, a gradual
union of the two liquids takes place through the membrane.

This interchange, which is called osmosis, continues until the two
liquids are equally mixed ; consequently, the final result is the same as if
no membrane separated the two liquids, though the process is essentially
different ; for the diffusion currents must be modified by the molecular
forces which the molecules of the membrane exert on the liquids in con-
tact with them. If two liquids are
poured into the arms of a U-tube
(Fig. 38) so that they are in con-
tact at A they will mix, but the
level will remain the same in both
tubes, i.e., equal portions of each
liquid pass into one another in equal
time ; if, on the other hand, a mem- FIG. 38.

brane is placed at A the liquids will

mix, but the column of liquid will rise in one tube above the original
level and sink to a corresponding amount in the other. From which it
follows that in the mixing of liquids through a membrane the interchange
is unequal, i.e., more of one liquid passes than of the other. The current
through the membrane is a double one. Thus, if a saturated salt solu-
tion is placed in one arm of the tube and an equal quantity of distilled

52 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

water be placed in the other, the salt solution will soon be found to have
increased in volume and the water to have decreased. If the character
of the two liquids is then examined it will be found that the distilled
water is no longer pure, but that it contains salt ; while the saline solu-
tion will be no longer saturated, but of much less density. Salt has
therefore passed through to the water and water passed through to the
salt solution. There has been, however, as is evident, a difference in
the rapidity with which the two substances have traversed the mem-
brane. That this process is not at all analogous to nitration — in fact is
directly opposed to it — is seen in the continued ascent of the column of
liquid in one arm of the tube, showing that the water passes to the salt
solution even against a continually increasing hydrostatic pressure.
The tendency is therefore for nitration currents to form in the opposite
direction to the osmotic current. If one liquid is water and the other
salt solution, the amount of water passing to the salt solution for each
equivalent of salt passing to the water is called the osmotic equivalent
of the salt. The osmotic equivalent is dependent upon the chemical
nature of the body and the concentration of its solution.

Thus, for sodium chloride it is 4.3, meaning that for every gramme
of salt which passes through the membrane 4.3 grm. of water will pass
in the opposite direction to the salt. For sodium sulphate it is 11.6;
potassium sulphate, 12 ; magnesium sulphate, 11.7 ; alcohol, 4.2 ; sugar, 7.1.

In general the osmotic equivalent increases with the temperature,
and varies very greatty with the concentration of the solutions.

The rapidity with which different bodies diffuse through a porous
membrane is independent of their osmotic equivalent, but is directly
dependent upon their chemical nature and solubilit}T, increasing with
solubility ; and bodies nearly related as to their chemical composition
are also, nearly related as to rapidity of diffusion. The rapidity also
increases with increasing difference of concentration between the two
liquids and with increase of temperature.

When two solutions of" the same substance but of different densities
are allowed to diffuse into one another, the denser decreases in density
and the lighter increases, and the same alterations of volume occur as
would be the case were one of the liquids pure water. The osmotic
equivalent is in both cases the same, but in the former case the rapidity
of osmosis is much less.

If two solutions of substances of different chemical composition are
allowed to diffuse, the rapidity will increase with increase in the chemical
affinity between the two substances.

All colloids pass with difficulty through organic membranes, but as
they have a strong affinity for water they draw it with vigor through
organic membranes ; hence, their osmotic equivalent is very high, though

PHYSICAL PKOCESSES IX CELLS. 53

the current of water to the colloid is ver}' slow, possibly because the
large molecules of the colloids readily stop the pores of the membrane.
Albumen in solution passes more readily through a membrane to mix
with salt solution than with water. A very concentrated solution of
salt, however, prevents osmosis of albumen by simply removing the water
from the albuminous solution.

When a solution of a diffusible substance, together with a solution
of a colloid, is placed on one side of a membrane and pure water on the
other, at first none of the colloid passes through the membrane, but
simply water to the colloid and the diffusible substance to the water;
hence, albumen may be freed of its salts by diffusion (dialysis), or, if a
mixed solution of sugar and gum is subjected to dialysis, only the sugar
passes through the membrane.

An exception to this is seen when albumen and salts dialyze with water.
First the salts pass, then the albumen passes into the salt 'solution.

Just as we found there were two kinds of imbibition, — the capillary
and molecular, — so are there two kinds of osmosis, which differ somewhat
according as the partition between the two fluids is a porous, inorganic
solid, or an organic tissue capable of absorbing liquid by imbibition. In
the case of a porous, inorganic partition the phenomena of osmosis are
entirely governed by capillarity and the laws of diffusion of liquids.
Certain liquids have a greater tendency to enter capillary tubes than
others. When, therefore, two miscible liquids are separated by a porous
solid, which may be regarded as a collection of capillary tubes, the liquid
which has the greater affinity for the walls of the tube will enter to a
greater extent than the other, and will meet the other fluid advancing in
the opposite direction, but with less force on account of its lesser affinit3\
The two liquids thus coming into contact with each other will diffuse into
each other, and the pores will be occupied with a mixture of two liquids,
for one of which the walls of the tube will have a greater affinity than
for the other. Then, although diffusion will take place from this mixture
into the liquid of greater affinity, the latter continually forcing out some
of the mixture, the liquid of lesser affinity will continually increase in
volume.

In the case of organic membranes, the power possessed by the mem-
brane of imbibing different liquids enables osmosis to take place, while
the direction of the current is governed by the affinity of the liquids for
the membrane. Whichever liquid has the greater affinity for the mem-
brane will pass in greatest amount. Here, for the sake of simplifying
the matter, we may assume that the liquid wrhich has entered the inter-
molecular spaces of the membrane is, to a certain extent, governed by
the same conditions which apply to the entrance of liquids into capil-
lary tubes.

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

When an organic tissue has absorbed liquid by imbibition, its inter-
molecular spaces being filled with that liquid, the liquid, which becomes
superficial on the far side of the membrane, is in direct continuity with
the body of the liquid having the greater affinity for the membrane, and
in direct contact with the liquid of lesser affinity. Diffusion phenomena
therefore commence.

When a membrane has a tendency to imbibe water, it will absorb
more water than salt solution, if placed between water and a salt solu-
tion, and will increase in volume. In every pore or intermolecular
space of the membrane, therefore, the layer of liquid in contact with
the sides of the pores, or with the solid molecules, will contain less
salt than water.

From the affinity which the two liquids exert on one another this

condition will not remain constant,
and the rapidity with which the inter-
change takes place will depend upon
the affinity of the two liquids for
one another ; but the interchange
will not occur in the same manner
as if no membrane were present, i.e.,
equal quantities of salt solution and
water will- not substitute one an-
other. Such an interchange will
only occur in the centre of the pore,
while on the wall of the pores only
water will pass ; consequently the
salt solution will increase in volume
and the water will diminish corre-
spondingly, while the rapidity of
motion along the walls will be less
than in the centre of the pores on
account of the attraction of the
walls for the water.

Therefore, the greater the concentration of the salt solution the
higher will be the osmotic equivalent, since the difference of affinity of
the membrane for the water as compared with the salt solution will be
the more marked. This, however, only applies to salts whose solutions
are also imbibed by the membrane ; where this is not the case increased
concentration produces a decrease in the osmotic equivalent, for in the
latter case there will be more tendency for the membrane to hold the
layer of water in contact with the walls of its pores.

Different membranes will consequently modify the osmotic exchange
of liquids taking place through them.

FIG. 39.— DIAGRAM ILLUSTRATING
OSMOSIS.

This figure represents a diagrammatic section of a
single, capillary pore in an organic membrane separating
salt solution and water. From the greater affinity of the
membrane for water than for salt solution, the former
passes in a layer in contact with the circumference of the
tube, while the salt solution passes only in the centre of
the tube. Therefore, more water than" salt solution will
traverse the membrane.

PHYSICAL PROCESSES IN CELLS. 55

Thus, dr}" membrane will show a higher osmotic equivalent than
fresh membranes or dried membranes moistened, from the fact that the
membrane retains more water by imbibition, while the passage of the
salt is facilitated.

If an animal membrane separates water and alcohol, the water will
pass in much greater amount, for membrane absorbs water mifch more
readily than alcohol or a mixture of water and alcohol.

Rubber or collodium membranes, on the other hand, allow alcohol
to pass with greatest readiness, as such membranes absorb alcohol more
readily than water.

The general phenomena of osmosis may he well illus-
trated by the egg-osmometer (Fig. 40). This is prepared
by picking off a little of the shell from one end of an egg,
taking care to leave the shell-membrane intact, while a
glass tube is cemented around a small hole pierced through
both shell and shell-membrane at the opposite end. The
end at which- the shell has been removed and the membrane
left undisturbed is then immersed in distilled water. After
a time it will be found that water has passed from the out-
side to the interior of the egg, as shown by the increased
volume, the white of the egg'being forced up into the tube
cemented on the open end of the egg. At the same time
the addition of nitrate of silver to the water in which the
egg was immersed will show, by the white precipitate
formed, that the chlorides have passed from the inside to
the outside of the egg. No trace of albumen, however, is
to be seen in the distilled water. The salts of the egg, or
its crystalloids, have thus passed by osmosis through the
egg-membrane, water has also passed, while the egg-albu-
men, a colloid, has been retained.

These facts, already alluded to, that crystalloids in solu-
tion will pass through an animal membrane, while colloids
will not, has been made use of in a process which is fre-
quently employed by the chemist to separate bodies of these
two classes. Thus, albumen, or any other colloid, may be
entirely freed from crystalloids, such as salt or sugar, by
placing it on one side of a membrane with a large quantity
of distilled water, which is frequently renewed, on the other.
The salts pass through the membrane to the water, their FlG- A4°K~ s

place being taken by water, while the albumen, with the ILLUSTRATE Os-
exception of becoming more diluted, remains unchanged. MO TIC ACTION.
This process is termed dialysis. . (Flint.)

Osmotic phenomena, consequently, may be referred to the following
causes (Wundt) : —

1. The affinity which the two liquids exert on one another.

2. The relative affinity which the membrane exerts on the two
liquids.

3. On the narrowness of the pores through which the liquids diffuse.

4. On the overcoming of the adhesion of the liquids to the walls of
the pores through increase of temperature.

The importance of this process in the action of the animal organism is
very evident. Nearly all animal tissues are, during their entire life, in

56 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

a state of tension from imbibition (swollen) ; therefore, all tissues permit
the entrance of watery and saline solutions, and prevent entrance of
liquids not miscible with water. The absorption of most of the dissolved
food-stuffs, and the removal of deleterious matters, etc., by the glands
from the blood rest on osmotic processes. The results as to the different
osmotic* equivalent of different substances ; the behavior of different
membranes to diffusion ; the different capability of animal matter for
imbibing different solutions, all point to the way in which the glands
remove different substances from the blood where no other explanation
can be found but a membrane and cells capable of absorbing certain
solutions. The presence of certain salts in the contents of certain cells
is without doubt instrumental in shaping the capability of those cells
for absorbing definite solutions.

9. DIFFUSION OF GASES.— In the living organism, in the cell, the
vital activities are only carried on when there is an unbroken supply of
oxygen conveyed to the cells either in the form of a free gas or in
haemoglobin. And, on the other hand, the organism cannot exist unless
there is some provision made for the removal of C02, continually formed
in physiological oxidation, and which itself is a dead^ poison to cell
activity. These two gases are, therefore, the most important which have
to be considered.

In pulmonated, air-breathing animals there is also a continual exhala-
tion of watery vapor ; there is also a continual circulation of N in the
lungs of animals, as N forms four-tifths of the atmosphere.

Gaseous interchange in the organism rests mainly on the laws of
diffusion and absorption of gases, though these laws are subject to some
slight modification as contrasted with their application to inorganic
matter.

Ity gaseous diffusion is meant the mutual mixing of two or more
free gases ; and, as in liquid diffusion, it results in a uniform mixture.

Gases which pass into a vacuum fill it completely and uniformly; this
is also the case when the space into which a gas streams is already occu-
pied by a gas which is chemically indifferent to the first ; a space filled
with an indifferent gas behaves to another gas precise^ like a vacuum.

If two flasks, each provided with a stop-cock, are connected, one
vertically above the other, and the upper one filled with Irydrogen, the
lightest of gases, and the lower one with carbon dioxide, a heavy gas, if
the stop-cocks are now opened, in a short time it will be found that half
of the hydrogen, in spite of its lighter specific gravit}^, has descended
into the lower flask, while half of the carbon dioxide has ascended
against gravity into the upper flask, so that each flask will contain a
uniform mixture of the two gases (Fig. 41). Each gas has diffused into
the other as into a vacuum, and what holds for the diffusion of two

PHYSICAL PKOCESSES IX CELLS.

57

erases applies also to the diffusion of several gases ; so that the general
rule may be formulated : If a number of gases exerting no chemical
influence on each other are allowed to enter a space, each gas will diffuse
itself uniformly through that space.

If the amount of gas in any given space is small or large, or, in
other words, no matter what the gaseous pressure may be, another gas
will enter that space precisely as if it were a vacuum.

The importance of these laws in explaining the mechanism of
gaseous interchange in respiration is very evident. The atmosphere is
composed of a mechanical mixture of about f nitrogen and | oxygen.
In the process of inspiration a variable amount of this
gaseous mixture is drawn into the lungs. It then meets
with a gaseous mixture which contains less ox}-gen than
the atmosphere (for a certain amount of the ox}Tgen
taken in in previous inspirations has been removed by
the blood), and which contains a considerable volume of
carbon dioxide removed from the blood.

Phenomena of diffusion, therefore, at once commence
between the air alread}' in the lungs and that which has
entered in inspiration. The air in the lungs becomes
gradually poorer in oxygen and richer in carbon dioxide,
as the air-cells are approached. Diffusion tends to equal-
ize this difference ; the oxygen of the inspired air diffuses
into the deeper portions of the lungs, the carbon dioxide
diffuses from the deeper to the upper portion, the process
being a constant one; for the difference in the relative
volumes of the two gases in the upper air-passages is
maintained by repeated expirations, by which C02 is
removed, anil inspirations, by which more oxygen is FlG ^

brought into the lungs.

The COa formed in respiration by animal organisms, and thus
removed from them in respiration, distributes itself uniformly through
the atmosphere, so that there is everywhere a uniform percentage,
unless there is a local temporary increase ; but then this soon becomes
equalized by diffusion, permanent increase being prevented by the
absorption processes in the vegetable kingdom.

The tension of 0 in the atmosphere is far greater than that of C02,
as the 0 is present in far larger proportion, and conversely.

Diffusion leads finally to the theoretical result, that all gases in any
given space, as in the atmosphere, exist under the same pressure ; when,
therefore, there is anywhere a temporary increase in the tension of a gas,
diffusion commences and tends to continue until there is a uniform
distribution and mixing of the different gases.

58

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

If two different gases are separated by a porous partition, the gases
will mix through that partition. The phenomena under such circum-
stances are similar to what has been described in the case of liquids
under osmosis ; that is, that different gases pass with different degrees
of rapidity through the partition, so that the volume of gas increases on
one side of the partition and decreases on the other. If an unglazed,
porous, earthenware cup (such as is used in a Grove battery) is closed
witli a cork through which passes a long, vertical, glass tube, whose end
dips into a vessel below containing water, and the cup is covered with a
bell-jar containing hydrogen or illuminating gas, the hydrogen will pass
through the walls of the cup to the inside faster than the air from the
inside can diffuse out. The volume of gas in the interior increasing^
bubbles of air will escape through the water from the end of the tube.
If now the bell-jar be removed the hydrogen will
diffuse out from the cup faster than the air can
enter, the volume of gas within the cup will decrease
and the water will rise, from atmospheric pressure,
within the tube. If oxygen be used within the cup
instead of atmospheric air, it will be found that the
hydrogen will diffuse four times as fast as the oxygen.
The density of hydrogen is 1.; that of oxygen 16.;
therefore, the law has been made that the rapidity
with which different gases under similar conditions
(equal pressures) diffuse through thin, porous par-
titions into a vacuum or into other gases is in inverse
proportion to the square root of the density of the
gases (Graham's law).

These general facts may be illustrated by another
very simple experiment. If an unglazed earthenware
cup be closed by a cork in which a water-manometer
is inserted and then placed in a larger glass vessel containing vapor
of ether, the air from the inside of the cup will diffuse out faster than
the five-times-heavier vapor of ether will diffuse in, and the water in
the open arm of the manometer will sink (Fig. 42).

There is, however, here a marked difference from osmosis, for in the
diffusion of gases through inorganic partitions or dry organic membranes
the nature of the partition is without influence on the rapidity of diffusion.
The rapidly of diffusion depends only on the specific gravit3T of the gas.
10. ABSORPTION OF GASES. — Exactly as gases diffuse into spaces
already occupied by other gases, so also will they diffuse into the inter-
molecular spaces of liquids, without any chemical attraction between the
gas and the fluid being essential. If a glass tube, closed at one end, is
filled with dry, ammoniacal gas, its open end immersed in mercur}-, and

FIG. 42.

PHYSICAL PROCESSES IN CELLS. 59

then a small quantity of water introduced into the tube, the water will
almost instantly absorb the gas, which will entirely disappear, and the
mercury will rise in the tube, and, with the water, entirely fill it.

Just as without so also within liquids, gases exert no pressure on
each other; so that a number of gases may diffuse at the same time into
any given liquid.

We meet, in this solution of gases in liquids, with laws analogous
to those which govern the solution of solids in liquids. Every liquid
absorbs at amr given temperature a fixed quantity of an y given gas, just
as a certain quantit}' of liquid will only dissolve a given quantit}^ of
a salt. The volumes which a given liquid at a fixed temperature will
absorb of different gases are very different, the most readily-liquefied
gases being most readily absorbed. The volume of any gas that may
be absorbed b}- a liquid varies greatly with the temperature. As the
temperature increases capability of absorption decreases, until at 100° C.
water absorbs no gas at all. The exact opposite holds in the case of
solutions.

The co-efficient of absorption is the volume of gas which a liquid in
free communication with a gas can absorb. It varies with every liquid,
every gas, and every temperature. According to Bunsen, a unit of
volume of water absorbs —

Gas. Temperature. Volume.

< 00 1.7967

CO2

N

0

200
00

200
00

200

H . 00

.9046
0.02034
0.01401
0.04114
0.02838
0.0163

With every increase of pressure the liquid will absorb uniformly-
increased amounts of gas.

Gases absorbed by liquids do not lose their power of diffusion.
Hence, if we bring a liquid which contains a gas under a definite tension,
e.g., H20 with C02. in communication with a space containing another
gas,H, the C02 diffuses out of the HaO into the space containing the H.
C02 will continue to leave the water until it exists in equal pressure
without and within the liquid ; so, also, H will diffuse into the water until
it has a uniform tension without and within the liquid. An absorbed
gas is therefore given up when the tension of the gas is less in the space
in communication with the liquid than the tension of the gas in the liquid.
When two or more gases are mixed together their absorption by a liquid
is proportional to the relative volumes of the gases present in the mix-
ture, or to the different gaseous tensions.

In the cell in the animal organism this gaseous interchange occurs

60 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

through the cell-wall or the walls of capillaries, etc. These organic
tissues, which we have seen to be always filled with liquid, offer very little
resistance to the passage of a gas. The animal fluids communicate
through these delicate moist tissues almost directly writh the gases of the
atmosphere.

Gases formed by cells, or gases which pass from the exterior to the
interior of cells, or even the passage of gases through the membranes of
the lungs or gills of animals, are not governed by the law of the dif-
fusion of gases given above, but their transfer through an animal mem-
brane is governed by the co-efficient of absorption of that tissue for the
different gases. This may be illustrated by a very simple experiment
devised by Draper, who does not appear, however, to have appreciated
its application to gaseous interchange in the animal bod}'. The law of
the diffusion of gases through porous partitions is that the rapidity of
the diffusion is inversely as the square root of the densit}' of the gas.
If the finger be dipped in soap-water and then rapidly passed over the
mouth of an empty bottle so as to leave a horizontal film, and the bottle
then placed under a bell-jar filled with carbon dioxide, the film soon
swells up into an almost hemispherical dome. Or, if the bottle be filled
with carbon dioxide, and then exposed to the atmosphere after its mouth
has been covered with a sonp-film as before, the film is promptly
depressed into a deep concavity and bursts. Now, if the film is regarded
as a porous partition, the air, being of many times less density than the
C03, should diffuse much more rapidly, according to Graham's law. The
reverse, however, is the case. Water, however, of which the film consists,
has a much higher co-efficient of absorption for C02 than it has for oxygen
or nitrogen. The C02 is therefore absorbed more rapidly by the film
than the gases of the atmosphere, and from its solution in the film dif-
fuses rapidly into the atmosphere. The state of affairs is similar in the
case of gaseous interchange in animal cells.

The membranes of cell are not porous partitions, but are tissues
whose molecular interspaces are filled with liquids. That a gas may pass
through such a membrane it is necessary, therefore, that the gas be first
absorbed by the liquid in the cell-membrane. The readily-absorbed gases,
such as CO2, will thus diffuse through cell-membranes more rapidly than
those with a lower co-efficient of absorption, such as N, H, or O, the
rapidity of absorption being further governed, not only by the co-efficient
of absorption, but by the gaseous tension and the temperature. After
having passed through the cell-membrane gases will, of course, diffuse
into the liquid or gaseous media surrounding those cells, according to the
tension of those gases already present.

In the case of terrestrial animals this medium is the atmosphere,
which is composed of 21-volume per cent, of 0 and 79 per cent, of N,

PHYSICAL PROPERTIES OF TISSUES. 61

with traces of C03. If we imagine in the first place that the tissues are
at first free from gas, according to the co-efficients of absorption and
pressure, they will absorb definite volumes of these gases.

If we assume that the co-efficient of absorption of the animal liquids
for these gases is the same as water, as is actually nearly the case, the
co-efficient of absorption for O will be nearly double that of N, and the
volumes absorbed will be as 34.91 to 65.09. This is actually the case in
large bodies of water, as lakes, etc.

Under the conditions we have imagined, of course, only a trace of
C02 would be absorbed. ' We know, however, that C0a is a constant
result of cell life ; therefore the tension of C02 in animal fluids is far in-
excess of that in the atmosphere ; consequently, instead of an absorp-
tion of C02 by the tissues from the air, we will have an exhalation taking
place. Similar conditions apply in the case of watery vapor.

Hence, the gaseous interchanges between the organism and the
atmosphere under the laws of absorption and diffusion are as follow : —

Absorption of O and N.
Exhalation of CO2 and H2O vapor.

In animals, however, by far the greater part of 0 and COa are
carried in chemical combination with haemoglobin, and not in mere solu-
tion in the fluids of the body. These conditions, as well as the mechanism
of gaseous interchange in the lungs and tissues, will be considered in
greater detail under the subject of Respiration. At present enough has
been said to show that the laws of diffusion and absorption are the
fundamental principles which underlie these processes.

II. THE PHYSICAL PROPERTIES OF TISSUES.

We have found that the different animal tissues furnish illustrations
of both the solid and liquid forms of matter, var3*ing from a perfect
fluid to a solid of almost mineral consistence, and that midway between
these extremes what may be termed the semi-fluid tissues are of the
greatest importance in the physical and chemical operations of the
organism. We know, further, from anatysis of the organic tissues, that,
no matter what their consistence, they all contain a large proportion of
water in their composition ; it is to the amount and the manner in wrhich
this water is held by the tissues that nearly all the physical properties
of the tissues, particularly of the semi-solid tissues, are due.

We have already seen that in inorganic bodies, though they may
be rich in water, the water is either chemically united to that body, or is
held mechanically in capillary pores ; while in organic matter the water
occupies the intermolecular spaces. The tissues, therefore, resemble
solutions in this respect ; thus, in a salt solution the water occupies the

62 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

intermolecular spaces of the salt. In solutions, however, the solids are
bound to the water; in tissues, the reverse.

Since all fresh, organic tissues contain water, their specific gravity
must be comparatively low ; drying, by driving off the water, while
decreasing their weight by the amount of water displaced, will increase
their specific gravity, though even then, like all organic bodies, they will
be specifically lighter than most minerals. The specific gravity of dif-
ferent tissues will also vary according to the nature of their special con-
stituents; thus, adipose -tissue will represent one extreme, bones and
teeth the other, and tissues which are rich in fat, like the nervous tissues,
will be of less specific gravity than those which contain inorganic
matters.

As the specific gravity of the tissues depends upon their constitu-
ents, it will vary according to the relative proportions of those con-
stituents at different ages, in different individuals, and in different
nutritive states. No fixed figures can, therefore, be given to represent
the specific gravity of the different tissues, but, though not constant, the
following represents the average specific gravity of the most important
tissues of the human body : —

Bones, ........... 1.656

Elastic tissue and tendons, 1.12

Muscles, . , • . . 1.073

Arteries, . ' . 1.096

Veins, . . . . 1.05

Nerves, . ' . . . . . ... . . 1.046

1. COHESION. — It follows from what has been said as to the freedom
of molecular movement in most organic tissues, as shown in their capa-
bility of imbibition, that their cohesion must be less than that of most
inorganic solids. It is highest" in the bones, lowest in glands and , brain,
though it is comparatively high in nerves. Cohesion is there due to the
fibrous envelope (neurilemma) and not to the nerve-fibre; and as these
sheaths relatively increase as the nerve-trunks subdivide, the cohesion of
the fine nervous twigs of the skin is relatively higher than that of the
nerve-trunks.

The greater the amount of water contained in a tissue the less its
cohesion, for the wider apart will be the molecules, and the molecular
attraction decreases as the square of the distance which separates them.
Consequently desiccation increases cohesion. The order of cohesiveness
is inversely as the quantity of water; thus, the following list is arranged
with tissues of greatest cohesion and least water first, and as water
increases cohesion decreases : —

1. Bones. 4. Muscles. 7. Intestines.

2. Tendons. 5. Veins. 8. Glands.

3. Nerves. 6. Arteries. 9. Brain.

PHYSICAL PROPERTIES OF TISSUES. 63

In youth the tissues have less cohesion than in adult life, from the
greater preponderance in the former period of water ; while the cohesion
again declines in old age, especially in bone and muscle, even though
the proportion of water present also diminishes, from changes in the
quantity of inorganic elements.

The cohesion of airy tissue is not uniform in all directions, but, as is
well known, certain tissues may be ruptured in one direction more
readily than in another ; thus, a costal cartilage is more readily broken
transversely than longitudinally. This is even .more marked in fibrous
tissues, such as a tendon, where it is much easier to separate the longi-
tudinal fibres than it is to rupture them by traction. This may be
explained by the fact that the cohesion of any tissue is the resultant of
the forces which holds the ultimate molecule of the tissues together, as in
a single, fibre of connective tissue, and of the adhesive force, which
through the mediation, ordinarily of cement substance, holds several
collections of similar molecules together.

The forces which may act on a tissue to destroy its cohesion mny
operate in four different ways : by traction, b}' pressure, by flexion, and
by torsion. All the different tissues behave differently to each of these
modes of action.

The resistance to traction is measured by the force required to tear
apart the molecules of any tissue ; hence, the force required to produce
tearing in any tissue must increase with the cross-section of the tissue
subjected to strain, and when the cohesion of two different tissues is
compared in this respect the comparison must always be reduced to a
unit of cross-section. Thus, in the following table the numbers represent
the breaking weight in kilogrammes for every square millimeter of
surface (Wertheim): —

Bones, . . . .... 7 76

Tendons, . 694

Muscles, 0.054

Nerves, . 0.93

Arteries, . 0.16

Veins, . . 012

This resistance to traction is of great importance in the mechanics
of the organism. The cohesion of the bones, tendons, ligaments, and
muscles permit* of the accomplishment of mechanical work, while the
resistance, to distension of the different membranes of the body, such as
the aponeuroses, fibrous membranes, etc., is of great value in numerous
physiological operations.

The resistance to pressure is especially seen in the bony skeleton,
articular cartilage, and intervertebral disks. In the bones this is especially
very marked. Thus, it has been found that from 1110 to 2300 kilo were
required to crush a cube of bone from the compact substance of the

64 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

bones of the extremity 5 millimeters thick, while only 100 kilo were
required to crush a cube of the same size from the spongy substance.
The cohesion of the compact substance measured in this way decreases
to about the same degree when either the organic matter or the lime salts
are removed; it also decreases greatly when the water is removed,
showing a deviation from the general statement above made. This resist-'
ance to pressure plays an important role in the support of the body in
standing, walking, and jumping, and in the protection from injury of such
important organs as the brain, spinal cord, lungs, and heart.

The resistance to pressure in the osseous system decreases with age.
Thus, Fick has found that a prism of bone 1 square millimeter in size
from a man 30 years of age was crushed by a weight of 15.03 kilo, while
a similar piece from a man aged 74 years would not sustain a weight of
4.33 kilo. The bones of different animals also show great differences in
their resistance to pressure.

The resistance to flexion and torsion possessed by the different tissues
of the body also comes into play in certain physiological operations.
Thus, in inspiration the ribs and costal cartilages undergo a slight
amount of twisting and bending through the action, of the inspiratory
muscles, and regain their position during expiration. So, when a weight
is lifted and held horizontal by the hand the resistance to flexion pre-
vents bending of the bones of the arm.

The cohesion of the tissues is always greatest in the direction in
which the forces which act on those tissues is usually exerted. Thus,
when tissues are ordinarily subjected to the force of traction, their co-
hesive force is most developed in a longitudinal direction, and such tis-
sues, like tendons and ligaments, are fibrous in structure. When the
pressure or force to which tissues may normally be subjected does not
lie in any one but in many different directions, as in the resistance
which serous membranes and aponeuroses offer to distension, such mem-
branes are also fibrous in structure ; but the fibres, instead of being
parallel to each other as in tendons, in which traction is the only force
to which they are subjected, are interlacing and cross each other in
every direction. Finally, when pressure is the force which must be
resisted, we find the tissues taking the form in which such resistance
may be best offered ; the compact bony tissues are therefore arranged in
arches, as in the head of the femur, or in the form of hollow tubes,
as in the shafts of the long bones, — two forms which, with the greatest
economy of material, offer the greatest resistance to pressure. In the
case of the femur its upper end is not only subjected to pressure from
the weight of the bod}r, but also to flexion ; for the head of the femur
is not in a line with the long axis of the bone, but lies to one side and
is connected with the shaft of the bone by an oblique neck. The

PHYSICAL PROPERTIES OF TISSUES.

65

sirrangement of the compact substance of the bone is especially fitted to
overcome these direct or indirect pressures (Fig. 43).

2. ELASTICITY. — The elasticity of the tissues varies in the same way
AS their cohesion. The moist tissues have, as a rule, a very slight elas-
ticity ; that is, they offer slight resistance to external forces which tend
to change their form, and in most of the tissues which are rich in water,
as the brain and glands, the elasticity is incomplete ; that is, the original
form is not regained after the distorting force ceases to act. On the
other hand, in the elastic tissues and muscles the force must be excessive
to produce permanent distortion.

The cohesion of a body is its resistance to tearing forces ; elasticity is
•developed as resistance to alteration in form, and refers to the property by
which the original form is regained. The elasticity of a body is therefore
great when a great force is required
to produce change in form, and
vice versa; while the completeness
of the elasticity is expressed by the
perfection with which the original
form is regained after the distorting
force ceases to act. Thus, the elas-
ticity of lead is great but incom-
plete ; of rubber, is small but
perfect.

Elasticity cannot be measured
toy stretching force alone, but com-
pressing, twisting, and bending
forces must also be considered.
The resistance to each of these
forces is the same. The less exten-
sible a body is, the less compressible
is it also, and the more rapidly it
vibrates when bent from its position of equilibrium.

Organic tissues which are poor in water, as wood and bone, and
which possess high elasticity, behave to stretching weights like inorganic
bodies, i.e., the increase in length is proportionate to the weight. In
the soft tissues, of less but more complete elasticity, the increase in
length produced by heavy weights is proportionately less than that due
to smaller weights. The cause of this lies in the greater extensibility of
such tissues, through which they are more stretched by small weights
than is possible in rigid bodies, because in the latter a much smaller ex-
tension would exceed the limit of cohesion ; though the use of weights
of very great difference shows that the extensibility of rigid bodies is
probably also governed by the same laws.

5

FIG. 43.— DIAGRAM OF THE STRUCTURE
OF THE NECK OF THE HUMAN FEMUR.
(Ward.)

The fibres. A, by their rigidity, and the fibres, B, by
their tenacity, tend to the support of the weight, as
illustrated in the bracket, while the latter fibres inter-
lace with the arciform fibres, F.

66

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The laws for elastic changes in form of all bodies, including the soft
organic tissues, is expressed in the diagram given below (Fig. 44).

The spaces on the line A B represent the extending weights. The
spaces on the line B C represent the increase in length. Thus, if the
extension of any given tissue by any given weight equal the ordinate,
A D, the increase in extending weight by regularly increasing amounts
will not produce a proportional increase in length. Each increase will
be less than that produced by the previous lesser extending weight, and
the line which connects the limits of extension will be a curve which
gradually tends to form a horizontal line, — in other words, a hyperbola.
In a corresponding figure, representing the extension of an inorganic bod}',
the line D C, instead of being a curve, would be a straight line, and the
spaces on the line B C from B to C would be equal, showing that the
extension increases regularly with uniform increase in extending weight,
A p with the exception above

alluded to, when very
great difference in ex-
tending weights is made
use of. This difference
between organic and in-
organic bodies is, without
doubt, attributable to the
greater extensibility of
the former.

The organic tissues
have still another char-
acteristic which distin-
guishes them from the inorganic bodies, viz., when a tissue has been
extended by a weight, if the weight is allowed to remain the extension
gradually increases, and may not be complete for days or months ; this
is called elastic after-working. It is present in all elastic bodies, though
in rigid bodies it is much less marked, and its limit is sooner reached.

The weight which will stretch a prism one square millimeter in area
and one meter long one meter, provided the limit of cohesion is not
thereby passed, is called the co-efficient of elasticity.

The following figures, according to Wundt, give the co-efficients of
elasticity of some of the more important organic tissues : —

Bones, . - . . ..". .- . . . . 2264.

Tendons, .' ..... . . . 1.6693

Nerves, . ....'.. . . . 1.0905

Muscles,. , ... ;- 0.2734

Arteries, ., . . "... 0.0726

The smallness of these co-efficients is recognized when it is remembered
that for cast-steel it is 19881.

C

FIG. 44.

PHYSICAL PROPERTIES OF TISSUES. 67

Elasticity is a property of the tissues of the animal body which is
of great importance in man}' physiological operations. It is a force
which acts either against constant forces, such as gravity, or temporary
forces, such as muscular action. Thus, the intervertebral disks, through
their elasticit}', serve to deaden the shock given to the spinal column in
jumping; the elastic ligaments of the spinal column serve to preserve it
in its normal position without there being a constant strain on the muscles,
and in animals in whom the backbone is horizontal it serves to counteract
the weight of the abdominal viscera. In the herbivorous animals the
3'ellow elastic tissue of the ligament-urn uuchae serves to assist the muscles
in supporting the head.

In expiration the elastichy of the costal cartilages and ribs, together
with that of the lungs, — forces which have to be overcome in inspiration,
— tend to restore the thorax to its natural form, and thus drive the air out
of the lungs.

The elastic tissue of the arteries tends to aid the intermittent pro-
pelling force of the heart in producing a constant forward motion of the
blood. When the heart contracts it drives a definite quantity of blood
into the arterial system, already filled with blood, and thus still further
distends the arteries. During the pauses between the contractions of the
ventricles the elastic tissue recoils, from the removal of the distending
force, on the contents of the blood-vessels, and, backward motion being
prevented by the closure of the semi-lunar valves, drives the current of
blood forward in the vessels. This point will again be alluded to in more
detail under the subject of the Circulation.

In addition to these properties most of the tissues of the animal
body are also flexible and extensible, the degree varying great!}- accord-
ing to the structure of the parts. Flexibility and extensibility must not
be confounded. Flexibility means capability of being bent or twisted ;
extensibility means capability of being increased in length. Thus, the
tendons are flexible, but not extensible ; were they capable of being in-
creased in length it would be at the expense of the force developed by
muscles. Tendons are, however, very flexible; they adjust themselves
to the position the part may occupy, so that sometimes they transmit
muscular force at right angles to the line in which the muscle acts. Liga-
ments, again, are flexible, and also somewhat more extensible than tendons.
In joints they permit of the free play of one bony surface on the other,
and yet by their inextensibility serve to keep the articular surfaces in
apposition. In dislocations the articular ligaments are rent, and the bony
articular surfaces are no longer in contact: in sprains the limit of elas-
ticity of the ligaments has been passed ; that is, they have been stretched
beyond the point at which their elasticity enables them to regain their
original form, and partial ruptures take place.

68 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

All the connective tissues are originally flexible and extensible ;
these properties become greatly modified in the subsequent development
of the tissues of this group. Thus, in cartilage and bone, extensibility
has very largely disappeared, especially in the latter, but they are of high
elasticit}'. In dense fibrous tissue, such as aponeuroses, flexibility re-
mains, but extensibility has become greatly reduced ; hence the intense
pain produced in inflammation below such tissues ; for being inextensible
swelling is restrained, and the pressure produced by the products of in-
flammation on the nerve-endings is greatly increased.

3. OPTICAL CHARACTERISTICS OF TISSUES (Wundt). — (a) Ee fraction. —
All organic tissues possess a higher refractive index than water. By this
is meant that when a ray of light passes obliquely out of one medium
into another of different density, it is bent out of its path in a straight
line at the surface of separation of the two media, the ratio between the
angle of incidence and the angle of refraction being the index of refrac-
tion. Though comparative measurements of the different tissues have not
been made, we can recognize the difference by the sharpness of outline
in microscopic examination. Thus, cell-wall, nucleus, and nucleolus are
recognized by their difference in refractive powers. When two tissues
have the same refractive power they cannot be distinguished by the eye,
and if no refractive power is possessed they are homogeneous.

Fat, elastic tissue, and horn have the highest refractive power.
Watery solutions, as in the vacuoles of plant-cells and in secretions, have
least refractive power. Albuminous matters, gelatin-giving intercellular
substance, and mucin have about the same refractive index.

(b) Power of Absorbing Color*. — In very thin sections most vegetable
and animal tissues appear colorless. In thick sections, when examined
by transmitted light, the different colors are absorbed in different degrees.
Yegetable tissues absorb the most refractive rays ; therefore, in sections
of increasing thickness they appear at first yellow and then red. The
same rule applies to animal tissues, even when freed from blood, e.g.,
epithelium and cartilage. Many tissues owe their color to deposits in
them of special coloring matters. When this is intense many rays of
light are entirely extinguished, and in the spectra of such bodies portions
of the spectrum are either entirety absent or dark absorption-bands
appear in different parts of the spectrum.

The points of occurrence of these absorption-bands are definite and
characteristic for each different substance. The spectra of certain bodies
of physiological importance, such as the blood, biliary coloring matters,
etc., will be referred to under their appropriate headings in the sections
on Special Physiology.

(c) Double Refraction. — A large number of bodies of crystalline
structure have the property of splitting a single incident ray of light pass-

PHYSICAL PROPERTIES OF TISSUES. 69

ing through them into two rays ; hence, when an object is seen through
such a crystal it appears double, the bifurcation of the ray of light being
spoken of as double refraction.

Many of the animal tissues are doubly refractive, though this prop-
erty is weaker in fresh tissue than after drying. Double refraction is
only faintly developed in connective tissue, especially in its youngest
stages. Elastic tissue is more highly doubly refractive, as are also car-
tilage, bone, nerves, muscles, nails, and hair.

Double refraction permits the recognition of the molecular structure
of organized tissues. A body whose molecules in all directions are
arranged in the same manner produces only single refraction ; one whose
molecules are arranged in different directions in different proportions
produces double refraction, i.e., splits the ray of light into two ra}^s,
which are polarized perpendicularly to one another, and whose vibrations
are therefore in two planes perpendicular to one another. Simple glass
is a single refractive medium, but if compressed or stretched in one
direction it becomes doubly refractive. The double refractive body can
either, as in the last example, refract the ray more or less in one direction
than in the direction perpendicular to it, or the light can be transmitted
in three perpendicular directions with different velocities. In the inor-
ganic world crystals furnish examples of all three cases.

Crystals of the regular system (tesseral) are isotropic (singly
refractive). In tetragonal and hexagonal forms, which possess an unequal
axis and two or three perpendicular equal axes, the refraction is either
greater (positive) or less (negative) in the direction of the unequal axis,
and such bodies are said to have a single optic axis. Other crystalline
forms have three axes, characterized by the transmission of light with
different velocities. They have two optic axes not coinciding with the
axes of crystallization.

In organized bodies all of the above cases are also met with. Most
mature tissues are doubly refractive. The optic characteristics are not,
however, changed by pressure or stretching.

We must conclude from this that the doubly-refractive tissue-mole-
cule is suspended in a singly-refractive medium, and that this molecule
is unaffected in pressure or stretching just as it remains unaffected in
imbibition. Organic tissues are therefore analogous to crystals in their
molecular arrangement ; and this view is strengthened by the fact that
many organic substances which are apparently anything but crystalline
in their structure, such as albumen, gluten, and chondrin, possess the
power of rotating the plane of polarized light.

The most important examples of double refractive power are seen in
the muscles and nerves. These will be considered under their special
headings.

70 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

4. ELECTRICAL PHENOMENA. — Electrical phenomena may occur in
animal and vegetable tissues under various conditions.

Frictional electricity occurs when dry epidermal tissues (hair, outer
epidermis) and other bodies of rough surface are rubbed together, as on
the skin and clothing. It has no physiological significance.

Currents produced by chemical differences in tissues may be seen in
plants when a point of the exposed interior is connected with a point of
the external surface, the internal section being negative to the exterior.
Such currents probably only exist when contact by conductors is made
between these two surfaces.

In certain animal and vegetable tissues there appear to be elementary
parts, which are actively efficient in developing an electrical current.
Among such phenomena belong the electrical phenomena observed in
certain plants, as the Dionaea muscipula; in certain animals, as the torpedo
and electric eel, and in the currents developed in muscles and nerves of
all animals. The latter will receive consideration under the subjects of
Nerve and Muscle.

III. MECHANICAL MOVEMENTS IN CELLS.

It has been seen that the processes by which cells absorb and give
up liquids and gases are reducible to purely physical laws. We have
further alluded to the fact that the characteristics of the nutritive proc-
esses in animal as distinguished from vegetable cells is the reduction of
complex organic compounds in the former to simple, inorganic substances ;
while in the vegetable cell, simple, inorganic, elementary compounds are
built up into complex organic matter. In vegetable cells force is, there-
fore, rendered latent ; in animal cells force is liberated.

In the animal cell this liberation of energy may take on the form of
animal movements from ttie contractility of protoplasm ; or it may result
in the development of heat or of electricity. The consideration of the
processes which lead to this liberation of energy will be deferred until
after the chemical constituents of cells have been discussed, while heat-
formation and the development of electricity will be studied under their
appropriate headings in Special Physiology.

The movements seen in animal and vegetable organisms may be the
result of external causes, such as friction, heat, or chemical action, or
they may be apparently spontaneous.

Two classes of movement may be distinguished : —

1. Those which are produced by varying tension in the cell-mem-
brane, from varying degrees of imbibition of the cell-contents.

2. Those which are peculiarly protoplasmic in nature.

1. MOTION PRODUCED BY IMBIBITON IN CELLS. — The first of these is
especially illustrated by many of the forms of motion which occur in the

MECHANICAL MOVEMENTS IN CELLS. 71

vegetable kingdom, such as the turning of leaves toward or away from
the light, the regular motion of certain algae, such as diatoms, desmidia,
oscillatoria, as well as the irritative motions of certain plants, such as the
sensitive plant (Mimosa pudica), or the Venus' Fty-Trap (Dionxa mus-
cipula); all of these motions depend upon a change in the physical state
of imbibition of certain cells. In the Mimosa pudica, the plant in which
motion is most marked, and apparently most closely analogous to that
occurring in the animal kingdom, motion of three different parts may be
recognized.

While at rest during the day-time the leaf-stems of the sensitive
plant form an acute angle with the main stem, the secondary leaf-stems
diverge, and the leaves are opened out so that they form a plane surface.
When evening comes the leaf-stem sinks downward, the leaves approach
each other, as when the fingers of 'the open hand are adducted to the
middle finger, and the leaflets themselves close up so that the sur-
faces which during the da3r-time are the uppermost now come in contact
with each other. If the entire plant is shaken the same changes occur
as have been just described to take place during the night ; or if the
under part of any one of the leaf-stems is gently touched, the closing
motion is localized in that part of the plant. If, however, the upper
portion of the leaf is touched, no change is produced in the position of
the leaves or of the stem. The under part of the leaf-stem is seen to be
cylindrical in shape, and this represents the sensitive portion of the
plant.

Briicke, to whom we are indebted for the explanation of the
mechanism of this movement, has found that this cylindrical structure
which underlies the leaf-stem is composed of a bundle of vessels running
through the centre, and between it and the outer green bark there is a
layer of very succulent cells, which on the upper and non-sensitive side
of the stem are comparatively thick walled, while on the under side the
cells are provided with very delicate membranes. If a portion is cut
out of this cylindrical stem, the ends immediately become retracted so
that each extremity takes on a funnel-like form. If such a cylindrical
piece is then divided in the direction of its long axis, each part becomes
bent in the form of a bow, so that the external epidermal side is longer
than that bounded by the vascular bundle. This change in tension of
the cells is due to a change in distribution of the cell-juice. When the
membrane of the under portion of the leaf-stem is touched the cell-juice
flows from the lower to the upper cells and into the intercellular spaces;
the tension of the upper cells therefore becomes increased, while that of
the lower cells becomes reduced. The stem, therefore, sinks and the
leaves close. Movement occurring in the mimosa as a consequence of
mechanical irritation, therefore, depends upon differences in degree of

72 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

turgescence of certain cells, and has nothing in common with animal
motion.

The Dionxa muscipula, or Venus' Fly-Trap, furnishes another illus-
tration of movement of parts occurring in the vegetable kingdom. The
form of the bilobed leaf, which is the movable part of this plant, is
shown in Fig. 45. The two lobes stand at rather less than a right
angle to each other, and on each of the inner surfaces are three minute
filaments projecting inward. The margins of the leaf are prolonged
into spikes, into each of which a bundle of spiral vessels enters. When
any one of these filaments is touched, even by so slight a pressure as
would be produced by contact with a hair, the leaves instantly come into
apposition, and the spikes interlock like the teeth of a rat-trap. The
upper surface of the leaf is covered with minute glands, which furnish a
secretion having the power of digesting organic substances. When

insects come in contact with
these filaments, the leaves close
so as to imprison them, and
the insects are digested by the
acid secretion stimulated by
their contact, and absorbed.

In this plant the chief seat
of the movement is in the thick
mass of cells which overlies the
central bundles of vessels in
the mid-rib. When any one

FIG. 45.— VENUS' FLY-TRAP (Dionoea musdpuia). of these filaments on the in-
LEAF VIEWED LATERALLY IN ITS EXPANDED , « ^^1,1

STATE. (Darwin.) ternal surface of the leaves is

touched the impulse travels in

all directions through the cellular tissue, independently of the course of
the vessels, to the cells at the mid-rib. Fluid thus flowing from the
upper cells to the lower, the lower cells greatly increase in tension, while
the upper ones become relaxed and the leaves come into apposition.
Opening of the leaves is accomplished by a reverse process. In this
plant there is therefore to be seen not only a mechanical irritation,
which produces mechanical motion by purely mechanical means, but also
a chemical irritation through contact of various substances with the
leaf, which results in the production of a digestive secretion.

2. PROTOPLASMIC MOVEMENTS. — Protoplasmic movements, which may
be seen in both the animal and vegetable kingdoms, may be of various
kinds. We may meet with movements of free protoplasm, or of proto-
plasm while contained within cell-walls.

The peculiarity of protoplasmic motion lies in the fact that the
particles of the contractile mass do not move around any fixed point,

MECHANICAL MOVEMENTS IN CELLS. 73

but that all the particles, as in a liquid, are capable of mutual rearrange-
ment of position. Further, the stimulus to motion is not invariably
applied from without, but may be self-originating in the interior of the
mass. Protoplasm is thus contractile, irritable, and automatic.

Protoplasm, wherever found, is a transparent, colorless, apparently
homogeneous mass, refracting light somewhat more strongly than water,
but less than oil. Where protoplasm may be separated into layers, as in
the ectosarc and endosarc of some of the lower animalcules, protoplasm
may be doubly refractive, and when the direction of motion of the
protoplasm is constant the optic axis coincides with the line of motion.
Protoplasm, as previously indicated, possesses considerable power of
imbibition, moderate cohesion, and great extensibility, the degree of each
of these physical attributes varying in different forms of protoplasm,
and at different times and under different conditions for the same
protoplasm.

Protoplasm also usually contains a variable number of granules of
foreign matter, which are passive in the motions of protoplasm, but
which themselves may manifest oscillatory movement (Brownian motion).
The reaction of protoplasm is usually faintly alkaline or neutral.

Protoplasm may produce movement by means of prolongations of
cells, or by the contraction of organized matter resulting from the
metamorphosis of cell-contents. We have therefore to consider —

First. — Protoplasmic and cellular motion, whether limited by a cell-
membrane, or occurring in free protoplasm.

Second. — Motion of the protoplasmic prolongations of cells, as seen
in ciliary movement ; and

Third. — The contraction of substances resulting from the metamor-
phosis of cell-contents, as seen in muscular tissue.

1. Movements in Protoplasmic Contents of Cells. — In addition to
the Brownian movement, or oscillatory movement of granules which is
seen whenever minute particles, whether organic or inorganic, are sus-
pended in a fluid, and which are simply due to varying currents produced
by differences of temperature, the motion in the protoplasmic contents
of cells may be either circulatory (cyclosis) or may result in changes of
form. Circulatory movements are seen in numerous vegetable cells,
particularly when the protoplasmic contents have decreased somewhat
in amount so as not to fill the entire interior of the cell; the protoplasm
is then heaped up against the walls of the cells, and sends prolongations
across the interior. These cell-contents may then manifest movements,
either of changes of form or of circulation of starch granules, etc.,
which are imbedded in the protoplasm.

If a cell of the Tradescantia virginica is examined under the micro-
scope, the protoplasmic cell-contents will be found to be arranged in the

74

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

form of an irregular net-work, as represented in Fig. 46. These proto-
plasmic threads are the seat of changes, both of form and position. The
single filaments may become thicker or thinner, or a new filament may
spring out from and enter and unite with adjoining filaments, or may
undergo division into several others, the process being analogous to that
already described as characterizing the amoeba. In. addition to this
motion in the cell-contents, rotatory movements may also be seen to take

place in the protoplasm which is in
contact with the walls of the cell,
rotation occurring in a constant
direction and with almost uniform
rapidity around the cell-nucleus, the
imbedded chlorophyll and starch-
granules rotating in a mass without
any decisive change in their relative
positions. Such rotatory move-
ments are seen in the leaf-cells of
the Vallisneria, and various other
plants. Similar motions are also
seen in the paramoecium and other
infusoria.

In young animal cells the same
character of movement is often
present ; often when a membrane is
absent or is very flexible the pro-
toplasmic movements cause a change
in the entire shape of the cell, and
the motion so produced cannot be
distinguished from those of free
protoplasm.

Occasionally protoplasm be-
FIG. 46.-TRADESCANTIA CELLS," AFTER comes free by escaping from the

interior of cells, such as the so-called

r»laarrmirl«5 of m VJTOTnvPPtPS 1T1 whioll
Piabn IliyXOIiryCt «!3, 11.

not only an internal granular move-
ment but also a change of external

shape may be made out. Similar phenomena are also seen in those
organisms which consist of masses of free protoplasm, such as the
monera, rhizopods, polyps, and infusoria. Such protoplasm possesses
in an eminent degree the property of contractility, — a term originally
applied to striped and unstriped muscles. The changes in form of
masses of free protoplasm is identical in nature with that observed in
muscular contraction.

* «.

A represents the fresh cell suspended in water ; B the
same cell after moderate, local electrical stimulation.
The irritated region extends from a to b, the protoplasm

int° clumps' at c and d' as a result of the

MECHANICAL MOVEMENTS IN CELLS.

75

The contractility of protoplasm may be manifested by either
partial or total contractions, the latter tending to cause the protoplasm
to assume a spherical shape. Partial contractions are much more
common, and consist in contractions along certain circumferences of the
mass of protoplasm, and thus lead to the production of irregularity in
outline. Movements so produced are described as amoeboid movements
from the fact that they are best seen in the amoeba.

Amoeboid movements have already been described, and are exempli-
fied in many of the cells of which the bodies of the higher animals are
made up. Thus, the colorless blood-corpuscles, lymph-cells, and corneal
corpuscles possess throughout their entire life the power of changing
their form in a manner entirely similar to that possessed by the aimsba
(Fig. 47).

FIG. 47.— AMCEBOID MOVEMENT IN A COLORLESS BLOOD-CORPUSCLE OF THE
FROG. (Engelmann.)

The temperature was gradually raised from a tow, and then gradually reduced.

The most striking illustration of this form of protoplasmic move-
ment, seen in adult animals, is exemplified in the motions of pigment-
cells in the skin of the chameleon. As is well known, the chameleon is
capable of changing the hue of its skin, and this is simply due to the
varying degrees of contraction of the pigment-cells, which are situated
below the epidermis. When these cells send out branching prolonga-
tions to the exterior, the skin surface of the chameleon, from the larger
amount of pigment exposed, will take on a dark hue. In the different
stages of contraction of these pigment-cells the tint of the skin will
vary according as the pigment-cells are seen through a thicker or thinner
layer of yellowish or almost colorless epidermal cells.

76

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The two extremes of position of these pigment-cells are represented
in Figs. 48 and 49.

FIG. 48.

FIG. 49.

PIGMENT LAYER OF THE SKIN OF THE CHAMELEON IN DIFFERENT DEGREES
OF CONTRACTION. (Briicke.)

The frog also, as is well
known, is another illustration
of a change of tint produced
by precisely similar processes.

From the fact that the
movements of these pigment-
cells appear to be under the
control of the nervous system,
they offer an illustration of a
transition stage between the
independent, automatic move-
ment of free protoplasm, as in
the body of the amoeba, and
the specialization of the func-
tion of movement in the nerv-
ous ganglia, nerves, and muscle-
cells of higher animals.

In certain of the low forms
of life protoplasmic motion
may take on the form of minute
contractile threads thrown out
from the body of variovis rhiz-
opods and monera, which dif-
ers from the amoeboid move-
ments just described. In this
case long and thin protoplasmic
threads in great number extend in every direction from the central mass ;
these threads, on whose surfaces fine granules are often seen in active

FIG. 50.

MECHANICAL MOVEMENTS IN CELLS.

77

motion, are not themselves, usually, the seat of an}* active change in form,
although they slowly and gradually become longer or shorter, or perhaps
even divided. They are also capable of being entirely withdrawn into
the contractile body-mass. Such a form of motion, or rather the forms
resulting from such motion, are represented in Fig. 50.

2. Ciliary Movement. — By ciliary movement is meant the pendulum-
like motion possessed by protoplasmic prolongations of fine hair-like
threads of numerous animal and vegetable cells.

In many of the infusoria the entire external body surface, or a certain
limited portion of it, is supplied with minute hair-like appendages, which,
by their oscillation, serve as organs of propulsion. In vegetable spores
cilia are distributed in a similar manner, and likewise serve as propulsive
organs.

FIG. 51.— CILIATED EPITHELIAL CELLS FROM THE NASAL Mucous MEM-
BRANE OF THE Cow, MAGNIFIED 500 DIAMETERS. (C. F. Mutter.)

In the animal kingdom ciliary movement is seen under numerous
forms on ciliated epithelial cells lining the nasal passages, antrum, tear-
duct and sacs, pharynx and Eustachian tube, middle ear, trachea,
bronchi, uterus and Fallopian tube, vas defferens, epididymus, central
canal of the spinal cord and brain-ventricles, while cilia also serve as the
organ of movement in spermatozoa.

The form of the cilium is, as a rule, that of a narrow, hair-like
thread. In all of the ciliated epithelial cells of the higher animals, as
well as in most spermatozoa, and in man}7 of the lower animals and
plants, the length of such cilia may vary from 0.05 mm. to 0.005 mm.
(Fig. 51). They are structureless in appearance and colorless, and
possess a considerable amount of flexibility and elasticit}'. Under the
influence of various agents they may either swell up by imbibition or

78 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

shrivel when desiccated, and their appearances then undergo the same
changes as will be described under the alterations of protoplasm. The
solutions which coagulate albuminoid bodies also coagulate the ciliate
prolongations of cells. Caustic alkalies and most of the concentrated
acids dissolve them. In fact, cilia behave to all reagents in a very
similar manner to protoplasm. All cilia are invariably connected with
a protoplasmic base, and are never on firm membranes. Therefore,
when cilia are found in the higher animals on epithelial membranes the
free surface of the cell possesses no membrane, but the protoplasmic cell-
contents, in a manner similar to that which is found in the epithelial cells
of the villi of the small intestine, is somewhat condensed, apparently
non-contractile, homogeneous, or striated, and not capable of imbibition.
Such a surface might therefore be described as a protoplasmic cuticle.

Cilia pass through this condensed layer of protoplasm to be directly
in contact with the protoplasmic contents of the cell below. On each cell
of a ciliated epithelial membrane, from ten to twenty such cilia will be
distributed over the external surface. In lower forms of animals, .as in
the spermatozoa of all vertebrates, ciliated cells ma}^ possess but a single
cilium, as seen in many of the unicellular algae and flagellata.

Ciliated epithelial cells are always cylindrical in shape and are
nucleated. When a portion of ciliated membrane such as that obtained
from the mouth or nasal pharynx of the frog, or from the nasal chamber
of almost anjr animal, is placed under the microscope, the thread-like
prolongations of these cells will be found to be in constant motion, by
which the cells of one locality make a rapid bending motion in one
direction, and then more slowly bend themselves back to their original
position. The amplitude of these oscillations varies greatly with the
character of the cell and certain external conditions, but on all cylin-
drical epithelial cells taken from the 'same localit}^ is about equal, and,
although the bending may be as much as 90°, it usually varies from
about 20° to 50°. The rapidity of oscillation of eacli cilium may be
about six or eight in the second, although under certain circumstances
it may be considerably higher, since it is influenced by a number of
external conditions, such as temperature, amount of water contained by
imbibition, etc.

The mechanical force exerted by this pendulum-like motion of the
cilia is very considerable. In cells which, like the spermatozoa, are
supplied with a single cilium (Fig. 52), the screw-like motion of this
appendage is sufficient to produce rapid motion of the entire organism.
In the case of ciliary membranes, the vibration, having a greater intensity
in one direction than in another, is sufficient to produce forward motion
of light bodies brought in contact with them. Thus, if the mucous mem-
brane is dissected from the pharynx of the frog and fastened by pins on

MECHANICAL MOVEMENTS IN CELLS.

79

a board, any light bodies placed in contact with the ciliated surface of
the membrane will be moved comparatively rapidly forward in the
direction of oscillation of the cilia; or if the body of the frog is bisected,
and a glass tube passed in the month and out the oesophagus, which is
cut off at the point where it enters the stomach, the motion of the ciliated
epithelium lining the pharynx and oesophagus will be sufficient to cause

FIG. 52.— SPERMATOZOA OF DIFFERENT ANIMALS. (Thanhoffer.)

P, b, a, spermatozoa of Paludina vivipara: Hn, of Helix nemoralis ; B, of Blaps mortisaga ; Bi, of
bull; V, of mole; K, of dog; D. of bat: Em, of man; E, of mouse; C, of canary-bird ; L, of horse; Pa, b,
of rat, with sperinatoblasts ; J, of sheep ; B*-, of frog ; R, of Raja batis ; Pa, a", spermatoblasts.

the body of the frog to advance at a comparatively rapid rate, — as
much possibly as one millimeter in the second, or even more. It has been
estimated that, in oblique or vertical upward movements, each square
centimeter of ciliated membrane can perform in one hour 0.8 gramme
millimeters of wor.k, or the cells can lift their own weight more than four
meters high (Bowditch). This motion of bodies placed in contact with

SO PHYSIOLOGY OF THE DOMESTIC ANIMALS.

--

'.ciliated surfaces is evidently dependent upon the fact that the intensity
of motion is greater in one direction than in the other; otherwise, of
course, the effect would be negative.

Since ciliated epithelium, as has been already shown, lines most of
the tubular structures of the animal body, the effect of the vibratory
motion of the cilia will be to propel onward fluids and light particles in
contact with the surfaces of the membrane. Thus, the cilia of the
Fallopian tube, by their vibrations, serve greatly to assist the onward
passage of the ovum through the oviduct.

Ciliary motion persists only as long as the cilia are in contact with
the protoplasmic contents of cells, although Briicke has found that it is
not necessary that the entire cell be in contact with the cilia ; for if the
free surface of .a ciliated membrane is carefully shaved with a sharp
knife and the portions cut off examined under a microscope, it will be
found that many of the ciliated cells have been divided, and yet, provided
a certain portion of the cell-contents is still in contact with the cilia, the
latter will still manifest their normal movements. Ciliary movement
may persist after the death of the individual where that ciliary motion
is not concerned in producing movement of the entire organism ; thus,
in the ciliated infusoria anything which destroys the life of the animal-
cules will arrest ciliary movement; but, in the higher animals, in the
cold-blooded groups, motion of ciliated epithelium may persist for days
after the death of the animal; while, even in the warm-blooded animals,
a number of hours after the death of the organism, the cilia will still be
in vibration. This indicates that, in the first place, ciliary movement is
not under the control of the nervous system; and, secondly, that it. is
independent of the state of the entire organism, — at any rate, in the
higher forms of life, — since it may persist long after the irritability of
nerves and muscles has disappeared. Temperature produces the same
effects, nearly, on ciliary movement as it exerts on other protoplasmic
movements ; thus above 45° C. ciliated motion ceases, while at 0° C. it
also is arrested, to, however, return again when the temperature is raised.

Increase of temperature between these two limits produces increase
in the rapidity of oscillation of cilia, while decrease of the temperature
produces retardation.

Every alteration in degree of watery imbibition of epithelial cells
exerts an influence on the ciliary movement ; especially on the degree of
frequency and amplitude of vibration. Increasing the amount of water
in the epithelial cells above the normal amount may, at first, increase the
vigor of oscillation, but when a certain maximum is passed motion is
gradually arrested, as in heat-tetanus ; the cilia coming to rest while bent
forward, both cells and cilia being swollen and more transparent, and the
nucleus appearing as a distended, watery vesicle. When such a con-

MECHANICAL MOVEMENTS IN CELLS. 81

dition is reached the normal condition of the cells may be again restored
through the use of desiccating agents, such as salts, which have an
affinity for water, provided the watery distension has not lasted too long,
nor has passed a certain degree. Abstraction of water again, on the
other hand, reduces the rapidity, amplitude, and mechanical force of
movement, while the cells and cilia become shriveled and motion is
arrested. Like all other evidences of protoplasmic activity, a certain
supply of oxygen is necessary for the maintenance of ciliary motion,
and here again the same conditions may be determined as will be
described under the conditions necessary for protoplasmic movement.
So also various chemical influences, alkalies, acids, anaesthetics, and
poisons produce disturbances of motion dependent upon their influence
on the protoplasmic contents of the cells. The influences of electricity
on ciliary movement have not been, as yet, very clearly made out,
although they also appear to be in accord with the results obtained from
the action of electricity on protoplasm.

These facts serve to show that ciliary movement is a form of pro-
toplasmic movement ; for, not only is such motion dependent on the con-
nection of the cilia with the cell-contents, but all cilia on a single cell
vibrate synchronously, and their motion is dependent upon the condition
of the protoplasmic contents of the cells. Anything which interferes with
the manifestations of force in protoplasm will interfere with ciliary motion.
Ciliary motion, nevertheless, differs from other forms of protoplasmic
movement in that it occurs in definite directions, and, with the exception
of the spermatozoa and other ciliated organisms, on fixed surfaces.

Cilia are contractile but not automatic or irritable, while the con-
tents of ciliated cells have apparently lost their power of independent
contractility. Cilia may, therefore, be regarded as the organs of move-
ment of certain cells. They, consequently, represent a certain stage of
specialization of function.

3. Movement in Specialized Contractile Tissue. — In the contraction
of muscular tissue, specialization of function has advanced a step farther.
Free protoplasm originates its own stimulus to contraction, is therefore
automatic, and is itself contractile. In ciliated cells the contractile
impulse originates in the protoplasmic contents of the cells, which, how-
ever, have lost their power of contractility, and transfers the stimulus
to contractile organs, the cilia, which are not themselves automatic.

In muscular tissue movement depends upon three histologically
different tissues : the nervous ganglion, which is automatic and originates
the contractile impulse ; the nerves, which conduct this impulse to the
muscles, which, like cilia, are contractile but not automatic.

The phenomena of muscular contraction will be considered under
Special Physiology.

82 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

GENEKAL CONDITIONS GOVEKNING PROTOPLASMIC MOVEMENT.

The motions of protoplasm are governed by a large number of con-
ditions which are similar for protoplasm, whether of animal or vegetable
origin. This fact therefore points to the identity of protoplasm of ani-
mal and vegetable forms of life.

1. Temperature.— For every variety of protoplasm there is an
upper and lower temperature beyond which spontaneous motion ceases.
The minimum temperature at which motion is possible is usually 0° C.;
the maximum is 40° C. Between these limits the rapidity of motion
usually increases with the increase of temperature, and the temperature
at which the motions are most active usually lies several degrees below
the maximum temperature, at which point heat-tetanus, or heat-rigor, —
in other words, universal contraction of protoplasm, — occurs, resulting
in the assumption of spherical forms analogous to the condition pro-
duced by prolonged mechanical, chemical, or electrical irritation. If the
temperature is then reduced, the protoplasm may regain its power of
spontaneous contractility. At the maximum temperature no optical
changes occur in the protoplasm, but if the temperature is raised above
this point the protoplasm becomes shriveled and opaque from the coagu-
lation of the albuminoids of protoplasm. Vacuoles often form, and the
power of contractility is permanently lost. As the temperature is
reduced toward the minimum the movements become slower, and con-
tractility is finally extinguished. No optical changes are, however, so
produced, and an increase of temperature will now renew the power of
contractility. Contractility is therefore destroyed by an excess of heat, —
is suspended by a low temperature.

The changes in shape, as a consequence of change in temperature, are
represented in Fig. 53. From a to c the temperature was 12° C. The
protoplasm — the white blood-corpuscles of the frog — during that time
changed its form but little. The preparation was then placed on the
warm stage of the microscope and heated to 50° C. Almost imme-
diately the movements became more active, passing through the forms as
shown from d to Z. At m commencing and at n complete heat-rigor is
shown, while at o and p are shown the commencing movements restored
by subsequent cooling.

2. The Degree of Imbibition. — The amount of water held in com-
position by the protoplasm is also of influence on the capability for
spontaneous motion. For every form of protoplasm there is a maximum
and minimum quantity of water of imbibition be}Tond which movement
ceases. Contraction is impossible when, as a rule, less than 60 per
cent, or more than 90 per cent, of water is held by protoplasm.
Within these limits the rapidity of contraction increases with the amount

CONDITIONS GOVERNING PROTOPLASMIC MOVEMENT.

83

of water, and consequently with the increase of volume and decrease in
the index of refraction of the protoplasm. As the maximum amount of
water becomes approached the spherical form is assumed ; so that, there-
fore, distilled water, as pointed out in the section on imbibition, kills
protoplasm, possibly by the extraction of the salts which are necessary-
for the life of protoplasm. Thus, salt-water fish are killed by placing in
fresh water; the fresh water is then found to increase in its inorganic
constituents, which thus evidently must be extracted from the tissues
of the animals with which it is in contact. So also desiccation produces
shriveling of the protoplasm and an entire disappearance of all power of
movement, although in the lower forms of life vitality is not destroyed,

FIG. 53.— AM<EBOID MOVEMENT IN A COLORLESS BLOOD-CORPUSCLE OF THE
FROG. (Engelmann.)

The temperature was gradually raised from atom, and then gradually reduced.

but becomes latent ; and when the proper percentage of moisture is again
supplied the protoplasm will regain its power of contracting.

This is seen in the infusoria and various low forms of animal and
vegetable life, which may be preserved indefinite! jr when desiccated, and
ma}* be restored to active life by placing them in a condition to absorb
moisture.

3. TJie Supply of Oxygen. — Protoplasmic movements require the
constant supply of oxygen, although they may continue to live in a
medium of much lower oxygen-tension than is seen in the atmosphere.
Higher tensions of oxygen than are found in the atmosphere will reduce
the motions of protoplasm, which are, however, again renewed when the

84 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

pressure of oxj^gen is diminished. All protoplasmic motion is rapidly
arrested in a vacuum.

4. Various Chemical and Physical Agents. — Various chemical agents
are capable of modifying the contractility of protoplasm. Thus, a slight
excess of acid or of alkali will arrest protoplasmic movement; hence,
protoplasmic motions in the cells of various vegetable organisms, such
as cara, will be arrested, after two or three minutes, in a one-tenth of one
per cent, soda solution. Dilute acids cause coagulation of protoplasm,
and will perhaps explain the poisonous action of carbon dioxide and the
necessity of its removal from cells as rapidly as formed. Various poisons,
such as ether and chloroform, interfere with the activity of protoplasm
of all forms, and the similarity of action serves to still further demon-
strate the identity of protoplasm. Thus, the alkaloid veratrine produces
effects on all forms of protoplasm similar to those so well marked in
muscular tissue.

Protoplasm, also, like muscular and other irritable tissue, responds
to various forms of artificial stimuli, though the degree of susceptibility
to such stimuli may vary in different forms of protoplasm. Electrical
currents, when powerful, are capable of killing protoplasm, causing it to
assume a spherical shape, and to become opaque, shriveled, and granular.
Feeble currents slow the spontaneous motions of protoplasm, while
strong currents arrest them. Where the contractile tissue is inclosed
in tubular sheaths and the assumption of the spherical form so rendered
impossible, as in muscular tissue, an attempt is made to approach the
form as nearly as possible. Such protoplasmic cylinders when stimulated
become shorter and thicker.

Sudden changes of temperature are also capable of producing either
increase or decrease in the contractility of protoplasm, the change being
more marked the more rapidly the variation in temperature occurs.

Absence of light also serves finally to arrest protoplasmic motion,
while its presence will lead to increased vigor of contraction, as already
referred to in the changes in the contractile pigmented cells of the skin
of the chameleon and frog.

SECTION III.
CELLULAR CHEMISTRY.

I. CHEMICAL CONSTITUENTS OF CELLS.

IN the consideration of the structure of organized bodies we found
that, no matter how complicated their form, all organized matter was
capable of being resolved into a unit of organization, which we termed,
with Briicke, an elementary organism or cell.

Cells, therefore, are the simplest schematic form to which all the
various forms of organized bodies are capable of being reduced. Chemi-
cal investigation of organized bodies further shows that they are equally
simple as regards their elementary composition. Of the sixt3'-five chemi-
cal elements only seven enter with any degree of constancy into the forma-
tion of organic compounds ; these are oxygen, nitrogen, hydrogen, carbon ,
sulphur, phosphorus, and iron. By far the greatest number of all organic
compounds are composed only of the three elements, carbon, hydrogen,
and oxygen, va^ing in the different relative proportions of each. In
one group, represented by the organic acids (succinic acid, C4H604), even
if we assume that all the hydrogen present is associated with oxygen in
the proportion to form water, there always remains a considerable excess
of oxygen unaccounted for. In the second group, represented by the
carbo-hydrates (glycogen, C6H1006), we have twice as much hydrogen as
oxygen, or, in other words, the oxygen and hydrogen exist only in the
proportion to form water. In the third group, composed of these ele-
ments, carbon, hydrogen, and oxygen, and represented by the fatty acids
(oleic acid, C^Hs/^), if we suppose that all the oxygen is united with
the hydrogen in the proportion to form water, we have still a consider-
able excess of hydrogen unaccounted for. Such bodies are, therefore,
termed h}'dro-carbons.

In another group of organic compounds, and one of the most im-
portant of the constituents of cells, we find nitrogen associated with
carbon, hydrogen, and oxygen. Such a group we would therefore term
the nitrogenous, in contradistinction to the non-nitrogenous.

To this group belong the highly complex organic products (complex
as regards their molecular arrangement), which contain sulphur and occa-
sionally phosphorus, arid still more rarely iron, and which are represented
by the albuminous bodies ; the nitrogenous organic acids and bases, the

(85)

86 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

organic alkaloids and indifferent crystalline bodies, some of which contain
sulphur, are other members of this group. As yet only three substances
of organic origin are known to contain phosphorus ; these are lecithin
(found in the blood, bile, and serous fluids), glycerin-phosphoric acid
(derived from the former, and found in the same localities), and nuclein
(found in pus-corpuscles, yelk of egg, and semen). In the living organism
these organic compounds are in a state of solution in a relative^ large
amount of water, and either associated or chemically united with a small
percentage of inorganic matter, which modifies, in all probability, the
nature of the former, and is itself not without value in the vital processes.
All organic compounds are readily decomposable, either through the
action of various chemical reagents, elevation of temperature, or through
the processes of fermentation and putrefaction. As the result of all these
changes in organic matters simpler compounds are produced. The more
complex the molecule of organic matter, the more readily is it subjected to
decomposition. The character of these changes, as well as the nature of
some of the substances which result from change of various kinds in
organic matter, will be subsequently discussed.

Of the inorganic constituents of cells by far the most abundant is
water, which forms the great bulk of organic bodies. Many vegetable
matters may contain as much as 90 per cent, of water, while the animal
tissues may contain 75 per cent, or more, though the percentage is by no
means constant, and may vary in single tissues according to different
plrysiological or pathological conditions. The inorganic constituents of
cells are taken up by the cells already preformed, and, as a rule, again
leave the cells in the form in which they entered it. The most prominent
exception to this rule is found in the case of carbon dioxide and sul-
phuric acid ; the former originating in the oxidation of the hydrogen
contained in the water of organic constituents, and the latter coming
from the oxidation of the sulphur contained in albuminoids. The inor-
ganic constituents of animal and vegetable cells in 110 way differ from
similar bodies found in inorganic matter. When found as constituents
of cells they have invariably been derived from the atmosphere or the
earth, have been absorbed, often without undergoing any change, by
vegetable cells, and have passed from the latter into the interior of animal
tissues. Inorganic matter is found in all animal fluids and tissues,
although with great variation as to amount. Certain inorganic constitu-
ents— such, for example, as water and sodium chloride — are found
invariably in all animal tissues and fluids, while other of the inorganic
cell-constituents are limited to the cells of certain special tissues.

The inorganic constituents of cells may exist either in the form of
gases, salts, free acids, or in certain forms of combination whose exact
arrangement has not yet been made out.

CHEMICAL CONSTITUENTS OF CELLS. 87

In addition to the elements which have been already mentioned as
forming part of the organic constituents of cells, and which, of course,
may exist in other forms, we find also, when organic matter is subjected
to combustion, chlorine, fluorine, silicon, potassium, sodium, calcium,
magnesium, manganese, iron, and occasionally copper and lead, in the
ash. Of the other elements of organic bodies in incineration the carbon
is converted into carbon-dioxide, part of which remains in the form of
carbonates in the ash, part of the hydrogen uniting with oxj-gen to form
water. Another portion unites with nitrogen to form ammonia, while the
phosphorus and sulphur remain as oxygen compounds, sulphuric and
phosphoric acids, united with different bases also in the ash.

Of the various chemical compounds which are found in the interior
of cells, and which have entered it, either from accidental contact or as
foods, or as resulting from the chemical processes in cells, we may make
three different groups : —

1. Those which, already formed, exist in inanimate nature, are
absorbed, and again leave cells without undergoing any change while
forming constituents of organized bodies. Such substances are repre-
sented by the inorganic constituents of animal cells.

2. This group comprises those which are already formed exterior to
the cells, and which, in the process of assimilation by the cells, undergo
a change simply in their mode of molecular arrangement, without under-
going any profound chemical metamorphosis. Such constituents are
seldom, if ever, removed from the cells in the form in which they entered
it, and are, in the chemical process occurring in the interior of the cells,
always reduced to simpler forms. The organic constituents of cells form
this group. They may be either nitrogenous or non-nitrogenous in
composition.

3. We meet also with a class of compounds which are themselves
developed in the vital processes in cells, as the result of the metamorphosis
of either the organic constituents of cells or of the food-products which
have been assimilated by the cells. Such bodies may be removed from
cells either as complex, organic, excretory products (as types of which
urea and kreatin may be mentioned), or they themselves may undergo
more profound decomposition before being removed from the interior of
the cells. The examination of protoplasm, wherever found in the animal
or vegetable kingdom, will show that it contains examples of each of
these three classes of compounds.

The chemical constituents of organic bodies may, then, be divided
into two different groups, — the organic and the inorganic. The organic
may again be subdivided into the nitrogenous and the non-nitrogenous.
Proteids, with their derivatives, represent the nitrogenous group ; the
hydro-carbons and carbo-hydrates, with their derivatives, the non-

88 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

nitrogenous group. Water and various salts belong to the second, or
inorganic group. These will be taken up in turn : —

CONSTITUENTS OF CELLS.

I. ORGANIC. II. INORGANIC. •

Water and Salts.

A. Nitrogenous. B. Non-nitrogenous.

Proteids and
their Derivatives.

1. Carbo-hydrates. 2. Hydro-carbons.

Starches and Sugars and Fats and Oils,

their Derivatives.

A. NITROGENOUS ORGANIC CELL-CONSTITUENTS — PROTEIDS AND

THEIR DERIVATIVES.

General Characteristics of Proteids. — Proteid, or albuminous
bodies, is the name given to a number of neutral, nitrogenous products
of complex nature widely distributed throughout the animal and vege-
table kingdoms, and agreeing more or less in chemical composition and
properties with the white of an egg. They are found dissolved in the
fluid media of the animal body, as constituents of the digestive juices,
and in different degrees of solidit}* in the various tissues. They are
never, during health, eliminated from the body in excretions. They are
present during all periods of life. The higher plane of organization of
man and the higher animals depends mainly upon the abundance and
variety of the albuminous constituents of their tissues; for, while in
plants the cell-walls are largely composed of non-nitrogenous matter,
such as cellulose, in animals analogous parts are formed of various
complex albuminoids.

Proteids are organic, colloidal bodies, composed of carbon, hydrogen,
oxygen, nitrogen, sulphur, and occasionally phosphorus. They are
absolutely essential to life, whether animal or vegetable, but are exclu-
sively of vegetable origin ; that is, although they may be assimilated
and modified by the vital processes occurring in animal cells, they
must first have been preformed by the chemical processes occurring in
vegetable cells. When found as constituents of the tissues of car-
nivorous animals they have been derived directly, with but slight
modification, from the herbivora which have served for their food,
while the herbivorous animals find them invariably ready formed in
the tissues of vegetables which serve as their food, and which require
but slight modification to be converted into the constituents of the

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 89

animal tissues. Animals, therefore, do not have the power of manu-
facturing albuminoids, although they may transform albuminous bodies
of one kind into those of another. Thus, casein may be transformed
into the albuminous constituents of muscle-tissue ; it may be combined
with other substances so as to form, for example, the haemoglobin of
the blood-corpuscles, or may become so modified as to form what are
termed the derived albuminoids of the different tissues.

After serving the purposes of the organism such bodies are excreted,
not as proteids, but as products resulting from their retrograde meta-
morphosis. All albuminous bodies are so intimatety associated with
inorganic matter that their isolation in a pure state is a matter of the
greatest difficulty, or, it may be, impossibility ; consequently the inciner-
ation of albuminous bodies — a process which is accompanied with the
development of an odor like burning horn — always leaves an ash composed
of potassium and magnesium phosphates and small quantities of carbo-
nates. If sulphur is regarded as a constant and normal component of
proteids and not as an occasional accidental addition, they all possess a
very high molecular weight. In all forms of proteids the percentage of
chemical elements entering into their composition is only subject to
slight variation in the different classes. Thus, according to Hoppe-Se}"ler,
C. may vary from 52.7 to 54.5 per cent.; H., 6.9 to 7.3 .per cent.; N.,
15.4 to 16.5 per cent. ; O., 20.9 to 23.5 per cent.; S., 0.8 to 2.0 per cent.

Physical Properties. — When dry, albuminous bodies form perfectly
amorphous, yellowish, brittle masses without odor or taste, and closely
resembling gums in appearance, and, like gums, hygroscopic to a high
degree: they rotate the plane of polarized light to the left, and in watery
solutions, which are nearly always opalescent, are not, as a rule, capable
of osmosis, — a fact, which seems to show, as Brucke has pointed out,
that their condition in the form of fluid is more one of particulate
suspension than of true solution. When shaken with fluid oils, the latter
are mechanically separated into minute particles, each of which is sur-
rounded by a layer of the albuminous solution (emulsion). Some are
soluble in wrater, others not; nearly all are insoluble in alcohol and
ether ; most are soluble in strong alkalies and acids, but' in the process
of solution undergo chemical change. Most of the albuminous bodies
may exist in two modifications, either in a soluble or in an insoluble
form. They exist usually in the soluble form in animal and vegetable
cells, but become insoluble by the action of heat and various chemical
reagents.

When 'watery solutions of albuminous bodies are evaporated in a
vacuum, or at 40° to 50° C., a yellowish, brittle, soluble residue is left;
in other words, albumen may be recovered unaltered in general prop-
erties in the dry form from solutions when subjected to evaporation by

90 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

gentle heat. When heated much above this point albuminous bodies
then pass into the insoluble form (coagulated proteids).

Chemical Properties. — Proteids are precipitated out of their solu-
tions by the following reagents : the stronger mineral acids, acetic acid
and potassium ferro-C}*anide ; acetic acid and sodium sulphate, lead
acetate, mercuric chloride, tannic acid, powdered potassium carbonate
added in bulk to saturation, alcohol, ether, and several other substances.

Iodine stains most proteids yellow, — a point which may aid in their
recognition under the microscope.

Their presence in solution may be recognized by the following
processes : —

First, by coagulation. When solutions of albuminoids are gently
heated, provided the amount of albumen contained is at all appreciable,
a firm coaguluin results when the solution has been warmed up to 60°
or 70° C. The temperature at which coagulation occurs will vary in
different forms of albuminous bodies, and according to the reaction and
chemical characteristics of the solvent. If a small amount of a dilute
acid is added to a solution of an albuminous body coagulation will be
found to occur at a lower temperature than if the solution be neutral ;
while, on the other hand, the presence of a small amount of alkali will
prevent coagulation occurring until the temperature has been raised
above the point at which it occurs when the solution is neutral. If a
large amount of alkali be present coagulation by heat will be rendered
impossible. Neutral salts in small amount in albuminous solution will
also lower the temperature of coagulation, whether the solution be
faintly acid, faintly alkaline, or neutral. The coagulation of albuminous
bodies by heat is only possible when they are in solution, and therefore
seems to show that the change from the soluble to the insoluble form
produced by heat is not so much dependent upon the heat as upon the
heat combined with moisture ; for if the albumen be separated from
solution by evaporation below the point of coagulation, the dried albumen
so obtained will still possess the power of solubility in water : and yet,
if placed in a perfectly dry tube the temperature of the albumen ma\' be
raised far above the point of coagulation without any change occurring
in the albumen, i.e., without its losing its power of subsequent solubility
in water, and of being coagulated when that solution is raised to tha
coagulating point.

Second : If a solution which is supposed to contain albumen is
acidulated with acetic acid, a few drops of potassium ferrocyanide then
added, and the fluid boiled, albuminous bodies will be precipitated.

Third : If the fluid is acidulated with acetic acid and a small
quantity of a strong solution of sodium sulphate then added, and the
fluid then boiled, a firm, white coagulum will result.

* NITROGENOUS ORGANIC CELL-CONSTITUENTS. 91

The first and third of these tests may be used for separating albu-
minous bodies from other substances in solution, — a process which is
often necessary in the examination of organic fluids. So also if the fluid
is acidulated with acetic acid, and then added to a large bulk of strong
alcohol, albuminous bodies may thus be coagulated, and their separation
from other ingredients of the solution rendered possible.

A precipitate produced by boiling alone is not a sufficient proof
of the presence of albumen, since certain substances, such as calcium
phosphate in human urine and calcium carbonate in the urine of her-
bivora, will be thrown down by boiling. If the precipitate is permanent
on the addition of nitric acid after boiling, albumen is present, since the
salts above mentioned will be redissolved by the acid. Alkali may also
hinder the coagulation of albumen by heat, and an acid reaction is there-
fore essential for the emplo3^ment of this test.

Occasionally albumen is present in solution in amount too small to
be detected by any of the preceding tests. The detection of traces of
albumen is then rendered possible by various color reactions.

The Biuret Reaction. — When a small amount of caustic potash
solution is added to a dilute solution of cupric sulphate a precipitate of
cupric hydrate will be thrown down. If an excess of potash is now
added, the precipitate will be redissolved and the fluid take on a light-
blue color. If, however, albuminous bodies be present in solution, and
this procedure be carried out, on solution of the precipitate of cupric
hydrate the fluid will take on a violet color instead of u blue. This test
may be used to detect the presence of albuminous bodies in extremely
small amount in solution. It may be also used for the recognition of
the albuminous nature of solids. If a solid body which is supposed to
contain albuminous bodies be touched first with a drop of cupric sul-
phate solution, then with a drop of potash solution, and then washed
with water, the spot so treated will be found to have a violet color.
This test is also used for the recognition of peptone. A solution of
peptone so treated will become red instead of violet.

Xantho-proteic Reaction. — When albuminous bodies in solution are
boiled with nitric acid, the solution and coagulum, if one be present,
take on a yellow color. If the solution be then allowed to cool and
strong ammonia added, the upper layers of the solution, or the coagu-
lum, if any be present, will become orange colored.

Millon's Reaction. — If a little Millon's reagent* be added to a solu-
tion which contains albumen, if the albumen be present in considerable

* Millon's reagent is prepared by dissolving mercury in its own weight of nitric
acid by the aid of gentle heat. The solution is then poured into a glass vessel, and twice
its volume of water added ; a crystalline precipitate will separate in a few hours, and the
yellowish supernatant fluid, which may be readily decanted off, is Millon's reagent.

92 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

quantity, a dense, white precipitate will be formed, and when subjected
to heat the precipitate will become condensed into the form of a firm
coagulum, and will turn red. If but a trace of albumen is present the
fluid will simply take on a pinkish color.

Schnitzels Test. — When albuminoids in solution are treated with a
cane-sugar solution in small quantities and concentrated sulphuric acid
then added a beautiful red color is formed.

Adamkiewicz's Test.— If a solution of an albuminous body is strongly
acidulated with acetic acid and sodium chloride added in bulk, and then
strong sulphuric acid, the fluid will gradually assume a violet-blue color,
slightly phosphorescent, and gradually turning dark purple.

Frohde's Test. — When a mixture of sulpho-molybdic acid is added
to a solution of albuminous bodies a dark-blue color is produced.

Of the above tests the xantho-proteic and Millon's reaction may be
used for the microscopical detection of the albuminoids.

Albuminous bodies may be divided into the following classes : —

I. ALBUMENS. — Albumens are bodies which are soluble in water, and
when in solution are coagulated by heat (about 70° C.). They are not
precipitated from their solutions by dilute acids, carbonates of the alka-
lies, sodium chloride, or platino-hydrocyanic acid. When dried at about
40° C., or if evaporated at a lower temperature in a vacuum, they leave
a yellowish, friable, inodorous, gummy mass, which is still soluble in
water, and whose solutions possess all the properties of the original
solution. Albumens are precipitated from their solution by alcohol, if
alkaline salts are present. Albumens may exist in three different forms,
—serum-albumen, egg-albumen, and vegetable albumen.

1. Serum- Albumen. — Serum-albumen is found in blood, serum,
lymph, serous transudations, and animal secretions.

Serum-albumen may be obtained from blood-serum, or any serous transuda-
tion, by adding dilute acetic acid, drop by drop, until a flocculent precipitate forms.
This precipitate is then filtered off, and the filtrate, after neutralization with a
little sodium carbonate, is evaporated in a shallow dish to a small volume, not
allowing the temperature to rise above 40° C. The salts may then be removed by
dialysis, changing the water frequently outside of the dialyzer, and again evapo-
rating at 40° C. to dryness.

So obtained, serum-albumen always contains a slight percentage of
salts, but is soluble in water, forming a clear solution, which is somewhat
tenacious when concentrated.

In the dry condition it is a yellowish, brittle, transparent body
capable of being redissolved in water, and its solutions are then coagu-
lable by heat. Its solutions are opalescent, and possess a specific laevo-
rotation for yellow light of — 56°. It is precipitated out of its solutions
by alcohol, the precipitate being partially redissolved when the alcohol
is immediately poured off, but is not coagulated l>y ether. Most of the

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 93

salts of the heavy metals precipitate serum-albumen, as do the mineral
acids in large quantities, especially nitric acid. Its point of firm coagu-
lation is from 72° to 73° C., although turbidity sets in at about 60° C.
The presence of acetic or phosphoric acids, sodium chloride, or other
neutral salts, lowers the coagulation-point of serum-albumen, while the
presence of sodium carbonate necessitates a higher temperature. It is
precipitated by the strong mineral acids from its solution in dilute acids,
and the precipitate is readily soluble in concentrated acids ; egg-albumen
is not.

2. Egg-Albumen. — In many points egg-albumen, which is contained
in the meshes of the fibrous net-work of birds' eggs, closely resembles
serum-albumen. The points of contrast are that its specific rotation is only
— 35.5°, and when agitated with ether it is gradually precipitated. When
injected into a vein or the connective tissue, or when introduced in large
quantities into the stomach or rectum of an animal, egg-albumen is found
unaltered in the urine, while the injection of serum-albumen produces no
such albuminuria.

A solution of comparatively-pure egg-albumen may be obtained for testing
by breaking the whites of several hens' eggs into a beaker, cutting up the mem-
branes with scissors so as to free the albumen from their meshes, stirring well
with an equal volume of water, and filtering through muslin. The salts may then
he removed by dialysis.

Dry egg-albumen may be obtained by evaporating the above solution
to dryness at 40° C. So prepared, its physical properties agree closely
with those of serum-albumen. Its solutions have several properties which
enable it to be distinguished from serum-albumen. Hydrochloric acid
in small amount produces no precipitate ; in larger amount it causes a
firm coagulum, which is only with difficulty soluble in excess of acid and
in water and neutral salt solutions.

3. Vegetable Albumens. — Albuminous bodies are found dissolved in
plant-juices and in the form of a solid in various seeds, and form the
most important albuminoids for the nutrition of the herbivorous domestic
animals. Their general properties agree with those of egg- arid serum-
albumen, though they present certain variations among themselves in
composition and chemical properties. Thus, the coagulable substances
which may be extracted from peas and horse-beans dissolve readily in
lime-water and acetic acid, while the other vegetable albumens do not.

The vegetable albumens are, as a rule, poorer in carbon but richer in
nitrogen than albumen of animal origin, — a fact possibly accounting for
their lesser nutritive value and readiness of assimilation. They usualty
have phosphorus associated with them. Vegetable altnimen is soluble in
cold water, and its solutions are coagulable by heat ; with dilute acids
and alkalies it is converted into an albuminate. In the seeds of certain

94 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

plants there is contained a, variety of albumen which, when extracted
with warm salt solution and then allowed to cool, forms octahedral
cr}rstals.

Various forms of vegetable albuminous bodies have been described : —

Vegetable Caseins. — The seeds of the leguminous plants and oleagi-
nous grains differ from the cereals, properly so called, in that they do
not contain gluten, soluble in alcohol, but, in addition to the albuminoids
coagulable by heat, various other albuminous bodies which are insoluble
in pure water but soluble in alkaline solutions, from which they may be
precipitated by acetic acid, the precipitate being soluble in excess.
According to Dumas and Cavours,this substance may even be coagulated
by rennet, and is therefore closely analogous to the casein of milk, to be
subsequently considered. Three different forms of vegetable casein-like
bodies have been described. Legumin, which forms the greater part of
the proteid constituents of the leguminous plants ; almonds and the
lupins contain a substance analogous to vegetable casein to which the
name of amandin, or conglutin, has been given ; while the part of gluten
which is insoluble in alcohol is of similar nature, and has been termed
gluten-casein.

Legumin. — The watery extract of the seeds of the leguminous plants
often has an acid reaction, without doubt due to the presence of phos-
phoric acid, which appears to be a necessary component of vegetable
casein. Legumin may be obtained by the agitation of powdered legu-
minous seeds with seven or eight times their weight of a one-tenth of
one per cent, solution of potassium hydrate. After about six hours the
fluid is decanted and allowed to stand from twelve to twent3r-four hours
at a low temperature, and the residue which then forms is again washed
with water. The washings are then collected and precipitated with dilute
acetic acid, and the precipitate, washed again with dilute alcohol, is
finally precipitated by concentrated alcohol and ether.

Freshly precipitated legumin is only very slightly soluble in cold
water. Legumin may, however, be extracted from the powdered seeds
of the leguminous plants by cold water, its solubility in water being then
due tO'the phosphoric acid of the seeds. It is readily soluble in alkaline
solutions, from which it is precipitated by acids and solutions of metallic
salts. It is soluble in dilute hydrochloric and acetic acids. When boiled
with water it becomes coagulated and insoluble in alkaline solutions and
in acids. By prolonged ebullition with sulphuric acid it undergoes
decomposition, with the formation of leucin and ty rosin and small quan-
tities of aspartic acid. Legumin is also present in oats.

Amandin, or conglutin, is contained in sweet and bitter almonds,
and is separated from them in the same manner as legumin. It is dis-
tinguished from legumin by a greater solubility in dilute acids, though

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 95

its general properties coincide with those of legumin. It is distinguished
from it, however, by being more soluble than legumin in dilute acids. A
substance analogous to vitellin has also been found in the seeds of
various plants. It is also termed crystallized vegetable casein.

Gluten, or vegetable fibrin, exists in a large number of grains, par-
ticularly those of the cereals, and plays an important part in the nutritive
value of vegetable foods. It also exists in the growing parts of plants,
and in various vegetable juices. It is a compound albuminous body,
which differs from all others in that it is soluble in water and in alcohol
when traces of free acid or alkali are present. It is only partly and
imperfectly soluble in pure water. It may be readily obtained by
washing flour under a stream of water, by which the starch is removed,
and the gluten then remains in the form of an elastic, grayish mass.
Gluten is only partly soluble in alcohol. According to Ritthausen,
gluten contains at least four albuminous substances in addition to
vegetable albumen, which has been already described; a body insoluble
in alcohol, which is gluten-casein, or the vegetable fibrin of Liebig, and
three nitrogenous substances soluble in alcohol, to which the name of
gluten fibrin, gliadin, and mucedin have been given.

1. Gluten-Casein. — To prepare this body, fresh gluten is washed first
with alcohol, and the insoluble residue is then agitated with two-tenths of
one per cent, potash solution, which dissolves out the gluten and leaves an
insoluble residue of starch and fatty matters. From the fluid gluten-
casein is precipitated in flocculi by the addition of acetic acid sufficient
to give a faint acid reaction. It is then washed with water and alcohol,
and after desiccation the gluten-casein so prepared is insoluble in hot
and cold water. Boiling water, however, causes it to undergo some
modification, which renders it insoluble in alkalies and acids. In the
fresh state it is soluble in acetic acid, and in alcohol acidulated with
acetic acid. All weak alkaline solutions dissolve fresh gluten-casein,
and cause it when dry to first swell up and then dissolve. It is precipi-
tated out of these solutions by acids and the mineral salts, forming
combinations with the latter. Its properties are very similar to those of
legumin and conglutin. It contains more sulphur and less nitrogen
than legumin.

2. Gluten-Fibrin. — This body is obtained by distilling the alcoholic
solution of gluten until the fluid does not contain more than 40 percent,
of alcohol ; a mucilaginous mass rich in gluten-fibrin is then deposited,
and may be purified by washing with absolute alcohol and precipitating
with ether. It then forms a coherent, tenacious mass, insoluble in water.
Its separation from the gliadin and mucedin of gluten depends upon the
fact that all are soluble in dilute alcohol, and that gluten-fibrin is almost
insoluble in water and very weak alcohol. As the alcohol is distilled off

95 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the gluten-fibrin separates. It dissolves in warm, dilute alcohol, and
forms a brownish-yellow solution. When such solutions cool, and as
they undergo evaporation, a white or grayish pellicle forms on the surface,
which disappears on agitation. It is more soluble in absolute alcohol
than either gliadin or mucedin. Gluten-fibrin is readily dissolved in
dilute acid and alkaline solutions, and is precipitated from these solutions
by neutralization, or by the addition of metallic salts.

3. Gliadin, or Vegetable Gelatin. — This body is one of the principles
of gluten which is soluble in dilute alcohol. It is obtained by agitating
gluten with strong alcohol, which removes gluten-fibrin, dissolving the
residue in 1 per cent, potash solution, and, after having precipitated the
solution with acetic acid, by extracting the precipitate with alcohol of
75 per cent, at a temperature of 38° C. By this means only gliadin is
dissolved, while the mucedin remains. Vegetable gelatin then separates,
as the fluid cools, in the form of a gelatinous mass. It may be purified
by dissolving in acetic acid and neutralizing the clear solution with
potash; the precipitate is then again washed with alcohol and ether. In
the fresh state vegetable gelatin has the consistence of a thick mucilage.
Absolute alcohol causes it to contract to a hard and yellowish-white
mass. Cold water causes it to again swell up and dissolves part of it,
and the solution may be precipitated by tannic acid. Submitted to long
boiling with water, gliadin becomes insoluble and undergoes partial
decomposition. Dilute alcohol dissolves it more readily than pure water.
It is insoluble in absolute alcohol. It is very soluble in acids and dilute
alkalies, and while in solution in alkalies may be precipitated by the
metallic salts, but its solution in acetic acid is not precipitated by
mercuric chloride. It contains a considerable percentage of sulphur.

4. Mucedin. — This substance has been but little studied, and is only
to be distinguished from vegetable gelatin by its greater solubilit3r in
water. Its method of isolation has been already indicated in the pre-
ceding paragraphs.

These substances approach one another very closely in chemical
composition, and it would appear from the processes employed in their
isolation that it is by no means certain that they have been obtained
pure. On the other hand, their analogy to corresponding bodies of
animal origin is not sufficiently striking to justify an analogous nomen-
clature.

For the preceding account of their properties we are indebted
mainly to Wiirtz ( Chimie Biologique}.

II. GLOBULINS. — Globulins are bodies which are insoluble in water
but soluble in dilute solutions of sodium chloride. They are coagulable
by heat when in solution, and, while soluble in dilute acids and alkalies,
are in the process of solution changed into derived albumens. They are

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 97

precipitated by alcohol and by carbonic acid, and by the addition of a
large quantity of water to their solutions ; sodium chloride added in
bulk to their solutions, as a rule, precipitates them.

Five different kinds of globulins have been recognized.

1. Vitellin. — Yitellin is found in the yelk of eggs and in the crys-
talline lens. It may be prepared by shaking the yelks of eggs with
separate portions of ether until all the yellow color is removed, dissolv-
ing the residue in dilute sodium chloride solution, filtering and precipi-
tating the filtrate with excess of water. So obtained, it always contains
lecithin. It is not precipitated by the addition of sodium chloride in
substance to its solutions. It is soluble in dilute acids, and is readily
converted into syntonin, and by neutralization and re-solution with
alkalies into alkali albuminate. Its point of coagulation ranges from
70° to 80° C. It is also coagulable by alcohol.

2. Myosin. — Myosin is formed in the rigor mortis of muscles, and
probably also in the gradual death of all forms of protoplasm. It is
precipitated from its solutions in dilute sodium chloride by the addition
of common salt in excess. It is also precipitated from its solutions by
excessive dilution with water. Its general properties will be more closely
considered under the chemistry of muscles.

3. Paraglobulin. — This substance will be described under the con-
sideration of the coagulation of the blood. Hammarsten states that a
very much larger quantity of this body is found in the blood of domestic
animals than has been heretofore supposed. According to him, more
than half of all the albuminoids in the blood consists of paraglobulin.

4. Fibrinogen. — This is also a globulin found in the blood, and its
consideration will likewise, for the present, be deferred.

5. Globulin, or Crytstallin, is contained in the crystalline lens, and
it resembles vitellin in that it is not precipitated from its solutions by
saturation with sodium chloride, but it is readily precipitated by alcohol.

Representatives of the group of globulins are also found in the vege-
table kingdom. According to Dr. Sidney Martin, vegetable globulins'
may be divided into two classes, namely, vegetable myosins and vege-
table paraglobulins. The myosins, obtained from the flour of wheat,
rye, and barley, have similar properties ; they are all readity soluble in
10 to 15 per cent, sodium chloride solution, and are precipitable from this
solution by saturation with sodium chloride or magnesium sulphate.
They are soluble in 10 per cent, magnesium sulphate solution, and are
coagulated in this solution at a temperature of 55° to 60°. If the salt is
dialyzed away from the saline solution of myosins, the latter is precipi-
tated ; but the precipitate is no longer a globulin, since it is insoluble in
saline solutions. It is soluble in dilute acids and alkalies (0.2 per cent.) ;
it is precipitable from these solutions by neutralization, the precipitate

7

98 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

being soluble in excess of alkali or acid ; that is, the myosin has been
converted into a proteid having the properties of an albuminate. If
the saline solution of myosin be placed in an incubator at a temperature
of 35° to 40°, in twelve to eighteen hours a fine flocculent precipitate
falls, while the globulin disappears from the solution ; this takes place
more rapidly if the saline solution is diluted. The precipitate exhibits
the same properties as the precipitate of the globulin by dialysis ; that
is, at a temperature of 35° to 40° the globulin is transformed into an albu-
rn mate. The ready transformation of the soluble globulin of wheaten
nour into an insoluble albuminate is one of the phenomena which take
place during the formation of gluten.

The second class of vegetable globulins, the paraglobulins, is in dis-
tinct contrast with that of the myosins. Two proteids of this class
have been found, one in papaw-juice, the other in the seeds of Abrus
precatorius (jequirity). Both these globulins exhibit the following
properties : they are soluble in saline solutions, and are precipitated by
saturation with sodium chloride and magnesium sulphate. In a 10 per
cent, solution of magnesium sulphate, they coagulate between 70° and
75° C. When precipitated from their saline solutions by dialysis, they are
still soluble in solutions of sodium chloride and magnesium sulphate of
10 to 15 per cent., not being transformed into albuminates. Nor are
they precipitated by long exposure (over three days) to a temperature
of 35° to 40°. > u .,«!

III. FJBRINS. — Fibrins are solid albuminous bodies .'insoluble in
water and sodium chloride, and which swell up to a stiff' jelly in dilute
acids. When so treated iibrin is coagulable by heat. The fibrin of the
blood is produced in the process of coagulation of the blood ; its prop-
erties will be studied with the subject of blood coagulation.

IV.. DERIVED ALBUMINATES. — Derived albuminates are bodies which
are insoluble in water or sodium chloride solutions, but are readily soluble
in dilute acids or alkalies. Their solutions are not changed by heat.
When neutralized they are precipitated from their solutions, the pre-
cipitate being soluble in excess. Derived albuminates may exist in two
different forms, — acid albumens and alkali albumens.

1. Acid Albumen. — When a native albumen in solution is subjected
to the action of a dilute acid, such as hydrochloric acid, at a tolerably
warm temperature its solutions readily lose their power of coagulating
when boiled. If, however, the acid is exactty neutralized by the addition
of any alkali the albumen is at once precipitated, and the precipitate is
again redissolved by an excess of alkali. The native albumen is thus
converted into a form of albuminous body which has become insoluble in
water and uncoagulable by heat.

When acid albumen is precipitated out of its solution by the

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 99

addition of an alkali and then subjected to heat, the acid albumen so
suspended in water becomes coagulated, and is then indistinguishable
from any other coagulated proteid. After precipitation by neutrali-
zation, if the precipitate be then dissolved in lime-water, its solution in
lime-water will be coagulable on boiling. Acid albumen is precipitated
out of its solution by the neutral salts, such as sodium chloride, and by
gallic acid and metallic salts.

The conversion of albumen into acid albumen from the action of a
dilute acid is a gradual process. If a solution of egg-albumen be acidu-
lated with dilute hydrochloric acid, and subjected to a temperature of
about 40° C., it will be found, if tested from time to time, that a coagulum
still occurs on boiling. The amount of proteid so coagulated by heat
will steadily decrease, and the amount of precipitate obtained by neutral-
ization will increase correspondingly. After only ten or fifteen minutes it
will be found that if the solution of acid albumen is exactly neutralized
all the albumen will have been converted into acid albumen, and if
the precipitate is then filtered off and the filtrate tested with the various
proteid tests it will be found that all the proteid has apparently disap-
peared ; or, in other words, has been converted into acid albumen.

A certain degree of temperature is necessary for this conversion.
If a mixture of albumen solution and dilute acid be surrounded by ice,
the process of conversion into acid albumen will be extremely slow. If
warmed up to about 40° C., or, in fact, any distance below the tempera-
ture of coagulation of the albumen, the process of conversion will be
very much more rapid.

If finely-chopped muscle is washed in water so as to remove all the
soluble albuminous bodies and blood, and the remainder be covered with
a large quantity of dilute hydrochloric acid (0.2 per cent.), and kept for
about twenty-four hours at a temperature of 40° C., it will be found that
the greater part of the muscle will be dissolved ; if the supernatant fluid be
filtered off and neutralized, an abundant precipitate of acid albumen will
be thrown down in flocculi, which will gradually settle. The acid
albumen in this case is derived from the.n^osin of the muscle, and
indicates that the globulins as well as the albumens are capable of being
converted into derived acid albumen. Acid albumen so obtained from
muscle is frequently spoken of as S3'ntonin, but is apparently identical
in its general behavior under the different tests to the acid albumen
derived from either egg- or serum-albumen. So also in the preliminary
stages of gastric digestion of proteids a product is first formed which
appears to be identical in character with acid albumen, or syntonin, and
is termed parapeptone. It also is precipitated from its solutions by
neutralization, and is apparently formed solely through the action of the
acid of the gastric juice on proteids.

100 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Any of the coagulated proteids may be converted into acid albumen
through solution in the mineral acids. If a solution of albumen is
gently heated to boiling with dilute hydrochloric acid, no coagulum will
be formed, from the fact that in the gradual elevation of temperature the
albumen in solution has had time to be converted quickly into acid
albumen through the action of the acid. If, now, a small quantity of a
concentrated mineral acid, especially hydrochloric, be added, an abundant
precipitate will form, and this precipitate is soluble in an excess of
mineral acid, especially if subjected to heat.

It is thus shown that acid albumen is soluble in concentrated mineral
acids. It is insoluble in them when they are moderate^ concentrated,
and it is soluble again when they are ver}' dilute. Egg-albumen, in
certain respects, differs from serum-albumen in its behavior to dilute
acids. If dry serum-albumen is dissolved in a concentrated mineral
acid, it is readily converted in its process of solution into acid albumen.
If this solution of serum-albumen in concentrated acid is then diluted
with twice its volume of water, acid albumen will be precipitated, and if
the precipitate is filtered off it may readily be dissolved in water, from
the fact that it still holds clinging to it enough acid to make a dilute
acid solution. Therefore, it is not a solution of acid albumen in water,
but in dilute acid. Egg-albumen is less soluble in concentrated nitric
acid or hydrochloric acid, and when precipitated from such a solution it
is less readily dissolved in water.

Fibrin also is soluble in concentrated mineral acids, and is rapidly
converted into syntonin ; therefore, it may be said that all proteids are
capable of being converted into derived albumens.

Syntonin, dissolved in dilute hydrochloric acid, rotates the plane of
yellow light — 72° to the left, and this degree of rotation is independent of
the concentration of the solution, but may be increased to — 84.8° if the
solution is heated. Syntonin contains sulphur, as may be readily shown
by dissolving some syntonin in liquor potassse, and adding a solution of
lead acetate and boiling ; the fluid will then become brown from the
formation of lead sulphide. When precipitated from its solutions by
neutralization acid albumen forms a white, gelatinous substance insoluble
-in water and sodium chloride solutions, but soluble in lime-water (in
which solution, as already stated, it undergoes partial coagulation when
boiled), and in dilute acids and alkaline solutions. If, to the solution in
> lime-water, after having undergone partial coagulation through boiling,
magnesium sulphate be added, a still further precipitation will be caused.
Cold solutions of acid albumen are not precipitated by magnesium sul-
phate, even if the acid albumen be dissolved in an alkaline solution. If,
however, the solution of acid albumen and alkali be warmed, it is then
precipitated by the addition of magnesium sulphate or calcium chloride,

NITKOGENOUS OBGANIC CELL-CONSTITUENTS. 101

indicating that, in all probability, the boiling has served to convert the
acid albumen into an alkali albumen. Acid albumen shows all the
reactions of proteids already described. It may be separated from
liquids in which it is dissolved by boiling with hydrated oxide of lead.

2. Alkali Albumen. — If any native albumen in solution is. subjected
to the action of a dilute alkali, such as sodium or potassium hydrate, it
will undergo changes somewhat similar to those produced by the action
of an acid. Alkali albumens, or alkali albuminates, may, therefore, be
described as albuminous bodies which are insoluble in water or sodium
chloride, but readily soluble in dilute acids or alkalies. Their solutions
are not changed by heat. When neutralized the}'' are precipitated from
their solutions, the precipitate being soluble in excess of acid, unless
alkaline phosphates are present ; an excess of acid is then required to
produce precipitation. In this conversion heat facilitates the process,
and, as in the case of formation of acid albumen, the conversion is a
gradual one. When alkali albumen is precipitated from its solution in
alkalies by neutralization with an acid, if an excess of acid be added it
is again rapidly dissolved, through its conversion into acid albumen. or
S3rntonin. This conversion of alkali albumen into acid albumen is more
readily accomplished when the alkali albumen has been freshly precipi-
tated. If some time has been allowed to elapse after the precipitation
b}' neutralization, it will still be converted into syntonin by the action
of an acid, but not so readily as when freshly precipitated, unless sub-
jected to heat (about 60° C.). If alkaline phosphates are present in the
solution the alkali albumen is not precipitated on neutralization, but
enough acid must be added to convert the basic phosphate into
acid phosphate, and, when this is accomplished, the slightest addition
of an acid, even of C02, will then be sufficient to precipitate alkali
albumen.

Alkali albuminate may exist either in the form of solution or as a
solid. If undiluted white of egg is stirred up with a concentrated solu-
tion of caustic potash, or with undissolved caustic potassium hydrate,
it will gradually be converted into a stiff jelly. If this jelly is washed
with water so as to remove the excess of alkali, it may be dissolved
in warm water, and will then behave like alkali albumen obtained by the
action of alkalies on albuminous solutions. If, before solution in water,
the solid alkali albuminate has been washed until most of the alkali has
been removed, passing a stream of carbon dioxide through the solution
will be sufficient to cause precipitation.

If some pieces of solid alkali albuminate are placed in an acid just
strong enough to show an acid reaction after the introduction of the
albuminate, the latter will become milky-white, shrivel up, and form an
elastic mass, the so-called pseudo-fibrin, which will swell up in dilute

102 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

(0.1 per cent.) acids without dissolving, but which is soluble in the caustic
alkalies, and may be precipitated by neutralization.

Alkali albumen, like other albuminous bodies, is also precipitated
from its solutions by metallic salts. With alcohol no precipitate is
yielded, and alkali albumen is said to contain no sulphur, the sulphur of
the albumen from which it is made being removed by the alkali in the
process of conversion. It therefore differs from acid albumen and from
casein, which contains sulphur.

Alkali albumen or albuminate is present in all young cells, in blood-
corpuscles and blood-serum, in muscle, pancreas, nerves, crystalline lens,
and cornea. It would seem that alkali albuminate may exist in various
forms, judging by the difference in effect produced on polarized light by
alkali albumen produced from different sources. Thus, alkali albumen
produced from serum-albumen has a Isevo-rotatory power of — 86° ; from
egg-albumen, of — 47°, and if prepared from coagulated egg-albumen it
may be as high as — 58.8°.

Casein is a form of alkali albuminate which is present in milk. It
yields potassium sulphide when left to stand with liquor potassae, and
still more quickly when heated with it. It may be prepared from milk by
shaking the milk with caustic potash and ether, removing the ether and
precipitating the albuminate with acetic acid, and washing the coagulum
with water, alcohol, and ether. The other properties of casein will be
further studied under the subject of Milk.

Alkali albumen, therefore, differs from acid albumens in its not being
precipitated on neutralization if alkaline phosphates be present ; by its
being precipitated by magnesium sulphate in substance in cold solution,
but in not being coagulated when boiled in lime-water ; and it contains no
sulphur.

V. COAGULATED PROTEIDS. — It has already been seen that the action
of heat on solutions of egg- and serum-albumen, globulins, or on fibrin
when suspended in water, or dissolved in saline solutions, serves to
coagulate them and to convert them into an insoluble form. Absolute
alcohol produces a similar effect on the same bodies ; coagulated proteids
are insoluble in water, dilute acids and alkalies and neutral saline solu-
tions, and, although they are soluble in the strong mineral acids, their
solubility is dependent upon the fact that through the action of the acid
they are converted into dem^ed albumens. They are readil}7 converted
into peptones through the action of the different digestive juices (gastric
and pancreatic juices). When freshty formed the}r are white, flocculent, or
cheesy masses which, under the microscope, are entirely amorphous;
they hold water and salt solutions with great tenacity. Their chemical
characteristics have been very little studied.

YI. AMYLOID SUBSTANCES OR LARDACEIN. — This is a substance which

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 103

appears to be a derivative of fibrin, and is found as a deposit in numerous
of the organs of the bod3^ such as the spleen, liver, etc. It is insoluble
in water, alcohol, ether, dilute acids, and alkaline carbonates, and is not
dissolved by the digestive juices. When acted on by concentrated hydro-
chloric acid it passes into solution and is converted into syntonin, which
may be precipitated by dilution with water. With sulphuric acid it dis-
solves when boiled, forming a violet solution, and with strong sulphuric
acid it is converted into leucin and tyrosin. In its composition it appears
identical with other proteids. It behaves differently, however, to certain
of the proteid tests, and must, therefore, be regarded as a modified
proteid. Thus, with iodine, instead of the yellow color produced with
other proteids, a reddish-brown color is formed. With iodine and
chloride of zinc or sulphuric acid a violet-bluish color is produced, thus
resembling cellulose in its reaction, to which similarity it owes its name
of amyloid, though it must be remembered that this is the only point of
similarity between amyloid substances and the starchy bodies ; for it
contains nitrogen, which is absent from all starches, and it cannot be
converted into sugar. Aniline violet on amyloid substance causes a
reddish-violet color, and is a test which may be readily used for detecting
the presence of amyloid degeneration in various animal organs. Amyloid
substance yields the Millon's and xantho-proteic reactions.

VII. PEPTONES. — A peptone is a modified form of proteid which
occurs -when any of the albuminous bodies, with the exception of lardacein,
are subjected to the action of gastric or pancreatic juices, prolonged
boiling at high temperature under great pressure, or by the action of
heat and dilute , acids at moderate temperature. Their general charac-
teristics will be referred to under the subject of Digestion.

In addition to the above classes of albuminous bodies, albumen has
been said to exist under two other forms, that of meta-albumen and para-
albumen, although as 37et very little is known about their characteristics, or
in fact whether they are not simply ordinary albuminous bodies modified by
the accidental addition of some other substance. Thus, meta-albumen
might possibly be regarded as a mixture of albumen and mucin, since it is
precipitated by alcohol without undergoing coagulation ; it is not coagu-
lated by boiling, although its solutions become cloudy when heated, and
it is not precipitated by acetic or hydrochloric acids, or acetic acid and
potassium ferrocyanide. It is, however, precipitated by mercuric chloride
and gallic acid. It has been found in ovarian cysts, and in the fluid of
ascites. When precipitated by alcohol the precipitate is again soluble in
water. Para-albumen has also been found in the fluid of ovarian cysts,
where its presence was supposed to be characteristic, but has also been
found elsewhere. It is precipitated b}^ alcohol, and when so precipitated

104 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

may redissolve again in water. It is not completely coagulated by boil-
ing. It is rendered turbid by acetic acid, the cloudiness being removed
by an excess of acid or sodium chloride. It is precipitated by nitric
acid, potassium ferrocyanide and acetic acid, mercuric chloride, and ace-
tate of lead.

ALBUMINOIDS.

In the development of the different tissues of the animal body
the native albumens already described, which exist in the ovum and
embryonic cells, assume a modified form, the condition under which
such a modified albumen is present varying considerably in dif-
ferent tissues ; as already pointed out, the difference in the different
tissues, especially in the different members of the connective-tissue
group, is dependent upon the modification which the albuminous con-
stituents of those cells have undergone. Such bodies have a chemical
composition very closely allied to that of native albumens. They
are complex, nitrogenous compounds, but they present certain proper-
ties in contrast with the true albuminous bodies. As they appear to
result from the transformation of those bodies in the animal econonvr,
not as a rule being found in the vegetable kingdom, they may be spoken
of as the albuminoids of special tissues.

In the connective-tissue group are included a number of different
tissues, such as white connective tissue, elastic tissue, tendon, bone,
cartilage, and dentine, which at first sight appear to have few if any
points in common. Yet all these tissues fulfill the same subservient
function of connection and support, all originate from the same layer
of the blastoderm, and in different periods of life are often changed
from one form into the other. The cells of all these tissues are capable
of developing a more or less homogeneous intercellular substance, whose
chemical composition differs in the different members of this group.

When any of the various forms of connective tissue proper are
macerated for some days in lime-water or baryta-water, the various
elements fall asunder from solution of the connecting cement, which
may be precipitated from its solution by dilute acids. This body is
mucin. If the ground substance of the different connective tissues after
the removal of mucin is boiled in water, they nearly all yield substances
somewhat similar to glue ; hence they are called collagenous bodies.

We will take these up in turn.

1. Mucin. — Mucin, or the cement substance, is found in all mucous
secretions as a result of special cell action, and jn the tissue of mollusks,
and is the substance to which their tenacious character is due. It is
found in embryonic connective tissue, and serves to bind together the
fibres of tendons, and of connective tissue and epidermis, and is found

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 105

in synovial secretions. Mucin may be prepared from the salivary glands
by making a watery extract, filtering and precipitating mucin by acetic
acid ; the precipitate may then be washed with water, with alcohol, and
with ether to remove fat. Mucin may also be obtained from tendons by
washing well, cutting up into small pieces, extracting them with water to
remove soluble albuminous bodies and salts, and then allowing them to
stand for several days in lime- or bai'3'ta-water. After filtration, acetic
acid will precipitate the mucin, which at first is granular, but afterward
flocculent in appearance, and which may be washed with dilute alcohol
or dilute acetic acid. It also may be prepared from ox-gall by precipi-
tating with its own volume of alcohol to remove the coloring matter and
proteids, dissolving the precipitate in lime-water, after washing with
fresh alcohol, and precipitating the mucin from its solution in lime-
water by acetic acid.

When freshly precipitated, mucin is a glutinous body which may be
suspended but not dissolved in water. Mucin is soluble in concen-
trated but not in dilute mineral acids. It is also soluble in liquor
potassae and lime-water, and the solution is viscid and nearly neutral.
When in solution it is not coagulated by boiling, but is precipitated
in an insoluble form by acetic acid. Its solutions are precipitated by
mineral acids, the precipitate being soluble in a slight excess of acid.
It is not precipitated by metallic salts, with the exception of acetate
of lead. When boiled for twenty or thirty minutes with dilute sul-
phuric acid it acquires the power of reducing the ordinary sugar tests.
It again loses this power on prolonged boiling. A body similar to
acid albumen is formed at the same time. No precipitate is produced
with solutions of mucin by acetic acid and potassium ferroc3Tanide
unless other albuminoids are also present. It gives no precipitate
with mercuric chloride, and does not give the biuret reaction for albu-
minous bodies ; with Millon's reagent it gives a red color. It therefore
possesses several properties which are divergent from those of or-
dinary albuminous bodies, and is evidently a proteid body modified
through the differentiation of the protoplasm of the cells of the con-
nective-tissue group.

Mucin appears to be digested by pancreatic but not by gastric juice.
Mucin is not soluble in water or alcohol, but swells up very much in the
former, particularly in the presence of certain salts. When the mixture
is filtered part of the mucin often passes through, and causes a turbid
precipitate. The mixture in water possesses no viscidity; it, however,
becomes clearer and more tenacious if sodium chloride is added.

2. CollagenoKS Albuminoids. — Collagenous albuminoids, of which
gelatin is the type, are albuminous bodies found in connective tissue,
cartilage, and bone. They contain a little less carbon and more nitrogen

106 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

than the true albuminous bodies. They are termed gelatinous because
gelatin, which is formed by the action of boiling water on these tissues,
is the most important representative of the group. It contains — ,

a. Collagen.

b. Gelatin.

c. Chondrogen.

d. C lion drill.

a. Collagen, or gelatinous substance, forms the organic basis of
bones and teeth, and of the fibrous parts of tendons, ligaments, and
fascia. It derives its name from the fact that by prolonged boiling it is
converted into gelatin or glue (Ko/l/ld). Collagen is prepared from bones
by soaking in repeated changes of dilute hydrochloric acid; or from
tendons by removing mucin by means of lime- or baryta-water, then by
repeated washing with water, and finally with very dilute acetic acid.
When fresh it is soft, but it shrinks and becomes hard when dry, or when
alcohol is added. Collagen is insoluble in cold water; it swells up on
dilute acids, and becomes transparent ; through the prolonged action of
dilute acids collagen dissolves, the solution containing gelatin and acid
albumen, the latter, perhaps, being produced by the action of the acid on
the residual matter of the connective-tissue cells. It dissolves in liquor
potassse, and in 'boiling dilute acids or in boiling water it dissolves and
is rapidly converted into gelatin.

6. Gelatin. — Gelatin is prepared, as already indicated, by boiling
collagen, or any of the connective-tissue group, in water, and when the
solution cools it forms a jelly the consistence of which depends upon
the percentage of gelatin present.

Gelatin, prepared as indicated above, is a product of the trans-
formation of connective tissue by the prolonged action of boiling water.
It is favored by high temperature (120° C.), as in Papin's Digester, and
the presence of a minute quantity of acid. When dry it forms a
yellowish or, if pure, a transparent, tasteless solid, closely resembling a
gum in its general appearance and characteristics. It is insoluble in
cold water, but when immersed in cold water is able to absorb by
imbibition forty times its own weight. It then will form a stiff, tenacious,
jelly-like mass. If dry gelatin is boiled in water, it is readily dissolved,
and when the solution in water cools the gelatin sets into a stiff jelly if
more than 1 per cent, of gelatin is present, the consistence of the jelly
depending upon the quantity of gelatin dissolved. When boiled for a
long time in water, or if boiled with an acid or alkali, this property of
gelatinizing is lost and two peptone-like bodies result.

Gelatin is insoluble in alcohol, ether, and chloroform. It is soluble
in warm glycerin, such solutions having the power of gelatinizing when
cooled.

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 107

In solution gelatin rotates the plane of polarized light to the left
( — 130° at 25° C.). In watery solutions gelatin is precipitated by tannic
acid, alcohol, and mercuric chloride ; but not hy acetic acid, which serves
to distinguish it from chondrin ; nor by potassium ferrocyanide and acetic
acid, which separates it from other proteids; nor acetate of lead, which
precipitates chondrin. When boiled with cupric sulphate and potassium
hydrate, the blue solution becomes red without depositing oxide of
copper. Gelatin readily undergoes putrefaction, and among the products
leucin, ammonia, and some of the fatty acids are found.

c. Chondrogen. — Chondrogen is found in the intercellular substance
of l^aline cartilage, and in the cartilage of bone before ossification. It
derives its name from the fact that when boiled with water it forms
chondrin, — a point which serves to distinguish it from fibro-cartilage,
which, when treated in the same way with boiling water, forms gelatin, and
not chondrin. Chondrogen is insoluble in cold water, but if dried before-
hand, when immersed in cold water will swell up slightly. It swells very
slightly in acetic acid, and may be dissolved by the concentrated mineral
acids and caustic alkalies. When subjected to prolonged boiling with
water it dissolves and forms an opaline solution, which forms a jelly
when cooled.

d. Chondrin. — As just stated, chondrin is the result of prolonged
boiling of .chondrogen in water. When solutions of chondrin in water
cool the}" form a stiff jelly, which is insoluble in cold water, but soluble
in alkalies and ammonia. When solutions of chondrin are evaporated,
a hard, translucent, yellowish, gummy mass results, which is insoluble
in alcohol and ether, swells slightly in cold and dissolves tolerably
readily in hot water and solutions of the alkalies. Prolonged boiling of
watery solutions of chondrin destroys its power of gelatinizing, though
the other properties of chondrin are not thereby altered. It is precipi-
tated from its solutions by alcohol. It differs from gelatin in that it is
precipitated by the mineral acids even when they are dilute ; an excess
of the reagent dissolves the precipitate. It is also precipitated by
solutions of sulphurous acid. It is precipitated by acetic acid, the
precipitate not being soluble in excess unless some alkaline salt be
present. It is precipitated in abundant flocculi by solutions of alum,
which readily dissolve in an excess, and the fluid becomes clear and
transparent. It is precipitated with acetate and subacetate of lead,
nitrate of silver, and cupric sulphate. Tannic acid and chlorine water
precipitate it, as in the case of gelatin. It rotates the plane of polarized
light to the left. Chondrin also is readily decomposable, and when
subjected to prolonged heat with concentrated l^drochloric acid is
decomposed, with the formation of nitrogenous compounds which have
the power of reducing the cupro-potassium test ; a body resembling acid

108 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

albumen is formed at the same time. The same changes follow prolonged
boiling with dilute sulphuric acid. There are some grounds for supposing
that chondrin is not an individual albuminoid, but that it is rather a
mixture of gelatin, mucin, and salts, since its general characteristics are
similar to what might be possessed by a combination of these bodies.
All the connective tissues, therefore, possess a body which may be
transformed into gelatin by boiling, and a cement substance, mucin.

The following statements represent in a few words the distinctive
characteristics of mucin, cliondrin, gelatin, and albumen: —

Mucin. — Precipitated by acetic acid, the precipitate is not dissolved
by sodium sulphate.

Chondrin. — Precipitated by acetic acid, the precipitate is dissolved
by sodium sulphate. Precipitated by lead acetate, alum, silver nitrate,
and copper sulphate.

Gelatin. — Not precipitated by acetic acid, nor by acetic acid and
potassium ferrocyanide, nor by lead acetate.

Albumen. — Dissolved by acetic acid, the solution is precipitated by
potassium ferrocyanide, or by the addition of alkaline salts and heat.

Gelatin and chondrin are mostly to be recognized by their hot
solutions forming a jelly when cooled. This, as already mentioned, is not
invariably the case, as the property is lost by prolonged boiling, or by
boiling with acids.

Closely allied to these collagenous albuminoid constituents of the
connective tissues we meet with two other albuminoids which have many
points in common with the above, with the exception that they do not
form jellies when their solutions cool. These two bodies are Elastin,
obtained from elastic tissue, and Keratin, a nitrogenous body of epithelial
origin.

3. Elastin. — Elastin is the albuminoid principle contained in yellow
elastic tissue. When yellow elastic connective tissue is boiled with
water, after mucin has been removed, collagen is dissolved. The residue
which remains is mainly composed of elastin. Elastin may be prepared
by macerating the ligamentum nuchae of the ox with ether, and then hot
alcohol, to remove the fats ; boiling water, to remove collagen and convert it
into gelatin, and 10 per cent, caustic soda, and then acetic acid, allowing
the boiling in water to continue for at least thirty-six hours, and in the
acetic acid for at least six hours. After being subjected to the soda, the
remaining tissue is again boiled with dilute acetic acid, well washed with
water, and afterward the acid neutralized. After washing with hot
water a brittle, yellowish mass is obtained, which recovers its elasticity
and fibrous appearance if soaked in dilute acetic acid.

Elastin is insoluble in cold or boiling water, and offers remarkable
resistance to chemical agents, unless boiled for a very long time. It is

NITROGENOUS ORGANIC CELL-CONSTITUENTS. 109

insoluble in alcohol, ether, ammonia, or acetic acid, but it dissolves in
caustic potash. Its solutions, however, do not gelatinize. When once
dissolved in caustic potash the alkali may be neutralized without throw-
ing the elastin out of solution. Tannic acid is the only acid which will
precipitate it. Elastin gives the xantho-proteic and Millon's reactions,
and its place among the albuminoids, therefore, seems warranted. When
boiled for a long time with sulphuric acid it undergoes decomposition,
with the formation of leucin and tyrosin. Elastin contains no sulphur.

4. Keratin. — The epithelial tissues of the animal body — nails, bone,
epidermis, and epithelium, as well as horns and feathers — are mainly
composed of a substance closely allied to albumen, as it gives leucin and
tyrosin on decomposition, to which the name of keratin has been given.

Keratin contains sulphur in loose combination, and is in some re-
spects closely related to elastin. Keratin is insoluble in alcohol and
ether, swells up in boiling water, and is soluble in the caustic alkalies.
It is not liable to decomposition. When one of the epithelial structures,
such as horn, is subjected to the action successively of boiling water and
alcohol, ether, and dilute acids, this substance, keratin, remains behind.
But when so obtained it has by no means a constant composition,
and it is probable, therefore, that keratin is rather a mixture of several
nitrogenous bodies than a single albuminoid.

Decomposition of the Albuminous Bodies. — As already mentioned,
albuminous bodies are the most unstable of all organic compounds, and
we have the strongest reason for believing that, even while in the interior
of animal and vegetable organisms, the albuminous constituents of proto-
plasm are continually the seat of various forms of decomposition which
result in the production of simpler organic and inorganic forms. As we
know but very little as to the molecular constitution of the proteid
bodies, nothing positive can be said as to the complex chemical processes
which result in the production of simpler organic forms. The subject
has been a favorite field of research for organic chemists, but as yet
scarcely anything tangible has resulted from their labors. An immense
amount of valuable information has been attained, but the applicability
of the facts so reached to physiological processes is not as yet clearl}^
assured. The chief end products of the decomposition of proteids in
the animal cell, which is essentially one of oxidation, are water, carbon
dioxide, and urea. What the nature of the substances are which are in-
termediary between these end products and albuminoids we do not clearly
know, except that certain ones, such as leucin, tyrosin, certain of the
carbo-hydrates, such as glycogen and fats, are of constant occurrence
and of great importance. The subject of the decomposition of albumen
under various chemical and physical agents is an extremely interesting
one, but it falls more within the province of works on organic chemistry.

110 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In our study of the processes of metabolism of the animal body, in
which we will attempt to trace the course of the food-stuffs after their
entrance into the body and in their elimination as various effete products,
this subject must necessarily be touched upon ; the consideration of the
part of this subject which is at all capable of practicable application will
be deferred until then.

It may only be mentioned here that the simpler an organism the
simpler must be the chemical changes in its constituents. Thus, we find
that in the elementary vegetable organisms their entire structure is made
up of protoplasm, which is practically almost solely albuminoid ; we have
then appearing chlorophyll, cellulose, starch, and in still higher forms the
various sugar groups, vegetable acids, alkalies, etc. In the animal body
a similar state of affairs holds. We m&y say that the body of an amoeba
is composed of simple albuminous matter. In the development of 'organs
we have a development of supposed chemical derivatives of protoplasm,
and the higher the state of development of the organism the more com-
plex will be the changes which have resulted from the original proto-
plasm. As we have already mentioned, these cell-constituents are organic,
nitrogenous and non-nitrogenous, and inorganic bodies. All of the sub-
stances which we have heretofore considered are examples of derivatives
or modifications of protoplasm, and as protoplasm is essentially albumi-
nous they are, therefore, the examples of a modification of albumen. In
the waste of albuminous tissues we have an immense number of inter-
mediary bodies, partly belonging to the various aromatic series, between
albuminous bodies and the simpler end products, water, carbon dioxide,
and urea. These bodies result from a progressive series of oxidations,
and will receive consideration under the subject of Nutrition.

FEKMENTS.

Various animal and vegetable cells will often be found to contain
a class of bodies which are closely allied in composition to albuminous
substances, since they contain carbon, nitrogen, hydrogen, ox3^gen, and
sulphur. From the fact that they are able, under certain conditions, to
produce reduction in the complexity of organic compounds with the
action of water without acting through the development of chemical
affinities, and without themselves undergoing change, such bodies are
termed soluble ferments, and are derived directly from modifications of
the protoplasm of the living organisms in which they originate. Al-
though they are apparently allied to albuminoids in their chemical con-
stitution, yet when purified they fail to give the proteid reactions ; and
although we may be pretty sure that such bodies are derived from
the physiological splitting up of proteids, we have no exact knowledge
as to their structure. When obtained dry by various processes, which

NITROGENOUS ORGANIC CELL-CONSTITUENTS. Ill

will be considered under the study of the individual ferments in the
section on Digestion, they are amorphous, colorless powders, which are
highly soluble in water, resemble gums somewhat in appearance, and are
precipitated from their solutions by alcohol, corrosive sublimate, and
lead acetate. One of their remarkable points of contrast to albuminous
bodies is that, when precipitated from solution in water or glycerin by
absolute alcohol, if the precipitates are filtered off and dried, they are
again perfectly soluble in water, and are still capable of exerting all their
actions ; hence, their precipitation is more of a mechanical nature than
chemical. Further, when the precipitates formed by the above reagents
are decomposed by sulphuretted hydrogen a wateiy extract of the pre-
cipitate will still preserve the original properties of the ferment ; in other
words, the soluble matter is restored to the water unchanged, and still
preserves its specific properties. The ferments are with difficulty freed
from albuminoids, and it is in all probability the albuminoid which is
chemically precipitated from their solutions by the above reagents, and
which in this precipitation carries with it mechanically the ferment.
Consequently, this property of the ferment of being precipitated by the
above reagents is dependent upon the albuminous bodies which are
nearly always associated with it. We shall, further, find that this prop-
erty of being carried down by precipitates from solutions is the basis
of nearl}r all the methods which have been employed for the isolation of
the different digestive ferments.

Ferments obtained from the animal and vegetable kingdom may
have the most varied functions. We have but little information
concerning the soluble ferments from a chemical point of view. We
do not even know whether they all have the same chemical compo-
sition, and differ only in some unknown manner in their specific activit3r.
They only are active at a temperature below 60° C., and when in the
presence of water ; at the temperature of boiling water they are perma-
nently destroyed; at lower temperatures their activity is suspended.
They do not themselves appear to be influenced in the phenomena offer-
mentation which they inaugurate ; ferments are also inactive in the pres-
ence of various chemical agents, such as alcohol, the stronger mineral
acids, and all the large group of substances which are known as antisep-
tics. Ferments may be of two kinds ; either organized ferments, such
as the yeast-plant, malt, vibrios, bacteria, etc., — substances which are
themselves elementary, cellular organisms, — or the so-called unformed
ferments, or enzymes, substances which invariably originate in the interior
of animal and vegetable protoplasm, and are soluble and not organized.

This latter group comprises all the ferments with which we are par-
ticularly interested. Their specific action is in many cases closely analo-
gous to that of the formed ferments. There are, however, several points

112 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of contrast between them. Organized ferments are destroyed by com-
pressed oxygen ; soluble ferments are not. Solutions of borax prevent
the action of the unformed ferments, but are without influence on the
formed ferments. The organized ferments during their action reproduce
themselves ; the soluble ferments do not act. All the soluble ferments
have a high percentage of ash, sometimes as much as 8 per cent. Under
the action of ferments, fermentable bodies yield substances whose nature
is dependent on that of the ferment. So that any individual ferment-
able substance under the influence of different ferments will split up into
different substances.

The following are the important ferments found in animal organ-
isms : ptyalin, found in the saliva and converting starch into sugar ;
pepsin, found in the gastric juice and in the presence of a dilute acid
converting albuminous bodies into peptones ; the milk-curdling ferment,
or rennet, found in the gastric juice and coagulating milk in neutral or
acid media; the amylolytic ferment of pancreatic juice, converting starch
into sugar ; the proteolytic ferment of pancreatic juice, converting proteids
into peptones in an alkaline medium; the fat-ferment of pancreatic juice,
splitting up neutral, fatty bodies into fatty acids ; the milk-curdling fer-
ment, also said to exist in pancreatic juice ; the inversive ferment, found
in intestinal juice and converting cane-sugar into inverted sugar; and
the liver-ferment, converting gtycogen into sugar. The general subject
of the nature of the changes produced by these substances will be con-
sidered in the next section ; the mode of action of the digestive ferments
will be considered under the subject of Digestion.

B. NON-NITROGENOUS ORGANIC CELL-CONSTITUENTS.

I. CARBO-HYDRATES. — The carbo-hydrate tissue-constituents are
composed of carbon, hydrogen, and oxygen, the latter two in the propor-
tion to form water. Although occasionally present as constituents of
animal cells, they are almost exclusively produced by the vegetable king-
dom, and present many interesting examples of isomerism. They may
be divided into the three following groups : —

(a) STARCHES (C6H10O5).

(6) GRAPE-SUGAR GROUP (C6HiaO6).

(c) CANE-SUGAR GROUP (CMH22On).

The members of the first group may, through the action of dilute
acids or the di astatic ferments, be transformed in great part into the
second group. The latter undergoes alcoholic fermentation when in
contact witli malt.

(a) THE AMYLOSES, OR STARCH GROUP 7?(C«H1006). — This group
includes starch, dextrin, glycogen, cellulose, granulose, and inulin.

NON-NITBOGENOUS OEGANIC CELL-CONSTITUENTS.

113

1. Starch, or amylum (??(C6H10O6) or CmllaoOjg), is almost univers-
al^ distributed throughout the vegetable kingdom, and is the first evi-
dence of the decomposition of CO2 of the atmosphere by vegetable cells
(6 CO3-{-5 H2O = C6H10O6-|-12 0). It is particularly abundant in the
cereals, in seeds of the leguminous plants, and in the potato, and in cer-
tain roots, tubers, soft stems, and seeds. It forms rounded masses which
lie in the plasma of the plant-cells, becoming converted, in the process of
germination in seeds and bulbs, into soluble dextrin and sugar. Under

FIG. 54.— STARCH-GRANULES, AFTER LOEBISCH.

A, pea-starch ; B, rice-starch ; C. oat-starch ; D, wheat-starch : E, bean-starch : F, millet-starch ; G, corn-starch ; H, rye-
starch ; I, lentil-starch ; K, potato-starch ; L, buckwheat-starch ; M, barley -starch.

microscopic examination starch appears as rounded, glistening granules
composed of a series of concentric rings. These granules vary in appear-
ance and size according to their source. In size they may vary from
0.004 mm. in diameter, as when found in beet-seeds, to 0.16 mm., as in
potato-starch (Fig. 54).

In the following table (after Karmarsch) the diameter of the starch-
granules from different sources is given. Microscopic examination of

8

114

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

0.140 (0.10-0.185).

0.140

0.07

0.063

0.050

0.050

0.036

0.031

0.02-0.03

0.028

0.022

0.025

0.009

different " meals," by the shape and size of the granules, will thus permit
of the recognition of adulteration with inferior meals : —

Mm.

Starch granules from Potatoes (average),
Arrowroot,
Sago,
Beans,

Peas, "

Wheat,
Rye,
Oats,
Corn,
Tapioca,
Rice,
Barley,
Buckwheat,

The striated appearance is due to the fact that starch is composed
of two substances, — cellulose and granulose, arranged in concentric
layers, the cellulose always being external. Granulose stains blue with
iodine, — not by the formation of a chemical compound, but by the deposit
of the iodine around the starch-molecules, — and cellulose stains a faint
yellow. These two substances may be separated by digesting, at 60° C.,
one part of starch in forty parts of saturated salt solution containing
1 per cent, of free hydrochloric acid. The granulose then passes into
solution, while the cellulose remains. Examined in this waf , potato-
starch has been found to contain 5.7 per cent, cellulose, wheat-starch
2.3 per cent., and arrowroot 3.10 per cent. Under the action of dias-
tatic ferments granulose is converted into sugar, while cellulose remains
unaltered. A third substance has been distinguished in starch which is
termed erythrogranulose, and it differs from granulose in taking on a red
coloration when treated with iodine. It has a stronger affinity for fodine
than granulose. Hence, when starch-mucilage is treated with very dilute
iodine solution a red color is produced, but when a large quantity of
iodine is added, a deep-blue coloration, from the fact that the reaction
of the iodine with the granulose masks the erythrogranulose reaction.

Pure starch is a white, tasteless, and odorless substance which is
almost entirely insoluble in cold water. In boiling water the granules
swell up from the imbibition of water by the granulose, the cellulose
envelopes burst, and the granulose dissolves. It is to the presence of
the cellulose envelope that the insolubility of raw starch in cold water is
due. When the cellulose membranes are destroyed or comminuted, as by
grinding with powdered glass, a part of the granulose is then dissolved
in the water, and by repeated washing nearly all the granulose ma}7 be
removed and the cellulose envelopes alone remain. In boiling water,
while the starch is said to be soluble, the condition is more strictly one
of a high degree of imbibition of the starch. Like other colloids, starch
is incapable of dialysis, and forms a mucilaginous emulsion. A solution

NON-NITROGENOUS ORGANIC CELL-CONSTITUENTS. 115

of granulose in water rotates the plane of polarized light strongly to the
right. According to Pay en, when starch is placed in a saturated solu-
tion of potassium iodide, or potassium bromide, it swells up to a stiff
jelly and increases twenty-five to thirty times in volume. This mass
may then be dissolved in water, with only a slight residue of starch-
cellulose. Dilute acids will also dissolve granulose.

The alteration of starch through the action of the dia static ferments
will be described under the consideration of the action of the digestive
juices on the different food-stuffs. When starch is boiled with dilute
acids similar products result.

When starch is subjected to dry heat at 150° to 160° C. it is gradu-
ally transformed into dextrin. When moisture, however, is present, quite
different compounds result, the starch being completely decomposed, with
the formation of carbon dioxide, formic acid, etc. In still higher tem-
peratures small quantities of brenzcatechin are formed, — a fact which is
pf especial interest, as it indicates the possibility of the conversion of
carbo-hydrates into members of the aromatic series. Oxalic acid results
from heating starch with nitric acid.

The test for starch is iodine, which, with raw starch, or with starch-
mucilage, gives a deep-bine coloration which disappears on heating, to
return on cooling, if the heat has not been too prolonged. Starch is
also precipitated from its solutions by tannic acid in the form of a yellow,
flocculent sediment which is dissolved on heating.

. • ^ 2. Cellulose (C6H10O6). — Cellulose forms the wall or cell-membrane
of vegetable cells, and may be regarded as the skeleton of plants. It is
formed by vegetable protoplasm out of other carbo-li3Td rates, such as
starch and sugar, and is capable of being again reconverted into other
members of the same group. It only very seldom occurs in a perfectly
pure condition. Young plants contain purer cellulose than older plants;
in the latter there is a greater percentage of ash. Cotton and Swedish
filter-paper are forms of comparatively pure cellulose. Cellulose is very
hygroscopic, but ammoniacal cupric oxide solution (Schneider's reagent)
is its only solvent. In sulphuric acid it first swells up and then dissolves
and forms a substance which is stained blue with iodine. This substance is
termed ani3'loid, but must not be confounded with the amyloid substance
of pathologists, which has been already described under the albuminous
bodies. Cellulose is also capable of being converted into the sugar
group by prolonged action of acids. Woody fibre is a modified form of
cellulose, which is due to the deposit within the cellulose of nitrogenous
substances ; it then has acquired a greater power of resistance to various
mechanical and chemical agents. In woody fibre cellulose has become
associated with a body richer in carbon and poorer in oxygen than cellu-
lose, and which is termed lignin ; its formula is C10H240U. The lignin

116 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

constitutes about 50 per cent, of wood, the other half being composed of
cellulose, upon which the lignin is deposited. Iodine stains cellulose of a
yellowish color unless hydriodic acid, potassium iodide, zinc iodide, sul-
phuric acid, phosphoric acid, or zinc chloride are added with the iodine.
With any of these reagents, combined with the iodine, the cell-membrane
or cellulose is stained blue. It is not known, however, in what way these
agents assist the reaction.

3. Dextrin (C6H1006). — Dextrin, or British gum, is the name given
to a group of substances which may be regarded as intermediary products
in the conversion of starch into sugar. It may also be obtained by boil-
ing starch with dilute acid, although in this operation the sugars are also
obtained. There is some doubt as to whether it exists ready formed as
a constituent of vegetable cells. In commerce it is manufactured by
heating dry starch up to 400°. Through the action of the dry heat the
starch becomes yellowish in color and soluble in water. Dextrin is in-
soluble in alcohol and ether; it should not reduce the sugar test unless,
as is apt to be the case, it is associated with sugar. It rotates the ray
of polarized light strongly to the right, from which it derives its name
( dexter = right), and is readily converted by the action of dilute acids,
or the diastatic ferments, into sugar. According to Bernard, dextrin is
found in the blood of both the herbivora and carnivora, though in greater
amount in the former. When found in the animal body it originates
partly from the giycogen of the liver and partly from the food. The test
for dextrin is the formation of a mahogany-red color when iodine is added
to its solutions. When heated this color disappears and does not return on
cooling, — a point of importance as serving to distinguish dextrin from
giycogen, another member of this group. Dextrin is precipitated out
of its watery solutions, which are alwa}^s turbid, by alcohol, lime-water
and ammonia, and acetate of lead. With iodine in solution in potassium
iodide, dextrin gives a violet coloration.

4. Giycogen. — Giycogen, or animal starch, or, more properly speaking,
animal dextrin, wiU be discussed at length under the subject of Special
Physiology.

5. Inulin (C6H1006). — In its composition and characteristics inulin
is closely allied to starch. It is found in the roots of the Lobeliaceae,
Campanulaceae, and Gordeniaceas ; it owes its name to the fact that it wras
first discovered in the root of the Inula helenium. Dried dahlia-bulbs
contain 42 per cent, of inulin. In the autumn inulin is found in
greatest amount ; in the spring it becomes converted into Isevulose.
Inulin is only found dissolved in plant-juices, and never as a solid
deposit ; and since inulin by itself is insoluble in water, it must then owe
its solubility to the presence of some other substance.

Inulin may be obtained \>y boiling dahlia-bulbs in water, enough

NON-NITKOGENOUS ORGANIC CELL-CONSTITUENTS. 117

calcium carbonate being added to neutralize the acid reaction. After
filtering and concentration, inulin separates from the extract in the form
of crystals. By boiling with dilute acid, inuliu is converted into
Isevulose.

(6) THE GLUCOSES, OR GRAPE-SUGAR GROUP ?i(C6H1206). — This group
comprises grape-sugar, or dextrose, galactose, inosite, and Isevulose, or
sugar of fruits.

1. Grape-Sugar (C6H12O6-|-H2O). — Grape-sugar, or glucose, is widely
distributed throughout the vegetable kingdom, as a rule accompanying
fruit-sugar, and Js also normally found dissolved in many of the animal
j uices. It owes its name to its being found in grapes, where it is associated
with Isevulose. It rotates the plane of polarized light to the right, and is
consequently designated as dextrose. As a product of the action of
the diastatic ferments on starch and the majorit3T of the carbo-l^-drates,
it acquires an especial importance for the animal organism. Grape-sugar
also occurs in the vegetable kingdom associated with other bodies to form
glucosideSj from which it may be separated by treatment with acids or
ferments. Most of these bodies contain only C, H, and O; some, such
as solanin and amygdalin, contain N in addition, and in others S is also
found. Grape-sugar seldom occurs in well-formed crystals, but ordinarily
in crumbly, white masses, which, under the microscope, are seen to consist
of small, rhombic tables. It has a sweetish taste, and is soluble in water
and alcohol. At 100° C. grape-sugar melts and loses its water of
ciystallization. At higher temperatures it becomes brown, and is con-
verted into caramel, CuH^Oj,. At still higher temperatures it is
completely decomposed into CO, C02, marsh-gas, acetic acid, acetone,
aldehyde, and other products. If heated with a strong solution of
caustic potash grape-sugar decomposes, with heat production, into lactic
acid, brenzcatechin, formic acid, and other products, accompanied by
the development of a brown color. If nitric acid is then added, an odor
of burnt sugar and formic acid is produced. Grape-sugar is readily
soluble in water, but less so than cane-sugar. It is also less sweet than
cane-sugar. It is very slightly soluble in alcohol and insoluble in ether.
Glucose combines with different acids and bases to form glycosates or
saccharates. Grape-sugar has a great affinity for oxygen, and it is
therefore a powerful reducing agent. This property is seen in the
reduction of cupric oxide in an alkaline solution, and has been made use
of for a qualitative and quantitative test of its presence. Thus, if one
molecule of grape-sugar is mixed with five molecules of cupric sulphate
and eleven molecules of sodic hydrate the copper will be precipitated
completely, and the filtrate will be free from sugar. In watery solutions
grape-sugar is unstable, since it is readily decomposed under the action
of ferments. This fermentation, produced under the influence of yeast

118 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

or malt, is termed alcoholic fermentation, and is accompanied by tlie
development of carbon dioxide, with small amounts of glycerin and
formic acid. The fermentation caused by the lactic acid ferment, or
decomposing nitrogenous matter, results in the final development of
butyric acid.

Various tests have been proposed for the qualitative and quantitative
estimation of grape-sugar. Of these it may be mentioned that in
solutions of cupric hydrate in the presence of free alkalies, when subjected
to boiling, grape-sugar reduces the cupric oxide into red or yellow
anhydrous cuprous oxide (Trommer's and Fehling's test). Basic nitrate
of bismuth is reduced by grape-sugar to bismuth oxide (Bottger's test).
When boiled with half its volume of liquor potassse grape-sugar solutions
acquire a bright-brown color, due to the formation of melassic acid. If
nitric acid is now added, the odor of formic acid is evolved (Moore's
test). For the methods of quantitative estimation of sugar solutions
and further details as to testing for sugar, references must be made to
text-books on physiological chemistry.

2. Lsevulose. — As with dextrose and cane-sugar, Isevulose is also
abundantly distributed through the vegetable kingdom, especially in the
acid fruits. It forms a colorless, non-e^stallizable s}rrup, with almost
as much sweetness as cane-sugar. It derives its name from its property
of rotating the plane of polarized light strongly to the left (at 15° C.=
— 106°). It is as powerful a reducing agent as grape-sugar. When
placed in contact with malt it undergoes alcoholic fermentation without
first being converted into dextrose. Lsevulose is also formed in what is
termed the inversion of cane-sugar. When cane-sugar is subjected to
the action of dilate mineral acids, or the intestinal juices of animals, it
is turned into the so-called inverted sugar, which may be regarded as a
mixture of equal portions of dextrose and Isevulose.

3. Inosite (C6H12O6 -|- 2H2O). — Inosite is a saccharine body which
is found in the heart-muscle and in most of the organs of the body,
especially of the horse and ox. It is also found in certain plants, es-
pecially in the unripe fruit of the Papilionacese. Inosite crystallizes in
long, colorless, efflorescent tables, and in cabbage-like aggregations,
which when dried break down into a white mass. It has a sweetish
taste, is easily soluble in water, but insoluble in alcohol and ether. Its
solutions are optically inactive. It does not reduce the copper test for
sugar. It is incapable of undergoing alcoholic fermentation, and is not
decomposed by caustic alkalies or weak acids. It is precipitated from
its solutions by lead acetate and ammonia. If inosite is evaporated
almost to dryness on a strip of platinum-foil with nitric acid, and the
residue moistened with a little ammonia and calcium chloride solution;
and again evaporated, a beautiful red coloration is produced (Scherer's

NON-NITROGENOUS ORGANIC CELL-CONSTITUENTS. 119

test). By means of this test it is claimed that the presence of 0.005
grain of inosite may be recognized. In contact with decomposing organic
matters inosite may undergo lactic acid or butyric acid fermentation.

(c) SACCHAROSES, OR CANE-SUGAR GROUP ft(C12H220u). — This group
comprises saccharose, or cane-sugar, lactose or milk-sugar, maltose or
malt-sugar, and arabin, found in gum arable.

1. Saccharose, or Cane-Sugar (C12H22OU). — This substance is found
widely distributed throughout the vegetable kingdom in the juices of
various plants, trees, and fruits. It is derived from changes occurring
in starch in the ripening of the fruits. Cane-sugar is said to be the
origin of all forms of vegetable sugar, which in the process of vegetation
is partly broken up into glucose and laevulose. Cane-sugar crystallizes
in large, colorless rhomboidal prisms, which are soluble in one-third
their weight of water, the solubility being greatly increased b\r heat ;
thus, at 0° C., 100 grammes of a saturated sugar solution contain 65
grammes of sugar ; at 14° C., 66 grammes ; and at 40° C., 75.75 grammes.
The solutions of cane-sugar rotate the plane of polarized light to the
right (-f- 73.80°); with various metallic salts and oxides it forms chemical
compounds, which are termed saccharates. When carefully heated to
160° C., it melts into a clear, pale, yellowish fluid, which on cooling
forms a transparent, amorphous mass — -the so-called barley-sugar. If
the temperature of 160° is prolonged, cane-sugar is transformed into
laevulose and glucose. When subjected to a higher temperature with
moisture more profound chemical changes are produced. Carbon dioxide
is developed, and a firm, carbonaceous mass containing a trace of
brenzcatechin and caramelin may result. In the dry distillation of
sugar large quantities of carbon dioxide and small quantities of carbon
monoxide and marsh-gas are set free, while the distillate contains acetic
acid, as well as substances allied to aldehyde and acetone. Under various
circumstances, such as the action of dilute mineral acids, ferments, and
prolonged heating of a watery solution in a closed vessel, cane-sugar
becomes inverted; that is, divided into a mixture of glucose and
laevulose.

Cane-sugar is not directly fermentable, but when converted into
dextrose and Isevulose may then undergo fermentations similar to those
of grape-sugar. Cane-sugar is easily acted on by oxidizing agents, but
less readily than is grape-sugar. It does not reduce alkaline cupric
hydrate solutions, nor is it precipitated by acetate of lead, although
ammonic lead acetate precipitates it. Strong sulphuric acid chars cane-
sugar, but dissolves grape-sugar. Cane-sugar is not directly assimilable
by the animal economy. When introduced into the intestinal canal it is
first changed into invert sugar before being dissolved. When injected
into the veins it is eliminated unchanged by the kidneys.

120 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

2. Maltose. — Maltose is the form of sugar which results from the
action of a diastatic ferment, or dilute acids with heat, on starches. It
resembles cane-sugar in many respects, but has the power of reducing
alkaline solutions of cupric hydrate, although its reducing power is one-
third less than that of dextrose. It rotates the plane of polarized light
strongly to the right, even more so than dextrose (-{-150°). It is capable
of undergoing fermentation, and, through the action of dilute acids with
heat, may be converted into dextrose. It is this form of sugar which in
all probability invariably results from the digestion of the carbo-hydrates
in the animal body under the influence of an amylolytic ferment, and will
be again alluded to in the chapters on Digestion.

3. Lactose, or Milk-Sugar (C12H220u-J-HaO). — Lactose resembles
cane-sugar closely in its properties, but is more stable, and, like dextrose,
1ms the power of reducing the sugar tests. It rotates the plane of polar-
ized light to the right, the degree of the rotation diminishing with the
age of the solution. It is found only in milk; it crystallizes in hard,
white, rhomboidal prisms ; is soluble in six parts of cold and two and
one-half parts of hot water ; insoluble in alcohol, ether, and only slightly
sweetish. It is only fermentable with difficulty. It will again be alluded
to more at length under the subject of Milk.

4. Arabin. — Arabin is capable of being converted by means of dilute
sulphuric acid into a sugar which is termed arabinose, and is closely
analogous to dextrose. It is the main constituent of gum arabic. It
polarizes light to the right, reduces the copper sugar tests, but is in-
capable of fermentation.

II. HYDRO-CARBONS, OR FATS. — Fats may be either of animal or vege-
table origin, and occur either deposited within the interior of cells, or in
the form of solution or suspension in animal or vegetable juices. In the
animal body fat is especially formed in the cells of the connective-tissue
group, either through fatty degeneration of the protoplasmic cell-contents
of the connective-tissue corpuscles, or by the absorption of fat brought
to them by the cells by a vital process analogous to the feeding of the
timceba, or the absorption of fat from the intestinal canal of animals. In
the formation of adipose tissue by either of these processes the proto-
plasmic cell-contents gradually become displaced, the nucleus lying
against the cell-membrane, while the cell-contents consist mainly of a
globule of oil. During the life of the organism the fatty contents of
cells are always of a fluid consistence, and, in the case of animals, only
solidify when cooled below a certain point, which is characteristic of
the different individual fats. In the vegetable cell the fats remain per-
manently fluid, with but few exceptions, in the form of oils. As animal
fats solidify, a partial process of crystallization into groups of acicular
crystals often takes place. When within the interior of cells fats are

NON-NITROGENOUS ORGANIC CELL-CONSTITUENTS. 121

stained black by perosmic acid ; this reagent is, therefore, a delicate
microscopic test for the detection of fats, and, since fat is a constant
constituent of nervous tissue, is used as a means of recognizing this
tissue. In vegetable cells fat is partly produced directly from CO2 and
H2O, and also through the transformation of starch ; the latter is its
mode of origin in oily seeds and fruits where it is stored up until required
for germination and growth.

The natural fats are, without exception, compounds of a triatomic
radical, propenyl or glyceryl, combined with three atoms of a monatomic
fatty acid, namely, either palmitic, stearic, or oleic acids. The fats
formed by the union of these acids with the radical glyceryl are termed
palmitin, stearin, and olein.

A few fats contain other glycerin ethers, such, for example, as are
found in butter. At the ordinary temperatures, fats are either solid, like
tallow; semi-solid, like butter and lard ; or fluid, like oils. These differ-
ences depend upon the differences in their composition. The more
stearin or palmitin there is present, the more the fats tend to solidify ;
while the more olein there is, the more fluid are they. All fatty bodies
become fluid considerably below the temperature of boiling water. In
the pure condition fats are odorless, tasteless, and of alkaline reaction.
When kept in contact with the air, they become rancid from the setting
free of fatty acids and the oxidation of glyceryl, with the resulting pro-
duction of volatile fatty acids and glycerin. In this process they acquire
odor and taste, and have an acid reaction. Fats have a lower specific
graA7ity than water. All fats are completely insoluble in water, but when
water contains bodies such as gum or albumen in solution, fats will then
remain mechanically suspended in the form of an emulsion, which is
merely the breaking up of the oil into minute globules. When fluid, fats
render paper which is coated with them transparent (grease-spots).
Many of the fats are soluble in alcohol, especially when hot, and all are
soluble in ether, chloroform, the volatile oils, benzol, and carbon disul-
phide. When fats contain small quantities of free fatty acids they will
form a permanent emulsion with sodium carbonate solution. This prop-
erty has been used by Briicke as the means of detecting the presence of
free fatty acids, and, in all probability, the production of an emulsion in
the digestion of fats by pancreatic juice is due partly to this fact. When
subjected to dry distillation, acrolein is formed in conjunction with other
acrid and aromatic products. When fats are boiled with alkalies, soap
is produced by union of the alkali with the fatty acid, forming a soluble
salt, or soap, while glycerin passes into solution. The glycerin may like-
wise be displaced by inorganic bases, such as lead, and glyceryl hydrate
or glyceryl alcohol (glycerin) is produced. This replacement of glyceryl
by other bases is termed saponification. The presence of glycerin may

122 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

be recognized by the development of acrolein when boiled with glacial
phosphoric acid. Under the influence of certain ferments fats split up
into glycerin and a &tty acid by combining with the elements of water,
thus : —

C3H5(OC16H310)3+3H20:=C3H5(OH)3+3(C16H310,OH).
Tripalmitin. Water. Glycerin. Palmitic Acid.

The composition of the four principal fats is represented in the
following formulae : —

Glycerin, C3H5(OH)3.

Palmitin, C3H5(OC16H31O)3. Palmitic Acid, C16H31O,OH.
Stearin, C3H5(OC18H35O)3. Stearic Acid, C18H35O,OH.

Olein, C3H5(OC18H330)3. Oleic Acid, CI8H33O,OH.

Butyrin, C3H5(OC4H7O)3. Butyric Acid, C4H8O2.

Stearin. — Stearin is the chief constituent of the more solid fats.
Its melting point varies between 53° and 66° C. It is insoluble in cold
alcohol and in ether, but is soluble in both when boiled. It never occurs
in the vegetable fats. It crystallizes from boiling alcoholic solutions in
brilliant quadrangular plates.

Palmitin. — This fat is the chief component of the animal fats, but
also is largely found in fats of vegetable origin. It is more soluble in
cold and hot ether and alcohol than is stearin. Its melting point is
45° C. It crystallizes in fine needles.

Olein. — When pure, olein is a colorless oil which is fluid at the
ordinary temperature and solidifies at 0° C. When exposed to the air
it absorbs oxygen and becomes yellow. It dissolves all other fats,
especially at 30° C. It is soluble in cold absolute alcohol and ether.
It is more abundant in vegetable than in animal fats.

Butyrin. — Butyrin is found in butter. It is a pungent liquid ; and
when it decomposes, butyric acid, to which the odor and taste of rancid
butter are due, is set free.

Spermaceti is found in the cranial sinuses of whales, and is a deriva-
tive of cetyl alcohol (C16H33)O. This is a solid body which melts at
50° C., and when saponified yields in addition stearic, myristic, and
lauric acids.

Bees-wax is also a form of animal fat, which is likewise capable of
saponification, the radical here being cetyl alcohol. Waxes possess
many points in common with the fats, but are not acted on by the
digestive juices.

Margarin. — Formerly this name was given to a substance which was
supposed to be a special fat, but which is now known to be a mixture of
stearin and palmitin. It occurs in the form of needle-like crystals which
are often found in the interior of fat-cells, and which were supposed to
be a glycerin ether of a hypothetical acid, — margaric acid.

INORGANIC CELL-CONSTITUENTS. 123

The percentage composition of the animal fats varies only within

narrow limits : —

c. H. o.

Horse-fat, . . . . . 77.07 11.69 11.24

Ox 7650 11.90 11.59

Sheep " 76.61 12.03 11.36

Pig 16.54 11.94 11.52

Dog " 76.63 12.05 11.62

Cat 76.56 11.90 11.44

The Average.
76.5 12.0 11.5
Formula, C62H99O6.

Of the different domestic animals, horse-fat is 3rellow, and begins to
melt at 30° C. Its essential component is olein. Ox-fat contains prin-
cipally stearin and palmitin, and but little olein. It is white, melts at
43° C., and solidifies after melting at 36° or 37° C. Mutton-fat contains
principally stearin. Its melting point is 46°. It solidifies at from 35° to
40° C. Pig.fat is white, and contains large quantities of olein ; melts
at 41°, and solidifies after melting at about 30° C.

Adipose tissue is made up as follows : —

"Water. Membranes. Fat.

Ox, 9.96 1.16 88.88

Sheep, 10.48 1.64 8788

Pig, 6.44 1.35 92.21

C. INORGANIC CELL-CONSTITUENTS.*

The inorganic constituents of cells enter them already formed, and,
as a rule, leave them without undergoing change'. About the only
exceptions to this statement are found in the case of carbon dioxide,
the water formed by oxidation of the hydrogen of organic compounds,
and the sulphur of various excretory products, which, eliminated
through the intestines and kidneys, originates in the sulphur of
albuminous compounds. The inorganic cell-constituents differ in no
way from similar compounds found elsewhere. They originate in the
earth and atmosphere, become constituents of vegetable organisms,
and then, through absorption in foods, enter into the composition
of animal bodies. The amount of inorganic matter found in cells,
including of course water, is greater in weight than the organic cell-
constituents. The inorganic constituents may exist in the form of
water, salts, gases, and certain elements whose exact mode of combina-
tion has not yet been thoroughly determined. All the inorganic constit-
uents of the body, in some period of their existence as such, are in the
form of solutions. They enter the organism in solution, are deposited

* In the preparation of this section the author is especially indebted to Gorup-
Besanez, " Lehrbuch der Physiologischen Chemie."

124

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

as constituents of tissues perhaps in the solid or even crystalline form,
but are again eliminated from the body in solution ; this applies not only
to the salts, but also to the gases and acids. Many of the physical prop-
erties of various tissues depend aJmost solely upon their inorganic
constituents. In this connection it is only necessary to mention the
bones and teeth. Wherever cell growth is taking place certain salts are
essential, since no form of protoplasm is able to carry on its existence
without a supply of salts, the nature of which may differ in the case of
different cell forms ; thus, for example, calcium salts are not only
essential for the development of the bone-cells, but accompany the
albuminoids of all growing tissue ; blood-corpuscles require iron and
potassium phosphate, and all forms of cell growth require sodium
chloride.

1. WATER. (H20). — Of the inorganic constituents of cells water is by
far the most abundant, and is the most important. In fact, all organisms
may be said to live in water ; for if their entire body is not surrounded by
water, all contain water in large amounts, and all their vital processes are
dependent on watery solutions. Water is destined, by entering by imbi-
bition into solid tissues, not only to preserve the physical condition
which is essential to the preservation and manifestations of the vital
phenomena of protoplasm, but it holds in solution many of the salts
essential to the vital processes of the economy. It also constitutes a
large proportion of the fluids of the body, such as the blood, lymph, chyle,
and secretions. It is in greater amount in embryonic tissue, and decreases
as adult life and old age are reached. In the higher animals it may
exist in 70 per cent, or more, while in some of the lower forms of life as
much as 90 per cent, may be reached. The amount of water in different
organisms, and in the same organism at different times, is subject to
very great variation. It not only constitutes the great part of the secre-
tions of the animal body, but it also forms a large proportion of even
the densest tissues of the animal or vegetable body. Thus, in the
enamel of teeth two-tenths of one per cent, of water is present, while in
dentine 10 per cent, and in bones 22 per cent, of water is found.

The following table represents the amount of water in 1000 parts of
different animal tissues : —

Organs. Water. Solids.

Enamel,

2 998

Ivory,

100 900

Bone, .

216 784

Fat, .

299 701

Elastic tissi

le,

496 . 504

Cartilage,

550 450

Liver,

693 307

Bone-marrow,

^

697 303

White brain-substance, 700 300

INORGANIC CELL-CONSTITUENTS.

125

Organs.

Skin, .
Brain,
Muscles,
Spleen,
Thymus,
Nerves,
Connective
Heart,
Kidneys,
Gray brain-
Vitreous bo

tissn
subsi

dy,

e,
tance

Water. Solids.

720 280
750 250
757 243
758 242
770 230
780 220
796 204
792 208
827 173
858 142
987 13

Fluids.

Water.

Solids.

Blood, $ .

... . .791

209

Bile, ....
Milk
Plasma,

864
891
901

136
109
99

Chyle, ...
Lymph,
Serous fluids,
Gastric juice,
Intestinal juice,

928
983
959
973
975

72
17
41
27
25

Tears,
Aqueous humor,
Cerebro-spinal fluid, .
Saliva,
Sweat,

982
986
988
995
995

18
14
12
5
5

The condition of semi-solidity of organic tissues, which we found to
be so essential to the carrying out of the physical processes in cell life,
is rendered possible by the amount of water and the condition in which
it is held by the different cells. A remarkable ' fact in connection with
the manner in which water is held by the animal organism is that there
are certain tissues and organs in which the percentage of water found is
in excess of the percentage of solids, without the organs assuming the
fluid form; indeed, again, there are certain semi-solid organs whose per-
centage of water is even greater than that of the animal fluids ; thus, the
kidneys contain a larger percentage of water even than the blood. This
shows therefore that the manner in which the water is held by such
tissues must be different from that in which it exists in the animal fluids,
where it occupies more or less the role of a medium of solution. The
consistence of many fluids in the animal body is not dependent so much
on the amount of water present as on the nature of the substances which
are in solution; thus, mucus has a considerably larger percentage of
water than blood, and yet is apparently a denser fluid. As already de-
scribed in the section on Physical Processes in Cells, the water of the
semi -solid organic bodies enters their elementary intermolecular spaces,
and it is a peculiarity of organized bodies that they may absorb a
quantity of water greatly in excess of their own weight without losing
their semi-solid condition. In such cases it is not water alone that is
absorbed, but water always containing different inorganic salts in solution.

126 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

A certain part of the water found in animal tissues is held in com-
bination, as in water of crystallization, both in organic and inorganic
molecules. This amount is, however, inconsiderable as contrasted with
that held in other manners. Water is also found as a vapor in the air
contained in the respiratory organs of animals.

By far the greater part of the water found in the animal and vege-
table body has entered from without; in the former case through the
food and drink, and in the latter from rain or from the absorption of
moisture from the soil. In the case of the animal body a certain amount
of water is apparently formed within the animal economy, since it has
been found that under certain circumstances the amount of watery vapor
exhaled through the lungs and skin, and that passing through the kid-
neys and intestines, is in excess of the amount of water taken internally,
the body still preserving its uniform weight. Again, as we shall find in
considering the subject of respiration, the volume of carbon dioxide
eliminated through the lungs is smaller than the amount of oxygen taken
into the blood in inspiration. Ten to twent}7-five per cent, of oxygen
disappears in this manner, and must, therefore, have formed other com-
binations in the body than those whose end product is C03. Since it is
readily conceivable that the hydrogen of hydrogen compounds is set free
quite as readily as the carbon of carbon compounds, a certain amount
of this hydrogen may evidently unite with oxygen to form water, not by
a direct oxidation of the hydrogen, but through the gradual union of
the oxygen with a long series of oxidation products whose terminal is
H20, just as CO2 results from the final union of ox}'gen and carbon, and
not by a direct oxidation of carbon in. the animal body. Such an origin
of water in the economy is further supported by the fact that the amount
of hydrogen contained in organic compounds in the excretions is less
than that which is contained in similar combinations in the food. Thus,
it has been estimated that a man receives daily forty grammes of hydrogen
in organic combinations with the food, while only six grammes are dis-
charged in such combinations in the excretions ; hence, thirty-four
grammes, or about 85 per cent, of the hydrogen so introduced, remains
unaccounted for. Since hydrogen does not leave the body as a vapor,
nor in any notable amount in any other inorganic compound but water,
the surplus must be converted into water. The estimates are that in
man about three hundred grammes of water are formed daily in this
way, — probably from the decomposition of carbo-hydrates where hydro-
gen and oxjrgen are present in the proportion to form water.

Organisms not only live in water, but they may be said to live in
running water (Hoppe-Seyler) ; for they are continually taking in water,
which may contain other food-stuffs in solutions, and are continually
eliminating water which contains the products of their tissue-waste.

INOKGANIC CELL-CONSTITUENTS. 127

Plants get rid of water through evaporation from their entire external
surface, while water is absorbed by their roots.

Water leaves the animal body through the kidneys, skin, lungs, and
intestines, that passing daily through the kidneys being about half of the
total amount of water eliminated. The relative proportion between the
amounts eliminated by these organs is subject to very great variation, and
depends upon numerous external and internal conditions, which will sub-
sequently be alluded to. It may, however, be here mentioned that of the
water taken as food but a small amount leaves the body in the faeces ; in
m*n the amount so eliminated is only 4 per cent., while the remaining 96
per cent, leaves the body through the kidne}^, lungs, and skin. Water,
therefore, does not simply pass through the alimentar}' canal, but is ab-
sorbed by its mucous membranes, enters the blood, and thence becomes
a constituent of the different tissues.

Water is a necessary solvent for various organic and inorganic con-
stituents of the body, and it alone, by entering into the condition of im-
bibition in the tissues, enables the various physical and chemical proc-
esses which constantly occur in cells to take place, and occasions their
semi-solid state, their elasticit}', flexibility, and transparency. Through
its evaporation from the external surface and through the lungs it serves
to abstract heat, and therefore is, to a certain extent, a temperature regu-
lator. As water is an essential constituent of organic bodies, its loss,
which is constantly taking place, must be continually replaced ; in the
higher animals a demand for an increased supply of water is indicated
by what is known as thirst. This will subsequent^ demand consideration.

The removal of water from lower forms of cell life entirely suspends
all evidences of vitalit}' ; through desiccation life in such forms is said
to be rendered latent. A renewed supply of water will again restore all
the phenomena of cell life. None of the higher plants or animals can
support loss of water beyond a very moderate amount without causing
permanent loss of vitality ; seeds and infusoria may be completely dried
and recover their vital properties when supplied with heat and moisture.
Although water is an essential constituent of all cells, it may, neverthe-
less, act as a poison if absorbed in too great amount.

Protoplasm of all kinds is killed by immersion in distilled water ;
this fact may be partly due to the diffusion currents which are thus in-
augurated,, the essential salts being removed from the protoplasm, and
their place being taken by water.

Freezing of various parts of plants and then subjecting them to
rapid thawing by exposure to the rays of the sun causes their death by
first abstracting water from the solids and causing its aggregation in a
crystalline form, and then by sudden melting causes drowning out of
neighboring parts while more remote portions still suffer from want of

128 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

water. If the thawing is slowly accomplished the water has time to dif-
fuse and restore the normal condition of imbibition. In this way is to
be explained the fact, which may be frequently observed in cold spring
and autumn mornings, that of the parts of plants which are frozen those
which are exposed to the direct rays of the sun are killed, while those
which are protected from the sun's heat thaw out gradually and regain
their vitality. So, also, red blood-corpuscles may be frozen and gradu-
ally thawed without being destroyed, but if rapidly thawed are dissolved.
On this fact, undoubtedly, rests the practical point that frozen animal
parts must not be rapidly warmed, but have their circulation only gradu-
ally restored ; hence, the common practice of rubbing with snow.

2. SODIUM CHLORIDE (NaCl). — Of the saline constituents of cells
sodium chloride is the most widely distributed, and is present in larger
amount than any other salt in all the tissues of the animal body, with
the exception of the bones, teeth, red blood-corpuscles and striated
muscle-cell. It is especialty worthy of notice that the amount of sodium
chloride in most organs, especially in the blood, is almost constant and
is independent of the amount of this salt contained in the food. Its
distribution in the body is also remarkable. In the blood-plasma it is
abundant, while it is almost absent from the blood-corpuscles which are
suspended in the plasma. It is abundant in chyle, lymph, saliva, gastric
juice, mucus, and pus, and is present in only small quantity in muscle-
juice and many glands. Sodium chloride is present in the form of a
solution in water, and in the removal of the fluids from the semi-solid
tissues by pressure the greater part of the salt is taken away with the
water. The relative proportion of sodium and potassium chlorides in
different parts of the animal body is about as follows : —

QUANTITY OF SODIUM AND POTASSIUM CHLOBIDES IN 1000 PARTS IN THE

Bones,
Blood, .
Bile,

NaCl.
7.02
2.70
5.58

KC1.

2.05
0.28
0.55

2.13

4.50
0.02

Gastric juice,
Sweat,
Saliva,
Milk

1.45
2.23
1.53

087

Lymph, 5.67
Sebaceous matter, . . . . . . .5.00
Urine, 11.00

Pancreatic juice, 7.35

All the sodium chloride found in the animal body has entered it
from without. It leaves the body in the urine and excrement, perspira-
tion, nasal and buccal mucus. By far the greater part is eliminated
through the urine, though the total amount eliminated falls short of that
taken in the food. A certain amount of the sodium chloride taken in as

INORGANIC CELL-CONSTITUENTS. 129

food undergoes chemical decomposition in the bod}', as will be alluded
to in the subject of Nutrition. Thus, the potassium chloride of muscles
and red blood-corpuscles apparent!}^ originates in a double decomposition
of sodium chloride and potassium phosphate into sodium phosphate and
potassium chloride. Possibly the hydrochloric acid of the gastric juice
and the sodium salts of the bile have similar origins.

Sodium chloride is absolutely essential to the manifestation of life ;
in a physical sense, it is of great importance, from the influence which it
exerts over diffusion, particularly in the degree of absorption from the
alimentary canal. The conditions which follow the deprivation of
sodium chloride, and a more detailed account of its relations to the
nutritive processes and body will again be referred to more at length
under the subject of Nutrition.

3. POTASSIUM CHLORIDE (KC1). — Potassium chloride is usually a
companion of sodium chloride, although in certain tissues, such as the
red blood-corpuscles, and in muscles, it occurs in greater amount than
the sodium salt, while it is almost absent from the blood-plasma, where
a slight excess of potassium salts appears to act as a poison to the heart.
A similar toxic effect is also exerted by potassium chloride on muscles
and nerves.

In the herbivora potassium chloride is, as a rule, in excess over
sodium chloride. The salivary glands and kidneys appear to be the
special organs for its elimination.

4. SODIUM AND POTASSIUM CARBONATES (C08Naa, CO,XaH, 3(CO,)-
Na4H2, CO8Ka, CO8KH).— These salts are found in the ash of various
organic substances, wrhere they have probably originated from the
decomposition of various organic acid compounds of sodium and potas-
sium. In various animal juices, however, and especially in the blood
and urine of herbivorous 'animals, and in the blood of the omnivora,
sodium and potassium carbonates exist already formed. When car-
nivorous animals are fed on a vegetable diet their urine contains
considerable quantities of carbonates of the alkalies, resembling thus the
urine of herbivorous animals in reaction and constitution ; it will be
alkaline in reaction, turbid, and deposit a calcareous sediment, instead of
being acid and clear, as is normally the case in the urine of carnivora.
It is also interesting, in this connection, to notice that the urine of the
suckling calf before being weaned is clear and acid, as among carnivora;
when the calf is placed on a vegetable diet the urine becomes turbid
and alkaline. Further, if herbivorous animals are allowed to fast, their
urine becomes acid and clear, for they are then living at the expense
of their own tissues, and are practically carnivorous. Sodium carbonate
is also found in the lymph and the parotid saliva of the horse.

These salts, when found as constituents of animal cells and fluids,

130 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

come in part from without, and are in part formed within the organism
through oxidation processes occurring within the body. Thus, after the
ingestioh of various vegetable matters containing vegetable acids the
urine of omnivorous animals becomes alkaline through the elimination
of carbonates of the alkalies, thus explaining the alkaline reaction of
the urine of these animals. Carbonates of the alkalies so formed in the
animal body, or when taken in foods, may be eliminated in this manner
through the urine, or they may themselves undergo decomposition, and
their carbon dioxide be eliminated through the lungs. When present in
solution they seem to assist in the various processes of oxidation
occurring in the body; they appear to assist in the emulsification of fats,
and in the blood the neutral carbonates of the alkalies appear to serve
in part as carriers of the carbon dioxide of the blood. They further
may modify the physical processes of diffusion occurring within the
mism.

5. CALCIUM CARBONATE (C03Ca). — Calcium carbonate is a normal
constituent of the shell of birds' eggs, of the bones and teeth, the urine
of herbivorous animals, the parotid saliva of the horse, and is the prin-
cipal constituent of the so-called otoliths, or the small, inorganic masses
found in the internal auditoiy organs of man and different animals. In
the animal body it is partly in a state of solution and partly deposited
in the solid form. In the former condition it is found in the urine and
saliva of the herbivora, where its solution is rendered possible by carbon
dioxide. In the solid form it is deposited either in amorphous or 'crys-
talline form, as in deposits of sediment in the parotid saliva of the dog
and in the urine of herbivora. It originates from without, either in the
water taken internally or as a carbonate in vegetable food. The latter
explains its abundance in the urine of the herbivora, where the calcium
salts of organic acids are decomposed into carbonates. Only a part of
the calcium carbonate which enters the organism from without leaves it
as such. In many cases, as in man, it undergoes decomposition into
calcium phosphate. Its importance for the animal economy is not thor-
oughly understood.

6. MAGNESIUM CARBONATE (C03Mg). — This salt is frequently a com-
panion of calcium carbonate, particularly in the urine of herbivora. Its
presence in bony tissue is apparent!}' doubtful. It has been found in
human urinary calculi, but only in small amounts. The herbivorous ani-
mals in their food nearly alwa3rs absorb considerable amounts of mag-
nesium phospate, and since this salt is absent from their urine it would
appear that the magnesium carbonate is formed in the animal body from
the magnesium phosphate of vegetable food.

7. ALKALINE PHOSPHATES (PO4Na8, P04^a3H, P04NaH2, P04K8,
P04KaII, P04KHa). — Phosphates of sodium and potassium are constant

IXOBGAXIC CELL-CONSTITUEXTS. 131

constituents of all animal fluids and tissues. In the ash of the blood of
the herbivorous animals a smaller amount of the alkaline phosphates is
found than in the carnivora. Grain-eating animals show a larger amount
of phosphatic salts in the ash of their blood. Omnivora occupy a mean
between the two. On account of their great solubility in the organism
the phosphates must nearly always exist in the form of a solution, espe-
cially in the acid fluids, as in urine, muscle-juice, and the parenchymatous
fluids of certain glands. In muscles, together with lactic acid, they
occasion the .acid reaction of the muscle-juice.

Phosphates are taken into the animal body with food, though they
may also doubtless originate in the blood through a double decom-
position of potassium phosphate and sodium chloride into sodium phos-
phate and potassium chloride. The alkaline phosphates leave the body
through the kidneys and intestines. The former is the case especially in
the urine of the carnivora, where it forms twelve-thirteenths of the
total amount of these substances eliminated. In the urine of the
herbivora but small amounts of phosphates are found, in spite of the
fact that in their food phosphates of the alkalies and earthy phosphates
are invariably present. This is to be explained by the supposition that
the salts of the organic acids, with the alkaline earths, undergo decompo-
sition into earthy phosphates and carbonates of the alkalies, the latter
being eliminated through the urine. From their great abundance and
wide distribution in the animal economy, it follows that they must be of
great importance.

The phosphate of potassium is especially abundant in the blood-
cells, ovum, and in muscular tissue. In the latter case, combined with
lactic acid, it is the main cause of their acid reaction, while phosphate
of sodium is found in blood-plasma. These salts enter the organism as
constituents of food, either in the form in which they are found or as
the result of decomposition of the earthy phosphates and other alkaline
salts. This is especially probable on account of the great abundance of
potassium phosphates and potassium chloride in the fluids of muscle and
other tissues, while sodium chloride and sodium phosphate, being found
in abundance in the blood, it is evident, from the proportion in which
these different substances are found in the different tissues, that they
have not been derived directly from the blood. Again, it is to be
remembered, that the herbivorous animals in their food receive almost
solely potassium salts, and, since sodium phosphate is necessary for the
integrity of their blood, it is clear that this must be formed in the body
through the decomposition of potassium phosphate and sodium chloride.
In the blood the alkaline phosphates give to the plasma its alkaline
reaction, to which its great capacity for dissolving carbon dioxide is
apparently due, since it has been found that water, which holds only

132 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

one per cent, of sodium phosphate in solution, is able to retain twice the
usual amount of carbon dioxide in solution.

The phosphates of the alkalies are eliminated from the animal body
through the kidneys, intestines, and skin. In carnivorous animals, whose
blood is rich in phosphates of the alkalies, the urine is the main path of
elimination. Through the production of acids, such as uric, hippuric,
and sulphuric, the latter originating from the sulphur of albuminoids
and their derivatives, a part of the base is withdrawn from the alkaline
phosphate, and, as a consequence, the alkaline phosphate now becomes
neutral or even acid, thus explaining the production of an acid reaction
in urine from the presence of dihydrate sodium phosphate (P04NaH2).
Since phosphoric acid, or acid phosphates, in solution give to fluids
their power of dissolving calcium and magnesium phosphates, the urine
of the carnivora and omnivora is therefore able to hold in solution the
earthy phosphates so eliminated. In the case of the herbivora the state
of affairs is somewhat different. Here but small amounts of phosphoric
salts are found in the urine, although alkaline and earthy phosphates are
found in large amount in their food. In this case the phosphates of
the food undergo decomposition, and a great part of the base is united
with carbonic acid, and so eliminated as alkaline carbonates in the urine,
forming thus the characteristic of the urine of herbivorous animals, the
earthy carbonates being held in solution by the free carbon dioxide. The
phosphoric acid of the phosphates taken in the food of herbivorous
animals in greater part unites with calcium and magnesium, and is
eliminated through the intestine. Wherever free acid is developed in the
tissues of the body acid phosphates are nearly always present and in
part contribute to the formation of this acid reaction. This is the more
remarkable when it is remembered that these* phosphates have originated
from the blood, where they always exist in the form of basic or neutral
salts. The explanation of the mode in which this alkaline phosphate is
in the different tissues converted into an acid salt is to be explained
through the development in the tissues of organic acids, which, as
already alluded to in the explanation of elimination of the phosphates,
takes a portion of the base from the alkaline phosphate, so developing an
acid salt.

Phosphates appear to be absolutely essential to the development
of tissue. This is indicated in the first place by their great abundance
in all forming tissues, and even in organizable fluids, and in the fact that
the tissues of herbivorous mammals are quite as rich in the phosphates as
that of the carnivora, although in the former case they are nearly absent
from the blood, and in the latter case are very abundant. In special
tissues, such as the muscles, nerves, blood-corpuscles, and ovum, they
appear, from their exceptional abundance, to have some special functions

INORGANIC CELL-CONSTITUENTS. 133

to fulfill. This seems indicated by the fact that the nervous tissue in
solutions of alkaline phosphates may preserve its irritability much
longer than when in contact with any other fluid. In the tissues the
phosphates of the alkalies occur as acid salts ; it therefore would seem
that tissues in their growth require the presence of free phosphoric acid;
In the case of the blood, on the other hand, an alkaline reaction is
essential for its vital phenomena, and it appears that, provided the
alkaline reaction is preserved, the salt to which this alkalinity is due is
of minor importance. Thus, in the carnivorous animals the reaction is
attributable to the excess of alkaline phosphate, in the herbivorous
animals to the carbonates. In omnivorous animals the preponderance
of these different salts varies according to the character of their diet.

8. CALCIUM PHOSPHATE (2(PO4)Ca8, 2(P04)CaH4).— This salt is
present, without exception, in all tissues and fluids of the animal body ;
in bones and teeth nearly two thirds of their weight is due to the
calcium phosphate present. Of all the inorganic constituents of the
body, with the exception of water, it is the most abundant. In most of
the pathological ossifications and concretions calcium phosphate consti-
tutes the major portion. Thus, nearly all the urinary calculi in the ox
are formed by calcium phosphate, and it is also a constituent of the
mulberry calculus of man. So, also, calculi which develop around some
foreign nucleus are largely calcium phosphate. Calcium phosphate also
forms the greater part of the ash of albuminous bodies, with, as far as is
3'et known, the single exception of elastin. It is present in the tissues
of the human body in the following proportions : —

QUANTITY OP CALCIUM PHOSPHATE IN 1000 PARTS IN THE

Enamel of teeth, . . . . . . . . 885.

Dentine, ' . 643.

Bones, .......... 576.

Cartilage, . . .40.

Milk, ' .- ' . . . . 2.72

Blood, -< .... 0.30

Bile, . . . • 0.92

Urine, 0.75

The greater part of calcium phosphate in the organism is deposited
in the form of a solid salt in the bones and teeth, in the form of the
tricalcium orthophosphate (2(P04)Cas). It is also in the same form
present in nails, hair, and hoofs. When it is found in solution, as is the
case with all of the animal fluids, it being by itself perfectly insoluble in
water, its presence is only to be explained as chemically united with
albuminoids, although possibly it may be in minute amount in solution
in fluids which contain sodium chloride or free carbon dioxide. In the
urine of carnivora and omnivora calcium phosphate is present as an acid
salt (2(P04)Ca"H4), which is in itself soluble in water. In the alkaline

134 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

urine of the herbivora but little calcium phosphate is present, and this is
not dissolved, but merely suspended, and readily deposits as a sediment.
In the solid tissues the lime phosphate appears to be simply deposited in
the interstices of the .organic bases, and it may be removed — as, for
example, from bone — by prolonged maceration in dilute hydrochloric
acid, without altering the form of the bone. As Dalton says : " In the
bones, teeth, and cartilage 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 character 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 macer-
ation in dilute muriatic acid, leaving behind the animal substance, which
still retains the original form of the bone or cartilage." The bone so
treated preserves its outline perfectl}', but has entirely lost all rigidity,
and may be twisted up, and the long bones may often be tied into a knot.
Calcium phosphate, therefore, gives to bone-tissue its rigidit}^ Conse-
quentl}T when, either through some faulty process in the organism or
through the deprivation of calcium salts from the food, this substance is
not deposited in normal amounts in the bones, the latter become soft,
flexible, and deformed, forming the affection known as rachitis ; or, in
adult life, a similar morbid softening of bones may take place from
a defective deposit of calcareous matter, and a progressive yielding of
the bony skeleton takes place, constituting the disease known as osteo-
malacia.

The greater part of the calcium phosphate enters the body in the
food, being contained in both animal and vegetable articles of diet. In
suckling animals the milk contains, in its normal condition, a sufficient
amount of calcium phosphate to supply the growing organism with its
requisite quantity. When taken in vegetable food, where, of course, it
is ordinarily present as a union of calcium with one or more of the
organic acids, in the animal body, as already referred to, it undergoes
decomposition into calcium phosphate and carbonates of the alkalies.

9. MAGNESIUM PHOSPHATE (2(P04)Mg8, 2(P04)MgH4). — Like cal-
cium phosphate, magnesium phosphate is found in all the tissues and
fluids of the animal body, though in far smaller amount, with the excep-
tion of muscle and the thymus gland, where the magnesium phosphate
is in excess. The bones of the herbivora contain more magnesium phos-

INORGANIC CELL-CONSTITUENTS. 135

phate than those of the carnivora. The combination 2(P04)Mg"H4 is
often found in the urine of the herbivora when fed on grain, and is
occasional!}' met with in intestinal concretions under the same conditions.
Its origin, physiological importance, and mode of disposition in the body
is apparently identical with that of the alkaline phosphates. Occasion-
ally magnesium phosphate undergoes crystallization, as in the urine of
the rabbit and in suckling calves.

10. SODIUM AND POTASSIUM SULPHATES (S04K2, S04Na2). — These
salts are to be regarded as normal constituents in small amount of most
of the animal fluids and tissues. They are not, however, found in the
milk, bile, or gastric juice, their presence in the ash being without impor-
tance, since in incineration of sulphurous organic compounds the sul-
phuric acid, liberated in this process, unites with the carbonates and
alkaline bases. A certain amount of these salts is held in solution in the
blood and in the urine, though the}' are less abundant than either the
chlorides, phosphates, or carbonates. When present in the animal body
they are in the form of solution. Only part of the sulphates found in
the animal body is derived from without, since it is possible that
through the oxidation of sulphur of organic compounds sulphuric acid is
formed, which leaves the body united with alkaline bases. These salts
are excreted from the body through the urine, where a greater part of the
sulphuric acid is not derived from the sulphates contained in the food,
but through the internal oxidation of sulphur-holding compounds. This
is especially shown by the fact that an abundant animal diet increases
the amount of sulphates in the urine hand in hand with the increase of
urea, while a vegetable diet decreases it. The sulphates partly con-
tribute to the acid reaction of the urine of carnivora.

The entire quantity of sulphur in the body of an adult man has been
estimated at about one hundred and ten grammes, and to keep this
amount constant at least one gramme must be taken daily in the food,
where it is combined with albuminoids. A part of this sulphur passes
into the hair and nails, part is consumed in the manufacture of various
complex, sulphur-holding compounds, such as taurin, taurocholic acid,
gelatin, chondrin, mucin, etc., while part is eliminated in the form of
sulphates.

11. HYDROCHLORIC ACID (HC1). — The presence of free hydrochloric
acid has as yet only been shown to exist in the case of gastric juice of
mammals. Its origin and importance will be considered under the sub-
ject of Gastric Juice.

Oxygen, nitrogen, and carbon dioxide are also constant constituents
of animal fluids and tissues, and their importance will be discussed under
the subject of Respiration.

A few other inorganic substances have been found as more or less

136 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

constant ingredients of animal substances, but they are present in such
small amounts, or in such variable quantities, that their importance has
not been clearly established. These are magnesium chloride, calcium
fluoride, ammonium carbonate, magnesium-ammonium phosphate, calcium
sulphate, silicon, iron, manganese, and copper.

In vegetable tissues nearly all the constituents of the animal cell are
found deposited or in solution. They serve to give greater solidity to
the so-called skeleton of plants, and are also without doubt of importance
in the vital processes of vegetable protoplasm. Thus, it has been found
that the amount of albumen in germinating seeds stands in direct propor-
tion to the amount of phosphate which the plant receives as food ; also,
that without potassium salts plants cannot grow. Their interest to us as
constituents of vegetable organisms is simply dependent upon their ren-
dering such substances suitable for animal foods. They will therefore
receive the necessary consideration under the subject of Foods.

II. THE CHEMICAL PROCESSES IN CELLS.*

The great mass of organized bodies, both animal and vegetable, are
what might be described as carbonic acid compounds, associated in vari-
able amounts with hydrogen, oxygen, and nitrogen. Plants are able,
from inorganic substances, such as CO2, H20, N03H, NH,, H2SO4, P2O6,
to develop organic compounds, the difference between such bodies as
entering into and as leaving plants depending merely upon the difference
in their proportion of oxygen. The inorganic bodies, which serve as
food for plants, are what are known as combustion products ; that is,
they already contain the maximum quantity of oxygen which is able to
enter into their composition. Organic bodies, on the other hand, contain
in all cases less oxygen than will satisfy the affinities of their constituent
elements. They therefore are capable of undergoing further oxidation,
or, in other words, may be said to be combustible. The plant-cell, there-
fore, must be able to deoxidize the inorganic compounds of its food and
set free oxygen ; and this deoxidizing force must evidently be greater
than the affinity exerted by the oxygen for the elements with which it
was in composition. This deoxidizing power possessed by plants is only
capable of manifestation in the sunlight, and is a function of the green
coloring matter, the chlorophyll of plants. The animal cell, on the other
hand, in its nutritive operations exhibits the reverse process of oxida-
tion. The inorganic compounds which in the vegetable cell become
organic, that is, deoxidized, in the animal cell become again oxidized and

* For the preparation of this section special acknowledgment is due to Wurtz,
" Chimie Biologique ; " Wundt, " Lehrbuch der Physiologic ; " Gorup-Besanez, " Physi-
ologische Chemie ; " Ranke, " Grundziige der Physiologic ; " Hoppe-Seyler, " Physiolo-
gische Chemie ; " Schiitzenberger, " Fermentation ; " Nageli, " Theorie der Garung."

CHEMICAL PEOCESSES IN CELLS. 137

again rendered inorganic, or become combustion products. They are,
therefore, restored to the mineral world by the animal in the same form
in which they were originally absorbed by the vegetable.

Vegetables and animals are the depositories and agents of life on the
surface of the earth. The essential characteristic of the vital operations
of the former is their power of elaborating organic from inorganic ma-
terial. Animals are charged to destroy, after assimilation, the results of
the vital operations of the vegetable. The animal kingdom is thus subor-
dinate to the vegetable, and organic life represents a closed circle of
metamorphosis of matter. Plants appropriate inorganic matter out of
the surrounding inorganic nature, out of the ground and air, and convert
it into the constituents of their own tissues. They then become food for
animals, are converted into animal tissues, and are again returned to the
ground and air as inorganic compounds. Thus, the carbon of the carbon
dioxide of the air becomes the carbon of cellulose or starch, of sugar, of
fat, of gum, and of albumen in the plant ; as food of animals it then
becomes the carbon of various animal tissues. In the vital processes of
the animal the carbon of the tissues undergoes oxidation, and is returned
to the atmosphere through the expelled air as carbon dioxide, or, in
other words, in the form in which it originally left the atmosphere. An
analogous circle might also be traced for the other constituents of the
animal tissues.

We can thus understand how the constituents of animal and vege-
table cells may in all essential points be analogous; but, while this is so,
the chemical processes in each are very different. Green plants, in their
capability of deoxidizing inorganic food elements, are dependent upon
power from without — the heat and light from the sun. They therefore
store up energy in their tissues. Animal cells, in oxidizing the materials
derived from the vegetable world, liberate a force, as in all other forms of
oxidation, which in this case represents an equivalent of mechanical
energy precisely equal to the force rendered latent in the nutritive proc-
esses in the vegetable. In the animal cell this energy may take on the
form of heat, electricity, or light, as in certain organisms, or mechanical
movement.

1. The Vegetable Cell. — The assimilative processes in the vegetable
cell are dependent upon the presence of protoplasm, which in its modir
fied form as chlorophyll has the power of making use of the sunlight for
purposes of organic deoxidation, and constitutes the most powerful re-
ducing body known. The properties of chlorophyll are not exactly
known, as it has probably never been prepared in a perfectly pure state.
In the chlorophyll granules are often to be found, the results of its organic
activit}^, such as starch-granules; but their precise mode of formation, or
the precise share which chlorophyll has in producing their formation, is

138 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

not well known. The optical properties of chlorophyll are very remark-
able. Fresh alcoholic solutions in ether, even when very dilute, give a
broad band in the red line of the spectrum, and between the red and the
orange. The most luminous portions of the spectrum are the red and
green parts. When concentrated ethereal solutions of chlorophyll are
examined in the spectroscope, only the red rays pass. Concentrated
solutions of chlorophyll give a red fluorescence with reflected light.
When subjected to the action of light solutions of chlorophyll change their
color, probably in a manner similar to that which accompanies the vital
processes of the vegetable protoplasm in which chlorophyll is contained.

In all its forms protoplasm, whether animal or vegetable, contains
albuminous bodies in a state of solution in water, and associated with
compounds of an inorganic nature. Carbo-hydrates, hydro-carbons, and
ferments are also nearty invariably present. It may be assumed that the
albumen is the highest and last product of the chemical activit}^ of vege-
table cells, while starch probably constitutes the first evidence of proto-
plasm activit}r, and is the mother-substance out of which other carbo-
hydrates, such as cellulose and sugar, as well as fats, are manufactured.

Plants develop various modifications of albuminoids, which are
apparently identical with the different forms of albuminous bodies found
as constituents of animal cells. Thus, in growing and germinating
plants a globulin-like body is found in large amount, as well as a sub-
stance similar to myosin and vitellin in combination with lecithin and
certain inorganic substances. Albumen is found in especially large
quantities, with large amounts of starch, in the seeds of plants ;
hence, the undeveloped plant finds in these two substances, albumen and
starch, material ready prepared for building up its tissues until it
reaches a grade of development in which it is able to manufacture these
organic compounds from the elements. When the first leaves and roots
are formed, then the plant commences its independent existence. The
evidences of this, as we have already seen, consist in the appropriation
of C02, H20 and NH8, with a corresponding liberation of oxygen.

Since all vegetable matters contain carbon and water, their con-
stituents may be regarded as more or less modified C02 molecules.
Thus, sugar may be regarded as CO, in which one equivalent of oxygen
is replaced by two equivalents of hydrogen (Liebig).

Carbonic Anhydride. Grape-Sugar.

'8 CH2

or6(CO2(H20)) = 6(CH2O) -f 6O2 = C6H12O6 +6O2.

Carbon dioxide, therefore, in the formation of organic matter, may
be regarded not as decomposed, but as changing the arrangements of its
molecules. We have found that plants in their nutritive purposes assimir

CHEMICAL PKOCESSES IN CELLS. 139

late carbon, hydrogen, nitrogen, and various inorganic substances. We
will attempt to give a general idea as to the processes by which these
substances are absorbed by plants, and the way in which in their tissues
they are combined to form organic compounds.

First, as regards carbon. The carbon of plants is without doubt
derived from the CO2 of the atmosphere, or in solution in rain-water
which is absorbed b}' the leaves and roots, which under the influence of
the sun is broken up in the body, and whose oxygen is liberated. The
oxygen given off in the day-time by plants has been found to be some-
what less than* that which is contained in the C0a which has been
absorbed. This would seem to indicate that COS is only reduced to CO,
since it is known that part of the oxygen comes from the decomposition
of water. This hypothesis is further rendered more probable by the
readiness with which CO combines with other bodies. Thus, it unites
with Cl at the ordinary temperature, and combines directly with hydro-
gen to form formic acid. Doubled, — that is, united with itself, — the
radical oxide of carbon, or carbonyl CO, constitutes the oxalic radical
C202, or oxatyl. The acid which contains this radical, — that is, oxalic
acid, — can be formed by an incomplete reduction of COa and H2O in the
presence of mineral bases ; various organic acids may thus originate in
vegetable cells. Taking the simplest cases, the important acids, formic
and oxalic, may be formed in this way, the one with one atom of carbon,
the other with two. Thus, with one molecule of water

CO2 + H2O — O = CH2O2 = formic acid.
2 CO2 + H2O — O = C2H2O4 = oxalic acid.

Developing this idea, Liebig has shown that the organic acids once
formed may give rise to aldehydes by a subsequent reduction. Formic
aldehyde represents formic acid less one atom of ox^ygen ; oxalic alde-
hyde, or glyonal, oxalic acid less two atoms of oxygen, thus : —

CH 2 O2— O = CH2O = formic aldehyde.
C2H204 — O2 = C2H202 = glyonal.

The formation, therefore, of aldehydes in vegetables represents a
certain stage of reduction of CO, and H2O. Even more complex
substances, but less rich in oxygen, will result from further decompo-
sition.

The examples above given, especially in the case of formic aldehyde,
are particularly important, as there is scarcely any doubt that formic
aldehyde plays an important role in vegetable synthesis. Thus, six
molecules of formic aldehyde will form one molecule of glucose : —

Again, on the other hand, by the dehydration of aldehydes resins may
be formed, as it is well known how readily ordinary aldehydes become

140 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

converted into resinous bodies by losing water; while, again, ammonia
through its combination with aldehydes may give rise to nitrogenous
bodies, such as alkaloids. We therefore see that in the appropriation of
the carbon and the carbon dioxide of the atmosphere the carbon becomes
fixed to form these various bodies synthetically in vegetable protoplasm,
while the oxygen is liberated.

As regards the assimilation of hydrogen in the synthetical processes
occurring in vegetable cells, this evidently occurs from the decomposition
of water, as is proved by the circumstance that the oxygen liberated,
while sometimes less, is often in excess of that which is contained in the
C03 absorbed. Thus, in the vegetable cell the carbo-hydrates, such as
cellulose, starch, gum, and sugar, are made by the simultaneous reduction
of carbon dioxide and water under the influence of solar radiation.

For nitrogen, the atmosphere is the sole source, though it may
possibly to a certain extent be derived from the nitrates in the soil.
When obtained from the atmosphere it is held in solution in the form of
salts, possibly in rain-water. All decomposing organic matters set free
ammonia, and therefore nitrates, particularly of potassium, are powerful
fertilizers, and increase vegetation b}^ supplying the nitrogen which is
essential in the development of albuminous bodies and crystallized
nitrogenous vegetable constituents.

Of the minerals which are essential to vegetable life, such as
phosphates, silica, salts of lime and magnesium, and alkaline salts, they
are obtained partly from the atmosphere and partly from the soil. They
are contained in large amounts in all parts of vegetable matter, and will
deserve special consideration under the subject of the vegetable diet of
the herbivora. The mineral constituents of the soil and atmosphere
therefore play an important part in the phenomena of the development
of vegetable life. This we have seen to be essentially one of reduction.
In separating the oxygen from carbon and hydrogen a portion of their
affinity for ox}^gen is restored to these latter elements. For in CO2 and
H20 this affinity is completely satisfied ; that is, the energy which resides
in the atoms of carbon and hydrogen has not been destroyed by combi-
nation and transformation, and when these atoms unite with oxygen this
energy is dissipated as heat. To reduce these combinations, therefore,
the energy thus latent in the form of heat must be restored to the atoms
of carbon and hydrogen. Thus vegetables, in decomposing water and
carbon dioxide, making use of the heat of the sun, not only convert atoms
of carbon, hydrogen, and nitrogen into organic substances, but have at
the same time accumulated chemical energy. For all organic compounds
are capable of uniting with oxygen ; in other words, are combustible.
The energy restored under the name of affinity to the atoms is hence
derived from a portion of the solar radiation which is absorbed by plants

CHEMICAL PEOCESSES IN CELLS. 141

and is converted into affinity. This is the indispensable condition of
the reduction of COa and H2O and the elaboration of organic compounds ;
or, in other words, " there can be no vegetation without the sun."

The process which we have found to take place in vegetable cells
only holds good in the case of green plants under the influence of the
sunlight, for there is in all cases a double chemical process going on in
plant-cells. The assimilation through deoxidation of organic com-
pounds under the influence of sunlight has already been described.
This process is, however, limited to the chlorophyll plants, and in them to
the time when they are exposed to the sun's light and heat. Another
process, however, is continual!}7 going on in all forms of vegetable cells.
The products' of assimilation undergo within the vegetable cells various
chemical changes which are not accompanied by a liberation of oxygen,
but by a change of molecular arrangement, associated with the absorption
of a small amount of oxygen and the setting free of carbon dioxide.
These changes are independent of the sunlight, and result in a diminution
of the mass of assimilated materials. That a plant may increase in size
it is necessary that the deoxidizing activity and assimilation produced in
the sunlight should overbalance the loss through oxidation which is
continually going on, whether in darkness or light. This latter process
in plants, by which they absorb ox}Tgen and set free carbon dioxide, is
clearly analogous to the processes of respiration in animals. This res-
piration in plants is, however, very feeble, and is far overbalanced by the
processes of assimilation ; therefore, as a rule, although the elaboration
of vegetable products is accompanied by accumulation of force, the
vital processes in plants which are not connected with assimilation are,
as in animals, dependent upon oxidation processes, and may be accom-
panied by the liberation of heat and electrical movement of protoplasm,
and the formation and growth of cells. In the case of the non-chlorophyll-
bearing plants, such organisms absorb organic matter already elaborated ;
the parasitic plants may, therefore, be regarded as a connecting-link
between the animal and vegetable kingdoms, especially as some of the
lower forms of the former are also possessed of chlorophyll, by which
they are enabled to decompose CO, under the influence of the sun. A
curious exception to the characteristics of the vegetable chemism is tlie
power which certain plants possess of attracting, seizing, and digesting
insects. The so-called insectivorous plants of Darwin and Hooker, such
as the Drosera rotundifolia, Darlingtonia, Nepenthes, etc., are supplied
with special urn-like vessels, in which the animals are trapped and
digested. They are lined with glands that secrete both the sugary fluid
to attract the insects and a true digestive juice, containing pepsin and
acid, which is poured out when the plants are stimulated by contact with
digestible substances. This secretion will turn fibrin into -peptone, but

142 PHYSIOLOGY OF THE DOMESTIC ANIMALS

is without action on starches. It therefore closely resembles animal
gastric juice.

Still another analogy may be traced between the animal and vege-
table kingdoms. Under certain circumstances plants develop heat, as in
germinating seeds, or in flowers during fecundation. Sugar is the sub-
stance in such cases whose combustion sets free heat. It exists in
germinating seeds, and disappears during germination, from the action
of a diastatic ferment analogous to the glycogen ferment in animals.
The analogy is, however, not perfectly complete, as the plants manu-
facture their starchy material from inorganic materials ; animals must
obtain it ready-made.

In the dark the processes of assimilation of plants are entirely
suspended. Then carbon dioxide is given off, and oxygen is absorbed,
for the processes of respiration or oxidation still continue. During the
day the carbon dioxide, which is constantly absorbed by the roots and
leaves, is in the leaves broken up into oxygen, which is set free, while
the carbon remains tixed. At night C02 is also absorbed by the roots,
but is exhaled from the leaves without undergoing change : for, as we
have found, for its deoxidizing purposes chlorophyll requires the assist-
ance of sunlight and heat. It is also possible that a part of the C02
which is set free during the night is not only derived from C02 absorbed
from the leaves and roots, but also is the result of oxidation by a part
of the oxygen which is absorbed.

2. The Animal Cell. — The relationship which we have traced
between the chemical processes of plants and the atmosphere and soil
around them is reversed in the case of animal cells ; for, while green
plants absorb the inorganic constituents of the earth and atmosphere,
and from them build up complex, inorganic compounds, the oxygen of
the atmosphere in the animal permits of the reduction of its complex tis-
sues and constituents. For the green plants the atmosphere forms one of
their chief foods; for animals it is the great agent which permits their
tissue changes, on which all liberations of energy depend. In green
plants the chief vital phenomenon is the liberation of oxygen ; in ani-
mals it is the absorption of oxygen. In plants the liberation of oxygen
is an index of increase in weight ; in animals the absorption of oxygen
leads to a loss of weight. That the animal cell may retain its com-
position unaltered it must be supplied with its tissue-constituents.
Unlike vegetable cells, the animal cell is incapable of manufacturing
these tissue-constituents from inorganic elements. The most that the
animal cell may do is to transform a member of one class of its con-
stituents into another member of the same group. Thus, the animal cell
may transform the albuminoid matters contained in vegetable cells into
albuminous bodies which are peculiar to animals. It may transform the

CHEMICAL PROCESSES IN CELLS. 143

proteicls of one class into those of another. It ma}' transform casein of
milk into the proteids of blood and other tissues. Animal cells are, how-
ever, the seat also of certain synthetical processes, such as the formation
of haemoglobin from albumen and iron, with other inorganic matters, the
possible reformation of albumen from peptone, and the building of com-
plex albuminoids, such as mucin. All animal foods, nevertheless, orig-
inate in the vegetable kingdom. Even carnivora are dependent on the
vegetable kingdom for their sustenance ; for the herbivora, feeding on
vegetable diet, become the prey of carnivorous animals, which are there-
fore dependent on the vegetable matters which serve to nourish the tissues
of the animals which serve as their food. In the vegetable cell albumen
is the end product of its chemical processes; in the animal cell it is the
starting point. Albuminoids represent the main or essential tj'pe of
foods which must be supplied to the animal cell. When introduced into
the interior of cells, albuminoids undergo a progressive oxidation and
simplification, by which lower complex substances are formed. The
mode of decomposition of albuminoids, as well as of all organic bodies
in general, is different in different cells. This difference is seen in the
very first modification of the albuminous matters of food, which may be
converted into casein, myosin, etc.. according as the resulting albuminous
body is destined to be a constituent of milk, muscle-cell, etc. Then,
again, after being deposited in cells the subsequent processes differ in
different cases, according to the nature of the cell-membrane or inter-
cellular substance, or the function of the special cells in the organism.
Finally, the development of the end products of the oxidation of the
albumen of cells differs in the cells of different tissues, though in all
cases the chemical processes in cells result in the formation of carbon
dioxide, water, and ammoniacal compounds.

The most striking example of the products resulting from the oxi-
dation of proteids is the formation of fat from albumen. In adipose
tissue and in fatt}^ degeneration of various organs the protoplasmic con-
tents of cells become replaced by oil, formed evidently at the expense of
the albuminoid constituents of the protoplasm. So, also, carbo-hydrates,
such as glycogen, maybe produced from a splitting of the albuminoid
foods. In addition to the carbo-hydrates and fats thus formed, a large
number of nitrogenous bodies are liberated in the oxidation of the
albuminous molecule, and might be termed ammonia compounds, such as
kreatin, uric acid, urea, etc. Such bodies are, as a rule, richer in ox}Tgen
than albumen.

The carbo-hydrates and fats are also subjected to progressive oxida-
tion in the animal body, and result, in the former .case, in the production
of organic acids, such as lactic, formic, and oxalic, and in the latter in
the formation of fatty acids. AS already several times mentioned, the

144 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

chemical processes in the animal cell result in the formation of C03, IT20,
and NH8 compounds, and hence return to the earth and air the matters
originally absorbed by the plant-cell, and in the same form. These end
products are, however, only gradually formed as the result of a long
series of intermediary oxidation products, which are formed partly
through processes of splitting, by which complex molecules, usually
through Irydration, are decomposed into two or more simpler compounds
through the action of certain ferments. Through these means the
organic cell-constituents become progressively poorer in carbon and
richer in oxygen and nitrogen, thus losing their organic characteristics
and becoming gradually more nearly allied to inorganic bodies, until
finally the inorganic end products are reached.

The following table, based on hypothetical formulae, indicates the
manner in which complex albuminous molecules may become gradually
reduced to simpler forms (Gorup-Besanez): —

Haemoglobin, . . . C600 H960 N154 FeS3 O179

Albumen, . . . . C90 H139 N22 S O30

Lecithin, .... C42 H84 N P O9

Taurocholic Acid, . . C26 H45 N S O7

Glycocholic Acid, . . C26 H43 N O6

Hippuric Acid, . . C9 H9 N O3

Tyrosin, ... . . C9 Hai N O3

Leucin, . . . . C6 H13 N O2

Asparagin, . . . . C4 H8 N2 O3

Asparaginic Acid, . . C4 H7 N O4

Glutanimic Acid, . C5 H9 N O4

Guanin, ... . C5 H5 N5 O

Hypoxantliin, . C5 H4 N4 O

Xanthin, ...'.. C5 H4 N4 O2

Uric Acid, . C5 H4 N4 O3

Kreatin, . . . . C4 H9 ]ST3 O2

Allantoin, ...... C4 H6 N4 O3

Urea, ..... C H4 N2 O

Urea thus forms the termination of the decomposition series of the
organic nitrogenous molecules.

A similar progressive simplification may also be seen in the non-
nitrogenous organic constituents. Thus, according to Gorup-Besanez : —

Stearin, ...... C57 H110 O6

Palmitin, . .... . . C51 H98 O6

Olein, . ... . . C57 H104 O6

Stearic Acid, ..... C18 H36 O2

Oleic Acid, C18 H33 O2

Palmitic Acid, C16 H32 O2

Butyric Acid, C4 H8 O2

Succinic Acid, C4 H6 O4

Grape-sugar, . . . . . C6 H12 O6

Glycerin, ....... C, H8 O3

Lactic Acid C3 H6 O3

Acetic Acid, C2 H4 O2

Oxalic Acid C2 H2 O4

Formic Acid, C H2 O2

CHEMICAL PROCESSES IN CELLS. 145

Just as urea is readily broken up into ammonium carbonate, or
S and CO2, so also formic and oxalic acids, the terminals of the non-
nitrogenous organic molecules, readily undergo decomposition into
C0a and H,0.

It cannot be pretended that we are familiar with all the intermediary
stages of these retrogressive metamorphoses, yet we are possessed of
numerous facts, gained through the study of the decomposition of albu-
men by various chemical agents, which go far to fix the character of
these changes. Thus, in the artificial decomposition of albumen by
certain chemical reagents, asparagin, glutanimic acid, leucin, and tyrosin
are constantly met with ; and since these bodies occur in the process of
germination in seeds, and the latter two often in the animal body at the
seat of rapid break down of albuminoid matter, we may infer that a simi-
lar process normally occurs in animal cells. So, also, by various methods
of oxidation uric acid is readily converted outside of the body into urea,
allantoin, oxalic acid, and carbon dioxide; and there are many facts for
supposing that a similar conversion occurs in the animal body. Thus, the
administration of uric acid produces not an increase in the uric acid
eliminated, but in the urea and calcium oxalate ; and since uric acid is
normally present in but small amount in the urine of the carnivora, and
is absent in that of the herbivora, while we know that in certain organs
of both classes of animals it is formed in considerable amount, it must
undergo oxidation in the economy. This is further proved by the fact
that a reduction in the supply of oxygen leads to an increase in the uric
acid and a decrease of the urea in the urine. In a similar way is to be
explained the appearance of allantoin in the urine of cats and dogs when
fed on abundant animal diet.

A similar line of argument ma}7 be made to apply to the decompo-
sition of the non-nitrogenous tissue-constituents.

We are thus, to a certain extent, familiar with the starting point and
terminals of the series of decompositions which occur in the animal
bod}r, and with a few of the intermediary links in this chain. We shall
again have to return to this subject in the study of Nutrition.

3, Fermentations. — The word fermentation is derived from/ervere,
to boil, and owes its origin to the appearance presented by sugary fluids
when placed in contact with ferments ; gas is liberated, the sugar disap-
pears, and the product becomes alcoholic. While the term fermentation
was originally restricted to this process, it is now applied to many cases
in which an organic body when dissolved is modified, changed, and trans-
formed under the action of formed or soluble ferments. As regards the
action of fermentation only the results and processes of the soluble fer-
ments will here demand consideration.

The soluble ferments act on a large number of organic compounds,

10

146 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

their mode of action being largely the same in all. Water is always essen-
tial to the processes of fermentation, and the result is acquired by a more
or less simple splitting up of the organic molecule accompanied by hy-
dration. The nature of this splitting up is governed by the nature of
the body which is subjected to fermentation, and may be explained in
most cases by chemical processes in which the intervention of a living
organism does not appear. Ferments have been classified as follows in
the character of the change which they produce (Hoppe-Seyler) : —

CHANGE OF ANHYDRIDES INTO HYDRATES.

A. Ferments that Act like Dilute Mineral Acids at a High Temperature.

a. The conversion of starch into sugar, or glycogen into dextrin
and grape-sugar, as b}T the action of ptyalin, the amylolytic ferment of
the pancreatic or intestinal juices, diastase, or the liver-ferment. Thus : — -

= C6H1005+3(C6H1206).
Glycogen. Grape-Sugar.

or, in the case of starch : —

C24H40020+3H20=:C6H1005 +3C6H1206.
Starch. Water. Dextrin. Glucose.

b. The conversion of cane- into grape-sugar, as by the inversive
ferment : —

C^H^O^+H.O-CeH^Oe + CeH^Oe.
Cane Sugar. Grape-Sugar. Fruit-Sugar.

This reaction also gradually occurs through the action of water at
100° C., while starch requires a temperature of 170°, the resulting sugar
at the same time undergoing decomposition.

B. Ferments that Act like Caustic Alkalies at a High Temperature —
Fermentative Saponification.

a. Splitting up of fats into glycerin and fatty acids, as by the action
of the ferment of the pancreatic juice.

b. Splitting up of amydo compounds by hydration through decom-
position products, as

Urea. Ammonic Carbonate.

The changes in albuminoids produced by the pancreatic ferment and
in decomposition probably fall under this category.

CHEMICAL PROCESSES IN CELLS. 147

FERMENTATION PROCESSES, WITH TRANSFER OF OXYGEN FROM
THE HYDROGEN TO THE CARBON ATOMS.

a. Lactic Acid Fermentation. — Under the action of various ferments
sugar is converted into lactic acid. This occurs in the milk, and also very
probably in sugary solutions within the intestine. In the first stage of
this process lactic acid is produced as follows : —

C6H1206=:2C3H603. C12H22011 + H20^4C3H603.

In the later stages butyric acid, carbon dioxide, and hydrogen are
formed. Thus : —

2(C3H603):=C4H802+2C02+2H2.

b. Alcoholic Fermentation. — Under the influence of various of the
formed ferments, such as yeast-plant, grape-sugar undergoes fermentation
and results in the formation of carbon dioxide and alcohol.

c. Putrefactive Fermentation. — Ferments which cause putrefaction
are found in the lowest organisms, micrococci, bacteria, etc. Their action
is destroyed by heating above 53° C.

The most important ferments in the chemical processes occurring in
the animal body are the diastatic or sugar-forming ferments, found in
the saliva, pancreatic and intestinal juices, liver, and blood ; the peptone-
forming ferments, found in gastric, pancreatic, and, perhaps, intestinal
secretions ; the fat-ferment, found in pancreatic juice ; the inversive fer-
ment, found in intestinal juice ; and the milk-curdling ferments, found in
the gastric and pancreatic secretions. All the above ferments, with the
exception, possibly, of the last, are so-called hydrotytic ferments ; that
is, their action is accompanied by a process of hydration. Water is
essential to all forms of fermentation ; hence, ferments become inert when
dried. For the action of the proteolytic ferment of the gastric secretion
a faintly acid reaction is essential, as is also the case for the pepsin-like
ferment of the insectivorous plants, such as the Drosera and Dionsea,
which have the power of digesting albuminous bodies. An excess of
acid will, however, interfere with the action of the proteolytic, as well as
of the diastatic, ferments ; the same holds good for the caustic alkalies,
although an alkaline reaction favors the action of the proteolytic ferment
of the pancreatic juice. Salts of the heavy metals, as well as ether,
chloroform, and all the so-called antiseptics, prevent fermentation.

Further details as to the action of ferments will be considered under
the study of the digestive juices and the putrefactive changes in the
alimentary canal.

4. The Consumption and Development of Force in Cells*. The

development of force in cells is closely dependent on the chemical inter-

* Wundt, " Lehrbuchder Physiologie."

148 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

changes occurring in the interior of cells. The constituents of all
chemical compounds are held together by their chemical affinities, and
compound atoms hence exhibit a lesser tendency to form new combina-
tions than do free, uncombined atoms. When, however, a combination
is broken up, as by some external force, the separated atoms again tend
to unite. There is again a difference in the stability of chemical com-
pounds. In other words, new combinations are more readily formed in
some instances than in others. Thus, the loosely -held oxygen atom in
hydrogen peroxide (H202) is much more readily given up to form fresh
combinations than the closely-held atom of oxygen in H20. Thus, forces
which only exist as a tendency to produce motion are termed potential
forces; those, on the other hand, which actually manifest themselves in
movements are actual or kinetic forces. The tendency to combine is,
therefore, a potential force, which varies according to the free or com-
bined state of the atoms, and, in the latter case, according as the atoms
are held in loose or close combination. The atom released from chemical
combination acquires an increased potential force, while an atom which
passes from the free to the combined state loses in potential. In
ever}'' chemical decomposition, or the passage from close to loose com-
pounds, the potential force is developed, while in the formation of other
chemical compounds, or the passage from loose to close compounds, the
potential is diminished. The separation and union of the elements and
formation of chemical compounds are, therefore, movements of the
elements ; consequently, in their decomposition or composition actual
forces are produced. When atoms unite, a part of the force which before
existed as a tendency to form combination (the potential force) is
converted into actual or kinetic force, and the combination has lost
potential to that extent to which the tendency to form combinations is
satisfied. In decomposition the exact opposite holds. In order to break
up combinations an external force is required, and the amount of poten-
tial acquired by the atoms is precisely equal to the actual force employed.
It follows from this that in the act of every chemical composition actual
force is liberated, and in every chemical decomposition actual force is
rendered latent, or is converted into potential. In the first case the force
developed is equal to the potential lost in combination, and in the second
case the actual force rendered latent equals the potential force developed.
Where a loss of potential occurs, it is compensated for by a proportional
development of actual force, and vice versa.

The same rule applies to all forces in nature. Every development
of force is to be regarded as a change from actual to potential force or the
reverse, or the transformations of different forms of actual force. This
law is known as the conservation of energy. The forms of actual force
that we are familiar with are movements of masses, light, heat, and elec-

CHEMICAL PROCESSES IN CELLS. 149

tricity. All the actual forces have a tendency to be converted into a
single actual force, heat; thus, as the motions of bodies decrease through
friction and the resistance of the atmosphere, and as the electric current
meets with resistance, they are converted into heat. So, also, the form
of movement which appears as actual force in the formation of chemical
compounds is usually manifested by the development of heat, or occa-
sional light ; and the actual forces which disappear in chemical decompo-
sition are again usually represented by heat or light. Nearly all bodies
are chemical compounds ; that is, their atoms are bound together by
their affinity for their atoms. This also applies to the isolated elements
which, in their free state, exist as molecules of like atoms. So long as
no external force is brought to bear upon chemical compounds, there is
no tendency to decomposition or formation of new compounds.

Heat is the most ordinary external force which produces chemical
change. The stability of chemical compounds may therefore be meas-
ured by the amount of heat required to break up the compound. Every
compound, even the most stable, may be broken up if the heat is suf-
ficient. While C03 requires enormous heat to decompose it, the organic
compounds of carbon are decomposed at moderate temperature. Conse-
quently, in the latter case the atoms are loosely combined ; that is, in the
formation of this combination not all the potential affinity is converted
into actual energ}%but a considerable degree of potential, with a tendency
to form compounds, still remains. When to such compounds heat is
applied in a degree equal to the amount of actual energy liberated in the
formation of the compound, the atoms are liberated and again acquire
their original potential energy. If a new combination is now formed,
the potential is again converted into actual energy, and the latter, in the
form of heat, is proportional to the closeness of the new compound.
This is the process which is concerned in the burning of every organic
compound. Thus, by the artificial application of heat single atoms of the
combustible body and .of the atmosphere are separated and their combi-
nation results in the liberation of heat, which is itself sufficient to
decompose other atomic combinations, and the processes of combustion
goes on by itself. The entire amount of heat liberated equals the
difference between the amount of heat required to break up the organic
compound and the amount liberated in the formation of simpler, closer
compounds. If, on the other hand, atoms, if they are separated by
considerable force, do not enter into a closer but into a looser compound,
more actual energy is lost than is liberated, and a decomposition results
in which a certain amount of heat is used up, which in the new. combi-
nation is present as potential force for future combustions. The amount
of potential energy is therefore dependent on the closeness of the chemical
combination^ and not on the separation of the affinities. As a rule,

150 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the closeness of the combination is inversely proportional to its com-
plexity.

The degree of potential energy of a combination may be measured
by the amount of heat liberated in its combustion ; thus, a heat unit
is the amount of heat required to raise one gramme of water one
degree C. So one gramme of carbon yields 8000 heat units, or calorics ;
one gramme of hydrogen equals 34,000 heat units. These numbers are
greatly modified when the carbon and hydrogen are combined or enter
into combination with other elements. Thus, when pure carbon is
oxidized to CO2, the heat developed is less than when, with an equal
quantity of 0, CO, or combinations of CH and O and H20 are burned
to form C02. The higher the atomic weight of compounds, the greater
the amount of heat given off in combustion. Thus, fats yield more heat
than sugar and alcohol ; but while equal weights of such high atomic
bodies yield more heat in proportion to their weight, when compared
with equal quantities of oxygen consumed they yield less than simpler
bodies, as sugar or alcohol.

The elementary compounds which are found in animal and vegetable
cells in no way differ from those found in inorganic nature. Similar
elementary substances are found in the earth and atmosphere, and
become constituents of animal and vegetable organisms. In organisms
chemical affinity exerts the same sway as in inanimate nature. Acids
unite with bases to form salts within cells just as without ; no one of
the elementary constituents of cells has lost its power of uniting with
oxygen, and the products so formed are identical with similar bodies
formed elsewhere.

We have already traced the processes occurring in animal and
vegetable cells, by which these bodies are converted in the former from
simple elementary substances to complex organic bodies, and in the
latter again reduced to their simple elementary form. It is evident that
the animal and vegetable cells differing in the chemical processes which
occur within them will also differ in the transformations of energy which
occur within them. Thus, we have seen that vegetable cells containing
chlorophyll convert stable oxygen compounds of carbon and hydrogen,
COa and H2O, with liberation of oxygen, into the looser organic com-
pounds, such as starch, or, less frequently, glucose or fat. They therefore
return to atoms of these combinations a portion of their potential energy,
which in the original transformation into COa and HaO they had lost in
actual energy in the form of heat. To accomplish this, plant-cells require
the assistance of an external force, namely, the heat and light of the sun,
which they convert into a chemical potential force in the resulting
organic compounds. The condition is more complicated in cells which
possess no chlorophyll. Here, also, the reduction processes require an

CHEMICAL PROCESSES IN CELLS. 151

external force ; but in such a process as the manufacture of fat out of
carbo-hydrates, or the synthesis of albuminoids out of carbo-hydrates
and inorganic nitrogenous compounds, or the formation of starch,
cellulose, etc., out of glucose, the potential energy developed is not
derived from an external force, as the light in chlorophyll plants, but
from a force inherent in the cell itself. This force is manifested in the
oxidation processes occurring in colorless protoplasm, and which are
evidenced by the excretion of C02 and H3O as combustion products.
Thus, in the synthesis of higher carbo-hydrates from glucose a combus-
tion results, in which H2O is formed, and in it the two atoms H and O
are more closely united with one another; in this process potential energy
is transformed into actual force. In order to comprehend the formation
of fat or albuminoids out of oxygen compounds without a simultaneous
liberation of oxygen there must also always be an additional combustion
of looser-combined carbon into C02; from this it follows that pure
oxidation processes occur in such cells, such as the formation of
vegetable acids out of carbo-l^drates, volatile acids from fixed fatty
acids, — processes which yield a certain amount of actual energy in the
form of heat, of which a part is again rendered latent in the formation of
chemical potential energy. As a whole, in cells free from chlorophyll the
processes accompanied by the liberation of actual forces preponderate
over those in which actual energy is consumed. In every such cell,
therefore, there is an actual development of heat. A small part of this
actual energy, before being converted into heat, may be transformed into
the mechanical movements already described. Every independent organ-
ism which is free from chlorophyll manifests changes which result in the
same transformation of force as described above ; such examples are seen
in the case of the organized ferments.

The animal cells, on the other hand, directly appropriate highly
complex substances, such as albumen, fats, and carbo-hydrates, in which
a high degree of potential energy is contained. In the act of forming by
oxidation simpler compounds, such as C03, H20, and NH8, their potential
energy is transformed into actual force, partly manifested by heat-
production, and by protoplasmic contractile movements. In animal cells,
therefore, the main characteristic is the conversion of the potential
energy of organic compounds into the actual forces of heat and
mechanical movements ; the process being much the same as has already
been referred to as occurring in the vegetable cells free from chlorophyll,
differing mainly in intensity. A reverse process may be also present by
which actual force may be consumed and potential energy stored up, as
in the formation of complex albuminoids, such as haemoglobin, or in tho
re-formation of albumen out of peptones.

PART II.

SPECIAL PHYSIOLOGY.

(153)

BOOK I.

THE NUTRITIVE FUNCTIONS.

(155)

SECTION I.
FOODS.

IN comparing the metamorphosis of matter in animal and vegetable
organisms it has been found that in both cases there exists a certain
relationship between such changes and the surrounding media. In the two
classes of organisms, however, these processes are diametrically oppo-
site ; for, while we found that the higher plants remove for nutritive pur-
poses C02 from the atmosphere and returned 0 to it, the animal economy
retains a portion of the oxygen of the atmosphere, not remaining fixed
as such in the body, but to be again returned to the atmosphere as
C02 and H20. For plants, consequently, since we found that the carbon
of the CO2 and a portion of the hydrogen of the H2O become fixed in
their tissues, the atmosphere is a true food ; for animals it merely en-
ables tissue metabolism to take place, and permits of the maintenance
of animal heat. The development and growth of plants is dependent on
the liberation of ox}rgen and the appropriation of the inorganic con-
stituents of their foods. In animals life depends upon the constant
appropriation of oxygen, its union with the different constituents of the
body, and final elimination through the lungs and skin as C02 and HjO,
and through the bowels and kidneys in other simple compounds. There-
fore, through the absorption of oxygen there is produced no increase in
bulk of the animal body, but rather a decrease. To meet this waste
of the organism there must be a constant appropriation of tissue-con-
stituents. Such substances are called foods.

Nutrition may .be defined as the functions which are concerned in
the preservation of the individual. Foods may, therefore, be defined as
any substances which may serve nutritive purposes. The body being in
a constant state of mutation, the constituents of the organism are little
by little eliminated as the result of this mutation, and to preserve the
necessary balance must be replaced. There must, therefore, be an exact
correlation between the constituents of an organism and the aliments
required by that organism. The demand for aliment is governed by the
waste ; if the supply is not as great as the waste, the body loses weight.
If, on the contrary, as in youth, the supply is greater than the waste,
the body increases in weight. When the losses of the economy reach
a certain degree without a sufficient reparation having taken place,
when the disassimilation exceeds the assimilation, the sense of hunger

(157)

158 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

reveals the wants of the organism and creates a demand for food. If
these demands are not attended to, other more serious phenomena
result. These, as well as the sensations of hunger and thirst, will be
described at a later point.

Not only must the aliments taken to repair waste have a certain
weight, but they must also have a definite quality, since nitrogenous
and non-nitrogenous material, water and inorganic substances, all escape
through the various excretions, and their losses must be supplied by
analogous substances in quantities in proportion to the amounts lost
by excretion. Under all circumstances the foods of animals are or-
ganic, and these foods for the most part contain those inorganic sub-
stances already prepared which form the direct constituents of the
animal body ; the}7 are therefore analogous and equivalent to what they
replace. The animal economy does not, as does the plant, supply its
nutritive wants by synthesis and condensation of the substances con-
tained in its food ; but it requires the constituents of its flesh and
blood to be already formed in its food. In the flesh of the herbivora
the carnivora consume flesh similar to their own. In plants the her-
bivora obtain readj^-formed constituents of their flesh and blood. The
end products of the activity of plant life, vegetable albumen, and other
constituents of vegetable tissue, serve directly and without further exten-
sive chemical modification to supply the waste in the animal economy ;
consequently, plants act as the food-preparing organisms in the general
circle of life. Vegetable life must, therefore, first have appeared on the
earth, for it is a necessary condition for the existence of animal life ;
both herbivora and carnivora are dependent upon the vegetable kingdom
for food. In vegetable matters are repeated the most complex ingre-
dients of animal tissues. Chemists have been so struck by the similarity
of such bodies that they have designated them by the same names.
Thus, we have vegetable albumen, vegetable fibrin, vegetable casein,
representing the albuminous group. Among the carbo-hydrates we
have starches and sugars, and it is well known that fats are abundant
in the vegetable kingdom. Animals, therefore, find their tissue-con-
stituents ready-made in their food, whatever be its nature.

The principles of food, whether derived from the animal or vegetable
kingdom, and whether appropriated by the herbivora or carnivora, are
not retained in the organism in the form in which they are taken as food.
They must first be subjected to certain modifications before they can
become constituents of the animal tissue or juices ; in other words, they
cannot fulfill their nutritive purposes until they have been subjected to
preparatory modifications in the digestive tube. These modifications are
not in general very pr6found, and usually consist in reducing foods to a
soluble form, if not already so, or in reducing them to a state in which

FOODS. 159

absorption is possible. This is the sole end of digestion. The aliments
are in the digestive tract split up into their nutritive elements, which are
prepared for their absorption, while the non- nutritive portions are
expelled. Thus, the blood of animals is continually receiving additions
from the food, which it carries to different organs and tissues. Certain
of these are fixed or assimilated, replacing analogous substances rendered
unfit for carrying on the vital functions ; the others are modified and
destroyed. There is thus an incessant movement in the animal economy,
a continuous interchange of material, and a double current of entering
and expelled materials. This double current is marked by two series of
chemical phenomena, — the one terminating in the fixation of the nutri-
tive principles in the economy, in their assimilation ; the other in their
decomposition, their retrogressive metamorphosis, or their disassimila-
tion. The ensemble of these two chemical phenomena constitutes
nutrition.

Foods of animals are destined to supply the waste of tissues. They
must, therefore, to be complete, embrace all the tissue-ingredients which
are liable to waste. The statement, therefore, of these tissue-constituents
will be also a statement of the essential food-stuffs. The chief constitu-
ents of the blood, flesh, and other tissues, as we have seen, may be classi-
fied as follow : —

ORGANIC.
I

Nitrogenous. Non-nitrogenous.

Albuminous Bodies and Carbo-hydrates and

their Derivatives. Hydro-carbons.

INORGANIC.

Water, Sodium Chloride,

Alkaline Phosphates, Sodium Sulphate,

Phosphatic Earths (Calcium, Magnesium), Potassium Sulphate,

Magnesium and Calcium Carbonates, Iron,

Potassium Chloride, Silicon.

It is rarely the case, however, that these simple nutritive substances
are taken separate^ as food. Ordinarily the alimentaiy substances are
formed of mixtures, in various proportions, of the simple nutritive
substances. Thus, water that we drink contains mineral salts in solution.
Meat contains water, albuminous bodies, salts, and fats, while milk
contains all the alimentary principles. We must therefore distinguish
between simple nutritive substances and foods which contain several of
these bodies.

In addition to the simple food-stuffs, there are other substances not
belonging to any of the above classes which have certain nutritive values,
such as alcohol, organic acids, tea, coffee, and essential oils. These are

160 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

termed accessory foods, and have but little bearing on the study of
nutrition in the domestic animals.

Blood is the chief nutritive fluid of animals. What, therefore, is to
be converted into tissue must first be converted into blood; consequently,
the substances taken in food must be converted into blood, or, at least,
pass into the blood, to be of nutritive value. Blood contains about 80
per cent, of water and 20 per cent, of solids. Of the latter, 1| per cent,
is organic, consisting of albuminous bodies, fats, and carbo-hydrates, the
latter being represented by glucose and occurring in small quantities.
Blood, therefore, contains all the constituents of the tissues and the
elements for their formation, so arranged as to require but slight chem-
ical modification to transform them into tissue. Blood consequently
contains, in suitable form, all the organic elements necessary for the
formation of all the animal tissues and fluids. The constituents of the
blood and flesh of the carnivora are absolutely identical with the constit-
uents of the blood and flesh of those animals which serve as their food.
The nutritive processes of the carnivora consist, therefore, in a simple
nutritive conversion of the blood and flesh of herbivora. Suckling
animals, whether herbivorous or carnivorous, obtain in milk what might
be regarded as the equivalent of the flesh of their mother, since milk
contains representatives of all the constituents of blood, casein and
albumen representing the albuminous group, butter the fats, and milk-
sugar the carbo-hydrates. The same inorganic salts are also found in the
milk as in the blood, and water is present in large amount.

In the herbivora the nutritive processes are not less simple, since all
parts of plants which serve as their food contain representatives of albu-
minous, carbo-hydrate, and fatty tissue-constituents which are similar, or
almost identical, to those found in the animal tissues. Consequently, the
vegetable bodies which serve as foods for animals contain, ready formed,
the constituents of animal tissues, and the nutritive value of vegetable
foods is in direct relation to the proportion of these substances present.
It may therefore be said that animals are dependent upon the inorganic
matters of the earth and air for their food-stuffs ; for from these inor-
ganic constituents of the earth's surface plants indirectly create the blood
and flesh of herbivora, and in the blood and flesh of herbivora the car-
nivora, in a strict sense, may be said only to obtain matter of vegetable
origin with which the former were nourished. Animals, therefore, through
the mediation of plants are built up out of C02, H20, NH3, N03H, and a
few other inorganic compounds (Gorup-Besanez).

What has been said about the renewal of the organic tissue-elements
might be repeated for the inorganic tissue-constituents of animals. These
are also obtained, ready prepared and reacty for assimilation, by both
carnivora and herbivora. The inorganic constituents of the blood of the

VEGETABLE FOODS. 161

!

herbivorous animals are precisely similar to the inorganic constituents
of the vegetable matters which serve as their food. The inorganic con-
stituents of the blood are the same as the inorganic constituents of
tissues. Herbivora and carnivora therefore find in their foods their
necessary inorganic tissue-constituents. The statement above made that
animals must obtain in their foods constituents of their blood and tissues
ready prepared may be modified in the case of the fats ; for it has been
found that, so far from being derived from fats taken as food, the greater
part of the fats stored up in the body is derived from the breaking up
of other organic bodies, especially the albuminoids.

I. VEGETABLE FOODS.

The nutritive principles of vegetable foods are disseminated
in various proportions in different parts of all vegetables; there is
therefore no vegetable which is intrinsically incapable of serving as
animal food. But all vegetables do not contain these nutritive principles
in equal degrees, or in such a state as to permit of their isolation
and appropriation by the animal digestive apparatus ; nor are they in
all the vegetables free from noxious principles. Thus, some vegetables,
as the herbaceous plants, contain nutritive principles in all their parts ;
others, only in their roots, stem, bark, leaves, fruit, or juices. Some may
form suitable foods for a large number of different species of animals ;
others are only capable of nourishing a single" species ; and some plants
which are food for certain groups of animals are poisons to others. The
parts of plants above the ground — that is, their stem, leaves, flowers, and
fruits — are in general the most nutritious from the time when vegetation
is well commenced to the time of flowering, because then the nutritive
principles are not yet fixed in the organs of fructification, and the parts
in which they are disseminated are soft and tender. Earlier than this
the herbaceous plants are too watery and later too dry to prove very
nutritious. The stems of leguminous plants are nutritive while young,
while their leaves are suitable for food in all varieties of vegetation. The
roots of plants, when soft and succulent, serve as food for many animals,
such as the hog and bear, the tapir and hippopotamus, and when culti-
vated form valuable food for man. Soft and pulpy fruits, dried fruits,
nuts, hulls, and seeds, which are almost invariably rich in mucilaginous
matters, — with sugar, starch, oil, and nitrogenous principles, — are often
food for many animals. Under certain circumstances, parts of plants
which are usually but slightly nutritive, such as the bark, stems, and
roots, or even woody tissue, may serve as foods, especially after having
undergone partial decomposition, for many animals, particularly the
beaver and other rodents, and various insects.

11

162 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Vegetable foods differ from foods of animal origin in the respect
that the nutritive principles are not present in as concentrated form as
in animal foods, and the non-nitrogenous food-stuffs are present in much
greater abundance than the nitrogenous ; moreover, vegetable foods are,
as a rule, very much less readily digestible than animal foods, from the
fact that the nutritive principles are inclosed within cellulose capsules,
which offer great resistance to the solvent action of the digestive juices,
and which necessitates fine comminution before being capable of being
digested and absorbed. As a consequence of this the residue from the
digestion of vegetable matter is always very much more abundant than
from an animal diet, and hence the intestinal excreta of the herbivora
are alwajrs much more bulky than of the carnivora, or even of the om-
nivora. Another point of contrast between vegetable and animal food
is found in the difference of inorganic constituents of the ash. Vege-
table foods are especially rich in potassium and magnesium salts, and
comparatively poor in sodium salts, while chlorides are present in
extremely small amount, and phosphates in considerable quantities.
As already indicated, in vegetable tissues representatives of all
the different food-stuffs are to be found ; thus, vegetable albumen is
present, and in its characteristics appears identical almost with the
albumen of animal origin. So, also, are carbo-hydrates, oils, and inor-
ganic salts. The relative proportions of these substances vary in differ-
,ent plants. The usefulness, therefore, of different forms of vegetable
food for different nutritive purposes depends upon differences in the rela-
tive proportions of these constituents. The vegetable foods may be
given to our domestic animals in the fresh state, containing their natural
juices, when they are termed green fodder, or after having been dried
by.the sun, when they are called dry fodder.

» Green fodder always contains a large amount of water in proportion
to the solids present, the proportion often being 75 per cent, water to 25
per cent, solids. Of the solids the albuminous bodies may amount to 10
or 20 per cent., the non-nitrogenous extractive matters varying between
50 and 60 per cent., while cellulose is present in large amount. All edible
grasses and vegetable tops may serve as green fodder.

Dry fodder consists of the stems and leaves of various grasses and
plants after the major part of their water has been removed by evapora-
tion by the sun's heat. The proportion of water to solids in dry
fodder is reduced to 15 per cent, of the former to 85 per. cent, of the
latter. Of the solids of dry fodder cellulose constitutes from 20 to 40
per cent., a moderate amount of albuminoids and carbo hydrates, less
fat, and a maximum of inorganic matter.

Green fodder, as a rule, is more readily digestible than dry fodder.
Thus, experiments made by feeding oxen at one time with fresh red clover,

VEGETABLE FOODS. 163

and another time with the same material carefully dried, have shown the
following excess of matters digested in favor of 'the green fodder: —

Solids, . . •'.'-• . 2.3 to 5.5 per cent, more digested.

Proteids, . . . . 2.7 to 3.2

Carbo-hydrates, . . 4.1 to 5.6 " "

Fats, .... 2.4 to 21.0

Cellulose, . . . 2.6 to 6.2

The attempt has been made to attribute these results to the reduc-
tion in digestibility acquired in the processes of drying. This is not,
however, the case, since there is an actual loss of digestible matter in
the processes of fermentation which occur in the act of drying. Green
fodder is especially adapted for all ruminants, and for young horses after
the completion of the first year. Scarcely any single green fodder is,
however, suited for forming the single food of horses or* sheep. The
percentage of water of most green fodders in every stage of growth
amounts to from 70 to 90 per cent., and there are but few green fodders
which contain so little water that they may serve without the mixture of
any dry fodder for feeding sheep or horses. Cattle, on the other hand,
require a watery food, while hogs, on account of the arrangement of
their digestive apparatus, are only capable of digesting small amounts
of the youngest and most tender green foods. Green fodder, as a rule,
is the more nutritious the younger and more tender it is, since, in spite
of the greater amount of water contained in this period, it also contains
a larger amount of nitrogenous nutritive substances, is more stimulating
to the appetite, and is more readily digested. Thus, it has been found
that in the English bay grass (Lolium perenne) the composition varies
as follows (Pott) : —

Water. Cellulose. Proteids.
On the 6th of May, . . . 81.2 17.7 27.9

From the 25th to the 27th of May,

On the 10th of June, .

On the 24th of June, .

On the 10th of July,

On the 22d of July,

On the 15th of August,

83.5 21.4 16.0

82.9 22.4 14.8

82.4 23.6 12.8

82.2 32.5 11.9

76.9 28.6 12.5

74.8 29.7 7.8

Similar results have been obtained in the case of clover and prairie
hay. From the fact that green fodder in early spring is so rich in pro-
teids it is advisable in this time of the year to administer it mixed with
chopped straw that the fodder be not too rich in nitrogenous compounds.

The following represent the principal vegetable food-stuffs : the seeds
of the grains, or the cereals ; the hulls and fruits of the leguminous plants ;
the vegetables, as potatoes, turnips, and beets ; and hay, grasses and
straw, of the green and dry fodders : —

1. THE CEREALS. — Wheat, barley, corn, rice, and oats belong to this
group, and are valuable food-stuffs. Their chemical composition is

164 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

subject to variations dependent upon the mode of culture, the nature of
the soil, and the climate. They all contain a small amount of water and
cellulose in proportion to a large amount of solids (over 80 per cent.) in
which non-nitrogenous extractives and inorganic matters are in excess.
The following table gives their average composition : —

In 100 parts. Wheat. Rye. Barley. Oats. Bice. Corn.

Water, - .< . . . 13.6 15.3 13.8 13.5 13.2 13.9

Albumen, .... 12.4 11.4 11.2 11.9 7.8 10.1

Fat, 1.7 1.7 2.1 5.8 0.7 48

Carbo-hydrates and non-
nitrogenous extractive

matters, .... 67.9 67.8 65.5 57.5 76.4 66.8

Cellulose, .... 2.7 2.0 4.8 8.1 08 2.8

Ash, ... . . .1.7 1.8 2.6 3.2 1.1 1.7

The cereal grains, of which wheat may be taken as a t}rpe, consist
of a number of layers arranged eccentrical^. As many as seven different
layers have been recognized. Externally there is the external membrane
or epidermis; within that the epicarpium ; 3d, the endocarpium ; 4th, the
pigment-layer, or the testa, which in wheat is a reddish-brown membrane,
and gives to wheat-grains their characteristic color; 5th, the tegmen, or
external nuclear membrane, below which are found a number of dice-
shaped cells (the perisperm), which were formerly spoken of as gluten-
cells, in which, however, the contents are mainly starch ; and it is within
the endosperm that the albuminous contents is contained between the
starchy granules. For, if a granule of wheat is divided and touched
with a drop of Millon's solution, it will be seen that the contents of the
endosperm only stain purple, while the shells and the so-called gluten- -
cells remain unchanged.

When wheat is subjected to the action of a digestive fluid the
albuminous bodies of the endosperm are dissolved and the starchy
granules become separated, while the hulls and so-called gluten-cells
remain entirely unaffected. The hulls contain a certain amount of
albuminous bodies, and are employed in bran and in black bread, and
have considerable nutritive value. In the so-called gluten-cells a ferment
seems to be present which has been called cereal in, and which seems to
interfere in some way with digestion, and as a consequence, although
bran-bread is to a certain extent nutritious, it is yet difficult to digest.
In grinding, the external hulls or capsules are bursted and the contents
reduced to a fine powder in the mill, and thus become more digestible.
Hulls which are separated from the internal contents by milling always
contain a certain amount of albuminous matter and starch clinging to
them, so that even the chaff, or the hull or bran, contains considerable
amounts of nutritive matter, and may be used as fodder. Bran from
wheat has been found to contain 13 per cent, water, 14.5 per cent.

VEGETABLE FOODS.

165

albumen, 2 per cent, fat, 53 per cent. carbo-h}'drates, and 17.5 per cent,
cellulose.

The preparation of bread depends upon the fermentation produced
through the action of the yeast-plant in rye- or wheat-meal mixed to a
thick paste with water, the so-called dough, and allowed to ferment at
about 30° C. Through the action of the yeast part of the starch is
converted into dextrin and sugar, of which a part again undergoes
further decomposition into carbon dioxide and alcohol. The bubbles of
the former serve to render the dough light and porous. In baking the
gas-bubbles expand through the heat and render the bread still more

FIG. 55.— SECTION OF A WHEAT-GRAIN, MAGNIFIED 610 DIAMETERS, AFTER

PEKAR. (Thanhoffer.)
1, epidermis ; 2, epicarpium ; 3, endocarpium ; 4, testa ; 5, tegmen ; 6, perisperm ; 1, endosperm.

porous, and therefore more permeable to the digestive juices and more
readity digestible, while in the action of the heat a certain amount of
starch is still further converted into dextrin and sugar. The nutritive
properties of bread depend upon the starch, dextrin, sugar, and
albumen which are contained within it. Bread, therefore, contains all
the nutritive principles in some amount, as a certain amount of oils and
inorganic salts are also present, although the carbohydrates are present
in the largest proportion. It has been estimated that a man, to obtain
the necessary amount of albumen required for his daily ration, would
have to consume three pounds of bread daily.

Oats, rye, and corn also have their various constituents arranged

166

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in concentric layers, in which also the so-called gluten-cells are to be
recognized, as well as numerous free starchy granules. The relative
proportions of the different constituents vary in different samples, and
hence the nutritive value of these grains depends upon the method of
cultivation, etc. Corn and rye are especially rich in starch, but are
poorer than wheat in albumen. By soaking in boiling water, — the only
way in which rice is used as a food, — the starch-granules become par-
tially converted into soluble starch, through the rupture of the cellulose
membrane and solution of the granulose in water. So prepared, the
starch of corn and rice is capable of being entirely absorbed, while only
20 to 30 per cent, of the albuminous matter escapes. Barley and oats
are food-constituents which are especially valuable for horses when a
large amount of nutritive principles in a concentrated form is required.
R}Te is poorer in albuminous principles than wheat, but is, nevertheless,
a valuable food-stuff. From the point of view of the percentage of
albuminous matter, wheat occupies the first place in nutritive value of
the cereals. In 1000 parts 135.58 parts of albuminous matters are
present. The amount of starch of wheat is only exceeded by the carbo-
hydrates found in corn and rice. The following table, after Thanhoffer,
shows the amounts of these substances present in 1000 parts of the
principal cereals, leguminous plants, and tubers : —

In 1000 parts. Wheat.

Bye.

Barley.

Oats.

Buckwheat-
grits.

Corn.

Albumen, 135.37

107.5

122.5

90.5

78.0

70.0

Starch, 558.64

555.0

482.5

503.5

457.0

637.0

Dextrin, 46.5

84.5

.

.

.

.

Sugar, 48.5
Cellulose, 32.5

28.75
49.5

97.5

116.5

233.6

Fats, . .

• .

' ..' *'•

• •

5.9

• •

In 1000 parts.

Peas.

Beans.

Lentils.

Potatoes.

Albumen,

223.5

225.2

265.0

13.0

Starch,

.

.

.

154.5

From the above table it is seen that the amount of starch present
in rye is somewhat less than that of wheat, but that it contains nearly
twice as much dextrin ; and yet the cellulose, which is almost entirely indi-
gestible, is in larger amount than in wheat. In barley, again, there is usu-
ally a larger amount of albuminous matters than in wheat, but also three
times as much cellulose, and a considerably smaller amount of starch.
Barley grown in Southern latitudes is said to have a higher percentage
of albuminous matter than is represented above. Oats, again, contain a
smaller amount of albumen, a larger amount of cellulose, and a larger
amount of starch than barle}^. It thus falls considerably below wheat
in albuminous and starchy matters, but exceeds wheat in the amount
of cellulose present. Rape-seed, again, contains twice as much cellulose
as oats, and even less albumen than starch. Corn contains the smallest

VEGETABLE FOODS. 167

amount of albuminous matter of all of the cereals, but a larger amount
of starch than any, and also contains a considerable quantity of oil, and
is therefore a useful food for fattening purposes. Rice contains only
5 per cent, of albuminous matter and 82 per cent, of readily-digestible
starch.

The nutritive value of oats is very largely governed by the character
of manure, and other modes of cultivation. The composition of oat-
grains, according to Pott, is about as follows :*

Solids . . .86.3 per cent.

Proteids, . . . . . . . .12.0

Fats, . . . . . . . .6.0

Carbo-hydrates, . . . . . .56.6

CeUulose, . . ... . . 9.0

Ash, . . . . , . . .2.7

The nitrogenous matters of oats consist in part of albumen (0.46
to 2.3 per cent.), gliadin, the so-called vegetable casein, the latter appear-
ing to be almost identical with gluten-casein and legumin. In addition,
oats appear to contain a nitrogenous alkaloid, the so-called avenine,
which possesses the property of acting as a nerve stimulant. This is
more abundant in darker sorts of oats, its amount depending upon con-
ditions of climate, soil, etc. It may amount to 0.9 per cent. It also has
been found by Ellenberger and Hofmeister that oats contain at least three
ferments, — an amylolytic, a proteolytic, and a lactic acid ferment. These
ferments are destroyed by the temperature of boiling water, but in the
stomach of the domestic animals exert their activity, and are to be
regarded as important factors in the gastric digestion of these animals.
The most active of these ferments is the starch ferment. It has been
found that in a digestion of three hours' duration with water 2 per cent,
of sugar resulted from the action of this ferment alone. The lactic acid
ferment is considerably weaker, and it is stated that in a digestion of
three hours' duration 0.1 per cent, of lactic acid was formed, while 0.2
per cent, was formed in seven hours. The proteid ferment is stated to
dissolve from 0.5 in three hours to 1 per cent, of proteids in six hours.
These results were obtained by the simple digestion of a mixture of oats
and water, kept at the temperature of the body. They have a practical
application to the subject of digestion as occurring in animals, and point
to the fact that in disturbances of digestion in domestic animals the
administration of vegetable food in a raw state is preferable to its use
after boiling, and will further, perhaps, explain the high degree of digesti-

*It will be noticed, in comparing the different tables of the composition of vegetable
fodders, that there is considerable discrepancy in the percentages given of the different
nutritive principles. This is to be accounted for by different effects of cultivation, etc.,
in the various samples analyzed.

168

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

bility possessed by oats. Wolff has found the following amounts to be
digested of the different constituents of oats : —

Proteids. Fats. Carbo-hydrates.

Ruminants, . 77.3 per cent. 82.4 per cent. 73.7 per cent.
Horses, . . 86.0 " 77.6 " 76.3 "

The carbo-hydrate constituents of oats are represented principally
by starch, although from 3 to 6 per cent, of sugar, 1.25 to 4.51 per cent,
of gum and dextrin have been found. Oats are, above all, the best force-
developing food for horses, — a fact which is universally recognized. To
foals at first only crushed oats should be given, the transition to whole
oats being only gradually accomplished. Oatmeal is also a good addition
to the food of milk cattle, and is said to increase both the amount of
milk and the amount of butter. As a fattening food for cattle oats are
not preferable to other cereals. In the natural form oat-grains are not,
as a rule, sufficiently masticated by the ruminants, and therefore their
maximum nutritive properties are not appropriated. It is therefore the
custom to feed oats to these animals either crushed or in the form of oat-
meal. Sheep, which as a rule masticate their food better than other rumi-
nants, are for this reason capable of digesting larger amounts of oats.
Oats are also a valuable food for birds. In Pomerania geese are fattened
almost solely on this food. It has, however, the disadvantage of causing
a thin and unpleasant adipose tissue in these animals. In America oats
are roasted with suet, and it is stated that hens fed on this food are
especially prolific. Oatmeal is richer in cellulose than the other meals,
but it is also at the same time richer in proteids and fats. The average
composition of oatmeal, according to J. Konig, is about as follows : —

Water,

Proteids, .

Fats,

Sugar,

Gum and dextr n,

Starch,

Cellulose,

Ash, .

10.1 per cent.
14.3 ••

5.7

2.3

3.1
60.4

2.2

2.0

Oatmeal is especially valuable as an accessory food in the nourish-
ment of young animals, especially young dogs, when it may be mixed
with milk.

Oat-straw has the following composition (Pott) : —

Solids,
Proteids,
Fats,
Carbo-hyd
Cellulose,
Ash, .

rates,

?

86.6 per cent.
3.3
1.4
42.5
33.3
6.2

It is the most nutritious of the cereal straws. Ruminants digest of
the proteid matters 40.7, fats 30.1, carbo-hydrates 45.5 per cent.

VEGETABLE FOODS. 169

In the form of chopped fodder it is a valuable addition to the food
of the ruminants and horses. Care must be taken that the straw has not
been kept in a moist place ; otherwise, when fed to milk cattle, an unpleas-
ant taste will be given to the milk.

It has been stated that of all the cereals oats are the richest in oil
and albuminoids, according to Mr. Richardson (Amer. Chem. Journ.,
October, 1886), the average for the former being 8.14, and for the latter
14.31 per cent. The composition may be placed as follows, in its dis-
tribution in the kernel and hull : —

Kernel. Hull. Whole Grain.

Water,

. 4.85

1.57

6.42

Ash, ....
Oil, ....
Carbo-hydrates,
Crude fibre,
Albuminoids,

. 1.50
. 5.70
. 46.96
. 0.97
. 10.02

1.68
0.24
20.41
5.36
0.74

3.18
5.94
67.37
6.33
10.76

70.00 30.00 100.00

It is thus seen that Richardson's analysis of American oats differs
from that given by other authorities. He places the percentage of water
lower than that of other aualysists, whilst 'the principal increase of
solids is found in the oil and inorganic constituents, his estimation of
proteids agreeing with that of others. The constituents of oats are,
however, very greatly subject to the climate in which they are grown,
and Mr. Richardson has found the average albuminoids in the grains
distributed as follows over the different sections of the United States : —

Northern States, 10.96 per cent.

Southern States, 10.66 "

Pacific Slope 9.60 "

Atlantic Slope, 10.76 "

Western States, 11.24 "

These figures are, however, dependent upon the percentage of husk,
and not on peculiarities of their kernel, and therefore the proportion of
husk to kernel and the compactness of the grain prove to be the most
important factors, and the weight per bushel the best means of judging
of the value of the grain. Oats having the husk are necessarily heavier
in weight per one hundred grains. The heaviest oats are from the Pacific
Slope, and the South ranks next, owing to the large size of the grain.
In weight per bushel, however, the fluffy husk of the Southern grain makes
it the lowest in the country, while the Pacific Slope contains the highest
weight per bushel, as also in size and weight per hundred, showing the
grain to be plump and well-filled. The heaviest weights per busliel
determined by Mr. Richardson were found in specimens from Colorado
and Dakota, weighing 48.8 and 48.6 pounds. The lightest were from
Alabama and Florida, 24.7 and 26.9 pounds, respectively. He found an

170

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

average of 37.2 pounds, the common legal weight being 32 pounds to the
bushel.

Of the group of hordeum (barley) various representatives are useful
as green fodder, but more especially their grains and straw. The com-
position of barley -grains is greatly modified by the locality of growth
and mode of cultivation. The following represents about the average
composition : —

Solids; . 86.2 per cent.

Nitrogenous bodies, . . . . 11.2

Fats, 2.1

Non-nitrogenous bodies, 65.5

Cellulose, 5.2

Ash, 2.2

The proteids of barley consist in a large part of gluten-casein,
gluten-fibrin, mucedin, and albumen. No gluten can be obtained from
barle3^-meal. The carbohydrates consist of starch, from 1 to 2^ per cent,
sugar, and 1 to 7 per cent, dextrin. The digestibility of the barley-grain
is placed by Wolff as follows : —

Proteids, .

Fats,

Carbo-hydrates,

Ruminants.
77 per cent.
100

87 "

Horses.

80.3 per cent.

42.4 "
87.3

Hogs.

78.2 per cent.
68.4 "
90.0 "

The barley- grains are, therefore, readily digestible, and in the form
of meal form a food of the first class in nutritive properties for cattle,
and are especially valued for the good influence which they exert on the
quality and quantit}^ of the milk and butter. For horses also they may
be used to a certain extent as a substitute for oats, given in the entire
form, mixed with chopped straw. To old horses or foals, on the other
hand, barley should be given as meal, or after being crushed. It has
been .stated that if the barley-grains are swallowed whole they swell up
in the stomach, and may produce serious colic. Therefore, the animals
should receive water about half an hour before being fed with barley-
grains. The Arabs make Use of barley almost solely as food for their
horses, and administer it in the entire condition. Barley-meal has the
following composition : —

Solids,
Proteids, .
Fats,

Carbo-hydrates
Cellulose,
Ash, .

87.7 per cent.
11.6

3.6
52.0
14.3

6.2

Barley-meal is frequently adulterated with various mineral sub-
stances, such as cla}^, chalk, or plaster, which may cause it to prove
hurtful. Such adulterations may, however, be readily recognized by
microscopic examination. Barley-straw, especially, as is often the case,

VEGETABLE FOODS.

171

if grown with clover, forms one of the best of the cereal straws, the
straw of winter barley being, however, the poorest in nutritive substances
of any form of straw.' The following is the composition of barley-straw : —

Solids, .. ;

Nitrogenous matters

Fats,

Non-nitrogenous extractive matter ,

Cellulose, .

Ash, .

85.7 per cent.

3.4 "

1.4
34.7
41.8

4.4 <« '-

The following is the composition of barley-straw when grown with

clover : —

Solids, ... . 85.7 per cent.

Nitrogenous bodies, . 6.5 "

Fats, ..;-... . 2.0 "

Non -nitrogenous extractive matters, 32 5 "

Cellulose, ... . 38.0 "

Ash, .... . 6.7 "

Barley-straw, therefore, grown with clover, almost approaches an
average hay in nutritive value. The ruminants digest the following
amounts of the different constituents of barley-straw : —

Proteids,

Fats, . . • .

Non -nitrogenous extractive matters,

20 per cent.
41.6 "
54.1 ".

Barley-bran agrees in its general properties with the bran of the
better cereals. It contains —

Solids, 85. 8 per cent.

Proteids, 3.1

Fats, 1.5

Carbo-hydrates, 38.5

Cellulose, 30.3

Ash, 12.4

Barley-bran frequently contains large quantities of the barlej'-bristles,
and should then only be given to animals after being boiled or steamed.
Given dry, the bristles stick in the tongue, and produce inflammatory
reaction. Steamed barley also is a valuable food. By malting, the barley
undergoes mechanical and chemical alterations which lead to the
increase in its digestibility, and, although the starch is turned into sugar,
there is, nevertheless, in the process of malting a loss in nutritive con-
stituents of the total solids, especially of the nitrogenous bodies. In
sprouting there is likewise a loss of proteids, carbo-hydrates, and fats.

Buckwheat is often used as a green fodder, and its grain is fre-
quentty administered as dry food. The green buckwheat contains —

Solids, . * . .

Proteids

Fats,

Non -nitrogenous extractive matters,

Cellulose,

Ash,

15.0 per cent.
2.4
0.6
6.4
4.2
1.4

172

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In digestibility the green buckwheat is almost comparable to clover,
but contains a much larger percentage of water, and is not, therefore,
well suited to constitute the sole food for cattle. When given to cattle
not more than fifty kilogrammes per thousand kilogrammes body weight
can be given, the remainder of the food consisting of dry food. On feed-
ing with buckwheat the milk and the butter assume a beautiful yellow
color. The green buckwheat is entirely unsuitable for sheep and hogs,
either freshly mown or for grazing, and in them frequently causes serious
disturbances. On account of its large percentage of water it is only
suitable for horses as an accessory food. The conversion of the green
buckwheat into hay offers great difficulty on account of its large percent-
age of water. The grains of buckwheat are principally used as food.
They contain —

Solids,
Proteids,
Fats, .

Non-nitrogenous extractive matters

Cellulose,

Ash, .

86.8 per cent.
10.1

1.5
59.5
15.0

1.8

They are thus not especially rich in nitrogenous matters and contain
large amounts of cellulose, and belong, therefore, to the more indigestible
cereals, but form a good additional food for draught horses, sheep, milk
cattle, and fattening cattle. When, however, given in large amounts to
ruminants and hogs, they are apt to produce very serious disturbances,
especially in summer. In winter, on the other hand, the buckwheat is
less hurtful a food, though it is advisable to cease its administration at
least two weeks before grazing commences. Buckwheat-meal contains —

Solids, . . .

Proteids,

Fats, .

Non -nitrogenous exti active matters

Cellulose, .

Ash, . ...

84.0 per cent.
15 0 "

35 "
43.0 "
19.0 "

3.4 "

Buckwheat-meal is, therefore, relatively rich in proteids, and in spite of
its considerable amount of cellulose is a good fattening food for hogs. It
is frequently adulterated with the seeds of various weeds. Buckwheat-
straw belongs to the most useful of this class of fodders. It contains — •

Solids,

Proteids,

Fats, .

^Non-nitrogenous extractive matters,

Cellulose,

Ash, .

89.9 per cent.

4.1

1.4
32.9
44.3

5.0

It contains somewhat more cellulose than most of the straws of the
different cereals, and is, therefore, perhaps more indigestible, but it is
also richer in proteids.

VEGETABLE FOODS.

173

2. The LEGUMINOUS PLANTS stand next in nutritive value to the
cereals. They are composed of the peas, beans, and lentils. By boiling
with water their hulls become ruptured, and their contents readily sub-
jected to the action of the digestive juices. The leguminous plants are,
therefore, principally used in the form of soups or broths.

The hulled fruits contain a maximum of albuminous matters, and
the kernels of oily fruits more fats than the cereals.

Beans are seldom used as green fodder, or as the principal article of
diet, since they are too rich in nitrogen ; they form, however, an admi-
rable addition to the diet of cattle, sheep, and horses.

Peas, both as a green fodder and as grain, form highly nutritive
foods. Green peas are especially good as a food for milk cattle, and give
a pleasant taste to the butter. Dried peas are also highly digestible
and nutritious. They contain —

Solids,
Proteids,
Fats,
Non-nitrog
Cellulose,
Ash, .

enou

s ext

racti

ve mattei

s,

86.8 per c
22.4
3.0
52.6
6.4
2.4

Of these nutritive principles —

Proteids.

Fats.

Non-nitrogenous
Extractive Matters.

Ruminants digest 88. 9 per cent. 74.7 per cent. 93. 3 per cent.
Horses " 83.0 " 6.9 " 89.0 "

Hogs " 85.0 to 90 36.0 to 67 95.0 to 99

The grains are best given chopped up with straw, when they form an
excellent food for draught horses, of which amounts equivalent to half of
the ordinary corn ration may be given. They are also a fattening food
of the first rank for hogs, and, like barley, greatly improve the character
of their fat and flesh. When given in large amounts to milk cattle, they
are apt to make the butter too hard. The straw of peas is also readily
digestible, and of good pea-straw ruminants digest 60.5 per cent, of pro-
teids, 45.9 per cent, of fats, and 64.4 per cent, of non-nitrogenous extract-
ives. When in good condition, pea-straw may even serve as a substitute
for hay for j'oung cattle. For milk cattle but small amounts should be
given, or else the quantity of milk will be reduced. Unfortunately, pea-
straw is apt to be contaminated with that of various weeds and fungi.

The following table gives the average composition of the principal
representatives of this group, as contrasted with the potato: —

In 100 parts.
Water, .
Albumen,
Fats

Lentils.
. 12.5
. 24.8
. 1.9

Peas.
14.3
22.6

1.7

Beans.
14.8
23.7
1.6

Potatoes.
76.0
2.5
0.2

Carbo-hydrates,
Cellulose,
Ash,

. 54.8
. 3.6
. 2.4

53.2
5.5

2.7

49.3
7.5
3.1

20.2
0.4
0.5

174

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

3. BULBS and BOOTS, represented by the potato, beets, etc., constitute
another group of vegetable foods.

Potatoes are of very much less nutritive value than either of the
preceding groups of foods, from the fact that they contain but a small
amount of albuminous matters, but a very large amount of starch. Large
amounts of water are present in bulbs and roots which serve as food, with
small amounts of solids (86 to 14). Of the solids, the carbo-hydrates
constitute 80 per cent, or more, while the other nutritive substances
and inorganic salts are in proportionately small amount. Even of the
amount of albumen present only about one-fourth appears to be capable
of digestion in the alimentary canal.

In the vegetables, such as beets, asparagus, and cabbages, there is a
large per cent, of water, — from 80 to 90 per cent., — but only 2 per cent, of
albuminous matter, 2 to 4 per cent, of starch or gumni}^ substances, a
small amount of sugar, and 1 to 1.5 per cent, of cellulose. Their nutritive
value is therefore slight.

Fodder-beets (Beta vulgaris, mangold-beets), of which a large variety
is met with, form valuable articles of fodder, those with the round roots
being usually more rich in nutritive constituents. The nutritive qualities
of beets are further increased by the character of the soil and climate,
mode of culture and manuring, and are especially proportional to the
slowness with which they are grown. Fodder-beets have, as a rule, the
following constituents : —

Solids,
Proteids, .
Fats, .

Carbo-hydrates,
Cellulose, .
Ash, . . ",

Sugar-beets contain —

12.0 per cent.
1.1
0.1
9.1
0.9
0.8

Solids, ... 18.5 per cent.

Proteids, 1.0

Fats, 0.1

Carbo-hydrates, 15.4

Cellulose, . . . • 1.3

Ash, 0.7

The principal difference, therefore, between fodder-beets and sugar-
beets, is found in the larger percentage of solids in the latter, consisting
principally in the greater amounts of sugar. The percentage of sugar
is further increased by potassium manures, and is greater in beets grown
in cold, high localities than in warm places. It also is in proportion to
the length of time, after growth is complete, that the beets are kept in
the ground, especially when they have sprouted. Nitrogenous manures
and manures rich in phosphates increase the proteid constituents of the
beets, although all the nitrogen in the beets is not to be recorded as

VEGETABLE FOODS. 175

proteid. Nitrate of potassium, nitric and oxalic acids, magnesia and
other alkalies are constituents of beets, and will often explain the pur-
gative action exerted by many forms of beets. As regards digestibility,
Wolff has found that the ruminants digest of sugar-beets — proteids 62.0,
carbo-hydrates 95.2 per cent. ; of fodder-beets — proteids 75.6, carbo-
hydrates 95.3 per cent.

These experiments would seem to show that sugar-beets are less
digestible, — a state of affairs which hardly seems probable. On account
of the large percentage of water beets contain they can only be used as a
fodder with certain restrictions. They are best given in the raw state,
chopped up into pieces, although the chopping must not be too fine ; other-
wise mastication and thorough mixing with the saliva will be, to a large
extent, prevented. They are especialty suited for milk cattle, combined
with dry foods, twenty-five kilogrammes being given daily, and will serve
to improve the amount and quality of the butter and milk.

Sugar-beets cannot be given in as large an amount as fodder-beets,
on account of their higher percentage of nutritive principles. For young
cattle, as well as sheep, on account of their large percentage of water,
but small amounts may be given. Thus, one-third to one-half of the total
food for these animals may consist of chopped-up raw beets. For hogs
the beets may serve as the principal food, especially when given boiled,
although here also they may act as a purgative, and it is better that the
food should not be more than one-half constituted of the beets. For
horses, beets, on account of their high, percentage of water, are only
exceptional^ employed. Beets are best -preserved by placing under the
ground directly after harvesting, care being taken to select a perfectly
dr\T localit}^. Beet-top leaves are also v«ry frequently used as fodders.
Fresh beet-leaves contain —

Solids, 10.7 per cent.

Nitrogenous matters, 2.2

Proteids, 0.4

Carbo-hydrates, 4.8

Cellulose, 1.5

Ash, 1.8

On account of the large percentage of water and oxalic acid con-
tained within them, beet-tops frequently act as violent purgatives. They
are, however, rich in proteids, and are quite as digestible as the best fresh
hay, and in their fresh condition are suitable in small amounts for feeding
to milk cattle. If, however, they be given in excessive amounts, or con-
stitute the sole food of milk cattle, the percentage of fat in the milk
undergoes a rapid decrease. Not more than one-third of the total amount
of food, therefore, should be constituted of beet-tops.

4. GRASSES. — In addition to the above nutritive substances, domestic
animals may be nourished on the various grasses, hays, bran, and straw.

176

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The following table gives the average composition of different members
of this group: —

In 100 parts. Prairie Hay.

wy
Best.

e-»rraw.
Ordinary.

Grass.

Water, . ... . . 130

13.8

18.6

75.0

Albumen, . .. . 9.5

3.9

1.5

3.0

Fats, .

3.1

1.0

1.5

0.8

Carbo-hydrates and n
extractive matters,

on-n

trog(

nous

40.9

34.7

32.4

13.1

Cellulose, . .

26.7

40.1

43.0

6.0

Ash, . .

6.8

6.5

3.0

2.1

Esparcet (Onobrychis saliva} is one of the most digestible and valu-
able of the different forms of clover, and may be regarded as a type of
this group. Mowed during the blossoming, it contains in the green state :

Solids, . . .

. 21. 5 DCI

• cent.

Nitrogenous substances, .
Fats
Non- nitrogenous extractive matters,
Cellulose, . . . . .
Ash, ..''...

3.5
0.7

8.5
7.6
1.2

According to Wolff, its digestibility in the ruminants is as follows : —

Proteids.
72.5 per cent.

Esparcet-hay contains —

Fats.
66.7 per cent.

Solids, . .

Nitrogenous matters,

Fats,. . • . "•• . •

Non -nitrogenous extractive matters,

Cellulose, .

Ash,.

Non-nitrogenous
Extractive Matters.

78.3 per cent.

85.1 per cent.
13.3
2.5
34.5

29.0
5.8

All forms of fodder undergo in time considerable deterioration in
the amounts of their nutritive constituents, especially if preserved in
localities where the}' are accessible to the air, moisture, light, and warmth.
Fermentative processes are started up by the presence of various forms
of the lower organisms and occasion a reduction in both the non-nitrogen-
ous and proteid constituents of fodders. Thus, prairie hay, when fresh,
has a nitrogenous percentage of 1.81 per cent., while, if kept for two
years, it falls to 1.68. So long a time as this is, however, not necessary
for the evidence of considerable loss of nutritive principles. Thus, Wolff
has found the constituents of second-crop hay to vary as follows : —

Proteids, .... .
Fats,. . ... ,.

Cellulose,

Non-nitrogenous extractive matters,

In December.

14.36

. 4.01

26.44

XNon-niirogeiious exiraciive mailers, . 40
Inorganic constituents, .... 9

45.71

,48

In April.

14.34

4.24

27.18

44.80

9.44

VEGETABLE FOODS. 177

The more the fodders are protected from the air, the less will be the
loss. Thus, it has been found that corn kept in an open space free to the
air will form in a given time twice as much carbon dioxide as if kept in a
closed space, — of course, it being evident that the greater the formation
of carbon dioxide, the greater will be the loss. The moister the locality,
also the greater will be the deterioration in nutritive qualities. Thus,
oats in thirty months will lose 7.2 per cent, more of their solids than oats
kept in closed vessels. Similar facts also apply to the preservation of
the moist fodders, such as potatoes, beets, and green fodder. Sprouting
of potatoes and beets is likewise accompanied by great loss of nutritive
substance, and the presence of solan ine in a sprout may even cause it to
become poisonous. Thus, Krammer has found that in potatoes with the
sprout from 1 to 2 cm. long there is a loss of 3.18 per cent, of starch,
when the sprout is 2 to 3 cm. long a loss of 5.26, and when it reaches 4 cm.
in length there has been a loss of 9.88. Moulding, likewise, reduces the
amount of nutritive substances, in addition to the hurtful action of the
moulds themselves. Thus, in sound potatoes there will be an average
amount of solids of 23.8 per cent., while mouldy potatoes will average
only 20.6 per cent. Age of fodders not only occasions loss in absolute
amounts of nutritive \constituents, but also diminishes their relative
digestibility. Thus, Hofmeister has found that sheep which will digest
of clover-hay, when half a year old, 68.4 per cent, of proteids and 73.4 per
cent, of carbo-hydrates, when one year old will digest only 65.0 per cent,
of proteids and 63.1 per cent, of carbo-hydrates, and when four years old
50.7 per cent, of proteids and 40.7 per cent, of carbo-hydrates. The same
facts apply likewise to other forms of hay.

The preservation of grain by stowing it in close chambers is a very
ancient one. The process of ensilage as at .present carried out is per-
formed simply by placing green-fodder crops, such as grass, clover,
vetches, etc., in an air-tight chamber of almost any construction, and,
after treading the mass down, covering it with boards on which pressure
is exerted, either by dead weights or mechanical means. The grass or
other substance may be chopped if thought desirable, and salt may also
be added. When preserved in this manner grass may be kept for a long
time, and will produce, when opened, a food resembling steamed hay
which is greedily consumed by cattle. The whole loss occasioned by
this process is but small, and the process of change occurring in food so
preserved has been carefully studied by Mr. A. Smetham. He found that
fermentation of various kinds had occurred, and he was able to detect a
small quantity of alcohol, as well as various acids, of which acetic, lactic,
and butyric were the chief. The amount of the acids was not sufficiently
great to render the silage unfit for food, and the practical results of
feeding with it were decided!}7 satisfactory. By allowing the temperature

12

178 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to- rise above 125° F. the ferments are destroyed and the production
of organic acids thus largely prevented, and a sweet silage is produced
which possesses the characteristics of old hay to a much more marked
extent than by the old or "sour" process. This process is especially
valuable in wet seasons as a means of preserving the crop. It is also
invaluable for preserving second crops. A succulent food is obtained in
place of a dry one with but little loss in nutritive constituents ; certainly
less than occurs during hay-making in wet weather, although there is but
little increase in the digestibility of the grass.

Vegetable matters all contain from two to eight times as much potas-
sium as sodium, and, as we shall again refer to under the subject of
Nutrition, explains the fact that the herbivorous animals need an extra
ration of sodium chloride.

Straw is difficult to digest, is only but slightly nutritive, and requires
large quantities of the digestive secretions for the solution of its nutri-
tive constituents. Straw is somewhat more readily digested by the
ruminants than by the horse. Straw, of different kinds, has about the
following composition : —

Water,
Albuminous bodies, .
Fats, ....
Extractive matter and
hydrates,

Barley-
Straw.

. 14.3
. 3.0
. 1.4
carbo-
. 31.3

Oat-
Straw.

14.3
2.5

2.0

36.2

Pea-
Straw.

14.3
6.5

2.0

33.2

Bean-
Straw.

17.3

10.2
1.0

32.5

Cellulose, .
Inorganic matter,

. 43.0
. 7.0

40.0
5.0

40.0
4.0

34.0
5.0

100.0 100.0 100.0 100.0

Yery frequently various forms of vegetable food will produce dis-
turbances of digestion in the domestic animals from the mixing with
them of various forms of adulteration, or. from various defects in the
character or quality of the food. The capability of recognizing .this in
a general way is, therefore, desirable. Thus, spoiled hay or hay which
has lost its inorganic constituents likewise loses its normal greenish color,
and is of a dirty-gray or brown tint ; while acid fermentation or putre-
faction in all fodders may be recognized by the characteristic odor and
taste. Good oats must be clean and composed of perfectly-formed mealy
granules, and possess a certain definite specific gravit}'. Unripe or
frozen oats have a less specific gravity and a less nutritive value, while
spoiled oats are recognized by a musty smell and an unpleasant, burning
taste. The quality of the ha}^ will, of course, depend upon the quality
of the ground and its botanical constituents, the time of cutting, and
the mode of preservation. In order to judge of the quality and nutri-
tive value of hay it may be divided into three different groups. In the
first group are the sweet grasses (graminese)', in the second, the acid

VEGETABLE FOODS. 179

grasses; in the third, all other grasses. The richer the hay is in the
sweet grasses, in clovers, and leguminous plants, the better it is. The
richer it is in acid, marshy grasses, and the like, the poorer it is. Hay
cut in. summer is better and more nutritious than that cut in autumn, and
so with second crop or after-cut. In the latter also the aromatic hay-
odor is wanting. Hay which has been wet by the rain, so losing a large
part of its inorganic matters, and that which has been kept for several
years, has but little more nutritive worth than straw. Analysis has shown
that clover and prairie ha3rs which have been exposed to the rain for one
or two weeks may /lose as much as 12 per cent, of their nutritive matters.
Hay which contains poisonous plants, mud, dust, or worms or cater-
pillars, or when it has become spoiled by putrefaction or fermentation,
is likewise hurtful.

In the manufacture of various food-products residues are often left
which ma}' be of considerable nutritive value for our domestic animals.
Such residues have a somewhat similar composition, usually, to that of the
original parts of plants of which they are formed ; the relative proportions
of the different constituents will, however, vary, as more or less of cer-
tain substances are removed in the process of manufacture. Of the dry
residues the various milled foods, such as meals and flours of the dif-
ferent cereals, are the most important. They contain usually 80 per
cent, of solids. The}^ are especially rich in albuminoids (over 20 per
cent.) and fats (5.10 per cent.), and are, therefore, valuable adjuvants
to foods which are poor in these nutritive principles.

The residue from beer-breweries (beer-mash, brewers' grains) is also
a valuable food. It contains 20.25 per cent, of solids, composed largely
of albuminoids, with a relatively small proportion of non-nitrogenous
matters (1:2), somewhat more cellulose, and a considerable amount of
fat and inorganic matter.

Chemical analysis of fresh brewers' grains shows the following-
average composition : —

Solids, . . . ... . . 22 3 per cent.

Proteids, 4.6 "

Fats,. / 1.6 "

Non-nitrogenous extractives, . . . 9.9 "

Cellulose, . . ... . . 5.0 "

Assuming that 73 per cent, of the proteids is digestible, fat 84 per
cent., extractives 64 per cent., and cellulose 39 per cent., the average
amounts of digestible matters may then be placed as follow : —

Proteids, . . . •. . . . . 3.9 per cent.

Carbo-hydrates, 10 8

Fats, 0.8 "

The proportion of nutritive matter may thus be placed as 1 : 3.4.
The fresh residue from breweries contains a large percentage of

180

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

water, and therefore readil}' decomposes in summer in a few hours,
and then is a very dangerous fodder. The only method of permanent
preserving is by drying, and this necessitates a complicated and trouble-
some process. In cool weather the residue may be preserved for one
or two weeks under fresh water. Fresh beer residue is an admirable
fattening food for both cattle and hogs and for milk cows, though when
sour it affects both the quantity and quality of the milk. When fresh this
food is not so well suited for sheep and horses as when dried ; in the
latter condition, from the high percentage of nitrogenous constituents,
it is comparable to the cereals.

The residue from distilleries, the so-called distillery mash or swill,
forms a valuable article of fodder, but one whose composition is subject to
the greatest variations, depending upon the character and mode of treat-
ment of the substance manufactured. All such residues are, in their natu-
ral condition, very rich in water; and since in distillation only the starch
and sugar serve for the production of the spirits, all the other nutritive
substances remain, with slight alteration, in the residue ; so that the solids
of the latter are relatively very rich in nitrogen. Most of these residues
in their fresh condition are readil}7 devoured by the domestic animals,
and their nutritive effect is increased by administering them warm and
mixed with less nutritive substances," such as dry fodders rich in cellu-
lose, which are less readily taken by cattle. On the other hand, their great
richness in water is a disadvantage on account of the increased demand
for nutritive substances so occasioned. The high percentage of water,
soluble proteids, and other unstable substances in distillery residue
leads to their ready decomposition, or souring, in which condition they
are, of course, not suited for fodder, on account of the disturbances of
digestion and alterations of milk which they produce; the objection to
this class of foods is largely due to the danger of using a spoiled article.
So also residues from which the spirit has not been entirely removed are
likewise hurtful when given as food. The most common of these resi-
dues are those obtained from the distillation of potatoes, corn, rye,
beets, and malt.

Potato Residue. — The residue from the distillation of potatoes will
vary greatly in the percentage of nutritive constituents according to
the more or less complete extraction of the spirit,
illustrates this : —

The following table

F

Solids, . - .
Proteids, . . ' .
Fats,
Non-nitrogenous extract
ive matters, .
Cellulose,
Ash,

otato Residue.
3.8-8.7 ave
0.8-1.9
0.1-0.23

1.1-5.6
0.5-1.4

rage 7.7
1.1
0.2

4.6
0.9
07

By Hollef
Proc

6.05 pel
1.14
0.19

3.56
0.69
0.70

reund's

ess.

• cent.

VEGETABLE FOODS. 181

In the potato residue starch has been largety removed, while the
other constituents remain but little unchanged, with the exception that
the ferments are, of course, added to the residue, the proteids being to a
certain extent changed into peptones. Potato residue is less nutritive
than that from the cereals, and is, under all circumstances, unsuitable for
constituting the sole article of diet ; since it is not only too watery but
too poor in inorganic materials, especially of phosphates,- — an objection
which does not apply to the same extent to the residue from the distilla-
tion of the cereals. Fresh potato residue, in which condition it should
alone be used, sterns to assist in the production of milk, especially
when given warm, and may constitute one- or two-thirds of the total
daily ration, the remainder being composed of dry fodder. Fattening
sheep may receive from two to ten kilogrammes per one hundred kilo-
grammes of body weight, if given in too large amounts, seriously affect-
ing the flesh of the animal. For horses potato residue is in general too
wratery, and only animals while at rest, or while doing light work, can
stand it. In using this article of food care should be taken that the
potatoes have not sprouted, otherwise they will contain solanine, and in
consequence be poisonous.

Corn Residue. — The residue remaining after the distillation of corn
is richer in both proteids and fats than that from potatoes. It contains —

In a Fresh Condition. Pressed.

Solids, . . . . 9.4 per cent. 28 4 per cent.

Proteids, .... 2.0 8.6

Fats, ..... 1.0 3.2
Non nitrogenous extractive

matters, .... 4.9 12.7

Cellulose, .... 1.0 2.3

Ash, ..... 0.4 1.5

The same statements apply for the administration of these sub-
stances as food as have already been made concerning the potato residue.
Milk cattle cannot, however, receive more than thirty kilogrammes of
this daily, since it will, in larger amounts, damage the character of the
butter-fats; while they ma}' receive as high as fifty kilogrammes daily of
the potato residue.

Eye Residue. — The residue from the distillation of rye-whisk}- is, in
consequence of the higher nitrogenous and lesser oily constituents of
the rye-grains, richer in proteids and poorer in fats than the corn residue.
It contains —

Solids 9.9 per cent.

Proteids, . . . -. . . .2.1

Fats, 0.6

Non-nitrogenous extractive matters, . . 5.9

Cellulose, 0.9

Ash, . . 0.5

182 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

This substance is one of the most useful of the various distillation
residues, unless, as is often the case, the grain which has undergone the
fermentation has contained the seeds of the Agrostemma yithago, when
it will possess poisonous properties.

Beet Residue. — The residue from beet distillation contains only 9
per cent, of solids, 0.9 per cent, proteids, 0.1 per cent, fats, 6.2 per
cent, non-nitrogenous extractive matters, 1.2 per cent, cellulose, and 0.6
per cent, of ash. It is, therefore, the poorest in nutritive substances
and the richest in water.

For preservation of the distillery residues, either they may be dried,
especially when mixed with various forms of dry fodder, or they may in
the fresh condition be preserved b\' the mixture of salic3'lic acid, one
gramme for every fift^-four pounds. A process of preservation which is
frequently employed depends upon the souring of the fresh residue in
the formation of lactic acid fermentation, — a process which is accompanied
by great loss of non-nitrogenous and proteid constituents. In spite,
however, of this loss in nutritive constituents, this method furnishes a
cheap and simple mode of preserving distillery residues.

The residue from the extraction of sugar from beets, from starch
out of wheat and potatoes, and that remaining after the alcoholic fer-
mentation of starchy and sugary substances, as in the distillation of
spirits, are all valuable food stuffs. All these substances contain but
small amounts of solids, and the proportion of nitrogenous to non-
nitrogenous matters is somewhat lower than in the raw material ; but
inorganic matters and fats are present in considerable amount and
render them important accessory foods under certain circumstances.

The diffusion residue from the extraction of sugars from beet-roots
furnishes a readily digestible form of food which is richer in water and
poorer in inorganic constituents than the sugar-beets. It contains —

Solids, . . . . 10.2 per cent.

Nitrogenous matters . . 0.9

Fats, . . . . . 0.05

Non-nitrogenous extractive matters, 6.3

Cellulose, .... 2.4

Ash, . . . . . . 0.6

For cattle and hogs as much as one hundred kilogrammes per one
thousand kilogrammes of body weight of this fresh residue may be given
as food, only larger amounts may be given to animals which are desired
to fatten rapidly. Larger quantities of this fodder alter both the char-
acter and quantity of the meat and the fat of animals and the character
of the milk. For draught cattle it is unsuitable, as is also the case for
sheep, with the exception of fattening sheep, which may stand it almost
as well as cattle. Horses can only receive small amounts, — ten to twenty
kilogrammes per thousand kilogrammes of body weight, — and then only

VEGETABLE FOODS. 183

when not worked. This residue can only be given when in a perfectly
fresh condition, or when well preserved.

The residue after the extraction of oil from the seeds of the
various members of the cotton-plants (Gossypium herbaceum), or so-
called cotton-seed cake, furnishes a valuable food for fattening and milk
cattle. The seeds are inclosed in a capsule, which bursts as the fruit
ripens, and which are covered by white fibres which form the so-called
cotton. After the removal of the cotton, the seeds, which have a hard
shell, contain an oily, greenish-white nucleus, from which the oil is
removed by pressure. The residue from this process of extraction of
the oil is by no means constant in its composition, and is therefore not
always suitable for a food. For example, many of the cotton-seed
cakes contain both parts of the indigestible hull of the seed and con-
siderable cotton, and are therefore only suitable for manures. When
such an article is given to cattle serious disturbance of digestion is pro-
duced, and may even prove fatal from obstruction and inflammation of the
alimentary canal. In England the cake produced from the Eg3Tptian
seeds forms a favorite article of fodder. The most nutritious and most
readily digestible are the cakes from the hulled seeds. The following-
table gives their composition : —

Cotton-
Seeds.

Oil-Cake from
Unhulled Seeds.

Oil-Cake from
Hulled Seeds.

Solids,

91.1-92.3

85.8-93.4

85 7-92.3

P rote ids, ....

22.7-22.8

18.0-28.3

19.7-49.2

Fats?

29.3-30.3

4.8- 9.8

5.4-19.7

Non-nitrogenous extractive

matters, ....

7.6-15.4

24.9-36.7

10.5-29.3

Cellulose, ....

16.0-24.7

17.0-27.0

3.5-11.4

Ash.

8.0

6.6

7.4

The oil-cake from the hulled seeds constitutes one of the most
nutritious of all fodders. From digestion experiments on ruminants
Wolff has found the following amounts to be digested: —

Protpuls T^ata Non-nitrogenous

Fats' Extractive Matters.

Hulled cakes, 84.7 87.6 95.1

Unhulled cakes, .... 73.4 90.8 46.2

The higher digestibility of the oil-cake from the hulled seeds is with-
out doubt to be attributed to the large amount of cellulose in the hulls.
The oil-cake from the unhulled seeds is of a dark-brown color, while that
from the hulled seeds when fresh is greenish, but also becomes brownish
with age. Both of these forms of fodder are often contaminated by the
accidental mixture of various substances, such as particles of iron from
the presses, and when kept in moist places with various forms of moulds
which lead to the development of ptomaines and other poisonous alka-
loids, and so may explain their hurtful action. The American cotton-seed

184

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

TABLE I.
AVERAGE PERCENTAGE COMPOSITION OF THE ORDINARY FOODS.

According to Kuhn.

According to
Wolff.

|

o

o

II

'•£

o

a

"-' 53

r£

C}

• a

FOODS.

1

1

a
o

If

Sa

K%

iji

w5

1

O

a
§><a

| a
'3 a

§

II

o

43 O

1

2

1

fil

4

3

4

u

II

.

1

1

£r
0

g

£*

£

1

s

.2* be
Q

£

I. Green Fodder.

Prairie grass, . . .

75.0

25.0

22.9

3.0

13.1

0.8

6.0

2.1

2.4

9.9

0.4

Red clover, . „ ..

80.2

19.8

18.4

3.6

8.5

0.7

5.6 1.4

1.7

8.7

0.4

White clover, . . .

80.2

19.8

18.45

4.0

8.0

0.85

5.6 1-4

//. Dry Fodder.

Prairie hay, . '. .

14.3

85.7

79.2

9.5

40.3

2.3

27.1

6.5

5.4

41.0

1.0

Clover-hay, . ... .

16.0

84.0

78.4

13.4

36.4

3.2

25.4

5.6

7.0

38.1

1.2

Oat-straw, ....

14.3

85.7

81.3

4.0

35.6

2.0

39 .71 4.4

1.4

40.1

0.7

Bean -straw, . . .

17.5

82.5

76.7

9.9

31.8

1.5

33 5

5.8

5.0

35.2

0.5

Wheat-straw, . . .

14.3

85.7

81.8

3.1

37.5

1.2

40.0

3.9

Rye-straw, ....

14.3

85.7

81.6

3.0

33.3

1.3

44.0 4.1

.

.

Barley-straw, . . .

14.3

85.7

81.3

3.4

34.7

1.4

41.8

4.4

///. Roots and Bulbs.

Potatoes, . . . .

75.0

25.0

24.1

2.0

20.7

0.3

1.1

0.9

1.2

21.8

0.3

Fodder-beets, . . .

88.0

12.0

11.2

1.1

9.1

0.1

0.9

0.8

0.5

10.6

0.1

IV. Grains and Fruits.

Barley ....

13.8

86.2

84.0

11.2

65.5

2.1

5.2

2.2

8.0

58.9

1.7

Oats

13^7

86.' 3

83^6

12^0

56^6

6.0

9^0

2.7

9.0

43^3

4 0

Corn

12^7

87^3

85*6

10^6

65*7

6.5

2.8

1.7

8.4

60.6 4 8

Wheat,

14.' 3

85! 7

84^0

13^2

66^2

3.0

1.7

.

Rice,

13.7

86.3

86.0

7.8

74.5

0.2

3.5

0.3

.

.

Peas,

13.2

86.8

83.4

22.4

52.6

3.0

6.4

2.4

_

<

Beans,

14.1

85.9

82.8

25.1

46.7

1.6

9.4

3.1

23.6

50:2

1.4

V. Food- Products.

Oat-meal, . .

12 0

88 0

87.6

17.7

63.9

6 0

Corn-meal, ....

9.0' 91.0

89.5

is'. 2

70.' 5

3.8

0.9

Rve-rneal, ....

14 2 85 8

84.2

11.7

69.3

20

1 2

1.6

11.7

69.3

2.6

Rapeseed-cake, . .

11.5

885

81.5

31.6

29.3

9.6

11.0

7.0

25.3

23.8

7 7

Wheat-bran, . . .

13.0

87.0

81.0

14.5

53.6

3.5

9.4

6.0

11.8

44.4

3.9

Malt,

10.1

89.9

82.7

24.2

421

2.1

14.3

7.2

12.8

51.6

1.7

Brewers' grains, . .

777

22.3

21.1

46

9.9

1.6

5.0

1.2

3.9

11.8

0.8

Potato-mash, . . .

92.3

7.7

7.1

1.4

4.6

0.2

0.9

0.6

1.0

4.0

0.1

VI. Animal Foods.

Cows' milk, . . .

88.0

12.0

11.3

3.2

45

3.6

.

0.7

3.2

4.5

3.6

Skimmed cows' milk,

90.0

10.0

9.2

3.5

5.0

0.7

.

0.8

3.5

5.0

0.7

Goats' milk, . . .

78.0

12.0

11.0

3.4

4.3 3.3

.

1.0

.

Flesh

75.9

24.1

22.8

20.0

1.9

0.9

1.3

.

.

Meat residue (from

extracts), . . .

11.5

88.5

84.8

72.8

• •

12.0

3.7

69.2

• •

11.2

VEGETABLE FOODS.

185

cake is of a bright-yellow color. If dark in color it has either been
subjected to pressure while too hot, or has spoiled from being kept in too
moist a place, and hence is of poor quality. In good condition it should
have a pleasant, oily smell and a nutty taste, and should be hard and
dr3'. When in good condition such a fodder is readily taken by domestic
animals; although, especially if not perfectly fresh and of the first
quality, the cattle must be gradually accustomed to it. Under all cir-
cumstances it is advisable to administer it dry, mixed up with other
forms of fodder. In contact with hot fluids it develops an extremely
unpleasant taste. To milk cattle from three to five pounds, to draught
oxen three to four pounds, and to beeves six pounds for every thousand
pounds of body weight may be given. Sheep and cattle may receive
from one-half to one pound, and horses one to two pounds. An
additional advantage of this substance as a fodder is its great cheap-
ness.

The table on the preceding page gives, in the first eight columns,
the percentage composition of the various forms of food-stuffs which may
be employed for the nutrition of the herbivorous domestic animals. The
last three columns give the average degree of digestibility of their

organic constituents.

TABLE II.

PERCENTAGE CONSTITUENTS OP SOLIDS IN ORDINARY FODDERS.

FOODS.

Nitrogen-
ous Con-
stituents.

Non nitro-
genous
Extractive
Matters.

Fats.

Cellulose.

Ash,

Prairie grass, ....
Red clover,

12.0

18.4
11.0

52.4

42.8
46.9

3.2

3.8

2.8

24.0

28.0
31.6

8.4
7.0

7.7

15.7

43.1

3.7

30.0

7.5

4.8

41.5

2,5

46.0

5.2

Bean -straw, ....

12.1
8.0

38.4

82.8

2.0
1.2

40.5
4.4

7.0
3.6

Fodder-beets, . . .
Barley, .....
Oats

9.3
13.0
14.0

75.6
76.0
65.6

0.9
2.4
7.0

7.5
. 6.1
10.4

6.7
2.5
3.0

12.1

75.0

7.5

3.4

2.0

29.2

54.1

2.1

10.8

3.8

Rapeseed-cake, ....

35.7
13.7

33.2

80.5

10.8
'2.4

12.4
1.5

7.9
1.9

Wheat-bran, ....
Malt
Beer-mash (brewers' grains),
Potato-mash, .
Frpsh milk

15.8
27.0
20.7
18.1
26.6

61.8
46.8
44.4
59.8
37.4

4.3
2.3
7.1
2.6
30.0

11.0
15.9
22.4
11.7

7.1

8.0

5.4
7.8
6.0

Skimmed milk, ....
Flesh,
Meat residue (from extracts),

35.0
83.0
82.2

50.0

7.8

7.0
3.8
13.6

• •

8.0
5.4

4.2

186

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

TABLE III.

THE CONSTITUENTS OP FOODS, ARRANGED ACCORDING TO THEIR PERCENTAGE
COMPOSITION IN SOLIDS AND DIFFERENT NUTRITIVE PRINCIPLES.

PERCENTAGE OF
SOLIDS IN
FOOD-STUFFS.

PERCENTAGE IN THE SOLIDS OF

Nitrogenous
Constituents.

Non-nitrogenous
Extractive
Matters.

Fats

Cellulose.

Over 80 per cent.

Over 30 per cent.

Over 80 per cent.

Over 10 per cent.

Over 40 per cent.

Malt.

Meat.

Potatoes.

Fresh milk.

Oat-straw.

Meat residue.

Meat residue.

Rye-meal.

Meat residue.

Bean-straw.

Rapeseed-cake.

Rapeseed-cake.

Rapeseed-cake.

Corn.

Skimmed milk.

Bran.

Between 70 and

Oats.

80 per cent.

Barley.

Barley.

Beans.
Rye-meal.

Over 20 per cent.

Beets.
Corn.

Oat-straw.

Beans.

Between 5 and

Between 20 and

Hay.
Bean-straw.

Malt.
Fresh milk.
Beer-mash.

Between 60 and
70 per cent.
Oats.

10 per cent.

Corn.
Brewers' grains.
Oats.

40 per cent.

Prairie hay.
Clover-hay.
Red clover.

Bran.

Skimmed milk.

Prairie grass.

Beer-mash.

Between 15 and

Between 50 and

20 per cent.

60 per cent.

Clover.

Beans.

Potato -mash.

Grass.

Bran.

Skimmed milk.

Between 2 and

Between 20 and

Clover-hay.

5 per cent.

30 per cent.

Grass.
Potatoes.

Between 40 and
50 per cent.

Bran.
Meat.
Red clover.

Between 10 and
20 per cent.

MaH-

Flesh.
Brewers' grains.

Between 10 and
15 per cent.

Hay.

Malt.
Beer-mash.

Clover-hay.
Grass.
Hay.

iviai u.
Rapeseed-cake.
Wheat-bran.

Oats.
Rye-meal.

Clover-hay.
Red clover.

Oat-straw.
Barley.

Beans.
Oats.

Barley.

Oat-straw.

Rye-meal.

Bean-straw.

Malt.

Corn.
Grass.

Between 30 and

Beans.
Bean-straw.

Hay.

40 per cent.

Bean-straw.

Milk.
Oil-cake.

Under 10 per cent.

Under 20 per cent.

Red clover.
Beets.

Under 10 per cent.

Beets.

Under 10 per cent.

Under 2 per cent.

Beets.
Barley.
Potatoes.

Milk.

Potatoes.

Meat.

Potatoes.

Corn.

Potato-mash.

Straw.

Meat residue.

Beets.

Meal.

VEGETABLE FOODS. 187

The percentage of starch and sugars in fodders has been recently
investigated by Mr. E. F. Ladd, and he gives the following tables as
representing his results : —

No.

Substance.

Invert
Sugar.

Sucrose.

Per cent, of Nitrogen-
Starch, free Extract as
Sugars and Starch,

1.

Fodder-corn, . .

900

0.40

13.87

53.48

2.

Corn- fodder, .

2.50

1.43

22.88

53.32

3.

Sorghum, . . .

17.60

3.40

12.19

64.21

4.

Alsike clover, . fc '•

.

.

74.63

33.81

5.

Red clover, average

for 21, .

388

2.48

9.38

35.40

6.

Timothy, av. for 21,

2.23

6.21

19.72

55.69

7.

Prickly comfrey,

6.22

0.80

8.14

33.87

8.

Cactus, top,

5.92

9.96

30.00

9.

Cactus, stump,

2.80

3.60

17.10

41.12

10.

Meadow hay, .

m

f

24.32

49.32

11.

Wheat-straw, .

22,42

59.52

12.

Oat -straw,

23.18

51.14

13.

Oats,

53.20

81.05

14.

Wheat, .

1.64

2.36

57.91

76.37

15.

Wheat-flour, .

3.64

8.36

61.88

86.77

16.

Wheat-middlings, .

3.20

6.40

41.44

75.31

17.

Wheat-bran,

1.60

4.40

45.60

83.53

18.

Ship-stuff,

2.08

5.92

41.46

83.07

In red clover the following are the variations : —

Invert sugar, . . from 5 20 per cent, to 2.60 per cent.
Sucrose, . . . " 3.80 " 1.20

Starch, ..." 13.90 5.58

For timothy the following represent the highest and lowest per-
centages : —

Invert sugar, . . from 5.00 per cent, to 2.40 per cent.
Sucrose, . . . "7.60 " 4.68

Starch,. . . . "2261 " 17.55

The percentage of sugars and starch in timothy varies according as
the estimations are made : while in full bloom or after the seeds are
formed, but before they are fully matured. This is shown in the follow-
ing table : —

Per cent, of Nitrogen-
Invert Sugar. Sucrose. Starch. free Extract as

Sugar and Starch.

Early-cut, . . . 3.72 5.96 18.07 52.73

Late-cut, . . . 2.32 540 21.66 60.24

It thus would appear that as hays approach ripeness the per cent, of
sugar is diminished, while the starch is increased. Mr. Ladd was unable
to trace any relation between the per cent, of sugars and starch and the
kind of fertilizer applied to the soil, and was unable to confirm the usual
statement that a potash dressing increased the starch-contents of the
timothy.

188 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

II. ANIMAL FOODS.

The most important of the foods of animal origin are milk and
animal flesh, or meat.

1. MILK will be considered more at length under the Secretions,
details being given as to the composition and characteristics of the milk
of different animals. It is at present only necessary to refer in outline
to its composition to indicate in a general way its nutritive value. Milk
contains an average, in 100 parts, of 85.7 parts water, 5.4 parts of
albuminous bodies, 4.3 parts of fats, 4 parts of sugar, and 0.6 parts of
inorganic salts. Of the inorganic salts, potassium phosphate, calcium
phosphate, and potassium chloride are in greatest abundance, while
sodium chloride is in smaller amount ; iron has also been found to
be present. Milk, therefore, contains examples of all the different
nutritive principles, proteids, carbo-hydrates, fats, and salts, and these
arranged in the proportion which is best suited for nutritive purposes.
All mammals, in the earliest period of their extra-uterine life, are
nourished solely on milk, and their rapid growth and development in
this period is without doubt largely dependent upon the manner in
which the different food-principles are combined in milk. Milk, there-
fore, may be regarded as a tj^pical food. Buttermilk is the name
which is given to the fluid which remains after the fats have been
removed by churning. It is less nutritious than milk to the extent to
which the fats have been removed, but, all the other principles remain-
ing, it may serve useful nutritive purposes. It has an acid reaction,
from the fermentation of the milk-sugar into lactic acid. Cheese
consists of the casein and fats, the casein being coagulated, either
through the spontaneous development of acidity, when it is termed
a curd, or by the addition of the milk-curdling ferment from the stomach
of the calf. It therefore consists principally of albuminous bodies and
fats, the whey, in which the salts and sugar remain dissolved, being
largely forced out by pressure. It is hence well suited to form an
addition to foods which are poor in albuminoids and fats, as in certain
vegetables, such as potatoes and rice. The whey of milk contains the
sugar and lactic acid, which is developed from the fermentation of the
sugar, salts, and a certain amount of milk-albumen. It also has con-
siderable nutritive value, and seems especially to stimulate intestinal
peristalsis, and therefore to be, to a certain extent, laxative.

2. MEAT. — Next in value to milk as food comes the flesh of animals.
The nutritive principles of meat are contained within the muscle-fibre ;
the juice obtained by subjecting muscle to pressure contains myosin and
ordinary albumen, inosite or muscle-sugar, and glycogen, as representa-
tives of the carbo-hydrate group, while within the connective tissue

ANIMAL FOODS. 189

around the muscular fibres fat is nearly always to be found. Meat,
therefore, also contains members of the proteid group, carbo-hydrate and
fatty food-stuff's, together with a considerable amount of inorganic salts.
Hence, meat is also an excellent food. Albuminous bodies are in greatest
amount ; then come the fats, then the carbo-l^drates, and finally the
different salts. Ordinarily lean meat may be said to c'ontain an average
of 73.5 per cent, of water, 26.5 per cent, of solids (of which 21 per
cent, is albuminous and 1.5 per cent, gelatinous, 1.5 per cent, fats, 1
per cent, carbo-hydrates, and 1 per cent, inorganic salts). Of the latter,
three-fourths consist of acid phosphate of potassium, one- seventh of earthy
phosphates and iron, and about one-fifteenth of potassium chloride. The
flesh of different animals differs in composition, as is shown by the
following table : —

In 100 parts Flesh. Ox. Calf. Pig. Horse. Chicken. Fish (Pike).

Water,
Solids,
Albuminous bodies, .
Fats, ....
Carbo-hydrates,
Salts, ' .

76.7
23.3
20.0
1.5
0.6
1 2

75.6
24.4
19.4
2.9
0.8
1.3

72.6
27.4
19.9
6.2
0.6
1.1

74.3
25 7
21.7
2.5
0.6
1.0

70.8
29.2
22.7
4.1
.1.3
1.1

79.3
20.7
18.3
0.7
0.9
0.8

It is thus seen that meat is especially distinguished by its high albu-
minoid constituents, which amount to four times that contained in milk.
Chicken-flesh and that of other birds is richer in albuminoids than that
of mammals, while the flesh of fish is poorer, though even here 18 per
cent, of albuminous bodies is present. Meat alone forms the food of the
carnivora onty, and, as we shall find that carbo-hydrates may be developed
from the decomposition of albuminoids, carnivorous animals will, there-
fore, require an immense amount of albuminous bodies, and therefore a
very great volume of meat. If carbo-hydrates are added to the meat
diet of the carnivorous animals the volume of the latter ma}T be very
considerably reduced and still the animal preserve its nutritive equilib-
rium. In a diet of raw meat animals always run a risk of taking entozoa
or parasites, such as trichina, into their interior. The preparation of
meat by prolonged boiling destroys all the parasites, and therefore serves
to render even infected meat harmless. When meat is placed in cold
water the inorganic salts and a certain part of the albuminous bodies
(about 3 per cent.), together with the so-called extractives of meat,
such as kreatin, xanthin, and hippoxanthin, pass into solution along
with small amounts of lactic acid. When the water is warmed up to
45° C. a certain amount of soluble albuminoids undergo coagulation and
form coaguli, Mrhich float on the surface of the water. As the tempera-
ture of the water is increased the external surfaces of the meat first un-
dergo coagulation, and so prevent further escape of the muscle-juices.
Meat which has been subjected to prolonged boiling thus preserves a

190 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

considerable nutritive value, since it contains still 16 or 18 per cent, of the
albuminous bodies and a small quantity of nutritive salts, and is readily
digestible in the alimentary canal. If meat is placed in water which is
already boiling the external surfaces are at once coagulated and but little
of the nutritive juices escape, so that, therefore, meat so prepared has a
greater nutritive value than meat which is placed in cold water and then
graduall}T subjected to boiling. The more rapidly, therefore, the exter-
nal surfaces of the meat are coagulated, as, for example, by roasting, the
greater will be the proportion of nutritive substances retained. In roast-
ing the haemoglobin of the blood becomes decomposed, and the meat
then takes the characteristic brown color of roast meat, while at the same
time a number of aromatic substances, to which the peculiar odor and
taste of roast meat are due, are developed. By soaking meat in brine
putrefaction is prevented, but meat so salted loses a certain degree of
nutritive value from the fact that a considerable quantity of albuminous
bodies and extractive matters and salts pass into the pickling solution.
Smoked beef is protected from decomposition by the development of
phenol in the smoke ; this substance is an energetic preventive of decom-
position. Beef so dried preserves nearly all of its nutritive principles,
only having lost in water. Meat-broth obtained by boiling meat with
water has usually an acid reaction, from the lactic acid of meat, and con-
tains a greater part of salts and extractive matters of meat, together
with a certain amount of gelatinous albuminoids and a small amount of
fat. Meat-broth will contain about 1.4 per cent, of solids, but is of slight
nutritive value, since it contains scarcely any albuminoids or carbo-
hydrates, and but an extremely small amount of fats. It consists almost
solely of the extractive matters and salts, and is, therefore, simply of
value as a means of supplying the inorganic salts of meat. From the
extractive matters and the potassium salts present it is to a certain ex-
tent a stimulant, since it simply in this way produces a greater secretion
of digestive juices. Beef-tea, prepared by putting meat in cold .water
and gradually raising the temperature, has a higher nutritive value than
the commercial beef extracts from the fact that the soluble albuminoids
have time to pass into solution in the water before their temperature of
coagulation has been reached. The composition of meat will be given
in greater extent under the subject of Muscles.

Eggs, especially those of the hen, are also valuable nutritive articles,
containing also examples of all the different food-stuffs ; thus, one hun-
dred parts of egg, the shells having been removed, consist of 73.9 per
cent, water and 26.1 per cent, solids. Of the latter 14 percent, is
albuminoid, 10.8 per cent, fat, a small amount of sugar, and 1 per cent,
of inorganic salts, especially sodium chloride, potassium phosphate, and
a small amount of oxide of iron.

INORGANIC FOODS. 191

Eggs are also frequently used as food for calves and stallions when
rubbed up with the shells. To fattening calves three eggs ma}" be admin-
istered daily, rubbed up, shells and all, with their daily supply of milk,
and serve to give an especially pleasant flavor to their flesh. For stallions,
ten to fifteen eggs may be given with their usual food.

III. INORGANIC FOODS.

By inorganic foods are meant those inorganic compounds which
are found in the different tissues, secretions, and excretions of the
organism, which,, being essential to the vital processes of the organism
and being continually removed, must be constantly replaced. Inorganic
substances are indispensable to a proper nourishment of animals, but
they are not usually taken in their simple form, but as constituents of
animal or vegetable matter, or in the fluids which are drunk. Of the
inorganic foods, water, common salt, salts of lime and potassium, and
iron are indispensable, as they are the necessary constituents of the
blood, lymph, bones, and different tissues, and are continually being
removed in the nutritive processes of the econom^y.

1. WATER. — Water, as an alimentary principle, is taken into the
system, either alone as a drink, or in combination with articles of food;
in both of which cases it is also associated with a certain amount of
inorganic salts, as animals, unless pressed by great thirst, will refuse to
drink distilled water. For certain animals, such as rabbits and kangaroos,
which seldom or never apparent^ drink water, enough fluid for their
needs is contained in the succulent vegetables which serve as their
food; for if rabbits, for example, are fed on dry food, such as bran, they
will then require water, and will drink it like other animals. So also
sheep, which, as a rule, require but small amounts of water because
of the succulent character of their food, if in dry localities, or if
they are fed on dry food, will also hunt for water, like other animals
susceptible of thirst. Water not only carries into the system materials
capable of solution, but it holds matters in suspension which in some
cases may be nutritious, in others poisonous. The purest water is not
necessarily the best for animals or man, nor is dirty water necessarily
injurious. Drinking-water must possess certain qualities. It must be
fresh, clear, without odor, and of a certain taste. It should always con-
tain gases and mineral matter in solution, but be free from organic
substances. The presence of the latter, which are always injurious, may
be recognized by the addition of a small amount of potassium perman-
ganate solution to the suspected water, when, if organic substances are
present, the bright-purple solution will become a dirty brown. Drinkable
water should contain from 20 to 30 per cent, of its volume of air in

192 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

solution. It also should contain a considerable amount of carbon
dioxide, to which the flavor of water is due. The dispersion of these
gases by boiling gives to water a flat and disagreeable taste. The
inorganic salts held in solution in natural waters may vary within very
wide limits, both as to their nature and quantity ; ordinary drinkable
water contains about twenty-five to one hundred centigrammes of solid
residue per liter. Of this, carbonates, sulphates, alkalies, chlorides,
and earthy matters are the most constant constituents, although various
other substances, such as sulphur, iron, and lime, are contained in
waters of different localities, forming the so-called mineral-spring waters,
whose composition is subject to the very greatest variation,

2. NUTRITIVE SALTS. — Of the salts which are essential for the nutri-
tion of animals the most important is sodium chloride. This substance
enters largely into the composition of all animal tissues and fluids, and
when not supplied in proper amount produces great disturbances of nutri-
tion, and a morbid craving for it has often been noticed. The effects of
the deprivation of salts, -or the so-called salt hunger, willbe alluded to
under the subject of Nutrition. Even the administration of an extra
ration of salt is sometimes of advantage; thus, the experiment has been
made of feeding two bullocks on food which in one case contained a
daily ration of five hundred grains of salt, while no salt was supplied to
the other. For five months no very evident results appeared ; but changes
then commenced which were very marked, even to the unpracticed eye.
In the bullock to which the salt had been supplied the hair was smooth
and glistening, and in the other rough and tarnished. This distribution
Of salt in the diet was continued for a year, when the animal which had
been kept without salt had a rough and tangled hide, with patches where
the skin was entirely bare, while the other, to whom five hundred grains
of salt had been supplied daily, had all the appearance of a healthy, stall-
fed animal, was much more vivacious, and would have brought a much
higher price in the market.

In addition to sodium chloride, phosphates, carbo-hydrates, and sul-
phates are also of great nutritive value, and are required for the main-
tenance of a proper nutritive condition of the animal. Carnivorous
animals receive a proper supply of phosphates in the animal foods,
especially in bones, whereas the herbivora derive them from the grasses
on which they feed. Phosphatic manures owe their value largely to the
contribution of phosphates which they make to the soil, and hence to
the grasses grown on them. The lime salts, as has been already indi-
cated, are essential for the development of the solidity of bones, and
when reduced in amount lead to various deformities of the bony
skeleton. Even suckling animals receive in the milk of their mothers
when normal a sufficiency of these inorganic matters ; thus, a suckling

DIET OF ANIMALS. 193

calf receives daily fifty-two grammes of inorganic matter in the milk
of the mother, and a calf six months old appropriates in its fodder
an amount of phosphoric acid corresponding to thirty-six grammes of
calcium phosphate ; while a horse fed on hay and oats receives daily
about one hundred and sixty-eight grammes of calcium phosphate.
Occasionally animals are seen to eat earth. This, with the exception in
the case of birds, where gravel is required to assist in the comminution
of the food in the gizzard, is to be explained by the insufficiency of inor-
ganic matter in the food. Thus, the earth-eating Indians in South
America are said to consume earthy matters from the fact that their
corn is poor in salts.

IV. THE DIET OF ANIMALS.

The complexity of food-stuffs is essential to the sustenance of
the organism. The food must contain albuminoids for the recon-
struction of the tissues, carbo-hydrates and fats for calorification
and the formation of adipose tissue, and the saline matters for the
different secretions and tissues. If any one of these food-constit-
uents is not represented in the diet, the food, even although in
excessive amount, will be incapable of preserving health. Experi-
mentation has proved that single alimentary principles will not sustain
life. Magendie showed long ago that dogs fed exclusively on non-
nitrogenous substances, such as sugar, gum, olive oil or butter, in a short
time died of marasmus, the appetite soon being lost, ulcerations forming
on the cornea, and death occurring with all the symptoms of starvation
after about four weeks. After death all fat was found to have disappeared
from the body ; the muscles were atrophied ; the urine alkaline and
deprived of uric acid and phosphates, so as to resemble the urine of her-
bivora. Similar results were obtained whether the animals were fed with
oil, with gum, or with sugar alone. Any one of these substances was
found to be incapable of sustaining life. Objection might naturally be
urged against these experiments that the dog being a carnivorous
animal, a diet of non-nitrogenous food was not adapted to his nutritive
needs ; but the repetition of Magendie's experiments by Tiedemann and
Grmelin with the goose, by feeding on gum arabic and water, sugar and
water, and raw or uncooked starch, overcomes the force of this argument.
In all cases death occurred in from two to three weeks with all the
symptoms of starvation, even though the examination of the excreta
proved that the substances given had been digested. In all cases the
appetite gradually failed, diarrhoea set in, and death occurred .from
exhaustion and starvation. It thus seems clear that, even though
digested, a non-nitrogenous diet alone will not sustain life, either in the
carnivora or in the herbivora. A similar state of affairs holds for

13

194 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

nitrogenous diet. Dogs fed exclusively on gelatin soon refuse to take
it, and die of hunger. Fibrin alone will also not sustain life, death
occurring on the fortieth to the eightieth day, while albumen, whether
raw or cooked, if given alone, has been found to be incapable of sustain-
ing life even as long as fibrin. Gluten alone has been found capable of
sustaining life, probably because it is not a pure nitrogenous matter and
always contains starch, vegetable albuminoids, and salts ; so that, there-
fore, the experiments made with gluten, in which nutrition seemed to be
tolerably well preserved, will not disprove the general statement that
single nutritive principles are not capable of sustaining life. Finally,
again, a mixture of nitrogenous matters, such as fibrin, albumen, and
gelatin, although more nutritious than when any one of these is given
alone, is always incapable of supporting life for more than about four
months.

These results show that a simple, easily - digestible substance,
whether nitrogenous or non-nitrogenous, alone is incapable of supporting
life. An aliment must contain the four groups of nutritive principles
given above. Blood, meat, grasses, and grains are aliments, any one of
which, when taken alone, will sustain life. Thus, milk contains casein,
an albuminoid, together with albuminous bodies allied to serum-albumen,
which supply nitrogenous elements necessary for tissue development. It
contains sugar and fats for producing heat, and it contains salts in
amounts required for the development of all the tissues. Hay, again,
and grasses always contain a mixture of several kinds of plants, their
stems, leaves, and seeds always containing vegetable albuminous matters,
sugar, starch, mineral salts and fats. Observation has, however, shown
that the association of different alimentary substances already complex is
favorable to nutrition, not only by the different degrees of stimulation
which they exert on the different portions of the digestive tract, but by
the variety of nutritive matters which they render for absorption. A
number of apparent exceptions seem to offer themselves to the truth of
this statement ; thus, where we find birds feeding almost solely on a
single article of food, and alwa}^s maintaining a high state of nutrition ;
and yet it only requires a little reflection to show that such foods are
invariably themselves highly complex, and contain within them examples
of all the different food-stuffs. So, also, the larger ruminants will thrive
on a prolonged diet of any one single food; and yet here, also, the only
foods on which nutrition may be so preserved must be those which con-
tain examples of all the different food-principles.

It is not only necessary that an aliment should contain all the differ-
ent food-principles, but that they should be present in considerable quan-
tities and in definite proportions ; otherwise nutritive equilibrium will be
destroyed. The essential relations between the relative proportions of

DIET OF ANIMALS.

195

these different food-stuffs will be discussed when we consider the nutri-
tive value of foods.

We may, however, here call attention to the fact that in an animal
in whom no excessive demands for work are made a proportion of one
part of nitrogenous to eight of non-nitrogenous food-stuffs will be sufficient
to maintain the body weight. When, however, the animal is worked,
then the proportion between nitrogenous and non-nitrogenous food must
be increased from 1:5 to 1:3. The following table, after Liebig, shows
the proportion of nitrogenous to non-nitrogenous principles in some
of the most common foods : —

Cows' milk,
Beans and peas, .
Ox-flesh, .
Pigs' flesh,

1
1
1
1
1

2 to 1 : 4
2
1.7
3
1

Potatoes, .
Oatmeal,
Wheat-flour,
Rve- and barlev-mea

1
1
1

10
5
4.6
5.7

The aliment which is well adapted to nourish one species of animal
is not necessarily suitable for another. Thus, a vegetable food which
furnishes the maximum of its nutritive principles to a ruminant, which
is capable of perfectly dividing it and retaining it for a long time in its
complicated gastro-intestinal apparatus, will be of little value to such an
animal as a horse for the directly opposite reasons. Further, the food
which may be nutritive for an animal with a perfect masticatory appa-
ratus will be useless to one in whom the teeth have not appeared or have
been lost ; or it may serve for a beast of burden which has need of blood
and tissue producers, and not for a fattening animal, or a cow kept
entirely for milking. The alimentary ration must correspond to the
losses of the organism, and must, therefore, be proportionate to the work
done and the animal's size ; thus, a man under ordinary circumstances
requires 20 grammes of nitrogen and 330 grammes of carbon daily, rep-
resented by 1000 grammes of bread and 286 grammes of meat. The
horse needs 7500 grammes of hay and 2270 grammes of oats, representing
10 kilo of hay and 2 kilo of oats for every 100 kilo of body weight. Loss
of weight occurs if this daily ration is reduced only one-tenth. For the dog
40 grammes of meat are necessary for each kilo of body weight, and here
also the animals lose flesh if these rations are decreased only one-tenth.
If the bodily losses are increased by work or by the secretion of milk,
or if the animal is in the growing period, when the size and weight of the
body should increase, it is also indispensable that these rations should
increase. In cases where extraordinary demands are made on the forces
of the animal, as in beasts of burden, the supplementary foods are then
to be given, in small volume, and should then be of extremely nutritive

196 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

nature in concentrated form, so as not to tax the digestive organs. Thus,
for workingmen meat shoulcl represent the accessory rations ; for horses
oats is the suitable form. For if the extra food is given to the horse in
grasses it becomes impossible to work him because of the overdistension
of the alimentary canal necessitated by the greatly increased volume of
food required. Again, in fattening animals or in animals kept for milk-
ing purposes the diet must be rich, in albumen, in fats and carbo-hydrates.
Equivalent values of different amounts of different foods cannot be deter-
mined by chemical analysis alone, as will be shown when the nutritive
A^alues of the different foods are considered. That two foods should
have the same nutritive value they should contain equal proportions of
nitrogenous matters, carbo-hydrates, salts, etc., in equal volumes. They
should possess equal stimulating properties to the digestive tract, and
should be of equal digestibilitj^. It is a general rule that animal matters
are more nutritive than vegetable matters, bulk for bulk. They are,
further, more varied in composition, and are more readily assimilated.

The mode of diet suitable for different animals, the character of
their food and its nature, varies very widely in different classes of ani-
mals, whether carnivorous, herbivorous, or omnivorous. Each of these
classes has a special mode of alimentation, as especially emphasized by
Colin, which is governed by the characteristics of its digestive organs.
In each of these three groups of animals a number of subdivisions may
be established. Thus, among the carnivora there are animals which only
eat living prey ; others, only decomposing animal matter ; others, again,
only insects.

Among the herbivora, some only eat grasses; others, only grains;
others, roots and leaves, etc. The mode of alimentation suitable to each
of these species is closely dependent upon the digestive organs of each,
and governs its habits, instincts, and characters, and is dependent largely
upon the modes which it possesses of attack and defense.

The carnivora, especially those belonging to the group of mammals,
have a strikingly characteristic organization. Their incisor teeth are cut-
ting, their canine teeth long and pointed, as are also the cusps of their
molar teeth. Their jaws are short ; their masseter and temporal muscles
enormously developed, lodged in deep temporal fossae, and attached
to highly-curved zygomatic arches ; their oesophagus dilatable ; their
stomachs large ; their intestines short and simple, and their caeca small
or absent. Their feet are divided and furnished with more or less pointed
claws. They are admirably organized for the discovery of their prey by
acute sight or acute sense of smell or hearing ; their agility or cunning
enables them to surprise and seize their prey, and their strength to tear
it to pieces; while their jaws are powerful enough to crush the bones,
and their gastric .juices powerful enough to dissolve them. Such animals

DIET OF ANIMALS. 197

are the lion, the tiger, the jaguar, and all cats. The carnivora which
feed on living prey are always ferocious. Those which feed on dead
nnimal matter are usually cowardly, as the vulture, hyena, jackal, etc.
As a rule, they seek their prey alone and seldom hunt in flocks or
herds. They differ in their manner of searching for food. Some lie in
wait for their food and surprise it, others chase it ; some feed almost
solely on fish, others on mammals. The general rule, however, holds
that animals seldom, if ever, feed on their own species. Carnivorous
animals invariably devour the herbivorous. There are, however, many
exceptions to this ; thus, swans have been said to eat their own kind ;
ducks and ravens are said to have eaten birds of their own species ; while
it seems well established that wolves and rats both destro}T each other
for food ; so. also, the sow has been known to eat her young ; but all
these are merely exceptions to the general rule that animals, even when
pressed by the most extreme hunger, refuse to devour flesh of their own
species. These animals differ greatly in their mode of devouring their
food. Some consume their prey when freshly killed; others simply con-
sume the blood ; some wait until decomposition has commenced; while
many bury the remains, to wait until again pressed by hunger.

Among carnivorous birds we always find a mode of prehension of
food suitable to the character of their diet. Insect-eating birds have, as
a rule, long, narrow beaks, with prehensile tongues. Fish-eating birds
have beaks which enable them to seize and consume their prey.

Herbivora are of a very different organism from carnivora. Their
molars are flat, or have tuberculated crowns ; their jaws are longer, more
slender, and less strong ; their stomachs are always more ample from the
fact that in vegetable food the nutritive principles are in less relative
bulk than in animal food ; their intestines are larger, longer, and more
complicated, and often have special diverticulse for the retention of food ;
their senses are not as delicate as those of the carnivora. The}", as a
rule, want means of aggression, while the instincts, courage, and cunning
of the carnivora are absent. While many of them are provided with
defensive organs, as a rule they depend upon their speed for their pro-
tection.

Herbivorous animals are divided into the grass-eaters, the herbivora
proper; the granivora,OY seed-eaters; the fructivora, or those which feed
on fruits. Of the large herbivora, the solipedes, of which the horse and
ass are examples, and the ruminants, are the most prominent examples.
In the savage state they live exclusively on herbs and leaves, and never
eat roots or fruits. Others, such as the hippopotamus, rhinoceros, and
the elephant, prefer roots, but eat leaves and herbs, and in the domestic
state all may^ live on dry forage. Others belonging to this same group,
such as the castor and beaver, and the rodents generally, will eat the bark

198 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of trees. All the herbivora are possessed of instincts which enable them
to select the vegetable foods which are most suitable for them, and will
reject others. Thus, it has been found, as mentioned by Colin, who has
made a close study of this subject, and to whom the author is largely
indebted, that a horse will eat 262 different kinds of plants, and has been
seen to reject 212 ; the ox will eat 275 and refuse 218 ; the sheep will eat
387 and refuse 141 ; the hare will eat 449 and refuse 125 ; and the pig,
which is omnivorous, and yet which can be sustained by vegetable food,
has been found to devour 172 different kinds of vegetable matter and
reject 171. Different circumstances, such as changing seasons or migra-
tion from different localities, may compel them to feed on plants which
are otherwise ordinarily refused. Their instinct leads them, further, to
avoid venomous plants when mixed with other plants, or unless greatly
pressed by hunger. Different plants are poisonous articles of food to
some animals, while other plants are poisonous to others. Here it is only
necessary to mention that the ox and rabbit may eat belladonna with
impunity, the goat hemlock, the horse aconite, while goats and sheep
avoid most of the solanacese.

The omnivora are permitted, by their organization and instinct, to
devour both kinds of food, and, as a consequence, their habits are not so
sharply characterized as either of the two above-mentioned groups. They
ma}r live either on exclusively animal or exclusively vegetable diet, accord-
ing to circumstances. The pig, the rat, gallinaceous fowls, flat-footed
birds, the raven and crow are all omnivorous. Many animals placed
among this species from the characteristics of their organization appar-
ently belong to the carnivora, such as the bear, the fox, and dog ; and
these animals are also omnivorous, although to a less-marked degree than
the preceding examples. The hog and wild boar live on roots, insects,
and reptiles. Rats and mice, strictly speaking, are. omnivorous, since
they devour ever}Tthing that comes within their reach.

The duck, which ordinarily seeks aquatic regions, where it can feed
on tender vegetable shoots and small aquatic animals and insects, may
also be brought to live on a purely vegetable or even a purely animal diet.
Also, the fox will live on fruits when animal food is not accessible. Bears,
while distinctly carnivorous in their type of organization, are also omniv-
orous animals, and will often live exclusively on roots, honey, etc. So
the sea-otter may be brought to live 011 vegetable matter when fish cannot
be obtained. The dog, again, is strictly carnivorous in its organization,
and yet can live on purely vegetable matter, and in its state of domesti-
cation this diet seems to suit him best. A great number of animals
belonging to these species have distinct tastes for certain mineral sub-
stances, especially common salt; and this is, above all, marked in the
herbivora, which perish when deprived of salt, and, as is well known, will

DIET OF ANIMALS. 199

seek salt, and congregate at certain periods of the day at points where
salt is to be found, and will eat earth when sodium chloride is not to be
obtained. This, as already mentioned, is to be explained by the fact that
vegetable matters are poor in sodium salts and rich in potassium salts.
So, also, the granivorous birds will devour gravel, stones, and sand from
an instinct which leads to their taking such substances into their gizzard
to enable them to properly triturate their food ; for, in the granivorous
birds, the nutritive principles of the seeds are inclosed within dense mem-
branes. They are not provided with teeth for the mastication of food,
and, were no means supplied for crushing or triturating their food,
would starve to death with their stomachs full of the most nutritious
seeds.

The diet most in harmony with the organism, teeth, alimentary
canal, etc., of animals may be modified if the force required of animals
is increased artificially. Thus, the horse in a state of nature is never
granivorous or fructivorous, but only eats herbs ; when in the service of
man grains are necessary to reduce the bulk of food, for horses cannot
work if their stomach or alimentary canal is distended with forage. By
the administration of oats the duration of the feeding time and of the
period of digestion is reduced. There is economy of the digestive secre-
tions, the stomach is much less distended, and there is less time required
for digestion ; hence, herbivorous animals in domestication become
largely granivorous, and oats form a large portion of their food, for oats
are always nutritious in small bulk and readily digested. They eontain
all the food-elements in suitable proportions ; the large amount of nitro-
gen which they contain render them particularly suitable for repairing
waste in the muscular system, especially when work is demanded of them.
Oats nourish, therefore, without fattening. Since the process of diges-
tion in the herbivora and carnivora, and the ultimate nature of their
food-stuffs is identical, it is natural to suppose that their nutritive habits
may be changed ; thus, the herbivora may be brought to feed on animal
matter, while the carnivora may be led to feed on matters of purely vege-
table origin. Numerous facts of this kind have been over and over
again reported. The most striking of all is seen in the results of the
domestication of the common cat. Here a typical carnivorous animal
by education and habit becomes almost herbivorous. So, also, pigeons
have been accustomed to eat meat to such a point that they will after-
ward refuse seeds. In Iceland, where vegetation is sparse, the native
horses arid oxen have been seen to feed upon fish, and it is even stated
that they have been seen to enter the water and fish for themselves. The
starting point of this change from the herbivorous into the carnivorous
t}rpe is found in the fact that all animals after their birth are carnivo-
rous ; for in suckling animals there is but little if any difference in their

200 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

organism from that of the carnivora. Even in such a typical group of
herbivorous animals as the ruminants we find that in them, when new-
born, the complex stomach is rudimentary and their alimentary canal
differs but little from that of the carnivora, simply foreshadowing what
will ultimately be developed when the animals are placed upon a purely
herbivorous diet. Among the carnivora the most typical examples will
sometimes refuse vegetable nourishment, and the tiger and lion and the
eagle have been known to die of starvation rather than touch it ; never-
theless, an eagle has been educated to eat and digest bread. The native
repugnance to certain foods is often overcome b}7 cooking, and it is with-
out doubt to this circumstance that man is omnivorous in character.
Thus, dogs and cats do not eat corn, but they will eat bread. This is,
however, in all probability to be explained by the fact that the uucrushed
seeds are incapable of digestion by carnivorous animals, since their
organs of mastication do not permit of the liberation of the nutritive
principles from their undigestible envelopes. Cooking, nevertheless, does
lead many animals to eat food which is unnatural to their species ; thus,
the rabbit will refuse raw meat, but will often willingly accept and digest
boiled meat. Certain animals are both carnivorous and herbivorous.
This is especially illustrated among the birds, where some are fructivorous
in winter and insectivorous in summer ; so the small fructivorous monkey
will eat insects and seek for eggs and little birds scarcely hatched. Even in
the same groups of animals some are carnivorous and some herbivorous ;
thus, among plantigrades and the cetaceans we have examples of each.
It is worthy of notice, however, that when forcing the diet is arrested
and animals are restored to their native state, they will again return to
their natural food. The herbivora forming the food of the carnivora,
and feeding themselves on vegetable matters for the maintenance of
their species, must consequently be in excess of the carnivora.

We thus see that the choice of food is controlled by the animal's
habits and appetites. Herbivorous quadrupeds graze and consume
grasses, bulbs, and grains suitable to the organs of their digestive
apparatus, while the carnivora devour the flesh of the herbivora, and
show aversion to the carcasses of animals allied to themselves in their
habits. An artificial mode of existence forces on animals predilections
which in a state of nature are not observed. In nature they are essentially
moderate in their desires, but when domesticated will eat what they
would in a state of nature avoid, and never appear to be satisfied,
devouring much more than when in the field, filling themselves to
repletion. In their natural state the exercise connected with the selection
of food is of great importance to the health of the herbivora. They
cannot fast long, like the carnivora, nor can they in a single meal con-
sume enough to enable them to pass hours or days in a state of torpor

DIET OF ANIMALS. 201

with a distended alimentary canal before again called upon by the
demands of hunger. The domestic animals will sometimes kill them-
selves by overeating when food is continually placed before them, but
that is only when they are from their surrounding circumstances relieved
from traveling for food and water ; where their time is not, therefore,
largely occupied in exercise and in watching for disturbing causes. So,
if treated artificially, animals should be managed according to their
habits. The collection of food further varies in our different domestic
animals : one bolts flesh and coarsely-ground bones, to be deposited in a
capacious stomach ; another rapidly swallows large volumes of food and
lodges it for awhile in a crop or paunch, to be again regurgitated and
masticated at leisure. The fowl crushes its food beyond the crop or
stomach in the gizzard. The ox swallows large volumes of food which
have been subjected to scarcely any mastication, to return them at leisure
to the mouth to be remasticated. The horse collects and at once
thoroughly grinds and mixes food with saliva, and rapidly passes it from
its stomach to its intestines without the functions of rumination. Habit,
therefore, materially influences the collection of food, its retention, and
appropriation to the wants of the animal, and is itself governed by the
type of the organization of the digestive tract (Gamgee).

On the basis of the above considerations we may indicate in a general
wa}r the fundamental principles which must underlie a rational system of
feeding. In the first place, it is evident that the daily ration must be
appropriate to the normal mode of feeding and digestive peculiarities of
the species ; further, the digestive power in different animals varies not
only in different species for the same food, but it varies in different indi-
viduals of the same species of different ages. The capacity of the
stomach must be considered, that the appetite may be satisfied without
the stomach being overloaded. Experiment has proved that the solipedes
should receive daily 2 per cent, of their body weight in solids, and rumi-
nants 2J per cent, of their weight.

In the second place, the food must be adjusted with special reference
to the demands which are made upon the animal economy, whether for
work, fat, or milk production. Special directions for so adjusting the
rations will be given after the composition of the food-stuffs and the
nutritive changes occurring in different animals in various conditions
have been considered. It may be here mentioned, however, that good
hay is taken as the type of a food for the larger herbivora, and that it
shows a nutritive proportion of one part of nitrogenous matter to 4.8
parts of non-nitrogenous constituents, cellulose being disregarded. This
proportion, therefore, represents the normal relation between the nitroge-
nous and non-nitrogenous matters in the natural diet of the herbivora ;
and although this proportion under certain circumstances may be widened

202 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to 1 : 8 or contracted to 1 : 4, the digestibility, and therefore the nutri-
tive value, of the fodder is interfered with if these limits be passed.

In the case of hay, again, the amount of fatty constituents is to the
nitrogenous matters as 1 : 3.7. If this proportion be contracted to 1 : 2.2
the horse will still be able to accomplish its normal amounts of work ; but
if reduced below this for the horse, or below 1 : 3 for the ox, the full
nutritive value of the food will not be appropriated. These figures, of
course, refer to the digestible percentages of the fodders, and by referring
to the tables of the composition of the different food-stuffs, which will be
subsequently given, it will be found possible to construct dietary tables
according to the demands on the animal economy.

It may thus be added to the general statements which have been
made in the early parts of this section that not only must all animals
receive representatives of the different food-constituents, but that the
herbivora must not receive more than eight or less than four parts of
non-nitrogenous matter to one of proteid, and not less than two parts
of proteid to one of fat.

SECTION II.
DIGESTION.

I. GENERAL CHARACTERISTICS OF THE DIGESTIVE APPARATUS.

DIGESTION is the preparation of food for absorption, and is usually
accomplished by the introduction of the food into a special cavity com-
municating with the exterior, where it undergoes such changes as will
enable it to pass through the walls of the blood-vessels. Foods of
animals, as alreacty shown, are usually solids ; that they may be ab-
sorbed and enter into the blood of animals they must first be reduced
to a fluid condition; this solution is the object of digestion and is
accomplished by means of the different secretions poured out by the
alimentary canal. It is evident, therefore, that the alimentary tract must
consist of a cavity to contain these digestive fluids ; must communicate
with the exterior to permit of the entrance of food and removal of
indigestible residue ; that it must be provided with motor organs for
determining the entrance of food, and that its walls must be capable
of elaborating digestive secretions and absorbing the results of the
digestive process. Digestion, therefore, includes a number of complex
processes : the prehension of food and in many cases its mechanical
comminution or mastication by special organs; secretion, or the mode
of production of the digestive fluids ; absorption, or the means of con-
veyance of the digestive products into the blood stream; and finally
defecation, or the expulsion of the non-nutritious residue. If the
digestive tract is considered from the point of view of these different
purposes, it will be found to be very differently constituted in different
members of the animal kingdom, its state of development governing the
complexity of all accessory organs.

In the higher animals it consists of the mouth, the pharynx, gullet,
stomach, intestine, and anal aperture. In its development it is found
to be simply a continuation of the external surface reflected inward as
we would turn in the finger of a glove. Consequently, in the gradual
evolution of the alimentar}' canal from its simplest to its most com-
plex form, we find every grade of such reflection, from a mere depression
in the external surface, as in the amoeba, to the long and complicated
intestinal tube of the ruminant. In all cases this is the mode of origin
of the alimentary canal ; consequently, food, when within the alimentary

(203)

204

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

canal, is still practically in contact with the external surface, and, there-
fore, still outside the body. To enable it to pass through the walls of
the digestive cavity into the circulatory system is the object of diges-
tion, and we shall find that this is accomplished by the production of
more or less profound chemical changes in the food-constituents.

The length, capacity, and complexity of the digestive canal are
governed by the complexity of the food. Yegetable feeders, therefore,
of all classes of animals, have a more highly developed alimentary canal
than animals of the same class which feed on animal food. With this
modification, the statement may be made that there is a gradual in-
crease in complexity of the digestive organs as the animal scale is
ascended.

In the amoeba we find the simplest possible representative of a
digestive function. When alimentary substances come in contact with
i

FIG. 56.— PARAMCECITTM BITRSARIA, AFTER STEIN. (Huxley.)

1. The animal viewed from the dorsal side. A, cortical layer of the body ; B, nucleus ; C, contractile
chamber: D D', matters taken in as food : E, chlorophyll grannies.

2. The animal viewed from the ventral side. A, depression leading to B, mouth : C, gullet : D,
nucleus; D', nucleolus: E. central sarcode. In both these figures the arrows indicate the direction of
the circulation of the sarcode.

, 3. Paramoecium dividing transversely. A A', contractile spaces; B B', nucleus dividing;
C C', nucleolus.

the soft external surface of the amoeba a temporary depression or
pocket forms around them, and b}r the gradual deepening of this de-
pression and closing of a wall around it a cavity is formed and the
alimentary substances gradually brought to the interior of the mass.
Within this temporary chamber the alimentary substances are removed
and appropriated, while the undigestible residue is removed by a process
the reverse of that concerned in its introduction. The amoeba there-
fore has, strictly speaking, no digestive organs, but it temporarily de-
velops a cavity at the point of contact with the food.

In certain of the infusoria, such as the paramcecium, we have a
single portion of the external body surface specialized as the orifice of
entrance for the food-stuffs. An oral aperture (which in this illustration

CHAEACTEKISTICS OF THE DIGESTIVE APPAKATUS.

205

is bordered by cilia) is, therefore, the first point of specialization of
the digestive tract. No digestive tube is, however, yet present, but the
orifice in the walls of such an animalcule communicates directly with a
central body-cavity, and the orifice of entrance and exit of the food is
the same (Fig. 56).

In the hydra there is a definite oral aperture, or mouth, leading to
a permanent body cavity, and this opening serves also for the inlet of
food and the outlet of the undigestible residue. The hydra has, how-
ever, advanced a step in specialization, since it is provided with definite
prehensile organs (tentacles) for the seizure of food (Fig. 57).

There are apparently, however, no true digestive secreting organs in
the hydra, since the internal body cavity appears to be strictly the same
as the external surface. Hydrse have even been everted, so as to make

FIG. 57.— HYDROZO A. (Jeffrey-Bell. )
A, hydra viridis attached to duck-weed ; B, a single specimen

magnified; C, hydra in diagrammatic section.

E C, ectoderm : E N, endoderm ; M, mouth ; B C, enteric

cavity ; T, tentacles.

FIG. 58.— FLTTSTRA. DIAGRAMMATIC
SECTION OF A SINGLE CELL, OF
FLUSTRA, OR "SEA-MAT" (GREATLY

MAGNIFIED). { Wilson.)

A A, ciliated tentacles ; B, mouth ; C, gullet ;
D, stomach; E, intestine: F, anus; G. nervous
ganglion : H H, general body cavity ; I, testis ; K,
ovary ; L«, ectocyst, or outer membrane of body ;
M, endocyst. or inner membrane of body ; N. re-
tractor muscle, by the action of which the animal
can withdraw the ciliated tentacles.

the original outside surface the lining surface of the digestive cavity, and
digestion was still quite as efficiently performed. Similar types of digest-
ive organs are seen in sponges and in the jelly-fish. In the latter,
however, a step still further has been made in the development of chan-
nels for the distribution of the nutritive substances.

A true alimentary canal should have two openings, one for the
ingress of food, the other for the egress of excreta. The simplest form
of such an .organ is seen in the flustra, or sea-mat, and in the sea-urchins
(Fig. 58.) In these organisms both the mouth and the vent develop con-
stricting muscles. In the animals of which the worm is the type (Figs.
59 and 60), the digestive tract is either a straight tube running from one
end of the bod}r to the other, or it ma}T be divided into little pouches or
saccules. as in the leech (Fig. 61).

206

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

•M

In the myriapods and larvae the same general plan is continued, the
alimentary canal still being a simple tube passing from one extremity
of the body to the other, with an oral orifice and vent, but in these
animals showing a division into gullet, stomach, and intestines (Fig. 62).
A difference is also met with according as the animals are carnivorous or
vegetable-feeders. In the former the canal is narrow and nearly straight,
with a slight dilatation representing the stomach,
while in the herbivorous species it is complicated
by saccular pouches to delay the onward progress
of the food. In the tunicata the division of the
alimentary canal into gullet, stomach, and intestines
is more marked, since we have in them a distinct
O3sophagus, stomach, small and large intestines. In
the crustaceans there exists a definite digestive
apparatus, with the first appearance of distinct
glands having for their function the secretion of
digestive juices, crustaceans especially having a
voluminous liver which secretes a yellowish-green

fluid of the nature of bile. In the crustaceans
•CG

OES

CP

FIG. 59. — DIAGRAM OF
THE ALIMENTARY CA-
NAL, OF AN EARTH-
WORM, AFTER BAY
LANKESTER.

M, mouth; PH. pharynx;
OES, oesophagus; CG, calcare-
>us glands; CP, crop; G, giz-
zard ; I, intestine.

FIG. 60.— TRANSVERSE SECTION OF EARTH-WORM TO SHOW
POSITION AND RELATIONS OF THE INTESTINES, AFTER
CLAPAREDE. (Jeffrey- Bell.)

A, cuticle; B, hypodermis; C, layer of circular muscles: D, layer of longitudinal
muscles; I, enteric cavity; M, "green layer; " N, dorsal vessel; O, liver.

the liver has become a symmetrical, lobulated organ, instead of the
numerous small folliculi which are found in earlier forms around the
alimentar}^ canal, and which pours its secretion into the upper part of
the intestine. In the higher crustaceans, such as the crabs and lobsters,
there is a short, wide sac, provided with internal hard, calcareous dent-
icles, which serves the purpose of a gullet, stomach, and gizzard. The

CHAKACTEKISTICS OF THE DIGESTIVE APPAKATUS.

207

intestine is short, nearty straight, and simple ; sometimes it is also pro-
vided with caeca. In insects there is a great variation in the form and
length of the canal, depending on the stage of metamorphosis ; nearly

FIG. 61.— DIGESTIVE
CANAL OF THE
LEECH (Sanguisuga
medicinalis), AFTER

NUHN.

oe, oesophagus: v, stom-

FIG. 62.— VISCERA OF A CATERPILLAR. (Rymer Jones.)
GH. oesophagus: HI, stomach; IM, intestine: K, biliary vessels: QR, salivary

ach; vt, cascal appendages; glands: P. salivary ducts; ABC, trachea; D E E E E,' air-tubes ; FFF, epiploon, or
r. rectum ; a, anus. fat-mass ; V X Y, cjeca.

208

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

always, however, a gullet, craw, gizzard, large and small intestines, and
numerous glandular appendages may be recognized (Fig. 63).

In the vermiform larvae the alimentary canal is a straight tube passing
from one end of the body to the other, the dilatations which represent
the stomach and crop appearing later. Caeca are also then present, and
there is hence a division into small and large intestines. In mandibulate

insects, as in the wasps and beetles,
the crop and stomach are glandular,
and the gizzard, unlike that of birds,
is placed above the stomach, and
has muscular walls and a chitinous
lining-membrane. In insects the
form of the liver has again returned
to that of long, slender tubes, pouring
their secretion into the intestine,
and which are believed to represent
biliary canals (Fig. 63). In carniv-
orous insects the crop and gizzard
and large intestine are less developed
than in those which feed on vege-

Fio. 63.— DIGESTIVE APPARATUS OF HONEY-
BEE (Apis mellifica), AFTER LEON Du-
FOUR.

rjl, salivary gland; rjlv, poison-gland: »(, sting; oe,
oesophagus ; vm, vasa malpjghii ; c, colon ; r, rectum ;
ingl, crop.

FIG. 64.— ANATOMY OF THE OYSTER.

(Perrier).

F, moxith ; E. stomach : I. intestine ; A. anus ;
GG', nervous ganglia; MT, mantle; B, branchiae.

table food, thus indicating in them the first appearance of the distinction
between the herbivorous and carnivorous animals, showing that the com-
plexit}'" of the alimentary canal is in direct proportion to the complexity
of the food. The intestine is narrow, convoluted, and but seldom has a
mesentery; distinctions between small and large intestines are but imper-

CHARACTERISTICS OF THE DIGESTIVE APPARATUS.

209

fectly indicated. The intestine terminates in an expansion, the cloaca,
into which the reproductive organs open.

In bivalved mollusks like the oyster (Fig. 64) the gullet and
pharynx are absent and the mouth communicates directly with the
stomach, which is imbedded in a large glandular organ, the liver, and the
intestine after making a few turns passes directly through the heart. In
univalved mollusks like the snail the
gullet is long, the crop is frequently
present, and the stomach is some-
times double, the anterior portion
provided with teeth and serving as
an organ of mastication or as a giz-
zard (Fig. 65). A lobulated liver is
also here present; the intestine is
convoluted, passes through the liver,
and usually terminates in the an-
terior part of the body. The highest
mollusks, such as the cuttle-fish
(Fig. 66), show a marked advance
in complexity, the highest stage of
development of the alimentary canal

s v

FIG. 65.— DIAGRAMMATIC SECTION OF SNAIL.
(Wilson.)

A, foot ; B. operculum : C, tentacles : D. mouth ; E, sali-
vary glands: F, stomach: G G, intestines: H. amis; I, liver;
L. aperture of gill-chamber: M. oviduct: N. gill-chamber;
<). floor of gill-chamber: P, gill of breathing organ; ST. heart;
W, cephalic, X, pedal, and Y, branchial ganglia.

FIG. 66.— DIAGRAMMATIC SECTION OF A
FEMALE CEPHALOPOD (Sepia offid-
nalis). (Huxley.)

A, buccal mass surrounded by the lips, and showing
the horny jaws and tongue : B, oesophagus ; C, salivary
gland ; D, stomach ; E, pyloric caecum ; F, the funnel ;
G, the intestine ; H, the anus ; I, the ink-bag ; K, the

duct of the left side: O, the ovary; P, the oviduct; Q,
one of the apertures by which the atrial system, or water
chambers, are placed in communication with the ex-
terior; R, one of the branchiae; S, the principal ganglia
around the oesophagus ; M, the mantle ; SH, the internal
shell, or cuttle-bone : 1, 2, 3, 4, 5, the margins of the foot,
constituting the so-called arms of the sepia.

being accompanied by the appearance of definite organs of circulation
and of the nervous system.

In vertebrates the complexity and perfection of the alimenta^ canal
has advanced still further, and we find in them that the buccal cavity,
which in fish and amphibians is single, in the reptiles is divided into two
divisions, — a nasal or respiratory portion and a buccal or digestive

14

210

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

portion. The teeth here also commence to be especially developed.
Fishes have a short, simple, wide alimentary canal and stomach, separated
by a marked constriction from the small intestine, but the separation of
the stomach from the gullet is less marked, being indicated often only by
the difference in structure of the mucous membrane ; hence, in these
animals regurgitation of food is easy, and is the method which is often
employed for the removal of indigestible residue. A form of rumination
is also said to occur in certain fishes, the food being regurgitated to the
mouth and remasticated by the teeth or pharyngeal
bones, as in the carp. In fishes (Figs. 67 and 68)
the stomach is usually bent like a siphon, the
intestine is straight and short, with but in rare
cases any distinction betwreen large and small
intestines. There is no distinct ileo-caecal valve,
but sometimes a caecum is present. The intestine
is rarely supported on a mesentery.

In the amphibious reptile the type of the
alimentary canal is somewhat similar to that of
the fish, though the distinction between the large
and small intestines is better marked. The oesoph-
agus is short, dilatable, and muscular, and the
stomach is tubular and may be bent upon itself.
A distinction between large and small intestines

FIG. 67.— INTESTINAL CANAL,
OP THE STURGEON.
(Cam*.)

BB, pharynx and cul-de-sac of
the stomach ; A, pylorus : C, pancre-
atic appendices of the pylorus ; below
are seen the convolutions of the small
intestine terminating in the spiral
large intestine.

FIG. 68.— STOMACH OF THE SALMON-TROUT (Carus),
SHOWING THE PANCREATIC APPENDICES OF THE
PYLORUS AT A.

is readily made. The influence of the food on the development of the
alimentary canal is seen in the long, coiled intestine of the vegetable-
feeding tadpole, as contrasted with the short intestine, of the insectivo-
rous frog and toad. The crocodile (Fig. 69) has a more complex stomach
than any animal lower in the scale. It is a sort of blending of the
digestive organ of the cuttle-fish and the bird, having powerful muscular
walls, with muscular fibres radiating from a central tendon in a manner
very closely similar to that seen in the gizzard of the bird. The

CHARACTERISTICS OF THE DIGESTIVE APPARATUS.

211

crocodile, therefore, forms the connective link in the development of the
digestive tube between reptiles and birds. In this animal the duodenum
is also first seen, the liver and pancreas emptying into it, and the mesen-
tery first makes its appearance as a constant organ. The alimentary
canal of reptiles is simpler than that of birds, but resembles the bird
more than the fish. The oesophagus varies with the length of the neck, and
is wide and dilatable in the ophidia. It joins the stomach without any
constriction, its mucous membrane becom-
ing glandular. In the serpents the cardiac
portion of the stomach is long, saccular,
and dilatable, while the pylorus is narrow
and muscular. The intestines are short
and wide in the carnivorous species, but
long and furnished with caeca in vegetable
feeders.

tomach

L

B

FIG. 70.— DIGESTIVE APPARATUS OF
BIRDS.

FIG. 69.-STOMACH OF CROCODILE. (Rymer Jones.) D Ajp^^^-Njj^^dg^

C. oesophagus : A. muscular fibres of stomach radiating from B, creas: H, duodenum; I, small intestine; K,
the central tendon, as in the gizzard of the bird ; D, commencement of Caeca. : L, large intestine • M M ureters • N
duodenum. oviduct; O, cloaca.

In bir.ds there is a most marked difference in the length and develop-
ment of their alimentaiy canal, dependent upon the nature of their food,
the granivorous and fructivorous birds having intestinal tubes of greater
length and complexity than those which live on animal diet (Fig. 70).
In all cases the stomach is well separated from the oesophagus, the
length of the latter being, of course, dependent upon the length of the

212

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

neck of the bird, while its width and dilatability depend upon the nature
of the food. In granivorous birds we meet with the first indication of
the development of the cesophageal pouches for the retention and macer-
ation of food, — organs which are identical in function with the first three
pouches of the mammalian ruminant stomach. The locality and character
of these pouches vary in different birds.

In the granivorous birds this organ, which is termed the crop, is
located at the lower part of the gullet. It may be double, as in the case
of the pigeon, and distinctly arrests the food and retains it in contact
with fluids to enable it to become macerated before being passed down
to the digestive organs proper. In flesh-eating birds, such as the pelican,

FIG. 71.— HORIZONTAL SECTION OF GIZZARD OF GOOSE, AFTER GARROD.

A, in contraction ; B, in relaxation.

the pouch is located higher up in the digestive canal, ordinarily below
the lower jaw, and here seems to be more of a reservoir for storing food
than as a distinct commencement of the digestive apparatus. Fruit- and
insect-eating birds are not supplied with any such reservoirs, while the
turkey, ostrich, goose, swan, and most of the waders, have a highly-
developed crop ; the pigeon, as before stated, having two, one on each
side of the oesophagus. The stomach in birds differs according as their
diet is vegetable or animal. Granivorous birds have a small, straight,
dilatable stomach, called the proventriculus. communicating above with
the gullet and below with a highly muscular organ, the gizzard (Fig.
71), lined with horny epithelium, usually containing gravel or sand,

CHAKACTEKISTICS OF THE DIGESTIVE APPARATUS. 213

and which has for its function the crushing and mastication of food. The
proventriculus, ventriculus succenturiatus, or true glandular stomach,
varies in form and size in different birds, being sometimes wide and
straight and sometimes round. In the rasorial birds it is wider than the
gullet and smaller than the gizzard. Its mucous membrane is thicker
than that of the oesophagus, and furnished with tubular glands which
secrete an acid digestive secretion. In the grain-eaters these glands are
sacculated, or expanded into compound follicles, the disposition of the
glands varying in different species. The gizzard, ventriculus bulbosus, the
third or muscular stomach, is a more or less flattened, ovoid organ, hav-
ing two apertures at its upper part, one communicating with the proven-
triculus, the other with the small intestine. The gizzard is feebly devel-
oped, or may be even absent in carnivorous birds, such as the crow and
the raven, and is there simply a membranous expansion of the stomach,
free from secreting membrane, and bearing close analogy and function
with the membranous cardiac extremity of the stomach of the horse.
The intestines of birds are, as a rule, relatively to the size of the body,
shorter than those of mammalia, but longer than those of reptiles. In
birds of prey, as a rule, they are not more than twice as long as the body,
including the bill, but in the osprey they are eight times as long. In
fructivorous and granivorous birds they are much longer. The duodenum
forms a loop, embracing the pancreas. The division between small and
large intestines is not clearly marked, as villi are found in both. The
point of entrance of the caeca, which are most developed in birds feed-
ing on vegetable food, marks the union of small and large intestines.

In all the groups of animals already referred to the stomach occupies
a position in the long axis of the body. It is only in mammals that its
position becomes transverse (Fig. 72), and we notice that even in these
animals this transverse position becomes more accentuated during its
state of functional activity. Thus, when fasting the pyloric orifice of
the stomach sinks and the organ tends to assume a longitudinal position ;
when filled with food it undergoes a partial rotation on its own axis, the
pyloric orifice ascends, and it now becomes transverse.

In mammals the oesophagus is only destined to convey food to the
stomach ; it has contractile walls, but few or no glands, and the pouches
which we have recognized in the birds are represented in but a single
group of mammals, — the ruminants, — and here they are situated so low
down in the oesophagus as to be ordinarity described as divisions of the
stomach. Their function and structure prove that they maybe regarded,
nevertheless, as oesophageal pouches. The diameter of the oesophagus
varies according to the food which serves as the normal diet for these
animals. It is large and readily dilatable in carnivora, which bolt their
food entire ; it is narrow in the herbivora ; and in those animals which

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

thoroughly masticate their food, as in solipecles, it is narrow and less
distensible than in ruminants, where the preliminary mastication is less
complete.

B'-

FIG. 72.— DIGESTIVE TRACT OF THE DOG, AFTER BERNARD.

P, parotid gland; G, -submaxillary gland : G", sublingual gland; OE, oesophagus, or gullet;
ht carotid ; C, jugular vein ; PP. lungs, that on the left opened to show the bronchial tubes, arteries,

"I, right auricle of the heart; H', left auricle: F', right
ventricle ; O, left ventricle ; P', pulmonary artery ; T T, thoracic duct ; F, liver ; B, gall-bladder, enter-

ed, right carotid ; C, jugular
and veins; VC', superior ve

na cava ; K, aorta ; H, rip

ing the intestine by the duct, B'; E, stomach; R, spleen; S, Pecquet's reservoir: J, lymphatics; M,
mesenteric ganglia; VP, trunk of portal vein; V V, origins of portal vein ; W, pancreas; VC. inferior
vena cava ; D, duodenum ; VL, lacteals ; I, small intestine ; Q, caecum ; R, colon, or large intestine.

CHAKACTEKISTICS OF THE DIGESTIVE APPARATUS. 215

The stomach is charged to contain the food until it has undergone
the chemical modifications which are essential to its absorption. It forms
a reservoir which is in mammals clearly separated from the oesophagus
and the intestine, and which, as already stated, occupies a transverse
position in mammals, longitudinal in reptiles and the oviparous verte-
brates, while its transverse position commences to be indicated in birds.
The stomach may be either simple or complex. In carnivora, whose
lood is eas}' of solution, it is a single cavity lined with a uniform mucous
membrane abundantly supplied with glands which secrete an acid fluid,
the gastric juice, which has for its function the conversion of albuminous

FIG. 73.— STOMACH OF DIFFERENT MAMMALS AND OF A TURTLE. (Thanhoffer.)

1, stomach of seal ; 2, stomach of hyena : 3, stomach of cricetns : 4, stomach of manate ; 5, stomach
of camel; 6, stomach of sheep; 7, stomach of lion; 8, stomach of horse.

c, cardia ; p, pylorus ; 1, 2, 3, 4, 1st, 2d, 3d, and 4th stomachs ; v, ventriculus ; /, fundus ventriculi.

foods into peptones. The complication of the stomach in mammals
progresses in insensible degrees, and in a general way is in proportion to
the indigestibility of the food (Fig. 73). At first^the division of the
stomach into pouches is only indicated by a difference in structure and
properties of the mucous membrane of the cardiac and pyloric portions
of this vis'cus. This difference is, to a certain extent, present in all
animals, even in the carnivora, where it is confined simply to a histologi-
cal difference in the nature of the glands of these two portions of the
stomach. No difference is, however, evident to the naked eye in these
animals. In the horse the separation into a cardiac and pyloric pouch is

216 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

indicated by a groove seen on the external surface of this organ and in-
ternall}T b}T a sharp demarcation between the glandular mucous membrane

FIG. 74.— POSTERIOR SURFACE OF STOMACH OF HORSE. (Strangeways.)

A, left cul-de-sac; B, right cul-de-sac; C, greater curvature: D, lesser curvature; E, oesophagus; F, duodenum.

of the pyloric portion and the membranous portion of the cardiac end.
In the solipedes (Fig. 74), therefore, the general appearance and char-
acters of the stomach correspond with those of the carnivorous birds,

FIG. 75.— STOMACH OF HOG, INFLATED. (Strangeways.)

A, cardiac portion ; B, its accessory cul-<1e-sar, ; C. pyloric portion ; D, lesser curvature ; E, greater curvature ;
F, oesophagus ; G, pyloric orifice.

where we have a separation into a glandular and membranous portion;
the difference between these animals consisting in the fact that in such
birds it is the cardiac extremity which is glandular, and the pyloric

CHARACTERISTICS OF THE DIGESTIVE APPARATUS. 217

extremity, or the rudiment of the gizzard, membranous, while in the horse
the reverse holds. In the hog (Fig. 75) the division into pouches is
more marked by the appearance of a distinct, curved, conical diverticulum
at the cardiac extremity of the stomach. In the porcupine three or four
contractions are marked, and in the kangaroo, porpoise and other ceta-
ceans, and many rodents a large number of dilatations, separated by
marked constrictions, are to be noticed (Fig. 76). In other animals this
complication is not only in external form, but also in internal structure,
the highest degree of complexity being found in the ruminant, where
the stomach, so called, is divided into four distinct gastric sacs, com-
municating with each other only by small orifices, whose function and
structure will occupy us later (Fig. 77). This complication is found not

FIG. 76.— STOMACH OF THE DUGONG, AFTER SIR EVERARD HOME.

rloric portion : C, constriction between the 1
the stomach ; F, oesophagus ; G, intestine.

A, cardiac portion of stomach ; B. pyloric portion : C, constriction between the two ; D D, tubular prolongations
of T

only in mammals, but also in birds ; but, whatever may be the external
form of the organ, the function is always the same, — to supply an acid
secretion for the solution and digestion of certain constituents of the
food, — and where reservoirs are present their function is simply to
retain food until, as in the case of the ruminant, it may be again masti-
cated ; or in all cases to enable the food to undergo preparatory changes
before being subjected to the action of the gastric secretion.

The intestine is the prolongation of the stomach, and its shape as a
canal is again regained. In its simplest form in the lowest animals it is
a short tube of uniform size, with the same structure and properties from
one end to the other, as seen in invertebrates, in most reptiles and fishes,
and, among the mammals, in the hedgehog and the bat. In the higher

218

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

classes it is divided into two forms, the small and large intestines. The
small intestine is destined for the absorption of food-products, and for
the elaboration of the digestive secretions for the solution of food-stuffs
which have escaped the action of the gastric juice. We find its walls,
therefore, supplied with tubular glands secreting the so-called intestinal
fluid ; and emptying into the small intestine we find in all cases two large
glandular organs, the liver and pancreas, secreting alkaline fluids which
have a greater or less importance in digestion. In the small intestine of
mammals are also to be found special organs for assisting the absorption

FIG. 77.— STOMACH OF ADULT SHEEP, DRIED AND INFLATED ; ONE-FIFTH

THE NATURAL SIZE. (TlianJi offer.)

B, rumen ; R, reticulum ; S, omasum ; O, abomasum : c, cardia : p, pylorus ; br, oesophagus : cb,
cardiac valve; be, oesophageal gutter; r, pillars of the rumen; rn, opening of the reticulum; on, open-
ing of the abomasum, or fourth stomach ; b, valve between reticulum and omasum ; e, duodenum.

of food, the so-called villi, which are simply conical expansions covered
by mucous membrane, whose function, together with that of the folds of
the mucous membrane, is simply to give increased surface for absorption.
In the higher animals the small intestine is divided arbitrarily into three
divisions, the duodenum, or the portion of bowel directty in communica-
tion with the stomach, which is always curved and usually free from
mesentery. Following this we have the jejunum, so-called because ordi-
narily found empty, and following that the ileum.

The intestinal canal is supplied with muscular fibres, arranged
longitudinally and in concentric rings, being red-striped muscular fibres

CHAEACTEKISTICS OF THE DIGESTIVE APPAKATUS. 219

in the mouth, pharynx, and anus, and pale, unstriped, involuntary fibres
elsewhere. The contractions of these muscular fibres in the small and
large intestines serve to cause the onward progression of the food or the
so-called peristaltic movement of the intestines. The mucous membrane
of the alimentary canal is epithelial in nature in the mouth, pharynx,
and gullet, and in the first three pouches of the ruminant stomach, and
in the cardiac half of the stomach of the horse. It is free from glands,
and is simply protective in nature. In the entire stomach of carnivorous
animals, the fourth stomach of ruminants, and the pyloric half of the
stomach of solipedes, as well as through the entire extent of the in-
testines of all mammals, it is glandular, and furnishes a more or less
active digestive secretion.

Sensory nerves are supplied to the two extremities of the digestive
tube, while the intermediary portions are supplied with nerves whose
stimulation seems to lead to secretion, and not, as a rule, to individual
sensations.

The extent of mucous membrane varies natural!}' with the length,
diameter, and complexity of the alimentary canal. It is, therefore, less
in carnivora, greater in omnivora, and immense in herbivora. The extent
of surface, therefore, depends upon the complexity of the food. The
more concentrated the food, as in carnivora, the less surface is required
for producing secretion, and the less for its absorption. In animals
living on a vegetable diet, where the nutritive principles of the food are
mixed writh a larger amount of non-nutritious residue, a greater surface is
required for secretion, greater time is required for digestion, and a
greater surface must be supplied for the absorption of digestive matters ;
we find, therefore, that in herbivorous animals the intestinal tube is
always longer, more complicated, and supplied with a larger extent
of mucous membrane than in the carnivora. Even in the herbivora
we find a difference in the distribution of the mucous surfaces ; thus,
the horse and ox are both herbivorous animals : the former is a
monogastric animal, the latter a pol}*gastric, or ruminant. The former
digests little by its stomach, and much by its intestinal tube; the
latter readily digests more by its vast and complex stomach than by its
narrow and small intestinal tube. Both, however, from the fact that
they are herbivorous animals, have a great extent of mucous mem-
brane, which may be twice or three times as extensive as their ex-
ternal body surface. Thus, the cutaneous surface of the horse is about
five or six square meters, while its mucous gastro-intestinal surface
may be as much as twelve square meters, of which one-thirtieth is
represented by the stomach and the rest by the intestines. An ox, on
the other hand, of about the same size, has a mucous membrane of about
seventeen square meters, of which nine square meters represent the

220 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

membrane of the stomach. Consequently, the solipede has a mucous
membrane about twice, and the ruminant about three times, as extensive
as its cutaneous surface, while the mucous membrane of the stomach
alone of the ox is one and one-half times as extensive as the skin sur-
face. In the carnivora — the dog or the cat, for example — the mucous
membrane, from the simple character of their food, is very much less
extensive in proportion to their external body surface, being only about
two-thirds as large as their skin surface. The omnivora, again, occupy a
mean between the carnivora and the herbivora.

The length of the alimentary canal, in a less strict degree, however,
is also subordinate to the character of the alimentation. In the herbiv-
ora the intestinal tube may be as much as twenty-eight times the length
of the body, while the intestinal canal of the carnivora is only three or
four times as long as the body. There are, however, many exceptions
to this rule. Thus, the dromedary has an intestinal tube only five times
as long as its body ; the ram twenty-eight times as long ; the deer twelve
times ; the rabbit nine ; elephant seven ; the hyena eight, and the seal
twenty-eight times as long as its body length. In these apparent excep-
tions, as, for example, in the case of the seal, a carnivorous animal ,
though there is an intestinal tube twenty-eight times as long as its body,
we have the proportion of mucous membrane still preserved ; for, where
in herbivorous animals we have a comparatively short tube, its diameter
is always proportionately great, while in the case of carnivorous ani-
mals, where the tube is long, its diameter is accordingly small. Thus,
the alimentary canal of the horse is shorter than that of the ox, the
former being about ninety feet ; but it is very much more capacious.

Change in the normal diet of animals leads to changes in the rela-
tive dimensions of their intestinal canals. Thus, the alimentary tube of
the wild boar is shorter than that of the domestic hog, since its habit in a
state of nature is more carnivorous than in domestication. The domes-
ticated cat, living on a mixed diet, has an intestinal tube which is longer
than the cat in a state of nature, and the same difference also applies to
the domestic ox as contrasted with the buffalo.

The relative capacity of the alimentary canal is even more strictl}'
definable in different species according to their alimentation. The herbiv-
ora always have a greater capacity of intestinal tube than the carnivora.
In all cases the volume of the stomach is in inverse proportion to that of
the capacit}' of the intestine. Thus, in the horse the stomach is capable
of containing from about sixteen to eighteen litres, while the capacity of
the horse's intestine varies from one hundred and twenty-five to three
hundred litres. In the ox the stomach contains two hundred litres, the
intestine one hundred litres. The value of these differences will be
studied later. They serve simply to indicate the immense expanse in

CHARACTERISTICS OF THE DIGESTIVE APPARATUS. 221

the alimentary canal of the herbivora. The extent of surface for absorp-
tion in the intestinal tube is still further increased by the formation of
plicie, or folds of mucous membrane, and from what has been said above
we would naturally expect that these are more extensive and more highly
developed in the herbivora than in the carnivora. This is well exem-
plified in the case of the ox, whose stomach, which is capable of contain-
ing two hundred litres, has onhr two square meters of external surface,
and yet whose internal mucous surface amounts to nine square meters.
Such an immense increase of internal over external surface could only
be accomplished by the throwing up of the mucous 'membrane into folds.
In the intestine, again, which is capable of holding about sevent37-five
litres, the square surface externally amounts to fifteen or sixteen meters,
showing, therefore, that in the ox the mucous coating of the intestine
is more simple.

The carnivora are distinguished by a large, voluminous stomach,
coated throughout with a secreting mucous membrane, and the intestine

FIG. 78.— C^CUM OF A DOG, INFLATED. (Strangeways.)

A, ileum ; B, caecum ; C, colon.

is simple and deprived of folds. With the exception of the cetacea and
a few edentata, the subdivision into a small and large intestine prevails
throughout the entire group of mammals. The greater the length of
the small intestine, the more is it convoluted. Yilli are always absent
from the large intestine. A well-marked ileo-caecal valve, with but few
exceptions, is situated at the junction of the small and large intestines.

At this point, also, is almost invariably found a diverticulum,
called the caecum, which varies very greatly in size and functional impor-
tance in different animals, these differences also being dependent upon
differences in regimen. In the carnivora the caecum is only a spiral
appendix, as seen in the dog (Fig. 78), and the large intestine is divided
into the ascending, transverse, and descending portions, as in man ; there

222

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

is no floating colon, and, while the mucous membrane is sacculated to a
certain extent, the folds are by no means as extensive as in the herbivora.
In the omnivora the caecum resembles that of the horse in having three
longitudinal bands and transverse constrictions, and has increased in
complexity from that of the carnivorous animal. It is absent in the
bear and weasel. The caecum reaches its highest degree of complexity in
the monogastric herbivora. In these animals, as in the horse (Fig. 79), it
becomes greatly enlarged, convoluted, condensed into folds, has special

Fro. 79.— CAECUM AND GKEAT COTTON OK HORSE. (Strangeways.)

A, caecum; B C, its muscular bands; D, termination of ilenm: E, first, E'. second, F, third, and
F', fourth divisions of colon ; G, pelvic flexure; H, origin of floating colon. The arrows indicate the
course of the food through the colon.

valves and glands, and in the horse may contain six gallons of fluid,
being three times as large as the stomach. In the solipede and rodent
the caecum therefore reaches its highest stage of development, and has
special digestive functions to fulfill. In the ox, whose small intestine
differs but little from that of the horse, although it is smaller in calibre

CHARACTERISTICS OF THE DIGESTIVE APPARATUS. 223

and twice as long, from the fact that the increased complexity of the
stomach furnishes the necessary differences for the digesting of the
food the caecum is smooth and devoid of longitudinal and transverse
bands (Fig. 80). Its free extremity is blunt, rounded, and directed back-
ward, and floats free in the abdomen, while its other extremit3r, having
received the insertion of the ileum, is continuous with the colon, which
also is free from bands, and soon becomes constricted, and then, preserv-
ing about the same diameter throughout, is arranged in an elliptical
coil between the folds of the mesentery. In the ox there is no distinction
between the great and floating colon, as in the horse. The total length of
the large intestine in the ox, from the caecum to the rectum, is about
thirty-six feet, but its capacity is much less than in the horse.

Further details as to the functions and structure of the different
parts of the alimentary canal in the various domestic animals wilt be

FIG. 80. C.ECUM AND ORIGIN OF COLON OF AN Ox, INFLATED. (Strangeways.)

A, terminal portion of the ileum ; B, caecum ; C, origin of colon.

given during the consideration of the subject of digestion. So far the
aim has been merely to indicate, in a general wa}r, the adaptability of
the digestive organs to the character of the food.

The following tables, compiled by Colin, represent the different
comparative dimensions and capacities of different parts of the ali-
mentary canal in the domestic animals. They offer confirmation of the
statement already made that the functional activity of the stomach and
digestive tube being in inverse ratio, in those herbivora with capacious,
complex stomachs the intestinal tube will always be less developed than
in the monogastric herbivora, where the role of the stomach in digestion
is secondary to that of the intestine.

224

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

LENGTH OF DIFFERENT PORTIONS OF THE INTESTINE COMPARED WITH THAT

OF THE BODY.

ANIMAL.

Parts of Intestine.

i

S

8

.s

S3

1

Minimum in
Meters.

Maximum in
Meters.

Ratio between
Body Length
and that of
Intestine.

Horse, .

Small intestine, . .
Caecum, . . .

Fixed colon, . „•'
Floating colon,

0.75
0.04
0.11
0.10

22.44
1.00
3.39
3.08

16.00
0.81
2.91
2.35

31.60
1.28
4.00
3.44

1:12

Total length, . . .

1.00

29.91

22.07

40.32

Ass, . .

Small intestine, .
Caecum,
Fixed colon,
Floating colon, . .

0.67
0.06
0.17
0.10

12.00
1.02
3.00
1.85

1:11

Total length, .

1.00

17.87

Mule, .

Small intestine, . ' .
Caecum,
Fixed colon,
Floating colon, . *

0.70
0.05
0.13
0.12

18.56
1.21
3.50
3.23

1:11

Total length, . . '

1.00

26.50

Small intestine, . • ...'.'
Caecum . . « .

0.81
0.02

46.00

0.88

41.00
0.78

51.00
1.00

1:20

Ox,

Colon, . . •;-.. ;.

0.17

10.18

9.25

11.00

Total length, .

1.00

57.06

51.03

63.00

Dromedary, .

Small intestine,
Caecum, . . " .
Colon, ...

0.63
0.01
0.36

31.20
0.40
17.72

1:15

Total length, . • .

1.00

49.32

Sheep and Goat,

Small intestine,
Caecum, . . . •. -. y
Colon, .

0.80
0.01
0.19

26.20
0.36
6.17

15.32
0.21
4.10

33.00
0.45
' 8.49

1:27

Total length, .

1.00

32.73

19.63

41.94

Hog, . i

Small intestine,
Caecum, ....

Colon, . . -,. ' •

0.78
0.01
0.21

18.29
0.23
4.99

14.79
0.20
4.32

20.14
0.25
5.55

1:14

Total length, .

1.00

23.51

19.31

25.94

Dog, ^ .

Small intestine,
Caecum, ....

Colon, . ; V .

0.85
0.02
0.13

4.14
0.08
0.60

2.00
0.03
0.23

6.10
0.16
1.05

1: 6

Total length, .

1.00

4.82

2.26

7.31

Cat, .

Small intestine,
Large intestine,

0.83
0.17

1.72
0.35

1.27
0.30

1.94
0.40

1: 4

Total length, .

1.00

2.07

1.57

2.34

Rabbit,. • ..

Small intestine,
Caecum, ....
Colon, ....

0.61
0.11

0.28

3.56
0.61
1.65

3.30
0.50
1.41

3.90
0.76
1.85

1:10

Total length, .

1.00

5.82

5.21

6.51

CHAKACTEKISTICS OF THE DIGESTIVE APPARATUS.

225

ABSOLUTE AND RELATIVE CAPACITY OP THE STOMACH AND INTESTINE OP
THE DOMESTIC ANIMALS.

ANIMAL.

Parts of Intestine.

Ratio.

Mean in
Litres.

Minimum
in .Litres.

Maximum
in Litres.

Horse,

Stomach, ....
Small intestine,
Caecum, ....
Fixed colon,
Floating colon and rectum,

0.085
0.302
0.159
0.384
0.070

17.96
63.82
33.54
81.25
14.77

10.00
38.30
16.20
55.00
10.00

37.50

105.00
68.00
128.00
19.00

Total capacity, .

1.000

211.34

129.50

357.50

Ass,. . .

Stomach, ....
Small intestine,
Caecum, ....
Fixed colon,
Floating colon and rectum,

0.097
0.229
0.201
0.397
0.076

10.00
24.00
21.00
41.50
8.00

Total capacity, .

1.000

104.50

Ox, .

Stomach, ....
Small intestine,
Caecum, ....
Colon and rectum, .

0.708
0.185
0.028
0.079

252.50
66.00
9.90

28.00

215.00
56.00
8.80
26.00

290.00
76.00
11.00
30.00

Total capacity, .

1.000

356.40

305.80

407.00

Dromedary,

Stomach, ....
Small intestine,
Caecum, . .
Colon, ....

0.810
0.131
0.011
0.048

245.00
39.50
3.40
14.60

Total capacity, .

1.000

302.50

Sheep and Goat,

Rumen, ....
Reticulum, . .
Manyplies,
Abomasum,
Small intestine,
Caecum, ....
Colon and rectum, .

0.529
0.045
0.020
0.075
0.204
0.023
0.104

23.40
2.00
0.90
3.30
9.00
1.00
4.60

Total capacity, .

1.000

44.20

Hog, . .

Stomach, ....
Small intestine, - . ..
Caecum, ....
Colon and rectum, .

0.292
0.335
0.056
0.317

8.00
9.20
1.55

8.70

7.50
8.60
1.50
6.10

8.50
9.80
1.60
11.30

Total capacity, .

1.000

27.45

23.70

31.20

Cat, .

Stomach, ....
Small intestine,
Large intestine, "- .

0.695
0.146
0.159

0.341
0.114
0.124

0.287
0.095
0.118

0.378
0.127
0.130-

Total capacity, .

1.000

0.579

0.500

0.635

Dog,

Stomach, ....
Small intestine,
Caecum, ....
Colon and rectum, .

0.623
0.233
0.013
0.131

4.33
1.62
0.09
0.91

0.65
0.25
0.01
0.07

8.00
3.00
0.20

2.20

Total capacity, .

1.000

6.95

0.98

13.40

15

226

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

COMPARISON OF THE GASTRO-INTESTINAL Mucous SURFACES WITH THAT OF

THE SKIN.

ANIMAL.

Organ.

Partial
Mucous
Surface
in Square
Meters.

Total
Mucous
Surface
in
Square
Meters.

Skin
Surface
in
Square
Meters.

Ratio
between
Mucous
Surface
of
Stomach
and
Intestine.

Ratio
between
Skin and
Gastro-
intestinal
Mucous
Surfaces.

Stomach

0.40

Small intestine, .

4.39

Horse,

Caecum, ....

1.50

14.95

5.50

1 : 29.87

1 : 2.18

Fixed colon, . .

4.29

Floating colon, . - . .

1.37

Rumen, .

2.00

Reticulum,

0.43

Ox, . .

Manyplies,
Abomasum,

5.56
1.18

17.23

5.80

1 : 7.61

1 : 2.97

Small intestine,

5.60

Caecum, . . .

0.46

Colon, ...

2.00

Stomach, ....

0.19

Hog, . .

Small intestine,
Caecum, ....

1.66
0.11

2.81

1 : 13.22

Colon, ....

0.83

Stomach, . . .

0.12

r>og) .

Small intestine,
Caecum, ....

0.32
0.005

0.52

0.88

1 : 3.36

1 : 0.59

Colon, ....

0.06

.

Stomach, ....

0.02

Cat, .

Small intestine,

0.07

0.12

0.21

1 : 4.15

1 : 0.58

Large intestine,

0.02

II. PREHENSION OF FOOD.

1. PREHENSION OF SOLIDS. — By the term prehension of food is meant
the different methods emplo3Ted by animals in seizing their food and
conveying it to the oral aperture of their alimentary canal. Man}T aquatic
animals, whose food consists of small particles diffused through water,
are supplied with an apparatus for producing currents so as to bring
such substances within their reach. This is especial^ true in the case
of fixed forms of life which are unable to go in search of their food.
Thus, the sponge and sea-mat, and various other of the lower forms of
life, obtain their nourishment by the production of currents in the water
through the vibration of cilia lining or surrounding the opening of their
alimentary canal. In infusoria, also, we find similar arrangements,

PEEHENSION OF FOOD. 227

either in the form of cilia or even in tentacles. In the lowly-organized
rhizopods and amoebae, their soft, jelly-like body is simply applied to
the food, which then and there enters their body substance. The most
marked illustration of the mode of seizing food by means of prehensile
tentacles is found in the case of the hj'dra or polyp, — small organisms
whose bodies are not usually longer than one centimeter, and which, as
already described, are supplied with a single body cavity, around the
single opening of which are long, slender, retractile tentacles, themselves
often provided with cilia, and which are capable of grasping small sub-
stances which may serve as their food and conveying them to their
digestive sac ; the adhesive power of these tentacles is increased by a
number of minute spiral filaments, the so-called "urticating cysts,"
which by some observers are supposed to be offensive weapons, and are
used to paralyze the small organisms that serve as their food. The jell}--
fish furnishes another example of a similar method of seizing food.
These prehensile tentacles may be few and simple, as in the hydra; very
numerous, as in the sea-anemone; and often of great length and irregular
form, as in the medusae.

Bivalve mollusks, like the oyster and the clam, employ the vibration
of cilia for creating currents to bring the nutritive matters suspended in
water within their reach. When the food is solid permanent prehensile
organs are usually present, though they may be extemporized, as in the
case of the amoeba, where any portion of the body surface which is
accidentally in contact with food may serve as a prehensile organ to
draw matter into the interior of its body. In a higher stage of develop-
ment we find that tentacles are absent, but that their function is assumed
by flexible portions of their body, commonly called arms, which are
provided with a number of minute adhesive organs, which serve to seize
their food, and whose flexibility enables them to convey it to their oral
aperture. This form of prehension of food is seen in the star-fish. In
the sea-urchin a considerable advance is seen in the method of prehension
of food. The mouth itself is there the prehensive organ, and is provided
with five sharp teeth, each standing in a single jaw, and capable of being
projected so as to seize as well as masticate the prey. Univalve mollusks,
such as the snail, have again another organ, the tongue serving as an
organ of prehension. In this case the tongue is long and covered with
minute recurved teeth or spines, by which the food is seized and drawn
into the mouth, the upper part of which is armed with a sharp, horny
plate. In the cuttle-fish, again, the organs of prehension of food have
advanced still further in their development. The tongue is still present
as a prehensile organ; the jaws, represented by a pair of hard mandibles
like the beak of the parrot, and working vertically ; and in addition to
these several powerful prehensile tentacles, provided with powerful

228 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

suckers, or adhesive organs, which serve to grasp its food and to bring
it within the mouth.

In the articulates, in addition to the suctorial contrivance already
mentioned, innumerable modifications of the mouth are seen, that being
the organ which in this group constitutes the main prehensile organ, its
modifications corresponding to the character of the food; thus, the earth-
worm has a muscular upper lip, by which it secures the earth which con-
tains its food, and which serves to bring it within the mouth. In other
worms, again, the gullet is so constructed that it can be turned inside
out to form a proboscis for seizing prey. In such instances it is nearly
invariably supplied with horny teeth. Millipedes and caterpillars have
powerful horny jaws, working horizontal^ , while the centipedes have a
second pair, which are really modified feet, terminating in curved fangs
containing a poison-duct. In the crab, the legs and feet serve not only
for progression, but also for the mastication of food, as is also the case
in the lobster, where the seventh pair of feet are enormously developed
and furnished with powerful, crushing pinchers, those on one side of the
body being smooth, the other knobbed. Scorpions have, again, a small
pair of claws for prehension of food, and a smaller pair of forceps for
holding the food in contact with the mouth. In the spider the claws are
wanting, and the forceps ends in a fang or hook, which is perforated to
convey venom. Biting insects, such as the beetle, have distinct buccal
appendages, consisting of two pairs of horny jaws, which open one above,
the other below, the oral aperture; the upper are called mandibles or
pinchers, the lower the maxillae, which support the palpi. The former
are armed with sharp teeth. The maxillae are similar, but smaller, and in
some insects have appendages which are called palpi or feelers, which not
only select but hold the food steady while it is crushed .by the mandibles
and maxillae. Such appendages represent a free pair of jaws. All
invertebrates Vnove their jaws horizontally.

In all vertebrates the jaws move vertically, and are in many instances
the main or sole organ for the prehension of food. In fishes the jaws are
always prehensile and often provided with teeth, which, being sharp and
curved inward, are prehensile organs ; where teeth are absent, as in the
sturgeon, the food is drawn in by suction. The hog-fish has a single
tooth, which it plunges into its prey and then bores a hole with its saw-
like tongue. The fins or tongues of fish are not prehensile.

In reptiles the jaws, teeth, or tongues may serve as prehensile organs,
while in reptiles prehensile lips are never present. Thus, the turtle has
a mouth provided with horny jaws, the crocodile sharp, curved teeth, and
the frog, toad, and chameleon, glutinous tongues for seizing their food.
In chelonians the jaws are horny, and are supplied with small teeth in
ophidians; in the larger saurian s the teeth are powerful, while they are

FREHEXSION OF FOOD. 229

delicate and complex in the insectivorous species. Serpents crush their
prey in their coils before swallowing it.

All birds use their toothless beaks in procuring food. Birds of prey
also seize with their claws, while certain birds, such as parrots and wood-
peckers, also employ their beaks as prehensile organs. The beak in birds
varies in shape according to their food. Thus, it is short and strong in
graniverous birds ; long and slender in insectivorous birds. In birds
which catch their prey on the wing, as the swallows, it is short and
gaping ; strong and curved in birds of prey which tear their food ; long,
conical, and of great strength in borers, as in the woodpecker ; short and
curved in the parrot tribe to enable them to crush nuts ; delicate and
tapering in humming-birds to allow them to penetrate the corollas of
flowers ; long, strong, and pointed in most fish-eaters, as the heron, stork,
and king-fisher ; shovel-shaped in many aquatic birds, such as the duck
and goose ; or it may be fashioned to hold fish, as in the pelican, albatross,
penguins, etc. In the cross-bills the mandibles when closed overlap, —
a conformation which enables them to extract the seeds from fir-cones.
Finally, in the young pigeon, which feeds by placing its bill in the mouth
of the mother-bird, the lower mandible is elongated and boat-shaped, and
of greater size than the upper. Hence, it acts as a spoon, and becomes
relatively smaller as the pigeon grows. In parrots and woodpeckers the
tongue is also prehensile.

The tongue in birds and reptiles, besides being the seat of the sense
of taste and an organ of deglutition, is often the sole organ for the pre-
hension of food, the mechanisms concerned in this operation, that is, the
extension and retraction of the tongue, differing in birds, reptiles, and
mammals. In birds the forward and backward movements of the tongue
depend upon the muscles which move the hyoid bone. The horns of this
bone in birds are arched and extend up behind the occiput, and give
attachment to a muscle which is wrapped around them, and is then in-
serted in the inferior and posterior surfaces of the rami of the lower jaw.
This muscle, which is termed the conic muscle of the hyoid bone (Vicq
d'Azyr), by its contraction advances the tongue by bending the arches
of the hyoid bone, at the same time drawing them forward. Retraction
of the tongue is accomplished by the recoil of the elasticity of the
hyoid arches, when these muscles relax, aided by the serpo-hyoid muscles
(Duvernoy). These arches are much larger in the woodpeckers than in
other birds.

The mechanism of movement of the tongue in reptiles is much more
complicated, and differs somewhat in the four orders of this class. In
general it may be said the movements of the tongue in reptiles depend
on the two principal means employed separately in birds and mammals ;
that is, the intrinsic muscles of the tongue and the hyoid muscles.

230 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In the chelonians the hyoid cartilage is of variable shape, but in the
main resembles somewhat the hyoid bone of the bird, and is moved by a
somewhat similar mechanism, excepting that the conic-hyoid muscles are
not wrapped around the hyoid arches. The tongue in this species is
muscular and glandular, but not extensible.

In the saurians (especially in the crocodiles) the tongue resembles
that of the chelonians in its slight degree of mobility, and the hyoid
bone has a somewhat similar shape. In some saurians the tongue is
glandular, in others very muscular and quite extensible.

Most of the ophidians have the tongue hidden in a sac, non-glandu-
lar, and composed of the union of two muscular cylinders which become
separate at the tip, forming the well-known forked tongue of serpents.
The tongue is proportionately long and extends some distance down
beneath the trachea. The posterior extremity of the sac terminates in
two cartilaginous plates, which unite anteriorly and constitute the hyoid
arch. By means of muscles which originate from the lower jaw and first
ribs, and which are inserted in the hyoid arch, the tongue is extruded
from the mouth.

The tongue of the batradiians, with the exception of the salamanders,
differs greatly from that of other reptiles. Its anterior extremHy is
convex and is fixed to the arch of the chin, while its posterior extremity
is free. To be extended from the mouth it must be reversed, and it is
the posterior tip which is extruded, while it is withdrawn by a reversal
of this motion. These movements are accomplished by the contraction
of the genio-glossus and hyo-glossus muscles, — the only ones which have
any connection with the tongue.

In quadrupeds, although in some cases we find a special contrivance
for the seizing of food, as in the trunk of the elephant, the snout of the
tapir, the long tongue of the giraffe, and the extensible, viscid tongue
of the ant-eater, the teeth are the chief organs of prehension, aided by
the lips and, in some cases, the tongue. Such animals as may stand
erect on their hind legs, as the squirrel, bear, and kangaroo, use their
fore legs for holding food and bringing it to the mouth, but never use
one of them alone. Clawed animals make use of their feet in securing
prey, but the food is conveyed to the mouth by movements of the head
and jaws. In the rhinoceros the upper lip is prolonged into a finger-like
point, which in these animals, as well as in the dromedary, is the prin-
cipal organ of prehension of food,

In man and monkeys the distinguishing prehensile organs are
found in the hand, and we find that the first office that the hand instinct-
ively performs in both species is to carry food to the mouth.

Therefore, according to the mode of life for which an animal has
been formed, we observe a variety in the arrangement of parts destined to

PKEHENSIOX OF FOOD. 231

gather food. In the higher animals we find prehensile organs represented
in lower animals by special organs which in different species form a
single type of prehensile organ. Thus: in lower forms of life we have
tentacles, or the lip may serve as the chief organ of prehension, or the
tongue or the jaws ; while in the higher mammals we find all these
organs together serving the purpose of conveying food to the mouth.

In the latter, which are of the same prehensile type as man, the
radius and ulna are isolated and movable, one on the other, and there
are distinct fingers, nails, or claws, as in monkeys, carnivora, and most
rodents. In all animals which use the fore limbs as prehensile organs,
this separation of the radius and ulna is invariabty to be found. In
the large mammals the anterior limbs are only for support, and such
animals are usually herbivorous. In them the radius constitutes the
principal bone of the forearm, while the ulna is very small and almost
always fused with the radius ; so no motion between the two is possible.
There are, however, numerous exceptions to this, and in animals where
it would be least expected. For instance : in the elephant the volume of
the ulna is superior to that of the radius, and its carpal extremity is
greater than that of the radius, and both are distinct. This also is the
case in the rhinoceros ; but in both these animals the motions of pro-
nation and supination are impossible. Most of the herbivora have a
forearm terminating in one or two single fingers or phalanges surrounded
by a hoof, and in these the radius constitutes the main or sole bone of
the fore extremit}'. The development of the ulna and the fingers are in
direct ratio.

In the domestic animals the prehension of food is accomplished by
different organs, which have different degrees of usefulness and develop-
ment in different types. In the dog and cat the fore limbs have inde-
pendent radii and ulnae, a certain amount of pronation and supination is
possible, and they indicate, to a certain extent, the prehensile power of
the hand as seen in man and monkeys. Where, as in the herbivorous
quadrupeds, the fore limbs are destined solely for support and progression,
a long neck and peculiarly shaped head favor the use of the tongue, lips,
and teeth, which in these animals are the sole prehensile organs. The
tongue and lips are supplied with muscular tissue : hence the power of
motion.

In the horse the upper lip is the principal organ of prehension.
This organ is supplied with circular muscular fibres, as well as ele-
vator and depressor muscles, the elevator being especially efficient in
curling and elevating the upper lip so as to grasp food. The elevator
of the upper lip terminates in a broad Y-shaped tendon, which is inserted
in the free part of the upper lip (Fig. 81). The tongue has extrinsic
and intrinsic muscles, which favor its protrusion and enable it to grasp

232

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the food and draw it within the mouth. The extrinsic muscles are
connected with the hyoid bone and chin, and render possible the pro-
trusion and retraction of the tongue ; the intrinsic muscles permit of

FIG. 81.— AFTER GAMGEE AND CHAITVEATT.

1 and 2, attricnlar muscles ; 3, scutiform cartilage: 4, external scuto-auricular muscle; A A,
ular branches of first pair of cervical nerves ; B B. anterior auricular nerves ; C, terminal fibres of the
supraorbital nerve; D, superficial branch of the lachrymal nerve; Y, tendon of muscle to elevate upper
lip ; Z, naso-transversalis muscle.

the change of shape of the tongue required in mastication and deglu-
tition. The tongue is, further, covered with a mucous membrane, on
the dorsal surface of which are numerous more or less horny papillae,

PREHENSION OF FOOD.

233

which in the cat tribe acquire especial hardness. The arrangement
of these papillae is characteristic of the different animals. Four kinds
of papillae have been recognized, — the filiform, or thread-like; the
mushroom-shape, or fungiform ; the conical ; and the so-called circum-
vallate papillae, which are in shape similar to the fungiform papillae,

FIG. 82.— TONGUE OF HORSE. (Gamgee.)

FIG. 83.— TONGUE OF Ox. (Gamgee.)

but which are surrounded by a circular groove. By the distribution
of these papillae the tongue of the horse can readily be distinguished
from that of the ox, — a point of some consequence, since horses' tongues
are sometimes sold in the market as beef-tongues. The tongue of the
horse is long, with a well-marked middle depression, or raphe, with a

234

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

broad, flattened spatula-shaped tip. At either side of the middle line
toward the root of the tongue is a very large compound circumvallate
papilla (Figs. 82 and 83). In the ox the tongue is pointed, thicker, and

FIG. 84.— THE " PARROT-MOUTH" MALFORMATION OF THE HORSE'S MOUTH. (Gamgee.)

deeper, and with two diverging rows of papillae, each containing from
eleven to thirteen papillae, at the base of the tongue.

In the horse the sensitive and mobile upper lip is the main organ in
the collection of food. The nose, aided by the sense of touch, serves to
indicate the substances suitable for food; the upper lip serves to carry the
food between the incisor teeth, so that it may be firmly held, while by an

active jerk and twisting motion of the
head the grass is cut, hay pulled from
the rick, or branches severed. In stall-
fed animals loose food is taken from
the manger by the lips, aided by the
tongue. If the incisor teeth are badly
formed, as in the projection of the upper
incisor teeth over the lower, as in the
malformation termed "parrot-mouth,"
grazing will be prevented (Fig. 84). So
also swelling of the gums or of the
palate, as in dentition, may act as a
mechanical impediment to the action of
the incisor teeth and prevent grazing
(Fig. 85). The position assumed by
the grazing horse is characteristic. The fore legs are separated, one
fore leg usually being advanced, or may be flexed, since the neck is not

FIG. 85.— PREHENSILE EXTREMITY OF

THE JAWS OF THE HORSE. (Colin.)

PREHENSION OF FOOD. 235

long enough to reach the ground : the lips then carry the grass between
the teeth. A horse cannot live on very bare pasture, since the grass must
be long enough to be grasped by his prehensile upper lip ; and he there-
fore cannot enter into competition with close-biting animals, such as
sheep, since they will deprive a field of the best and youngest plants as
fast as they come through the ground.

In the ox the tongue is the main organ of prehension of food, since
the upper lip is short, has but slight power of motion, and is blended
with the cartilaginous, solid muzzle, which is covered by a thick, secret-
ing membrane. The tongue of the ox is, however, provided with great
mobile power; it may project far from the mouth, and, curving like a
sickle, the animal may seize and draw food into the mouth. It is rough;
pointed, covered with recurved, sharply -pointed papillae so as to strengthen
its grasp on bodies with which it comes in contact. In grazing, the
tongue is protruded, curved around the grass, which is thus drawn into
the mouth and then cut by the pressure of the lower chisel-like incisors
against the elastic pad which occupies the position of the upper incisors.
The ox also is unable to feed on very short grass.

In the sheep and goat the upper lip has a certain degree of mobile
power, more than that possessed by the ox, but not as great as that of
the horse. It, however, is unable to grasp food., and merely aids the
incisors and tongue in grazing. The tongue is also more freely mova-
ble than in the horse, and the combination of the mobile lip and prehen-
sile tongue enables it to feed close to the ground. Here also the upper
incisors are absent, and grass is cut by the pressure of the lower incisors
against the cartilaginous elastic pad of the upper jaw.

The pig in its native state feeds by rooting out plants, roots, and
nuts from the ground, and is provided with a strong and mobile snout,
having a bony and cartilaginous basis, and moved by powerful muscles.
It acts like a spade in digging up the ground, while the lower lip is short
and pointed, and is enabled to gather food loosened by the digging action
of the snout. The passing of a ring through the snout of a hog entirely
destroys its natural methods of collecting food, and animals so treated
are dependent upon artificial feeding, and if left to their own efforts
would starve. Pigs are omnivorous, but yet their incisor teeth are so
shaped as to prevent them from grazing.

Carnivorous animals, such as the dog and cat, feeding principally on
meat and animal matters, fix their food with the forelegs, grasp it between
their powerful jaws, using here mainly the canine teeth, and lacerate it
by a backward jerk of the head. They are biting animals, and as a con-
sequence their cheeks are loose and ample, their mouths open widely,
and their teeth are pointed and curved back. The lower jaw only is used;
and it is said that when the lower jaw is fixed carnivorous animals,

236 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

with the single doubtful exception of the dog, are unable to close
the mouth.

2. PREHENSION OP LIQUIDS.— In the lower forms of animal life pre-
hension of liquid is accomplished by absorption through the general
external body surface, and in many cases, as, for instance, in the tape-
worm, where neither mouth nor stomach are present, the fluids so
absorbed carry also the nutritive matters in solution into its interior.
Many other animals which live on liquid food are provided with special
organs for absorption ; thus, in the leech there is a mouth or sucker,
provided with minute teeth for piercing the skin of other animals, while
in the mosquito there is a sharp, bristle-like tube for piercing the skin,
and in the louse there is a sharp suc'ker, armed with barbs to fix it
securely during the act of sucking. In certain insects which live on
viscid or fluid food, as the butterflies and moths, the mandibular append-
ages are modified from their usual form described in the preceding
section, and take on the form of a long, spiral tube, the proboscis, which
can be unfolded and protruded into flowers. A sucking proboscis also
is found in many flies and gnats. In fleas and bugs the mandibles are
penetrating and suctorial. In the higher animals no special prehensile
organs for the absorption of liquids are present, it being accomplished
by means of the apparatus already described for the prehension of
solids. Four methods for the prehension of liquids have, however, been
described by Colin: — •

a. Suction, as in the drawing of milk by young animals.

b. Pumping, by the immersion of the lips and the piston-like action
of the tongue within the mouth, on the principle of the common pump.

c. Aspiration, where the vacuum is produced by an inspiratory
movement, as well as by the motion of the tongue.

d. By lapping or ladling the fluid by the tongue into the mouth.

a. Suction. — In suckling, the teat is grasped by the lips, or, it may
be, even by the teeth, and the mouth closed around it. The tongue is
then pressed against the teat and withdrawn into the mouth, producing a
vacuum, and from the atmospheric pressure on the exterior of the breast
the milk then enters the mouth. There is, therefore, no danger of milk
entering the windpipe, since inspiration is not at all concerned in the
process of suckling ; hence, aquatic animals, like the cetaceans, may
suckle under water. In solipedes and ruminants, during suckling, the
tip of the tongue is often fixed between the teeth and the nipple ; the
vacuum is then made by the reduction in volume of the anterior part of
the tongue, while the base becomes applied to the roof of the mouth.

During the act of suckling, the sterno-thyroid and the sterno-, omo-,
and thyro-hyoicl muscles contract together, and so depress the larynx
and hyoid bone, while at the same time the hyoid bone is advanced by

PREHENSION OF FOOD. 237

the contraction of the genio-hyoid muscle, the root of the tongue being,
therefore, likewise depressed and drawn forward. At the same time
the genio-glossi muscles, contracting with their antagonists, the hyo-
glossi, have the effect of drawing the body of the tongue directly back-
ward, while the organ itself becomes flattened. The cheek-muscles are
entirely inactive in the act of suckling.

b. Pumping. — The process of drinking by means of pumping with
the tongue is employed by the horse and ruminants and most herbivora.
The lips are immersed below the surface of the water, which seldom or
never rises above the level of the nose ; a small space is opened between
the lips, and the tongue is withdrawn in the mouth by a mechanism
similar to that employed in suckling ; the tongue thus acting as a piston,
the pressure of the atmosphere on the water without serves to force it
into the mouth, and it is then carried by a motion of deglutition to the
phaiynx and gullet.

That drinking in the horse is not due to the production of a vacuum
in the mouth by inspiration has been proved by performing tracheotomy
on a horse, when, of course, the production of a vacuum by inspiration
would be impossible, and yet it was found that this operation did not in-
terfere with suction and drinking. So also a case has been reported of a
horse who was unable to drink, in whom, on examination, it was found
that a second molar tooth of the upper jaw had been lost, and a fistulous
tract led through to the nasal cavit}r. The tongue, therefore, was unable
to produce a vacuum, even when the nose was immersed below the surface
of the water, from the large nasal chambers and pharynx being in direct
communication through the fistula with the fore part of the mouth. Here
evidently was sufficient proof of the fact that drinking in these animals
was not due to any inspiratory effort. In the case reported, plugging the
fistula served to restore the power of drinking. Even without this proof,
however, the anatomical relation between the mouth and pharynx in the
horse is sufficient to show that in these animals breathing cannot occur
through the mouth in drinking, or in any other natural action of the or-
gans situated in the oral chamber; for. the soft palate forms a complete
partition between the mouth and the throat, and can only be elevated to
allow the passage of fluid or solids backward by compression, such as
that which occurs in swallowing.

c. Aspiration. — In this method of drinking the vacuum is produced
by the respiratory apparatus ; the mouth, then, is not entirely closed, and
air is also drawn in, the water and air together causing a rushing sound,
the palate is raised, and both the air and water enter the pharynx,
the water being swallowed with a part of the air. This method of
drinking is jerky, since H must be interrupted for respiration, as the
nose may be immersed in water ; and although it has been said to occur

238 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in the pig, and often has been noticed in the horse, there is considerable
reason for doubting that this is ever a normal method for the prehension
of liquids.

d. Lapping. — This method of the prehension of liquids is seen in
the carnivora, as in the dog and cat; since their mouths are relatively
much larger than the herbivora, they cannot be immersed in water up to'
the commissure of the lips without also immersing the nose. Such ani-
mals, therefore, spoon up water with the tongue, like taking water to the
mouth with the hand. The tongue is protruded, its tip rendered cup-
shaped by the action of its intrinsic muscles, and a small amount of
water lifted up and carried by the repeated protrusion and retraction of
the tongue to the mouth. The process is a very slow one, and is seen'
only in caruivora.

Various other animals have different modes for the prehension
of liquids. Thus, in the elephant the trunk is a combined force-pump
and suction-pump. The trunk being immersed in water, by inspiratory
efforts it is filled with fluid; the tip is then directed toward the mouth
and the water is forced through it into the mouth. Birds drink by
filling their lower beak with water, elevating their heads and allowing the
water to flow back into their pharynx without the production of any
motion of deglutition. The single exception to this manner of drinking
seen in the birds is in the case of doves and pigeons.

III. MASTICATION.

The term mastication is given to the purely mechanical operations by
which the alimentary matters, through the action of jaws furnished with
teeth, are comminuted in the mouth,. and is, in most animals, a necessary
preparation for the submission of food to the action of the gastric juice.
Its importance and completeness differ in different animals, depending
upon the. nature of their food. Animals, such as the carnivora, which
feed on readily digestible matters, do not need this preliminary prepara-
tion, and as a consequence the food of carnivora is swallowed in bulk
without having been subjected to any, or, at best, to but slight division
in the mouth. This applies also to all animals which feed on liquid or
soft foods, where a masticatory apparatus is not needed. All animals
which feed on grain and other vegetable matters require the process of
mastication to render the food susceptible to the action of the digestive
juices ; for, as we have found in these animals, the food-constituents are
inclosed in unjdelding envelopes which resist the action of the digestive
juices. To enable the nutritive matter to be released from these sub-
stances, such foods require mechanical subdivision before they can prove
of nutritive value.

MASTICATION. 239

In the bird, which is not supplied with a masticatory apparatus as
ordinarily understood, — that is, in whom mastication does not occur in
the mouth, — we have a supplementary organ, the gizzard, which serves the
same purpose in comminuting the food. In these animals, therefore, the
operation of mastication is performed in the abdominal organs and is
involuntary. Voluntary mastication performed in the mouth only occurs
in mammals, and is seen in its typical form in the herbivora, in a less per-
fect degree in the carnivora, while the omnivora occupy a mean between
the two.

Mastication is a complex act, and requires the action of active and
passive organs ; that is, the muscles of mastication, the jaws and teeth,
while it is aided by the tongue, lips, and cheek. In all vertebrates the
jaws move vertically, the nature and degree of the movement varying
with the nature of the food. In the carnivora the lower jaw is alone
usually movable, and its extent of motion is very much greater than in
the herbivora. The lower jaw is moved by five muscles on each side, the
temporal, the masseters,the two pterygoids, and digastric muscles, while
in the solipedes the stylo-maxillary muscle constitutes an auxiliary
muscle of mastication. The action which a muscle exerts is dependent
not only on the bulk of the muscle, but on the angle of insertion of the
muscle in the bone. The more acute the angle, and the nearer the point
of insertion to the articulation, the more extensive will be the excursion
of the movable part in the contraction of the muscle, and the greater
will be its velocity of movement. The more perpendicular the insertion
of the muscle, and the greater the distance between the point of insertion
and the articulation, the greater will be the power developed in the con-
traction of the muscle. The latter is the arrangement which generally
characterizes the muscles of mastication ; they are inserted perpendicu-
larly in the lower jaw, and at a considerable distance from the maxillary
articulation. The arrangement of the parts and the motions in mastica-
tion differ in different animals.

In the carnivora the articulation of the lower with the upper jaw is
by a transverse cond3rle fitting into a canal-like groove in the temporal
bone, the canine teeth and molars overlap, and, the lower jaw being nar-
rower than the upper, the only motion therefore possible is a simple up
and down movement (Figs. 86 and 87).

In herbivora the articulation of the lower with the upper jaw is above
the level of the molar teeth, and permits of a forward, backward, and
lateral, as well as an up and down, motion*. Three distinct t}rpes of her-
bivora, with reference to their mode of mastication, may be recognized.

First, the rodents, which have only two kinds of teeth, two highty
developed incisors in each jaw ; the canine teeth are absent, while the
molars, which are compound teeth, have a flat crown and transverse rows of

240

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

enamel. The temporal fossae are small, their zj'gomatic arches are slight,
and the maxillary condyle, instead of being transverse, as in the carnivora,
is antero-posterior, and articulates with the glenoid cavity in the same
direction, the articulating surface in these animals being a sort of
eanal or gutter running from before backward (Figs. 88 and 89). The
arrangement of the articulation ^^\ /?

of the upper and lower jaw, as
well as the mode of insertion
of the muscles, favor a backward

FIG. 86.—

HEAD OF CARNIVORA— DOG.
(Beclard. )

FIG. 87.— INFERIOR MAXILLARY BONE OF
CARNIVORA — POLAK BEAK. (B&clard.)

c, profile view of articular condyle of lower jaw (condyle of
right side) ; ct, front view of same condyle.

and forward motion of the lower jaw, which is, therefore, the character-
istic motion of rodents.

Second. — In the ruminants the jaws are long and feeble, the canine
and upper incisor teeth are absent, while the molars are compound teeth
with a flat crown, with the enamel arranged in antero-posterior layers.
The condyle of the lower jaw articulates with a plane or almost convex
glenoid surface of the temporal bone, and this mode of articulation,

FIG. 88.— HEAD OF RODENT— MARMOT.
(Beclard.)

FIG. 89.— INFERIOR MAXILLARY BONE OF
RODENT— CAPYBAKA. (Beclard.)

b, right articular condyle of lower jaw.

together again with the arrangement of muscles, permits of a rotatory
motion of the lower jaw, which is therefore a characteristic trait in the
mastication of the ruminants (Figs. 90 and 91).

Third. — In the solipedes and pachydermata three kinds of teeth are
present, and both of the above kinds of movement ; that is, rotation and

MASTICATION.

241

forward and backward motions are possible, but are not present in as
great a degree in this case as in the two preceding types of herbivora.
These animals, therefore, occupy a mean between the rodents and
ruminants (Fig. 92).

1. THE MOVEMENTS OF THE JAWS. — The mouth is opened by depres-
sion of the lower jaw, which is
effected in all animals by the
digastric muscles, aided, in the
horse, by the stylo-maxillary
muscle, which is in reality a
short branch of the former. The
lower jaw is depressed very
largely by gravity ; hence, in all
animals we find such a slight
muscular power acting as de-
pressor of the lower jaw as con-
trasted with the large number
of powerful muscles which pro-
duce its elevation. When the
mouth is opened the maxillary
condyle turns on its axis and
its posterior part, which, when
the jaws are closed, is in con-
tact, as in the horse, with the
subcondyloid apophysis, leaves this surface and moves anteriorly.
In carnivorous animals the condyle being fixed in a gutter-like glenoid
cavity, rotation on its axis is the only motion which is noticed.

FIG. 90.— HEAD OF HORNED RUMINANT— Ox.
(Btclard.)

FIG. 91.— HEAD OF HORNLESS RUMINANT— CAMEL. (Btclard.)

In all animals the finger placed below the zygomatic fossa will
distinguish the forward and backward motion of the coronary process
as the mouth is opened and closed. In carnivora the extent to which

16

242 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the lower jaw may be depressed is ve^ much greater than in the
lierbivora ; in the latter, as in the horse, eight to ten centimeters being
the extent of separation of the lower from the upper incisors. The
digastric muscle is comparatively feeble, and would appear to pull the
jaw back, but really it tends to advance it, since it is a lever of the
third class. In the hare, rabbit, and ox the digastric muscle has only one
bell}7, and in the ox is joined to the same muscle of the opposite side
by transverse muscular fibres ; in the dog there is no intermediary
tendon in the digastric muscle. The development of the digastric de-
pends upon the character of the food of animals. In the horse, sheep,
and ox, where it is small, it is a double muscle, and is inserted more
anteriorly in the lower jaw than in carnivorous animals, where it is
large. The conditions, therefore, are most favorable for its action in
lierbivora on account of its different insertion. This muscle antagonizes
the temporals, masseters, and pterygoid muscles.

FIG. 92.— HEAD OF SOLJPEDE— HORSE. (B&clard.)

The representative of the digastric in the lower vertebrates, as in
reptilia, according to Mr. G. E. Dobson, is a bundle of muscular fibres
arising from the occiput and inserted into the posterior extremity of
the mandibular ramus, its functions being simply those of drawing the
angle of the mandible backward and upward, and so separating the
jaws in front. This is also its form and function in birds and most
mammals, though in man, monke^ys, and rodents the muscle is made up
of two bellies with an intermediate tendon, which is often connected
by ligament with the hyoid bone. Mr. Dobson has traced an interesting,
connection between the mode of feeding and the type of the digastric
muscle. In the group of animals in which this muscle is connected
with the hyoid bone, the species swallow their food while in the erect po-
sition, with the head bent forward on the chest and the long axis of the
cavity of the mouth at right angles with the oesophagus ; in the other
this muscle is free, and all the species feed while resting on their

MASTICATION. 243

anterior extremities, having the long axis of the mouth in a line with
the oesophagus. Thus, among certain rodents and arboreal insectivora,
which habitually sit erect while feeding, holding their food between their
fore feet, the anterior bellies of the digastrics are large and united, and
the intermediate tendons well developed and connected by fascial bands
with the hyoid bone, and by their deep surfaces with the mylo-hyoitf
muscles, as in the rat and the common dormouse. In the water-vole
(Arvicola amphibius), however, the digastrics are connected together in
front by fascia alone, and the upper margin only of their middle part
is tendinous, and not connected with the hyoid bone. These animals
live on vegetable substances obtained while swimming, and habitually
hold the head stretched out in a line with the body.

The mouth is closed by elevation of the lower jaw, and is the
reversal of the previous motion. Here powerful muscular action is re-
quired, since in the closure of the jaws, in many cases, great force is
needed. It is accomplished by the temporals, the masseter, and pterj*-
goid muscles. In carnivora the temporal is the principal elevator of the
lower jaw. Its volume is proportionately enormous, the temporal fossa*
occupying the entire surface of the parietal bones back to the occipital
spine. In herbivora and rodents the masseter muscles are the most
highly developed; their origin being from the zygomatic arch and a
portion of the superior maxillary bone, and being inserted in the lower
jaw, in the solipedes on both faces of the coronoid processes, as far
back as the last molars. Both of these muscles act as levers of the
third class, as is very evident in the rabbit, where the coronoid processes
are much lower than the articulation of the lower and upper jaw. In.
the carnivora, the coronoid processes being separated b}' a considerable
space from the condyle, the conditions are most favorable for the action
of the temporal muscle. From the oblique direction of its fibres it tends
to produce drawing back of the lower jaw, where, as in the herbivora,
this is possible.

The masseter muscle is developed in inverse proportion to the tem-
poral. It is, therefore, the principal elevator of the jaw in the herbivora
and in the rodents. It rises from the zygomatic spine in solipedes, the
maxillary tubercle in ruminants, to be inserted in the lower jaw. It is
also a lever of the third class ; its fibres are directed backward and
downward in the herbivora, and it may^ serve, therefore, as in the rodents,
to assist in the forward motion of the lower jaw ; its greatest power is de-
veloped when the resistance to the elevation of the lower jaw is between
the molar teeth, while its origin, being on a plane external to its insertion
in the lower jaw, as in the horse and rabbit, it may aid in lateral motion
of the jaw in animals where this motion is not rendered impossible by
the mode of articulation of the jaws, or by the overlapping of the teeth.

244 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The pteiygoid muscles, especially the internal, which is usually the
largest, are also elevators of the lower jaw, and are most developed in
herbivorous animals ; they are also levers of the third class, and are, to
a certain extent, concerned in the production of lateral and antero-
posterior motion of the lower jaw in animals where these motions are
possible. Propulsion of the lower jaw, or antero-posterior motion, is
most marked in the rodents, although it is also present to a less degree
in solipedes and ruminants, but is impossible in carnivora on account of
the shape of the articulation of the jaws. In this motion the maxillary
condyles slide forward on the glenoid fossae of the temporal bone in ani-
mals where there may be a subcondyloid apophysis posteriorly and no
restricting surface anteriorly. This motion is quite marked in the pig,
which has a triangular condyle, but attains its maximum development in
the rodent. This motion is accomplished by means of the masseter
muscle, aided by the external pterygoids ; for in the rodents, and in a less
degree in ruminants, the origin of the most posterior fibres of the mas-
seter muscle are in advance of their insertion in the lower jaw. This
obliquity in direction of the masseter fibres, in contraction of this muscle,
therefore serves to move the jaw forward.

The retraction of the lower jaw, which of course occurs only in ani-
mals in which forward motion is possible, is accomplished by means of
the temporal muscle, the digastric being not concerned in the process,
since backward motion of the jaws only occurs in closing the mouth,
while the digastric in its contraction opens the mouth and even tends to
advance the lower jaw somewhat.

Lateral movement of the lower jaws is more or less pronounced in
all herbivora, but is most marked in the ruminants ; it never occurs in
the carnivora, as already explained, on account of the shape of the con-
dyles and overlapping molars, and the crossing of the canine teeth. The
lateral motion of the lower jaw is not a simple lateral displacement
parallel to the axis of the lower jaw; that is, it is not equal at both ex-
tremities of the jaw, but is an angular deviation very marked at the in-
cisor teeth, and is a rotation of the lower jaw around one condyle of the
inferior maxillary bone, the incisor teeth describing an arc of a circle,
whose centre is one condyle, which thus moves very little, while the oppo-
site condyle advances and partly leaves the articular surface, as may be
determined by placing the finger in the temporal fossa, when the coronoid
process on the side opposite to that toward which rotation is taking place
may be felt to move forward. In this lateral motion of the lower jaw
the axes of the molar teeth cease to be parallel, the incisor arch passing
one-third to one-half its extent to one side of the upper arch or pad
which represents it in the ruminants ; the molar teeth of the upper and
lower jaw are in contact on the side toward which rotation is occurring,

MASTICATION. 245

while they cease to correspond on the opposite side. It is, therefore, to
a certain extent, a circular motion, in which the axis of the lower jaw
crosses that of the upper. A further peculiarity of this lateral motion
of the lower jaw is that it is alternative; that is, there is not a deviation
first to the right and then to the left, but if the motion is first a deviation
to the right in the process of mastication it returns again to its central
position and again rotates to the right. This may occur for half an hour
or more in solipedes, and in ruminants in both first mastication and in rumi-
nation ; then the motion may be reversed, and may occur as a left lateral
deviation for a similar length of time. The camel is the only animal
which furnishes an exception to this method of mastication. In it the
lateral motion is alternative ; the deviation occurring first to the right
and then to the left of the central position. In solipedes this motion is
apparently not as marked as in the ruminants, but this difference is
merely apparent, it being to a certain extent concealed b}r the long lips
of these animals. It is, therefore, more evident but not actually greater
in the ruminants than in solipedes. Lateral motion of the lower jaw is
produced by alternate contractions of the pterygoids, especially the in-
ternal, the external being very small in ruminants, and by the nmsseters ;
when the deviation occurs to the right the motion is produced by con-
traction of the right masseter and left internal pterygold muscles. When
the deviation occurs to the left it is produced by contractions of the left
masseter and right internal pterygoids, the action of the pterygoids being
more marked in ruminants than in solipedes from the fact that in the
former animals the palatine ridges are nearer together ; therefore, the
lateral power of the pterygoid muscles is more marked.

2. THE ACTION OF THE TEETH IN MASTICATION. — The teeth are passive
organs of mastication, which are imbedded in the alveoli of the jaws.
Teeth may be divided into three different parts : the crown, or the part
which projects into the mouth above the gum; the neck of the tooth, where
it passes through the gum ; and the root, which is imbedded in the alveolus.
Teeth may be of two different kinds, — either simple, where the entire
external surface of the tooth is covered by enamel; or compound, where
two different substances, enamel and dentine, compose the free surface.
When a tooth is divided longitudinally it is found to consist of three
different substances ; the hardest, and that which in simple teeth covers
the crown, is termed the enamel, and passes over the neck of the tooth,
becoming gradually thinner, and only partially covering the fang. The
enamel (Fig. 93) is composed of pentagonal or hexagonal prisms, or
enamel fibres, of about one five-thousandth of an inch in diameter,
closety packed together and arranged in a radiating manner from the
surface of dentine below. The enamel contains no nutrient vessels, and
when destroyed is not renewed. The bulk of both crown and fang of

246

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

a tootli is constituted of what is known us dentine, a section of which
reveals it to be formed of a densely packed mass of curving tubes with
distinct walls, imbedded in a dense, bone-like matrix, which run from the
pulp-cavity to the outer surface of the dentine near which they ramify.
The material between the tubules or the matrix of the dentine is a per-
fectly homogeneous substance, containing nearly the whole of the earthy
matter contained in the tooth, arranged in all animals in superimposed
layers. The tubules are the one four-thousandth of an inch in diameter,
and when fresh contain nerve and vascular processes from the pulp.
The third substance found in teeth is known as the cement, or crusta
petrosa, and in the simple tooth merety covers the fang, whereas it dips
in between the layers of enamel in com-
pound teeth on the crown, and when the
tooth is wholly inclosed within its cavity
also covers the crown (Fig. 94). In
carnivora the teeth, as already remarked,
are simple ; in other words, their crowns
are permanently covered with enamel, and
when in extremely old subjects the incisor

FIG. 93.— ENAMEL PRISMS, AFTEK KOLLIKER.

(Klein.)
A, in longitudinal view; B, in cross-section.

...c

FIG. 94.— SECTION THROUGH A
CANINE TOOTH OF MAN, AFTER
WAL.DEYER. (Klein.)

A, crusta petrosa, with large bone-cor-
puscles; B, interglobular substance; C, den-
tinal tubules.

teeth and canine teeth wear down, — then only does the dentine of the
teeth become exposed. In herbivora compound teeth are invariably met
with. In other words, on the free surface of the teeth of herbivora
different substances of varying degrees of density and hardness are
always met with, the function of which is to insure a constantly rough
surface for the purposes of grinding; for a good mill-stone is composed of
materials which wear with different degrees of rapidity, and thus, always
remaining rough, most effectually grinds the substances over which it
passes. In the compound tooth, as found in the herbivora, the cement has
originally covered the entire crown, but as the tooth is erupted simply
remains on the biting or grinding surface of the tooth. Thus, in the

MASTICATION.

247

incisors of a horse, the free surface, with the exception of the crown, is
covered with enamel alone (Figs. 95 and 96). On the biting surface of
the incisor tooth, when freshly erupted, is always found a central spot
composed of cement, the enamel dipping in to form a cavity or depres-
sion on the free biting surface of these teeth. By the change in shape

FIG. 95 —DIAGRAM OF FRESHLY-ERUPTED
INCISOR OF LOWER JAW OF HORSE.
(Nuhn.)

c, depression in table of tooth : *, cement, which rapidly
disappears except from infundibuluin ; z, enamel ; c«,
dentine.

— X

FIG. 96.— LOWER INCISOR TOOTH OP
HORSE. (Nuhn.)

c, worn-down surface of table of tooth, showing the
alternate layers of enamel, s : z, dentine ; and x, dis-
colored cement filling infundibulum.

Cl

of this central depression in the incisor teeth of the horse, through the
gradual wearing down of the surface, an index is furnished of the age
of the horse, — a matter which will subsequently be alluded to.

The molar teeth of herbivorous animals are chiefly compound teeth, —
that is, the enamel dips down below the surface of the crown, and in
some animals, as in the elephant, the com-
pound teeth" may be regarded as a series
of flattened teeth arranged side by side in
the jaw, and connected only by the
cement, or crusta petrosa (Figs. 97 and
98). This substance is like that invari-
ably found covering the fangs of teeth,
but which only in compound teeth appears
upon the crown. The pointed fang or
fangs of teeth are pierced by an opening
which communicates with a cavity in the
centre of the body of the tooth, called
the pulp-cavity, which contains blood-
vessels and nerves which enter through
the opening in the fang, and in the pulp-
cavity ramify over a delicate fibro-cellular
structure constituting the pulp (Fig. 99).

The pulp is continuous over its surface with an infinite number of small
projections which extend into the tubes of dentine in the inner structure
of the tooth.

These three different substances, which constitute the substances of

FIG. 97.— SECOND UPPER MOLAR OF
HORSE, SHOWING WEAR OF
TABLE. (Nuhn.)

<•»', depression on table; pi, depression on
side; s, enamel ; 2, dentine; Cae, cement; a, ex-
ternal or buccal surface; t, internal or oral

248 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the teeth, var}^ in their chemical composition, and, as a consequence, in
their different degrees of hardness, dependent upon the varying amount
of inorganic matter found within them, thus : —

Dentine. Enamel. Cement.

Organic matter, . . . .28.01 3.59 32.24

Inorganic matter, . . . 71.99 96.41 67.76

The sharp angles and prominences on the crown of the compound
tooth are formed of enamel, as is the entire free surface of the simple
tooth. The deeper hollows in the crown of compound teeth are formed
by the wearing of the cement, while the substances varying in hardness
between these two are formed by the dentine. The fang of the tooth,
where inserted in the alveolus, is further covered by a membranous
lining, the periosteum, which is soft and contains vessels and nerves, and
which is reflected into the pulp-cavity through the opening in the fang
of the tooth. When ossified, this membrane forms osteo-dentine.

cae

FIG. 98.— HALF OF A FOSSIL, TOOTH OF ELEPHANT (Dens lamellosus). (Nuhn.) .
I, the single segments, or secondary teeth ; s, enamel ; z, dentine; cae, cement.

Teeth are entirely absent in birds, but are generally present in
fishes, amphibia, reptiles, and mammalia. In the latter class alone are
two sets of teeth met with : the first, the deciduous or milk-teeth, which
are only temporary, fall out and give place to the permanent teeth. With
the exception of a few fishes, such as the sheep's-head, and certain her-
bivorous reptiles, the teeth in fishes, amphibia, and reptiles as a class, are
solely prehensile ; they serve simply for seizing and dividing their prey
into portions small enough to be swallowed. It is only in the mammals
that the teeth serve actually as organs of mastication.

The teeth of fishes present greater varieties than those found in any
other class. They may be almost innumerable or they may be reduced to
a single tooth, as in the lepidosiren, which has only a single dental plate

MASTICATION.

249

in each jaw and a small tooth on the nasal bones; or, in many fishes, as in
the sturgeon and amphyoxus, they may be entirely absent. Their shape
is also subject to great variation. In the lowest forms of fish they are
short and blunt, and well fitted for grinding sea-weed and crushing shell-
fish ; such teeth are seen in the ray -fish. But in most fish the teeth are

FIG. 99.— DIAGRAM OF PREMOLAR TOOTH OF CAT, WITH ALVEOLUS, AFTER
WALDEYER (MAGNIFIED THIRTY DIAMETERS). (Thanhoffer.)

A, bony wall of alveolus : zo. enamel prisms : zh, enamel coating: h, spaces in the base of the enamel
prisms; D, dentine: d<-, dentinal tubules: fh, gum, with alveolar periosteum below it; C, cement; ch,
cement spaces; fb, tooth-pulp; i, nerve entering pulp ; and c, pulp blood-vessels.

usually small and conical, generally cylindrical, but sometimes flattened,
straight, curved, bent side wise, or even barbed ; or their edge may be ser-
rated, as in sharks generally ; or the base may be broader than the apex,
as in the sharks. The teeth of fishes are by no means limited to the free

250 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

maxillary and free mandibular bones, or the lower and upper jaws. In
some fishes, as in the carp, all the teeth are in the back of the mouth,
while in most fishes there are teeth not only on the maxillary and man-
dibular bones, but also on the bones around the middle part of the mouth;
even, sometimes, being found on the median line of the palate. In cer-
tain cartilaginous fishes the teeth depart from the usual rule, in conse-
quence of which they are mostly inclosed in the bone on which they rest,
but are attached by ligaments, so as to allow the teeth to be bent back-
ward in the mouth by pressure. In most fishes the enamel and cement
substances are absent, the body of the teeth being composed simply of
dentine, which on its external surface is more compact than when found
in mammals. The teeth of fishes are, as a rule, replaced several times
during life, especially in the cartilaginous fishes.

In amphibia, fine, prehensile teeth are found on the upper jaw and
palate-bones of the frogs and salamanders; more seldom on the lower jaw
also. In toads only palatal teeth are present.

In reptiles the jaws may be either covered with a thick, dense horn,
which assists in dividing the food, or they may exhibit the most perfect
dentition, as in the saurians.

The number of teeth is always very large, and while in crocodiles and
many lizards they are limited to the jaw-bones, they also exist on the ptery-
goid or palatine bones, and on the roof of the mouth of most ophidians.
The t^ypical form of the teeth of reptiles is conical, and they vary greatly
in size, from the minute tooth of the blind-worm to the powerful canine-
like teeth of the crocodile. They are sometimes c}'lindrical, but may be
flattened, or even have serrated margins. Their surface is smooth, or is
notched. In serpents they are relatively longest, and present a remark-
able structure in the case of the poison-teeth or fangs, which are strongly
curved and contain a canal opening at both ends of the tooth : on the
anterior or convex aspect of the teeth above, close to the gums, and
below on the concave surface, a short distance from the point of the
tooth. These teeth are usually confined to the upper jaw, and the canal
serves to convey the secretion of the poison-glands, by the duct, to the
substances in which the tooth is imbedded, the poison being forced out
by muscles which join the gland-capsule and compress the gland. The
poison-fangs are fixed to the superior maxillary bones, but, since these
in poisonous serpents are movable, the teeth can when at rest either lie
flat upon the gum, or they can be brought into a vertical position in the
act of striking. Reptilian teeth always contain dentine and cement, and
sometimes, also, enamel and true bone, the dentine differing slightly from
that of mammals, its substance being traversed by canals which commu-
nicate with the pulp-cavity. As the teeth of the reptile wear away they
fall out, and are replaced by an almost unlimited succession of new ones.

MASTICATION. 251

In birds teeth are never present as organs of mastication, their
place being taken by the muscular gizzard; but the horny coating of the
jaws is developed in successive laminae, especially seen in the parrot,
which forms the beak, and which serves, in the prehension of food, the
same purpose as the prehensile tooth of other animals.

In the mammal the greatest variety^ is met with in the number,
the shape, and external characteristics of teeth. They may vary in
number from one in the narwhal to as many as one hundred and ninety
in the dolphins. In the elephant there are at most ten, but usually only
six, namely, one entire molar, or sometimes parts of two on each side
of both jaws, together with the two tusks of the upper jaw. In the
rodents the ordinary number is twenty, but there are sometimes only
twelve, while in the hare aud rabbit there are twenty-eight. In rumi-
nants and commonly among the mammalia there are thirty-two ; but
forty-four (as in the hog and mole) is said by Owen to be the typical
number. When more than forty-four teeth are present, as is occasion-
ally the case in the lowest groups, the%y are of the reptilian type, as in
the porpoise.

Three kinds of teeth, as already mentioned, are met with : the in-
cisors, which are chisel-shaped for cutting and gnawing ; the canines,
which are longer and conical for tearing food ; and the premolars and
molars, which are variously cusped and tuberculated, and either flat-
tened at the sides for cutting or broad at the summits for grinding.
The incisors are smallest in the insectivora, larger in the carnivora, of
great strength in the herbivora, and especially strong in the rodents.
These vary in number : the lion has six in each jaw ; the squirrel two
highly-developed incisors in each jaw ; the ruminants none in the upper
jaw; the elephant none in the lower jaw; wThile the sloth has none at all.
The canine teeth are prominent, conical, and larger than the other teeth
in the dog and cat tribes ; but not so in man.* They are also large in
many non-carnivorous animals, as in the ape, bear, musk-deer, and others
where they are used as weapons of offense and defense. There are
never more than four, and are wanting in rodents and most herbivora.
The carnivorous molars are generally flat, ridged, or tuberculated, the
anterior ones being, as a rule, very small ; they overlap like the blades
of a scissors, and are, therefore, cutting and not grinding teeth in these
animals. The more purely carnivorous the species, the fewer the number
of molars. The herbivorous molars are provided with tubercles, as in
the quadrumana, man, and most omnivora, or are marked with trans-
verse ridges of enamel and dentine in the ruminants, solipedes, pachy-
dermata, and rodents. The premolar teeth are preceded by milk-teeth ;
the true molars have no predecessors. In mammals the teeth are con-
fined to the jaw-bones, fit closely in the sockets, may have one or more

252 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

fangs, each of which has its own socket lined with periosteum. Mam-
mals have, as a rule, two sets of teeth, — the deciduous and permanent
teeth ; and when the latter are worn down they usually loosen and fall
out, since they undergo little or no repair. An exception to this state-
ment is found in the case of the rodents, where the teeth continue to
grow from the fact that the fang remains open and the hollow at the
base into which the pulp extends — the so-called enamel organ — is per-
sistent, and fresh dentine is constantly being formed within the pulp
and fresh enamel upon the anterior surface. The unequal wear of the
hard coating of the enamel in front and the dentine behind preserves
throughout the whole life of the tooth its chisel-like edge. In many
animals sex exercises a remarkable influence on the development of the
teeth. Thus, in the anthropoid apes the upper canine teeth in the male
are more than twice the size of the analogous teeth in the female ; while
the tusks of the bear and of the male elephant and musk-deer are
larger than those of the female. So also in the solipedes the canine
teeth are absent in the female, while in the ox tribe, although temporary
incisors appear aboAre the gum in both jaws, the permanent incisors are
not developed in the upper jaw, but remain in a rudimentary condition
within the bone.

By the formula of dentition, or the dental formula, is meant the con-
venient method of reproducing in numerals the number and nature of
teeth found in different animals. To distinguish these teeth the letter
i is used to indicate the incisors, the letter c the canines, pm the pre-
molars, and m the molars. The upper rows of figures represent the teeth
of the upper jaw and the lower those of the inferior jaw, the formula
usually simply representing the teeth on one side of the mouth; doubling
the numbers given therefore represents the total amount of teeth. In
the dog the formula is as follows : —

'

That of the cat is :—

Man: —

1 2-2 ' C l-\ ' Pm 2^2 ' m 3^3 '

In herbivora the incisor teeth vary in importance in our grass-feed-
ing animals, and are absent in the upper jaw of ruminants, where their
place is occupied by the nbro-elastic pad already referred to. . Ruminants
have thirty-two teeth, — eight incisors and twenty-four molars. In the
horse there are two pairs of tushes, or canine teeth, and twelve large

MASTICATION. 253

molars in the upper and lower jaws. In front of the molar teeth there
are sometimes rudimentary teeth, which are called wolf-teeth. In the
horse the molar teeth have their grooves produced by the cement ar-
ranged longitudinally on the crown. In the stallion there are twelve
incisors, — six in each jaw, of which the upper are the longest, while the
central are the largest and the corner teeth the smallest, — four canine
teeth, and twenty-four molars; in all forty. In the mare there are thirty-
six teeth, the canine teeth being wanting. The free surface of the incisor
teeth, with the exception of the table, is covered with enamel, while the
fang is covered with cement. As the incisor tooth comes through the
jaw the cement which originally covered the entire body of the tooth
remains on the table of the tooth in a depression which is called the
infundibulum. As the enamel of the table of the tooth wears away
around this central infundibulum the dentine of the bod}^ of the tooth
within is gradually exposed. We, therefore, have three different substances
composing the table of the incisor teeth of the horse (see Figs. 95 and
96), — the outer ring of enamel; within that, concentrically, the exposed
dentine ; and within that again the more or
less triangular ring of enamel which com-
posed originally the wall of the infundibulum,
and which was continuous with the enamel
covering the crown of the tooth. Within
this, again, is a more or less circular or tri-
angular portion of cement by which the
infundibulum was originally filled. Occa-
sionally in front of the infundibulum a still
denser substance than the dentine will be FIG. 100.— INCISOR TOOTH oy

RUMINANT. (Nuhn.)

met with, which is called osteodentme, and 8,enamel; Z)dentine; cd,pu]p.cavity.
which is due to the exposure of the ossified

covering of the pulp-sac. This is also called the dental star. Two sets
of teeth are found in the horse, of which the first, or milk-teeth, are
wider and have distinct necks, are convex and are grooved posterior^.
The incisors at first are almost perpendicular, but become more and more
horizontal as the teeth wear down ; the lower permanent incisors have
one groove, the upper two.

In ruminants thirty-two teeth are met with, the incisors being found
only in the lower jaw. Eight incisors and twenty-four molars are met
with. The incisor teeth in the ruminant are always somewhat loose, their
table is always inclined, and the anterior border sharp (Fig. 100). The
molars are compound teeth which wear down and continue to grow even
to an advanced age of the animal. The inferior molars have their tables
inclining outwardly, the upper incline inwardly, while, as in the solipedes,
the molars of both sides cannot be in apposition at the same time, since

254 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the molar arches of the upper jaw are wider apart than those of the lower
jaw : and when the molars are in contact the incisors do not touch, thus
saving unnecessary wearing.

In the omnivora, as represented by the hog, there are forty-four
teeth, — twelve incisors, four canine or eye teeth, twenty-four grinders, and
four so-called wolf-teeth.

In the carnivora three kinds of teeth are met with. They are the
incisors, which are twelve in number, are sharp and cutting, and when
first erupted have three cusps on their free extremity, the lateral cusps
being on a lower plane than the central cusp. They thus, therefore,
resemble a fleur-de-lis. In carnivorous animals the two central incisors
are smaller than the next two, and these smaller than the next teeth. The
canine teeth are four in number, two in each jaw, and attain considerable
length, being larger in the upper jaw than in the lower, are pointed and
curved backward. The molars are variable in number, augmented . in
volume from the first to the penultimate, which has large cusps and is
termed the dens sectorius. The teeth of carnivorous animals, with the
exception of the incisors, preserve their pointed form unaltered.

In the dog the first three molars of the upper jaw do not come in
contact with the first four molars of the lower jaw, which correspond to
them, even when the mouth is closed. The highest cusp of the dens
sectorius, however, rests on the posterior surface of the first tuberculated
molar of the upper jaw. The incisors are cutting teeth, the canines tear-
ing, and the molars crushing or cutting, like scissors, but not grinding
in function.

The character and shape of the teeth vary in the different members
of the carnivorous group ; in the bear, which is essentially in type car-
nivorous, but which is an omnivorous animal, the molars are less pointed
than those of the pure carnivora, and approach in nature the shape
of the teeth of omnivora, of which man may be taken as a type. " In
the cat tribe all the teeth are very pointed.

The teeth are mechanical instruments without sensation, but serve
as conducting organs of sensibility, like the hair; since in man they are
sensitive to cold, therefore they are also probably sensitive in other
animals. They transmit sensations of resistance, which must be less
acute in animals, such as the carnivora, which are accustomed to
crush bones, and thus convey information as to the solidity of matters
between the teeth and regulate the degree of muscular effort required in
mastication. The articulation of the teeth with the alveoli is in the form
of a pyramid whose base is external. In mastication, therefore, pressure
is transmitted to the bony walls of the alveoli, and the sensitive pulp is
protected, unless the teeth are loose in their sockets, when mastication
becomes painful.

MASTICATION. 255

TO DETERMINE THE AGE OF THE DOMESTIC ANIMALS BY THE TEETH.*

It is chiefly by the incisor teeth that we can tell how old a horse
is, and it is important to consider the change in shape and general
appearance which these teeth undergo. There are temporary and per-
manent incisors. The first have a broad crown, flattened somewhat
from before back, with a wearing surface far wider from side to side
than from behind forward. They have a distinct neck, and a narrow,
sharp fang. The appearance of the temporary teeth is shelly, and there
is a well-marked depression or iufundibulum on the upper aspect. The
front of the tooth is of a pearly white, and is grooved or fluted. The
permanent incisor is much larger than the tempora^ tooth ; its crown
thicker, of a duller color, and the cavity or infundibulum is deeper. The
neck of the tooth is not so well defined, and as the animal acquires age
we find a ver}T remarkable change in the shape. This is seen in Fig. 101, B,
which represents different sections of the permanent incisor, as its surface
appears from progressive wear. It is from birth to the age of eight
years that from the condition of the " marks" or dark cavities in the
table of the incisors we can determine the age of the horse. There are,
however, deceptive cases.

The molar teeth are rarely looked at in determining the age of the
horse, but they furnish valuable corroborative evidence, especially in
young animals. They are not easily examined, but it is their number
which in the colt confirms or negatives the opinion expressed as to the
animal's age. The recentl}'-formed molar has a shelly character (Fig.
101 , C) and prominent tubercles of enamel, which soon wear down to form
a broad, grinding surface, and then the young and old teeth are not
easily distinguished.

The horse has six incisors above and six below. They are compound
teeth, as shown in Fig. 101 at A, and the cavity extends downward,
having beyond and a little in front of it the pulp-cavity, which in old
horses as the teeth wear down is indicated by a dark, hard structure,
which then fills it, and which is called osteodentine.

The temporary incisors are in perfect apposition as the colt
approaches two years, and not seldom an animal, especially a pony, has
been bought for five years of age from the temporary teeth being mis-
taken for the permanent incisors. The temporary incisor is gradually
displaced by pressure from the permanent. The latter advances, and has
a shelly aspect, seen in a, Fig. 101, at B. At b the incisor tooth indicates
two years' wear; at c five years', at d nine years', and at e about

Disease.

*This chapter is taken from Gamgee, " Our Domestic Animals in Health and in

• i^.. "

256

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

seventeen years' friction. The shape of the wearing surface of the tooth
is of great importance in determining approxi-
mately the age of the horse. Before eight
years the eruptive changes and periodic appear-
ances of the teeth are very regular and valuable in
indicating age. The foal at birth indicates the
fast approaching eruption of the two central
incisors. Sometimes these are through the gum
when the animal is foaled ; if not they appear
within the first month. Three molar teeth on
each side of both upper and lower jaws are prom-
inent, and in apposition for wear at the same time.
One incisor on each side of the two central ap-
pears at six weeks, and then time is allowed for
the jaw to grow. The cavities of reserve with
teeth forming in them grow behind the teeth first
formed, and by nine months the corner incisors
appear, and gradually grow until the animal is a
year old, when all the colt's incisors are in full
use. Within one and two years of age little can
be seen beyond a gradual wearing down of the
temporary teeth, and the protrusions through the
gums of the fourth molar on each side of the two
jaws. At two years the worn aspect of the
incisors indicates the approaching displacement
of the central ones, and the fifth molar protrudes
through the gums.

Between two and three years the central per-
manent incisors displace the temporary, and are
readily recognized by their size, yellowish color
of enamel, and dark infundibulum. At this age
the middle incisors are often knocked out to make
the horse look "three off" or "coming four."
This often retards their eruption, which is always
complete at four years, when the sixth molar tooth
on either side of both jaws is also advanced
sections of per- through the gum. B\' this time the three tempo-

rhHay ihetbie°fbeco°mee3 triZgu! ™y molars, or grinders, which are noticed shortly

lar from wear, a, on eruption; 6, «, -,. ,, ,

at two years ; c, at five years : d, at after birth, have given way to permanent teeth.

nine years; e, at about seventeen „ . .

The lower tushes are felt through the membrane

le of molar tooth of horse,

^gSoves1 arrangement between the corner, and first molar as early as
three years of age, but they only appear above it
between four and five. It is at this age that the horse's mouth becomes

FIG. 101.— TEETH OF
HORSE. (Gamgee.)

A. Longitudinal section of per-
manent incisor of horse shortly

15 Years. 18 Years. 24 Years.

FIG. 102.— CHANGES FROM AGE IN THE INCISOR TEETH OF THE HORSE. ( Wilckens.)

17 (257)

258

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

fully furnished, and by five the whole of the incisors are in full wear,
and indicate the extent to which they have been worn proportionate to
the period since their eruption. The central incisors then appear as
shown in 6, Fig. 101, B, whereas the corner teeth, having just protruded,
are shelly, as shown in a.

At six the central incisors lose their mark ; at seven this occurs
with the middle one, and at eight all the infundibula are worn out, and
the plate of the tooth is clean and only very slightly marked in the
corner teeth. Beyond this period the horse is stated to be aged. The
incisors protrude straighter from the receding jaw; the teeth become

narrower, and their wearing surface becomes
triangular, as seen at c, d, and e, Fig. 101, B.
This distinguishes the old animal.

The table on the preceding page, taken
from the " Encyclopadie der gessammten
Thierheilkunde," indicates the wear of the in-
cisors of the horse at different ages (Fig. 102).
Dentition in the Ox. — The incisor teeth of
the lower jaw of the ox are simple, and eight
in number (Fig. 103). From the periods of
eruption of both temporary and permanent
teeth being regular, the latter being much
the broader, the age of the animal is readily
determined. Further, the sharp teeth become
more and more blunt and narrow, until in old
cattle they are reduced to very small stumps.
The wear of the incisors commences on the free border, both in the decid-
uous and permanent teeth, the enamel being worn gradually from .the
table of the tooth, from the anterior border posteriorly, the dentine being
exposed in zigzag lines, which at the sides extend further toward the
neck of the teeth than in the middle. When the enamel is all gone from
the table of the incisors (after the tenth year), the entire crowns of the
teeth wear down until, in extreme age, only the necks are left. The
following table gives the succession of changes in the ox : —

FIG. 103.— LONGITUDINAL SEC-
TION OF INCISOK TOOTH OF
RUMINANT. (Ellenberger.)

C, tooth-cavity ; G, enamel ; E, pulp-canal ;
D, dentine.

SlMONDS.

SlMONDS.

GlRARD.

TABLE OF EARLY AVERAGE

TABLE OF LATE AVERAGE

TABLE OF LATE AVERAGE

(IMPROVED BREEDS).

(IMPROVED BREEDS).

(UNIMPROVED BREEDS).

t

1

No. of Teeth.

£

1

No. of Teeth.

2*

1

No. of Teeth.

1

9

2 permanent incisors

2

3

2 permanent incisors

2

3

2 permanent incisors

2

3

4

2

y

4

3

0

4

2

9

6

3

3

6

4

0

6

3

3

8

3

9

8

5

0

8

MASTICATION.

259

The following figures, from the " Encyclopedic der gessammten
Thierheilkunde," indicate the changes occurring with age in the incisor
teeth of cattle (Fig. 104).

Newborn. 8 Days. 4 Weeks.

12 Years. 14 Years. 16 Years. 18 Years. 20 Years.

FIG. 104.— CHANGES FROM AGE IN THE INCISOR TEETH OF THE Ox. (Wilckens.)

Dentition of Sheep. — In the sheep it is by the displacement of tem-
porary and eruption of the permanent teeth that the age of the animal
is determined.

TABLE OF EARLY DENTITION.

TABLE OF LATE DENTITION.

Years.

Mos.

No. of Teeth.

Years.

Mos.

No. of Teeth.

1

0

Central pair of temporary

1

4

Two permanent incisors.

incisors replaced by per-

manent.

1

6

Second

2

0

Four " •

2

3

Third

2

9

Six

3

0

Fourth " "

3

6

Eight "

260

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

These changes are also indicated in the following diagrams from the
" Encyclopadie der gessammten Thierheilkunde " (Fig. 105).

2 Months.
(Milk-Teeth.)

Years.
(2 Broad Incisors)

% Years.
(4 Broad Incisors.)

2M Years.
(6 Broad Incisors.)

4 Years.
(8 Broad Incisors. )

Over 7 Years.
(8 Broad Incisors.)

FIG. 105.— CHANGES FROM AGE IN THE INCISOR TEETH OF THE SHEEP. ( Wilckcns. )

Teeth of Carnivora. — All the carnivora have simple teeth ; i.e.,
covered entirely over the crown by white enamel. There are three pairs
of incisors, one pair of canines, and a certain number of molars. It is
the last premolars, or the first true molars, which are emplo^yed in chew-
ing flesh; they are prominent and sharp. Behind these, especially in the
dog, the teeth are armed with round tubercles on their surface, destined
for crushing or grinding action, and in breaking bones or gnawing long-
grass the dog may be seen -to push the substance between these back
molar teeth.

Dentition in Dog. —

6 1-1 6-6

Incisors - ; canines — ; molars = 42.

6 1-1 7-7

The dog is born with his eyes shut ; they open on the tenth or fifteenth
day after birth. The whole of the milk-teeth are usually cut then, or
very shortly after. Between two and four months the central incisors
and often even the middle ones of both upper and lower jaws drop out,
and speedily the whole of the permanent teeth are fully developed, so
as to complete the mouth by eight months.

The inferior incisors begin to wear by fifteen months. Fig. 106
shows the milk-teeth in a puppy two or three months old ; Fig. 107 in a
year-old dog. At eighteen months, or two 3rears, the inferior central
incisors are much worn, and between two and three years the middle
ones also (Fig. 108) ; the worn incisors bear a striking contrast to the

MASTICATION.

261

young teeth, as seen in Fig-. 107, where the edge or border of the tooth
is divided into three lobes, of which the most prominent constitutes the
point of the tooth. Between three and four 3* ears the upper central
incisors are worn, and between four and five the whole give indications
of much use (Figs. 109 and 110). Beyond this age the teeth are very
uncertain. The bluntness and yellow color of the tusks and other
teeth offer the best signs of increasing age.

FIG. 106.— MII.K-TEETH IN A PLTPPY
2 OK 3 MONTHS OLD. (Gamgee.)

FIG. 107.— DENTITION IN A YEAR-OLD DOG.
(Gamgee.)

FIG. 108.— DENTITION IN A TWO-YEAR-OBD DOG. (Gamgee.)

FIG. 109.— DEXTITIOX IN DOG BETWEEN
3 AND 4 YE A us OF AGE. (Gamgee.)

FIG. 110.— DENTITION IN DOG 4 OR 5 YEARS OF
AGE. (Gamgee.)

Dentition in the Pig. — The pig is born with eight teeth, which are
foetal incisors and foetal tusks. At one month four incisors are cut,
besides three temporanr molars on either side of each jaw. Two more
temporary incisors are added to each jaw at three months, and all the
milk-teeth are then in position. The jaws and teeth grow, and at six
months in most animals, but not .in all, a small tooth comes up on either
side of the lower jaw, behind the temporary tusks, between them and the
molars, and in the upper jaw directly in front of the molars. These
teeth have been mistaken for tusks. The fourth molar in position

262

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

appears through the gum also at six months. The corner incisors are
displaced and permanent ones cut at nine months. The permanent tusks
are also cut at this period, as well as the fifth molar on either side of
each jaw. At one year the middle incisors are changed and the tusks
appear of considerable size. The deciduous molars are likewise shed at
one year and succeeded by permanent. At eighteen months the denti-
tion of the pig is completed by the cutting of the lateral incisors and the
last or sixth molar. The succession of teeth in the pig is shown in the
following table : —

At
Birth.

One Month.

Three
Months.

Nine
Months.

Twelve
Months.

Eighteen
Months.

-n , i < Incisors.
Foetal \ Tusks, . .

4
4

4
4

4
4

. • -'

Temporary incisors,

4 central.

8 central
and lateral.

8 central
and lateral.

4 lateral.

• •-"?

Permanent incisors,

4 corner.

8 central

12 central,

and corner.

lateral.and

corner.

Permanent tusks, .

".•>

.

•

4 (cutting}.

4

4

Total in both jaws,

8

12

16

16

16

16

Other Signs of Age in Domestic Animals. — In horned animals the
horns grow annually a certain length, and this is shown by the appear-
ance of an extra ring every year at the root of the horn. .For the first
two years the rings are so indistinct that, in calculating the age in an
animal five or six years old, the first ring indicates a three-years' growth,
so that an animal with six rings must be regarded as eight years old.

Fraud may be practiced to destroy the marks of age. Angularity of
form, sharpness of bones and gray hair are not easily disguised, but teeth
can be filed and marked and horns scraped. Making false marks on teeth
is called " bishoping." Gray hairs may be painted, called "gypping."
In old horses the remarkable depressions behind the orbits are some-
times pricked and blown up with air; this is called "puffing the glym."

Some of the abnormal conditions of the teeth are the persistence of
temporary teeth, so that twelve incisors may be present in the lower jaw,
or the permanent teeth may fail to develop. One or more teeth may be
absent, from removal or from faulty development.

In the following table the order of dentition of the domestic animals
is recapitulated : —

MASTICATION.

263

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264 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

3. The TONGUE, LIPS, and CHEEKS are accessory organs of mastication,
and act by maintaining the food in its position between the teeth. In
many animals, particularly the horse, as already mentioned, the lips have
a high degree of prehensile power, and when the upper lip is paralyzed,
as by section of its motor nerve, prehension of food in the horse is
impossible. When the lips and cheeks are paralyzed, again, even in
animals in which these organs do not serve for prehensile purposes, mas-
tication is impossible, or at least rendered extremely difficult, from the
fact that their loss of motor power prevents their keeping the food
between the teeth ; their loss of sensibility prevents the determination
as to when the food has acquired the proper degree of comminution, and
their insensibility prevents these organs avoiding being themselves
lacerated by the teeth. This especially applies to the occurrence of mas-
tication between the molar teeth. Here, when the buccinator muscles
are paralyzed, through paralysis of the facial nerve (seventh pair), the
food collects in the pouches formed by the relaxed cheeks, and cannot be
properly masticated. The sensibility of the lips and cheek is derived
from the fifth pair of nerves.

The tongue is also an important organ of mastication ; it serves in
a large group of animals for the prehension of solids and liquids ; it is
of great importance in starting the process of deglutition, and in man it
is one of the principal organs of articulation. By its high degree of
sensibility it aids in mastication in determining the degree of comminu-
tion of the food, and in keeping the particles of food between the teeth
during their mastication; its mobility enables it to act as a sort of hand
in the necessary movements of the bolus of food in the mouth. Its
muscles are striped and voluntary in nature and arranged in four different
layers ; an upper and lower layer, passing from the root to the tip of the
tongue, and an upper and lower oblique layer. These muscles form a
complicated net-work of fibres which, b}^ varying degrees of partial con-
traction, permit not only changes in the shape of the tongue, but also in
its position within and without the mouth. The extension of the tongue
is accomplished by the muscles passing from the chin to the body of the
organ, the genio-giossus muscles. The retraction of the tongue is accom-
plished by means of the muscles arising from the hyoid bone and styloid
process, — the hyo- and stylo-glossus muscles, — and by the longitudinal
fibres in the body of the tongue. The different alterations in shape of
the tongue are accomplished by the contraction of its intrinsic muscles.
Thus, when the upper longitudinal fibres of the tongue contract the tip
of the tongue is elevated. When those of the inferior layer contract the
tip of the tongue is depressed, and by contraction of the upper oblique
layers the tip of the tongue is formed into the spoon shape which is so
useful in the prehension of liquids in the cat tribe. The motor power

MASTICATION. 265

of the tongue is derived from the Ii3'poglossal nerve ; its sensation is
derived from the lingual branch of the fifth nerve and the glosso-pharyn-
geal, both of these nerves being also concerned in the special sense of
taste.

We see from the above that the act of mastication differs very decid-
edly in nature according to the type of organization of the animal, and
its characters result from the configuration of the jaws, the play of the
muscles, and the form of the teeth. Thus, we find that the movements
of mastication in carnivorous animals are restricted to a simple eleva-
tion and depression of the lower jaw, this mode of mastication being
dependent upon the mode of articulation of the lower with the upper jaw
and the overlapping of the upper molar and canine teeth. Mastication,
therefore, in these animals is reduced simply to a process of section,
laceration, and crushing. The incisor teeth have but slight functional im-
portance, and are confined in their action to cutting. The canine teeth
are the principal organs of mastication, and exert a lacerating or tearing
function, while the molars are crushing in function and, from the fact
that they are highly tuberculated on their free crown surface, no process
at all analogous to grinding can occur between them. When in these
animals bones are crushed, such an operation only occurs on one side at
a time. In animals of the cat tribe, from the highly pointed character
of their molar teeth, crushing of hard articles of food is performed with
greater difficulty than in animals in whom the molar teeth have a more
blunt, tuberculated crown. Thus, animals allied to the dog can more
readily crush bones than the cat tribe. When the molar teeth are
brought into play, as in crushing a bone, the substance is usually fixed
by the fore paws, while the flesh is torn from the bones l>y the canine
teeth, and then the bones are drawn between the molar teeth by the action
of the tongue, the lips being loose and pendulous and enabling the mou'h
to be opened back bc}rond the level of the molar teeth: so that, therefore,
even large bones may partly be placed between the molar teeth, while the
remainder remains without the mouth. Crushing is then accomplished
by powerful contractions of the temporal and masseter muscles on one
side of the jaw at a time, and are accompanied by motions of the head
on the side on which mastication is taking place, and usually by the
closure of the eye on the side in which this operation occurs.

In the herbivora the movements of mastication are much more com-
plicated, and, as we find, differ in nature, the most marked extremes
being found in the rodents and the ruminants. In all herbivora the
lower jaw is always the narrower, and therefore both sides cannot act at
once. The jaw is longer, less powerful, and we find among the her-
bivora differences in the series of movements for the necessary com-
plete comminution of the food with which these animals are sustained.

266 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

A cutting motion is required, fulfilled by the incisor teeth, which are
consequently most highly developed in the rodents; and a grinding
motion, accomplished by the molars. As we have already found, the
lower jaw is capable not only of elevation and depression, but also of
advancement, retraction, and rotation, and all these motions are required
in the mastication of food by the herbivora. This motion is unilateral,
and may occur continuously on one side for fifteen minutes, and then
alternate to the opposite molars, and we shall find that the secretion of
the parotid salivary gland coincides with the side on which mastication
is taking place. This peculiarity of secretion is seen in all ruminants
and most herbivora, and has been even claimed to take place in man.

The duration of mastication depends upon the natural group to
which the animal belongs, on its age, and therefore the condition of its
teeth, and the character of its food. Carnivora require but slight mas-
tication of their food, and, in fact, mastication, as seen in the herbivora,
may in them be said to be entirely absent, the movements of mastication
in carnivora being simply confined to tearing the food into pieces small
enough to be swallowed. The herbivora, from the nature of their food,
need a longer time for reducing it to a condition of fine comminution,
and we find among the herbivora differences in the duration of mastica-
tion, according as the animals are ruminant or non-ruminant. The non-
ruminant animals, such as the horse, chew their food thoroughly and
once for all. It has been estimated by Colin that a horse will require one
and one-fourth hours for the mastication of four pounds of dry hay, and
of this amount will make sixty to sixty-five boluses, and, accordingly,
sixty to sixty-five motions of deglutition, while the rate of mastication
will be about seventy to eighty strokes of the teeth per minute. If any-
thing interferes with the secretion of saliva the duration of mastication
will be very much prolonged. One of the main objects of mastication
in the herbivora is to aid in the maceration of the food. Where, as in
the solipede, the food must be thoroughly macerated and comminuted
before reaching the stomach, the duration of mastication will naturally
l)e much longer than in the ruminant, where the food is simply subjected
to a few strokes of the teeth and then swallowed, to then undergo pro-
longed maceration in the rumen of these animals, and to be again
subjected to a second mastication in the mouth. In both animals,
although in a more marked degree in the horse, suppression or inter-
ference with the flow of saliva will prolong mastication; again, the drier
the food the greater will be the amount of mastication necessary before
the food can be comminuted and macerated sufficiently to be swallowed.
Therefore, grazing animals will require a less degree of mastication of
their food than those which are fed on grains or dry fodder. In the
ruminant the first mastication is three times as fast as the mastication

MASTICATION.

267

in the horse for the same amount of food, while the second mastication
is proportionately lengthened. As the teeth become worn away, masti-
cation becomes more and more difficult, and proportionately more and
more prolonged. In the horse the molar teeth are used up faster than
the incisors, and if it were not for the fact that the incisors become more
and more horizontal, the molar teeth could no longer come in appo-
sition. The influence of the secretion of saliva on mastication has been
determined by Colin experimentally, by making a fistula of the duct of
the parotid glands and allowing the saliva to escape externally from the
mouth. His results are shown in the following table : —

ALL THE SALIVA

SALIVA OF ONE

SALIVA OF BOTH

POURED INTO MOUTH.

PAROTID ESCAPING.

PAROTIDS ESCAPING.

No. of
Boluses.

Duration of
Mastication
of One
Bolus.

No. of
Strokes of
Teeth.

Duration of
Mastication.

No. of
Strokes of
Teeth.

Duration of
Mastication.

No. of
Strokes of
Teeth.

1

35 Seconds.

39

30 Seconds.

33

45 Seconds.

38

2

33

42

29

30

43

47

3

25

31

37

44

35

35

4

27

36

33

36

80

79

5

30

39

47

42

115

114

6

35

41

45

38

60

63

7

25

37

23

33

110

101

8

25

34

33

35

95

95

9

42

47

40

45

100

101

10

40

40

25

30

65

68

As regards the importance of thorough mastication, it is hardly
necessary to add anything further. We have found that its importance,
of course, varies in accordance with the nature of the food. Carnivora,
as has been mentioned, require mastication simpty to be perfect enough
to tear their food into pieces small enough to be swallowed, and in the
herbivora we reach the opposite extreme, and find there the group of
animals in whom a thorough mastication is of the utmost necessit}7.
From our considerations of the nature of vegetable foods w^e know that
the nutritive principles of these foods are contained within resisting,
tenacious envelopes. To enable these substances to be acted upon by
the digestive juices, and therefore to be absorbed, these envelopes must
be first mechanically ruptured, and this in the herbivora is the main
object of mastication.

Where we find mastication imperfectly performed, we have, as an
invariable sequence, imperfect digestion, and we find that the grasses and
seeds, and so on, which escape mastication pass through the intestinal
canal entirely unaltered and are found in the excreta unchanged, and, in
the case of seeds, without even having lost their power of germination.

268 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

They are, therefore, perfectly inert as regards any action to which they
may be subjected by the digestive juices. In the omnivora we find
mastication occupying a mean as regards importance between the her-
bivora and the carnivora. Where an omnivorous animal feeds on vegetable
diet the performance of mastication is as important as in the herbivora ;
while when on a meat or animal diet its importance becomes reduced to
the secondary degree in which it is seen in animals of a purely carnivo-
rous type.

IV. DIGESTION IN THE MOUTH.

THE SALIVARY SECRETION. — The salivary glands appear in most verte-
brates as tubular glands, as in insects, but in the mollusks they take on
the lobular form which characterizes them in the vertebrates. In birds
the salivary glands are small in the species which live on soft animal food
(waders and web-footed species), while they are larger in the graniverous
birds. In birds the saliva is mainly to assist in deglutition by lubricating
the food, as buccal mastication does not occur in these animals. In
certain birds, as the woodpecker, the salivary secretion assists in the
prehension of food. In the fishes, from the nature of their food, which
requires no mastication, we find the salivary glands almost entirely absent,
even in such groups as the cetaceans which belong to the general di-
vision of mammals. Here, also, we find that their food requires no pre-
liminary subdivision before being swallowed. As has been already
mentioned, one of the uses of the saliva is to assist in mastication ; where,
therefore, mastication is not performed we have in such animals a corre-
spondingly rudimentary condition of the salivary glands. On the other
hand, in nearly all animals which possess buccal or pharyngeal teeth
there is usually a glandular apparatus whose secretion, by macerating the
food, is destined to facilitate mastication and deglutition. In a general
way it may be said that in most cases where there are permanent prehen-
sile organs salivary glands are also present (Letourneau). Thus, the fly
emits on the particles it is about to draw in a brown liquid which dilutes
them. In reptiles the salivaiy glands become very highly developed, and
in certain of them their secretion acquires a poisonous character. In
chelonians and saurians the salivaiy apparatus consists principally of
lingual glands. In the chameleon they are located in the tongue and
secrete the sticky fluid which is of importance in their mode of prehen-
sion of food. Their maximum development is, however, reached in
mammals, with the exception of the cetaceans, as already alluded to,
where the lacrymal glands are also absent, and is especially marked in
the herbivora, whose food requires the finest comminution in the mouth.
In the ant-eater the salivary apparatus is enormously developed, the
glands covering the fore part of the neck and even extending to the chest,

DIGESTION IN THE MOUTH. 289

and a special reservoir, or salivary bladder, exists beneath the mouth. In
these animals also the saliva, through its viscidity, assists in the prehen-
sion of food. In the carnivora mastication is incomplete ; since the food
of carnivorous animals contains a large quantity of water, the salivary
glands of these animals are therefore relatively small, and their function
is confined to the production of a secretion which may act simply as a
lubricant and assist in deglutition. In the herbivora, on the other hand,
from the necessity for perfect subdivision required by their food, they
are relatively very large. The salivary glands thus reach their highest
development in the rodents, the pachyderms, solipedes, and ruminants.

Colin has divided the salivary glands into two different types. The
anterior system, or the mucous type, which empty their secretions into
the mouth in the neighborhood of the incisor teeth, comprise the
submaxillary and sublingual glands ; these glands are most developed
in carnivora and in aquatic animals, whose food must be lubricated for
deglutition, but not masticated. The posterior system, or serous type,
which empty their secretions into the mouth near the molar teeth, are
most developed in animals whose food requires thorough mastication, as
in the herbivora, and especially in non-ruminants. The parotid is the
type of this system. The glands which form these two systems are not
all developed in the same proportion. Thus, in the anterior system,
composed of the submaxillary, sublingual, and the gland of Nuck, the sub-
lingual maybe very small and the submaxillary very large, the former
being rudimentary in the dog. Again, they are rudimentary in the
dromedary, and are extremely highly developed in the ox. Again, as
regards the posterior system, in the horse the parotids are enormous,
while the submaxillary glands are rudimentary. In the ox the reverse is
the case. In herbivorous animals these glands have their largest volume,
but there is no relative proportion between the volume of the glands and
the volume of the secretion which the}r produce. Thus, in the ox the
weight of the salivary glands will amount on an average to six hundred
and twenty-four grammes ; the horse to five hundred and nine grammes ;
the pig, three hundred and five ; sheep, eighty-three; dog, twenty -five;
and the cat, ten. The parotid is the largest salivary gland in all animals
with the exception of the dog, and here the submaxillary gland is the
largest. In the pig, ox, and sheep the sublingual glands are sometimes
double, the one part emptying its secretion by a long duct opening at
the papilla at the side of the fraenum of the tongue, the other by a num-
ber of coiled ducts at the side of the floor of the mouth.

In addition to these large salivary glands the fluid in the mouth is
also poured out by glands located in its mucous membrane, forming
the so-called buccal, lingual, palatine, and pharyngeal glands. The
secretion formed by all these glands combined is termed mixed saliva.

270 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

It is evident from the varied sources of the buccal fluid that the
saliva is by no means a homogeneous fluid. If collected from the
mouth by expectoration, or in the lower animals by, holding the mouth
open and stimulating the surface of the tongue and the cheeks by any
sapid substance, as by the vapor of ether or acetic acid, or even me-
chanically, the fluid poured out will be found to be opalescent or more
or less turbulent, with a decided froth on its surface, from the air-
bubbles retained through its viscidity, and when allowed to stand in a
glass will deposit a sediment of epithelial cells and the so-called salivary
corpuscles. It will, therefore, form three different layers : the lower
one composed of this deposited sediment ; the middle, of a clear, though
opalescent, watery fluid ; while the uppermost layer will be more or less
frothy. Where a specimen of saliva remains standing for two or three
daj's exposed to the air the froth will disappear, and its place be taken
by a thin pellicle of carbonate of lime. When filtered, saliva forms a
watery fluid with alkaline reaction. Occasionally, where it appears to
have an acid reaction, the acidity is due to the fermentation of some
retained fragments of food in the mouth, as occurs after prolonged fast-
ing in diabetes and other pathological conditions; the secretion of the
salivary gland is invariably alkaline. Frerichs states that 0.15 gramme
sulphuric acid is necessary to neutralize the alkalinity of human saliva
collected during smoking.

The specific gravity of mixed saliva varies somewhat in different
animals. It has been placed at 1004.5 in the horse; 1010.2 in the pig;
1010 in the cow; 1007.1 in the dog; and from 1002 to 1006 in man.
D-eprivation of water is said to cause the saliva to acquire a higher
specific gravity ; thus, in the horse the normal specific gravity of 1004.5
or 1005, may be raised to 1007.4 after the animals have been deprived
of water for twelve hours.

The amount of saliva varies ve^ largely according to a number of
different conditions. Colin places the average daily secretion of saliva
in the horse at eighty-four pounds, and in the ox at one hundred and two
pounds ; while in the dog Jacubowitsch obtained in a hour 49.19 grammes
of parotid saliva, 38.94 of submaxillary and 24.84 of sublingual saliva.
We will, however, again return to the volume of saliva and the different
conditions modifying the rapidity of secretion when we come to con-
sider the secretion of the separate glands.

When- examined under the microscope mixed saliva is found to con-
tain numerous epithelial' cells from the cavity of the mouth, often debris
of food, inorganic particles of tartar from the teeth, various forms of
minute bacterial organisms, and the so-called salivary corpuscles. The
latter closely resemble white blood-cells in appearance, but are somewhat
larger, and are nucleated protoplasmic cells without a cell-membrane.

DIGESTION IN THE MOUTH. 271

When placed on the warm stage of the microscope they may often be
seen to be the seat of amoeboid movement, and to contain numerous
granules which exhibit the Brownian movement.

The chemical composition of the mixed saliva varies somewhat in
different animals. The solids are epithelium and mucin, ptyalin, serum-
albumen and globulin, and salts. The following table represents some
of the different anatyses which have been made of this secretion in
different domestic animals. According to Lassaigne, mixed saliva con-
tains as follows : —

Horse.

Water, 992.00

Mucus and albumen, ....... 2.00

Alkaline carbonates, . . . . . . . 1.08

Alkaline chlorides, 4.92

Alkaline phosphates and phpsphate of linie, . . traces.

1000.00
Cow.

Water, 990.74

Mucus and albumen, 0.44

Alkaline carbonates, 338 00

Alkaline chlorides, ....... 2.85

Alkaline phosphates, ....... 2.49

Phosphate of lime, 0.10

1000.00

Sheep. . .

Water, 989.00

Mucus and albumen, . . . . . . 1.00

Alkaline carbonates, ....... 3.00

Alkaline phosphates, . . . . . . :. 1.00

Alkaline chlorides, 6.00

Phosphate of lime, traces.

10CO 00
Man.

Water, 995.16

Solids, 4.84

Mucus and epithelium 1.62

Soluble organic matter, . . . . . . 1.34

Sulpho-cyanide of potassium, 0.06

Inorganic salts, 1.82

Dog.

Water 989.6

Solids, 10.3

Soluble organic matter, . . . . . . 3.58

Inorganic salts, 6.79

The following represents the quantitative composition of the ash
of the saliva of man and the dog (Jacubowitsch) : —

Man. Dog.

Salts, 1.82 6.79

Phosphoric acid, 0.51 ) n ft0

Sodium, . 0.43 S

Lime 0.03

Magnesium 0.01 $

Alkaline chlorides, . , 0.84 5.82

272 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The salts consist mainly of phosphates of sodium, potassium and
magnesium, and alkaline chlorides. One of the most remarkable con-
stituents of the saliva is the sulphocyanide of potassium which is found
in small amounts in many but not in all salivary secretions. Treviranus
in 1814 first made the observation that when saliva is mixed with a solu-
tion of oxide or chloride of iron and hydrochloric acid a bright-red
coloration is produced, which was recognized by Gmelin to depend upon
the presence of the sulphocyanide of potassium. It is said by Gmelin
to be present in largest amount in the saliva of the dog ; it is almost con-
stantly present in the saliva of man and in the saliva of the horse. It
probably, however, may be detected in the saliva of all animals by dis-
tilling the saliva with phosphoric acid and catching the first drops that
pass over on filter-paper treated with dilute hydrochloric acid and ferric
chloride, and then dried. Its presence may also be recognized by the
fact that paper, impregnated with tincture of guaiacum and then dried,
with an almost colorless solution of sulphate of copper, is colored blue
by the saliva. The reaction by which potassium sulphocyanide is recog-
nized— that is, the red color which it forms with an iron salt — is possessed
also by meconic acid ; the two substances may be distinguished, how-
ever, in a very simple manner. If a few drops of a solution of mercuric
chloride, or if a few mercuric chloride crystals, are added to saliva which
has been colored red by the perchloride of iron, the color is at once dis-
charged. When, however, the red color is due to the presence of
meconic acid and an iron salt, the red coloration is permanent, even
after the addition of corrosive sublimate.

The origin of this salt is not known, although the majority of
authorities seem to attribute its presence to a spontaneous decompo-
sition of the saliva, since saliva which has been standing for some time
will give the reaction in a more marked degree than when entirely fresh.
This view is still further strengthened by the fact, determined by Ellen-
berger and Hofmeister, that extracts of the salivary glands of all the
domestic animals, whether made from dried or fresh glands, with water,
carbolized or alkaline water or gtycerin, entirely fail to show this re-
action. Absolute data as to the origin of this salt are entirely wanting.
Its use in the economy is also clouded in obscurity, as it is eliminated
unchanged through the kidneys and may be recognized in the urine.
The chlorides in saliva may be recognized by filtering and acidulating
strongly with nitric acid ; the addition then of a few drops of a solution
of nitrate of silver to the saliva will cause quite a decided white precipi-
tate which is readily soluble in ammonia.

Of organic constituents, saliva contains albuminous bodies, as may
be recognized by the xanthoproteic and Millon's reaction ; it contains
mucin, as maybe determined by precipitating with acetic acid; and it

DIGESTION IN THE MOUTH. 273

contains a substance of the nature of a ferment, which is termed animal
diastase or pt3*alin, whose presence may be demonstrated by the power
possessed by the saliva of converting starch mucilage into sugar. Of
the albuminoid bodies, serum-albumen and a globulin-like bod}' which
may be precipitated by carbonic acid are the representatives.

The most important constituent of the saliva is the ptyalin. This
substance belongs to the group of soluble ferments, and is a product of the
cells of the salivary glands. It may be obtained, according to the method
of Colmheim, by adding a little phosphoric acid to mixed saliva and then
stirring with milk of lime until the alkaline reaction is restored ; the
white precipitate is then filtered off, and the filtrate shows scarcely any
albuminoid reaction, while it still possesses in an almost undiminished
degree its diastatic power. A considerable quantity of the ptyalin still
remains clinging to the albuminoid matters deposited in the precipitate,
and if this is washed with water the ptyalin is extracted, while it leaves
the albuminous matters still on the filter. If alcohol is added to the
watery extract of this precipitate, a flocculent, whitish precipitate is
formed, which may be collected by decantation and dried over sulphuric
acid. A grayish-white powder is thus obtained, which consists of pt}-alin
mixed with phosphates ; the latter may be removed by dissolving in
water, precipitating again by absolute alcohol, washing the precipitate
with dilute alcohol and then with a small quantity of water, and drying
at a low temperature. Ptyalin so obtained is a nitrogenous substance,
but not an albuminoid. It is readily soluble in water and glycerin and
possesses the power of converting starch and gtycogen into maltose,
and this property is exerted whether in a neutral or very faintty acid or
alkaline medium. An excess of alkali or of acid, as will be again referred
to, prevents its activity. The ferment may also be extracted from
the salivary glands by mincing fresh glands and covering them with
gtycerin. As the ferment is soluble in glycerin, it is extracted from the
gland-tissue, and may be precipitated again from the glycerin extract by
alcohol.

The saliva contains appreciable volumes of different gases in
solution, as determined by Pfliiger in the case of the submaxillary gland
of the dog. He estimates the different amounts of gases contained in
the saliva as follows : —

Oxygen, . . . . 0.4 to 0 6 volume per cent.

Nitrpsen. . . . . 0.7 to 0.8
Carlion dioxide, . . . 49.2 to 64.7

It is thus seen that saliva is the richest in CO, of any fluid in the
animal body. Only a small proportion of the above amount, however,
can be extracted with the gas-pump, showing that the remainder is held
in chemical combination. The amount capable of being pumped out

18

274

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

varies from 19.3 to 22.5 c.c., while from 22.9 to 42.5 c.c. of C02 are

liberated on the addition of phosphoric acid.

The secretions of the different glands of the salivary system present

several distinguishing points which will be alluded to in turn.

1. The Parotid Secretion. —
In order to study the pure secre-
tion of the parotid gland, the
saliva must be collected before
it reaches the mouth to be mixed
with fluid from the other glands.
This may be accomplished, in
man or in the dog, by catheter-
izing the parotid duct, an oper-
ation which is readily performed.
It is only necessary to open the
mouth and evert the cheek, when
the papilla of entrance m&y be
recognized on the inner surface
of the cheek, on a level with the
second molar tooth of the upper
jaw. A slender glass tube or

silver cannula may be readily inserted within the orifice of the duct and

the fluid collected as it flows through the tube. Where studies as to the

FIG. 111.— PAROTID AND SUBMAXILLARY GLANDS
OF THE DOG, WITH THEIR EXCRETORY
DUCTS. (Btelard.)

p, parotid gland: m, submaxillary gland; *, duct of Steno;
r, duct of Wharton ; v, masseter muscle ; /, temporal muscle.

FIG. 112.— RELATIONS OF THE PAROTID DUCT OF THE DOG WITH THE
FACIAL VESSELS AND NERVE, AFTER BERNARD.

The dotted line indicates the line of incision for finding the duct at the apex of the angle formed by
the vessels and nerve. V. vasculo-nervous fasciculus forming the inferior side of the ang'e : N, fasciculus
forming the upper side ; D, point of junction of these two fasciculi ; C, duct of Steno bisecting this angle.

mechanism of secretion have to be made, or where a considerable quan-
tity is to be collected, a more convenient method is to make a fistulous

DIGESTION IN THE MOUTH.

275
This may be

opening into the parotid duct before it reaches the mouth,
readily performed in the horse or dog (Fig. 111).

To make a parotid fistula in the clog, the animal usually employed in these
experiments, the hair is first shaved from the cheek, between the eye and the angle
of the mouth. On running the finger along the lower border of the zygomatic
arch, just before it is inserted into the superior maxilla, a slight notch is felt. It
is just at this point that the duct passes into the mouth. After chloroforming the
animal, an incision is made through the skin from this point, cutting obliquely in
a direction from the inner canthus of the eye to the angle of the mouth, passing
through the subcutaneous cellular tissue, when the facial artery and vein, branches
of the facial nerve, and parotid duct are found together, the duct pearly white in
hue, passing horizontally across the fibres of the masseter muscle parallel to the
nerve, usually about a quarter of an inch below it, while the artery and vein run
from above downward (Fig. 112). The vessels and nerves must be carefully
removed from before the duct, which is to be isolated and closed as near the
mouth as possible with a clip. A cannula may then be inserted into the duct. If
it is decided to retain the fistula permanently, the duct must be freed from the
connective tissue for as long a distance as possible, divided, and then brought out
at the angle of the wound, which is to be closed with sutures, one passing through
the duct to retain it in position. After a few days, when the wound is healing,
the duct will mortify and drop out, leaving a fistulous track to the gland, which
must be kept open by the daily passage of a fine probe, as it has a decided ten-
dency to close. A similar operation is readily performed upon the horse or ox,
where the large size of the duct renders it easily recognizable. After a cannula
has been inserted into the duct of the animal, its free extremity may be connected
by a piece of rubber tubing with a rubber bulb or glass bottle, in which the saliya
may be collected (Figs. 113 and 114).

FIG. 113.— PAROTID DUCT IN THE HORSE. (Bernard.)

The dotted line indicates the contour of the gland and the course of the duct of Steno.

The parotid gland of the horse is only in activity when the animal
is masticating food, while the parotid glands of the ruminants are con-
tinually secreting. The parotid glands constitute almost entirely the
posterior or serous system of the salivary glands, and furnish by far the
largest amount of the fluid which impregnates the food. The parotid

276

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

glands secrete alternately during mastication, both in the horse and

ruminant animals, and, in all probability, also in the omnivora, the

secretion occurring on the side
on which mastication is taking
place. Thus, when mastication
is takin» Place Between the right
molar teeth, then it is the right
parotid alone, in the horse, which
secretes, and it is the right
parotid in the ruminant which
has the highest activity. Ex-
IN THE HORSE, periments conducted by Colin,
by making a fistula of the parotid
ducts in the horse and the ass,

have demonstrated the truth of these statements. The following tables

represent some of his results : —

2,

FIG. 114.— PAROTID FISTULA
(Bernard.)

a, duct of Steno, with cannula inserted, and rubber bag for
collecting the saliva.

Experiment.

Time in Minutes.

Right Parotid. Left Parotid.

Side of Mastication.

1. Horse,

. 15

910 grammes. 200 grammes

Right.

f*

. 15

580

320

Right.

* *

,( .15

250

' 700

Left.

2. Horse,

15

570

< 620

Left.

"

. 15

510

820

Left.

"

. 15

500

* 800

Left.

«

. 15

480

750

Left.

"

. 15

720

420

» Right.

tt

. 15

540

800

Left.

"

. 15

600

740

Left,

3. Horse,

. 15

620

260

Right.

"

. 10

320

200

Right.

"

. .5

200

120

Right.

"

V . 15

410 .

230

Right.

"

. . 10

60

320

Left.

"

. 5

20

150

Left.

"

. 15

130

520

Left.

4. Horse,

5

160

85

Right.

•<

. 6

150

235

Left.

"

. 4

160

40

Right.

**

. .4

115

70

Right.

M

. . 4

95

165

Left.

"

. . 6

80

210

Left.

5. Horse,

3

50

110

Left.

*«

. 6

200

50

Right.

"

. 4

30

100

Left.

"

. 5

200

30

Right.

6. Ass,

. 15

120

10

Right.

*«

. 15

110

60

Right.

•«

. 15

80

170

Left.

"

. 15

150

15

Riffht.

"

. 15

30

160

Left

"

. 15

55

135

Left.

«

. 15

50 ' 165

Left.

DIGESTION IN THE MOUTH. 277

These results must not be regarded as absolutely correct, since, even
in the horse, the operation of making a fistula interferes with the normal
sequence of mastication, as it is always longest on the side which is
opposite to the fistula.

Ellenberger and Hofmeister found that the parotid of one side in one
horse secreted 1000 grammes in half an hour, the same amount in another
horse in a quarter of an hour, and in a third horse 4000 grammes in two
hours — oats, hay, and chopped straw being given as food. During the
pauses between the acts of mastication, the parotids of the horse, con-
trary to what is the case in the ruminant, are quiescent.

In ruminant animals this alteration of activity of the parotid glands,
although depending upon the side of mastication, is less readily deter-
mined than in the horse ; for when a fistula is made the ruminant animal
will continuously masticate on the opposite side to that in which the
fistula is present, and the maximum activity of secretion is therefore
taking place on the side opposite to the fistula. On the other hand, if
two fistulae are made the animal will change the direction of mastication
two or three times a minute, and the process of mastication is much in-
terfered with and the character of secretion altered. The inequality of
the secretion according to the side on which mastication is taking place
is also seen in the ruminant animal during the second period of mastica-
tion in rumination.

These experiments seem to show that mastication is the normal
stimulant of the parotid glands, though they also secrete during the
pauses of rumination. Further, these glands are insensible to other
stimulants, such as salt, acids, etc., brought into contact with the mucous
membrane of the mouth. Such stimuli produce no sensible secretion in
solipedes and no increase in the constant secretion of ruminants. So,
also, sight and odor of food have no effect on the secretion of the parotid,
even if the animals are in a state of great hunger.

The character of the parotid saliva also differs from that of mixed
saliva and that of the other salivary glands. It is thin, limpid, contains,
with the exception of a few epithelial cells, scarcely any formed elements,
and is invariably alkaline, except after prolonged fasting, when the first
few drops may have a slightly acid reaction from the contained carbon
dioxide. Great variation exists in the estimates of its specific gravity,
it having been said to vary from 1003 to 1012. It contains scarcely any
mucin ; when heated to boiling it becomes turbid, as also occurs after the
addition of alcohol or mineral acids, showing the presence of an albumen-
like body. It becomes clearer when CO, is passed through it. It con-
tains ptyalin. Sulphoc3'anide of potassium has been said to be absent
from the parotid saliva of the horse. The parotid saliva of the dog has
a specific gravity of 1004 to 1007, and when heated deposits a slight

278 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

sediment of calcium carbonate. When allowed to slowly evaporate on a
glass plate, crystals of sodium chloride and calcium carbonate are formed.
It is said to contain no diastatic ferment.

The parotid saliva of the horse contains large quantities of lime, and
when -allowed to stand in the air deposits beautiful crystals of the car-
bonate of lime. The parotid saliva is largest in amount; the two glands
of the ox are said to produce in an hour eight hundred to twenty-four
hundred grammes of saliva. As already stated, this secretion is inter-
mittent in the horse and constant in ruminants, where it is closely con-
cerned in the phenomena of gastric digestion.

The diastatic action of the parotid saliva is very active in rodents,
but little active in ruminants ; absent in the sheep, though in the latter
animal, as in the case of the horse and ass, watery infusions of the parotid
salivary glands will convert starch into sugar. In carnivora the parotid
gland is relatively smaller in amount and is almost inactive.

The following analyses have been made of parotid saliva: —

Man.

Water, . 993.16

Solids, . ... . < . ":••:. . . . 6.84

Organic matter, . . . . . ... 3.44

Chlorides and carbonate of lime, » , . . 3.40

Dog.

Water, . V . . '. " > .-'.-'» '. . 995.3
Solids, . .... '...., . ..... .... , . . 4.7

Organic matter, 1.4

Potass, sulphocyanide and alkaline chlorides, . •• . • "• 2.1
Calcium carbonate, . - • , '.*.'* v- - . . .» 1.2

Horse.

Water, . . . 992.92

Solids, . . . . 7.08

Epithelium and calcium carb. . . . . . 1.24

Soluble matter, . . . .' .. . . . 5.84

Alcoholic extractives, . . •••'.. '. .• . . . . 0.98

Soaps, . . , ..'..- . . , . . . . . 0.43

Cow.

Water, 990.7

Mucin and soluble organic matter, .... 0.44

Alkaline carbonates, 3.38

Alkaline chlorides, .-:..' 2.85

Alkaline phosphates, ....... 2.49

Calcium phosphates, . . . . . . . 0.10

Ram.

Water, 989.0

Mucin and soluble organic matter, 1.0

Alkaline carbonates,
Alkaline chlorides,
Alkaline phosphates,
Calcium phosphates,

3.0

6.0

1.0

traces.

DIGESTION IN THE MOUTH.

279

The parotid saliva of the dog contains 1.818 and 1.701 pro. mil.
volumes of combined CO,.

Salivary calculi are formed most usually in the parotid duct from
the deposition of lime salts, and contain no other ingredient of the
saliva.

2. TJie Submaxillary Secretion. — The saliva of the submaxillary
gland may be collected in man by inserting a small cannula in the opening
of the duct in the papilla of entrance at the side of the fraenum of the
tongue, or by aspirating it by a small syringe whose nozzle will grasp
the papilla air-tight. In animals the maxillary saliva may be collected
by means of a permanent or temporary fistula of the duct of Wharton.

FIG. 115.— OPERATION OF ISOLATING THE DUCT OF THE SUBMAXILLARY
GLAND IN THE DOG. (Bernard.)

a, digastric muscle drawn to one side ; b, mylo-hyoid muscle divided and drawn to one side ; c e, duct of
Wharton ; d, duct of the sublingual gland ; 1, lingual nerve.

To discover the submaxillary duct before its entrance into the mouth, after
etherization, the hair is shaved from the under surface of the lower jaw, an
incision made along the inner border of the ramus of the lower jaw from the
anterior insertion of the digastric muscle forward for about two inches, dividing
the skin and platysma, every vein that comes into view being tied with two
ligatures and divided between them. The mylo-hyoid muscle is then in view, and
is to be very cautiously divided at its middle, avoiding the mylo-hyoid nerve,
which lies upon it. If the portion still in connection with the ramus of the jaw
is elevated, the submaxillary and sublingual ducts will be found running forward

280

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

side by side, near to the ramus of the jaw, to enter the mouth, the submaxillary
duct being somewhat the larger and lying nearer the jaw ; the ducts are crossed
by the lingual nerve. Either duct may then be isolated or divided and treated as
in making a permanent parotid fistula (Figs. 115 and 116). In the horse, rumi-
nants, and rabbits the operative procedure is about the same as in the dog
(Fig. 117).

The submaxillarjr saliva obtained by catheterization or from fistulye

is a limpid, viscid fluid of alkaline
reaction. Its density is said to be
greater than that of the parotid or
mixed saliva, and may rise to 1025
after feeding. According to Eck-
hard, the submaxillary saliva be-
comes more consistent when exposed
to tbe air, and will precipitate a
flocculent deposit. Corrosive sub-
limate causes it to become almost
gelatinous without becoming turbid.
It contains a considerable quantity
of mucin, to which this viscidity is
due. Albumen seems to be almost
absent from the submaxillary saliva,
or to be present only in traces,
although the xanthoproteic reac-
tion1 will demonstrate the presence
of proteids. The diastatic power
of the submaxillary saliva of the
dog appears to be but slightly de-
veloped in the fresh saliva, although
it acquires this property by stand-
ing one or two days in the atmos-
phere. The following tables, after
Lassaigne and Herter, represent the anatysis of this secretion —

IIG. 116.— ANATOMY OF THE SUBMAXIL-
J.AHY AND SUBLJNGITAL GLANDULAR
REGION IN THE DOG. (Bernard.)

a a, digastric muscle; ft b, mylo-hyoid muscle;
c e, sublingual gland ; d. sublingual duct ; e, submax-
illary duct : ./' g, submaxillary gland ; 1, lingual nerve ;
2, chorda tymp'ani.

In the Horse.

Water, . »
Solids, .

Salts,

Organic matter,

992.5
7.5

2.575
4.925

In the Cow.

Water,

Mucin and albuminous matter,
Alkaline carbonates, . . .
Alkaline chlorides,
Alkaline phosphates,
Phosphate of lime,

9U 14
3.53
0.10
5.02
0.15
0.06

DIGESTION IN THE MOUTH. 281

In the Dog.

Water, 994.4

Solids, 5.6

Organic matter, 1.75

Mucin 0.66

Soluble ash 3.59

Insoluble ash 0.26

Carbonic acid in combination, 0.44

The submaxiljary saliva of other animals has been less studied than
in the dog; that of the rabbit, according to Heidenhain, is clear, not
viscid, and alkaline. It does not become turbid when exposed to the
atmosphere, contains albuminoids, but no mucin or ptyalin. It contains
1.23 per cent, of solids. The submaxillary saliva of the sheep is
strongly alkaline and slightly viscid. The first few drops are turbid,
but it then becomes limpid, to again become turbid when exposed to the

FIG. 117.— PAROTID AXD SUBMAXII/LARY FISTULA IN THE HORSE, AFTER

COLIN. (Thanhoffer and Tormay.)
K Kf, rubber bulbs for collecting saliva; PS, cannula in the parotid duct.

atmosphere; it contains considerable quantities of albuminoids and a
variable amount of mucin, but always less than in the saliA~a of the dog.
The submaxillary saliva of the pig contains no ptj'alin. The saliva of
the calf and other herbivora, with the exception of the rabbit, is said
to be rich in ptyalin. In the submaxillary saliva are found the so-called
morphological elements or salivary corpuscles, which appear to be identical
with the white blood-corpuscles and possess amoeboid movements.

282

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The secretion of the submaxillary glands is not unilateral, as in
the case of the parotid, and the side on which the greatest secretion is
taking place does not appear to be modified to any great extent by the
locality of mastication. The largest amount of submaxillary saliva is
secreted at the commencement of a meal and almost ceases during ab-
stinence,— a point of contrast with the parotid saliva. The stimulation
of the sense of taste by sapid substances is of the greatest influence on
the amount of submaxillary saliva. The following table, compiled by
Colin, illustrates these facts : —

Right Submaxillary Fistula in the Horse.

Time in
Minutes.

15
15
15
15
15
15
15
15
15
15
15
15
15

Amount in
Grammes.

31
26
24
22
17
23
19
22
31
50
23
20
26

Side of
Mastication.

Left.

R glit.
Left.

Right.
Left.

Food.
Hay.

Oats.

Right Submaxillary Fistula in the Cow.

Time in Minutes.
15
15
15
15
15
15
15
15
15
15
15
15

Amount in Grammes.
110
85
65
70
80
85
70
90
70
20
40
80

Food.
Hay.

Salt.

Juniper-berries.
Pepper.

Right Submaxillary Fistula in tlie Ram.
Time in -Minutes. Amount in Grammes. Food.

15
15
15
15
15
15
15
15
15
15
15
15
15

27

20

25

15

26

27

20

24

4

2

8

Hay.

Salt.

Hay.

Fasting.

Pepper.

Salt.

DIGESTION IN THE MOUTH. 283

The diastatic power of the submaxillary saliva varies very con-
siderably in different animals. It is active in all the herbivora, with the
exception of the rabbit and guinea-pig. In the sheep the submaxillary
saliva is more active than that of the parotid, while it is faintly active .in
the horse, and is almost inactive in the dog when freshly secreted. The
general characteristics of the submaxillary saliva vary in different
animals under different conditions, and are therefore subject to much con-
tradiction. The secretion reaches its excess during mastication follow-
ing prehension of food. It is suspended entirely during the mastication
of rumination (Colin, Ellenberger, and Hofmeister), — a fact which is
ver}T remarkable when it is recollected that the chemical stimulation
of the nerves of taste must be then much more marked than in the
hurried first mastication. The submaxillary glands are also nearly
quiescent in the intervals of rumination ; its secretion is called forth by
pilocarpine injections, but to a less degree than in the case of the
parotid.

It seems almost incomprehensible that the submaxillary, which
during rumination remains quiescent, should secrete actively during the

B

FIG. 118.— SUBLINGUAL GL.AND OF THE Ox. (Colin.)

A, submaxillary duct ; B, inferior duct of the sublingual gland ; C C, superior sublingual ducta.

mastication of a tasteless foreign body, such as a piece of string or wood
(Ellenberger). This fact can scarcely be explained but by supposing
that the products of fermentation occurring in the rumen exert an in-
hibitory influence on the secretory nerves of the submaxillary glands.
Its principal function seems to be to assist in the appreciation of the
sense of taste, and to act as a lubricant to aid in the first deglutition.

3. The Sublingual Secretion. — The collection of pure sublingual
saliva is accomplished in the same way as the submaxillary, although in
general it is more difficult, excepting in the case of the ox, where the large
size of the duct renders the operation very easy. In most animals,
however, it is extremely difficult to obtain it in a state of purity, as the
gland, especially in the ox, has a number of excretory ducts (Fig. 118).
The characters of sublingual saliva may partially be determined by
preventing the parotid and submaxillary secretions from entering the
mouth by li gat ing their ducts, and then collecting the fluids in the mouth

284 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

by an opening in the oesophagus. Such fluids, of course, are composed
of the sublingual saliva, together with the secretion of the buccal glands.
The sublingual saliva, obtained in man by the introduction of a fine
cannula, is secreted in isolated, clear, very viscid, alkaline drops; hardly
enough, however, has been collected to determine its properties. In ani-
mals it is very transparent, thick, and so viscid as scarcety to deserve the
name of a liquid, and when a cannula is inserted in the duct it flows from
the orifice in a continuous thread. It contains 2.75 per cent, of solids,
according to Heidenhain, while according to Kiihne the proportion may
rise to 9.98 per cent. Mucin and sulphocyanide of potassium have been
detected in it. It apparently contains no bicarbonate of sodium, as it
does not effervesce when acids are added to it. The sublingual secretion
is constant, though it is augmented greatly during feeding, and the prin-
cipal stimuli which call it forth are those which pass through the sense
of taste.

In addition to the above secretions, fluid is also poured into the
mouth by the various buccal glands. Its characters can only be studied
by ligating all the salivar}*' ducts. When this is accomplished in the dog
the mucous membrane in the mouth only remains moist as long as the
mouth is closed. Dry food is then only with the greatest difficulty mas-
ticated and swallowed, and the thirst of such animals is consequently
greatty increased. It follows from this that the secretion of the mucous
glands of the mouth must be very slight, and, in fact, only one or;two
grammes may be collected with the greatest care in an hour. It has an
alkaline reaction, and has been determined by Bidder and Schmidt to
contain 9.98 per cent, of solids. Attempts have been made to study the
properties of the secretions of the buccal glands by making aqueous
infusions of these glands after death. The superior molar glands, which
have been termed the accessory parotids in the ox, give a viscid extract
with water, while such an extract of the inferior molars is much less
viscid. Yery little has been determined as to the properties of these
secretions.

4. General Characteristics of the Salivary Secretion. — Although it
has been seen that each gland differs somewhat in its manner of secreting
nnd in the results of that process, nevertheless, the general salivary sys-
tem has certain distinguishing characteristics, which have been carefully
studied by Colin, according to the principal conditions in which ani-
mals may happen to be; thus, the conditions may vary, according as
the animal is feeding, ruminating, fasting, or whether stimulating sub-
Stances are in contact with the mucous membrane of the mouth. Dur-
ing feeding two of the glands secrete actively, though unequally ; as
has been seen, the parotid on the side of mastication gives double or
•treble as much saliva as the opposite gland. The amount is also greater

DIGESTION IN THE MOUTH. 285

when mastication is rapid, and is therefore greatest at the beginning of
a meal, unless after a very prolonged fast, when a certain amount of
time seems to be required b}^ the glands to reach their maximum activity.
The submaxillary glands secrete together, and each give about the same
quantity of saliva, although this amount is not one-third of that secreted
by the parotid, even in animals in which these glands appear to be of
about the same size. The linguals also secrete together, and the same
may be assumed of the molars and other glands. These characters may
be determined b}r making fistulse of the different excretory ducts of the
glands, and so conveying certain portions of the saliva out of the mouth
and then weighing the increase of weight in the food in its passage
through the mouth to a fistulous opening in the oesophagus. During
rumination the parotids have been found by this method, as well as by
the production of parotid fistulae, to pour out a large quantity of fluid,
even although the food has been already comminuted and thoroughly
moistened in the first mastication and during its sojourn in the rumen.
The quantity of saliva is very little less than that poured out by the first
mastication, and here also the parotids preserve their alternate, intermit-
tent action ; but the food does not pass between the incisor teeth in the
second mastication, so these teeth are inactive, and the anterior salivary
S3~stem remains almost quiescent. Though they continue to secrete, they
do not give anjT more fluid during this time than during abstinence.
This is a peculiarity of the salivary secretion during rumination, and
shows the relative independence of the different glands. During abstinence
new features are met with, which vary in different animals. In the fast-
ing horse the parotids are inactive, and the submaxillaries give only a
few drops of fluid, but the mouth is always moist, and the horse will
often be seen to swallow the fluids which collect in the mouth, even after
fistulse have been made for both parotids and both submaxillar}^ glands.
Hence, by exclusion, the fluid must have come from the linguals, tonsils,
and palatine glands. In the fasting ruminants the parotids are not in-
active. They pour into the mouth during abstinence about one-eighth or
one fourth as much as they secrete during mastication. Here, also, the
submaxillaries secrete little fluid, but the sublinguals, superior molars,
and palatine glands, judging by the viscidity of the fluid, must be more
or less active. This continued salivary secretion in the ruminant we will
find later to be of great importance in aiding the function of rumination.
Finally;. when stimulated by sapid substances we find marked differences
in the response of different glands to these stimuli. The parotids are
not sensibly affected, and the glands, which furnish a viscid saliva, are all
more or less stimulated, according to the chemical character and intensity
of the excitation, and the extent of surface to which it is applied, and
its duration.

286 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

5. The Quantity of Saliva. — As regards the total quantity of saliva
and the amounts contributed by the different glands, certain data may
be determined in all domestic animals by means of cesophageal fistulae.
To accomplish this, the food is first weighed, then the time of mastica-
tion determined, and finally the food is weighed again as it escapes from
an cesophageal fistula. By subtracting the weight of the food when
given from the weight as it is collected from the oesophagus, the amount
of fluid added may be determined. In this way Colin found that a
small horse secreted five thousand grammes of saliva in an hour, a
medium-sized horse five thousand two hundred grammes, and a large
horse in the same time eight thousand eight hundred grammes ; from
which it may be concluded that a horse feeding on hay secretes from five
thousand to six thousand grammes of saliva per hour. If oats are given
as food, the amount of saliva poured out is one-third less than the above;
only one-half as much is secreted when green fodder constitutes the food,
and only one-third as much when roots, such as beets or turnips, are
given. Further experiments have shown that dried fodder absorbs four
times its weight of saliva, oats a little more than their own weight, meal
twice its own weight, and green fodders half their own weight. Hence,
the amount of the salivary secretion varies with the amount of moisture
contained in the food. It is believed that after twenty-four hours' fasting
the salivation is more active at the commencement of the meal than when
hunger commences to be satisfied. The reverse, however, is the case for
the parotids, as they do not at once reach their maximum activity after
a long fast. The above statement, however, seems to hold for the sub-
maxillaries, as they are never completely inactive. But as the parotids
secrete the greatest volume of fluid, the food first swallowed is drier, and
therefore swallowed with more difficulty than later when the parotids
have acquired their maximum activity. Then the quantity of secretion
decreases with the activity of mastication.

The quantity of saliva poured out in twentj-four hours may be
estimated by means of the preceding data. For if hay absorbs more
than four times its weight of saliva, and the horse swallows one hundred
grammes of saliva each hour during fasting, it is easy to estimate the
total amount secreted. A horse which consumes five thousand grammes
of hay and five thousand grammes of dry fodder will require forty
thousand grammes of saliva for the deglutition of its food, to which
must be added about two thousand grammes for the eighteen hours of
abstinence, making in all forty-two thousand grammes, or eighty-four
pounds. In the ruminant the total amount of saliva secreted in twenty-
four hours is much larger. If we assume that an ox takes three hours
in a day to feed and five hours to ruminate, it is found that in six or
eight hours forty thousand grammes of saliva are secreted, and during

DIGESTION IN THE MOUTH. 287

the sixteen hours of abstinence sixteen thousand grammes are secreted ;
in all, fifty-six thousand grammes, or one hundred and twelve pounds.
This is certainly an inside estimate. In these animals, also, a less amount
is secreted with wet and green food. This immense amount of fluid is
again absorbed, and is, therefore, not lost to the economy. The part
which each gland plays in the secretion of this volume of fluid is also
determinable, and is a point of interest, since we already know that the
chemical composition and the function of the different secretions are not
uniform. The volume of saliva poured out depends on the dryness of
the food, and not, as has been claimed, upon the amount of starch which
it contains, indicating that the mechanical uses of the saliva are of
greater importance than its chemical functions.

The volume of the special salivary secretions cannot be computed
from the volume of the glands. Thus, the parotids of the horse are
four times as large as the submaxillary glands, and yet they secrete
twentA-four times as much saliva. The parotid of the ox is scarcely as
large as the submaxillary, and yet it secretes four or five times as much
saliva as the latter. In the horse the parotid furnished seven-tenths of
the total amount of fluids poured into the mouth, a fact which may be
readily determined by means of cesophageal fistulae, conjoined with
closure of the parotid duct. The submaxillary has been determined by
the above method to furnish about one-twentieth of the total salivary
secretion. These figures cannot, of course, be taken as being rigorously
correct, since the necessary operative procedures must more or less
modify the activity of the glands. In the non-herbivora the quantity
of saliva is much less. It has been estimated at fifteen hundred
grammes in twenty-four hours for a man, while in the dog the parotid
has been calculated to contribute twenty-four grammes, the submaxil-
lary thirty-eight, and the other glands twenty-four grammes in
twent3-four hours.

6. The Physiological Role of the Saliva. — The uses of saliva are
both mechanical and chemical. Mechanically, it assists in the formation
of the bolus of food, after having previously aided its mastication, and
acts as a lubricant in its passage to the stomach. It aids the apprecia-
tion of taste, and by lubricating the surfaces of the mouth and teeth
prevents the adhesion of viscid substances, and in man permits the
movements of rapid articulation. In the ruminant animals the en-
trance of saliva into the paunch is essential for the proper maceration
of food, so as to enable its regurgitation to the mouth in rumination.

The chemical action of the saliva on the food was discovered by
Leuchs in 1831, who found that the saliva was capable of converting
soluble carbohy^ rates into dextrin and sugar. The cause of this prop-
erty of saliva lies in the presence of ptyalin, the diastatic ferment of

288 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the saliva, which we have already found to exist in the saliva and the
aqueous extract of the salivary glands of most groups of animals.

Experiments as to the cliastatic action of the saliva may, therefore, be made
either with fresh, filtered saliva, with an aqueous or glycerin infusion of the sali-
vary glands, or with an aqueous solution of pure ptyalin. A mucilage for testing
the cliastatic action of saliva may be made by mixing one grain of powdered starch
into a thin paste with a few drops of cold water, and then adding the paste to 100
cubic centimeters of boiling water and allowing it to boil for ten minutes. Then,
after standing until the sediment has settled, the clear supernatant fluid is filtered
off and is ready for use. Equal quantities of cold starch-mucilage are poured
into three test-tubes, which are numbered one, two, and three ; tube No. 1 con-
tains starch-mucilage alone ; to tube No. 2 a few drops of filtered saliva are added;
an equal quantity of saliva is boiled thoroughly for a few minutes and added to
No. 3 ; in tube No. 4 is poured a small quantity of saliva alone. The four test-
tubes are placed in the hot-water bath or an oven at a temperature of about 38°
or 39° C. After a few moments the tubes may be removed for testing. If to
tube No. 1, which contained starch -mucilage alone, a few drops of dilute iodine
solution are added, a characteristic blue color is developed, showing the presence
of starch, while Fehling's solution will demonstrate the absence of sugar. If to
tube No. 2, which contains starch -mucilage and saliva, a few drops of the same
solution of iodine are added, no blue color will be developed, showing the absence
of starch, and the fluid will either remain colorless or may take on a more or less
marked reddish tint from the presence of dextrin, showing that the starch has
disappeared. If to another portion of the same fluid contained in tube No. 2 a
few drops of Fehling's solution are added and the fluid boiled, a copious yel-
lowish-red precipitate, due to the reduction of cupric to cuprous oxide, will be
formed, showing the presence of a considerable quantity of sugar. Sugar has,
therefore, in this test-tube replaced the starch. If a few drops of iodine are added
to the fluid of test-tube No. 3, which contained starch-solution and boiled saliva,
the reaction of starch will still be developed, and Fehling's fluid will show the
absence of sugar. Boiling, therefore, has prevented the conversion of the starch
by the saliva into sugar. The fluid of test-tube No. 4, which consists of saliva
alone, will give no reaction with iodine, while no sugar will be found with
Fehling's test, though the blue color may be turned to a violet from the presence
of proteids.

Starch-mucilage, when subjected to the action of saliva at a temper-
ature about that of the blood for a few moments, is converted into sugar.
This conversion is not instantaneous, although it was taught by Bidder
and Schmidt that momentary contact with saliva and starch was all that
was necessary to turn starch into sugar. An experiment which has been
long used to substantiate this view, and which appears at first to dem-
onstrate its truth, is really by no means conclusive. The experiment is
as follows: —

If into a beaker which contains a little saliva warmed up to 40° C.
is added, drop by drop, a solution of starch which has been colored blue
by iodine, as each drop falls it is decolorized. The view, however, that
the loss of color is due to the conversion of the starch into sugar is
erroneous, as was pointed out by Schiff. He showed that the decolori-
zation was due to the conversion by the saliva of the iodine into
hydriodic acid, and that many other organic fluids which would not con-
vert starch into sugar would decolorize the iodide of starch; thus, the
addition of morphine solution or of dog's urine to the iodide of starch

DIGESTION IN THE MOUTH. 289

discharges the blue color of the latter. In neither of these substances is
there the property of converting starch into sugar, but the result is due
to oxidation of the iodide. There are two practical points to be drawn
from this demonstration : first, since the starch is not instantaneously
converted into sugar upon contact with the saliva, even though mas-
tication be prolonged, by no means all of the starch in the food can be
converted into sugar in the mouth; and, second, starch cannot be
considered as a conclusive test for iodine in the various secretions.

It is often desired to test urine for iodine, as in cases of iodism, and all that
is deemed necessary is to add a solution of starch-mucilage to the suspected fluid,
and if the characteristic blue color does not appear it is concluded that no iodine
is present. This procedure is doubly fallacious, not only because these fluids
have the power of decolorizing solutions of the iodide of starch, but even when
iodine is present it is not in the form of free iodine but of hydriodic acid, the very
.agent through which this decolorization is effected. If, therefore, iodine is present
in such organic fluids, its presence can only be detected by the starch test by first
deoxidizing the hydriodic acid. This may be accomplished by soaking a piece of
filter-paper in starch-mucilage, drying, moistening with the suspected fluid, and
then allowing a drop of nitrous acid to fall upon it. If iodine is present in the
form of hydriodic acid, it will be deoxidized by the nitrous acid, and the free
iodine will form the characteristic blue color with the starch -paper.

The old view as to the saccharification of starch was based upon the
assumption that the diastatic ferment first converted the starch into dex-
trin, and that then dextrin through hy drat ion was converted into dex-
trose. This view has been shown to be erroneous by Musculus, who
found that the subject is very much more complex. He stated that in
the conversion of starch into sugar all the starch was not first trans-
formed into dextrin and then into sugar, but that these two bodies were
simultaneously formed, and he gives the following formula as represent-
ing this conversion : —

3C6H1005 + 2H20:=C6H1206-f2C6H1005
Starch. Dextrose. Dextrin.

Even this view has, however, been modified b}r subsequent observa-
tion. According to the view of Musculus, only 33 per cent, of sugar
could originate from the action of the diastatic ferments on starch ,
but it has been found that dextrin also is converted partially into sugar,
and from 20 to 30 per cent, of sugar may^ be formed in this way.
Estimates of the actual amount of sugar developed through the action
of the diastatic ferment on starch show that, instead of 33 per cent., over
50 per cent, of sugar will actually form ; so that, therefore, while the
starch may first be split up into dextrin and sugar, this dextrin also
undergoes partial conversion into a fermentable sugar. Consequently,
through the action of ptyalin, starch is first converted into dextrin and
sugar, and then the dextrin itself, through the action of the ferments,
undergoes subsequently a progressive hydration and results in the

19

290

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

formation of a farther quantity of sugar. In this conversion a number
of by-products are formed, which behave differently to iodine and to the
sugar tests, and in their action on polarized light. The following table
shows these changes in outline : —

Soluble starch,
Erythrodextrin,

Rotation.

2180

3.

4.
5.

Achroodextrin,

Maltose,
Grape-sugar,

210
190
150
150

58

12
12
28
61
100

Behavior
with Iodine.

Blue.
Red.

Colorless.

Other Tests.

Precipitated by tan-
nic acid and alcohol.

Not precipitated by
tannic acid and al-
cohol.

If a little saliva be added to warm, thick starch-paste, in one or two
minutes the thick mucilage will be converted into a thin, watery fluid,
which will not yield either a dextrin or sugar reaction ; it will still give
a blue with iodine. This is, therefore, the first stage in the diastatic
action of saliva on starch — the formation of soluble starch. If a longer
time is allowed to elapse before the testing is performed, sugar may then
be found in the fluid, even though it gives a distinct blue with iodine.
A few minutes later, testing will show the presence of a larger quantity
of sugar, and if iodine be added a blue color will be produced ; but on
diluting this and adding more iodine a violet color will appear, showing
the presence of erythrodextrin, together with soluble starch and sugar.
After a short time iodine ceases to give a blue, but yields a deep-red
color, which later still yields to a yellowish-brown color, and finally no
color at all on the addition of iodine, while all the time the quantity of
sugar goes on steadily increasing. These reactions show that the soluble
starch gives place to erythrodextrin, giving a red with iodine, and finally
to achroodextrin, which has no color reaction with iodine; while, from
the fact that the sugar continually increases as these substances dis-
appear, it is evident that the sugar results from the progressive conver-
sion of these different forms of erythro- and achroodextrin into dextrose,
or some other form of sugar. Musculus and 0 'Sullivan have proved
that the sugar which results from the action of diastatic ferments on
starch is maltose, which is a fermentescible sugar belonging to the group
of saccharoses, having a formula of C^H^On. This substance rotates
the plane of polarized light 150° to the right, while dextrose has only a
rotatory power of -j-58°, while it has a reducing power for the cupric
oxide sugar test of 61°, as compared to grape-sugar, which may be placed
at 100°.

In order to explain the above results it is necessary to assume that
the molecule of soluble starch is a composite molecule, composed of

DIGESTION IN THE MOUTH.

291

several members of the starch group C13H20010, and the assumption that
the molecule of soluble starch has the formula of 10(C12H20010) greatly
facilitates the comprehension of the progressive hydrolysis of starch by
diastase (Brown and Heron).

According- to this view, the composite molecule of soluble starch is
resolved through the action of diastase into two molecules of achroo-
dextrin and eight molecules of maltose by the following succession of
steps : —

One molecule of soluble starch --10(C12H20O10) -f 8(H2O) =

1. Erythrodextrin,

2.

3. Achroodextrin,

4.

5.-

6.

7.

8.

a 9(C12H20O10) -f (C12H22Oai) maltose,

ft 8(C12H20010)+2(C12H22011)

a 7(C12H20010)+3(C12H220:1)

n a.f(* w o \ i ^/n XT (\ \

The final result is thus represented by the equation : —

Soluble Starch.

Water.

Maltose.

Achroodextrin.

Through the action of the diastatic ferment, therefore, the large
molecule of gelatinous starch is first separated into its component mole-
cules of soluble starch, and if we assume that this composite molecule
of soluble starch is composed of an aggregation of ten groups of the
radical C12H20O10, then progressively each one of these radicals assumes
one atom of water and becomes a molecule of maltose, the remainder of
the starch molecule, at the withdrawal of each radical, constituting one
molecule of the intermediary dextrin series. The dextrin molecule thus
becomes smaller and smaller, that is, contains fewer and fewer component
radicals, the higher dextrins giving a red with iodine, while the lower
dextrins give no reaction with iodine (Roberts).

In order that starch should be converted by saliva into sugar, it
is necessary that the fluid be kept at the temperature of about 39° or
40° C. A temperature elevated above this will prevent conversion by
destroying the ferment, while a lower temperature will retard it, and the
temperature of freezing will prevent it completely, although the power
is not lost and may be regained when the temperature is again elevated.
This transformation is produced in a neutral or feebly alkaline medium,
and also, though to a much less degree, in a weak acid medium. An
excess of alkali, or even a slight degree of acidity (half of 1 per cent, of
hydrochloric acid), will prevent it completely. This is a point worthy
of note, since it indicates that the degree of acidity present in the
gastric juice during active digestion is sufficient to interrupt the action

292 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of ptyalin on starch. It will be found, however, that hydrochloric acid
does not appear in the gastric juice of the horse until the latter stages
of gastric digestion, the acidity in the early stages being due to the
presence of lactic acid. It has further been proved that lactic acid,
even when present in 2 or 3 per cent., will not arrest the conversion of
starch by the saliva. Therefore in the horse starch may still be con-
verted in the stomach into sugar. In the ruminant animal all the starch
is probably converted into sugar in the rumen, where the reaction is
alkaline, and here also, therefore, the acidit}' of the gastric juice does not
interfere with the digestion of starch, even though it may not take place
in the stomach, whatever starch escapes the saliva being acted on by
the pancreatic juice. In carnivora, where the gastric juice is highly
acid, starchy matters seldom enter into the composition of their food,
while in the omnivora, man especially, the saliva possesses a higher
diastatic power than in other animals ; therefore the conversion of starch
in the mouth will be much more rapid, and even though suspended in the
stomach, is again resumed in the small intestine under the action of the
pancreatic juice. So, also, when the amount of sugar formed reaches
from 1^ to 2J per cent., saccharin" cation is arrested, but will be renewed
when the fluid is diluted. The transformation of boiled starch mucilage
is very much more rapid than that of raw starch. This is due to the
fact that it is only the gfanulose of the starch granules which is con-
verted into sugar. In the raw starch granules the granulose is contained
in an unyielding cellulose envelope, and is not accessible to the salivary
ferment. When starch is boiled the cellulose envelopes are ruptured;
the granulose then passes partly into solution, and is then readity acted
on by the saliva.

The diastatic action of the saliva of different animals varies very con-
siderably. In almost all it is less active than in man, with the possible
exception of the saliva of the herbivora. The latter appears to be more
active on raw starch than that of the carnivorous animals. Thus, it has
been found that the saliva of the horse will convert crushed raw starch into
sugar in one-quarter of an hour, and it has been proved experimentally
that in the horse the conversion of raw starch into sugar, through the
action of the saliva, takes place in the stomach. It is worthy of note
that the individual salivary secretions of the horse appear to possess
this amylolytic power to a less degree than the mixed saliva. It has
been, however, found that, in addition to acting on starch, the saliva of
the horse is also capable of converting cane sugar into grape sugar.
The saliva of the horse is further inactive on the cellulose of ha}r.

Examination of the substances escaping from an oasophageal fistula
in the horse fed on starchy food shows that practically no conversion
of starch into sugar occurs in the mouth. This, indeed, would be ex-

"DIGESTION IN THE MOUTH. 293

pected from the fact that raw starch requires several minutes' contact
with the saliva of the horse to be converted into sugar. It is not to be
therefore concluded that the amylolytic power of the saliva is of no
practical value, since it will be found that in the horse the chemical
action of the saliva may continue in the stomach.

In the ruminants the diastatic action of the saliva is probably about
the same as that of the horse, but the conditions for the conversion of
starch into sugar are more favorable, since the saliva is constantly being
secreted, constantly swallowed and carried to the rumen, where it meets
with the most favorable conditions for acting on the starch — in other
words, an alkaline medium considerably diluted and an elevated tem-
perature.

Of the other animals, the following series represents the diastatic
action of the saliva, it being most marked in the first animal and least in
the last : hog, rat, rabbit, cat, dog, sheep, and goat. In all the domestic
animals the parotid saliva possesses the highest degree of amylolytic
power. The orbital gland of the dog appears to produce no amylolytic
ferment. All the so-called antiseptics and stronger chemical agents pre-
vent the action of the salivary ferment. The duration of the action of
human saliva on raw starch before the presence of sugar can be detected
is as follows : On potato-starch, after two to four days ; on starch from
peas, after one and one-third to two hours ; on wheat-starch, after one-half
to one hour ; on barley-starch, after ten to fifteen minutes ; on oat-starch,
after five to seven minutes ; on rye-starch, after three to six minutes ; on
corn-starch, after two to three minutes.

If raw starch is finely comminuted, as by grinding with powdered
glass, the time of the reduction is. considerably reduced.

Extracts, or the secretion of the different salivary glands in the
domestic animals, are entirely inert on fats, proteids, and cellulose.

7. The Mechanism of the Salivary Secretion. — The numerous inves-
tigations which have been undertaken to explain the mechanism of salivary
secretion have yielded results of far more importance than that which
they possess as bearing upon the secretion of saliva alone. It is from the
results of these experiments that has been deduced all our knowledge of
glandular secretion, its dependence upon the nervous system, and its rela-
tion to the circulation. In the case of the saliva it has already been men-
tioned that, under ordinary circumstances, in all animals the secretion of
the saliva is either remittent or intermittent. In other words, as a rule
but enough saliva is poured into the mouth during abstinence to keep the
surfaces moist. When, however, food is taken into the mouth and the
process of mastication commenced, or in the ruminant animal during
the process of rumination, the secretion of the salivary glands is at once
greatly increased in activity. Further, allusion has been made to the fact

294

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

that the quantity of saliva poured out varies under many different circum-
stances, as to the character of the food, and the side on which masti-
cation is taking place. It might be already concluded from this, that
the secretion, of saliva is a reflex action and is under the control of the
nervous S3Tstem. As long ago as 1832 Mitscherlich, from studies made
on a patient with a salivary fistula, first suggested, that the salivary
secretion was under the influence of the nervous system, and in support
of that statement alluded to the fact that while the secretion of saliva
was independent of the will, it might be called forth by stimulation of
the mucous membrane of the tongue and mouth, either chemically or

FIG. 119.— NERVES OF STTBMAXII/LARY AND STTBLINGUAL GT.ANDS. (Bernard.)

a, submaxillarv gland ; c c, duct of Wharton ; i 7i g, arterial branches to the submaxillarv gland ;
b, sublingual gland: d ft, sublingual duct: 1 1, lingual nerve; 22, chorda tympani : r, carotid a'rtery, on
which ramify fibres coming from the superior cervical ganglion; /, internal maxillary artery.

mechanically, stimulation of the nerve of smell, or ^stimulation of the
gastric mucous membrane by the food. It thus is clear that the secretion
of saliva is a reflex action, for which there must be an afferent fibre,
an independent nerve centre, and an efferent fibre. From the fact that
the submaxillary gland is the most exposed, and, therefore, the most
readily operated on, the influence of the nerves on the secretion of
saliva has been most studied in the case of this gland. The afferent
nerve fibres of this reflex circle, in the case of the submaxillary gland,
are the lingual branch of the fifth pair and branches of the glosso-

DIGESTION IN THE MOUTH. 295

pharyngeal — the nerves of taste. The centre is in the medulla oblon-
gata and the efferent fibre is the chorda tj'mpani, a branch of the seventh
— the facial — nerve (Fig. 119). The influence of these nerves on the
secretion of saliva is readily proved by experiment.

The animal on which this experiment is usually performed is the dog. The
operation is performed as follows : — A large dog is chloroformed and fastened in
Bernard's dog-holder. The hair is shaved from the lower surface of the jaws and
the side of the neck, and an incision made along the lower border of the lower
jaw, commencing about its anterior third and extending back to the transverse
process of the atlas, dividing the skin and platysma muscle. After clearing
away the connective tissue and fat, carefully avoiding the veins, the submaxillary
gland comes into view just below the angle of the jaw. It is then seen that the
gland lies in the angle formed by the junction of the two veins which go to make
up the external jugular vein (Fig. 120), one branch coming from above downward
directly behind the gland, and usually receiving a small vein from the gland
itself, while the lower branch runs horizontally below the gland, and is formed
by the junction of two other branches, one coming from above and the other from
below. The horizontal branch also very constantly receives a vein from the

FIG. 120.— VEINS OF THE SUBMAXILLARY GLAND OF THE DOG. (Bernard.)

g, submaxillary gland ; j, external jugular vein dividing into two branches: jl andj", veins which sur-
round the gland ; d, anterior glandular vein : d>, posterior glandular vein.

gland. Both branches which go to form the horizontal branch are tied, the one
coming from above receiving a double ligature where it comes from the ramus
of the jaw, and the otherwhere it joins its fellow, the intermediate portion being
removed. After having carefully removed the cellular tissue from the portion of
the wound in front of the gland, the thick belly of the digastric muscle comes
into view, its fibres running forward from its origin in the temporal bone to be
inserted in the middle third of the ramus of the lower jaw immediately in front
of the insertion of the masseter, from which muscle it is separated by a slight
groove. In front of the digastric, the floor of the wound is formed by the trans-
verse fibres of the mylo-hyoid muscle, crossed by the mylo-hyoid nerve, which
comes out from under the jaw at the point of insertion of the digastric muscle.
The connective tissue is then gradually to be cleared away with a blunt hook
from the surface of the digastric muscle and from the groove between it and the
masseter muscle, taking care to avoid, as the deeper portion is reached, the facial
artery, which passes over the jaw to run between these muscles, and the artery of
the gland, which conies from the facial artery and goes in this groove back to
the gland. In the same locality lie also the ducts of the gland and the chorda
tympani nerve. The digastric muscle is now to be separated by means of an
aneurism needle from the facial artery, avoiding all the adjacent structures, and
its muscular arterial branch tied. The muscle is then divided at its anterior third,

296

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

or where it is inserted into the jaw, and its posterior extremity seized with a pair
of artery forceps and gradually cleared back to its insertion in the temporal bone
and surrounded by a ligature. When it is assured there is nothing but muscular
structure in the grasp of the ligature, it is pushed back to the temporal bone and
tied, and the digastric muscle divided in front of the ligature and removed. On
carefully tearing away the connective tissue at the base of the wound and drawing
back the submaxillary gland, there is exposed a triangular cavity (Fig. 121).
This space is limited above and behind by the under surface of the submaxil-
lary gland, into the hylum of which enter the artery, chorda tympani and sym-
pathetic nerve fibres, and the glandular duct. Its lower margin is formed by
the genio-hyoid muscle, and its upper border by the ramus of the jaw and the
masseter muscle. The anterior portion of its floor is formed by the transverse
fibres of the mylo-hyoid muscle, on which ramify the branches of the mylo-hyoid
nerve. At the posterior portion of this space the external carotid artery enters
and runs along the base of the triangle, giving off first the lingual and then the

FIG. 121.— PARTS EXPOSED IN OPERATIONS ON THE SUBMAXLLLARY GLAND
OF THE DOG. (Bernard.

M, anterior portion of digastric muscle elevated with a tenaculum ; M', posterior extremity of the
digastric raised up so as to show the carotid artery, 1 1, and the sympathetic filaments ; G, sul.maxillary
gland elevated to show its posterior surface: H, submaxillary and snblingual ducts: J. external jugular

.

vein; J', posterior branch; J", anterior branch: D, glandular vein; F, origin of inferior glandular
artery; P, hypoglossal nerve; L, lingual nerve: T, chorda tympani; S S', divided mylo-hyoid muscle;
U, masseter muscle at angle of lower jaw ; Z, origin of mylo-hyoid nerve.

facial arteries, from off the latter of which comes the artery of the gland. Almost
immediately after entering this space the carotid is crossed by the large hypo-
glossal nerve, running forward to be distributed to the muscles of the tongue. If
this nerve is divided at the point where it crosses the carotid, and the central end
removed, the pneumogastric nerve comes into view, lying behind the artery. On
pulling to one side the vagus trunk, below and behind it can be seen the white
trunk of the sympathetic nerve, which here separates itself from the vagus to
form the superior cervical ganglion, from which two small filaments pass out to
accompany the carotid and the artery of the gland to enter the hylum. Some of
the sympathetic fibres also pass into the gland along the arterial branch which
comes from the temporal branch, and enter the exterior part of the gland. Then,
to expose the chorda tympani and salivary ducts, the fibres of the mylo-hyoid
muscle are to be divided transversely at about their middle, avoiding every nerve,
but tying all veins, and the upper half of the muscle reflected. The lingual nerve
then comes into view, passing from under the ramus of the jaw and running

DIGESTION IN THE MOUTH.

297

FIG. 122.— NERVES OF THE SUBM AXILLARY GLAND IN THE DOG. (Bernard.)

G, submaxillary gland ; K, submaxillary duct : C. primitive carotid ; L, lingual artery ; O, glandular artery, branch
of the facial ; H H', hypoglossal nerve divided so as to show the superior cervical ganglion; V, pneutnogastric nerve; P,

sympathetic fibres ; D, fibre from the first pair of cervical nerves ; R R, glosso-

l ganglion;
pharyngeal

nerve ; I, anterior filaments

of the superior cervical ganglion, forming the carotid plexus: P, fibre going to the submaxillary gland; Q, sympathetic
filaments ; M, mylo-hyoid nerve : U, lingual nerve, giving off the chorda tympani, T, which, after anastomosing with the
sympathetic filaments, is distributed to the submaxillary gland ; S, external branch of the spinal accessory nerve.

298 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

downward and forward, about parallel in direction with the hypoglossal. On
drawing the parts toward the middle line, the two salivary ducts are seen passing
along close together, immediately below the ramus of the jaw, the submaxillary
duct lying nearer the bone and being a little the larger. On tracing back the
lingual nerve to where it passes from under the jaw, it will be seen that a delicate
nerve-filament here leaves the lingual and curves backward along the ducts to
enter the hylum of the gland. This is the chorda tympani. Immediately after
the chorda leaves the lingual there is sometimes seen a small ganglionic enlarge-
ment, known as the submaxillary ganglion, and as the chorda tympani enters the
hylum it forms a slight ganglionic plexus with the sympathetic. The nerve- and
blood-supply of the submaxillary gland of the dog are further shown in Fig. 122.
Each of these nerves which it is desired to study should be carefully isolated and
surrounded with a thread, and a cannula should be inserted into the submaxillary
duct. To facilitate this, the duct should be freed slightly from the connective
tissue, and closed with a clip or ligature ; as the gland is passive, the chorda should
be stimulated with a very weak electric current for a few seconds, so as to distend
the duct with saliva, and a small slip of wood passed under it to act as a support.
If the duct is then seized with a pair of fine forceps and snipped with a pair of
sharp-pointed scissors, a cannula may be readily inserted.

The above is the mode of operation employed by Bernard, and permits of
the performance of all the more important experiments on the physiology of the
secretion of the submaxillary gland. Where it is simply desired to demonstrate
the secretory action of the chorda tympani nerve, the operation may be greatly
simplified by simply cutting directly down on to the mylo-hyoid muscle, dividing
its fibres transversely, and exposing the ducts and chorda tympani nerve by
turning the parts back toward the ramus of the jaw In the sheep, the operation
may be performed in the same manner, the duct originating in the union of a
number of roots. In the rabbit the operation is much more difficult, from the
extreme fineness of the duct and the fact that it is surrounded by the tissue of the
sublingual gland.

After having performed the operation as detailed above, the first
point which should be demonstrated is the fact that the secretion of
saliva is a reflex action, and that the reflex circle is as stated above. If
a few drops of vinegar are placed upon the tongue of a dog provided
with a submaxillary fistula, almost immediately a profuse secretion of
saliva will set in, and the fluid will run from the mouth of the tube. If
the trunk of the lingual nerve is divided near its entrance to the mouth,
and then vinegar or acetic acid placed on the animal's tongue, no
secretion will result, unless the stimulating fluid reaches the back of
the mouth, where it may come into contact with the terminal fibres of
the glosso-pkaryngeal nerve. If the central end of the divided lingual
nerve is stimulated with a weak electrical current, a profuse secretion
of saliva will be set up. Therefore the lingual nerve, and, to a certain
extent, the glosso-pharyngeal, constitute the afferent path by which the
sensory impressions necessary for the reflex action of saliva reach
the brain. The nerves of taste are, therefore, the afferent nerves for
the secretion of saliva. The nerve centre lies in the medulla oblongata,
and there probably exclusively, although Bernard thought that he had
shown that, under certain circumstances, the submaxillary ganglion
might act as a reflex centre for this process. The efferent nerve is the
chorda tympani. This nerve is a delicate filament which leaves the trunk
of the facial nerve in the Fallopian canal about four or five millimeters

DIGESTION IN THE MOUTH. 299

before it passes out of the st}Tlo-mastoid foramen, and then, arching
upward and forward, enters the middle ear, which it traverses from
behind forward, lying within the thickness of the membrana tympani.
Here for a space of six or eight millimeters the nerve is comparatively
isolated, lying between the handle of the malleus and the vertical process
of the incus. It then passes toward the Glaserian fissure, and leaves
the skull in the neighborhood of the spine of the sphenoid bone to join
the lingual nejve. It has already been stated that stimulation of the
central end of the lingual nerve calls forth a secretion of submaxillary
saliva. If, however, the chorda tympani nerve be previously divided,
stimulation of the lingual is without effect.

The simplest method of dividing the chorda tympani nerve is to cut it where it
crosses the tympanum. This may be accomplished by introducing a small sickle-
shaped knife into the external auditory canal, the animal being profoundly chloro-
formed, keeping the cutting edge upward, and passing the back of the blade
downward and forward along the inferior wall of the meatus until the tympanum
is reached. Pushing the blade through the tympanum, the knife is inserted in
the middle ear, and on depressing the handle of the knife in this position the nerve
is divided.

The fact that the chorda tympani constitutes the efferent nerve in
this reflex circle is not only proved by the experiment just alluded to,
where its division prevents the flow of saliva after stimulation of the
lingual, but ma}T be positively demonstrated by its stimulation. If the
chorda tympani nerve is directly stimulated with a weak induced electrical
current just after it leaves the lingual trunk, in a few seconds the saliva
begins to flow from the cannula, and runs in quite a stream.

It has thus been shown that the secretion of submaxillary saliva is
a reflex nerve mechanism; that the sense of taste is the normal stimulus,
and that this stimulus reaches the brain through the fibres of the lingual
and glosso-pharyngeal nerves, and is transmitted to the gland from the
medulla through the fibres of the chorda tympani nerve. We have now
to study the mechanism by which saliva is separated by the gland from
the blood and the influence of the various nerves and different conditions
of the circulation on this process.

If the submaxillary gland is exposed as described above, and the
chorda tympani nerve stimulated, not only is there a copious secretion of
saliva, but the appearance of the gland itself undergoes great change.
If examined before the nerve is stimulated, the gland will usually appear
pale. A, few arborescent vessels will be seen upon its surface, and the
blood which leaves the gland is dark, and the vein small. When, how-
ever, active secretion is produced through stimulation of the chorda
tympani nerve the surface of the gland becomes rosy red. Numerous
branching vessels are seen. The blood that flows from the gland is
almost arterial in hue, is much larger in quantity, and the veins are seen

300 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to pulsate synchronously with the heart. Evidently, then, stimulation
of the chorda tympani nerve increases the blood-supply of this gland,
either through an active dilatation of the vessels, or more probably
through an inhibition of a local vaso-motor centre. An analogous result
will be seen in the case of the depressor nerve, a nerve whose stimulation
produces paralysis of the vaso-motor centre and consequent dilation of
the blood-vessels. Two results then follow stimulation of the chorda
tympani, — an abundant secretion of saliva and a marked hyperaemia of
the gland. Before, however, the relation between these results are dis-
cussed, the influence of the sympathetic nerve 011 the submaxillary gland
must be alluded to.

As is well known, a constant result of stimulation of a fibre of the
sympathetic system is a contraction of the arterioles, and a consequent
diminution of the supply of blood in the parts supplied by the nerve. If
the filament which leaves the superior cervical ganglion and passes to
the submaxillary gland along the carotid is irritated with a weak induction
current, there is a momentary flow of saliva, and the character of the
secretion so produced differs from that which follows stimulation of the
chorda. Sympathetic saliva is very viscid, and can be drawn out in a long-
thread from the orifice of the cannula. It is of higher specific gravity
and richer in organic elements than that which follows stimulation of the
chorda. In other words, the chorda saliva contains a maximum quantity
of water and a minimum of organic elements, while in sympathetic saliva
the proportions are reversed. So, also, the effects of the sympathetic
stimulation on the blood-supply of the submaxillary gland differ from
those of the chorda tympani. If the sympathetic filament is irritated, the
arborescent vessels, especially over the surface of the gland, disappear,
and the tissue of the gland becomes pale and the vein of the gland con-
tracted and carrying a small quantity of black blood. In fact, therefore,
in both respects the function of the sympathetic and chorda tympani
nerves are antagonistic ; and if each nerve be stimulated alternatel}r at
short intervals with the current which applied alone to either nerve
would produce its characteristic effect, there is no result. Evidently,
then, there is a complete opposition in function in these two nerves.
But is the secretion of saliva simply dependent upon the vascular con-
dition of the glands? Does the gland act as a sponge, filtering out the
saliva from the material within the blood, the quantity being solely
dependent upon the quantity of blood in the organ; or is there some
special function possessed by the cells of the salivary glands, by which
the saliva is separated from the blood without being dependent solely
upon the supply of blood ? In other words, what is the mechanism by
which the salivary glands separate the salivary secretion from the blood ?
We know that as the blood passes through the capillaries of the systemic

DIGESTION IX THE MOUTH. 301

circulation it not only loses in oxygen and gains in carbon dioxide, but
there is also an actual reduction in the amount of fluid, due to the
transudation of the serum of the blood into the lymph-spaces. Such
transudation is due solely or mainly to blood-pressure, and does not
constitute a permanent loss to the blood ; for the fluids so poured out
into the lymph-spaces serve largely to nourish the tissues, and are then
pushed on into the lymphatic vessels by fresh quantities coming after
them, and finally again reach the veins, and thus re-enter the circula-
tion. Such transudations pervade all tissues, but in glandular organs
not only is there a constant loss from the nourishment of the tissues
forming the glands, but the secretions are produced at the expense of
these filtrates from the blood-vessels into the lymph-spaces of the gland-
ular tissue. Secretion is, thus, the passage of the substances from lymph-
spaces to the exterior of the body, for, as has already been referred to,
the alimentary canal may be regarded as such.

Various views have been proposed to explain the passage of the
constituents of the lymph so transuded from the blood-vessels into the
excretory ducts of the glands. The blood-pressure is evidently con-
cerned in forcing the serum of the blood through the walls of the
capillaries into the lymph-s paces, but here the blood-pressure ceases to be
of influence. For if a manometer is inserted into the submaxillary duct
of a dog and the chorda tympani nerve stimulated, the pressure in the
salivaiy duct will be found to be greater by far — one-third greater, at
least — than that of the carotid artery. Where, therefore, the pressure
is greater on the side of the excretory duct, blood-pressure of course
can be of no avail in causing the passage of the fluids through the
glandular tissue into that duct. Osmosis may to a certain extent be
concerned in producing the passage of the fluid through the gland-
membrane, though there are scarcely any data in favor of this view other
than that which is conceded in the fact that the stimulation of the chorda
tympani nerve may result elect rolytically in the production of certain
decomposition products which, having a strong affinity for water, might
extract water from the lymph-spaces into the gland-cells. The produc-
tion of heat in secretion to a certain extent favors this view, since it
has been found that the temperature of the saliva in the salivary duct
may be one degree or more higher than that of the blood. Secretion of
saliva can, thus, not be a process of mere mechanical filtration; for not
only do we find, as alread}' mentioned, the greater pressure on the side
of the salivary duct, and an actual formation of heat in the secretion,
but the secretion may even take place in the absence of the circulation.
Thus, if the chorda tympani is isolated in the rabbit, and the animal
then rapidly decapitated, the flow of saliva may still take place on
stimulation of the chorda, and it ma}T produce in a few moments double

302 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the weight of the gland in saliva, even although, of course, the circulation
has been arrested. Then, again, the action of various drugs on the
salivary gland show the independence, to a certain degree, of the vaso-
inotor and secretory effects of the stimulation of the chorda tympani.
If fifteen milligrammes of atropine in solution are injected into the
jugular vein of a dog and the chorda tympani nerve then stimulated,
there is no flow of saliva, but, on examining the gland, the vaso-motor
phenomena which were present under the same circumstances before the
atropine was injected may be seen. In other words, vascular dilatation
follows stimulation of the chorda tympani nerve after the administration
of atropine, while the secretion of saliva is prevented. Then, again, by
means of pilocarpine the paralyzing effect of the atropine may be antag.
onized and the gland may be made to secrete. The dose of pilocarpine
which, when introduced into the general circulation, would be able to
remove the effects of atropine would probably be fatal to the animal. If,
however, the drug is allowed to enter the circulation of the gland, a
much smaller quantity will be efficient without danger to the animal.
Thus, if seventeen milligrammes of pilocarpine are injected into the sub-
maxillary duct after atropine poisoning and the chorda tympani then
irritated, a slight secretion will be produced, passing off again as the
stronger effect of the atropine makes itself felt. Then, again, the activity
of the secreting cells may be paralyzed, and the circulatory changes
produced by certain drugs, such as sodium carbonate in 5 per cent,
solution or hydrochloric acid in y1^ per cent., injected into* the duct; but
as the increased pressure leads to trans udat ion, and as the cells cannot
secrete, oedema of the gland is rapidly produced when the chorda is
stimulated. Further, quinine injected into the duct influences vaso-
motor changes, although no secretion is produced even though the
secretory fibres of the chorda are not paralyzed. Evidently, then, the
chorda tympani nerve must contain two sets of fibres, — the one vaso-
dilator, not paralyzed by atropine, and the other the secretory fibres,
paralyzed by that poison. It is only by the existence of a class of nerves
which act through calling into activit^y the protoplasmic energy of the
secreting epithelial cells that these effects can be explained. When the
chorda is irritated two sets of impulses travel along the nerve, one
impulse acting on the blood-supply of the glands, while the other acts
on the secretory elements of the epithelial cells in a manner analogous
to that which occurs when a motor nerve going to a muscle is irritated —
the muscle contracts through the stimulation of the contractile elements
of the muscle-cells, and the blood-vessels dilate through vaso-motor influ-
ence. The result in both cases is probably of an electrolytic nature,
with the production of acid or alkaline decomposition products, and
these may serve as stimuli to the cells themselves, in the same way

DIGESTION IN THE MOUTH.

303

Vlf.

DUCT.

as when the same products (compounds of lactic or phosphoric acid
with lime) are directly brought into contact with the muscles. Indeed,
we may carry the parallelism still further, for we know that curare,
b}^ destroying the irritability of the motor nerves, will prevent contrac-
tion of all the muscles when their nerves are stimulated, in the same
manner that atropine will prevent the secretion of the gland when its
secretory nerve is stimulated. In both instances the vaso-motor phe-
nomena remain.

In the case of the parotid gland the circulation during secretion
undergoes the same changes as in the case of the submaxillary. Here,
also, secretory and circulatory
nerves have been determined. Vaso-
constrictor fibres have been found in
the sympathetic branches distrib-
uted to the parotid gland, while
the glosso-pharyngeal, according to
Heidenhain, contains fibres whose
stimulation leads to a dilatation of
the parotid blood-vessels. Both the
facial and the glosso-phaiyngeal
nerves contain fibres whose stimu-
lation leads to parotid secretion,
and if the auriculo-temporal nerve
is stimulated the secretion at once
commences ; if divided the secretion
stops. It has been found, however^
that the trigeminal nerve is not the
source of these secretory fibres, for
when the trigeminal is stimulated
within the cranium no parotid secre-
tion results. They are consequently
derived from the facial nerve, and
when this latter nerve is stimulated
within the cranium parotid secretion
results (Fig. 124). The passage of these glandular fibres from the facial
into the auriculo-temporal nerve has been explained in the following
manner by Bernard : If the facial nerve is divided at its exit from the
stylo-mastoid foramen, and the central end divided, parotid secretion is
produced, while stimulation of its peripheral extremity is without effect.
The secretory fibres do not pass through the chorda tympani, as was
formerly believed, for section of the chorda in the tympanum does not,
as in the case of submaxillary secretion, arrest the flow of parotid
saliva. Nor do they pass through the greater superficial petrosal nerve,

FIG. 123.— DIAGRAM OF NERVES SUPPLY-
ING THE PAROTID GLAND. (Yeo.)

The dark lines indicate the course of the nerves of
the gland. V, inferior division of fifth cranial nerve and
its (AT) auriculo-temporal branch; VII, portio dura;
SCG, superior cervical ganglion sending a branch to the
carotid plexus around the artery.

304 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

for extirpation of the ganglion of Meckel is without effect on the parotid
secretion. As a consequence, it must be concluded that these fibres
pass to the lesser superficial petrosal nerve, which anastomoses with
the otic ganglion. For it has been found that extirpation of the otic
ganglion, or section of the lesser superficial petrosal nerves, arrests sali-
vation. According to Heidenhain, the glosso-pharyngeal nerve also fur-
nishes secretory fibres to the parotid, the fibres passing from this nerve
to the nerve of Jacobsohn, and thence into the lesser superficial petrosal.
Relations between the parotid secretion and the excitation of the cere-
bral glandular nerves seem to be about the same as for the submaxillary
gland. The proportion of solids and salts augments with the intensity
of the stimulation, while the proportion of organic matter increases as
long as the glands are fresh, but diminishes if they become exhausted.

The secretory influence of the sympathetic on the parotid has been
the subject of considerable controversy ; the general opinion being that
the sympathetic influences the parotid secretion only by diminishing
the calibre of the capillaries. Certain authors have, however, held that
in certain species excitation of the sympathetic produces a temporary
increase in the parotid secretion. According to Eckhard, the parotid
of the sheep continues to secrete even after section of all its nerves,
being thus analogous to the secretion poured out by the salivary gland
after section of the chorda tympani.

From the above facts it appears that the secretion of saliva is com-
posed of two phases, — the first, a preparatory stage ; the second, the
essential stage.

The preliminary stage of salivary secretion is that of filtration of
serum of the blood into the lymph-spaces around the acini of the salivar}^
gland. This act is entirely under the control of the vascular nerves,
which, by changing the calibre of the blood-vessels, and by thus
increasing or decreasing the pressure within them, facilitate or hinder
the transudation of serum. The influence of the circulation on secretion
is, therefore, indirect. When the small arteries of the glands dilate
more blood passes through them, a larger amount of nutritive material
filters through into the lymph-spaces, and is appropriated by the gland-
cells, whose vital processes must be thus quickened.

The second stage is that of true secretion through the action of the
gland-cells, and, as has been already shown, is independent of the
circulation and is under the control of the secretory nerves. The nature
of these changes occurring in the act of secretion within the gland-cells
is to a certain extent rendered explainable from the study of the histo-
logical changes which occur within the gland-cells. As has been already
stated, the salivary glands ma3r be divided into two types, — the serous
and the mucous t}rpes. This distinction, which has only as yet been

DIGESTION IN THE MOUTH. 305

based upon the character of the secretion, is farther supported by actual
morphological differences in the character of the gland-cells. In the
serous glands, which are exemplified by the parotid of man and other
mammals, the acini are lined by a layer of granular cells, which, in the
quiescent condition, completely fill the acinus (Figs. 124 and 125). The
nucleus under such conditions is barely distinguishable, its presence
being obscured by the large number of granules present. As secretion
takes place, these granules disappear, seemingly being broken up and
used to form the secretion. During activity, therefore, the outer portion
of each cell of a serous gland becomes clear and transparent, and this
condition gradually spreads toward the centre of the cell. These
changes have been most studied in the parotid of the rabbit. When at
rest the nucleus is small, irregular, and devoid of nucleoli. When caused
to secrete by stimulation of the sympathetic nerve the cells become

FIG. 125.— PAROTID OF RABBIT AFTER IRRI-

FIG. 124.— PAROTID OF RABBIT IN THE TATION OF THE SYMPATHETIC NERVE.

RESTING CONDITION. (Heidenhain.) (Heidenhain.)

smaller, the nuclei become large and round, while the nucleoli may even
be detected, and the whole cell stains more deeply with carmine. It thus
appears that -during rest granules are manufactured, which disappear
during the activity of the cell.

In the mucous glands, of which the submaxillary or orbital glands of
the dog may be taken as a type, the appearances are more complex. When
a microscopic preparation is prepared of the resting salivary gland, the
cells only stain with difficulty with carmine, this apparently being due to
the presence of a large amount of mucin-like substance which occupies
the entire cell with the exception of a small amount of unchanged proto-
plasm, readily staining with carmine, which remains around the nucleus.
In such a section, prepared of the resting gland, in each acinus will usually
be found one or more half-moon shaped cells lying outside the muciparous
cells, which readily stain with carmine, which possess two or more nuclei,

20

306

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and seem to be cells in a state of active growth and multiplication.
When a similar section is prepared from a salivary gland which has been
exhausted by prolonged stimulation of the chorda tympani nerve, the
muciparous cells will, as a rule, have largely disappeared. All the cells
are now small in size and all stain deeply (Figs. 126, 127, and 128). It
would appear from this that in such a gland stimulation of the chorda
nerve leads to a discharge of mucin, or to a total breaking down of the

FIG. 126.— ORBITAL GLAND OF THE DOG IN THE RESTING CONDITION. (Heidenhain.)

FIG. 127.— ORBITAL GLAND OF DOG— COMMENCE-
MENT OF CHANGES DURING ACTIVITY, AFTEK
LADVOVSKY. (Heidenhain.)

FIG. 128.— ORBITAL GLAND OF DOG-
HIGHEST DEGREE OF CHANGE IN
ACTIVITY, AFTER LADVOVSKY.
(Heidenhain. )

entire cell, whose place is then taken by the new, rapidly growing, half-
moon cells. Both statements are probably correct.

It is thus seen that the secretion is the result of the activity of the
protoplasm of the secreting cell. During rest the mucous gland manu-
factures mucin at the expense of its protoplasm. When such a gland
secretes, the mucin is discharged and new protoplasmic cells are rapidly

DEGLUTITION. 307

developed. In the case of tine serous cells the changes are not so
readily recognizable, since the microscopic changes are less marked, but
the probability is that the same sort of processes occur. In the actual
formation of the secretion we have thus two processes concerned. We
have the development of mucin in the muciparous cells, and of ptyalin.
During activity, from dilatation of the capillaries, the blood-serum, more
or less modified in composition, reaches the acini, and from there passes
into the glandular cells, while at the same time the fluid filters from these
cells into the duct, and so constitutes secretion. The inorganic con-
stituents of secretion are, therefore, removed from the blood by a simple
process of osmosis, or filtration, while the organic constituents are the
results of active manufacturing processes occurring within the proto-
plasmic cell-contents.

V. DEGLUTITION.

By the term deglutition is meant the various co-ordinated muscular
movements which result in the passage of the food from the mouth to
the stomach.

The act of deglutition m&y be divided into three different stages.
In the first stage, which occurs in the mouth, the bolus of food passes
to the isthmus of the fauces, in the second stage it passes through the
pharynx, and in the third stage it traverses the»O3sophagus.

When the food has been sufficient!}' masticated it is gathered into a
bolus by the contraction of the muscles of the tongue, the tip of the
tongue being raised b}>- the intrinsic muscles of the tongue, aided by the
stylo-glossus,and the bolus passes back between the tongue and the hard
palate to the anterior portions of the fauces (Fig. 129). This transferring
of food from the mouth to the pharynx occurs when the teeth are in
contact, since the jaws must be closed to afford support to the hyoid
muscles, which we will find to be concerned in the later steps of the
process, and in the herbivorous animals is accomplished so rapidly that
110 more marked duration of closure of the jaws can be detected than at
any other time. When the bolus is very large mastication ceases at the
moment of deglutition, as in carnivora and other animals that swallow
the entire contents of the mouth at one movement. This first stage of
deglutition is entirely within the control of the will, and may be pro-
longed or accelerated, and the movements of the bolus are perceptible
to the sensory nerves of the part. When the bolus has once been placed
upon the dorsum of the tongue, the tip, middle, and root of the tongue
are successively pressed against the hard palate, and the contents of the
mouth are thus propelled toward the pharynx ; an active contraction of
the mylo-hyoid muscles then takes place, as may be recognized by the
finger placed below the lower jaw, the dorsum of the tongue is raised up,

308

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and the bolus of food forced from the mouth into the pharynx. Almost
at the same time the hyo-glossal muscles also begin contracting and,
especially those portions which are attached to the cornua of the hyoid,
cause the free surface of the tongue, which at rest looks upward and
backward, to move backward and downward upon the epiglottis and
mechanically close the glottis. The rapid narrowing of the space between
the mylo-hyoids and the palate which is thus brought about also rapidly
raises the pressure there. This effect is increased by the pull of the
hyo-glossal muscles, which gives the tongue a backward and downward

FIG. 129.— MEDIAN SECTION OF THE HUMAN HEAD, AFTER HENLE. (Mayer.)

Vp, the position of the soft palate during rest ; 1, orifice of Eustachian tube ; Vcl and Vc2, first and
second cervical vertebras; E, epiglottis; G, glo

cartilage ; 2, hyoid bone.

3ttis ; 4, arytenoid cartilage ; 5, cricoid cartilage ; 3, thyroid

movement. Thus, liquids and soft foods are squirted down the entire
pathway to the stomach before contractions of the pharyngeal or
oesophageal muscles can manifest themselves (Meltzer). Fragments
which happen to remain in the pha^nx are sent down later by the suc-
ceeding contraction of the constrictors and with a slowness peculiar to
these muscles (Fig. 130). When the bolus has passed the anterior pala-
tine arches its return to the mouth is prevented by contraction of the
palato-glossi muscles which lie in the anterior pillar of the fauces, and,

DEGLUTITION.

309

coming together, lie together like side-screens or curtains (Landois),
meet the raised dorsum of the tongue, and so form a partition between
the mouth and pharynx ; the occlusion is still further assisted by the
contraction of the stylo-glossi muscles, which elevate the tongue and
press it against the palate.

The second stage of deglutition then commences, and the bolus of
food is now entirely beyond the control of the will, and must pass down
the pharynx into the oesophagus, its ejection into the mouth again only

FIG. 130.— POSITION OF THE SOFT PALATE DUKING THE SECOND STAGE OF
THE ACT OF DEGLUTITION, AFTER FIAUX. (Mayer.)

A, soft palate ; C, bolus : E, orifice of Eustachian tube : B, tongue ; G, pharynx ; H, epiglottis ; I, oesophagus.

being rendered possible by an active coughing or gagging movement.
Its downward movement during this stage, which lasts while the food is
passing from the anterior pillars of the fauces to the entrance of the
03sophagus, is still attended by sensation.

The muscular movements of the second stage of deglutition are much
more complex than in the first. The phar}aix communicates with three
cavities, — the posterior nasal chamber, the O3sophagus, and the larynx.
Special mechanisms exist which direct the food downward toward

310

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the opening of the oesophagus and hinder its passage into the nasal
chambers and windpipe. As soon as the bolus of food reaches the
anterior palatine arches the soft palate is raised by the contraction of
the levator-palati muscles, and rendered tense and directed backward
toward the posterior walls of the pharynx, with which, in many animals,
as in the horse, it comes in actual contact (Fig. 131), and at the same
time the palato-pharyngeal muscles, which lie in the posterior arches of
the fauces, contract. These muscles have a bony insertion in the posterior
wall of the pharynx, and then are inserted into the soft palate. The
action of the levator-palati muscles has the effect of giving these muscles
fixed points of support. In their condition of rest they form a curved
line on each side from the centre to the back of the pharynx. When

FJG. 131.— ANTERO-POSTERIOB SECTION OF THE HEAD OF THE HORSE, SHOW-
ING THE ENTIRE MOUTH, PHARYNX, AND NASAI, CAVITIES. (Gamgee.)

1, genio-hyoglossus; 2, genio-hyoideus ; 3, section of the soft palate; 4, pharynx ; 5, oesophagus ; 6,
guttural pouch ; 7, pharyngeal opening of the Eustachian tube ; 8, cavity of the larynx ; 9, ventricle of
the larynx; 10, trachea; 11, superior turbinated bone: 12, inferior turbinated bone; 13, ethmoid cells;
14, portion of the cranial cavity which lodges the brain proper; 15, portion of the same which lodges the
cerebellum ; 16, falx cerebri ; 17, tentorium ; 18, upper lip ; 19, lower lip.

these muscles contract, downward motion of the soft palate having been
prevented by the action of the levator-palati muscles and approxima-
tion of their origin and insertion being thus prevented, the effect will
be to form a straight line between these two points. Merkel states that
the inferior portions of the phaiyngo-palatine muscles cross in the
middle line of the posterior wall of the pharynx, and thus act as a
sphincter in shutting off the nasal portion of the pharynx, the two
muscles forming a circular muscle, like the orbicularis oris. The dis-
tribution of these fibres is shown in Fig. 132. As a consequence, the
posterior pillars of the fauces will come together in the same way as
the anterior pillars to form a screen or curtain, which will shut off the

DEGLUTITION. 311

pharynx from the posterior nasal fossa, the uvula serving still further
to close the chink between their two free borders. An inclined plane
is thus formed, down which the bolus is pressed by the backward move-
ment of the tongue. At this stage the elevation of the soft palate
may readily be demonstrated by placing a light straw along the floor
of the nose, so that its posterior end rests on the soft palate (Landois).
If now a motion of swallowing is made, the end which projects from the
nose will descend, showing an elevation of the end which rests on the
soft palate. At the same time there is a distinct rise of pressure within
the nasal chambers. This may be shown by introducing a water ma-
nometer into one nostril and closing the other just before swallowing.
As the food passes behind the anterior palatine arch it is subjected
to the action of the pharyngeal constrictor muscles, which propel it
downward. The longitudinal fibres of the pharyngeal constrictors con-
tract and cause an elevation (or more strictly shortening) of the walls

FIG. 132.— DISTRIBUTION OF FIBRES OF THE PALATO-PHARYNGEAT, MUSCLES. (Luschka.)

A anterior, B posterior view.

of the pharynx, together with the elevation of the larynx, this elevation
being produced by a contraction of the stylo-pharyngeal and palato-
pharj-ngeal muscles, the lower jaw coming in contact with the upper
jaw through the action of the muscles of mastication. The food then
passes within the grasp of the upper constrictor of the pharynx, which,
contracting, serves to squeeze the bolus of food downward, passage
into the nasal chamber being prevented by the mechanism above alluded
to, and the bolus being propelled downward by successive contraction
of the upper, lower, and middle constrictors of the pharynx until it
passes into the oesophagus. The elevation of the larynx occurs when
the bolus enters the pharynx, and is due to the action of the genio-hyoid
and mylo-hyoid muscles. It is very perceptible in man, less so in animals
in which the larynx is very near or very far from the base of the skull,

312 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

as the deer, is very slight in the horse and most ruminants, and has more
of a forward motion, serving simply to bring the larynx beneath the
base of the tongue. The elevation of the larynx serves partly to prevent
the passage of food into the larynx. As the larynx is elevated the
arytenoid cartilages and both true and false vocal cords are approximated,
and as the thyroid cartilage ascends by the action of the laryngeal
muscles the epiglottis is depressed to cover the glottis. In this latter
operation the depression of the epiglottis is a passive and not an active
movement, the depression being due not to an action of any intrinsic
muscles, but to the ascent of the larynx beneath the epiglottis, and the
mechanical pressing downward of the epiglottis by the weight of the
bolus of food and the descent of the root of the tongue. The epiglottis
is not, however, essential to the prevention of the entrance of food
into the air-passages, since excision of the epiglottis in the dog, or its
removal by disease in man, does not interfere with normal movements
of deglutition. Colin has found, by inserting a finger into the larynx
through an opening in the trachea of a horse which was swallowing, that
the larynx at the moment of swallowing was suddenly elevated and
moved anteriorly toward the base ef the tongue, the vocal cords closed,
and the arytenoid cartilages came in contact with each other. Ity these
means food is prevented entering the larynx. He also found, by making
a fistula in the upper part of the oesophagus of an ox and inserting a
finger, that at each movement of swallowing the epiglottis was depressed,
and the entrance to the oesophagus elevated and thus approximated to
the isthmus of the fauces. In the horse the isthmus of the fauces is
very narrow, and the bolus passes with difficult}7, even if not very large,
and is often arrested behind the larynx, and yet does not cause coughing.
This is often seen after giving a bolus to a horse, particularly in cases of
angina. In ruminants the isthmus of the fauces is large and the phaiynx
is ample, and when the food sticks in the throat in these animals it is
usually in the cervical or thoracic portions of the gullet, which is also
the locality where the food is apt to be arrested in the pig.

In those animals which habitually swallow their food while the head
is bent forward, the digastric, in addition to its functions in depressing
the lower jaw, is also an aid to deglutition. Where, as in reptiles, birds,
and most mammals, the. position of the mouth with respect to the
oesophagus during the act of swallowing the food is almost in the same
right line, deglutition is easily effected by the mylo- and genio-hyoid
muscles drawing the hyoid bone and larynx forward and upward so as
to allow the masticated mass to get behind them, and so bring it within
the grasp of the pharyngeal muscles ; but in those animals which feed
while in the erect or semi-erect position, and the head bent forward so
that the cavity of the mouth is at right angles with the oesophagus, it is

DEGLUTITION. 313

evident that deglutition must be a much more complex action. In that
position the mylo- and genio-hyoid muscles are relaxed, and cannot act
efficiently in drawing the hyoid bone upward and forward so as to
allow the masticated mass to pass into the oesophagus, into which it has
to pass, in fact, around an angle. The difficulty is removed by the con-
nection of the digastric muscle with the hyoid bone. This muscle,
during the act of deglutition, causes the hyoid bone, larynx, and base of
the tongue to move through a segment of a circle, the anterior part of
the muscle drawing these parts forward ; they are then elevated by the
joint action of the anterior and posterior bellies, and finally drawn back-
ward l>y the posterior bellies, so as to force the masticated mass into
the oesophagus.

The second stage of deglutition is facilitated by the mucous secre-
tions of the parts concerned. This secretion ma}7 become enormous, as
in the dromedary, where the appendix to the soft palate and the pharyn-
geal pouch are very glandular. In all animals the secretion of the
mucous membrane of the mouth and pharynx, aided by the salivary
secretion, is amply sufficient to lubricate the food, so as to render deglu-
tition possible. It was already noted in the chapter on the salivary
secretion that the quantity of saliva poured out was largely dependent
upon the character of the food ; or, in other words, the drier the food
the greater the amount of lubricant needed, and, therefore, the greater
was the salivary secretion.

The second stage of deglutition is involuntary, and when the bolus
of food has passed beyond the anterior pillars of the fauces it is no
longer within the control of the will, and can only be returned to the
mouth b}7 vomiting or violent coughing. Therefore, in giving pills or
balls to animals the}7 have to be carried mechanically by the hand behind
the pillars of the fauces; they are then carried down to the stomach by
the involuntary contraction of the pharynx and oesophagus.

The third stage of deglutition occurs after the food has passed
through the pharynx and has entered into the oesophagus. This stage
of deglutition is much more prolonged than the two preceding stages,
and in the larger domestic animals the passage of the food by the
oesophagus may be followed by the eye and touch. Where the secretion
of saliva is scanty the duration of this stage becomes prolonged, and
sometimes, as in the horse, the food ma}7 become arrested in the lower
cervical portion of the oesophagus until pushed on by the next succeed-
ing bolus.

The rapidity of motion in the oesophagus varies. Liquids and very
soft foods are very rapidly swallowed, being actually squirted through
the oesophagus ; dry forage is swallowed very slowly. In the horse the
boluses have to be very small, from the narrow character of the gullet

314 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in these animals. Hence, if the bolus of food is larger than three or four
centimeters in diameter it is apt to be arrested. In the ox boluses double
the size pass without difficulty.

When once the alimentary bolus is within the grasp of the muscles
of the oesophagus it moves onward with considerable force. Mosso,
in his experiments made on the dog, found that even when the bolus
of food was held back by a weight of four hundred and fifty grammes
deglutition was not interfered with." When once the bolus of food
reaches the upper part of the oesophagus the pharynx falls, and the bolus
traverses the length of the oesophagus under the influence of the succes-
sive contractions of the circular and longitudinal muscular fibres. The
longitudinal fibres contract first, and draw up the oesophagus to meet the
advancing bolus, which is pushed down by the contractions of the annular
fibres behind it. Gravity is entirety without influence on the motions of
deglutition, as swallowing occurs equally well even when the head is on
a lower plane than the entrance of the oesophagus into the stomach.

The third stage of deglutition is involuntary and is unattended by
sensation, though pain may be intense when too large a- bolus or a hard,
irregular mass is swallowed ; so, also, very hot or very cold substances
may be recognized in their passage through the oesophagus by the sensa-
tions which they occasion. As a rule, however, the passage of food
through the oesophagus is entirely unattended by any feeling. Even
acids cause but little sensation:

That deglutition may be accomplished, it is essential that there
must be something to be swallowed. When the mouth contains saliva
alone the motions of deglutition may be made, but as the quantity of
fluid in the mouth decreases deglutition becomes more and more difficult,
until finally it is impossible. This fact indicates the reflex nature of
the motion of deglutition. As before pointed out, a reflex action re-
quires the presence of a stimulus, its conduction to a nerve-centre, and
the transmission of motor impulse through efferent nerves to a muscular
fibre. The stimulus for deglutition is found in the contact of food with
the mucous membrane of the mouth, pharynx, and oesophagus. The
sensory nerves come from the trigeminal, the glosso-pharyngeal, and the
superior laryngeal nerves. Excitation of any of these nerves produces
movements of deglutition.

In the case of the oesophagus the pneumogastric is the sensor}^
nerve. The centre of the movements of deglutition is found in the
medulla oblongata. The motor nerves are the glosso-pharyngeal, sup-
plying the muscles of the pharynx; the hypo-glossal, supplying the
muscles of the tongue ; the trigeminal and facial, supplying the muscles
of mastication, and the pneumogastric, supplying the muscles of the
and oesophagus.

DEGLUTITION. 315

In the horse, ass, dog, sheep, and ox the lower parts of the oesoph-
agus are supplied, as in man and the rabbit, by the recurrent fibres of
the vagi ; the upper portions are, however, supplied by a long branch
of the pharyngeal. nerve which descends in the walls of the oesophagus
as far as the thorax. In birds a similar state of affairs also holds.

Deglutition may be excited by mechanical contact with the fauces
in an animal in which the cerebrum has been removed; it is only
necessary that the -medulla remain intact.

Deglutition of liquids is performed by a mechanism which is almost
similar to that concerned in the deglutition of solids. The palate is raised
and made tense, the palato-pharyngeal muscles contract, the glottis rises,
the epiglottis descends, the pharynx ascends, and the gullet contracts as
in the case of deglutition of solids, the difference mainly consisting in
the rapidity with which liquids are forced through the oesophagus.

The motions of deglutition of liquids may be very rapid. Thus, in
the horse sixty-five to ninet}r motions may be made in each minute,
each swallow carrying one hundred and fifty to two hundred and fifty
grammes of liquid.

The rapidity of deglutition varies according to the animal and the
nature of the- food. The horse eating hay swallows thirty-five boluses
in fifteen minutes after having fasted for some time, and only ten or
twelve boluses in the same time as hunger commences to be appeased,
the weight of each bolus varying from fifty to one hundred grammes.
In swallowing liquids the horse moves the ears, advancing them at each
act of deglutition, at the same time closing the jaws. The masseters
may, therefore, be seen to move under the skin, and even the eyes to
move in their orbits. In ruminants during deglutition the ears either
remain motionless or move unequally. Rhythmical motion of these
organs as seen in the horse is absent in ruminants.

The act of deglutition is performed as described above in all air-
breathing animals. In all, from the mammalia down to the amphibia,
the pharynx communicates with the nasal chambers, the cavities of the
ear on both sides, the mouth, larynx, and oesophagus.

In the young kangaroo, while still retained in the abdominal pouch
of the mother, and in cetaceans, the upper part of the lar}Tnx is elongated
and projects into the posterior nares, so that during suckling the milk
passes down each side without any risk of entering the air-passages and
without interfering with respiration.

In fishes which respire in the water by gills the pharynx has no
communication with the nasal passage, while the larynx and trachea are,
of course, absent. Hence, the pharynx is here a mere passage leading
from the mouth to the oesophagus, and the process of deglutition is con-
sequently greatly simplified.

316 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

VI. HUMINATION.

In most animals the food after being swallowed enters the stomach
sufficiently comminuted to be at once acted on by the gastric juice. In
others, though imperfectly triturated, the food may be at once digested,
while in a third case the food is returned to the mouth for a second
mastication.

The first of these cases is seen in carnivora and omnivora ; the
second occurs in granivorous birds and crustaceans, where mastication
in the mouth is entirely absent, but where, as will be seen later, the
stomach is provided with an accessory organ, the gizzard, which is
capable of crushing and grinding the food.

The third case is seen in ruminants, where the food is carried to the
stomach after only having been subjected to a preliminary and partial
mastication in the mouth. It is then macerated by the fluids contained
in the stomach, and is again regurgitated to the mouth, to be subjected
to the final and complete process of mastication. .

Rumination, or the returning of food from the stomach to the
mouth for a second mastication, is peculiar to polygastric herbivora. It
differs from vomiting in that the motion is perfectly voluntary, is a nor-
mal physiological process, and the matters regurgitated are again swal-
lowed without leaving the mouth. All true ruminants have a multiple
stomach, although all animals with multiple stomachs are not ruminants.
Thus, in the bird three stomachs may be described, and in certain ceta-
ceans, as well as in certain edents, as the sloth, the stomach may be
divided into a number of different compartments and yet rumination not
take place.

The habits of ruminant animals necessitate some process by which
the food is hastily collected in a capacious paunch, to be again returned
to the mouth for mastication. Ruminant animals in a state of nature
instinctively rely on quickness of sight, acuteness of hearing, and agility
to enable them to elude their enemies. With a powerful prehensile
tongue, long and thick tufts of grass are rapidly carried into the mouth
and as rapidly swallowed. However tough the herbage may be, it is
slightly broken down by one or two strokes of the molar teeth ; it then
passes through the gullet into the capacious compartments which receive
the name of stomachs, but which are in reality pouches of the oesopha-
gus, and are situated between the latter tube and the true stomach. By
this arrangement herbivorous ruminants are therefore enabled to rapidly
stow away in these reservoirs a supply of food, where, on the approach
of danger, it maybe retained until an opportunity offers for its return
to the mouth, when it may be masticated at leisure. The stomach of

KUMINATION.

317

ruminant animals consists of the following parts: the oesophagus opens
into the rumen, or paunch, which communicates \)y an opening with the
reticulum, or water bag, this again with the third stomach, or psalter,
omasum, or many plies, which finally, by a small opening, communicates
with the fourth, or true stomach, or abomasum.

The histological structure of these compartments varies consider-
ably. Only the fourth stomach can be compared with that of animals
which possess but a simple, single stomach. The rumen is coated with
horny epithelial cells, arranged in rows in a manner somewhat similar to
the epidermal cells of the skin (Fig. 133). The similarity is further

FIG. 133.— SECTION OF WALL, OP THE RUMEN. (EUenberger.)

A, horny layer ; B, lower epithelial 1 aver: C. papilla;: D. submucous muscular layer ; E, inner muscular
coat ; F, ganglia ; G, external muscular coat ; H, serous coat.

completed in that the submucous connective tissue in the rumen is also
elevated into papillae, similar to those found in the thickness of the skin.
It is well supplied with muscles, and the muscular fibres in the sub-
mucous layer are tolerably well developed. But few glands are to be
found in the rumen, and these are simply of a mucous type, while acinous
glands pass through the submucous connective tissue down to the
muscular fibres below. The cavity of the paunch or rumen is by far the
largest of the four stomachs, and constitutes about nine-tenths of the
space represented by the ruminant stomach.

318 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The second stomach is called the honey-comb bag, or reticulum, and
in its histological structure differs but slightly from that of the rumen.
Its interior is likewise lined with horny, epithelial cells, arranged in
layers, and the inferior layers of the mucous membrane are arranged in
similar papillae. The reticulum owes its name to the peculiar arrange-
ment of the mucous membrane which lines it in small cells or cavities
not communicating with each other, but all Opening freely into the
general cavity.

In the camel and llama and other animals of the desert similar
collections of cells are found in the rumen also. In these animals they
consist of a number of large cells, arranged in parallel rows, and sepa-
rated from each other by folds, the free margins of which are thickened

-B-

FIG. 134.— STOMACH OF LL.AMA. (Colin.)

A, inferior extremity of the oesophagus ; B, single pillar of the oesophageal canal ; C, superior orifice
of the manyplies; D, reticulum; E. right, or anterior water-cells; F, inferior water-cells; G, fleshy
column separating the two groups of cells.

by muscular fibres or sphincters, capable of closing the opening by
which each cell communicates with the cavity of the rumen. There are
eight hundred of these cells in the camel and dromedary, and they all
usually contain water, for which purpose, indeed, they are believed to be
constituted. One group of these cells is situated to the left and the
other to the right (Fig. 134). These groups. of cells are each capable of
containing in the camel about five quarts of water.

The reticulum, or honey-comb bag, is the smallest of the four com-
partments, in the ox being fixed above by the oesophagus to the
diaphragm, connected with the narrow part of the rumen, and attached
below also to the di-aphragm. Its cavity communicates freely with that
of the rumen by a large opening.

RUMINATION.

319

The third stomach, or psalter, omasum, or many plies, is situated on
the right side of the rumen and reticulum, descending from before back-
ward, and is lined by mucous membrane, disposed in broad folds
(Fig. 135). These folds are of varying breadth, from twelve to fifteen
in number, and form almost complete partitions ; between them are others
gradually diminishing in size. The external surface of the mucous
membrane of these folds is coated with an epithelial layer, which, when
the rumen is not entirely fresh, is readily stripped off. Below this layer,

FIG. 135.— OMASUM AND ABOMASTJM OF THE Ox, LAID OPEN.

A, omasum, or manyplies. showing its folds: B, the opening communicating with the reticulum. or honey-comb bag; C,
aboiuasuin, the true digestive stomach, opened to show the plicae, D, of its mucous membrane.

which is called the horny layer, comes the mucous membrane proper. It
is also provided with papillae, which are larger and thicker than those
found in the reticulum. The mucous membrane consists of connective
and elastic tissue-fibres and blood-vessels. In the mucous membrane are
also found oblique muscular fibres of the unstriped variety. Glands are
entirely absent. The folds of the mucous membrane are papillated on
the surface, the eminences being flattened on the side and pointed at the

320

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

edge of each fold. When the contents of this stomach are examined in
animals slaughtered in perfect health they are always found dry, and
there is a disposition for the epithelium to become detached in shreds
and adhere to the pulp%y mass. In the hornless ruminants, such as
sheep, these folds are more or less rudimentary.

The cesophageal canal communicates on the left with the paunch
and reticulum, and on the right with the manyplies. Its direction is
from above outward and backward, the anterior pillar entering the
honey-comb bag and the posterior the paunch (Figs. 136 and 131). The
lower angle is raised above the level of the third stomach, especially
during the action of the gullet, so that it is only when the pillars of the

FIG. 136. — CESOPHAGEAL CANAL,, OPEN. FIG. 137.— CESOPHAGEAL CANAL, CLOSED

(Colin.) BY SUTURE. (Colin.)

A, inferior extremity of the oesophagus ; B, cardiac orifice ; C, superior orifice of the manyplies.

canal are at rest, and liquids or soft foods are descending, or when the
contents of the first and second stomachs strike against the canal, that
any food enters into the omasum.

The fourth stomach, or abomasum or rennet, corresponds in its his-
tological structure with the stamach of other mammals. Its mucous
membrane is arranged in numerous larger or smaller folds, on the
summits of which open the ducts of the gastric glands. It also is
supplied with muscular fibres, and with nerves, blood-vessels, and lym-
phatics. Its mucous membrane is arranged in folds, which are trans-
verse at the upper end, longitudinal in the middle, and gradually effaced
in the pylorus. The fourth stomach of the ruminant differs from that
of other mammals only in size and shape, and agrees in histological

RUMINATION.

321

structure. In the horse we find that a less important peculiarity is also
to be noticed.

After having undergone the first and incomplete mastication, the
food passes into the first and second stomachs, while fluid and finely
comminuted food ma}; enter all four compartments, passing directly
into the first two stomachs, and then, by means of the oesophageal
gutter, into the third and even into the fourth stomach. It was be-
lieved formerly that the oesophageal gutter conducted fluids entirely and
directly into the third and fourth stomachs, but Flourens proved, by
making fistulous openings into all four compartments, that immediately

FIG. 138.— STOMACH OF FULL-GROWN SHEEP, INFLATED AND DRIED ; ONE-
FIFTH THE NATURAL SIZE. (Thanhoffer.)

B, rumen : R, reticulum ; S. omasum : O, abomasum : c, cardia : p. pylorus : br, oesophagus ; <*,
cardial valve : bv, oesophageal canal ; r, pillars of the rumen ; rn, opening of the reticulum ; on, opening
of the abomasum ; b, valve between reticulum and omasum ; e. duodenum.

on drinking fluids entered all four stomachs almost simultaneously.
When an animal drinks the water enters the paunch and the reticulum,
since the oesophagus enters at the junction of these two reservoirs,
while a small quantity of liquid enters the third stomach directl}', and
from there into the fourth. Moreover, the reticulum is the seat of en-
ergetic contractions which force a part of its contents into the rumen
and into the third stomach : consequently it would seem clear that the
largest portion of fluid enters the first two stomachs and then passes
through to the others, though some directly enters the third and fourth,

21

322 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

being conducted by means of the cesophageal gutter. The amount so
conducted must, in the most favorable cases, be but insignificant, since
the oesophageal gutter is not a direct continuation of the gullet, but
joins it in an oblique angle directed toward the right side. The
explanation of the origin of the large amount of fluid invariably found
in the first and second stomachs would otherwise be impossible, for, as
already pointed out, the lining membrane of these two compartments is
but sparsely supplied with glands, and, therefore, they are incapable of
furnishing a secretion of their own.

The opening between the second and third stomachs is extremely
small. Coarsely comminuted food is therefore incapable of passing into
the manyplies, and accumulates in the first two reservoirs. The rumen
and honey-comb bag invariably contain food, even after animals have

FIG. 139.— STOMACH OF THE NEWBORN LAMB, DRIED AND INFLATED; TWO-
FIFTHS THE NATURAL, SIZE. (Tttanhoffer.)

B, rumen ; R, retieulum : S. omasum : O. abomasum : c, card i a ; p, pylorus ; fc, oesophagus ; eft,
cardial valve ; hv, oesophageal canal ; r, folds in rumen ; rn, opening into reticulum ; on, opening into
abomasum ; r, blood-vessels ; «, duodenum.

fasted for twenty-four hours. Thus, Colin found that in an ox which
had fasted twenty-four hours the rumen might contain one hundred and
fifty to two hundred pounds of food, three-fourths of which was water,
but little solids being found in the reticulum.

The coarsely ground food which first enters the paunch and reticu-
lum is subjected there for a variable time to the liquids contained in
those organs, — saliva, mucus, and water ; in proportion to the different
nature of vegetable food is its presence in the rumen prolonged. Liquids,
such as milk, which need no second mastication, pass chiefly into the
second and third cavities. The functions of the rumen are then dis-
pensed with, and, as a consequence, we find the rumen quite rudimentary
in suckling herbivorous animals (Figs. 138 and 139). The reaction of

RUMINATION. 323

the first two stomachs is slightly alkaline. Tiedemann and Gmelin
found it acid in calves, and Colin says it is also acid when digestion is
disturbed, from fermentative change occurring in the food. The food
left in the rumen and reticulum is subjected to a slow churning process,
and not to the active, grinding movements which were once thought to
aid in trituration and regurgitation of food, substances dropped into
the posterior pouches of the paunch gradually being forced forward into
the reticulum and back again, without any very sensible contractions of
the muscular walls of the viscous (Fig. 140). By exposing the interior
of the paunch in a young bull, Colin noticed the welling up of the fluid
and the production of distinct waves, indicating the commotion set up

FIG. 140.— RUMEN AND RETICULUM OF THK Ox, LAID OPEN BY REMOVING
THE LEFT WALJ. WHILE IN SITU.

A, gullet : B, reticulum ; C, anterior pouch of rumen : D. middle pouch : E, posterior superior pouch ; F,
posterior inferior pouch ; G K, pillars of the oesophageal canal ; I, entrance to the omasum.

in every portion of the contents. The newly swallowed food is therefore
speedily mixed, however long the animal may have fasted, with the por-
tions which must necessarily lodge in the lower pouches of the rumen,
even in the most perfect digestion (Fig. 141). It is evident that pro-
longed maceration in the paunch will reduce food to a pulpy mass, thus
facilitating the regurgitation of the food for a second mastication. All
soluble materials which the saliva and other fluids swallowed may dis-
solve are rendered fit for passage into the alimentary canal, and, how-
ever feeble the actions of secretion, the saliva swallowed is here in its
most suitable conditions for transforming starch}7 food into sugar. The

324 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

changes of the food in this stomach are probably of a fermentative
nature, as indicated by the nature of the gases which are constantly
present. Thus, C02, HaS, acetic acid, butyric acid, carbonate of ammo-
nium, chlorides, carbonates, phosphates and sulphates of sodium and
potassium, and carbonates and phosphates of lime, are almost constantly
found. The solids will, of course, vary in relative abundance according
to the food which has served as a diet for the animal. In the reticulum,
also, the food undergoes changes similar to those which have been ob-
served in the rumen ; in fact, the reticulurn ma}' be regarded as an exten-
sion of the paunch. Its special function appears to be to retain fluids,
as its contents are always liquid. Its reaction is also alkaline.

FIG. 141. — VERTICAL SECTION OF THE RUMEX AND RKTICUIATM. (Colin.)

AB, superior region ; C D, median region; E F. inferior region ; G II, the small arrows show the course followed by th«
food which passes from the posterior portions of the rumen to be ruminated.

As regards the mechanism of the rejection of food for the second
mastication, considerable diversity of opinion prevails. All authors,
however, agree in dividing the organs of rumination into the essential
organ — the stomach, and the auxiliary organs — the diaphragm and ab-
dominal muscles. It is not perfect!}- clear from which compartment the
food enters the oesophagus to be ruminated.

Colin, Chauveau, and others believe Hint it pnsses directly out of the
rumen into the oesophagus, while Haubner thinks that the assistance of
the water-bag is essential, and this seems most probable on anatomical
grounds. The rumen is an organ of immense size, and, as has been shown,
may contain as much as two hundred pounds of material, and its muscular

RUMINATION. 325

walls are proportionately weak. On the other hand, the reticulum is the
smallest of the four gastric compartments ; its muscles are, compara-
tively speaking, strong, and under stimulation of the pneumogastric
nerve it has been found to decrease one-third in volume. Furthermore,
the oasophagus communicates more directly with the second than with
the first stomach, its opening into the reticulum having somewhat the
shape of a funnel. The lips of the oesophageal gutter are not essential
to the formation of the cud, for Colin found that stitching the lips of
this canal together with wire sutures did not interfere with rumination ;
so, also, the reticulum has been found not to be solely concerned in this
operation, for Flourens excised a portion of this organ and sewed the
remainder to the abdominal walls in a sheep, and yet rumination was
possible. Colin has shown that the gradual insertion of food between
the pillars of the gullet is sufficient for the regurgitation essential to the
act of rumination. Moreover, that the oesophageal pillars are not essen-
tial to the formation of the cud is proved by comparative anatomy,
where we find rumination occurring in the llama and dromedary, where
only a single pillar is present. The contents of the first two stomachs,
as already mentioned, are subjected to a gentle churning motion, and the
tendency of the food is to strike forward against the pillars of the
oesophagus. As it presses forward by its own weight, and the slight degree
of impulse which the contractions of the rumen and reticulum give to it,
there is a contraction of the diaphragm and abdominal muscles, and this
causes a portion of the contents of these two compartments to engage in
the infundibular orifice of the gullet, whence they are carried upward by
reversed peristalsis.

The action of the abdominal muscles and diaphragm are necessary
to permit of rumination, for when, as was proved b}^ Flourens, the
diaphragm is paralyzed by section of the phrenic nerves, although
rumination may take place, the abdominal muscles will be called upon to
make an extra effort. When the abdominal muscles are paralyzed, as by
section of the spinal cord, rumination is then impossible. This is also
the case when both pneumogastric nerves are divided. That the
diaphragm and abdominal muscles are the organs whose contraction
determines the act of regurgitation is probable on other grounds. The
muscular fibres of the rumen and reticulum are largely of the pale,
unstriped variet}^, and their contraction is slow and prolonged. The
rapidity of the act of regurgitation points to its being produced by red,
striped, voluntary muscles. When the cud engages in the oesophagus, a
constant movement may be seen in the flank, more sensible than the
other respiratory movements, and which is due to contraction of the
abdominal muscles, an inspiration being followed by a rapid expiration.
This movement is coincident with the entrance of the bolus into the

326 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

infundibuluin of the oesophagus, and while it is due to the contraction
of the auxiliary organs, this contraction is not, under ordinary circum-
stances, very energetic, but becomes so when, as a consequence of
various diseases, the food in the rumen becomes more or less dry. The
ascent of the cud is not only due to the pressure of the contracting
abdominal and gastric muscles, but aspiration to a certain extent assists
its onward progress. At the moment of the act of rumination the glottis
is closed, and as the diaphragm contracts the thoracic capacity is
augmented and the bolus is drawn toward the thorax. When, and as
soon as the bolus of food is engaged in the oesophagus, it is carried to
the mouth with great rapidity by the action of the muscular fibres of
the oesophagus, the process being the reverse of deglutition; that is, the
longitudinal fibres first contract, and so widen the oesophagus, and then
the circular fibres successively contract below the bolus, and so force it
upward. The ascent of the cud is visible throughout the entire length
of the neck in most ruminants, particularly in those which are thin, or
which, like the camel, have a long neck. Its ascent is also perceptible to
the touch and to the sense of hearing. When the ear is placed over the
course of the oesophagus in a ruminant animal, various sounds may be
recognized during the act of rumination. In this position bubbling or
moist friction sounds can be heard from the region of the rumen, even in
the intervals of the rumination, due to the disengagement of bubbles of
gases in the process of fermentation which so often occurs in this viscus.
These sounds are most marked in animals which are fed on green fodder.
A sound very closely analogous to the pleural friction sound is also
heard in the same locality coincident with the movements of respiration.
It is due to the friction between the rumen and the diaphragm. The
peculiar bubbling sounds due to the motion of foods may also be heard,
and are dependent upon the entrance of saliva or food into the first and
second stomach and the passage of currents from the first and second
stomachs, and vice versa. In addition to these, rumbling and churning
sounds, due to the motion of the material in the rumen and produced by
contraction of the pillars of the rumen, may also be heard. During
active rumination, if the ear is placed over the cervical path of the
oesophagus, that is, over the left jugular, the passage of the bolus may be
distinctly heard. The ear perceives the tactile impression of a body
passing rapidly beneath it, and a sound is heard which by its peculiar
characteristics indicates that the bolus is impregnated with or accom-
panied by a quantity of liquid.

As soon as the bolus enters the mouth, a second sound is heard
which indicates the rapid downward passage of liquid. This may be
repeated two or three times at short intervals, and shows that the bolus
is accompanied in its ascent by a quantity of liquid, which, as soon as its

RUMINATION. 327

lubricating function has been served, is again swallowed. This fluid
consists partially of saliva and water, or, in other words, the contents of
the rumen and reticulum, and as the bolus of food enters the oesophagus
this fluid is mechanically driven in with it. Its presence is absolutely
essential to the act of rumination, for rumination is impossible in animals
when deprived of water, or in whom the secretion of saliva has been
interfered with.

As soon as the cud reaches the pharynx the soft palate suddenly
rises and the food is carried by the tongue between the molar teeth and
cheeks, the mechanism by which the food is prevented from entering the
nasal chambers and laiynx being precisely the same as has already been
described as taking place during deglutition. The amount of food
raised in each bolus varies from one hundred to one hundred and twenty
grammes. It is at first only coarsely ground, and not very soft or fluid,
but it soon becomes fine and comminuted and thoroughly macerated in
the second mastication, and is collected in a little cake on the back of
the tongue preparatory to swallowing a second time. Since the quantity
composing each bolus may be readily determined by withdrawing the
cud from the mouth as soon as it is rejected from the stomach, it is
possible to calculate how many of these rejections are necessary for the
mastication of the twelve to fifteen kilos of hay which constitute the
ordinary daily ration of an ox. Since it has been shown that dry fodder
absorbs in mastication and in the rumen four times its own weight of
fluid, twelve thousand five hundred grammes of hay will acquire a
weight of sixty-two thousand five hundred grammes. It is, therefore,
necessary that five hundred and twenty rejections, each of one hundred
and twenty grammes, take place. In order to permit all of this food to
undergo a second mastication, and as each bolus requires about fifty
seconds for its second mastication, at least seven hours would be
required for the process of rumination ; even if we admit that one-
seventh of the food is not masticated a second time, one-fourth the day
is required for rumination. The ox, therefore, cannot, like the horse,
be used for constant effort, as he requires time for rumination, and, as
will be shown directly, rumination is very readily interfered with by
any active exertion.

As soon as the bolus enters the mouth it is subjected to a second
mastication, which differs from the first only in being more regular and
more complete. The number, rapidity, and regularity of the movements
of the jaw in this second mastication appear, however, to be subject to
numerous variations. As already stated, the movements of the jaws are
unilateral; this also applies to the second mastication, although perhaps
less regularly. Unilateral rumination is seen in the ox, sheep, giraffe,
antelope, and other animals, and is most usual. Its duration may be as

328 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

long as a quarter of an hour, and then the direction of mastication may
be reversed, the change usually occurring as a new bolus enters the
mouth, and not during the mastication of one which has already entered
the mouth. In certain animals, as in the dromedary, the mastication of
rumination is alternate; that is, the lower jaw moves first to the right and
then across the centre line to the left, and so 'on. In young animals the
rhythm of mastication is always more irregular than in adult animals ;
the number of strokes of the teeth to each bolus varies according to the
species of animals, the age, the character of the food, etc. Thus, dry
food requires more chewing than green food, perhaps thus explaining
the statement that animals ruminate more in winter than in summer.
Young animals have a smaller number of teeth than older animals, and
therefore require a longer time for mastication, as is also the case in old
animals, where the teeth have become imperfect. The rapidity of motion
of the second mastication closely corresponds in character with the other
motions of the same animal. In those animals which are habitually slow
and sluggish in their movements, as the ox, buffalo, etc., the movements
of mastication will be slower and more deliberate than in animals, such
as the antelope and gazelle, in which the muscular actions are rapidly
performed. Even in animals of the same species it will generally be
noticed that the movements are more rapid in youth than in old age.
Toward the end of the period of mastication of the cud, the movements
of the jaws become considerably accelerated. If rumination is interrupted
from any disturbance, the bolus is held in the mouth for a time and mas-
tication again completed before it is swallowed. Even when so inter-
rupted the average number of strokes of the teeth to each bolus is not
interfered with. If the disturbance is sufficiently severe to prevent the
resumption of rumination, the bolus is held in the mouth for some time
and then swallowed by several rapid movements of deglutition. During
the mastication of the cud the bolus does not pass between the incisor
teeth, but remains between the molars. As has been stated, the move-
ments of mastication constitute the principal stimulus to the secretion
of the parotid glands. It is these glands, therefore, which secrete most
actively during rumination, while the salivary glands of the anterior sys-
tem are almost inactive. In the ruminant animal the secretion of the
parotid is never entirely suppressed, for the fluid which it pours out is
essential to active rumination. Since, if a fistula be made of the parotid
ducts, and the parotid saliva conducted outside of the mouth, even al-
though the animal be supplied with water, rumination becomes more and
more difficult, and after three or four days becomes impossible. The
saliva is therefore essential to active rumination. When the food enters
the mouth the secretion of the parotid again becomes more active, and
these glands have been estimated to pour out nine hundred grammes of

RUMINATION. 329

saliva each in one-quarter of an hour. Besides keeping the food in the
rumen moist and lubricating the oesophagus, the saliva secreted during
abstinence and the second mastication does not all pass into the rumen,
but some of it also passes into the many plies, and so serves to keep the
oesophageal gutter lubricated.

As soon as the mastication of the cud is complete, and the food thus
sufficiently comminuted and impregnated with a large amount of liquid,
it is a second time swallowed, the mechanism again being the same
as was described under the heading of deglutition. Only about four
seconds elapse from the time of deglutition of one bolus before the next
is formed and ascends to the mouth. Of this period, probably one and a
half seconds each is occupied by the descent of the bolus, the formation of
a new bolus, and the ascent to the mouth. When the cud has been swal-
lowed a second time it is now so finely divided that it is able to pass
through the opening between the second and third stomachs. It there-
fore largely follows the course of the oesophageal canal, and passes
rapidly into the manyplies, and from there into the true stomach, to be
subjected to the action of the gastric juices. Part of it, however, pos-
sibly falls directly into the rumen and reticulum, to be mixed with the
materials contained in these cavities.

In order that rumination may take place the stomach must be dis-
tended with food, otherwise the walls of the rumen will be flaccid and
the abdominal muscles will be ineffective in aiding in the passage of the
bolus upward through the oesophagus. Since, then, no digestion or
absorption occurs within the first three gastric compartments, an animal
under such a condition might die of hunger with its rumen still almost
filled with food. On the other hand, the paunch must not be very much
distended, or its walls will be paralyzed and will be prevented from re-
acting on its contents. Ruminant animals must always be well supplied
with water, and their secretion of saliva must be active. Rapidly grown
grasses from irrigated meadows distend the rumen far more in propor-
tion to their solid elements than other forms of food. The distended
paunch, however, soon diminishes in size, and then appears very empty,
and animals cannot ruminate as effectually as with harder and drier food,
as a certain bulk is required to permit of regurgitation. Rumination
does not, as a rule, commence until after the animals have been watered,
unless fed on green fodder or succulent roots, and even then they some-
times require water.

The position which the ruminant animal assumes during the act of
rumination is common to all ruminants, and is very characteristic. The
animal reclines slightly on one side, resting more or as much on the
chest as on the belly, the anterior limbs flexed under the chest, and the
posterior limbs brought forward and partly under the abdomen.

330 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Ruminant animals are very timid and easily frightened, so very
slight causes will arrest rumination. As soon as the attention is
attracted the animal abruptly ceases to ruminate, and if lying down
rises and often runs away. A sudden sound, a falling object, or some
strange sight may be sufficient for this, although, of course, animals in
domestication become less impressionable. Slight maladies prevent
rumination, as do excessive food and gases in the stomach, venomous
or narcotic plants, forced marches, fatigue, rut, and suffering of all
kinds. Even the separation of a mother from her young has been
known to temporarily arrest rumination. The longer rumination is
postponed, the more difficult is its recommencement, since food becomes
dry and compactly packed in the rumen and the inam^plies, and their
membranes become irritated.

It would appear at first sight as if the act of rumination was a
purely voluntaiy process, since the least psychical disturbance inter-
feres with its accomplishment. Nevertheless, like other complex co-
ordinated movements, such as deglutition and defecation, which are par-
tially under the control of the will, rumination is essentially reflex in
nature, and has for its point of departure the irritation of the terminal
filaments of the sensory nerves of the rumen. The centripetal path
of this nervous impulse lies in the pneurnogastrics, and explains the
suspension of rumination when these nerves are divided ; the automatic
nervous centre is located in the medulla oblongata, its precise position
being, however, unknown ; the efferent nerves are the motor nerves of
the stomach, diaphragm, and abdominal muscles, together with the
nerves going to the muscles of mastication and deglutition, and to the
parotid glands.

In goats narcotized with morphine Luchsinger was able to produce
all the movements of rumination by artificially stimulating the sensory
nerves of the rumen, either by pressure with the hand on the surface
of the rumen, electrical stimulation, or distensions by injections of warm
water. He also found that not only might the regurgitation and ascent
of the bolus be so produced, but that movements of mastication and
deglutition and salivation were produced even when by division of the
oesophagus the ascending bolus was prevented from reaching the mouth,
thus indicating that these processes also are gastric reflexes.

Rumination may thus be regarded as a species of vomiting, modified
in such a manner that there is no escape of the ejected matters from the
mouth, and that no more is regurgitated from the stomach at any one
time than can be conveniently masticated ; for as soon as the bolus
engages in the gullet the oesophageal pillars become firmly contracted
and the gastric orifice of the oesophagus remains closed until the cud,
having been subjected to a second mastication, again enters the stomach.

VOMITING.

331

VII. VOMITING.

By vomiting is meant the convulsive rejection of the contents of
the stomach through the mouth. It differs from rumination in that in
most cases it is a pathological and not a normal process, and that the
ejected matter usually escapes from the mouth, and is not again swal-
lowed. In certain animals, however, as in carnivorous birds and fishes,
vomiting constitutes the normal method by which indigestible sub-
stances are removed from the stomach ; thus birds readily reject the
contents of their crop, and the matter so rejected is often, as in the case
of pigeons, used for nourishing their young.

Fish, amphibia, and reptiles
readily vomit through the contrac-
tions of their stomachs, and by
this means indigestible matters
are removed. In frogs this
process occurs frequentl}' in June
and July, and then is of less fre-
quent occurrence as the winter
approaches, and when they pass
into their state of hibernation in
January and February is entirely
wanting. Among mammals there
exists the greatest difference in
the degree of readiness with
which vomiting occurs, the car-
nivora and most omnivora vomit-
ing with the greatest readiness,
although the pig with difficult}'
empties its stomach by vomiting.
The monogastric herbivora vomit
very rarely, and then only with the greatest difficulty. This differ-
ence in the degree of facility with which vomiting takes place is due
to the formation of the stomach and the character of the aliments
which it contains. In mammals, which vomit readily, as Colin has
pointed out, the stomach is simple, and the oesophagus is inserted
toward the left extremity of the stomach far from the pylorus. The
03sophagus has thin, extensible walls, with an infundibular dilation at
its insertion in the stomach (Fig. 142). In animals which do not
vomit the stomach may be either simple or have several compartments,
the cardiac orifice, in the former case, being near to the pylorus, and the
oesophagus having thick walls with a narrow orifice of entrance into
the stomach, which is constantly occluded b}* the contractions of the

FIG. 142.— STOMACH OF THE DOG. (Colin.)

A, oesophagus ; B, pylorus.

332

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

powerful sphincteric muscle (Fig. 143). In animals, such as the car-
nivora and omnivora, which readily vomit, the stomach contains sub-
stances which are generally soft and moist and frequently finely divided,
and when subjected to pressure readily escape into the dilatable cardiac
orifice of the gullet. In herbivora which do not vomit the stomach is
usually filled with imperfectly divided forage, imperfectly impregnated
with water as compared with animal tissues and closely mixed together.
When these matters are subjected to pressure, the liquids which they
contain are pressed out and escape into the intestines through the large

FIG. 143.— STOMACH OF THE HORSE. (Colin.)

A, cardiac extremity of the oesophagus ; B, pyloric ring.

and generally patent pyloric orifice. Pressure, therefore, simply serves
to reduce the volume of the gastric contents, while small portions only
are separated from the mass and engage in the oesophagus, and can then
only move upward with great slowness.

Vomiting is inaugurated by a special nervous impression, termed
nausea, which effects the combined action of the stomach, oesophagus, dia-
phragm, and abdominal muscles. The sensations of nausea are usually
accompanied by a copious secretion of saliva (by a reflex stimulation of
afferent fibres in the gastric branches of the vagus, the efferent nerve

VOMITING. 333

being the chorda t3Tmpani), which, together with air contained in the
mouth, is swallowed and so carried to the stomach. Vomiting is usually
preceded by a series of ineffectual retching movements, which are due to
spasmodic contractions of the abdominal muscles, but which are ineffective
from the fact that the sphincter ic muscle of the oesophagus remains
contracted. In ejecting the contents of the stomach into the gullet,
when vomiting commences, a deep inspiratory movement is made, and
by this means the diaphragm is depressed and by its contraction forces
the stomach down into the abdominal cavity, while at the same time the
oesophagus becomes partially distended with air. The glottis is then
closed and the abdominal muscles again spasmodically contract, while at
the same time the longitudinal fibres of the oesophagus by their contrac-
tion serve to open the orifice of the oesophagus into the stomach. As
long as the diaphragm remains in its contracted position and the glottis
is closed, the entire force of the contraction of the abdominal muscles
is expended on the abdominal contents, and as a consequence the stomach
is firmly compressed between the abdominal walls and the diaphragm.

The longitudinal muscular fibres of the oesophagus radiate from the
gullet over the walls of the stomach, and the contractions of the dia-
phragm having served to a certain extent to give a fixed point of
support to the oesophageal ends of these fibres, their contraction under
these circumstances will serve to pull open the orifice of the insertion of
the gullet into the stomach, thus overcoming the contraction of the
cardiac sphincter. The pressure to which the stomach is then subjected
by means of the contraction of the abdominal muscles forces some of
the contents of the stomach into the gullet, the mouth is widely opened
and the neck stretched to afford as straight a path as possible, and
the contents of the stomach are forcibly driven through the oesoph-
agus and ejected from the mouth. The entrance of the food into the
larynx is prevented by the closure of the glottis at the commencement
of the act, and toward its completion by a forcible expiration. Ordi-
narily the posterior pillars of the fauces are sufficiently closely approx-
imated to prevent the entrance of the ejected matter into the nasal
chambers; but when the vomiting is very violent their contraction is
overcome and the matters are forced into the nasal chambers and escape
by the nostrils as well as by the mouth.

Vomiting thus consists of two distinct operations, — the active dila-
tation of the cardiac opening by the contraction of the longitudinal
fibres of the oesophagus, and the pressure of the contracting abdominal
muscles on the contents of the stomach. As long as the oesophageal
ring is tightly closed, violent contractions of the abdominal muscles are
entirety ineffective in expelling the contents of the stomach. Without
the contraction of the abdominal muscles, even though the cardiac

334 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

sphincter may be relaxed, the stomach cannot entirely empty itself.
This indicates that the intrinsic contractions of the muscular walls of
the stomach are of little importance in ejecting the contents of the
stomach. This was demonstrated by Majendie, who showed that vom-
iting might take place in an animal from whom the stomach had been
excised and a bladder substituted for it. When such an operation was
performed on a dog, and the bladder connected with the oesophagus and
small intestine inserted in the abdominal cavity and the wound in the
abdominal walls closed, injections of tartar emetic were perfectly capable
of producing vomiting, thus showing that the contractions of the
walls of the stomach are by no means essential to the act of vomiting.

Schiff, however, found that if the cardiac sphincter was not removed,
or if the longitudinal fibres of the lower extremities of the oesophagus
were damaged, as by crushing, this experiment of Majendie would then
be ineffectual, thus showing that, while the contractions of the muscular
walls of the stomach are of no importance in the mechanism of vomiting,
the action of the longitudinal oasophageal fibres in overcoming the contrac-
tion of the cardiac sphincter is essential. This contraction of the longi-
tudinal fibres always precedes by a few seconds the act of vomiting, and
may be recognized by the insertion of a finger through a gastric fistula.
As a consequence of this opening of the sphincteric muscle, the pressure
within the stomach falls, as may be recognized by the connection of a
manometer with the interior of this organ.

In the normal process of vomiting the contraction of these fibres
is enabled to open the cesophageal sphincter, as pointed out by Foster,
through the support which descent of the diaphragm has given to the
stomach : consequently, in the horse the impossibility of the stomach
being so supported by the diaphragm will largely explain the difficulty
of vomiting in these animals ; for the longer the portion of gullet be-
tween the diaphragm and the stomach, the greater will be the effect of
the radiating fibres in pulling down the oesophagus and the less their
capability of dilating its orifice.

The nervous mechanism which governs this process of vomiting i&
complicated, and, as is well knowrn, it is a reflex action, and the afferent
impulses which excite this process may reach the vomiting centre in the
medulla oblongata through the most diverse paths. The vomiting centre
lies in the medulla close to the respiratory centre, and this connection is
probabty partly functional as well as anatomical, since, as is well known,
nausea may to a certain extent be overcome by rapid and deep respira-
tions. Mechanical stimulation of the fauces, irritation of the stomach,
obstruction of the alimentary canal, may all serve as stimuli which in-
augurate the action of vomiting.

Again, vomiting may take place by direct stimulation of the reflex

VOMITING. 335

centre in the medulla oblongata. In this way certain emetics, such as
tartar emetic, probably act, for they may produce vomiting even when
injected into the blood, and without reaching the stomach at all.

Again, vomiting may be produced by sensations coming from the
central nervous system higher up than the medulla ; thus, offensive smells
or tastes or disturbed cerebral circulation, as in sea-sickness, may pro-
duce vomiting. The efferent path of this action seems to lie mainly in
the pneumogastric nerve, for when this nerve is divided the cardiac
sphincter remains tightly closed, and vomiting is then impossible. Sec-
tion, therefore, of these nerves will, as a rule, prevent vomiting. The
efferent paths of the nervous impulses passing to the muscles of vomit-
ing are, of course, through the motor nerves supplying the gullet, the
larynx, and abdominal muscles.

In the horse, as is well known, vomiting occurs only under very ex-
ceptional circumstances. The explanation of this fact, as pointed out by
Colin, is to be found in the anatomical relations and physical conforma-
tion of the stomach.

In the first place, in the horse the stomach is never in contact with
the abdominal muscles ; hence, it is not readily subjected to pressure
when the abdominal muscles contract. Again, as already mentioned, the
portion of the oesophagus between the diaphragm and the stomach is
longer than in carnivorous animals, and, as the stomach cannot be sup-
ported by close contact with the diaphragm, the longitudinal fibres are
unable to overcome the permanent contraction of the cardiac sphincter.

In carnivorous animals which readily vomit the cesophageal orifice
is at the left extremity, far from the pylorus. An antiperistaltic action
tends to force food into the opening of the oesophagus. The gullet has
dilatable walls and an infundibular insertion into the stomach and
marked radiating fibres. The pylorus is narrow and nearly always
closed, while the stomach is large and directly in contact with the
diaphragm and abdominal walls, and is thus in the best possible condition
for being subjected to pressure through the contraction of these muscles,
while the cesophageal fibres are supported through the contractions of
the diaphragm.

In the horse, on the other hand, or the hare or rabbit, the oesophageal
orifice is in the middle of the lesser curvature of the stomach and near
to the pylorus. Its orifice is always closed by a powerful sphincter
muscle. It passes obliquely through the walls of the stomach, and is
further obstructed by folds of mucous membrane, and the pylorus is
large and nearly always patulous (Fig. 144).

Subjection of the stomach to pressure in the horse will, therefore,
still more tightl}' close the cesophageal orifice, and will force the contents
of the stomach into the small intestine. Occasionally, however, vomiting

336 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

has been noticed to take place in the horse. Under such circumstances
it is a symptom of the greatest gravity, and in most cases it will be
found to be due to the partial rupture of the walls of the oesophagus.

Ruminants, also, habitually do not vomit, but do so occasionally.
When the structure of the stomach of the ruminant animal is examined,
all the conditions would at first appear to favor vomiting. The gullet is
large, dilatable, and has a funnel-shaped opening into the stomach ; the
stomach is large, is in direct contact with the abdominal walls and the
diaphragm, and the pylorus is far removed from the cardiac orifice.
Nevertheless, vomiting, even when intense nausea is produced by emetics,

FIG. 144.— ANTERIOR HALF OF THE STOMACH OF THE HORSE, INFLATED,
SEEN FROM BEHIND. (MUller.)

Sch, oesophagus ; G, cardiac cul-de-sac ; kC, lesser curvature ; gC, greater curvature ; 1 A, mucous
membrane of the left half, and rA, mucous membrane of the right half of the stomach: R, dividing line
between right and left halves of the stomach ; F, fold projecting into stomach from the lesser curvature ;
L, peptic region ; Sch.1, mucous region ; gMs, muscular pillars surrounding the opening of the oesophagus ;
d, section of the muscular fold ; P, pylorus ; PH, pyloric cavity : E, constriction separating pyloric por-
tion from right half of stomach ; Z, duodenum ; Erw, pear-shaped dilatation of duodenum ; M, opening
of the bile and pancreatic ducts.

will but rarely take place, and wrhen vomiting does occur in these
animals it is the contents of the rumen and reticulum alone which are
expelled, while true vomiting should require the escape of the contents
of the fourth stomach. To enable this to take place, the material from
the fourth stomach would have to pass through the narrow openings of
all the three preceding stomachs. When matters are ejected from the
stomach through the action of emetics in a ruminant animal, if at all,
the contents of the rumen alone are ejected, and these ma}^ be again
swallowed, as in rumination, without escaping from the mouth.

GASTRIC DIGESTION. 337

VIII. GASTEIC DIGESTION.

Nearly all the digestive acts so far considered are purely mechanical
and solely preparatory to digestion in the sense in which the term diges-
tion implies production of changes essential to absorption. The food
has been seized, carried to the mouth and appreciated by the sense of '
taste, masticated and impregnated by saliva, swallowed, and in the case
of ruminant animals again returned to the mouth for further preparatory
change. When once, however, it enters the stomach — and it must be
remembered that in the strict sense of the word this term only applies to
the fourth stomach of ruminants — it is subjected to more or less pro-
found chemical and physical changes, which are described as resulting
from the processes of gastric digestion or clvymification. As has been
already seen, the organ in which these digestive changes are inaugurated
is not distinctly defined in all species of animals, its first appearance
being a mere swelling of the alimentary tube without any distinct line of
demarcation at either extremity. Such a rudimentary stomach is found
in all animals below the subkingdom of the articulates. In the mollusks
and articulates its separation from the intestinal tube and oesophagus
becomes more evident, while in insects the stomach, with its glandular
appendages, becomes an important organ of digestion.

In the fish the stomach is separated from the intestine by a narrow
pyloric orifice, but still lies in the direction of the long axis of the body,
as is also the case in many reptiles, though in the higher members of
this family and in the bird it acquires a considerable degree of com-
plexity and tends now to occupy a position at right angles to the axis
of the bodj-. The highest degree of complexity of the stomach is
found in the ruminant herbivora, and indicates that the diversity and
complexity of organization of the gastric parts is governed by the
peculiar alimentary habits and needs of the different species of animals.

Certain general properties and characteristics of gastric digestion
are common to all the higher mammals, while, again, certain special dis-
tinctive points are found in the nature of gastric digestion according as
the animals are carnivora, ruminant or non-ruminant herbivora, or
omnivora. These general characteristics will first be alluded to, and the
peculiarity of gastric digestion in carnivora, ruminants, and non-ruminant
herbivora will subsequently demand attention.

In the first place, we must consider the mode of accumulation of
food in the stomach, the changes in shape, and the motions thereby
inaugurated in that organ. Then we must study the secretions poured
out in the stomach as the result of contact of food with its walls, their
composition and properties, and mode of separation from the blood ;
then the changes which the food undergoes in the stomach and during its

22

338 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

gradual passage into the small intestine, with the consideration of the
influence of the nervous system. These steps in the process of diges-
tion often become characteristic of gastric digestion in the different
domestic animals.

If abstinence has continued for some time, the stomach will have
emptied itself of its contents more or less completely, and contracted so
as to obliterate its cavity in different degrees according to the different
species of the animals. In the dog and other carnivora, after abstinence
has continued for twenty-four or forty -eight hours, the stomach will be
found to be contracted to a small volume, and will be irregular and ovoid
in shape. Its mucous membrane will be thrown up into folds and its
cavity almost obliterated, while the reaction of its mucous secretion will
be neutral, or even alkaline. In omnivorous animals, such as the pig,
the stomach does not contract so completely, nor does it ever become
entirely emptied, but will, even after prolonged abstinence, be found to
contain a bilious liquid and fetid gases. In the horse, after prolonged
fasting, the distinction between the right and left half of the stomach
becomes more marked. The right half of the stomach behaves in these
respects almost like the stomach of the carnivora and becomes highly
contracted, with its cavity almost obliterated. The left portion of the
stomach, on the other hand, remains dilated and will nearly always be
found to contain saliva which is swallowed during abstinence. When
food enters the stomach after prolonged abstinence, it dilates insensibly
and changes its positions and relations. In the fasting condition the
pylorus sinks, and the stomach tends to assume, in this state of func-
tional inactivity, a position in the direction of the long axis of the body,
corresponding more or less with what is its normal state in lower groups
of animals, in whom the stomach is of minor importance. When food
accumulates in the stomach the pylorus rises, and the organ now occu-
pies a position at right angles to the axis of the body, while it rotates on
its own axis so as to cause the greater curvature of the stomach, which
in the position of rest is directed downward and to the left, in the state
of repletion of the organ to become transverse and directed anteriorly
(or downward in quadrupeds).

The mode of accumulation of food in the stomach varies according
to the character of the material swallowed. Soft and diffluent foods and
liquids will mix at once, and if the food is swallowed in voluminous
masses, as in the carnivora, or dry or in more or less firm boluses, as
in the herbivora feeding on dry fodder, and in the non-ruminants, the
first portions which enter the emptj' stomach are deposited in the cardia.
Those which go afterward push these toward the greater curvature and
toward the pylorus, while liquids and softer food fill up the interstices
between them.

GASTKIC DIGESTION. 339

The capacity of the stomach is, of course, very variable in different
animals in proportion to their size. It is very considerable in the car-
nivora; thus the dog's stomach may contain from two to ten litres; in
the hog seven to eight litres will represent the average capacit}' ; while
in the horse, in proportion to its size, it is relatively very much smaller,
the capacity of the stomach of the horse varying from sixteen to
eighteen litres, or only one-tenth or one-twelfth of that of the intestines.

In the ruminant the mean capacity is stated by Colin to be two
hundred and ninety litres. It must be remembered, however, that in the
latter case the stomach of the ruminant is never empty, no matter what
may be the duration of abstinence. Thus, Colin found sixty-five kilos
of dry food in the first three compartments of the stomach of a cow
which had fasted for a very long time; in another, after four days'"
abstinence, fortj-two kilos were found, while in a third sixtj'-six kilos
were found after a fast of two days.

In the horse, as the stomach fills up with food, the constriction
between the right and left halves of this organ disappears, and the stom-
ach then takes the shape as seen when distended by air after death. In
the horse, no matter how much distended, the stomach is never in contact
with the inferior abdominal walls, but is always separated from them by
the infra-sternal curvature of the colon and a portion of the gastro-dia-
phragmatic curvature. In carnivora the stomach is in contact with the
lumbar region above, and with the abdominal walls in the epigastrium
and hypochondrium. As the stonlach becomes expanded with food, the
cardiac and the pyloric sphincters become contracted, and the alimen-
tary matters by contact provoke contraction of the muscular walls of
the stomach, and so serve to mix up the food.

When the food first enters the stomach these movements are slight,
but they gradually become more and more vigorous, and cause a sort of
churning motion in the stomach, the food travelling from the cardiac
orifice along the greater curvature to the pylorus and returning by the
lesser curvature. At the pylorus the circular muscular fibres are the
seat of slow, rhythmical contractions, which serve to assist in the pas-
sage of the contents of the stomach into the small intestine. While
these movements seem to be started by the contact of the food with the
mucous membrane of the stomach, it is evidently not a mere mechanical
stimulation which produces them, since, when the stomach is fullest, and
when, therefore, this mechanical stimulation must be at its height, the
movements are the slightest, and become more vigorous as the stomach
empties itself. Apparently these contractions are started up by the
commencing acidity of the gastric contents, which, at first alkaline,
become gradually more and more acid as digestion progresses, coinciding
with the increase in vigor of the muscular movements of the walls of

340 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the stomach. The muscular movements of the stomach are not so regu-
larly peristaltic as in the intestines, on account of the want of symmetry
of the direction of the muscular fibres.

The nervous mechanism of the gastric movements has not been
thorough!}' cleared up. Numerous nervous ganglia have been found in the
walls of the stomach, and this fact, in addition to the observation which
has often been made, that these movements may occur in a stomach which
has been separated from the central nervous system, would indicate that
the ganglia start up these movements in this organ. Nevertheless, the
movements of the stomach are dependent on and governed by the central
nerv.ous symptom, since the movements of the stomach may be induced
by stimulation of the peripheral ends of the pneumogastric nerves when
the stomach is full. That the movements of the stomach are not, how-
ever, solely dependent on impulses coming through the pneumogastrics is
proved by their occurrence after these nerves have been divided. Stimu-
lation of the S3rmpathetic and coeliac plexus is said to evoke contractions
of the gastric walls, probably through changes in the blood supply of the
stomach. The vagus nerve is without doubt the principal path through
which the movements of the stomach are controlled by the central
nervous system.

The contractions of the muscular walls of the stomach not only
serve to mix the food contained in this organ, but also to bring all the
contents of the stomach in contact with the secreting portion of its
Avails. This is especially important in such animals as the horse, where
only one-half the organ is thus active.

The oesophageal sphincter is always tightly closed, especially, in
horses, where it is very firmly constricted, and so prevents the return of
the flood to the mouth, even when the stomach is strongly compressed.
The p}doric sphincter is not so powerful and its contractions are not so
prominent, but are, nevertheless, well marked in the carnivora, the pig,
and the ruminant.

In solipedes the contraction of the pylorus is only faintly marked,
and, as a consequence, the opening of the stomach into the intestines in
these animals, for reasons which will be given directly, is nearly alwa3*s
patulous. Oser has found that stimulation of the pneumogastric nerves
in the neck leads to an immediate contraction of the pylorus, the intensit}r
and duration of the contraction depending on the degree of stimulation.
Stimulation of the thoracic portion of the sympathetic nerve arrests the
spontaneous contractions of the pylorus, the influence of this stimulation
being progressive, attaining its maximum in one or two minutes and
then slowly declining. After the conclusion of the stimulation the
spontaneous contractions, which exist even after section of the vagi and
.splanchnic nerves, at first are feeble, and attain their normal degree in

GASTRIC DIGESTION. 341

about three minutes. The inhibitory action of the splanchnics in the
thorax is less marked than the motor action of the vagi; the inhibitory
power of the left splanchnic is greater than that of the right.

It thus would appear that the circular muscular fibres of the pyloric
ring are innervated by two antagonistic sets of nerves, the vagus being
the motor nerve and the splanchnic the inhibitory nerve.

When the food is received in the stomach it is gradually dissolved,
and we have, therefore, to study tho several processes which are concerned
in this action. The general outline of the characters of that change will
first be given, then the properties of the secretion to whose action it is
due, the action of this secretion on the various food-stuffs, the nature of
the resulting products, the conditions essential to gastric digestion, and,
finally, the mode in which the gastric juice is secreted.

The study of gastric digestion is especially a study of chemical
changes It was seen that in the mouth the food was not only subjected
to the chemical changes produced by the saliva, but that through
mechanical changes resulting from mastication and the close mixing of
the food with the saliva the materials destined to nourish the body were
brought into the most favorable conditions for subjection to the various
solvent juices of the economy. The first and the most important of these
with which the food comes in contact in its onward passage through the
alimentary canal is the gastric juice. In the experiments made on the
saliva the precedent was established of performing acts of digestion, or
at least acts introductory to digestion, outside the body, the natural
conditions being preserved as far as possible. In the study of gastric
digestion it will be found that this step is not unwarranted. All the
phenomena of gastric digestion may be as completely and conveniently
studied in an artificial stomach as in the living organ, a fact demonstrative
of the essentially chemical nature of the process.

Not only may such experiments be conducted outside of the body,
but they may even be performed with artificial gastric juice.

Such a fluid, or artificial gastric juice, of considerable purity may be obtained
by mincing the mucous membrane of the stomach of almost any animal, drying
the fragments between layers of filter-paper, and allowing them to remain for
twenty-four hours under absolute alcohol. They are then removed from the
alcohol and covered with strong glycerin. In a few days the glycerin will
become strongly impregnated with pepsin, the ferment of the gastric juice, and
may be preserved for almost any length of time The addition of a few drops of
this glycerin extract to one hundred cubic centimeters of hydrochloric acid of
.02 per cent: will produce a fluid of high digestive power, and one which is quite
permanent.

An artificial gastric juice may also be obtained by rubbing up the minced
mucous membrane of the stomach, from which the mucus has been removed by
gentle scraping, in a mortar with clean sand or powdered glass and water. It
should then stand for some hours, being occasionally stirred, and finally filtered.
The filtrate will contain pepsin and a small amount of peptones. Added to an
equal bulk of .02 per cent, of hydrochloric acid, it will form a powerful digestive
fluid, which may be kept for a long time, not even losing its powers when mouldy,

342 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

1. CHEMISTRY OF THE GASTRIC JUICE. — That the gastric juice m&y be
obtained pure for analysis a fistulous opening has to be made into the
stomach, since the various other methods employed by Reaumur and
Spalanzani, of allowing sinimals to swallow sponges and then withdrawing
them and obtaining the fluid by pressure, will not succeed in yielding
a pure gastric secretion, as it will evidently be contaminated with the
fluids of .-the mouth, pharynx, and oesophagus.

The method of performance of gastric fistula originated in the
account of the celebrated case, reported by Dr. Beaumont, of the Cana-
dian trapper, Alexis St. Martin, in whom an accidental gunshot wound
of the abdominal walls left a fistulous tract communicating with the
cavity of the stomach. It was through the data obtained by Beaumont
from a study of this case that the first facts as regards the chemistry and
physiology of gastric digestion were obtained. Led by an account of
this case, the production of a similar fistulous opening communicating
with the gastric cavity on animals was first shown to be practicable by
Blondlot, and after him by Bernard. Blondlot's method was to make an
incision seven or eight centimeters long in the linea alba, commencing at
the xyphoid cartilage. The walls of the stomach were stitched to the
wound, and, after adhesion had taken place between the peritoneal cover-
ing of the stomach and the abdominal walls, an opening was made into
the cavity of the former, in which a tube was inserted.

Bernard has, however, shown that it is not necessary to allow the
stomach to become adherent to the abdominal walls before opening it,
and the method which he recommended is one which is now generally
adopted.

In making a gastric fistula, an animal must, of course, be selected in which the
stomach is large and lies close to the abdominal walls. The horse is, therefore,
inappropriate for such experiments, since in the horse the stomach is small,
deeply seated, and not in contact with the abdominal parietes. On the other
hand, rabbits cannot be employed, since their stomachs are never empty; and
cats are very liable to die of peritonitis, to say nothing of the difficulty in their
subsequent management. In some birds with a muscular stomach, as, for example,
in the crow, gastric fistulae may be very satisfactorily made. The animal, how-
ever, which is, on all accounts, most suitable is the dog. Dogs are easily man-
aged, secrete pure gastric juice in abundant quantity, and are not very liable to
peritonitis.

In order to perform the operation of making a gastric fistula on a dog, the
animal is well fed, so as to distend the stomach, or, after fasting twenty-fourhours,
the stomach may be distended by an injection of air through the oesophagus, and
is then chloroformed and securely fastened. The first step is to shave the hair
from the abdominal walls in the epigastric region, and to remove all the hairs
carefully with a sponge, so as to prevent their entering the abdominal cavity. An
incision is then made through the skin, commencing at the lower margin of the
costal cartilages and about an inch and a half to the left of the linea alba, and
extending downward parallel to this line for a distance a little less than the
diameter of the flange of the cannula which it is desired to use. Each muscular
layer is then to be divided in a direction parallel to its fibres, every bleeding point
being tied before the peritoneum is opened, so as to prevent the entrance of blood
into this cavity.

GASTEIC DIGESTION.

343

When it is certain that all the bleeding has stopped, the peritoneum is to be
opened upon a director. On stretching open the wound the distended stomach
conies into view, its oblique muscular structure being plainly visible through its
serous covering. The gastric wall should then be seized with a pair of artery
forceps at a point where there are not many vessels and drawn forward. Two
strong silk threads are then passed into the walls of the stomach with a curved
needle, at distances from each other about equal to the diameter of the tube of
the cannula, and brought out again at a similar distance from the points where
they were introduced. An incision is then made into the gastric walls, between
the two threads, rather shorter than the diameter of the tube of the cannula. Im-
mediately some bubbles of gas escape and some of the fluid contents of the
stomach, which must be sponged off The opening into the stomach is now to
be stretched with a pair of blunt hooks until it is large enough to pass the inner
flange of the cannula, which is to be then introduced
and pushed into the stomach up to its outer plate.
The form of the cannula usually employed is repre-
sented in Fig. 145 ; it consists of two tubes, each ter-
minating at one end in a circular plate, the two tubes
being cut with a screw-thread, on the outside of one
and the interior of the other, so that the distance be-
tween the two plates, when the tubes are joined
together, may be altered at will. After the insertion
of the cannula the stomach is fastened to it by the
threads which were previously inserted, and the ends
of these threads passed through the abdominal walls
in such a way as to fasten the stomach to them, and
at the same time when tied together keep the edges
of the wound in the abdominal walls in apposition.
The sutures need not be carried through the perito-
neum, and no additional means of closing the wound
is necessary. After the animal has recovered from
the ansesthetic, the cannula must be left uncorked for
at least half an hour after the operation, for the dog is
almost certain to vomit, and were the cannula not open
the contents of the stomach would be apt to be forced
past the side of the cannula into the abdominal cavity,
and cause the death of the animal.

After the operation the animal must be fed on
milk for two or three days and kept in a warm place.
When recovering from the anesthetic the animal will
be very likely to make attempts to tear out the cannula
with his teeth, a result which would be apt to be fatal
to the dog. The only way this accident may be
guarded against is by careful watching. It will not
do to muzzle him and leave him, for if he then should
vomit he would choke to death. After the first day
the wound becomes so tender that no further attempts
at tearing out the cannula are usually made. On the
second or third day after the operation the margin of
the wound becomes much swollen, and it is then

necessary to lengthen the tube of the cannula so as to avoid ulceration of the
skin from pressure of the external flange. By this time adhesions have been
established between the edges of the wound in the stomach and the abdominal
walls, and the wound in the latter having healed, with the exception of the space
occupied by the tube of the cannula, the cavity of the stomach communicates
with the exterior by means of a more or less elongated fistulous tract (Figs. 146
and 147). The cannula may be closed by a cork or it may be fastened with a
valve.

If everything goes well, the dog will be ready for experiments in about a
week.

In ruminant animals fistulous openings may be made into anyone of the four
stomachs or gastric compartments, although, of course, an opening into the fourth
stomach is the only one through which gastric juice may be collected. The

FIG. 145. — CANNULA FOB
GASTRIC FISTULJE.
(Bernard.)

A B, section of the cannula; e,
flange of the cannula ; C, projections
on the interior of tube which fit in
key, D, so as to lengthen or shorten
tube ; E, opening of tube.

344

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

method of operation is the same as that employed in the dog. In recent times
special gastric fistulas have been performed by Klemensiewicz, who excised in the
living dog the pyloric portion of the stomach, and afterward stitched together the
duodenum and the remaining part of the stomach, thus establishing the continuity
of the latter organ. The excised part, with its vessels intact, was stitched to the

FIG. 146.— GASTRIC FISTULA, LAID OPEN. (Bernard.)

section of the abdominal walls; «, section of the walls of the stomach; c, folds of the mucons
membrane, E ; O, cicatricial tissue at the orifice of the fistula.

abdominal wall after closing its lower end by sutures. Heidenhain, by employing
the antiseptic method, was able to preserve three dogs out of seven thus operated
on. He also succeeded in isolating in the same manner the cardiac extremity of
the stomach by means of this operation ; therefore, it is rendered possible to obtain
pure gastric secretion from either the pyloric or the cardiac extremity of this

organ, and the characters of the
secretions from these parts are
rendered accessible for study.

In order to collect gastric
juice for analysis the dog must
be allowed to fast for at least
twenty-four hours, so as to
empty the stomach, and the
secretion of gastric juice may
be stimulated by tickling the
inner surface of the stomach
with a feather tied to a glass
rod. The gastric juice will then
flow along the glass rod out of
the stomach, and may be col-
lected in a glass beaker.

Bernard's method of stim-
ulating the flow of gastric juice
was to give a dog which had
been fasting for some time a
hearty meal of thoroughly
boiled tripe, which furnished a
normal stimulus to the gastric
glands, and, being almost indi-
gestible, does not contaminate the gastric juice to any great extent, and is there-
fore in some respects preferable to mechanical stimulation.

That the gastric iuice may be obtained perfectly pure, the salivary ducts
should be tied, otherwise the fluid obtained from the stomach will be more or less
mixed with the saliva.

FIG. 147.— GASTRIC FISTULA. (Bernard.)

E, stomach; D, duodennm ; M, muscles of the abdominal walls; O,
external orifice of the fistula.

GASTEIC DIGESTION". 345

Gastric juice may also be obtained from man either by withdrawing the con-
tents of the stomach by means of the stomach-pump, or it may be obtained, as
it has been done in several instances, through a fistulous opening made into the
stomach, either accidentally, as in the case of St. Martin, or, as in the case studied
by Kichet, in which the operation of gastrotomy was performed by Verneuil for
impermeable stricture of the oesophagus.

Gastric juice collected from a gastric fistula is a thin, limpid, almost
colorless liquid of strongly acid reaction and of a specific gravit}T of
about 1010. It has a peculiar odor which is generally characteristic of
the animal from which it is obtained. The filtered gastric juice of the
dog contains from 1.05 to 1.48 per cent, solids; of the horse, 1.72 per
cent., and of man, 1.2 1 per cent. It rotates the plane of polarized light
to the left, and it is not rendered turbid by boiling, and resists putrefac-
tion for a long time. The quantity of gastric juice secreted in twenty-
four hours is only with difficulty determined, and the great discrepancy
which exists between the various estimates which have been placed on
this amount shows that it must vary very widely under different con-
ditions. Thus, Beaumont estimated that one hundred and eighty
grammes of gastric juice were secreted daily; Griinewald, from studies
made on a similar case of gastric fistula, concluded that- 26. 4 per cent,
of the bod}' weight represented the amount of gastric juice dail}T poured
out ; while Bidder and Schmidt, from operations made on dogs, esti-
mated that the daily secretion of gastric juice corresponded to about
one-tenth of the body weight.

The gastric juice of a dog, even after having fasted for a long time,
can never be collected perfectly pure from a gastric fistula, since it
always is contaminated and mixed with remnants of undigested food,
sand, and hairs from the edges of the wound, etc. In the sheep it is
even more difficult to obtain perfectly pure gastric juice, since Bidder
and Schmidt have found that even after thirty-six hours particles of food
were still contained in the fourth stomach. When filtered, gastric juice
is always clear and limpid, almost colorless, or yellowish in the dog,
brownish in the sheep. Gastric juice resists putrefactive changes to a
remarkable degree, and may be kept for an almost indefinite period
without undergoing change.

Acids and heating produce no precipitation in gastric juice, as is
also the case with lime, chloride of iron, sulphate of copper, and ferro-
cj'anide of potassium; alkalies, on the other hand, produce precipitation,
which consists of calcium phosphate with iron and magnesium phosphate
and some organic matter. Corrosive sublimate always produces a pre-
cipitate, which consists mainly of the digestive ferments. Alcohol and
acetate of lead give an abundant precipitate, which consists mainly of
the ferment.

The gastric juice is poor in solids, containing not more than two per

346 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

cent. The usual salts found in animal fluids are also here present —
chlorides of sodium, potassium, calcium, and ammonium being in excess.
Phosphatic earths with some iron occupy the next place, while the
sulphates are either absent or present only in minute traces. The con-
stituents, therefore, of the gastric juice consist, in the first place, of two
soluble ferments, pepsin and the milk-curdling ferment, which represent
the organic constituents of the gastric secretion ; second, a free acid,
which is, in all probability, hydrochloric; and, third, the mineral salts.

(a) Pepsin. — Pepsin belongs to the category of soluble ferments.
As yet it has been impossible to obtain it in a state of absolute purity.

The procedure which gives the best results is that of Briicke. The mucous
membrane of the stomach is digested at 40° C. with dilute hydrochloric acid. It
is then neutralized with lime, which is thus precipitated, and carries down
mechanically with it the ferment, pepsin. This precipitate is washed and dissolved
in dilute hydrochloric acid, and to this is added a solution of cholesterin in four
parts of alcohol and one part of ether. The cholesterin throws the pepsin out of
solution. It is then washed with water and with ether. The ethereal layer is
poured off, and pepsin remains in watery solution, from which it may be 'obtained
by evaporation. Von Wittich treats the mucous membrane with glycerin, after
having allowed it to remain for twenty-four hours in alcohol, so as to precipitate
the proteids in the tissue of the stomach, and at the end of a week or two the
glycerin is filtered off, and pepsin may be obtained by precipitating the glycerin
solution of pepsin with absolute alcohol.

Obtained by either of these processes, pepsin is a yellowish powder,
which is soluble in water and glycerin and insoluble in alcohol. When
precipitated by alcohol from its aqueous or glycerin solutions it does
not lose its solubility in water, thus differing from the proteids; it is
not diffusible. When dried it may be warmed up to 110° C. without
losing its activity. While in solution it may be transformed into a sub-
stance which is less active, and which has been termed isopepsin by
Finckler. At 80° it becomes entirely inactive. Pepsin is also soluble
in dilute acids. If pure, pepsin should not give proteid reactions. It
should 37ield no precipitate with nitric acid, tannic acid, iodine, or
mercuric chloride. It is precipitated from its solutions by acetate of
lead and platinum chloride.

The proportion of pepsin in the gastric juice varies at different
periods of digestion. At the commencement of digestion it is present
in the smallest amount, and acquires its maximum between the fourth
and fifth hours of digestion. In man it is said to be present in amounts
varying from 0.41 to 1.17 per cent.

Without the addition of dilute acid pepsin manifests no specific
action, and the characteristic test of the presence of this ferment is
known as the pepsin test with fibrin. If a little fibrin, obtained by
whipping the blood as it flows from a divided vessel, is washed until
perfectly white and placed in a test-tube with a little gastric juice, and
warmed up to 35° C., the fibrin will entirely disappear. There will be

GASTKIC DIGESTION. 347

.no precipitate upon boiling, and but slight precipitation on neutraliza-
tion. Since no other substance will produce this result with fibrin, it is
.characteristic of the presence of pepsin with a dilute acid.

(b) Milk-Curdling Ferment. — As is well known, when milk is
brought into contact with the mucous membrane of the stomach, or:
when an infusion of the mucous membrane of the stomach is added
to milk, it coagulates. This process is made use of in the manufacture
of cheese, and was forinerly attributed to the acid of the gastric juice
or to the production of acidity in the milk from the development of
lactic acid from milk-sugar. It has, however, been shown that milk,
while completely neutral, may be coagulated by an infusion of gastric
juice, or by a neutral infusion of the mucous membrane; and since this
specific action of the gastric juice in curdling milk is destroyed by
boiling, it also is attributable to a specific ferment, which is termed the
milk-curdling ferment, or rennet.

This ferment produces coagulation of the casein of milk without
calling in in any way the action of the acid, and will produce its char-
acteristic results in solutions of casein which are entirely free from milk-
sugar and which are perfectly neutral.

Solutions of the milk-curdling ferment may be obtained by digesting
the mucous membrane of the stomach with glycerin. A few drops of
this glycerin extract, which also, of course, contains pepsin, will cause
a hundred cubic centimeters of fresh milk to coagulate within a few
moments if heated up to 40° C.

Severn! other methods have been proposed for the extraction of
milk-curdling ferment, but in all pepsin is nearly always present.

Hammarsten has found that by precipitating with carbonate of magnesium or
acetate of lead solution, a solution of milk-curdling ferment might be obtained
which is perfectly free from pepsin ; for although both ferments are carried down
by this precipitate, all the pepsin remains in the precipitate, while a considerable
amount of the milk-curdling ferment passes through the filter. By this means
Hammarsten was enabled to obtain solutions which would coagulate fresh milk in
'one to three minutes at the temperature of the body, even in neutral fluids, while
when acidulated they were entirely incapable of dissolving the smallest particles
of fibrin.

Little is known as regards the chemical reactions of the milk-curd-
ling ferment. It does not coagulate, when in wateiy solutions, by boiling,
nor is it precipitated by alcohol, nitric acid, iodine, or tannin. It is
precipitated by the basic acetate of lead ; it does not give a yellow
color with hot nitric acid ; it does not diffuse through parchment-
paper, and only with difficulty through unglazed earthenware. Milk-
curdling ferment is a less stable substance than pepsin and is destro3red
.at a lower temperature than pepsin ; thus, if a solution which contains
both pepsin and milk-curdling ferment is heated about forty-eight hours
to 37° or 40° C. in a .02 per cent. HC1. solution, it loses all power of

34-8 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

coagulating milk, while the pepsin remains unaffected. In neutral solu-
tions, on the other hand, the milk-curdling ferment may be heated up to 70°
C., or even may be boiled for a moment without being entirely destroyed.
Alcohol only slowly interferes with the milk-curdling ferment ; caustic
alkalies rapidly destroy it. Even .02 per cent, of caustic soda is suffi-
cient to cause a previously active ferment solution to become entirely
inactive. Salicylic acid does not interfere with its action. In common
with the other ferments, an almost infinitely small amount of this ferment
will coagulate an immense volume of milk. Hammarsten precipitated a
gtycerin extract of milk-curdling ferment with alcohol, dissolved the
resulting precipitate in water, and, since the percentage of solid in this
solution could be readily determined, was able to estimate that one part
by weight of milk-curdling ferment would coagulate at least from
four hundred thousand to eight hundred thousand parts of casein. The
milk-curdling ferment is entirely without action on sugar solutions and
is without influence in the digestion of albumen. It has been found that
milk-curdling ferment is principally secreted by the glands of the fundus
of the stomach, while the pyloric region furnishes but a small amount of
this ferment. Milk-curdling ferment may almost invariably be found
in wateiy extracts of the stomach of the calf and sheep, while in other
mammals and birds it is usually absent, and is scarcely ever to be de-
tected in the stomach of the fish, even although watery extracts of the
stomachs of these animals become effective after being first acidulated
and then after twenty-four hours again neutralized. This would seem to
show that the acid serves to develop milk-curdling ferment out of some
previously inactive body. The coagulation of milk by the milk-curdling
ferment is more analogous to the process of coagulation of the blood
than to our generally accepted ideas as to the processes of fermentation ;
for the casein, a soluble albuminoid body, through the action of rennet
simply becomes insoluble without undergoing any other change. Its
action is, therefore, directly opposed to that of pepsin, which converts
an insoluble albuminoid into a soluble bodty.

A difference also exists in the result of coagulation of milk, accord-
ing as this coagulum has been produced through the action of the
ferment or by the development of acid. In the latter case the precipi-
tate is still casein, in the former case it is cheese. In the former instance
the casein is precipitated in fine, tender flocculi, which are readily soluble
in dilute acid, but solutions that are coagulated by rennet are very much
less soluble.

The process differs still further in that the casein precipitated by
acids, if carefully washed, may be obtained perfectly free from ash.
Casein precipitated by a milk-curdling ferment, on the other hand, always
contains phosphate of lime, and this salt seems to be essential to the

GASTKIC DIGESTION. 349

action of the milk-curdling ferment ; for rennet is entirely ineffective
when the earthy phosphates are absent. Thus, if casein is precipitated
by an acid and dissolved in a small amount of alkali, after careful wash-
ing rennet is entirely incapable of producing a coagulum ; so also milk,
when subjected to dialysis, by which means the salts are removed, is
incapable of coagulating under the influence of rennet. As to whether
there is a chemical association of the phosphates in the production of
the coagulum by the action of rennet or not, or whether it acts merely
mechanically, is not known.

In addition to the milk-curdling ferment, which, as already stated, is
said to be entirely ineffective on milk-sugar, there appears to be still
another and third ferment in the gastric juice, different from both pepsin
and milk-curdling ferment, and which has for its action the conversion
of milk-sugar into lactic acid ; for both pepsin and rennet may be
destroyed by the action of a dilute caustic soda solution, and the result-
ing fluid will still be able to convert milk-sugar into lactic acid.

(c) The Acid of Gastric Juice. — The greatest controvers}^ has for a
long time existed as to the nature of the free acid of gastric juice. The
contradictions on this subject are evidently due to the fact that in the
process of anatysis the hydrochloric acid usually found might possibly
originate from the breaking up of the metallic chlorides which are con-
stantly found in this secretion.

Prout first separated hydrochloric acid from gastric juice by distil-
lation, and Lehmann suggested that when metallic chlorides are distilled
with lactic acid, hydrochloric acid will always pass into the distillate;
and on account of this objection it was for a long time believed that the
acidity of gastric juice was normally due to the presence of free lactic acid.

Schmidt's a'natysis of gastric juice, however, overcame this objection
raised by Lehmann, as he found in the secretion more hydrochloric acid
than could saturate all the bases present. Numerous proofs have since then
been brought forward which all tend to demonstrate that hydrochloric
acid in a free state is the cause of the acid reaction of this secretion ; thus
Richet proved by the degree of solubility in ether, according to the
method pointed out by Bertholet, who found that while mineral acids
were soluble in ether organic acids were insoluble, that the acid of gastric
juice must be a mineral acid, and from what he termed the coefficient of
partage with ether that acid was hydrochloric. Still another proof is
found in the fact that gastric juice behaves like mineral acids in giving
the color of sulphocyanide of iron when added to a solution of sulpho-
C}ranide of potassium and citrate of iron and quinine (Reoch) ; while,
still further, the addition of gastric juice to starch-mucilage containing
iodide of potassium will develop the blue iodide of starch by liberating
the iodine from the potassium.

350 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In addition to these tests, a number of reagents, such as tropeolin,'
methyl-violet, Congo-paper, etc., have been proposed to distinguish
mineral from organic acids. The best of the more recent tests is phloro-
glucin-vanillin, described by Wiesner and Gunzburg. Two grammes of
phloroglucin and one gramme of vanillin form a reddish-yellow solution
with thirty grammes of absolute alcohol. A drop of this solution in the
presence of a trace of a free mineral acid forms a brilliant red color, at
the same time depositing bright-red crystals. On the other hand , organic
acids, such as lactic or acetic acids, or even chlorides mixed with these:
acids, produce no change in coloration.

There is no doubt but that lactic, butyric, and other organic acids
may be present in gastric juice, but their origin is to be explained by;
their respective fermentations, from articles of food, or from decompo-
sition of their salts. The amount of free acid found in gastric juice ina>
state of health may vary from 0.02 per cent., as stated by Bidder and
Schmidt, which is probably a low estimate, to 0.5 per cent., as estimated,
by Heidenhain, in the gastric juice of the dog.

The degree of acidity of the gastric juice differs in different animals
and under different conditions. In the dog, Bidder and Schmidt found'
that one hundred parts of filtered gastric juice required 0.390 grammes
potassium hydrate for neutralization ; in the sheep, one hundred parts of
gastric juice required only 0.264 grammes potassium hydrate, indicating
in a general way that the degree of acidity of this secretion is higher in
the carnivora than in the herbivora.

The degree of acidity varies also with the stage of gastric digestion.
Rothschild, found, after the administration of fifty grammes of rare
meat and three hundred and twenty-eight grammes of water through the.
oesophageal sound in healthy individuals, that hydrochloric acid was the
only acid present. The degree of acidity was determined by removing
the contents of the stomach by the stomach-pump. The following table
shows the results of his investigations : —

After ihour, . . 0.74 per mille, HC1.

1 0.84

H hours, 0.99

2 1.40

2£ " 2.46

3 " stomach empty.

There seems to be certain reasons for supposing that hydrochloric'
acid is not entirely free, but in a state of partial combination with some
substance which does not entirely destroy its free acidity. Thus, gastric
juice has been found to dialyse differently from a solution of hydrochloric ;
acid of the same percentage.

Numerous theories have been proposed to explain the formation of
the free acid of gastric juice. No one of these views has reached the;

GASTKIC DIGESTION. 351

dignity of a demonstration. It is known that the acid is formed only
by the parietal cells of the gastric tubules, and the free acid is found on
the free surface of the gastric mucous membrane. An experiment
devised by Bernard serves to demonstrate this. For the production of
Prussian blue through the union of potassium ferroc3'anide and a salt
of iron, an acid reaction is requisite. Claude Bernard injected potassium
ferrocyanide, and afterward a solution of lactate of iron into the veins
of a dog. When examined after death, the blue color was found only in
the upper layers of the gastric mucous membrane, showing thus that
this locality was the sole seat of the acid reaction. As to the origin of
this acidity, it appears that the parietal cells of the gastric glands form
hydrochloric acid from the chlorides which the mucous membrane takes
up from the blood; for, if sodium chloride be withheld from the food,
the formation of hydrochloric acid ceases. The active agent in this
splitting up of the chlorides is probably lactic acid, which, by splitting
up sodium chloride, forms free hydrochloric acid, while the bases, forming
alkaline salts, are excreted by the urine. The renal secretion is, there-
fore, less acid during digestion than in the intervals of digestion.

The following tables represent the quantitative composition of gastric
juice in different animals : —

Water

Organic matter (especially ferments),
Sodium chloride, ....
Calcium chloride, .
Hydrochloric acid, . .
Potassium chloride, ., -. ..
Ammonium chloride, ..»,..
Calcium phosphate, )

Magnesium " > , 0.125

Ferric " )

2. THE ACTION OF GASTRIC JUICE ON THE FOOD. — The general solvent
effects of the gastric juice on food-stuffs may be roughty illustrated by
means of an experiment devised by Schiff, in which the stomach, removed
from the body and placed in an acid medium, is capable of digesting
itself. If the stomach is removed from a dog, minced into small pieces,
and infused in four or five hundred cubic centimeters of HC1 of 0.02
per cent, in an oven at 40° C., at the end of eight to ten hours the
fragments of the stomach will be found to be almost entirely liquefied.
In the structures of the stomach are found the principal animal sub-
stances which serve as nutriment. Albumen and fibrin of the blood are
present, muscular tissue, and connective tissue. These substances then
being dissolved, as may be demonstrated by the fact that the liquid,
which may be filtered off from the small, pulpy and yellowish residue, is
free from solid material, it remains only to determine in what form these
albuminoid constituents of the tissues are present in the solution.

352 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

As has been already stated, albumen is precipitated from its solutions
by boiling or by a concentrated mineral acid. If the filtrate from this
autodigestion of the stomach is boiled no coagulum will be formed, nor
will an addition of nitric acid cause any precipitate. . If albumen is
present in this solution, it must, therefore, exist in a modified form.

Millon's test and the xanthoproteic reaction will indicate in this
filtrate the presence of an albuminoid bod}7. If the filtrate be neutralized
by the careful addition, drop by drop, of a little liquor potassse, when the
fluid is perfectly neutral a precipitate will be formed. These tests show
that while albuminoid bodies do exist in the filtrate, they have been trans-
formed by the gastric secretions into other members of the proteid group.

Recollecting the statement made in a preceding chapter as to the
effect of dilute acid on albumen, it was found that if a dilute acid was
added to a solution of albumen, the albumen totally lost its power of
coagulating by heat and was rendered insoluble in water. It was there-
fore thrown out of solution by neutralization. When such a solution of
acid albumen was exactly neutralized, the filtrate was found to be entirely
free from proteid in solution. If, on the other hand, in this experiment
of autodigestion by the stomach the precipitate produced by neutraliza-
tion is filtered off, the filtrate will still show the presence of proteid in
large amounts. The results of gastric digestion are not, therefore, entirely
identical to the action of a dilute acid, for we find a portion of proteid
which is still soluble in neutral solutions and is nevertheless not coagu-
lated by boiling ; consequently, the modifications of albuminoids produced
by the action of the gastric juice are not due solely to the acid alone.

This fact can be still further demonstrated by a simple experiment.

In four test-tubes may he placed some fragments of boiled blood-fibrin. In
one tube are placed ten cubic centimeters of hydrochloric acid of .02 per cent.;
in No. 2 are placed ten cubic centimeters of artificial gastric juice made by
adding a few drops of glycerin-pepsin extract to dilute hydrochloric acid, as
already described ; in No. 3 are placed ten cubic centimeters of the same arti-
ficial gastric juice carefully neutralized; and in No. 4 ten cubic centimeters
of gastric juice thoroughly boiled. All of these tubes are then to be placed in
an oven heated by 40 degrees centigrade. At the same time, duplicates of tube
No. 2 are to be prepared, one being surrounded with ice and the other kept at the
temperature of the room. On examination of these tubes after four or five hours,
it will be found that in tube No. 1, which contained acid alone, the fibrin is
swollen up into a stiff jelly, but has not been dissolved. In No. 2, which con-
tained artificial gastric juice, the fibrin will have entirely disappeared. In No. 3,
which contained gastric juice neutralized, or, in otherwords, pepsin in solution, the
fibrin will be unaltered, while in No. 4, which contained the boiled gastric juice,
the appearances will be identical with those of No. 1 It may be learned from
this that fibrin is not dissolved by acid alone nor by pepsin alone, but that their
combination is necessary for its solution, while it is also seen that pepsin is
destroyed by heat. By referring to the other two tubes, it will be seen that the
fibrin will present the same appearance almost as seen in tube No. 1, showing,
therefore, that cold prevents the action of gastric juice. If, however, the tube
which was in the ice is placed in a warm oven, the fibrin will be rapidly digested,
showing that its solution was simply suspended by cold. The solvent action of
the gastric juice is, however, totally destroyed by boiling. If tube No. 1 be exactly

GASTKIC DIGESTION. 353

neutralized, the fibrin will regain its original appearance. If tube No. 3, which
contained the neutralized gastric juice, be acidulated to proper degree, the fibrin
will be dissolved. If tube No. 2 is neutralized, there will be a precipitate varying
in amount with the duration of the digestion. If that precipitate be filtered off,
the filtrate will still show the presence of a proteid body.

The results of gastric digestions are. thus, not dependent upon the
acidity of the gastric juice alone, for we find that when the neutraliza-
tion product is filtered off there still remains in solution in the filtrate
a large quantity of proteid matter. This substance is termed peptone,
and has the same elementaiy composition as albumen and gives most of
the proteid reactions, it, however, differing from the ordinanr proteids
in several respects. In the first place, solutions of peptone diffuse readily
and are readily filtered. Tlie}r are not precipitated by boiling and nitric
acid, acetic acid and potassium ferrocyanide, and saturation with com-
mon salt. They are precipitated from neutral or faintly acid solutions
by mercuric chloride, tannic acid, bile acids, and phosphowolframic acid ;
they will yield the Millon's and xanthoproteic tests, and with caustic soda
or potash and a small quantity of cupric sulphate they give a beautiful
purple-red color instead of the violet yielded by other albuminous bodies
(Biuret test). They rotate the plane of polarized light to the left. When
injected into the blood they do not appear in the urine, as is the case
with egg-albumen, but when injected in large amounts produce the S3^mp-
toms of a narcotic poison and prevent coagulation of the blood. When
dried, peptones are amorphous, transparent, 3^ello wish-white, hygroscopic
powders, while when freshly precipitated they closely resemble coagu-
lated casein in appearance.

When proteids are subjected to the action of gastric juice, the acid
first transforms the albuminous bodies into a substance analogous to acid
albumen, termed parapeptone, this substance thus standing midway
between the albumen and peptone. By the continued effect of the action
of the gastric juice, principally through the influence of the pepsin, the
parapeptone passes into a true soluble peptone, its formation being due
to the taking up of a molecule of water. Under the influence of the
hydrotytic ferment of pepsin, the greater the amount of pepsin, within
certain limits, the more rapidly the solution takes place, although it
seems that the pepsin is not used up in the process of gastric digestion ;
and if the degree of acidity be kept uniform, almost unlimited amounts
of albumen' may be digested by a small amount of pepsin. Large
amounts of peptones appear to interfere with the digestion of albuminous
bodies ; but if the peptones are removed as rapidly as formed, digestion
may go on until all the albumen is converted into peptones, or until the
acidity has disappeared.

The gastric juice only digests the albuminous constituents of food,
vegetable albuminoids being digested in the same manner and with the

23

354 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

same products as albuminoids of animal origin. On carbohydrates the
ferment of gastric juice is without effect, the cases reported in which
starch has promptly been converted into sugar in the stomach being
attributable to the action of saliva which had been swallowed. The sali-
vary ferment is not destroyed in the stomach, since saliva may be kept
for days together in contact with gastric juice, and if the acid be then
neutralized the diastatic power of the saliva may still be exerted. The
change of starch into sugar in the stomach will vary in intensity
according as the animal is carnivorous or herbivorous. In the former
case the saliva possesses but little diastatic power, and the food being
swallowed without mastication no conversion of starch into sugar may
be said to occur in the mouth, while the high degree of acidity of the
gastric juice will almost entirely prevent the action of saliva in the
stomach. Carbohydrates, therefore, when given to carnivora, pass
through the stomach almost unchanged, and are only converted into
sugar when brought into contact with the pancreatic and intestinal secre-
tions. In the case of ruminant herbivora the food and saliva are carried
together to the rumen, where the high temperature and alkaline reaction
favor the conversion of starch into sugar. In the non-ruminant her-
bivora, as in the horse and rabbit, the sojourn of the food in the mouth
is much more prolonged than in other animals, and time is given for the
partial conversion of starch into sugar to take place. When the uncon-
verted starch and saliva reach the stomach the process ma}^ still go on,
for, in the first place, the acidity of the gastric juice is much less in
these animals than in carnivora, and, in the second place, as will be shown
directly, the acid of the gastric secretion in these animals in the first
stage of digestion is lactic and not hydrochloric acid, and the action of
ptyalin may still take place in a fluid containing 2 per cent, of the former
acid, while it ceases in 0.5 per cent, of the latter. By the time, there-
fore, that hydrochloric acid has been substituted for lactic acid, it may
be concluded that the starch has been mainly converted into sugar.

Again, cane-sugar is slowly converted in the stomach into invert-
sugar, apparently through the influence of hydrochloric acid. Fats are
but slightly digested by gastric juice, it appearing that a small part of
the fat is broken up into glycerin and fatty acids. When adipose tissue
is subjected to the action of gastric juice, the albuminous cell-envelopes
are dissolved and the fat liberated in the form of free oil-globules, only
a small portion of which is broken up into fatty acids and glycerin, while
the remainder escapes into the small intestines to be acted upon by the
pancreatic secretion. When milk is introduced into the stomach, the
casein, through the action of the milk-curdling ferment, together with
the acid of the gastric juice, is coagulated and forms the curd, in which
the oil-globules are held. In a subsequent stage of digestion, the casein

GASTEIC DIGESTION. 355

is dissolved and converted into peptone, and the oil is again liberated.
When, therefore, artificial gastric juice is added to milk warmed to the
temperature of the body, the casein is rapidly coagulated and a toler-
ably firm, white curd is formed, floating in the clear fluid, the whey, which
contains the salts, milk-sugar, water, and albumen of the milk. As
digestion progresses, the casein being turned into peptone, the oil is set
free and the whey again becomes milky, from the oil again passing into
the state of partial emulsion.

Gelatin and connective tissues are dissolved and peptonized by the
gastric juice. When gelatin has been subjected to the action of gastric
secretion, its solutions no longer solidify when cold, but a gelatin-pep-
tone is formed which is soluble and diffusible, although it differs from a
true peptone. When muscular tissue is subjected to the action of gastric
juice, the sarcolemma becomes dissolved, the muscle-fibre breaks up
traiisversel}' into disks, which become dissolved and converted ultimately
into a true peptone. Horny tissues are unchanged by gastric juice, as
is also anryloid substance. Red blood-corpuscles are dissolved in the
stomach, the haemoglobin being decomposed into haematin, and the glob-
ulin is ultimately transformed into peptone, while the hsematin is partly
unchanged and partly converted into bile-pigment.

That the stomach is able to digest albuminous bodies of the most
varying nature, and yet escape digestion itself by its own secretion, is a
fact of which explanation has as yet never been clearty determined. It has
been attributed to the alkalinity of the blood in the tissues neutralizing
the gastric juice and so protecting the tissues of the stomach ; if that
were so, we would expect that the pancreatic secretion, being most active
in an alkaline medium, would be aided by the alkalinit}r of the blood in
digesting the walls of the intestine. The protection of the walls of the
stomach during digestion has been attributed to the mucus or the
epithelium lining the stomach ; both may, however, be mechanically
removed through a gastric fistula — and both are, undoubtedly, at least
partially removed in the use of the stomach-sound — and yet without the
walls of the stomach being digested.

The obscurity is rendered still more intense by the fact that under
certain circumstances the stomach does digest itself. If an animal be
killed during active digestion, and the body kept at an elevated temper-
ature, the walls of the stomach will be digested ; or if the stomach be
excised from an animal and covered with dilute hydrochloric acid, it will
be almost -completely dissolved. These facts have been attributed to the
absence of vitality ; but if the leg of a living frog be inserted through
a fistula into the stomach of a dog it will be completely digested, and
in the maintenance of a gastric fistula in dogs it will often be noticed
that the edges of the wound become corroded from the escape of gastric

356

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

juice along the sides of the cannula. The subject must, therefore, be left
where we started : the stomach during life does not digest itself, but its
immunity cannot be satisfactorily explained.

3. THE SECRETION OF GASTRIC JUICE. — The walls of the stomach are
constituted by four coats, composed externally of the peritoneum or
serous layer ; second, the muscular layer, composed of longitudinal, cir-
cular, and oblique unstriped muscular fibres ; third ^Q subrnucous layer
of connective tissue, in which are found numerous blood-vessels, lymphat-
ics, and glands; and, fourth, the inter-
nal mucous coat, in which are found
the glands of the stomach. The mu-
cous membrane is covered throughout
its entire extent by a single layer of
narrow, cylindrical, epithelial cells
similar to the ordinary mucus-secreting
goblet cells. The tubular glands of
the stomach are of two distinct kinds,
traversing the mucous membrane ver-
tically and differing greatly as they
are located in the cardiac or pyloric
portions of the stomach. The glands
found in the cardiac portion of the
stomach or fundus are called the peptic
glands, and consist of several short
tubules opening into a broad duct
which is lined by epithelial cells similar
to those on the free mucous membrane
of the stomach. The lower portions of
the tubes, those portions which alone
form the gastric secretion, are lined by
a layer of small granular, columnar,
nucleated cells (Fig. 148). These
cells border the lumen of the gland
and are termed the chief or central
cells. At various places between

these cells and the membrana propria are large, oval or angular granu-
lated, nucleated cells, which are termed parietal cells. These cells are
most numerous in the necks of the glands and less so in the lower ends of
the tubules (Fig. 149). They are stained deeply by osmic acid and
aniline blue, and bulge out the membrana propria opposite to where they
are placed, and are thus readily recognized.

The pyloric glands (Fig. 150) are generally branched at their lower
ends, several tubes opening into a single duct, which is long and wide.

FIG. 148.— GLANDS OF THE FUNDUS OF
THE STOMACH. (Heidenhain.)

GASTRIC DIGESTION. 357

The duct is lined by epithelium like that lining the stomach, while the
deeper part is lined by a single layer of short, fine, granular, columnar
cells.

It is thus seen that the glands of the fundus and pylorus are histo-
logically different, and it has been found by the method of partial fistula,
by excising certain portions of the stomach, that the character of the
secretions formed b}^ these cells is also different. Here also, as in the
salivary glands, changes occur in the interior of the cells according as
the gland is active or has been exhausted. During fasting the chief
cells of the fundus and all the cells of the pyloric glands are clear and
of moderate size. During digestion the chief cells become enlarged
or turbid and granular ; the parietal cells also enlarge, while the pyloric
cells remain unchanged, and only become enlarged toward the ter-

FIG. 149.— CROSS-SECTION OF THE GLANDS OF THE FUNDUS OF THE STOMACH.

(Heidenhain.)
A, through the body of the gland ; B, through the neck.

mination of digestion. Often during the last hours of digestion the
chief cells again become larger and clearer, the parietal cells diminish,
and the p3Tloric cells decrease in size and become turbid. We therefore
see that there are three different forms of anatomical elements found
in the stomach, and these different cells furnish different forms of gastric
secretion (Figs. 151 and 152). When the stomach is empty its reaction is
alkaline and its mucous surface is covered with a layer of mucus which
is formed from the cylindrical epithelial cells, which line the free surface of
the mucous membrane and dip into the ducts of the glands. The gastric
juice proper comes from the tubules which line the entire stomach with
the exception of the cardiac and extreme pyloric ends. Gastric juice,
as has been seen, contains pepsin, In^drochloric acid, and the milk-curd-
ling ferment. The pepsin is formed by the chief cells found throughout

358

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

all the tubular glands of the stomach. When these cells are clear and
large the}^ then contain their maximum amount of pepsin. After the
secretion of gastric juice has lasted for some time, these cells become
contracted and turbid and then contain but a small amount of pepsin.
According to certain authorities, pepsin is not directly formed in the cells
of these tubular glands, but results from the transformation, by means of
hydrochloric acid or sodium chloride, of a mother-substance or zymogen
which has been termed pepsinogen.

FIG. 150.— PYLORIC G.LANDS OF THK STOMACH.
( Hcidcnhain. )

FIG. 151. — PYL.ORIC GLANDS — COM-
MENCING CHANGES DURING DIGES-
TION, AFTER EBSTEIN. (Heidenhain.)

These statements as to the formation of pepsin are based upon the
fact that the secretion withdrawn from the isolated cardiac or pyloric
extremity of the stomach contains pepsin in abundance, although the
quantity is more marked in the secretion formed by the glands of the
fundus. So, also, in the frog, glands similar in character to those con-
taining chief cells are found in the tubules located in the lower portion

GASTEIC DIGESTION.

359

of the oesophagus. Here, also, the secretion poured out })y the glands
of this locality is alkaline, and yet contains pepsin, while a watery
infusion of this part of the frog's stomach is also highly peptic. On the
other hand, the hydrochloric acid is formed, according to Heidenhain,by
the parietal or associate cells, which are found onl}- in the glands of the
fundus. This statement, also, has been proved by the determination
that the secretion alone of the fundus during active digestion has an
acid reaction, while that of the pylorus never acquires any acidity. So,

FIG. 152.— GLANDS OF THE FUNDUS OF THE STOMACH. (Hcidenhain.)

A and At, during fasting ; B, first stage of digestion : enlargement of the chief cells and commencing turbidity ; C and
D, secqnd stage of digestion : the chief cells become smaller in size and more and more turbid.

again, in the frog these associate cells are found in the stomach, and not
in the tubular glands of the oesophagus, and it is known that in the
stomach alone free acid is formed. Again, in hibernating animals the
chief cells disappear, and in these animals the secretion of gastric juice
never acquires an acid reaction. The milk-curdling ferment is, probably,
also formed by the central cells, especially those of the pyloric extremity,

360 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

since it has been found that it is this locality of the stomach which
yields the milk-curdling ferment in largest amounts.

As regards the action of the nervous system on the secretion of
gastric juice, very little is known. It seems clear that this secretion,
like that of the saliva and of other glands, is a reflex process; for when
the stomach is empty there is no secretion of gastric juice, which only
takes place when proper stimuli are applied to the mucous membrane of
the stomach. Such stimuli may be either mechanical or chemical, and
the immediate result of their contact is to cause an increase in the
activity of the circulation through the walls of the stomach, with a con-
sequent increase in temperature which ma}^ amount to as much as
1° C. The mechanism of secretion, therefore, is, in all probability,
identical with that of other glands. The nerves which influence the
secretion are almost totally unknown, since no nerve has been found
whose stimulation leads to the secretion of gastric juice in a manner at
all analogous to that which results from the stimulation of the chorda
tympani in producing the secretion of saliva. It seems probable that the
centres whose reflex stimulation leads to the flow of gastric juice are
located in the stomach, for both the pneumogastric and sympathetic
nerves may be divided, and local stimulation of the gastric mucous
membrane will still lead to a flow of gastric juice. The pneumogastrics,
nevertheless, besides being the sensory nerves of the stomach, seem to be
concerned in the production of the vascular dilatation, which is of such
importance in the production of the secretion ; for, if both pneumo-
gastrics are divided during digestion, the mucous membrane of the
stomach becomes pale. The secretion of gastric juice is also undoubt-
edly in some way connected with the central nervous system, for Richet
has noted the fact that in a case of complete cesophageal stricture,
observation of the stomach through a fistulous opening into this organ
proved that the secretion of gastric juice followed the introduction of
acids or sugar into the mouth.

4. GASTRIC DIGESTION IN CARNIVORA — The importance of the stom-
ach in the operation of digestion varies greatly in different animals.
In the carnivora the action of the stomach is less constant than in the
herbivora, but is of greater importance. While its action is intermittent,
the intervals between its periods of activity and the duration of its
activity are more prolonged. Carnivora swallow their food in large frag-
ments, torn only small enough to be swallowed, and in many cases
swallow their prey entire. Their mastication is of slight importance, for
they feed on substances readily soluble in gastric juice, the only function
of the saliva being to render the food easy of deglutition, it having
scarcely any digestive function to fulfill. In carnivora, as already stated,
the conformation of the mouth, pharynx, and gullet enables large masses

GASTKIC DIGESTION. 361

of animal matter to be introduced into the stomach. The gastric mucous
membrane secretes gastric juice throughout its entire extent, and the
digestion in the stomach in carnivora is the most important stage in the
preparation of food for absorption. The secretion is rapidly poured out
after taking a meal, the activity being in accordance with the degree of
stimulation which the aliments exercise on this viscus. Thus, there is
less secretion formed when gelatin, gum, starch, and other indigestible
substances are swallowed, while the secretion is copious when meat, bone,
and other albuminous bodies are introduced into the stomach. The total
amount of gastric juice secreted by carnivora can only be determined
with difficulty. It has been stated as one hundred grammes for each kilo
of body weight — an amount which is evidently too large ; probably one-
fourth the amount would be nearer the truth. As the gastric juice of
the carnivora is obtained with the greatest readiness, it is the secretion
which has been most studied. It contains a larger percentage of acid
and pepsin than that of omnivorous and herbivorous animals, and in
equal time will digest four times as much cooked albumen as the gastric
juice of the sheep. It has been stated that a dog is able to digest one-,
fifth of his own weight at one meal. Nevertheless, the gastric juice does
not convert all the food taken into the stomach into peptones ; a large
part is merely disintegrated and passes into the small intestine to be
acted upon by the pancreatic juice. When excessive amounts of meat
are taken, as is occasionally the case in young dogs, it will escape entirely
unaltered through the intestines. Considerable time is required for
gastric digestion in carnivora. Thus, albumen given to dogs has been
found still coagulable by heat after a sojourn of three hours in the
stomach, indicating that in a certain portion digestion had not com-
menced. Again, coagulated albumen has been found^ unaltered after a
period of four hours ; fibrin has been found swollen and transparent,
but not dissolved ; while gluten, after having remained four hours in the
stomach, has been found almost unaltered.

Spallanzani states that masses of meat inclosed in tubes were found
partially undigested after eleven hours, while Colin claims that at least
twelve hours are required for a carnivore to digest the amount of meat
which it would take spontaneously at a single meal. Thus, Colin gave
to a cat which had fasted for twent.y-four hours two hundred grammes of
horse-meat, 'and found that five hours afterward the stomach contained
one hundred and fifty grammes of unaltered meat; but fort}T-five grammes,
therefore, or only about one-fourth, having been disintegrated. To another
cat two hundred grammes of horse-meat were given after fasting twenty
hours, and after twelve hours sixty-four grammes could still be recog-
nized. Similar data were also obtained in the case of the dog. It is not
astonishing that the food remains so long in the stomach. Time is given

362 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

for the digestion of ligaments, tendons, and often cartilages and bones,
and such substances will often remain in the stomach for days at a time.
The digestibility of certain kinds of animal food appears to be altered
according as the substances are cooked or raw ; gelatinous tissues, such
as tendons, are more readily digested when cooked, evidently due to the
conversion of the collagenous bodies into gelatin. Albuminous tissues,
on the other hand, especially the glandular structures, such as liver,
kidney, etc., lose in digestibility when cooked, unless the cooking is very
prolonged, when a stage of peptonization may be inaugurated. Muscular
tissue seems to be equally digestible when raw as when cooked. Feed-
ing on raw meat is the natural normal diet of the pure caririvora, and
even carnivorous animals in a state of domestication appear to digest
raw meat more regularly and with less diarrhoea than when fed on cooked
meat, which is often followed by a fetid diarrhoea; thus, a little raw meat
given to dogs will keep their skin supple, the hair soft, and their general
condition will be improved.

From what has been said, it is, then, clear that ordinary house refuse is all
that dogs require for food. When a number of dogs are kept, this will not, as a
rule, be sufficient ; so, then, it is necessary to give some further idea as to the
best and most economical plans of feeding a kennel of dogs. For ordinary feed-
ing in town, as recommended by Dinks and Mayhew, beef-heads, sheep-heads, feet,
and offal should be cleaned, chopped up, boiled in water, filling up the kettle as
the water boils away, until all the meat separates in shreds. To this may be
added a little salt and any cheap vegetable, such as cabbage, parsnips, potatoes,
or turnips. Put this soup aside, and then boil old Indian meal till it is quite stiff;
let it also get cold. When required, take as much meal as may be required, and
enough broth to liquefy it.

In the country, during the summer, skimmed milk, sour milk, buttermilk, or
whey may be used in place of the broth. In the winter the soup should be alter-
nated with meal — never use new Indian meal, it scours. Although Indian meal
has not as much sugar or albumen as oats, it does tolerably well ; but when a great
amount of work is expected of the dogs, as in a month's shooting excursion, oat-
meal should always be used, as a less bulk is more nourishing than Indian meal,
and old meal cannot always be obtained, or meat to make soup. Oatmeal-porridge
and milk are capital under such circumstances.

In a house there are always bones, potato-peelings, and pot-liquor : by clean-
ing all the potatoes, and throwing all into the dog-pot, the dogs are greatly
benefited. Rutabagas are good boiled in soup. Boiled meat alone seems to
destroy the scent of dogs ; so, also, greasy substances.

Alimentary substances introduced into the stomach are changed in
the way already indicated. All albuminous bodies are converted into
peptone. Starch may be slightly converted into sugar through the action
of the salivary ferment, or, after passing into the intestine, through the
action of the pancreatic ferment. Herbaceous matters are not digested
by dogs, even though often taken in great quantities, and they are either
again vomited, pass in the faeces, or may cause intestinal obstruction.
When raw vegetable substances are swallowed by carnivorous animals it
is only the salts of vegetable acids which are extracted, while the skele-
tons, containing starch and albuminous matters, remain behind. It is

GASTKIC DIGESTION. 363

probably the need of the extraction of these vegetable acids which leads
dogs so often in the spring to eat grass.

As the substances contained in the stomach are liquefied, they pass
gradually by the contraction of the walls of the stomach and relaxation
of the pylorus into the small intestine. Indigestible substances may
remain in the stomach, either to be vomited or finally to pass into the
intestine.

5. GASTRIC DIGESTION IN OMNIVORA. — In the omnivora gastric
digestion offers similar characteristics to those noted in the case of the
carnivora, though it is slower and less complete. Thus, Colin states that
after giving one thousand grammes of raw meat to a hog six hundred
grammes were found in the stomach six hours after feeding, while
undigested pieces were found in the small intestine. In another case a
hog which had received three kilos of meat with one litre of water had
only digested three hundred grammes in six hours. We thus see that
while the hog is an omnivorous animal, it is not less capable of digesting
animal matters than are the pure carnivorous animals. While this is,
however, the case, from their imperfect mastication they are less consti-
tuted for the extracting of nutritive principle from the vegetable matter
than the purely herbivorous animals.

The stomach of the hog is generally described as a simple stomach,
but it really represents a stage of transition between the simple stomach
of carnivora and the complex stomachs of ruminants. Even on external
examination, by the presence of a constriction at the cardiac and pyloric
extremity the presence of well-marked diverticula is evident. On
inspecting the interior, Ellenberger and Hofmeister, who have been
mainly followed in this description, show that the organ may be divided
into five distinct regions : 1. The cesophageal portion, which is coated
with a mucous membrane, cutaneous in character, similar to that lining
the O3sophagus, and which is separated by a distinct border from the
secreting membrane. It contains no glands, but is papillated, though to
a less degree than the left half of the horse's stomach. 2. The cardiac
diverticuium, lined with a white, thin mucous membrane, which is sepa-
rated by a fold of mucous membrane from the fundus of the stomach.
The mucous membrane of this portion of the hog's stomach is coated
with cylindrical epithelium and contains tubular glands, which are shorter
than the fundus glands, and composed of small, transparent, granular
cells, different from those found in any other region. Lymph-follicles
are numerous, and in some places so close together as to resemble
Pe3-er's patches. 3. The left zone, or fundus, constituting one-third or
one-half the stomach, lined with a glandular membrane, similar to that
of the cardiac diverticulum ; it contains, however, a smaller relative
number of follicles. 4. The central zone includes the greater curvature,

364 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and extends toward the pylorus and cesophageal portion, its extremities
being triangular. The mucous membrane in this region is very thick
and brownish-red in color, and contains the so-called fundus glands.
These are tubular in structure, longer, but subdivided to a less degree
than the pyloric glands. The ducts of these tubules are lined with epi-
thelium similar to that lining the cavity of the stomach, while the fundus
contains chief and associate cells similar to those found in the stomachs
of carnivora, with the exception that the associate cells lie in groups
external to the cylindrical cells. 5. The right or pyloric zone includes
the pylorus, as much of the lesser curvature as does not belong to the
cesophageal portion, and a small portion of the greater curvature. Its
mucous membrane is white in color, and in the pylorus very thin,
though much thicker at the entrance to the pylorus ; the submucosa
is sparsely developed. After death the pyloric zone is generally found
coated with a thick layer of mucus, stained yellowish from the bile. The
glands of this portion are considerably longer than those found elsewhere,
are subdivided and convoluted. Associate cells are entirely wanting in
the pyloric zone, the cells being cylindrical and granular or hyaline.

As Ellenberger and Hofmeister pointed out, the stomachs of mam-
mals may be divided into two different .groups, in one of which cesoph-
ageal diverticula, and in the other diverticula of the stomach itself,
represent the mode of deviation from the simple gastric form. When
both forms of diverticula are present, the true compound stomach is
represented. The gastric formation, with a divert iculum formed from
the glandular stomach itself, is met with in many herbivora and omniv-
ora, and such carnivora as live on highly indigestible animal substances.

In its simplest form the part near the pylorus is dilated into a
pouch-like expansion ; such a form is met with in the hog, but is still
further complicated by a saccular expansion at the cardiac extremity.
Such a formation evidently lengthens the period of retention of the
food within the stomach, and by an increase in the internal surface of
the stomach permits of a more continuous action of the gastric juice,
since it corresponds to an increase in the secreting surface.

In the development of the compound stomach through the forma-
tion of cesophageal dilatations, the stomach of the hog represents the
first stage.

The second stage is found in the stomach of the horse, where the
entire left half of the stomach may be regarded as an oesophageal
expansion ; and while the stomach of the horse from external view
resembles a simple stomach, internal examination shows that it is
practically a compound stomach.

The highest degree of development of the cesophageal pouches is,
of course, seen in the stomachs of ruminants.

GASTRIC DIGESTION. 365

The gastric juice of the hog contains the same ferments as are found
in the secretion of other mammals ; it dissolves albuminates and con-
verts them into peptone, parapeptone, and syntonin, and coagulates
milk, and, to a slight degree, as in the case of other mammals, splits up
fats into glycerin and fatty acids.

The secretion obtained from different portions of the stomach differs ;
that obtained from the greater curvature contains more mucin, more
acid, and more ferment than that from the other portions, while the
secretion from the cesophageal portion is free from ferment.

In the secretion from the greater curvature, as obtained by the
making of extracts with common salt, the degree of acidity varies from
0.03 to 0.07 per cent.

The portion of the stomach supplied with the associate cells con-
tains all the ferments in the greatest quantity. Small amounts are found
in the pyloric region, and a still smaller amount in the cardiac diver-
ticulum.

These ferments in the hog are with difficulty extracted with glycerin,
but are readily removed by means of dilute hydrochloric acid and salt
solutions.

Ellenberger and Hofmeister further claim that there is a diastatic
ferment in the mucous membrane of the hog's stomach, and they have
proved by carefully controlled experiments that the conversion of starch
into sugar by means of artificial gastric juice from the hog is actually
due to the presence of the ferment. It does not, however, seem clear
as to whether this ferment is actually produced in the gastric mucous
membrane, or whether it enters that membrane by imbibition from saliva
which has been swallowed. The gastric juice of the fundus of the stom-
ach of the greater curvature produces coagulation of milk, both in
alkaline and in neutral conditions ; this power is not possessed by the
mucous membrane of the cardiac sac, and only to a slight degree by the
pyloric portion. No lactic acid ferment exists in the hog's gastric juice.

The progress of gastric digestion in the hog has been carefully
studied by Ellenberger and Hofmeister, by administering definite amounts
of specific foods to hogs in whom the stomach had been emptied by
fasting and cleansed by copious administration of water. The animals
were then killed, at specific intervals after the administration of the
food, and the gastric and intestinal contents subjected to a chemical
examination. These authors' experiments were restricted to the cereals.
The largest number of experiments were made with oats, given dry, so
as to produce the greatest quantity of saliva. In other instances the
food was given moist, so as to reduce the secretion of saliva to a min-
imum. To those who received the dry food water was always given to
drink. The animals on whom these experiments were made were for a

366 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

few days previous to the experiment fed on such food as could be readily
recognized in the intestinal tube. For thirty-six hours before the exper-
iment no food whatever was given. The animals were then killed, after
the administration of a weighed quantity of food, at one, two, three,
four, six, eight, ten, and twelve hours after the termination of the meal,
an attempt being made to isolate the portions obtained from the dif-
ferent parts of the stomach, the cardiac and pyloric halves being kept
separate. The result of these experiments directed attention especially
to the progress of digestion, to the location of the gastric contents, the
nature of the acid and quantity of the ferment present, the duration
of gastric digestion, the source of gastric juice, and the character of the
gastric movements. Their experiments teach that the gastric digestion
of grains in the hog may be divided into two periods. During the
meal and for one or two hours afterward, digestion of starch alone takes
place, the starch being converted into soluble starch, dextrin, and sugar.
Simultaneously with the digestion of the starch, lactic acid fermentation
occurs, a considerable quantity of the sugar being in this way converted
into lactic acid. It does not appear from their results as to whether
cellulose, also, at the same time undergoes fermentation or not. During
this period the food becomes softened and swollen from maceration in
the fluids, and a great part of the soluble matters of the food pass into
solution, the digestibility of the vegetable albuminates being facilitated
b}' the presence of lactic acid.

The conversion of the starch into sugar occurring in this period
is due to the saliva, which the authors have found in the hog to pos-
sess amylolytic power in a high degree. It is strongly alkaline, and
therefore neutralizes whatever acid was first present in the stomach.
Later, the cardiac contents become acid, due at first to the presence of
lactic acid, which, as is well known, does not interfere with the action of
the amylolytic ferment. It is also probable that a certain amount of this
amylotytic ferment comes from the cardiac sac of the .hog's stomach,
which, as already mentioned, contains a special character of glands
whose extract always yields diastatic ferments.

As regards the degree of digestion in this period, the following
figures, taken from one of Ellenberger's and Hofmeister's experiments,
serve as an example : —

The animal had received 860 grammes of oats, representing 73
grammes of cellulose, 557 grammes of carbohydrates, and 93 grammes
of albuminoids. As a consequence, 22.5 per cent, soluble nutritive sub-
stances consisted of albumen. On analysis, only 47 grammes of undis-
solved albumen were found ; hence 34 per cent, of the insoluble albuminous
bodies had passed into solution.

In feeding with animal matters, naturally this first stage, which

GASTRIC DIGESTION. 367

might be called the am}'lolytic period of digestion, is absent. This
amylolytic period lasts for about three or four hours, including, of
course, the half-hour or hour occupied by the meal. The duration is,
however, longer in the cardiac sac than in the fundus and pyloric
portions of the stomach, where it becomes gradually converted into
what might be termed the proteolytic period, in which the proteids
become converted into peptones.

The digestion of proteids in the hog is first rendered possible
through the presence of lactic acid, During this stage of proteolysis
the digestive processes differ in the cardiac and pyloric portions of the
stomach, indicating that for several hours a well-marked difference
exists between the contents of these different regions of the stomach, in
the former of which only lactic acid and in the latter both hydrochloric
and lactic acids are present. This fact, for which we are also indebted
to Ellenberger and Hofmeister, is in opposition to the generally accepted
views as to the rapid diffusion and mixing of the gastric contents.

The second digestive period, in which, while the cardiac extremity
is still digesting starch, the pyloric half is digesting albumen, begins
at about the third or fourth hour of digestion, and may continue from
nine to twelve hours.

In the third period the digestion of starch ceases, from the great
development of hydrochloric acid, although it should be remembered
that up to the fourth hour of gastric digestion the cardiac fluid is still
capable of converting starch into sugar.

It thus would appear that digestion in the stomach of the hog con-
tinues from one meal to the other, although in a moderate meal part of
the gastric contents maj^ pass into the intestine three or four hours after
eating; but part, nevertheless, remains in the stomach, and may be
found there even thirty-six hours afterward.

These results further show that the degree of mixing of the con-
tents of the stomach produced by the gastric movements is by no means
complete, the first quantities being gradually pushed on toward the
P3*lorus by those coming afterward. The degree of acidity of the gastric
contents gradually increases. While at first alkaline, it gradually
increases in acidity so that three hours after the meal 0.07 per cent, acid
may be recognized in the left half of the stomach and 0.2 per cent, in
the right half. The acid within the left half of the stomach then com-
mences to increase, until finally it may amount to 0.3 per cent. When
the meals rapidly follow each other gastric digestion is interrupted, and
the undigested portion is forced into the intestine, undergoing digestion
there by means of the intestinal digestive fluids. As a consequence,
in large meals the amylolytic period is increased and the proteolytic
period decreased, while the degree of acidity more slowly approaches a

368 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

maximum. The degree of mastication is further of influence on the
completeness of the amylolytic change. When dried food is given
mastication is more prolonged, and the conversion into starch is more
complete than when soft, watery foods are given.

6. GASTRIC DIGESTION IN SOLIPEDES. — The simplicity and smallness
of the stomach in these animals, the vast size and valvular character of the
colon, and the importance and high degree of development of the caecum
are the peculiarities which characterize digestion in this group of
herbivorous animals. The type of digestive parts seen in the horse and
other solipedes are represented also in the pachyderms and among
rodents, where the intestinal tube is constructed on a similar plan. They,
therefore, possess many points in common in the mode of action of the
digestive parts. As indicated by Colin, the following points characterize
digestion in solipedes. First, the slowness of the mechanical prepara-
toiy stage of digestion ; second, the rapidity with which the work of the
stomach is effected; third, the rapiditj- of the passage of liquids into
the intestines, and their accumulation in the caecum ; fourth, the hardness
and globular form which the residue of alimentary matters assume in the
posterior parts of the large intestine.

Mastication, which was found in the carnivora to be insignificant,
.becomes in the herbivora an act of the greatest importance, for grass,
hay, corn, or oats can only be digested after the most perfect comminution
and trituration, for the vegetable nutritious matters are inclosed in
cellulose envelopes which are impervious to gastric juice. In the soli-
pedes rumination does not take place; hence, mastication is slow and
perfect and completed once for all. A horse cannot ordinarily eat two
thousand five hundred grammes of hay in less than one hour, or even
two if .the teeth are at all defective, while twenty to fort}r minutes are
required for the mastication of the same quantity of oats. Preliminary
chopping of food does not help digestion in sound animals, and cannot
replace the process of mastication in animals in which the teeth are
defective, for it is impossible to carry the process far enough unless the
substances are actually milled or ground to a powder. This, of course,
will liberate^the nutritive matters from their indigestible cells, and may
assist digestion in animals in which mastication is imperfectly performed.
Chopped food, in fact, may prove harmful by reducing the duration of
mastication, and so decreasing the amount of saliva poured out. Masti-
cation in solipedes is slow and prolonged, not only from the necessity
for comminuting the food, but also from the fact that in the mouth the
principal action of the saliva on the food commences.

As the foods enter the stomach they push to the right the mass
already present, and as the capacity is only fifteen to eighteen litres, this
organ cannot .contain. an entire .single meal. . . Thus, when a horse eats

GASTKIC DIGESTION. 369

five kilos of hay, representing one-half its daily ration, requiring two
hours for its consumption, and impregnates it with twenty litres of saliva,
the mass would occupy a space of twenty-eight to thirty cubic decimeters.
As the stomach is functionally most active when only two-thirds distended,
that is, while containing about ten litres, the stomach must, therefore,
till and empty itself two or three times during one meal. It is, therefore,
seen that the small capacity of the stomach has the effect of reducing the
duration of gastric digestion, and the greater the volume of food the
less will be the time that food will remain in the stomach. Consequently,
oats, taking up only one-fifth the volume of an equal weight of hay,
would remain in the stomach four or five times as long. This difference
in time during which different foods remain in the stomach is necessi-
tated, as indicated by Colin, by the different compositions of the food.
Thus, a horse fed on hay receives in this food 44 per cent, of carbo-
hydrates, which have been already partially modified by the saliva
and whose further transformation is completed in the intestine. Four
per cent, of fats is present, which, as has been seen, are not acted on by
the gastric juice, while only 7 per cent, of albuminous matter is
present. It is the albuminous matter alone which is digested by gastric
juice, and, since we have only 7 per cent, of albuminous matter pres-
ent in hay, it is evident that but a short time, comparatively speaking,
would be required for the digestion of this albuminous matter, which is
finely divided and in the most favorable condition for being subjected to
its solvent action. So, also, the horse fed on green forage receives in
its food 9 per cent, of carbohydrates, barely 1 per cent, of fat, and only
3 per cent, of nitrogenous matters which are digestible in the stomach.
Therefore, in green fodder but a short time is required for gastric diges-
tion. Ou the other hand, oats contain about 11 per cent, of nitrogenous
matter, and, consequently, we find that the small relative volume of oats,
as contrasted with other forms of vegetable foods, enables them to remain
longer in the stomach.

In the horse the performance of gastric fistulae is impossible on
anatomical grounds, and various attempts have been made to collect
gastric juice by performing cesophagotomy, — passing a sponge .through
a tube into the stomach, killing the animal after a certain time, tying
the pylorus, and collecting the contents. This method, however, fails
to secure a gastric secretion which is free from bile and pancreatic
juice. So, also, the use of the stomach-pump is rendered difficult or
impossible on account of the long and pendulous soft palate and the
discomforts and struggles which it causes in animals when attempts to
employ it are made.

By means of the method referred to above, the fluids obtained from
the stomach will always contain saliva and various food-products, as well

24

370 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

as the true gastric secretion ; but, since these substances are always mixed
in actual digestion, they will answer for the study of the process of diges-
tion, even although they will prevent accurate statements as to the
chemical constitution of this secretion. The gastric juice in the horse
is secreted only by the glands of the fundus from a surface about two
hand-breadths in extent. Extracts from this portion of the mucous mem-
brane contain more acid, more ferments, and, what is remarkable, more
mucin than extracts made from the pyloric portion. Ellenberger and
Hofmeister found that the degree of acidity immediately after eating was,
in the horse, only 0.084 per cent. After an hour the acidit}^ rose to
0.1 per cent., and still later to 0.2 per cent. Immediately after eating
no hydrochloric acid was present, but only appeared four or five hours
after the commencement of the meal. Lactic acid was always present,
apparently even in excess of hydrochloric acid. .This ma}r, perhnps, serve
to explain the fact that in the horse's stomach the change of starch into
sugar may go on even in the presence of 0.2 per cent, of acid, as organic
acids interfere less than mineral acids with this process. The charac-
teristics of the acid of the gastric juice have been found to depend upon
the food. Thus, these authors have found that the distribution of acids
was as follows : —

Hydrochloric Acid. Organic Acids.

1. Oats and chopped straw, . . 0.163 per cent. 0.287 per cent.

2. Oats, 0.490 " 0.610

3. Hay, . . ". . . . 0.022 " 1.798 "

It is thus seen that when the food consists of oats the maximum
percentage of hydrochloric acid is found in the gastric juice, while when
hay is given the mineral acid falls to a minimum, while the organic acids
are in excess. The importance of these facts is evident when it is remem-
bered that oats contain 12 per cent, of albuminous matter and 65 per
cent, of carbohydrates, including cellulose, while hay contains only 9 per
cent, of proteids and 70 per cent, of carbohydrates. Hence, when oats
are given, the excess of hydrochloric acid is especially favorable for the
peptonization of the proteid constituents, while it interferes with the
digestion of the carbohydrates. On the other hand, when hay is given,
the excess of organic acids, as already mentioned, does not interfere with
the action of pt3^alin on starch, while still permitting the peptonization
of the proteids.

The watery extract of the mucous membrane of the fundus differs,
as already mentioned, from that of the pylorus. It contains more mucus,
more acid, and more ferment. The fundus extract contains a ferment
which converts casein, fibrin, albumen, and gelatin into peptone in media
containing 0.15 to 0.5 per cent, of hydrochloric acid. While 0.6 per
cent, of hydrochloric acid arrests digestion, in the case of organic acids

GASTRIC DIGESTION. 371

it was found that the percentage might be considerably increased above
this point and yet digestion go on. Thus, the gastric extract appeared
to possess about the same degree of activity when lactic acid was present
in 2 per cent, as with hydrochloric acid present in 0.2 per cent. The
ferment is only diffusible with great difficulty, and resists, to a high
degree, putrefactive and alcoholic fermentations. Lactic acid fermenta-
tion does not interfere with its activitj7.

The ferment is soluble in water, glycerin, dilute acids, alkaline and
saline solutions, and loses its activity at 60° C. Such an artificial gastric
juice extracted from the mucous membrane of a horse's stomach will
digest animal tissues in the same way as extracts prepared from the
mucous membrane of the stomachs of carnivora. Extracts prepared
from inflamed mucous membrane are totally inactive. In addition to the
pepsin, the gastric juice of the horse also contains the milk-curdling fer-
ment and salts, lactic acid ferment, and traces of a diastatic ferment, all
of which may be precipitated by alcohol. The distribution of these
ferments and of the acidity of the gastric juice is the same as in the dog,
with the exception that no secretion takes place in the membranous car-
diac portion of this organ.

Gastric digestion in solipedes is more important than one might be
led to suppose, and continues, to a certain extent, from one meal to the
next, as the residue remains in the stomach until the next one is taken,
and therefore the stomach does not completely empty itself after twenty-
four hours. The characters of this residue will, of course, vary with the
nature of the food. Thus, the contents of the stomach after feeding with
oats is a dried, crumbling mass, containing 60 to 70 per cent, of water.
After feeding with hay the percentage of water may be as much as 80
per cent. The reaction is always acid.

Gastric juice obtained as above, by the method of Ellenberger and
Hofmeister, rapidly converts starch into sugar, although the ferment is
not derived from the stomach, but from the swallowed saliva.

The change of starch into sugar goes on in the stomach, as is proved
by the fact that gastric juice outside of the body will turn starch into
sugar, and by the fact that after feeding starch large quantities of sugar
ma}- be found in the contents of the stomach. The digestion of starch
is most -active in the first two hours of digestion and stops after five or
six hours, when the percentage of hydrochloric acid is most marked.

When dry food has been given, the conversion of starch into sugar
may continue much longer, from the large quantity of alkaline saliva
swallowed, and may go on in the left half of the stomach even while the
fundus is digesting proteids, the acidity being due to lactic acid. After
feeding with oats, as much as thirty-five grammes of sugar have been found,
while five to eight and one-half grammes of sugar have been found after

372 PHYSIOLOGY OF THE DOMESTIC ANIMALS

feeding with hay. Of course, this does not represent the total amount
formed, as a great deal will have been absorbed, some converted into
lactic acid, and some will have passed into the small intestine.

Ellenberger, Hofmeister, and Goldschmidt found that the naturally
mixed saliva of the horse possessed a stronger amylolytic action than
the artificially combined separate salivary secretions ; and that each
separate salivary secretion, though highly amylolytic, was less so than
the mixed secretions; and, finally, that the conversion in the horse's
stomach of starch into dextrin, sugar, and lactic acid occurred to a
greater degree than could be attributable to the fermentative action of
the saliva alone. The conclusion is, therefore, drawn that in the horse's
stomach amylolytic digestion is aided b}^ ferments developed in the
alimentary canal and in the food itself. This latter statement is con-
firmed by the fact, already mentioned, that Hofmeister has found in oats
an amylolytic ferment, which is destroj^ed at the temperature af boiling
water, but which is active at the body temperature, thus explaining the
fact that more starch is converted into sugar in the stomach than is
attributable to the action of the salivary ferment alone. Finally,
Goldschmidt has found that the digestion of starch in the horse is
aided by amylolytic ferments derived from the air, which are mixed
with the saliva in the mouth, and which rapidly develop in the oral
mucus ; --. j. t ....4,*, .r. rL- .-,.

In the horse's stomach vegetable albumen is rapidly digested mid
turned into peptone, which increases in amount with the duration of
digestion. After a large meal the peptonization is at first slight, since
the glands cannot form acid and pepsin fast enough to digest a large
meal rapidly. If, then, another meal is taken before the first is digested,
the former food is forced in an undigested state into the intestine.
After a moderate meal the digestion reaches its maximum in three to
four hours; in other words, digestion is then complete. The larger
quantity of peptone is found in the stomach after oats have been given
than after feeding with hay. Five to forty grammes of peptones have
been found after oats have been given, while only about six grammes
were found six hours after feeding with ha}'. Of course, these figures
do not indicate the total amount of peptones formed, since, probably, a
large portion would be absorbed almost as rnpidly as formed. As hay
absorbs four times its weight of saliva, it is readily digested at first
without water, but the digestion then becomes slow. Colin administered
twenty-five hundred grammes of hay to a horse, and then killed him.
Only seven thousand grammes of material were found in the stomach,
representing, therefore, but little more than one-half the amount given,
since the two thousand five hundred grammes of hay would have absorbed
ten kilos of saliva. Of this residue only one thousand grammes were dry

GASTRIC DIGESTION. 373

hay ; the remainder had passed into the intestine. Other animals killed
at longer periods after meals showed the passage of the food from the
stomach into the intestine was not as rapid toward the end of the
repast as at the commencement. There appears, therefore, to be two
periods in the digestion of hay in the horse : In the first, the materials,
as soon, almost, as they enter the stomach, are rapidly pushed into the
intestine by the food that comes later; in the second period, toward
the end of the meal, the sojourn is more prolonged, and chymification
is, therefore, more perfect. Tlie gastric digestion of hay appears to be
abbreviated by the ingestion of water, as the water carries into the
intestine a good deal of food. Digestion of hay does not appear to be
modified by previous chopping.

When oats are given as food, at the commencement of the meal, a
part always passes into the intestine, but, as oats only absorb a little
more than their own weight of saliva, the volume never becomes as high
as when hay is eaten. Colin reports, also, the following experiments :
A horse which had received two thousand five hundred grammes of
oats was killed two hours after the commencement of the meal. The
stomach, which, together with the oats and saliva, had received five
thousand grammes of material, was now found to contain six thousand
and seventy grammes, the addition being derived from the gastric juice
and the saliva which had been swallowed during the meal. Here, also,
two analogous periods may be made out, but less accented than when
hay is the food. It, therefore, seems evident that small meals, frequently
repeated, would serve to render the gastric digestion in solipedes more
perfect. Thus, in Paris, according to the statement of Colin, the horses
in the omnibus service make six meals from 4 A.M. to 9 P.M., and each
of these meals has three hours for digestion, with the exception of the
last, which has six. Water is only given when hay is included, and not
at other times. It follows that gastric digestion is not of equal impor-
tance for all kinds of food, and it is, therefore, possible so to distribute
the constituents of a meal as to allow of a longer gastric digestion of
oats, which have a greater percentage of albuminous bodies and carbo-
hydrates than hay. Therefore, in the feeding of a horse especial atten-
tion should be given to the sequence or to the order in which the different
constituents of the horse's meal follow each other, — a fact which is of
greater importance for the horse than for man, the carnivora, and the
ruminants, in which all the constituents of a meal may be kept in the
stomach until the digestion is completed. Experience has shown that
if oats are given first, subsequent eating of hay forces the oats into the
intestines before the digestion of the latter is complete ; consequently,
if given after hay, the sojourn in the stomach is much more prolonged,
while the hay, containing a minimum of albuminous matter, may be

374 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

partially digested in the stomach, and its subsequent changes completed
in the intestines. Consequently, oats should always succeed the admin-
istration of hay in the feeding of horses. So, also, water should not be
given after a meal of oats to the horse, or else it will wash the oats out of
the stomach before digestion is completed. Consequently, the water
should precede hay, and both liny and water should precede the admin-
istration of oats.

The short time that food remains in the stomach is probably the
reason that the horse does not readily digest animal food, although in
the Tartar steppes it is stated that horses become accustomed to a meat
diet.

In addition to true digestion, fermentative processes also occur in
the stomach, especially in the earlier stages of gastric digestion, when
the hydrochloric acid is absent or present only in small amounts. It
has been shown that hydrochloric acid is always in small amount in
the oesophageal sac, and in this locality lactic acid fermentation, as well
as fermentation of cellulose, undoubtedly may occur, though the time
which the food remains in this part of the stomach is too short to permit
of any extensive change of this character. It will be subsequently shown
that the conditions for the fermentation of cellulose are much more favor-
able in the intestinal canal of the horse than in the stomach.

7. GASTRIC DIGESTION IN RUMINANTS. — Gastric digestion, which has
been found to be much the same in carnivora and solipedes, takes on
a new form in the ruminant animals, and although the general result of
gastric digestion is the same in all, special means are concerned in the
accomplishment of this result in the ruminant that are not seen in ani-
mals with a simple stomach. This complication is practically due to the
preliminary and accessory changes which occur in the food before it is
subjected to the action of gastric juice. Hence, the changes in the first
three compartments of the stomach are without an analogue in the gastric
digestion of monogastric animals, while the fourth stomach reproduces
exactly the process that takes place in this viscus of the latter class of
animals.

Although the four gastric reservoirs of the ruminant are anatomi-
cally connected, they are, to a certain point, functionally isolated, each
one of them having tolerably distinct functions to fulfill. The first three
are concerned in the storing of foods and liquids in rumination, while in
the fourth alone true digestion takes place. This may occur during
rumination or Curing inaction of the first three stomachs.

The rumen receives almost all of the aliments when swallowed for
the first time, the greater part of liquids drunk, and a considerable
portion of the results of the second mastication (Fig. 153). It keeps
them stored up for a certain time in its interior, where they become thor-

GASTRIC DIGESTION.

375

ougbly macerated and soaked in fluid, and from which they are forced
into the resophagus during rumination or into the honey-comb bag dur-
ing the intervals of rumination. It is evident, therefore, that the food
contained in this pouch may undergo changes due to the movements to
which it is subjected, the temperature, and the action of saliva and other
fluids. The changes are, therefore, physical and chemical. The walls of
the rumen, by their contractions and resulting movements, may exert a
considerable amount of mechanical force on the aliments contained within
it, although this has been greatly exaggerated. Nothing like trituration
takes place, but simply thorough mixing of the new and old food together

FIG. 153.— STOMACH OF THE Ox. (Colin.)

A, rumen (left hemisphere) ; B, rumen (right hemisphere) ; C, insertion of the oesophagus ; D, reticulum ;
E, omasum ; F, abomasum.

and with fluid ; consequently, it is not necessarily the portion of food
which first enters the paunch which is the first to leave. The maceration
which the food undergoes in the fluids of the paunch is especially marked
in the case of grain and dry fodder, and is greatly assisted by the tem-
perature of the organ.

The fluids contained in the rumen consist, in a great part, of water
which has been drunk and a large quantity of saliva, which is swallowed
with the first mastication and in the intervals of the act of rumination.
The rumen has, however, no secretion of its own, since no secretory
glands are found in its walls. Its reaction, as already stated, is generally

376 PHYSIOLOGY OF THE DOMESTIC AXHIALS.

alkaline, and is derived from the saliva. Occasionally, the reaction of
the rumen may be found to be acid. This may be due to fermentation
occurring in the contents of this organ, and is especially seen in nursing
calves, in animals fed on roots, and in cases of faulty digestion. It
nearly always occurs in animals fed on green fodder, where the conditions
are favorable to the fermentation of sugar. Occasionally, also, the reac-
tion of the rumen, which may be found to be acid after death, is due to
the regurgitation of the contents of the fourth stomach into the first
three compartments. In the rumen the conditions are especially favor-
able for the digestion of carbohydrates, for the conditions are favorable
for the action of saliva, which is thus enabled to convert starch into
sugar. Cellulose, also, is said to be digested in the rumen through fer-
mentative processes to as much as 60 to 70 per cent. Salts, sugar, muci-
lage, gum, and other soluble substances may be dissolved out of the food
while in the rumen, and so prepared for absorption. No peptonization,
however, occurs ; for all the various bases, salts, and albuminoids which
may be detected in the contents of this organ come solely from the food
and the secretions and liquids which have been swallowed, and not from
any secretion poured out by the rumen itself. The function of the rumen
is, therefore, simply to act as a reservoir, in which the food, after being
swallowed, is collected, undergoes maceration, and is again, from time to
time, returned to the mouth for a second mastication. In this organ the
food becomes softened, as the result of impregnation with liquids warmed
to the temperature of the body.

The functional importance of the rumen is not equally marked at
all periods of life. This is especially seen in suckling animals, such as
calves, in whom the rumen is capable of containing one thousand one
hundred and seventy-fiv£ grammes, the reticulum one hundred, the
manyplies one hundred and sixty, while the cubic capacity of the
abomasurn may amount to three thousand five hundred grammes (Colin).
Hence, digestion in the suckling ruminant is accomplished almost solely
by the fourth stomach, and the rumen does not acquire its great pro-
portionate size seen in the adult ruminant until the animal commences to
live on a solid vegetable diet.

Although the reticulum may be regarded as an appendage to the
rumen, with which it communicates by a large opening, it also has a
special function to fulfill, which appears to be uniform in all ruminants.
It constantly contains fluid, since its base is on a much lower level than
the openings into the first and third stomachs. Fluid can, therefore,
only leave this compartment as a result of its own vigorous contractions,
such as precede the insertion of the cud into the oesophagus for rumi-
nation.

The function of the oesophageal canal is to assist in the transfer of

GASTRIC DIGESTION. 377

the contents of the reticulum into tlie manyplies. The entrance of the
contents of the ruinen through the contraction of its walls into the
reticulum leads to a contraction of the muscular walls of this compart-
ment, and the materials contained in it are thrown up against the edges
of the oesophageal gutter. Through this contact the cesophageal pillars
shorten so as to draw up the opening into the manyplies nearer to the
reticulum, at the same time turning spirally on their own axes, the left-
hand pillar being extended downward and to the right. The contents
of the reticulum thus find a means of ready entrance into the manyplies,
large particles being strained off by the papillae at the orifice of the
manyplies, and falling back into the reticulum.

Although the reticulum receives all the matter swallowed, its small
size prevents it from retaining more than a small portion, the remainder
being forced into the rumen and manyplies, the fluid and finely divided
solids alone entering into the latter on account of the small size of the
communicating orifice. Its function, therefore, is to assist in rumination,
particularly by supplying the fluids which ascend the oesophagus, and by
its contraction aiding in the ascent of the cud and in keeping up the
circulation between the contents of the first and second stomachs. It
also has no secretion proper, and the fluids found in it have the same
source and same functions as those found in the rumen.

If one could judge of the importance of an organ b}^ its complexity,
the functions of the psalter would play an especially important role in
the gastric digestion of the ruminant. In this compartment of the
stomach the openings are always narrow, are always close together, and
are both on the uppermost portion of this organ, while the free borders
of its folds are directed downward ; consequently, the manyplies, by
means of its folds and the narrowness of its openings, the one into the
fourth stomach being closed by a powerful muscle and numerous large
papillae, like a sieve, strains off solids and detays the passage of aliments
into the true stomach. The muscular fibres which run in the larger
folds are inserted into the borders of the orifice between the manyplies
and reticulum. When, therefore, the sphincter-muscle of this opening
contracts, after the entrance of the contents of the reticulum, the folds
are simultaneously drawn up, and the food is thus forced up to the base
of these partitions. At the same time, through the contraction of its
walls, the posterior extremity is drawn forward so that the prolongation
of the cesophageal canal becomes almost perpendicular to the opening of
the third into the fourth stomach. By this process not only the fluid in
the cesophageal canal, but a portion of the food previously in the many-
plies may enter the rennet. The contraction of these folds does not take
place only during rumination, but also during its intervals ; the water in
the contents of this compartment is then pressed out, and the residue

378 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

found in this stomach after death is alwa}~s dry. The mucous membrane
is, however, entirely incapable of absorption, and the dryness of its
contents cannot, therefore, be explained as due to the entrance of the
fluid from its contents into the blood. The psalter likewise furnishes no
secretion of its own, and the changes which occur in its contents are due
simply to the influence of the saliva and the fermentative process which
occurs in the two preceding stomachs. Its reaction is, however, often
acid, evidently due to the regurgitation of the fluids from the fourth
stomach. It is worthy of note that in the llama, the camel, and, to a
less extent, in the sheep the folds of the membrane in the third stomach
are but slightly developed, and there is no constriction between the third
and fourth stomachs, while the opening into the reticulum is particularly
narrow. This may possibly serve to prevent too great dryness of the
contents of this compartment in these animals, which are so frequently
deprived of water. Where obstruction of the stomach occurs, it is
nearly always to be found in this compartment.

The action of the first three stomachs is merely preparatory to
digestion. It is only in the fourth stomach that true digestion takes
place. Its secreting membrane is four or five times as extensive as that
of the right half of the stomach of the horse, and is relatively less in the
llama and dromedary than in other ruminants. The gastric secreting
membrane is, apparently, in all respects similar to what has already been
described in other animals, although the amount of pepsin and acid in
the gastric juice of ruminants is less than that found in this secretion of
carnivora. Pauli states that extracts made from the glandular portion
of the fuiidus of the fourth stomach of the ox possess a much greater
digestive power than similar extracts made from the pylori c portion ;
in other words, the amount of acid added being the same in both cases,
that the glands of the pylorus are poor in pepsin, the glands of the fund us
rich in pepsin ; and that the small amount of pepsin in the pyloric por-
tion is almost incapable of extraction with gtycerin, but is removed by
hydrochloric, acid and by common salt solutions. Pauli would infer
from these statements that, the histological structure of the ruminant's
stomach being similar to that of other mammals, the so-called chief cells
are not the peptic cells, but perhaps are .concerned in the elaboration of
other ferments, while the associate cells are the true peptic cells. We
have alreacty in another place discussed the grounds for attributing the
acid of the gastric juice to the action of the associate cells.

Since the aliments enter the stomach but slowly and graduall}r, and
some already in a fluid state, digestion in the stomach occurs under the
most favorable circumstances, and is rapidly completed. The pylorus is
narrow and guarded by a powerful sphincter, thus resembling that of
carnivora in contradistinction of what has been noticed in the horse, and

GASTKIC DIGESTION. 379

serves to keep back the aliments that are not thoroughly digested. In
other respects, gastric digestion in ruminants is similar to that seen in
other animals. In other words, albuminoids are converted into peptones;
gelatin is dissolved and converted into a diffusible gelatin peptone, and
milk is coagulated and its casein is converted into peptones. Adipose
tissue is dissolved and the oil liberated and partially split up into fatty
acids ; cane-sugar is slightly converted into inverted sugar through the
action of the acid ; starch which has escaped being converted into sugar
through the action of saliva in the rumen passes into the intestine to
be acted on by the intestinal secretions, for the degree of acidity of the
gastric juice is sufficient to interfere with the diastatic action of ptyalin.
Gastric digestion in ruminants is much more complicated than in other
animals, and comprises a series of operations which are carried on partly
simultaneously and partty alternately. The two first reservoirs are
concerned in rumination and in the maceration of food. The third
stomach has nothing to do with rumination, but acts as a strainer and
prevents substances passing into the fourth stomach until sufficiently
comminuted and softened to be subjected to the action of gastric juice,
while, finally, the fourth stomach is the true digestive organ, in which
the albuminous contents of the food are converted into peptone. It is
thus seen that gastric digestion in the ruminant is much more complete
than in other herbivora. Therefore, gastric digestion in these animals is
predominant, while intestinal digestion is simplified.

8. GASTRIC DIGESTION IN BIRDS. — Gastric digestion in birds differs
very essentially from that of mammals, the difference being dependent
on the difference of plan on which the alimentary tract is constructed.
The digestive parts are simplest in birds of pre}7, such as the owl, the
buzzard, and hawk. The oesophagus is large and dilatable, and is, as a
rule, not supplied with a crop. It is continuous, without any marked
line of demarcation, with the small longitudinal stomach, which takes on
a transverse curve where it ends in the small intestine. Where the
oesophagus terminates it has a calibre almost as great as the stomach,
so that the latter seems simply to be a prolongation of the O3sophagus.
The superior limit of the stomach is marked by a band of large glands,
which may often be seen from the outside of this organ, and which
almost seem to resemble the agminated glands of the small intestine of
the mammal. Below this the stomach contracts, and again dilates to a
more or less globular pouch, and again becomes contracted and united
writh the small intestine. The pyloric orifice in birds of prey is very
narrow.

In gallinaceous birds, such as the cock, the turkey, and the pheasant,
the gullet dilates at the lower portion of the neck (the crop) and then
contracts, to again expand .and form the ventriculus, which has thick,

380

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

glandular walls; then comes the gizzard, composed of two thick, red,
striped muscles, covered internally witli a thick, horny epithelium.
The gastric parts of this class of birds are therefore divided into three
sections — first, the crop, to act as a reservoir, in which the food is macer-
ated ; from this it is pushed gradually into the second, the stomach, in

which it undergoes gastric
digestion simultaneously
with the process of tritura-
tion which occurs in the giz-
zard, or the third digestive
compartment (Fig. 154).
Grains, etc., which form the
food of gallinaceous birds,
first go into the crop, which
they distend, and in which
they accumulate in consid-
erable quantity. Here the
food becomes softened and
takes on an acid reaction.
A comparatively profuse se-
cretion is poured out in this
pouch, whose properties
have not been thoroughly
investigated. By inserting
substances into the crop,
Spallanzani obtained one
ounce of fluid in twelve
hours from the crop of a
pigeon, and seven ounces of
the fluid from a guinea-hen ;
but although this fluid is
thus poured out in consid-
erable amount, it does not
appear to be very active in
softening the food. It is
not known that this secre-
tion has any digestive prop-
erties, although it seems
probable that starch would
here be converted into sugar, since grain remains in this compartment for
twelve or thirteen hours, or even much longer. After leaving the crop,
the food then passes into the ventriculus and gizzard. The ventriculus is
supplied with a large number of tubular glands, which secrete an acid fluid.

FIG. 154* — CROP AND STOMACH OF THE PIGEON.

( Bernard. )

M M, crop ; I, oesophagus : C, proventriculus : S, tubular glands of
stomach ; J, gizzard ; D, duodenum.

GASTKIC DIGESTION. 381

When, however, the food comes in contact with this secretion, it has not
yet been crushed or comminuted ; consequently it is incapable of being
acted on by the gastric juice, which is powerless to digest cellulose mem-
branes. The contact of the food with the walls of the ventriculus leads
to the pouring out of a profuse acid secretion. Bathed with this fluid,
the food then enters the gizzard, where it is reduced by crushing to a
homogeneous pulp. The gizzard has thick, muscular walls, with a hard,
hornj' epithelium lining it, and is capable of exerting very great force.
Thus, it has been stated that iron tubes capable of supporting a weight
of five hundred and thirty -five pounds were completely flattened out
after passing through the gizzard of a turkey. This crushing is indis-
pensable for the digestion of grains, and is aided by the presence of
gravel, etc., almost always to be found in this organ.

In carnivorous birds gastric digestion is simpler than in the her-
bivora. Such birds swallow their prey entire, if small enough to enter
the beak and O3sophagus ; if not, it is torn with the beak small enough
to be swallowed, and then the skin, hair, feathers, and all are carried to
the stomach with the flesh. As there is no crop in such birds, and the
ventriculus is but faintly distinguished from the gizzard, which is com-
paratively small, and whose walls have become thin and almost mem-
branous, we have, therefore, a simple process of gastric solution, since
the gizzard has lost its crushing power. The solvent power of the stom-
ach of carnivorous birds is very rapid and powerful, muscles, tendons,
and cartilages being rapidly dissolved. After about eighteen or twent}^-
four hours, bones and matters which have escaped digestion, or which
are insufficiently dissolved to pass into the intestine, are regurgitated
through the mouth, since the very narrow pylorus present in carnivorous
birds, as in carnivorous mammals, prevents the passage of everything
except fluids.

There exists, again, a t}*pe of birds, midway between the purely
omnivorous and the granivorous, where the gizzard has but moderate
thickness and power. These birds also vomit indigestible substances.

Birds have, in general, a very active digestion. Some may make as
many as twelve meals a day, in which they fill not only the stomach, but
also the gullet, pharynx, and beak, especially when feeding on soft sub-
stances like larvae or worms. Their appetite seems to return as soon as
there is the least place which can hold more food. The diet of birds
cannot be changed. The birds of prey, without gizzard or crop, cannot
feed on grains, although the gallinaceous birds maybe brought to accom-
modate themselves to an animal diet.

Colin states that morsels of meat fed to sparrows appear in the giz-
zard in less than an hour, and reach the intestine within an hour and a
half; while debris of food may be found in the faeces in four or five hours.

382 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

IX. DIGESTION IN THE SMALL INTESTINE.

As the aliments pass into the duodenum, after being subjected to
the action of gastric digestion, they immediately mingle with the three
other digestive secretions, — the bile, the pancreatic juice, and the intes-
tinal secretion.

I. BILE. — The bile is the secretion of the liver, and, strictly speak-
ing, occurs only in vertebrates. In the lowest invertebrate animals a
fluid somewhat analogous to the bile is poured directly into the intes-
tine, as the result of the secretion of cells attached to the intestinal
mucous membrane. In others it is formed by a series of convoluted
tubes surrounding the intestine, or, it may be, directly surrounding the
stomach. But although this fluid may be yellowish or brown, it is not
to be regarded as bile, since in invertebrates it never contains the specific
bile constituents, bile coloring-matters and acids, and the glands which
form it differ histologically from the liver. In all the invertebrates the
so-called bile is directly poured into the intestine ; in many vertebrates,
however, the excretory duct is in communication by a side branch
directed obliquely backward from the course of the duct with a reser-
voir for the bile, termed the gall-bladder. This reservoir is present in
all omnivora and carnivora, and in most herbivora, birds, and reptiles.
It is absent in certain of the group of herbivora. It is absent in the
solipedeSjthe horse, mule, and ass, and among the ruminants in the stag,
camel, and dromedary ; among the pachydermata, in the elephant, the
rhinoceros, and tapir ; in the wild boar, and in certain cetaceans ; while
in birds it is absent in the pigeon, cuckoo, paraquet, and ostrich. It is
also absent in the mouse and marmot. In the horse and elephant the
gall-duct is dilated to form a sort of pouch. The ultimate gall-ducts
all unite to form a single trunk, or ductus communis choledochus, which
in many animals, such as sheep and goats, communicates with the excre-
tory duct of the pancreas and pierces the wall of the duodenum obliquely
from below upward. As the result of this, an increase of pressure on
the intestinal contents simply closes the orifice of the duct, and regurgi-
tation of intestinal contents into the duct is impossible.

In the gall-bladder the bile becomes concentrated, and mucin is
added to it as a result of the action of the secretion of the mucous
membrane of the gall-bladder. Little or no mucin is found in bile com-
ing directly from the hepatic cells. The gall-bladder is necessary in
animals whose digestion, as in the carnivora, is intermittent. It is less
important for the herbivora, where digestion is nearly constant. The
liver differs from all other organs in its blood-supply. In proportion
to its size, it receives but a small supply of arterial blood, and although
an immense amount of blood passes through it, the greater part reaches

DIGESTION IN THE SMALL INTESTINE. 383

the liver through the portal vein, indicating the functional relation of
the liver to the process of intestinal digestion.

1. The chemical characteristics of the bile have been mostly studied
in the fluids found in the gall-bladder of the ox and in that obtained
from fistulae in dogs. In the fresh state, bile is a clear, thin, or more or
less tenacious liquid, which, with the exception of epithelial cells from
the gall-bladder, contains no morphological elements. It has. a neutral
or alkaline reaction. When fresh, in man and carnivora, it is of a golden
3Tellow or greenish-brown color ; it is green in herbivora (brownish-green
in the horse and ox, greenish-yellow in the hog, and dark green in
sheep). After standing exposed to the air, the brownish-yellow bile
becomes dark brown, and the greenish bile more intensified to a dark
green. Bile has a peculiar bitter taste, and when warmed a musk-like
odor. The specific gravity varies in different animals from 1008 to 1030,
the highest being found in bile taken from the gall-bladder of man.
Ox-bile is often yellowish-brown, though usually green in color, and
may be either clear or turbid ; it is alkaline, viscid, and contains a
large amount of mucin ; its specific gravity varies from 1022 to 1025.
Sheep's bile is usually green, is odorless, clear, alkaline, and, although it
contains mucin, is not viscid; specific gravity, 1025 to 1031. Calves'
bile is green or yellowish-brown, though sometimes golden yellow in thin
la}*ers ; it is clear, odorless, viscid, neutral in reaction, and contains but
little mucin; specific gravitj7, 1020 to 1027. Pig's bile is clear or dark
yellowish-brown or golden yellow (the latter when diluted), is odorless,
alkaline, contains large amounts of mucin, and is therefore very viscid ;
specific gravity, 1020 to 1027. Dog's bile is usually yellowish-brown,
and when diluted golden yellow ; it may be either neutral or alkaline,
contains mucin, and is clear and odorless; specific gravity, 1025. The
bile of all animals may be kept for several days, even at a high tempera-
ture, before putrefaction sets in. In the fresh secretion from the liver,
the solids in the bile of the cat, dog, and sheep amount to 5 per cent., in
the rabbit 2 per cent., and in the sheep 1-J- per cent. In the gall-bladder
in cats, dogs, and rabbits the solids rise from 2 to 20 per cent., in the
sheep to 8 per cent., in man from 9 to 17 per cent., and in the ox from
7 to 11 per cent.: the solids in the bile of man, the pig, and the ox consist
of only 1.5 per cent, of inorganic matter, and in the dog only 3.6 per cent.

Doer.

In 100 parts Bile. Man. Ox. Pig. , « ,

Fresh. From Bladder.
Water, . 86.3 90.4 88.8 95.3 85.2

Solids,

Bile salts,

Lecithin, cholesterin

Fats, soaps,

Mucin and coloring matter,

.Inorganic salts,

13.7 9.6 11.2 4.7 14.8

7.4) 7.3 3.4 12.6

> 8.0

3.0) 2.2 0.5 1.3

2.2 0.3 0.6 0.2 0.3

1.1 1.3 1.1 0.6 0.6

384 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

While the bile is entirely free from proteicls, it contains both organic
and inorganic constituents. The former group are represented by mucin,
a compound of sodium with two organic acids (glycocholic and tauro-
cholic), a coloring matter which undergoes various modifications and
whose origin is a source of considerable interest, lecithin, small quanti-
ties of fat and soap, and a small amount of diastatic ferment. These will
be considered in turn.

(a) Mucin. — Mucin gives to bile its viscidity, and is the product of
the mucous glands of the larger bile-ducts and gall-bladder. The longer
the bile remains in the gall-bladder, the larger will be the percentage of
mucin found in it, since the mucous cells in the walls of this reservoir
are the principal sources of this bod}7. In the bile of animals supplied
with a gall-bladder, mucin will be found in larger amounts than in ani-
mals in whom this appendage to the liver, as in the case of the horse, is
absent. The smaller bile-ducts are free from mucous cells, and, as a con-
sequence, bile coming directly from the liver-cells contains no mucin.
The longer the gall remains in the gall-bladder, the more will it deviate
from its general character when freshly secreted by the liver-cells. Yel-
low bile gradually becomes greenish, and its consistence will become
more marked from the addition of mucus. The general characteristics
of mucin found in the bile do not differ from those of mucin found else-
where. It may be precipitated by acetic acfd, and when bile containing
mucus is precipitated with alcohol it loses its viscidity.

(b) The Bile Acids. — The bile acids occur in the bile in the form of
compounds with sodium, and occasionally with minute amounts of potas-
sium, to form glycochplate and taurocholate of sodium, — two salts which
are highly soluble in water. The relative proportions of these two salts
vary considerably in the ,bile of many animals. In that of man, as well
as of birds, many mammals and amphibia, taurocholic acid is most
abundant. In other mammals, as in the pig and ox, sodium gtycocko-
late is in largest amount, while the taurocholate is more scanty. In the
bile of the dog, cat, bear, and other carnivora, taurocholate is almost the
sole representative of these salts, while the glycocholate is almost entirely
absent. In the bile of the pig, in addition to these two salts, the hyocho-
late of sodium is also present.

The gall of the hog contains, besides hyoglycocholic acid, another until
lately unknown acid, which occurs in larger quantity than the first known acid
(Jolin). It is, for the present, called B-hyoglycocholic acid. It is with difficulty
obtained pure, as neither it nor its salts are crystallizable. It is distinguished
from the A-acid by its behavior with saturated sodium sulphate solution, which
precipitates the sodium salt of the A-acid almost completely, and in a flocculent
Ibrin, whereas the sodium salt of the B-acid is only partly precipitated, and is
at first colored, and easily soluble in water. The purified salt is separated
from the alcoholic solution by means of ether, as a snowy-white, cheesy precipi-
tate, which soon shrinks to a yellowish mass, whereby much ether is pressed out.
This mass is easily soluble in water and alcohol, and the solutions allow them-

" DIGESTION IN THE SMALL INTESTINE. 385

selves to be concentrated to a syrupy consistency. The aqueous solution gives
a precipitate with barium chloride, which at first dissolves again, but with more
barium solution a lumpy barium salt separates, which soon changes to a tough,
shiny, silky mass. The salts of this acid have a very bitter taste, which is not,
however, as intense as that of the A-acid salts. The composition of the acid could
not, as yet, be determined. Analysis proved that the percentage of carbon is
much less in the B-acid than in the A-acid, .whereas the percentage of nitrogen is
about equal in both. By continued treatment with alcohol, the B-acid yields
cholalic acid. In how far this acid corresponds to the one obtained in a similar
manner from the A-acid has not yet been determined.

Various methods have been proposed for the separation of these salts from
the bile, of which only the following will be given. The bile from the gall-blad-
der of an ox should be evaporated to one-fourth its volume over a water bath,
rubbed up to a thick paste with animal charcoal, and completely dried at 100° C.
The hot mass should then be thrown into absolute alcohol, well shaken repeat-
edly, allowed to stand for two or three hours, and then filtered. A part of the
alcohol may be removed from the filtrate by distillation, and the bile salts may
then be precipitated, in the form of a resinous syrup, by the addition of a large
excess of ether. After standing a variable time, from one or two days to a week
or more, the time depending upon the anhydrous character of the alcohol and
ether, the so-called Platner's crystallized bile separates in a mass of glistening
needles. This crystallized bile consists of a mixture of taurocholate and glyco-
cholate of sodium.

These salts are insoluble in ether and readily soluble in alcohol and
water. Their aqueous solutions have a decided alkaline reaction, and
rotate the plane of polarized light to the right. Both these salts are
highly deliquescent, and when exposed to the atmosphere the crystals
absorb the mixture and break down into a thick, tenacious S3*rup.

To separate the two individual bile acids from each other, this mixture of
crystallized bile may be dissolved in a small volume of water, a little ether added,
and then dilute sulphuric acid. After stirring well, glycocholic acid crystallizes
in shining needles, the taurocholic acid remaining in solution. The crj'stals may
be collected on a filter, washed with water, dissolved in dilute spirits, and pre-
cipitated with excess of ether. "Or to the solution of Platner's crystals add
neutral and then a little basic lead acetate, when glycocholate of lead will be
thrown down. Collect on a filter, wash, and dissolve in hot alcohol, and remove
the lead by passing a current of sulphuretted hydrogen ; filter, and by the careful
addition of water to the alcoholic filtrate, crystals will be deposited. To the
previous filtrate from the glycocholate of lead add acetate of lead and ammonia ;
glycocholate and taurocholate of lead will be precipitated, and may be washed
and decomposed, as with the glycocholate." In the bile of oxen from certain
districts, glycocholic acid rapidly crystallizes on the addition of fivec.c. of hydro-
chloric acid and thirty c.c. of ether to each five hundred c.c. of bile. In other
.specimens this process entirely fails. No satisfactory explanation of this peculi-
arity has ever been given, though Hoppe-Seyler suggests that the acid removes
the base from the glycocholate, and the liberated glycocholate acid, being insoluble
in water, is precipitated. If this were the explanation, the process should invari-
ably succeed ; such is not, however, the fact.

The test for these two acids is known as Pettenkofer's reaction for biliary
acids. If a little cane-sugar in strong solution is added to a small quantity of bile
in a test-tube, gently warmed to about 60° C , and then an equal volume of strong
sulphuric acid allowed to flow down the side of the tube, a bright-purple color
forms above the level of the acid. This test may be even better shown by pre-
paring the bile as before (solution of Platner s crystals), warming gently, with a
cane-sugar syrup, then shaking well until a layer of foam forms on the upper
surface. If a small amount of sulphuric acid is poured down the inside of the
tube, the froth on the surface of the bile becomes bright purple in color ; or bile
may be diluted with cane-sugar solution, and a piece of filter-paper dipped into it

25

386 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and allowed to dry. Dropping a little sulphuric acid on the paper thus prepared
will in a few seconds produce a violet-red color. Proteids will also behave in the
same way as Plainer' s crystallized bile, but the reactions may be distinguished by
the fact that, when examined spectroscopically, two absorption bands, one near the
line E and the other opposite F, will be found when the bile is examined, and will
be absent from the color produced by this test with albuminoids. Amylic alcohol
will also produce a similar reaction, and here again the spectroscope will serve to
distinguish them. This test depends upon the fact that cholic acid is first pre-
cipitated by sulphuric acid in a whitish form, as may be readily seen in solutions
of crystallized bile, and then dissolved, assuming a cherry-red color, which
becomes gradually darker in hue. The pigments and, to a still more marked
degree, the presence of nitrates or chlorates will interfere with this reaction.

The source of the biliary acids is almost unknown, except that they
probably originate from the breaking down of albuminoids. They are
not found in the blood, but are formed in the hepatic cells, the nitrogen
possibly originating from the albuminoid, while the cholic acid radical
may be derived from the fats. These acids are compounds of taurin and
gtycochol with cholic acid, into which they may readily be split up by
prolonged boiling with alkalies or mineral acids.

Glycocholic Acid (C26H48N06). — Glycocholic acid occurs in large
amounts in the bile of herbivora, while it is only found in small quantities
in the bile of carnivora and omnivora. It originates from the union of
gtycochol with cholic acid, and, like taurocholic acid, is closely allied to
hippuric acid. When boiled with hydrochloric acid it is decomposed
into glycochol and cholic acid, the latter being a non-nitrogenous body.
The reaction is as follows : —

C26H43N06 + H20:=C24H4005+C2H5N02.
Glycocholic Acid. Water. Cholic Acid. Glycochol.

Glycocholic acid crystallizes in glistening, white needles, which are
nlmost insoluble in cold water, slightly soluble in hot water, easily
soluble in alcohol, and slightly soluble in ether.

Taurocholic Acid (C26H46"N '07S). — Taurocholic acid is the only acid
in dog's bile, as in that of other carnivora, though it can be obtained in
small amounts from ox-gall after the removal of glycocholic acid. It
contains sulphur, and forms white, glistening needles, which become
fluid when in contact with the air. Taurocholic acid is soluble in water
and alcohol and insoluble in ether. Of these acids only the alkaline
salts are soluble in alcohol and water. Out of a mixture of glycocholic
and taurocholic acid salts, acetate of lead will precipitate the glycocholic
acid as a glycocholate of lead. When filtered off, the addition of acetate
of lead and ammonia will precipitate taurocholic acid as a taurocholate
of lead, which may be easily dissolved in hot alcohol, and the lead
removed by passing a current of sulphuretted hydrogen through it.

Taurocholic acid originates in the breaking down of albuminoids,
from which the sulphur is derived, and its amount in the bile may be

DIGESTION IN THE SMALL INTESTINE. 387

increased by an increase in albuminoid diet, though not in the same
degree as occurs in the case of urea. It is rapidly decomposed into
taurin and cholic acid ; this decomposition also occurring in the
intestine.

Glycochol (C2H6y02), or glycin, is also formed by boiling gelatin with
dilute sulphuric acid. It is a crystallized body, slightly soluble in water,
insoluble in alcohol and ether. Its aqueous solutions have a faintly acid
reaction. It does not occur as such in the animal body, but, besides
being concerned in the origin of the bile acid, it is also found in the
urine, especially of the horse, united with benzoic acid in the form of
hippuric acid. It may be obtained from the glycocholic acid, as already
indicated, by boiling with strong hydrochloric acid.

Taurin (C2H,NS03) occurs in large, glistening columns as a product
of splitting of the bile acids. It is readily soluble in water, insoluble
in alcohol and ether. It is also found in the intestinal canal and in
the flesh of various fish and of the horse, and in the kidneys, spleen,
and lungs of various other animals. It is also found in putrid bile,
being then developed at the expense of the taurocholic acid in the
fermentation of the bile. It combines with various bases to form
salts. The bile acids may thus be regarded as compounds of glycochol
and taurin with cholic acid, whose chemical composition and general
properties are not certainty known. Cholic acid may be regarded, there-
fore, as the starting point of the biliary acids.

Cholic Acid (H^CwOs-f HaO). — Cholic acid is a constant product of
decomposition of biliary acids, nnd is therefore found in the intestinal
contents, occasionally in the urine of jaundice, but not in fresh bile or
elsewhere in the organism. Cholic acid occurs in an amorphous and in
a crystallized form; it is insoluble in water, soluble with difficulty in
ether, and moderately soluble in alcohol.

"It may be prepared by boiling bile with caustic potash for twelve to twenty-
four hours, then precipitating with hydrochloric acid, and, having washed the
deposit with water, dissolving it in caustic soda containing a little ether ; hydro-
chloric acid is next added, and after some time crystals form. The supernatant
fluid may be decanted, and the residue covered with ether ; drain off the ether in
a half-hour or so, and dissolve the deposit in boiling alcohol ; to this solution
add a little water until a permanent precipitate appears, and tetrahedric crystals
soon make their appearance."

(c) The Coloring Matters of the Bile. — The bile under different con-
ditions and in different animals contains a number of different coloring
matters, to which its different shades of color are due. The essential
coloring matter of fresh bile is bilirubin, to which the reddish-brown
color of the bile of man and the carnivora is due, and which appears
to be the starting point of the various coloring matters which are found
in the bile of different animals ; it also occasions the various -changes

388 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in tint which the bile undergoes after having been removed from the
bod}r. When bile remains for a considerable time in the gall-bladder,
and when bile is exposed to the air, provided the reaction remains alka-
line, the reddish-brown coloring matter, bilirubin, absorbs oxygen from
the atmosphere and acquires a greenish color ; it is then termed
biliverdin. In the bile of herbivora and most cold-blooded animals
this pigment exists naturally, and is present even before it passes into
the small intestine. Both these substances, bilirubin and biliverdin,
are insoluble in water, and their state of solution in the bile is to be
explained on the basis of their forming soluble combinations with alka-
lies, and partly to their being held in solution by the bile acids, in whose
solutions they are soluble. They are slightly soluble in ether and
alcohol, and readily soluble in chloroform and in alkalies. The test for
their detection is known as Gmelin's test, which is claimed to be suf-
ficiently sensitive to detect the presence of one part of bilirubin in eighty
thousand parts of solution.

The test is performed by adding nitric acid which contains some free nitrous
acid to bile. This causes a precipitate which disappears on the addition of fresli
acid, and results in the formation of a series of colors, passing through green,
blue, violet, red, and then yellow, and is due to the different degrees of oxidi-
zation of the red coloring matter of the bile. Various modifications have been
proposed for this test. Briicke recommends the addition of dilute nitric acid to
the suspected fluid, and then pouring a quantity of concentrated sulphuric acid
carefully down the side of the tube ; as it sinks to the bottom it liberates free
nitric acid, which produces' the characteristic play of colors ; or a concentric solu-
tion of nitrate of sodium may be added and then sulphuric acid. When only
traces of bile and coloring matters are present, the addition of the tincture of
iodine causes the appearance of a green color.

Bilirubin (C32H86N406). — Bilirubin, which is also called hsematoidin,
occurs as an amorphous, orange-yellow powder, which, by its precipi-
tation out of chloroform (obtained by boiling bile with chloroform),
may be crystallized in red prisms. This bile-pigment is more frequently
obtained from biliary calculi, especially those of the ox, which are con-
stituted almost entirely of this pigment and cholesterin.

The calculi should be powdered, exhausted with ether, and then with boil-
ing water containing a few drops of hydrochloric acid, which is added to separate
the bilirubin from the alkali with which it is supposed to be combined. The
residue is then to be washed in pure water, then dried, and then boiled with chlo-
roform and finally filtered. From the filtrate the chloroform may be distilled off",
the residue then extracted with alcohol, and ether and pure bilirubin will remain
behind. The amorphous, reddish powder which remains may be purified and
obtained in a crystallized form by re-solution in chloroform, which should be
allowed to evaporate spontaneously. In the preceding process the ether is em-
ployed to remove the fat and cholesterin, and water to remove the other soluble
biliary constituents.

Bilirubin is only slightly soluble in water, readily soluble in chloro-
form and benzole, and sparingly soluble in alcohol and ether. It seems
to play the part of an acid, and unites with alkalies to form combinations

DIGESTION IX THE SMALL INTESTINE. 389

which are insoluble in chloroform. Bilirubin is the most important
coloring matter, and from it originate the others. It is undoubtedly
formed in the liver-cells, though it is also formed in other localities.
Pathologically, it occurs in old blood-extravasations, where it was for-
merly described by Yirchow under the name of haematoidin crystals ;
physiologically, it is found in the corpora lutea, in the ovaries, and in
the borders of the placenta of the dog. Bilirubin evidently originates
in the haemoglobin of the red blood-corpuscles. All causes which pro-
duce breaking down of the red blood-cells and consequent jaundice,
such as poisoning by ether and chloroform, lead to the appearance of
bilirubin in the urine. This decomposition may also be produced by the
action of the alkalies of the bile acids, and it is therefore probable that
the physiological origin of the bile coloring-matter is due to the action
of the bile acids on the blood-corpuscles in the liver. When oxidizing
agents, such as nitrous-nitric acid, are added to a solution of bilirubin it
displays a succession of colors identical with that seen in the applica-
tion of Gmelin's test. Each of these stages represent a distinct pig-
mentary substance. The first which results, or the greenish color, is due
to the appearance of biliverdin.

Biliverdin (C32H36\408) occurs through the action of oxygen on
bilirubin, and is produced even when the solutions of the latter are
allowed to stand exposed to the air. This body is found in abundance
in the bile of cold-blooded animals, and is the principal pigment of the
bile of herbivora. Biliverdin may be prepared by making an alkaline
solution of bilirubin and exposing it to the air in a shallow vessel ; after
awhile the reddish solution becomes intensely green, and biliverdin may
be deposited as a green, amorphous powder by precipitation with hydro-
chloric acid, washing with water, dissolving in alcohol, and finally pre-
cipitating with water. Biliverdin then forms a green, amorphous powder,
which is insoluble in water, ether, and chloroform ; is soluble in alcohol,
acetic acid, and solutions of the alkaline carbonates. When subjected to
the action of nitrous-nitric acid this pigment also liberates a series of
different colors, which pass through the same sequence as those developed
by the addition of this acid to solutions of bilirubin, the only difference
consisting in the absence of the original red color. The first change is
from a green into a blue or violet color, and is due to the formation of
choletlin, which finally becomes yello wish-brown. Each of the coloring
matters of the bile has a distinctive absorption of the spectrum, which
is yielded when the solution is treated with nitric acid. The bile of
carnivora is usually free from absorption bands, unless an acid be
added, in which case the absorption bands characteristic of bilirubin
appear in the spectrum.

(d) Cholesterin (CjgH^O (H2O)) is also an important constituent

390 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of the bile, and forms the bulk of the so-called white gall-stones. Choles-
terin rotates the plane of polarized light to the left, and forms transparent,
rhombic plates, which usually have a small, oblong piece cut out of one
corner. Cholesterin is insoluble in alkalies, dilute acids and alcohol,
and cold water, and is soluble in hot alcohol, ether, glycerin, chloroform,
and soap solution and alcohol. In the bile it is kept in solution through
the union of bile salts. Cholesterin is widely distributed through the
body, occurring usually in the cerebro-spinal axis and nerves, and, in
fact, seems to originate from the breaking down of nerve-tissues. It is
likewise found in the yelk of eggs, in the spleen, and in various patho-
logical deposits in the animal body.

It may be prepared by powdering white gall-stones, boiling in water con-
taining caustic potash, filtering when cold, and washing the resulting mass with
boiling alcohol, and filtering while still hot. Cholesterin crystallizes out of the
alcohol when cold. It may be purified by redissolving in boiling ether, and
adding half its vglume of alcohol, and allowing it to evaporate spontaneously.
Cholesterin crystals give a violet color with 80 per cent, sulphuric acid (Mole-
schott).

When treated with nitric acid, dried, and touched with a drop of ammonia,
a deep-red color is produced, which is not altered by the addition of caustic soda.
(Schiff).

When dissolved in chloroform and agitated with an equal volume of strong
sulphuric acid, a blood-red solution is obtained, which becomes gradually violet,
blue, green, and then yellow, and then disappears if a trace of water is present.
The layer of sulphuric acid in this test shows green fluorescence. If crystals of
Cholesterin are heated with tolerably strong sulphuric acid, and afterward with
a little iodine, a play of colors is produced, passing from violet through blue,
green, red, and yellow to brown.

Among the other organic constituents of the bile, lecithin, which
belongs to the group of the complex nitrogenous fats, is to be men-
tioned. Its formula is C^H^NPOg. It occurs widely distributed through-
out the bod\', occurring especially in the brain, nerves, yelk of eggs,
semen, and pus. When pure, it is a colorless, partially crystalline body,
soluble in cold and hot alcohol, less so in ether, and soluble in chloro-
form, carbon disulphide, and fats.

It is not yet clearly established as to whether the lecithin found in
the bile and other secretions and tissues is derived from the breaking-
down of food-stuffs in pancreatic digestion, or whether it is found S3*n-
theticalty. The reabsorption of lecithin, however, is complete, since no
trace of lecithin or glycerin-phosphoric acid is to be found in the faeces.

(e) The Inorganic Constituents of the Bile. — Of the inorganic con-
stituents of the bile, iron is of special importance, as indicating the red
blood-corpuscles as the source of bilirubin, from which- process of decom-
position the iron also undoubtedly originates. No close relation, how-
ever, between its quantity and that of the bile coloring-matters has been
ever distinctty made out. The following table, after Hoppe-Seyler, indi-
cates the quantitative composition of the solids found in bile of the dog

DIGESTION IN THE SMALL INTESTINE. 391

drawn from the bile-duct, and after having remained some time in the
gall-bladder : —

From

Freshly

Bladder.

Secreted.

Mucin, . . .'.'"'• • .

0.454

0.053

Taurocholic alkali, . ' . . ...

11.959

3.460

0449

0.074

Lecithin, *.

2.692

0.118

Fats, . . . . . . .

3.841

0.335

Soaps, .•-

3.155

0.127

Organic bodies insoluble in alcohol,

0.973

0.442

Inorganic bodies insoluble in alcohol,

0.199

0.408

K2S04,

0.004

0.022

Na2SO4,

0.050

0.046

NaCl,

0.015

0.185

Na2Co3

0.005

0.056

Cas2(P04),
FeP04,

0.080
0.017

0.039
0.021

CaCO,

0019

0.030

MgO,

0.009

0.009

2. The Secretion of the Bile. — In contradistinction to the saliva and
gastric juice, the secretion of bile appears to be continuous: even during
prolonged abstinence, though reduced in amount, it is not suppressed.
Food exercises a marked influence on the quantity and composition of
the bile, every meal producing a maximum increase in the amount of
secretion which is reached between three and five hours after the com-
pletion of the meal. It then returns gradually to its original quantity,
to be again subjected to a second increase, which occurs between thir-
teen and fifteen hours afterward. This increased flow of bile, it will be
noticed, co-exists with the discharge of the contents of the stomach into
the small intestine, and it would appear, as has been determined experi-
mentally, that the application of the acid to the intestinal surfaces causes
a discharge of bile by causing reflex contraction of the bile-ducts and
gall-bladder.

Since in the herbivora eating and digestion are almost continuous,
the amount of bile secreted is much larger than in the case of the
omnivora and carnivora. The total amount has been estimated to be
about five hundred to six hundred cubic centimeters in twenty-four hours,
or fifteen grammes of bile with half of one per cent, of solids per kilo of
body weight. In the horse the amount excreted in twenty -four hours is
about five to six kilos. In dogs, the secretion is most active after a meal
of meat, a diet of fat, however, greatly reducing the amount of this secre-
tion. According to Bidder and Schmidt, for every kilo of body weight
each hour the

Sheep secretes . ' . . . 1.059 grammes of bile.

The dog " . » . . 0.824

The cat " ." . . . 0.608

The rabbit " . . 5.702

392 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Colin fixes the following amounts as the hourly secretion in the
domestic animals : —

In the ox, 100 to 120 grammes.

In the pig, 75 to 160

In the sheep, . . . . . 10 to 160

In the clog, . . . . . . 8 to 15

In the horse, . . . . . 250 to 300

It would seem, therefore, that the smaller the animal the greater the
relative amount of bile secreted in proportion to the body weight. Thus,
a guinea-pig weighing one kilo, and whose liver only weighed forty
grammes, secreted in twenty-four hours one hundred and seventy-five
grammes of bile, or more than four times the weight of the liver ; and as
the bile of the guinea-pig contains 1 per cent, of solids, one kilo of liver-
substance would, in twenty-four hours, form four kilos of bile with fifty
grammes of solids. Since the liver only contains 25 per cent, of solids,
it follows that in twenty-four hours one-fifth of all the solids in the liver
must be eliminated in the bile. According to Colin, the liver forms, in
twenty-four hours, in the horse six kilos, in the ox 2.64 kilos, and in the
sheep 0.34 kilos.

In contradistinction to the saliva, the bile is secreted under very
low pressure. Ever}7 slight obstruction to the flow through the duct
leads to reabsorption of the secretion by the hepatic lymphatic ves-
sels and consequent jaundice, thus showing the close connection
between the bile-ducts and lymphatics. This is also shown by the fact
that microscopic injections of the bile-ducts made after death, under
very low pressureT often pass into the lymphatics of the liver. While
the pressure under which the bile is secreted is comparatively low, as
compared with that of the saliva or that of the arterial pressure, it has
been stated by Heidenhain that the pressure under which the bile is
secreted is more than double that of the blood in the portal vein. In
the liver, therefore, as in the salivary glands, there can be no question as
to the formation of this secretion by a mere process of filtration ; it
can only take place as the result of special cell activity, the specific coiv
stituents of the bile, the bile acids and the coloring matter, being found
normally neither in the blood nor in any other tissue or organ, the cases
in which the}^ or their derivatives are found elsewhere than in the bile
being capable of clear proof that they have only reached those localities
through the bile. Even after extirpation of the liver, no accumula-
tion of bile coloring-matter can be detected in the economy. The specific
constituents of the bile must, therefore, be formed in the liver-cells, and,
as already indicated, there is considerable proof that the coloring matter
originates from the breaking down of the red blood-cells, the process of
destruction being probably due to the action of the bile acids, hsemo-

DIGESTION IN THE SMALL INTESTINE. ; 393

globin being thus liberated and then decomposed into bilirubin,the iron
escaping in the form of a phosphate in the bile. As regards the origin
of bile acids little is known, though they are probably derived from the
breaking down of albuminoids.

The action of the nervous sj'stem in modifying the secretion of the
bile is almost entirely unknown. No nerve has been found whose stim-
ulation leads to an increased flow of bile, or causes its arrest when
actively flowing. The splanchnic nerve has been noticed, when stimu-
lated, to cause an increase in the flow of bile from biliary fistulas, but this
action is evidently due to the production of contraction of the biliary
ducts.

3. The Physiological Action of the Bile. — The bile enters the intes-
tine, in most animals, associated with the pancreatic juice, as seen in the
horse, goat, and dromedary, while in the ox and Babbit the bile-duct is
separated fora considerable distance from the opening of the pancreatic
duct. The fact that it enters the intestine simultaneously writh the pan-
creatic juice, or even before it, shows that in its physiological action it
must be associated with the latter. Its action on the food-stuffs is of
but slight importance. On protejds it produces no distinct action what-
ever, and, in fact, would seem to interfere with the digestion of proteids
as commenced in the stomach. Thus, when bile, or a solution of tauro^
cholic acid, is added to the products of gastric digestion, a copious
precipitate takes place, which consists of coagulable albumen, syntonin,
and pepsin, — the latter being indicated by the fact that when this precip-
itate is filtered off and the supernatant liquid acidified it has no peptic
power. This precipitate is, however, redissolved in an excess of bile
or a solution of bile salts, and its object would appear to be, by precipi-
tating the parapeptone to delay its passage through the intestine and so
give the pancreatic juice time to act, while, at the same time, by precipi-
tating the pepsin the pancreatic ferments are protected from the solvent
action of the gastric juice. For we find that during active digestion,
as a rule, the contents of the small intestine are strongly acid in the
greater portion of its upper extremity, and were the pepsin not precipi-
tated the pancreatic ferments would be digested and therefore destroj^ed
through the action of the gastric juice. The re-solution of the precipi-
tate produced by bile in the products of gastric digestion is due to an,
excess of taurocholic acid. In most animals (ox, sheep, and horse), the
bile has been found to contain a ferment, present in small amount, which
is capable of converting starch into sugar. A similar action is also pro-
duced on glycogen. This action is, however, secondary, and of but little
importance in the digestion of carbohydrates, other than that the bile
assists the amjdolytic action of the pancreas. In the d'og's and pig's
bile no diastatic ferment is present.

394 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The principal function of the bile in digestion is the aid which
it renders to the digestion and absorption of fats. Bile has a solvent
action on fats in small quantities, and assists in the eraulsification of fats.
We shall iind that the pancreatic juice, in its action on fats, liberates
fatty acids. A similar action is also manifested, although to a very much
less extent, by the bile of the horse, ox, and sheep ; it is absent in that
of the hog and dog. These fatty acids, thus liberated, unite with the
alkalies of the bile and pancreatic juice and form soaps, and so greatly
assist in the formation of a permanent emulsion. By means of the
emulsion thus formed the absorption of fat is greatly assisted; while, in
addition, it has been found that when membranes are moistened with
bile, or with solutions of bile salts, the passage of fats through such
membranes is greatly facilitated. Thus, if two filters are moistened, the
one with a solution of bile salts and the other with water, oil will pass
with comparative readiness through the former, while it scarcely suc-
ceeds at all in passing through the filter moistened with water. Oil-
drops placed on the surface of bile spread into a thin layer, like solutions
of corrosive sublimate on mercury, and in tubes moistened with bile
the oil will rise above its level outside of the tube, — facts which point
still further to the assistance which the bile renders in the absorption
of fats. The bile of most animals contains a lactic acid ferment. On
other food-stuffs bile is quite inert.

It is evident from the above that the uses of bile must be manifested
in some other direction than as a digestive fluid ; for while it would be
presumed from the fact that we have here the largest gland in the body,
pouring an immense volume of fluid into the digestive tract at a point at
which digestion has barely commenced, that that fluid must have some
important role to fulfill in digestion, the facts above mentioned, attained
through chemical examination, show that this assumption is not entirely
warranted. Still another method of examination, that of the production
of permanent biliary fistulae, also shows that the functions of the bile are
not solely manifested in assisting in digestion. In other words, the bile
is not only a digestive secretion, even though of secondary importance,
but is also an excretion. The most valuable data as to the functions
which the bile fulfills in the economy are obtained from the maintenance
of biliary fistulae.

Biliary fistulas may be either temporary or permanent. The former
are of special importance for the study of the secretion of bile as to the
influence of drugs and other agents on the amount of bile poured out.
Dogs are most suitable for such an operation, which may be performed
upon them without any difficulty.

The dog should have been allowed to fast for several hours before the
operation, as then the gall-bladder will be apt to be filled with bile. After

DIGESTION IN THE SMALL INTESTINE. 395

anaesthesia has been produced, an incision should be made in the linea alba about
an inch and a half long and about two inches below the xyphoid cartilage, tying
each bleeding-point before the abdomen is opened. On pushing aside or tearing
through the omentum with the forefinger of the right hand, and carrying the
finger well down below the liver, a dense band may be felt running from the
liver to the duodenum, and consisting of the hepatic vessels, nerve, and common
bile-duct. Hooking the forefinger under this band, and drawing it carefully and
slowly forward, a blunt hook may be passed under it with the free hand, and the
vessels drawn out of the wound. They can be prevented from retracting into the
abdominal cavity by pushing the hook through so that the vessels lie upon its
handle, which rests transversely over the wound. The duct is easily isolated and
ligated at its entrance to the duodenum to secure the small blood-vessels on its
surface, and the cannula inserted and tied in the duct. On removing the stilette
from the cannula, a few drops of bile immediately escape. Probably, however,
a similar method, and one less likely to wound the hepatic blood-vessels, is to
open the abdomen at the right margin of the right rectus muscle, and then follow
the duodenum, which appears in the wound, and may be recognized by its large
size and absence of mesentery, up toward the stomach, where the duct may be
readily isolated and divided at its insertion into the duodenum.

Permanent biliary fistulas may also be made quite readily in dogs, and have
been undertaken to decide the question as to the excrementitious nature of the
bile. For this purpose the gall-bladder is selected for the fistula instead of the
ductus choledochus. The abdomen is opened in the median line, or, preferably,
at the right border of the right rectus muscle, care being taken not to wound the
large vessels which cross the wound on the inner surface of the abdomen, and
the common bile-duct isolated as before. It is then ligated close to its entrance
into the intestine and at its junction with the cystic duct, and the intermediate
portion excised.

The gall-bladder is then drawn down and fixed to the edges of the wound.
The operation may then be suspended until adhesion has occurred between the
walls of the bladder and the edges of the wound, and the bladder then opened ;
or it may be treated in the same manner as when making gastric fistulae, and a
cannula similar to the one employed in making gastric fistula? inserted at once.
In this mode of operation the object has been to exclude the bile entirely from
the intestine ; but Schiff has shown that less pressure is required to make the
bile pass from the hepatic duct into the gall-bladder than to force it through the
common duct into the intestine. This excision, then, of the common duct is
entirely unnecessary, apart from the fact that it sometimes fails in its object by
becoming restored ; since as long as the cystic fistula is kept open the bile passes
out of the wound, but when the cannula is closed it passes as normally into the
duodenum.

When the operation for the formation of a permanent biliary fistula
succeeds, and all the bile is conducted outside of the bod}', animals
rapidly lose weight and eventually die, under ordinary circumstances,
under the phenomena of starvation. Such a result depends upon the inter-
ference with the digestion of fats and upon the direct loss of bile salts.
Thus, Yoit has found that a dog weighing twenty kilos, which in its
normal condition was able to digest from one hundred and fifty to two
hundred grammes of fat, absorbing 99 per cent, of this amount, was only
able, after a permanent biliary fistula was established, to absorb 40 per
cent, of the fat given. The loss of such an amount of fat through im-
perfect absorption naturally produces a disturbance of nutritive equi-
librium. An animal which before the operation is able to preserve its
nutritive balance with a certain amount of meat and fat, is unable to do
this after the performance of a biliary fistula, and is compelled to call on

396 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the reserve store of tissue-albumen, and finally dies practically of starva-
tion. If the animals are allowed to lick the wound, and so cause the bile
to enter their alimentary canal, the phenomena of impairment of nutri-
tion are very much less marked. So, also, if they are fed on double
the amount ordinarily required to maintain their nutritive equilibrium,
the carbohydrates especially being in excess, the phenomena of mal-
nutrition may be largely prevented. In animals where the secretion of
bile is prevented entirely from reaching the intestines, we find that obsti-
nate constipation is usually added to the symptoms of disturbed nutri-
tion, and that the faeces which are occasional^ passed are clay-colored,'
with a most offensive putrefactive odor. It would, therefore, appear that
the bile, by acting as a stimulus to the mucous membrane of the intestine,
tends to maintain the normal peristaltic contractions of this part of the
alimentary canal, and to that extent, therefore, acts as a natural purgative,
while at the same time it largely prevents putrefaction and decompo-
sition. The bile is, however, largely an excretion. Many of its con-
stituents are removed unchanged, while some of them are reabsorbed and
again enter the blood-current. The mucin and cholesterin pass through
with the faeces unchanged. The bile-pigments undergo decomposition in
the intestinal tube, and are partly excreted with the faeces under the form
of hydro-bilirubin, a characteristic brown coloring-matter of excrement,
and are partly eliminated as urobilin by the urine. The bile salts are for
the most part reabsorbed by the walls of the upper portion of the small
intestine, only a small quantity of glycocholic acid being found in the
faeces. The taurocholic acid is largely absorbed, it being previous^,
perhaps, decomposed into cholic acid and taurin, the latter being con-
stantly absorbed, while part of the cholic acid may perhaps be removed
with the faeces.

II. THE PANCREATIC SECRETION. — The pancreatic fluid is poured
into the small intestine immediately after the entrance of the bile,
or in some instances simultaneously with it and the secretion of
B runner's glands. While the pancreas is one of the most constant
of all glands, existing in all mammals, birds, reptiles, in most fish and
insects, its anatomical form is subject to great variation in different
animals. In the dog, as in other mammals, most birds, and reptiles,
the pancreas is situated in the concaArity of the duodenum. Also in
the dog, and in other mammals in wrlrich the duodenal mesentery is
short or absent, this gland is thick, elongated, and bilobed, one portion
extending horizontally toward the spleen, while the other portion de-
scends at a right angle, parallel to the duodenum (Fig. 155). At the
angle the pancreas is closely adherent to the duodenum, and often over-
laps it, being connected by a multitude of small blood-vessels, while the
descending portion lies free in the abdominal cavity. There are in the

DIGESTION IN THE SMALL INTESTINE.

397

dog, in which the operation for making pancreatic fistulae is most usual
as in most other animals, two pancreatic ducts — the upper and smaller
one opening into the duodenum in the same papilla as the bile-duct,
while the larger and lower duct opens into the duodenum about two
centimeters lower down. These ducts communicate by frequent anasto-
moses, the lower being always selected for operation. In those animals
in which the duodenum has a wide mesentery, as in the rodents, the
pancreas forms an arborescent mass between the two layers of the mes-
enter}r. This is the plan of arrangement in the rabbit, and also in the

FIG. 155.— PANCREAS OF THE DOG. (Bernard.)

PP, pancreas; a, pylorus; ft, glands of Brunner ; c c', large pancreatic duct; d, eminence formed
by the duodenal glands ; e, small pancreatic duct at its opening in the intestina : /, a'nastomosis between
the large and small pancreatic duct: g, orifice of the biliary duct; h, orifice of small, and t, of the large
pancreatic duct; k' , anastomosis of the large with the small duct.

cat. In the rabbit the pancreas has two ducts, but the upper one,
which enters the duodenum with the bile-duct, is very small, while
the lower one is very long, and enters the intestine about thirty to
forty centimeters below the pylorus. In the cat, the arrangement
of these ducts is so irregular as to baffle all description. In most
cases there are several of them, and sometimes, as occurs quite con-
stantly in the seal, the upper duct passes into a sort of reservoir

398

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

before entering the intestine (Fig. 156). The arrangement of the pan-
creatic ducts in the bird is represented in Fig. 157.

The pancreatic juice is a colorless, alkaline fluid secreted by the
pancreas or the so-called abdominal salivary glands. It differs from the
other digestive secretions in that when freshly formed by a normal gland
it contains a large amount of proteids. Its composition varies with the
rate of secretion, and when studied as obtained through fistulae differs
accordingly as to whether a temporary or permanent fistula has been
made.

FIG. 156.— PANCREAS AND DUODENUM OF THE CAT. (Bernard.)

a, pylorus ; b, section of duodenum at the level of the glands of Brnnner; c ct, superior pancreatic
duct opening with the biliary duct into the intestine ; a, mucous membniie of the duodenum ; e, inferior
pancreatic duct: el, point of its anastomosis with the descending branch of the pancreatic duct ; h, com-
mon opening of the biliary duct and superior pancreatic duct; s, pyloric portion of stomach; v, biliary
duct; ppp', pancreas.

Temporary fistulas of the pancreas are best made on the clog, since in this
animal there is the greatest probability of escaping peritonitis, — a complication
which if present is disastrous to the success of the operation, for the pancreas is ex-
tremely susceptible to inflammation, and as a consequence the secretion becomes
perverted and its properties altered. The only difficulty in the operation consists
in finding the duct without injuring the gland or its numerous blood-vessels. To
be thoroughly successful the operation should be performed as rapidly as possible,
so as to avoid exposing the parts any longer than is necessary, while the pancreas
should be handled with the greatest gentleness. The operation should be per-
formed without employing an anaesthetic, to avoid subsequent vomiting and
possible vitiation of the secretion. The dog should receive a hearty meal of bread
and meat two hours before the operation, and then should be fastened on his
left side. • An incision should be made in the right hypochondrium, descending
downward from the end of the last rib about five centimeters and parallel with
the linea alba, every bleeding point being tied before the peritoneum is opened.
Passing the index and middle fingers of the left hand into the wound, the duode-
num is easily recognized. The fingers are then carried well down into the right
hypochondrium, and then backward to the convex surface of the duodenum, and
keeping their palmar surface directed upward, the fingers are carried behind the
duodenum and pancreas, which are then to be drawn together out of the wound.
The animal being in full digestion, the tissue of the gland is of a rosy-pink colora-
tion. By this manipulation the parts preserve their normal relation, and the an-

DIGESTION IN THE SMALL INTESTINE.

399

terior surface of the pancreas presents in the wound. The next step, and perhaps
the most difficult, is the finding of the duct, — a proceeding rendered difficult not
only by the extreme shortness of the duct, but by its being surrounded by nu-
merous blood-vessels, which bleed very easily and which bridge over the duode-
num and the overlapping edge of the pancreas. By keeping the anterior surfaces
directed forward this difficulty is reduced to a minimum, since here the duct is
nearer the surface and is only surrounded by a few small blood-vessels, while on
the posterior surface the vessels are
very large, and it is just back of a
large bundle of vessels that the
duct enters the intestine. On
carefully pushing aside with a
blunt hook the overlapping edge
of the pancreas at the lower border
of the angle formed by the trans-
verse and vertical portions of this
gland, and about two centimeters
below the ductus choledochns, the
larger pancreatic duct is seen and
may be distinguished from the
blood-vessel by its larger size and
white color. The finding of the
duct may be facilitated by the fol-
lowing observations : Where the
vertical segment of the pancreas
leaves the duodenum there is al-
ways to be found a thick vein
passing from the intestine to the
pancreas. Above this the pan-
creas lies directly under the gut,
joined to it by numerous bundles
of veins. The opening of the duct
lies usually in the space between
the first two of these or between
the second and third. After the
duct has been isolated, a thread
should be passed around it and it
should be opened with a pair of
fine scissors; a small silver can-
nula, about five millimeters in
diameter and ten centimeters long,
may then be inserted and pushed
up to the first division of the duct,
tying it securely by the thread
previously passed around the duct.
To make the cannula still more
firm, a stitch maybe passed through
the serous coat of the intestine and
then the cannula fastened there
also. The duodenum and pan-
creas are then returned to the ab-
dominal cavity, retaining the ends
of the thread and the free end of
the cannula in the wound, which
is then closed by sutures, first
sewing together the muscles and then the skin. Upon withdrawing the stilette
from the cannula a few drops of colorless, limpid fluid escape, which flow more
rapidly when the animal makes any movement and which is strongly alkaline
(Figs. 158 and 159). The secretion may be collected by fastening a rubber bulb
furnished with a stop-cock to the cannula. The bulb should be first compressed
so as to be emptied of air, the stop-cock closed and connected with the cannula.
On opening the stop-cock the tendency of the bulb to expand draws the fluid out
of the ducts. Generally the fluid is secreted quite rapidly, and may be collected

FIG. 157.— PANCREAS OF THE PIGEON. (Bernard.)

P, first -pancreas with its duct, V ; P' P", second pancreas
with two ducts, V V" ; H, biliary duct opening into the duode-
num, D, below the gizzard, G; ch and h, secondary biliary duct3
opening into the ascending portion of the duodenum ; F, liver ;
S, stomach; P P' P", pancreas; a, opening in duodenum show-
ing a probe, b, inserted into secondary biliary duct.

400

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

for several hours. After the first day, however, the character of the secretion
alters and is no longer normal or suitable for study. If it does not flow rapidly,
it may be stimulated by injecting ether through a tube into the stomach. Vom-
iting stops the secretion. Usually after the second day the tube and threads
drop out, or else they may be gently removed, and the wound generally heals
readily and the duct becomes restored. The same animal may again be used for
the same purpose. One of the difficulties that will be met with in this operation
is that, since the duct is so short, the cannula is. very apt to slip out. This may
be partially remedied by having a cannula made with a little bulb on the end to
be inserted, or a T-shaped cannula may be used, the duodenal end of which must
be closed. If such a cannula is used it is better to have one made in two sec-
tions, one being first inserted in the duct and the other, which is to come out of
the wound, screwed in afterward.

In the ruminant animal the pancreas lies in part on the convolutions of the
colon, on the superior right portion of the rumen, extending over the fissure of the
liver to the second lumbar vertebra. Its duct, six, eight, or nine millimeters in
diameter, opens into the duodenum in the ox eighty to ninety-five centimeters

FIG. 1.58.— PANCREATIC FISTULA IN THE DOG. (Bernard.)

A, principal pancreatic duct; a, entrance of the duct into the intestine; a', lesser pancreatic duct;
a", ligature fastening the cannula to the intestinal wall ; //, ends of the ligature ; I, duodenum ; P P',
pancreas; T, cannula; V, rubber bulb; B, stop-cock.

below the pylorus, and in the sheep and goat at the opening of the bile-duct, and
is often free from gland-tissue for a space of from two to three centimeters. To
make a pancreatic fistula in the ruminant, an incision about ten to twelve centi-
meters long is made in the right flank parallel to the last rib and three or four
fingers' breadths removed from it. The pancreas then comes into view on open-
ing the abdomen, the duct may be readily exposed, and the cannula inserted. The
operation may be readily performed on the ox without uncovering the duodenum
from its omentum, and without dragging on the pancreas (Fig. 160).

In solipedes it is difficult to study the pancreatic secretion. The gland is
deeply situated against the vertebral column, its duct is surrounded by gland-
tissue up to its insertion in the duodenum, and it has very thin walls. To make
a fistula it is necessary to freely open the abdominal cavity in the median line
from the sternum almost to the pubis, to withdraw the colon from the abdomen,
open the duodenum and insert a tube through the opening of the pancreatic duct
and fasten it by a ligature, which must also include part of the gland. The colon
and duodenum are then to be replaced and the wound sewed up. This method

DIGESTION IN THE SMALL INTESTINE.

401

was first employed by de Graff on the dog, and has proved successful in the hands
of Leuret and Lassaigne on the horse.

As before stated, the operation as performed as above described does not
render the permanent collection of this secretion possible. It has been found that
when permanent fistulas are established, although they serve a useful purpose in
permitting the study of various conditions which may modify the secretion of
pancreatic juice, yet the fluid poured out by the glands under these circumstances
cannot at all be regarded as its normal secretion. For the purpose of establishing
a permanent pancreatic fistula, a small dog may be selected, since in small animals
the pancreas is nearer the middle line than in large dogs, and hence the parts are
not as much disturbed by the operation. The dog having been kept fasting for
twenty-four hours, so that the pancreatic vessels should contain as little blood as
possible, should be narcotized by a subcutaneous injection of morphine, and the ab-
domen opened by an incision about two centimeters long made in the linea alba and
about midway between the xy phoid cartilage and umbilicus . The duodenum and the

FIG. 159.— PANCREATIC FISTULA IN THE DOG. (Bernard.)

A, cannula on which is fastened the rubber bulb, B ; C, stop-cock.

pancreas are then to be drawn out of the wound and the pancreatic duct isolated and
opened by a little cut in one side; instead then of inserting a cannula, two pieces
of lead wire bent at an angle are to be introduced, one wire being passed toward
the gland -and the other into the intestine ; the remaining halves of each wire are
then to be twisted together so as to form a f -shaped piece, the middle limb of
which projects through the wound. Owing to the shape, the wires cannot fall out
and cannot move around in the duct. Fine wire should be selected somewhat
smaller than the calibre of the duct, so that the flow of the secretion will not be
interfered with. The duodenum and pancreas are then returned to the abdominal
cavity, care being taking to retain the wires in the wound, the duodenum is to be
stitched to the abdominal peritoneum, and the wound then closed. Inflammatory
adhesions take place around the wound and the wires cause the formation of a
fistulous tract which communicates with the ducts and through which, after a week
or so, the juice may be collected.

26

402

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Heiclenliain has employed a method of establishing permanent pancreatic
fistulas which he claims to have yielded in his hands satisfactory results. He
excises that portion of the duodenum which contains the opening of the pan-
creatic duct, restores the continuity of the gut, and sews the excised portion, after
division lengthwise, to the abdominal wound, so that the orifice of the duct opens
externally upon the abdominal surface.

1. The Chemical Composition of Pancreatic Juice. — The pancreatic
secretion differs in composition and physical properties according as it is
obtained from permanent or temporary fistulas, and according to the ani-
mal from which it is obtained. When obtained from temporary fistulas
in the dog, it is a clear fluid, almost of the consistency of syrup, very

FIG. 160.— PANCREATIC FISTULA IN THE Ox. (Colin.)

tenacious, and of strongly alkaline reaction. It contains few or no struc-
tural elements, though corpuscles similar to those found in saliva have'
been claimed by Ku'hne to exist, and occasionally free particles of oil. It
has a decided salty taste, and under the action of heat coagulates, as does
the white of egg, to a firm white mass. Alkalies prevent the coagulation.
When alcohol is added to the fresh pancreatic secretion it forms a copi-
ous, white, flocculent precipitate, which is subsequently in large part,
after filtration, soluble in water. When very dilute acids are added to
pancreatic juice, they at first form a turbid mass which subsequently
dissolves in excess of acid. This action is to be explained as due to the

DIGESTION IN THE SMALL INTESTINE. 403

production of acid albumen. Dilute acetic, lactic, and phosphoric acids
are without apparent action on pancreatic juice, but it is precipitated b}r
metallic salts, tannic acid, iodine, and chlorine- and bromine-water. The
pancreatic secretion obtained from a temporary fistula in a sheep is a
clear, tenacious fluid, which may be drawn out in threads like the white
of an egg. The first portions secreted are claimed to have a slightly
acid reaction, which soon becomes converted into an alkaline reaction.
The pancreatic juices of the horse, the rabbit, the chicken, and pigeon
behave in a similar manner, although the pancreatic secretion of the
rabbit only becomes turbid when heated, and does not form a firm eoagu-
lum, like that of the dog.

The pancreatic secretion differs from the other digestive fluids in
the large amount of solids, principally proteid in nature, which it con-
tains. Its specific gravity' as obtained from temporary fistulse'ma}- be
placed at 1030 ; obtained from permanent fistulae in the dog, the pancreatic
secretion is a thin, watery fluid, with a specific gravity onl}T of about 1010
or 1011; the lower specific gravity, of course, being due to the smaller
amount of solids. In the fluid from permanent fistuhe the solids amount
to 2 to 5 per cent., while in that obtained from temporary fistulae they
may rise to 10 per cent. Otherwise the fluid from permanent fistulse
agrees in most respects with that from temporary fistulse, it is clear and
colorless, alkaline in reaction, and of a sickly, saltish taste. When
heated it becomes turbid and may even coagulate, while it may also be
precipitated by alcohol, the precipitate being soluble in water. When
cooled down to the freezing point, it is said to deposit transparent mu-
cus-like coaguli. The pancreatic secretion, in contradistinction to that
of the gastric glands, is readily decomposed ; it then acquires a faecal
odor and colors chlorine-water red. After standing for some time, it
acquires an offensive, putrefactive odor and now no longer gives a red
with chlorine, but with nitric acid a bright-red color is produced. This
reaction is evidently due to indol.

The pancreatic secretion contains serum-albumen, alkali albuminate,
fat, soaps, and sodium salts, and is thus very closely allied to blood-serum
in composition; but it differs from it in containing four ferments, —
an amylolytic, a proteolytic, one which splits fats into glycerin and fatty
acids, and the milk-curdling ferment. The first three of these ferments
are precipitated by alcohol and are found in the pancreatic secretion of
both carnivora and herbivora. The existence of the milk-curdling fer-
ment is not entirely beyond question. Pancreatic juice is also stated to
contain peptones, leucin, and tyrosin, but it seems probable that these
elements are not found in perfectly fresh juice, with the exception, may
be, of a trace of leucin, but are formed through the digestion of the
albumen in the pancreatic juice by one of its own ferments.

404 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The following table represents the composition of the pancreatic
juice of the dog, as obtained from permanent and temporary fistulas : —

Temporary Permanent
Fistula. Fistula.

Water, 900.8 984.06

Solids, . .92.2 15.4

Organic matter, 90.4 9.2

Ash, . 8.8 6.1

The following table represents the analyses of the ash : —

Temporary Permanent
Fistula. Fistula.

Sodium, . . . . . . 0.58 3.31

Sodium chloride, . ' . . . .7.35 2.50

Potassium chloride, .... 0.02 0.93

Phosphatic earths with traces of iron, . 0.53 0.08
Sodium phosphates, . . . ....

Lime and magnesium, .... 0.32 0.01

The solids in pancreatic juice are, however, subject to great vari-
ation. Bernard found in the secretion from temporary fistulae in the
dog 8 to 10 per cent, of solids, Tiedemann and Gmelin 8.7 per cent, of
solids, of which 7.89 per cent, were organic and 0.72 per cent, ash, while
in the secretion of the sheep 3.6 to 5.2 per cent, of solids have been
found.

According to Hoppe-Seyler, in 1000 parts of pancreatic secretion,
obtained from a diverticulurn in the pancreatic duct of the horse, 982.5
parts were water, 8.88 parts organic matter, and 8.59 parts ash.

In the rabbit the solids have been placed at 1.76 per cent., while in
the ram 1.43 to 3.69 per cent, of solids have been determined through
various analyses.

The Pancreatic Ferments. — The pancreatic ferments may be together
extracted from the fresh gland by a process of mincing and extracting
with glycerin ; on adding alcohol to the glycerin extract, the proteo-
lytic and amjdolytic ferments may be precipitated. If, however, the
gland be first treated with alcohol before extraction with glycerin, the
proteolytic ferment will not be found in the solution, while the diastatic
ferment will be present in large amounts. It is claimed, however, that
if the pancreas of the ox be allowed to remain for a long time in
alcohol, and then extracted with glycerin, a preparation will be obtained
which contains all three of these ferments.

Various processes have beeji proposed for the isolation of these three fer-
ments. Danilewsky recommends for the isolation of the proteolytic ferment
that the pancreas should be taken from an animal killed six hours after a copious
meal, and, after washing, should be ground up with clean sand and digested for
two hours with water, at a temperature which should not rise above 30° C. The
mixture should then be filtered, and the filtrate, which contains both amylolytic
and proteolytic ferments, treated with an excess of calcined magnesia to remove
fatty acids, filtered, and added to one-third its volume of thick collodion, which
carries down the fibrin-ferment in a crumbly mass. The ether should then be
evaporated, and the resulting mass washed with alcohol and ether, and by now

DIGESTION IN THE SMALL INTESTINE. 405

precipitating with alcohol the proteolytic ferment may be isolated comparatively
pure. From the filtrate of the precipitate obtained with collodion the diastatic
ferment may be isolated by evaporating under an air-pump, filtering off the pre-
cipitate, again precipitating with alcohol, and dissolving the precipitate in a
mixture of two parts of water and one of alcohol, by which proteid matter is
removed. The remaining substance will convert starch rapidly into sugar, but is
without action on proteids.

Kiihne's method is to form an aqueous extract of a pancreas at the freezing
point and to precipitate with alcohol ; the precipitate is re-dissolved in water,
again precipitated with absolute alcohol, and the precipitate a second time re-dis-
solved in water and treated with acetic acid up to 1 per cent.

The same treatment is repeated a second time, and the watery solution, after
the addition of acetic acid, is warmed to 40° C. and then filtered. The filtered
liquid is made alkaline with sodium hydrate, by which the greater part of the
earthy salts and tyrosin are precipitated, the trypsin or proteolytic ferment is then
freed by dialysis from tyrosin, peptones and other crystalline substances, and
finally precipitated with alcohol.

Paschutin recommends a process for the isolation of these ferments which
depends upon the fact that solutions of different salts have special capabilities of
extracting the separate ferments. He found that sodium chloride, calcium chlo-
rate, and sodium sulphate were able to dissolve all three of the ferments, while
other solutions had special degrees of power in extracting the individual ferments.
Thus, the proteid ferment is especially dissolved by potassium iodide, potassium
arseniate, and potassium sulphate. The fatty ferment is readily extracted by
solutions of bicarbonate of sodium containing a small quantity of caustic soda,
while the diastatic ferment is most readily extracted by a solution of arseniate of
potassium to which a small quantity of ammonia has been added.

2. The Action of the Pancreatic Juice on Food-Stuffs. — When study-
ing gastric digestion, it was seen that all the different phenomena could
be most conveniently studied with an artificial fluid in experiments con-
ducted outside of the body. The same conditions prevail in the study of
pancreatic digestion. An artificial pancreatic juice may be made by
three different processes : —

First. The fresh pancreas of a dog killed some hours after a full meal is cut into
pieces, washed to remove the blood, and then infused for two hours in four
times its weight of water, warmed to 25° C., taking care to keep the mixture at
that temperature during the whole time of infusion. It is then to be filtered, first
through muslin and then through paper. Since the filtrate will be usually acid
from the development of fatty acids through the action of ferments on fats of the
pancreas, it must be neutralized with sodium carbonate. The fluid will be slightly
opalescent from the small amount of fat held in the form of emulsion. This
preparation has all the properties of pancreatic juice, although the degree of its
digestive action on proteids will depend upon the nutritive state of the pancreas
from which it was made. For, if the pancreas of a fasting animal was employed,
it will possess scarcely any digestive powers.

Second. An artificial pancreatic juice may be obtained by allowing a minced
pancreas to remain for two days in absolute alcohol, which is then to be filtered
off and the residue covered with glycerin ; this glycerin extract will contain a
considerable quantity of the ainylolytic ferment, while the quantity of proteolytic
ferment, as in the first, will depend upon the condition of the gland.

Third. The pancreas may be taken from an animal in full digestion, minced,
and rubbed up in a mortar with powdered glass. For each gramme of gland-sub-
stance, one cubic centimeter of 1 per cent, acetic acid shoulcl be added and mixed
thoroughly in a mortar for ten minutes, and then ten times its volume of glycerin
added, and the whole allowed to stand for three days. This preparation will con-
tain a much larger proportion of proteolytic ferment than was obtained by either
of the preceding processes, since the acetic acid seems to possess the power of
converting into ferment the zymogen, or the substance which yields the proteo-
lytic ferment.

406 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

(a) Action on Carbohydrates. — Valentin pointed out that the
pancreatic juice was capable of converting starch into sugar, and nearly
all that was stated with regard to the action of saliva on starch might be
repeated for the case of the pancreatic juice, with the single modification
that in the case of the pancreas the amylolytic power possessed by its
secretion is much stronger than that of the saliva. The secretion and
watery extract of this gland in both herbivora and carnivora, as well as
the secretion obtained from this gland in birds (chicken and goose),
rapidly convert starch into sugar. All the conditions which were found
to prevent the action of the saliva also hold here, with the single excep-
tion that a slight degree of acidity seems rather to favor the action. The
ferment through whose action the pancreatic juice is enabled to convert
starch into sugar is apparently formed in the gland-tissue by the trans-
formation of some previously existing material; since it has been found
that if the ferment is completely extracted from a fresh gland by glyc-
erin, and the inactive residue allowed to remain on the filter for five or
six hours exposed to the air, a further production of ferment occurs.
This new formation may be again extracted by water or gtycerin. That
this result is really due to the new formation of ferment, and not to the
occurrence of decomposition, is proved by the fact that if the wateiy ex-
tract of the pancreas is once deprived of its action on starch by boiling,
this power never returns in any stage of the subsequent decomposition.
So, also, a gland which has been exposed for twenty-four hours to the
air is more active than a fresh gland. The amount of starch which by
the action of pancreatic diastase is converted into sugar is almost infinite.
Roberts has calculated that pancreatic diastase is able to transform into
sugar and dextrin no less than forty thousand times its own weight of
starch. The rapidity with which starch is converted into sugar depends
upon the proportion of ferment brought to act upon it. So that all
grades of activity may exist between the apparently instantaneous con-
version of a small amount of starch with a large amount of ferment, and
the slow and gradual action of a small amount of ferment on a large
quantity of starch. The products which result from the action of pan-
creatic ferment on starch are entirely analogous to those which result
from the action of ptyalin or malt-diastase on starch. When the gland-
tissue is itself brought into contact with soluble carbohydrates, lactic
acid fermentation ultimate! 3' results. Glycogen is also rapidly converted
into sugar under the action of pancreatic diastase. Inulin and cane-sugar
are entirely unaltered by it. The amylolytic action of the pancreatic
juice is said to be absent in newborn children, appearing first after the
termination of the second month.

(b) Action on Fats. — In the small intestine the fats, which have been
seen to almost entirely escape the action of .the gastric juice, are broken

DIGESTION IX THE SMALL INTESTINE. 407

up into a state of emulsion, while a small quantity undergoes chemical
changes, in which fatty acids are liberated. The fatty acids thus liber-
ated combine with the alkaline bases of the bile and pancreatic juice to
form soaps. If oil, butter, or lard is stirred with pancreatic juice at a
temperature of 35° or 40° C., almost immediately a thick, creamy emul-
sion is formed which will stand for a long time. The presence of gastric
juice, even when in sufficient amount to neutralize the alkalinity of the
pancreatic juice, is stated by Bernard to have no influence on the emulsi-
fying property of this secretion ; but to produce it in its highest degree
the secretion must be normal, and that obtained from permanent fistula? is
much less efficacious than that from temporary fistulas. This emulsifying
power possessed by the pancreatic juice is due to the specific action of a
special ferment, termed generally the emulsive ferment, which is claimed
by Bernard to first emulsify and then saponify fats. It is certain that in
the small intestine the principal change is merely due to the production
of an emulsion, and nearly all the fat taken up by the absorbent vessels of
the small intestine is in the form of an emulsion and not of a soluble soap,
although both changes do occur in the small intestine ; the saponification
is, however, most marked after the fats have been absorbed. The emulsive
ferments, it has been claimed b}< Paschutin, may be readily extracted from
the pancreas by a solution of bicarbonate of sodium, and this solution
will readily emulsify fats. It is doubtful as to wrhat importance is to be
attached to this statement, since it has been already stated that a solu-
tion of bicarbonate of sodium constitutes an extremely delicate test
for the presence of fatty acids, and when such acids are present the
addition of the bicarbonate of sodium w^ill almost instantly form a per-
manent emulsion. Since, therefore, it is almost impossible to obtain fats
which are absolutely free from the presence of fatty acids, the above
statement is not by itself sufficient to prove that the emulsifjang power
of pancreatic juice is due to the action of a specific ferment. Other
proof is, however, found in the fact that the action of fresh normal pan-
creatic juice on neutral fats does result in the development of free fatty
acids and glycerin. This result may even take place when the pancreatic
juice has been diluted with twelve times its volume of water ; and although
gastric juice and hydrochloric acid seem to interfere with this action of
the secretion, the bile appears to facilitate it. Just as we found that the
solution of fibrin with acid in contact with peptic glands was a reliable
test for the presence of pepsin, so also the power possessed by the pan-
creas of decomposing fats and forming fatty acids and glycerin serves
for the recognition of the pancreas in lower animals, and, as emplo3Ted
with this object in view, has been highly perfected by Bernard.

The emulsive action of the pancreatic juice is destroyed by boiling,
and the digestive action on fats through the influence of pancreatic

408 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

juice is, therefore, of two kinds. Mechanically, it forms an emulsion
with the oil, while chemically it liberates the fatty acids with glycerin,
the formation of the emulsion being largely the result of the liberation
of fatty acids.

(c) Action on Proteids. — The action of pancreatic juice on proteids
coincides with that of gastric juice in so far that in both cases the con-
version is due to a ferment which is destroyed by heat, and that both
secretions convert proteids into peptones. Many points of contrast,
however, exist. In the first place, it was seen that gastric digestion
required the presence of dilute hydrochloric acid. In the case of pan-
creatic digestion it will be found that a half of 1 per cent, solution of
sodium carbonate produces the most active results. If a fragment of
.thoroughly boiled fibrin is placed in an artificial pancreatic juice, made
by adding a few drops of the glycerin-acetic acid extract to a 1 per cent,
solution of sodium carbonate, it will ultimately dissolve, but the process
will differ from that occurring in gastric digestion. After having
remained for an hour or two in contact with the pancreatic juice, the
fibrin will at first appear to be unaltered, but if it is stirred with a glass
rod, many small fragments dissolve, and on removing some of the larger
pieces and washing them with water, they are seen to be corroded and
as opaque as before, but not swollen and transparent, as would occur in
an analogous stage of gastric juice. Besides these superficial changes,
however, the properties of the fibrin have been considerably modified.
Undigested boiled fibrin is entirely insoluble in dilute acid, and if this
boiled fibrin, which has been partially digested by pancreatic juice, is
placed in a two-tenths of 1 per cent, solution of hydrochloric acid, it
will be rapidly dissolved, and form a solution of syntonin, which may be
precipitated by neutralization. Before being dissolved, therefore, boiled
fibrin is rendered by pancreatic juice more soluble in dilute acid than
even raw fibrin, which, as is well known, will not dissolve for many
hours.

Again, in this stage of pancreatic digestion, the boiled fibrin becomes
soluble in a 10 per cent, solution of sodium chloride, and is readily
coagulated by nitric acid and boiling; it thus appears that the first step
in the pancreatic digestion of boiled fibrin is to change it to a soluble
albuminoid, somewhat resembling raw fibrin.

Again, if the fibrin be allowed to remain in pancreatic juice until it
has been dissolved, a precipitate may be formed on neutralization which
is evidently of the nature of an alkali albuminate and analogous to the
parapeptone formed in gastric digestion ; while boiling will also produce a
precipitate, — a phenomenon which is entirely unrepresented in any known
stage of gastric digestion. Although, as already mentioned, an alkaline
reaction appears to favor pancreatic digestion, nevertheless, it appears

DIGESTION IN THE SMALL INTESTINE. 409

that proteids may be digested in pancreatic infusions with a neutral or
even faintly acid reaction ; it even appears that in the case of the pig
the pancreatic infusion is only active in digesting proteids when the
intestinal reaction is acid.

As already mentioned, the pancreas is not under every condition
capable of forming a secretion which will digest proteids, and under
many circumstances infusions of the pancreas will be entirely inert on
proteids. This would seem to indicate that while trypsin, or the proteo-
iytic ferment, is formed in the cells of the pancreas, it is preceded by
another substance termed zymogen, which is gradually in the normal
conditions of the gland converted into trypsin. In support of this state-
ment it may be mentioned that the pancreas obtained from the slaughter-
house or from fasting dogs is often inactive, while the most activitA' is
present about four or seven hours after feeding. It is supposed that the
zymogen, which is soluble in water and glycerin, and which is found in
the inner zone of the secretoiy cells, is, through the gradual action of
oxygen, converted into trypsin. This conversion normally occurs in the
interior of the gland during digestion, but even inactive glands may de-
velop trypsin through exposure to the air after death or by the action of
dilute acetic acid.

Schiff and Herzen claim that there is a close connection between the
action of the spleen and the development of trypsin, and they claim to
have demonstrated that the pancreas of an animal from whom the spleen
has been removed is incapable of digesting proteids, and that if such a
pancreas be rubbed up with a portion of spleen it will then acquire the
power of digesting proteids. This statement, however, needs further
confirmation.

When the pancreatic digestion of proteids is prolonged, in addition
to peptones, various other bodies make their appearance. Leucin and
tyrosin appear in large amounts, with traces of asparaginic acid, xanthin,
and a body which is colored red with chlorine- or bromine-water. The
longer the pancreatic digestion is prolonged, the larger will be the amount
of leucin and tyrosin present and the smaller the amount of peptone ;
from which it would appear that these crystalline substances result from
the gradual breaking down of the peptone itself.

Kiihne explains this result by supposing that the albuminous bodies
under the action of trypsin become converted into two forms of peptone,
to which the terms respectively antipeptone, which does not undergo
further change, and hemipeptone, the latter in normal digestion being
converted into leucin, tyrosin, etc., and readily undergoing putrefaction,
resulting in the formation of indol, skatol, and phenol.

If a pancreatic digestive mixture be neutralized so as to precipitate
alkali albumen, and then treated with an excess of alcohol, the greater

410 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

part of the peptone will be precipitated. If the alcoholic fluid be then
acidulated with acetic acid, boiled, and filtered, leucin and tyrosin will
separate when the nitrate is concentrated by evaporation. By heating
this deposit with water, the leucin, which is readily soluble in water, may
be separated from the tyrosin, which is not so soluble.

Leucin, or amido-caproic acid (C6H13NO2), belongs to the fatty bodies, and
is a constant decomposition product of albumen and various nitrogenous sub-
stances. Leucin occurs in the form of white, shining lamellae, which are insoluble
in ether and chloroform, readily soluble in alkalies and acids, especially when
hot. It readily crystallizes from its solutions in hot water in spherical masses,
composed of groupings of thin, white, glistening needles. When a few crystals
of leucin are placed on platinum-foil and evaporated gently with a drop of nitric
acid, if a few drops of caustic soda are added to the colorless residue a yellow or
brownish mass is obtained, which forms an oily drop. (Scherer's test.)

If a dilute solution of leucin is boiled with cupric hydrate in excess, bright
violet scales are deposited on cooling.

Tyrosin (CgH^NOg) is a member of the aromatic group, and may be
obtained from almost any proteid under the action of strong oxidizing agents. It
remains in the deposit of pancreatic digestion of albuminoids, prepared as above,
after the leucin has been removed. By dissolving this residue in hot water, and
rapidly crystallizing by the addition of ammonia, tyrosin may be obtained in
tolerable purity. It then occurs in the form of fine, white, silky needles, gener-
ally arranged in sheaf-like bundles, which dissolve in hot dilute ammonia, and are
deposited on cooling the solution in brilliant, colorless, radiating stars. It is
insoluble in absolute alcohol and ether, almost insoluble in cold water, and
slightly soluble in hot water, but readily soluble in the mineral acids and in warm
dilute ammonia.

If a hot, watery solution of tyrosin is treated with a few drops of Millon's
reagent to boiling, a dark-red color appears, and when the solution is concentrated
deposits a dark-red precipitate. (Hoffman s test.)

The application of Scherer's test, as in the case of leucin, will form a reddish-
yellow residue, which will become brown on the addition of caustic soda.

In the small intestine the pancreatic juice never alone comes in
contact with food-stuffs, but it meets with undigested matters mixed
with the results of gastric digestion, and therefore with the acid gastric
juice and bile.

In the animal economy, therefore, the activity of the pancreatic
juice must be different from that which has been stated as occurring
outside of the bod}r, when the operation of the pure pancreatic juice is
alone considered.

When the acid chyme from the stomach reaches the small intestine,
the alkalinity of the bile, pancreatic and intestinal secretion, to a certain
extent, partially neutralizes the acid of the gastric juice.

It has been found that when pancreatic juice is mixed with gastric
juice, the activity of the resulting medium will depend greatly upon the
relative proportions of these two fluids. As a rule, gastric juice, by
digesting trypsin, renders the pancreatic secretion entirely inert. The
process occurring in the duodenum is, however, somewhat different :
for we have already found that the first effect of the bile is to precipi-
tate pepsin, and therefore the pancreatic ferment comes into contact with

DIGESTION IN THE SMALL INTESTINE. 411

the acid constituents alone of the gastric secretion, which, as has been
already mentioned, has but slight degree of acidity, and does not inter-
fere with pancreatic digestion.

The bile, on the other hand, while disturbing gastric digestion, con-
siderably assists the action of the pancreas, not only in facilitating the
emulsification of fats, but apparently also in some wa}' aiding the solvent
action of the pancreas on proteids. The pancreas, in addition to the
three ferments already described, is also said to contain a ferment which
coagulates milk, which ma}' be extracted from the gland by means of a
concentrated solution of common salt, the ordinary solvent used in
making rennet from the calf's stomach, and which in general is claimed
to behave like the milk-curdling ferment of the gastric juice.

This ferment has been found in the pancreas of the pig, the sheep,
the calf, the ox, and the fowl. The principal difference between the
action of the milk-curdling ferment of the pancreas and that of the
gastric juice lies in the fact that even 1 per cent, of sodium bicarbonate
does not prevent coagulation in the former case, while one-fourth of
1 per cent, in the latter case does. The pancreatic rennet is also quite
active in a neutral or even faintly acid medium. Boiling, as with other
soluble ferments, destroys its power. It may likewise be precipitated by
alcohol and again dissolved in water without losing its activity.

When a pancreatic digestive mixture is allowed to remain in contact
with food-stuffs, it rapidly acquires a putrefactive odor, and swarms with
microscopic organisms. Usually in eight hours a high degree of putre-
faction has taken place. It is to be supposed that a similar state of
affairs occurs in the small intestine, since the conditions are there favor-
able for the reproduction of bacteria ; for it is scarcely possible to assume
that the acidity of the gastric juice is sufficient to destroy the germs
which we must suppose are constantly taken into the alimentaiy tract.
A characteristic result of the putrefaction and decomposition of proteids
is indol, to which the ftecal odor of putrefying pancreatic secretion is due.
When salicylic acid is added to pancreatic digestive mixtures, they remain
free from odor, and the presence of indol cannot be detected. It there-
fore seems clear that indol is a result of putrefaction of the results of
pancreatic digestion, and is not normally a digestive product. Never-
theless, the constant presence of indol in the small intestine would show
that in this portion of the alimentary canal such putrefactive changes
almost invariably result.

In addition to indol, putrefying pancreatic solutions will develop
ammonia, carbonic acid, butyric acid, valerianic acid, acetic acid, phenol,
sulphuretted Irvdrogen, carburetted hydrogen, and hydrogen, — gases
which are also found in the alimentary canal.

While such putrefactive changes undoubtedly occur in the alimentary

412 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

canal, the extent to which these processes take place can be scarcely
estimated; of course, the more proteid which is so broken up, the greater
will be the nutritive loss to the economy, since such putrefactive products
have no physiological value. It may, therefore, be assumed that it is
only the excess of proteids which is so broken up, for under normal
conditions it may be assumed that peptone is absorbed as fast as it is
formed. In the case of the herbivora, whose long intestinal tract is
nearly always filled with residue of food, this decomposing process will
probably attain a higher degree than in the case of the carnivora. That
the intestinal contents are comparatively free from putrefactive odor in
these animals is not an objection to this statement, since it is always so
largely composed of cellulose and other non-putrefactive substances.

It has been found that the amount of indican contained in the urine
is a measure of the amount of putrefaction occurring in the intestine;
and since indican is present in the urine of herbivora in about twenty-
three times the amount found in the urine of man, it is evident that the
putrefactive process in the intestinal canal of the herbivora must be
also largely in excess. In addition to the fact that the proteids are
rapidly absorbed as soon as acted on by the digestive secretions, the
influence of the bile is also to be alluded to as a preventive of putrefaction.

3. The Secretion of Pancreatic Juice. — In the pancreatic secretion
the digestive juices reach their maximum as regards intensity of action
and variety of food-stuffs on which they act. Human pancreatic juice
has never been obtained in a condition of purity, and were it not for the
studies made on animals this branch of our subject would be an empty
page. The volume of this gland, which is very constantly present and
subject to a great variety of changes, is much larger in the carnivora
than in the herbivora. In the herbivora the secretion is constant, in the
carnivora it is intermittent, while in the ruminant its maximum activity
appears to coincide with the end of rumination, when as much as two
hundred to two hundred and seventy grammes may be secreted per
hour. During fasting in the ruminant, although not absolute^ sus-
pended, its secretion is greatly reduced in amount. In the horse, from
experiments made by Leuret and Lassaigne, Colin was able to determine
that the maximum hourly secretion was two hundred and sixty -five
grammes, or about the same as that of the ox, though part was probably
lost by not t}ang the supplementary ducts. As in the carnivora, so,
also, in the herbivora, this gland is extremely liable to inflammation,
which, of course, will affect the general result.

Another method by which the amount of pancreatic secretion
poured out was estimated was to ligate the bile-duct and pylorus, then
empty the intestine by pressure, and then to tie its lower extremity. In
this way six hundred to one thousand grammes of clear, limpid fluid

DIGESTION IN THE SMALL INTESTINE. 413

were collected in an hour, though, of course, the fluid was not derived
solely from the pancreas, but contained the secretion poured out by the
intestinal glands.

The pancreatic secretion in the hog has certain characteristics which
are readily determined. The fistula is made in the same manner as in
the dog, and it is then seen that the hourly secretion is five to fifteen
grammes, and that the activity of the pancreatic secretion is in inverse
ratio to that of the bile.

In the carnivora the study of this secretion is most readily carried
out. In the sheep it is open to difficulties, and has not been as
thorough as in the dog. No ratio between the size of the animal
or of the gland and the quantity of pancreatic juice is capable of
demonstration. Thus, the pancreas of the horse and ox weigh
each three hundred grammes ; both animals are about of the same

FIG. 161.— SECTION OF THE PANCREAS OF THE DOG IN THE FASTING CONDITION,
HARDENED WITH ALCOHOL AND STAINED \VITH CARMINE. (Heidenhain.)

size, and also secrete the same amount of pancreatic juice. In the
sheep the pancreas weighs from fifty to sixty grammes, or one-fifth as
much as in the large ruminants, and yet only pours out seven to eight
grammes per hour. In the hog the pancreas weighs from one hundred
and forty to one hundred and eighty grammes, and only secretes ten to
fifteen grammes per hour. These results, of course, cannot be too posi-
tive^ accepted, on account of the many disturbing causes.

In the pancreas, as in other glands, we may distinguish a period of
rest, during which the gland is pale and free from blood, and a period of
activity, during which it is swollen and its vessels gorged with arterial
blood. Changes occur, therefore, in the pancreas such as have been al-
ready described in the case of the salivary glands. In the carnivorous
animals the secretion commences when the food is introduced into the

414 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

stomach and rapidly reaches its maximum two or three hours thereafter.
Toward the fifth or seventh hour it decreases in activity, and about
twelve hours after feeding again becomes increased in amount, the second
increase being apparently coincident with the escape of the acid chyme
into the small intestine. The cells of the pancreas also undergo marked
histological changes during the period of active secretion. .In the pan-
creas of a fasting dog two zones may be recognized, the inner zone highly
granular in nature, and with difficulty stained with carmine, and a smaller
homogeneous outer zone which readily stains red. The nucleus, which is
generally irregular in shape, lies between these two zones (Fig. 161). If,
on the other hand, a microscopic inspection be made of an animal in full
digestion, the outer homogeneous zone will be found to have greatly in-

FIG. 162.— PANCREAS OF THE DOG IN THE FIRST STAGE OF DIGESTION. (Heidenhain.)

creased in extent, while the inner granular zone will be almost absent,
the whole cell being smaller and readily stained with carmine (Fig. 162).
After digestion has been completed, the appearance described in the fast-
ing cell will be again regained (Fig. 163). It would appear from these
facts that the secretion of the pancreatic juice is formed at the expense
of the granular material found in the inner zone of the secreting cells,
while these granules result from the amorphous homogeneous matter
found in the external zone, and which during digestion is built up from
the matter taken from the blood. We have already alluded to the fact
that to obtain an active pancreatic extract the gland must be taken from
an animal in full dig'estion, and that if the gland of a fasting animal be
rubbed up with glycerin and acetic acid, the glycerin extract from such
a gland will be strongly proteolytic. These results are to be explained,

DIGESTION IN THE SMALL INTESTINE. 415

as alreadjr mentioned, by the fact that the gland itself contains but little
ready-formed proteolytic ferment, but a substance termed zyrnogen,
which, from exposure to the atmosphere, or under the action of dilute
acid, is readily converted into ferment.

Heidenhain luis determined that the amount of zymogen in the pan-
creas coincides in amount with the extent of the granular zone ; there-
fore, in pancreatic secretion, as in the case of saliva, the act of secretion
possesses two phases : the first, the preliminary stage of separation from
the blood; the second, the stage of manufacturing of those constituents
into the specific ferments of the secretion.

As regards the action of the nervous S3*stem on the secretion of

FIG. 163.— PANCREAS OF THE DOG IN THE SECOND STAGE OF DIGESTION. (Heidenhain.)

pancreatic juice but little is known. Both section and stimulation of
the central end of the pneumogastrics temporarily arrest the flow of
pancreatic juice ; vomiting also has the same effect, the result being
probably due to the stimulation of this nerve. Stimulation of the gland
itself by, an induction current, as well as stimulation of the medulla
oblongata, seems to produce an increase in the secretion, but section of
the spinal cord does not raise it. When all the nerves going to the
pancreas are divided, a continuous flow of pancreatic juice commences,
and under these circumstances the fluid formed has but slight digestive
power, and its amount is not influenced by the taking in of food. Injec-
tions of ether into the stomach produce an increased flow of pancreatic
juice, while the secretion is suppressed in the dog, though not in the

416 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

rabbit, by the action of at r opine and by stimulation of the sensory

nerves.

The pressure under which the pancreatic juice is secreted is not
much higher than that of the bile, amounting only to about seventeen
millimeters of mercury.

III. THE INTESTINAL JUICE. — In addition to the fluids poured out by
the liver and the pancreas, the walls of the small intestine are also
abundantly supplied with glands, which pour out a secretion which
possesses a certain digestive value. The largest amount of this fluid is
poured out by the so-called duodenal follicles, or glands of Lieberkiihn,
to which is added the scanty secretion of the small, convoluted, tubular
Br miner's glands. The latter are morphologically identical with the
glands of the pylorus and stomach, and their cells are turbid and small
during hunger, while during digestion they are large and clear. In the
sheep the Brnnner's glands form a continuous laj^er and their walls pour
out a fluid containing mucin and ferments which possess the power of
dissolving proteids and of converting starch into sugar. Any data as to
the action of the secretion formed by these glands are, however, obtained
with the greatest difficulty on account of the smallness of the glands and
impossibility of isolating their secretion ; consequently, the greatest
uncertainty surrounds their functions.

The glands of Lieberkiihn are small, tubular glands set vertically in
the mucous membrane and are lined by c}dindrical epithelial cells, among
which numerous goblet, mucous cells may be found. These cells, appar-
ently, are the main source of intestinal juice, the so-called succus entericus.

Yarious methods have been proposed for obtaining the fluid poured
out by these glands. Thiry's method was to withdraw a loop of small
intestine from the abdomen, and excise a portion several inches in
length, leaving its blood supply intact, and then restoring the continuity
of the intestine by stitching together the ends above and below where
the excised portion had been removed. One end of the excised portion
was then closed by stitches, while the other extremity was kept open
and stitched into the abdominal wall. By this means a small portion of
the small intestine was isolated, and as it communicated with the exterior
the secretion which it formed could be readily collected. Yella improved
the method employed by Thiry by leaving both ;ends of the isolated
portion open, after restoring the continuity of the bowel, and stitching
them to the abdominal wound. It is evident that after this operation
the small intestine cannot be regarded as being in its normal condition,
for it is entirely removed from contact with the secretions and chyme,
and undergoes a considerable amount of atrophy ; and although its
secretion is not contaminated by any other digestive fluid, it cannot
be regarded as being in a normal condition.

DIGESTION IN THE SMALL INTESTINE. 417

Colin collected a considerable amount of fluid by placing a clamp on
the small intestine of the horse and emptying a considerable portion
below it by gentle pressure, and then clamping it several feet below the
upper clamp. In this Tvny he obtained from eighty to one hundred and
twenty grammes of fluid in half an hour from two meters of the small
intestine of the horse. He states, however, that this fluid may be greatly
increased by the injection into the loop of a solution of aloes, manna, or
soda; and since its composition coincides almost exactly with that of
blood-serum, it is probably an exudation. No reliable experiments seem
to have been made as to the digestive properties of the fluid obtained in
this wa}r.

Moreau has also succeeded in obtaining a large quantity of liquid
by clasping the intestine, as in Colin's method, and then dividing the
nerves going to the isolated portion of the intestine. In this operation,
also, it is probable that the fluid is an exudation, as it coincides almost
entirely with blood-serum in composition; and here also no experiments
as to its digestive powers have been made.

The author has employed a method for collecting the secretion of
the small intestine which is free from most of the objections which
may be urged against the methods already described. A fistula is made
into the duodenum in the same way as in making a gastric fistula, and a
small tube inserted. The operation is readily performed, but in a large
number of animals so treated the tube will tear out of the intestine, and
the experiment will consequently fail. When the wound lias healed the
dog should be allowed to fast for at least twenty-four hours, and then
the intestine washed out by an injection of lukewarm water through the
cannula. A rubber bulb is then to be inserted through the tube into
the small intestine and pushed back toward the stomach, taking care,
however, that it lies below the opening of the pancreatic and bile ducts ;
it then may be distended by water so as to occlude the intestine, and a
small bulb with a long tube is then pushed down the intestine and dis-
tended with water so as to occlude it below.

In this way a variable portion of small intestine is shut off from the
contents of the alimentary canal above and below, and its secretion in a
state of comparative purity, and in considerable amount, may be then
collected.

Obtained in this way, the intestinal juice has an alkaline reaction ;
its specific gravity, 1010; it gives no coagulum on boiling, and yields
Millon's reaction, and deposits a heavy precipitate when thrown into
absolute alcohol. Its composition in one hundred parts is as follows:
Water, 98.86 ; organic matter, 0.54 ; inorganic matter, 0.59. The inor-
ganic matter is represented by chlorides and sulphates and carbonates
of sodium and potassium. With chlorine-water no red is given, and in

27

418 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

certain instances it lias been found to turn acid on standing. As regards
its digestive action, it contains three ferments, which may be precipitated
by alcohol and again redissolved in water. It will rapidly convert
starch into sugar in a neutral or faintly alkaline medium, while 2 per
cent, of acid and 5 per cent, of liquor potassa will prevent it. This has
also been established by Ellenberger and Hofmeister to apply to the
intestinal secretion of the horse. There is a special ferment present
which will convert cane-sugar into invert-sugar, or a mixture of laevulose
and dextrose. This is the only secretion in the body which possesses
this power. The transformation of cane-sugar into invert-sugar is
represented in the following formula : —

SC^H^O^ +2H20 = C12H24012 + C12H24O12.
Saccharose. Water. Dextrose. Lsevulose.

The inversive ferment has been found by Bernard in the small intes-
tine of dogs, rabbits, birds, and frogs. Roberts has recognized it in the
small intestine of the pig, the fowl, and the hare, while Balbiani has
found it in the intestine of the silk-worm. It is absent from the large
intestine. When a watery infusion is made of the mucous membrane of
the small intestine, it possesses the power of inverting sugar, but loses it
when the infusion is filtered, seeming to indicate that the ferment remains
attached in such infusions to some of the formed elements contained in
the intestine. It is, however, possible to precipitate the ferment from
intestinal juice, and then obtain a watery solution of the precipitate
which will invert sugar. The intestinal juices will also dissolve proteids,
albumen, and fibrin, and convert them into peptone, after first passing
through a stage similar to that of alkali albumen. The action of the
intestinal juices resembles that of the pancreatic secretion in its general
characters and in the resolution of the fibrin peptone into leucin and
tyrosin and indol. The ferment which is concerned in the digestion of pro-
teids is apparently either not carried down by the alcohol, or is not capable
of resolution in water, for all the author's experiments failed in obtaining
an active solution of the ferment in water, acid, or alkali after precipi-
tation with alcohol. When fibrin is digested by the intestinal juices, a
peculiar substance is formed, which gives a red with nitric acid, the color
disappearing on heating.

IV. FERMENTATION PROCESSES IN THE SMALL INTESTINE. — In the
small intestine are found numerous examples of the lower organisms
which enter the alimentary canal through the foods and liquids which
are swallowed, and which induce various fermentations and putre-
factions in the contents of the alimentary canal, resulting in the evolu-
tion of various gases. These gases consist, in the first place, of air, which
is swallowed with the food, of which a large portion of the oxj^gen is

DIGESTION IN THE SMALL INTESTINE. 419

absorbed, while the nitrogen remains unaltered. Therefore, the oxygen
will be in smaller relative proportion, as contrasted with the nitrogen,
than is found in the atmosphere; the carbon dioxide, which is also
present, will, on the other hand, be in relative excess, since a certain
quantity of this gas diffuses from the venous blood into the interior of
the alimentary canal. Hydrogen, ammonia, and carburetted and sulphu-
retted hydrogen are also found as the results of various decompositions.

Y. INTESTINAL DIGESTION IN DIFFERENT ANIMALS. — The contents
of the stomach do not pass suddenly, but gradually, into the small
intestine, their entrance into this portion of the alimentary canal
not being due to the forcible contraction of the stomach, but to a
series of periodic relaxations of the pylorus, as a result of special
stimuli ; during the intervals, the pylorus is tightly closed. Transition
into the intestine rarely occurs before digestion has. made considerable
advances; the necessary stimuli, therefore, cannot be of a purely
mechanical nature, especially as it has been found- that mechanical stimuli
lead to more marked contraction of the p}'loric ring rather than to its
relaxation. The stimulus which leads to a relaxation of the pyloric
sphincter is probabty of a chemical nature, but its exact mode of opera-
tion is entirely unknown. It would seem, however, that fat is almost
incapable of causing an opening of the pylorus, for, no matter how much
fat be given in the food, nearly the same amount will be found in the
intestine after four, five, or twent3'-one hours, showing that the pylorus
allows no more to pass than may be taken up by the villi ; therefore,
there is never an accumulation of fat in the intestine.

If, during the latter stage of gastric digestion, a transverse section
is made through the duodenum, on the mucous surface will be found a
white, pasty emulsion ; then comes a yellowish, cheesy precipitate, pro-
duced by the bile, and in the centre will be found a thin, j^ellowish-brown
liquid, containing particles of undigested food. If such a section be
made still lower down in the intestine, further from the stomach, the
fatty layer will be found to have decreased in amount, while the central
fluid will be relatively more abundant, and becomes darker and darker
in color, until at the lower portion of the small intestine it is of a deep-
green color. Some of the fluid constituents contain many gas-bubbles.
The central fluid has alwajrs a more strongly acid or less alkaline reac-
tion than the portion of the intestinal contents in contact with the
intestinal walls.

As we have seen, the chyme, as it issues from the stomach, is sub-
jected to the action of the intestinal secretions before being ready for
absorption. The character of the chyme, as indicating the-character of
the digestive processes, varies in different animals, and has been closely
studied by Colin, whose description is here mainly followed. In

420 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

carnivora the chyme is scanty, gradually giving up matters ready for
absorption, and passes slowly through the intestine. Thus, seven to
eight hours after a meal of one thousand grammes of meat, only fifty to
one hundred grammes represent the weight of intestinal contents. The
small intestine in carnivora is never distended, as in the case of the
omnivora, and especially the herbivora, but it is always a flattened
cylinder. The stomach appears to regulate the amount which passes
into the small intestine. The small intestine in non-ruminant herbivora,
as the horse, receives large volumes of chyme from the stomach, and
rapidly disperses it through the entire small intestine ; but although
the small intestine has a capacity four times as great as the stomach,
it never contains as much as may be contained in the stomach when
distended, for after a meal the contents of the stomach are rapidly
distributed between the small intestine, stomach, and caecum. If the
contents of the small intestine of the horse be examined at various
intervals after feeding, it will be found that 40 to 50 per cent, of the
carbohydrates in the food have been digested in the stomach, while
30 to 50 per cent, of the albuminoids and 40 to 60 per cent, of the
non-nitrogenous constituents may still be recognized.

In the horse, the fluid found in the duodenum and jejunum is usually
acid in reaction, yellowish in color, turbid, and viscid. It is capable of
digesting proteids and starch, and its ferments may be precipitated by
alcohol and redissolved in water without losing their activit}^. In the
ileum the contents are usually alkaline in reaction, brownish-yellow in
color from the bile-pigments, turbid, but contain less mucin than the
duodenal contents. Intestinal digestion in the horse is of considerable
importance ; only from 23 to 52 per cent, of undigested albumen and
from 38 to 59 per cent, of undigested carbohydrates are to be found in
the duodenum, although there can be no doubt but that large amounts
of entirely undigested food pass from the stomach into the small intes-
tine. When the food has a prolonged sojourn in the stomach but 2 to
10 per cent, of its proteid constituents ma}^ be left untouched for diges-
tion by the intestinal secretions, but where this is not the case it may be
safely stated that at least 60 per cent, of the proteids have to be digested
in the small intestine. These facts would -seem to. indicate that in soli-
pedes digestion is almost continuous. In ruminant herbivora the state
of affairs is different ; there, the contents of the intestine only represent
one-eighth to one-tenth the amount contained in the stomach, and when
rumination is suspended but a comparatively small part of the food
remains unchanged to be acted on by the intestinal secretions. In car-
nivora, still another state of affairs occurs. The stomach holds almost
all the alimentary matter, only small quantities of liquefied chyme pass-
ing into the intestine, and as the gastric digestion in these animals is

DIGESTION IN THE SMALL INTESTINE. 421

very complete the contents of the small intestine amount to only one-
tenth or one-twentieth of the gastric contents. Aliments more or less
liquefied, according to the quantity of fluid contained in the alimentary
tract, present a different character iii each portion of the intestinal tube.
In solipedes, for example, in the small intestine they are mixed with a
thick, yellowish, viscid fluid; in the caecum they are suspended in a large
amount of fluid not deprived of viscidity ; in the great fixed colon they
are still soft, but as the floating colon is approached they acquire pro-
gressive dryness and are moulded into balls, which stick to the valvulae
conniventes.

The bile of the hog, as has been mentioned, contains no amylolytic
ferment, but is capable of emulsifying rancid fats. The intestinal juice,
according to Ellenberger and Hofmeister, contains a diastatic but no other
ferment, a statement which, in view of the general presence of the invert
ferment in the secretion, needs confirmation. The pancreatic juice con-
tains three ferments, and is, therefore, possessed of the same properties
as in other mammals. Consequently, in the intestinal canal of the hog,
albuminoids are peptonized, starch converted into sugar, and fats
digested and emulsified. Absorption in these animals is exceptionally
rapid, so that examination of the intestinal contents will reveal but
small amounts of digestive products. Peptone, espeeiall}-, seems to be
absorbed as rapidly as it is formed, while 69 to 75 per cent, of the
albuminous food-stuffs and 65 to 72 per cent, of the carbohydrates found
in the small intestine has been digested.

The reaction of the small intestine of the hog is usually acid through-
out half its extent, the acidity sometimes extending through five-sixths
its length.

After feeding, the first portions of the meal appear in the small intes-
tine in from three to four hours, while three hours later a portion of the
intestinal contents has already reached the caecum. Intestinal diges-
tion, therefore, in the hog is of but short duration.

One is accustomed to speak of the reaction of the small intestine as
self-evidently alkaline, and it is almost universally taught that as soon
as the acid chyme enters the duodenum its acid reaction, through
the influence of the bile and pancreatic juice and intestinal secretion,
at once passes into an alkaline reaction. This, however, is an error. As
a rule, an alkaline reaction is rarely met with until the very lowest por-
tion of the ileum is reached. It has been already mentioned that the
acid chyme produces precipitation in the bile, the glycocholate of sodium,
glycocholic acid, and mucin being carried down, while the acid reaction
is still maintained, and that this precipitate carries the pepsin mechan-
ically down with it. The importance of this is seen when it is remem-
bered that in acid solutions pepsin will destroy the pancreatic ferments.

422 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The pepsin is only released when the strongly alkaline reaction of the
lower portion of the small intestine dissolves the bile precipitate. It
can then do no harm, as pepsin is inactive in alkaline solutions; while, on
the other hand, the acid does not interfere with the pancreatic digestion,
since the pancreatic ferments are still capable of producing their charac-
teristic effects, even in a faintly acid medium.

The acid reaction of the small intestine is most marked in carniv-
orous animals, and in them, consequent^, putrefactive and fermentative
changes occur to a less degree than in omnivora and herbivora. In the
fasting horse the contents of the small intestine are invariably alkaline,
this reaction being more marked the greater the distance from the stom-
ach. In digesting animals, the acid reaction decreases below the point
of entrance of the bile and pancreatic juice, and becomes decidedly alka-
line at the lower portion of the small intestine. This holds in the horse,
ox, and sheep, whether fed on dried or green fodder, on oats, grain, or
roots. The cause of the alkalinity of the reaction of the intestinal con-
tents is due to the bile, pancreatic juice, and intestinal secretions, and is
more marked the more active is intestinal digestion. The acidity of the
intestinal contents when present is due not only to the acid gastric
juice, but also to the liberation of fatty and lactic acids from lactic and
butyric acid fermentations.

It is seen from the above that in the small intestine secretions are
met with which are capable of establishing digestion of the various food-
stuffs, so as to render them capable of absorption. Starch becomes con-
verted into sugar through the action of the pancreatic and intestinal
secretions ; cane-sugar is converted into invert-sugar through the action
of the special ferment of the intestinal secretion; fats are partially
saponified and emulsified through the influence of the bile and pancreatic
juice, while albuminoids, through the influence of the pancreatic and
intestinal fluids, are turned into peptones.

As regards the changes which occur in albuminoids in the small
intestine, it is worthy of note that in all probability the formation of
leucin and tyrosin has been greatly overestimated, for since the intestinal
juices are almost always acid, and since leucin and tyrosin only form
in alkaline digestive juices, perhaps these bodies never form normally in
the intestine. It is, at any rate, certain that but mere traces of leucin
and tyrosin are to be found in the intestinal contents during digestion
of large amounts of albumen. It is also worthy of note that the acid
reaction of the intestine does not interfere with the digestion of fats, for
the lacteals will be found filled with a milky emulsion after feeding, even
though the reaction of the intestinal contents is almost as acid as the
gastric juice.

At the lower end of the small intestine the reaction of the intestinal

DIGESTION IN THE LARGE INTESTINE. 423

contents is usually strongly alkaline, and we have then to deal with
processes which are evidently putrefactive in nature. But a small
portion of the nutritive parts of food will, however, be subjected to
these changes, since probably digestion, especialty in carnivora and
ruminants, is completed before this portion of the tract is reached.
Indol and phenol are here found, and result from the putrefactive changes
in albuminoids, while lactic acid, butyric acid, acetic acid, carbonic acid,
and hydrogen are met with and result from changes in carbohyd rates.
The different gases found in the small intestine have been already men-
tioned ; their character and amounts vary according to the nature of the
diet.

The following table represents their relative amount from different
diets in dogs : —

CO2. N. H. O.

Meat diet, . . . 40.1 45.5 13.9 0.5

Bread diet, . ... 38.8 54.2 6.3 0.7

Vegetable diet, . .47.3 4.0 48.7

X. DIGESTION IN THE LARGE INTESTINE.

The absorption of all the alimentary elements which are essential to
nutrition is in the carnivora achieved in the small intestine. In these
animals the caecum is absent or rudimentary, and the colon is short and
apparently uncomplicated ; but in the immense caecum of solipedes and
certain other herbivora the digestive process goes on, and the changes
which the food undergoes in this part of the alimentary tract now
deserve attention.

1. THE FUNCTIONS OF THE CAECUM. — The caecum, or blind gut, is that
portion of the large intestine which usually occurs as a diverticulum at
the point of junction of the small and large intestines, and in which the
contents of the former empty. In man and carnivora this reservoir is
rudimentary, and receives the alimentary mass after all its nutritive
properties have been extracted. In this class of animals, therefore,
the caecum can have no physiological function to fulfill. In reptiles,
batrachians, and the fish the small intestine is directly continuous with
the large intestine, scarcely increasing in diameter, and no caecal append-
age is present, the reservoir only being represented by a long, lateral
dilatation. It is only in mammals and in birds that one or two pouches
are found at the point of union of the small and large intestines, and
which furnish a new reservoir to the alimentary matters before permitting
them to enter into the large intestine to be finally expelled.

In birds, the caecum varies in development and importance according
to their normal diet. In the flesh-eating birds, the stomach and small
intestine are amply sufficient to produce the necessary chemical trans-
formations in the food to render it capable of being absorbed. Their

424 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

caeca are consequent^ rudimentary or absent. In vegetable-eating birds,
on the other hand, the caecum acquires a high degree of importance.
The caecal apparatus in these animals is double, and consists of two long
tubes, symmetrically located to the right and left, and connected with
the alimentary canal at the point of junction of the small and large
intestines. Their mucous membrane is arranged in folds, so as to
increase their internal surfaces. Their internal surface is supplied with
glands, which secrete a fluid, and with villi, which facilitate absorption.
While it thus would appear that in these animals, as we find it the case
in mammals, the development of the caecum is in proportion to the com-
plexity of the food, there are, nevertheless, certain exceptions to this
rule. In the nocturnal birds of prey the caecum is highly developed.
This is, perhaps, to be explained from the fact that it acts as a compen-
sation to the extreme shortness of the intestinal canal in this species.
On the other hand, in the gallinaceous birds the caecum is voluminous,
and yet in the pigeon it is entirely absent. This latter fact is, perhaps,
to be explained by the statement that in the pigeon the starchy mat-
ters are completely digested before the caecum is reached, while such
is not the case in the gallinaceae. Moreover, in the pigeon the crop is
double, so, perhaps, acting as a substitute for the caecum. In mammals,
also, the caecum varies in importance according to the character of the
substances with which they are nourished. In carnivora, such as the
dog and cat, whose foods are readily digestible and assimilable,
the caecum is absent or rudimentary. Its structure is analogous to the
large intestine ; that is to say, this organ forms part of the excretory
portion of the alimentary canal. The herbivora, on the other hand, find
their food in substances which are poor in nutritious principles, and in
which the nutritive matters are inclosed in resisting cellulose envelopes.
As a consequence, we find the digestive apparatus in these animals
reaching a high degree of perfection. Their apparatus of mastication is
complete; their salivary secretion abundant. Their intestine is extremely
long and of considerable volume, so as to multiply the secretory and
absorbent surfaces and prolong the action of the digestive juices.

We find in the ruminants a complex and voluminous stomach, where
the food is delayed for a considerable time before being subjected to the
action of the solvent juices : but in the horse and rabbit the stomach is
simple and small, and we find in the highly developed ca?cum a sub-
stitute for the voluminous gastric pouches of the ruminant. In these
animals the caecum takes on the form of an immense pocket, whose
length may exceed that of the body, and whose capacity may be two
or three times greater than that of the stomach, while its volume is
so great as to cause it to occupy the greater part of the abdominal
cavity. In structure, also, the caecum no longer resembles that of the

DIGESTION IN THE LAEGE INTESTINE. 425

larger intestine, but more nearly approaches that of the small intestine.
In it are found numerous folds of mucous membrane, villi, glands and
follicles, and large lymphatics.

Comparative anatomy thus shows that in all animals whose diet is
composed of substances difficult to digest and rich in cellulose, the
caecum is nighty developed, if some other organ is not specialized for
this purpose, as in ruminants. While its volume is proportionate to the
volume of food which these animals require for their nourishment, while
it is absent in the sable and those of the bear tribe which nourish them-
selves on fruits or substances easily digested, and while it is slightly
developed in the carnivora and herbivora which feed on tender plants, it
is highly developed and acquires a value closely allied to that of the
stomach in animals whose ordinary food is composed of bulky vegetable
substances difficult to digest. Such a state of affairs is seen in most of
the rodents. It reaches its maximum development in the solipedes, the
rhinoceros, and some herbivorous marsupials. Its development, again, is
not only dependent upon the degree of the digestibility of the food, but
it is inverse with the size of the stomach (hence its great size in soli-
pedes) and with the presence of special organs to facilitate gastric diges-
tion (hence its small size in ruminants). In cases, therefore, where we
have a voluminous stomach provided with an extensive mucous mem-
brane and followed by a long small intestine, we may be sure the caecum
will be poorly developed. These facts prove that the caecum is a com-
pensatory organ to the stomach, and that the development of the two is
in inverse ratio.

Apart from the oesophageal dilatations of the ruminant, we have
certain other animals in which annexes to the alimentary tube serve to
assist in the digestion of almost indigestible food. These annexes may
replace the cesophageal pouches and caecum. Thus, we have in birds the
crop, analogous to the ruminant's pouches, highly developed in pigeons,
chickens, and geese, with the addition of a muscular, crushing stomach.
In these birds, with the exception of the pigeon, the caecum is also
present, and all together are needed for the digestion of foods. Here
the apparatus of mastication is absent. The crop, gizzard, and caeca all
fulfill the same end. In the solipedes, again, the caecum therefore fulfills
the same, general functions as the pouches of the ruminant's stomach,
which again are analogous to the crop of the gallinaceous birds.

Most of the earlier phj'siologists regard the caecum as a second
stomach from some obscure analogy of form, and from the fact that its
contents were said to be almost invariabty acid. This theory as to the
analogy of the functions of the caecum and stomach held until it was
discovered that the glands of the caecum, instead of secreting an acid
fluid, poured out an alkaline secretion like that coming from the glands

426 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of Lieberkiilm ; but just as the caecum is the recipient of the contents of
the ileum, and this often has an acid reaction, so may the contents of the
caecum be acid, especially in carnivorous animals, a fact which may serve
to illustrate the error of applying results found in carnivora to similar
functions in herbivora, where the processes are evidently different.

Colin claims that the reaction of the contents of the caecum in the
horse is almost invariably alkaline, and that to a greater degree than in
the small intestine, whether the animal be digesting or fasting. When
an acid reaction has been found in this cavity it is almost invariably to be
explained as due to acid fermentations occurring in the- food-constituents.

Ellenberger shows that the caecum has a special value in the horse.
In this animal, as we know, the small intestine is comparatively small,
with a relatively small extent of digestive mucous membrane. The
stomach is so small that it cannot contain the amount taken at one
meal, so the stomach forces its contents into the intestine even while the
animal is eating ; gastric digestion is, therefore, imperfect in these
animals. But, as the horse is nourished on substances which are diffi-
cult of digestion, it should possess a special digestive organ, which, by
its activity, should compensate for the loss of functional activity in the
stomach. Nothing can be more natural than to suppose that this sup-
plementary organ is found in the vast caecum of these animals, and wre
may admit that this is to a certain extent true, without being compelled
to acknowledge that this organ liberates an acid digestive secretion.
The caecum is, hence, of special importance in the monogastric herbivora,
where the small size of the stomach prevents accumulation of food and
drink. It is, therefore, a reservoir for intestinal digestion.

Its anatomical arrangement leads to the retaining of its contents.
Its bottom corresponds to the region of the xyphoid appendage, while
its narrow opening into the colon is in the most superior part, so that
everything to enter the colon must be forced up against gravity, and
should desiccation of its contents occur obstruction is sure to result,
and the result is apt to be fatal. In length it is about one meter, while
its capacity is from thirty-two to thirty-eight liters, or nearly twice as
large as the stomach. It has an extensive mucous membrane, well sup-
plied with glands, like the duodenal follicles (Fig. 164).

Ellenberger reports a number of experiments which he made on the
horse to determine the length of time the food remains in the caecum
and the alterations to which it is subjected there. To determine this, he
fed a series of horses during a certain number of da}<s with a certain
amount of food of known composition ; the animals were then killed at
given periods, and the contents of the intestine examined.

The results of these experiments showed that they might be divided
into four groups, according to the nature of the food given.

DIGESTION IN THE LARGE INTESTINE.

427

FIG. 164.— C-S:CUM OF THE HORSE. (Colin.)
A, caecum ; B, ileum ; C, colon.

428 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Thus, when dried peas are given, traces of them are to be found in
the caecum after the lapse of twelve hours. After twenty -four hours
grain and dry forage are still to be found in the caecum, and after thirty
hours chopped hay still remains in the caecum. After seventy -two hours
the greater part of the hay had alread}^ passed into the colon. Thus, in
resume, twelve hours after feeding, forage is to be found in the stomach,
with some traces in the jejunum and caecum; after twenty-four hours,
principally in the caecum, with a certain amount of residue in the jejunum ;
after forty-eight hours, in the ventral colon, with some debris in the
caecum; after seventy-two hours, in the dorsal colon; and after ninety
hours, in part in the dorsal colon and rectum.

As regards the functions of the caecum, it would appear that after
twelve hours already traces of food are to be found in the caecum, and
after twenty -four hours nearly all the alimentary mass has arrived at the
caecum, in which some is still to be found after forty -eight hours. Food,
therefore, usually remains twent3r-four hours in the caecum of the horse.
The contents are always alkaline, highly fluid, and of a special odor.
The color varies with the nature of the food.

From the fact that a larger amount of undigested food is found in
the caecum than in the colon, it follows that digestion must take place in
the caecum, its extent being placed by Ellenberger at from 10 to 30 per
cent, of the food ; the nature of this action is determined by examination
of the caecal contents.

The acid reaction of the stomach and upper portion of the intestine
gives place to an alkaline reaction in the lower portion of the ileum, and
that of the caecum is invariably alkaline. In the colon, again, the reac-
tion may become acid from fermentative changes in food.

Digestive changes are, therefore, merely the continuation of the
ordinary intestinal digestion.

Bureau has succeeded in obtaining a secretion from the caecum of
the rabbit, but in such small amount as contrasted with the quantity ob-
tained from the small intestine by the same method (double ligature) that
he concludes that the digestive processes occurring in the caecum are due
to the action of the intestinal fluids which come down from above.

In the duck, however, by ligating the caecum, after introducing small
fragments of cooked meat, a large amount of clear alkaline fluid may be
obtained, although the morsel of meat will have remained unaltered.
This fluid is said to have the power of converting starch into sugar, but
is without action on other food-stuffs.

By making caecal fistulae in rabbits, Bureau found, in the first place,
that the reaction was invariably alkaline. Raw meat appeared to be
unchanged in the caecum, while cooked meat becomes somewhat softened
and reduced in volume. Boiled starch is converted into sugar.

DIGESTION IN THE LAKGE INTESTINE. 429

Ligation of caeca in chickens caused diarrhoea, loss of flesh, and
death from inanition.

The most important function of the crecum is, in all probabilit}^, to
be found in the digestion of cellulose, which occurs in it. It is well
known that from 30 to 40 per cent, of cellulose disappears in passing
through the intestinal canal of the horse, and the poorer the food is in
true nutritive substances the greater will be the amount of cellulose
digested. Experiment has proven that the saliva, gastric juice, and
pancreatic secretion are entirely inactive on cellulose. On the other
hand, the fluids collected from the small intestine of a newly killed
horse have been found to dissolve from 40 to 78 per cent, of cellulose
(Hofmeister), and this power is lost when these fluids are previously
boiled, indicating the probable dependence of this digestive process on a
true ferment. Admitting these facts, the share which the caecum bears
in digesting cellulose is evident; it acts as a reservoir for fluids and
undigested food-stuffs coming down from above, and by its reaction,
temperature, etc., favors fermentative changes.

The nature of the substances resulting from the digestion of cellu-
lose are clouded in obscurity : the most natural presumption would be
that it was converted into sugar, but no experimental proof of this has
ever been adduced, though it is generally assumed that the cellulose in
digestion is changed into some nutritive substance, which is absorbed.
According to this, cellulose should be classed among the food-stuffs.
Unfortunately, this also does not admit of proof. It is well known that
in fermenting cellulose may be converted into marsh-gas, and Hofmeis-
ter's experiments seem to prove that the substance resulting from the
digestion of cellulose by the intestinal fluids of the horse is gaseous in
nature. While this may be so, and there is no denying that the gas may
be met with in the alimentary canal, it does not follow that all the
digested cellulose is converted into marsh-gas. For, as Ellenberger has
pointed out, we often meet with a lactic acid fermentation of sugar in
the stomach and intestine, but do not infer from that that all the sugar
which disappears from the alimentary canal has been converted into
lactic acid. The case may be similar with cellulose ; when in excess, or
not needed, it may and probably is converted into marsh-gas; when
needed by the economy, it is absorbed in some soluble form, probably of
the nature of a sugar. This view is supported by the fact already
alluded to, that the poorer the food the greater the quantity of cellulose
which disappears.

2. THE FUNCTIONS OF THE COLON. — The colon in the carnivora con-
stitutes a simple reservoir for excrementitious matters, and in the her-
bivora it is doubtful if it has a more important role to perform in the
digestive elaboration of food. In the walls of the large intestine are

430

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

found follicular glands, apparently similar to those in the small intestine,
and which furnish a secretion which it is claimed will turn starch into
sugar and albumen into peptone. The latter statement, which is made
by Thanhoffer, seems to need confirmation. It is, at any rate, clear that
the degree of digestion occurring in the large intestine must be slight,
since the greater part of the food-stuffs which reach the large intestine
have already undergone complete solution in the upper portion of the
alimentary canal. In the large intestine in carnivora the contents of the

FIG. 165.— CAECUM AND GREAT COLON OF THE HORSE. (Strangeways.)

A, caecum: B C, its muscular bands; D, termination of ileum; E, first, E', second, F, third, and
F', fourth divisions of colon : G, pelvic flexure ; H, origin of floating colon. The arrows indicate the
course of the food through the colon.

alimentary tube undergo no further digestive changes, but become more
condensed from the rapid absorption of water and other fluids which
takes place through its walls. In the solipedes the large intestine is par-
ticularly active as an absorbent, removing water and various fluids
secreted by the upper portions of the alimentary tube and the alimentary

DIGESTION IN THE LARGE INTESTINE.

431

principles which have escaped absorption in the small intestine. Its
enormous capacity, five or six times that of the stomach, enables it to
retain immense quantities of materials which move slowty, and which

FIG. 166,— INTESTINAL CANAI, OF THE Ox. (Mitller.)

a, duodenum : 6 and r, jejunum and ilenm : d, caecum ; e, colon, with its various convolutions : /, rectum ;
g, commencement of colon ; TO, mesentery of large intestine; m>, mesentery of small intestine.

are brought in contact with an immense extent of mucous membrane.
The contents enter by a narrow and valvular opening, and descend first

432 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to the substernal curvature, then they mount to the pelvic curvature,
which is always higher than the sternal curvature, and then up the dia-
phragmatic curvature, and finally descend abruptly, passing by the left
kidney to enter the convolutions of the floating colon, where they make
two ascents and two descents (Fig. 165).

The large intestine of the ox is shown in Fig. 166.

The interior arrangement of the colon consists in the formation of
pockets, in which portions of the contents remain temporarily, while the
centre of the gut is free. The disposition of certain parts of the colon
leads to a difference in the physical characters of its contents at different
points. The diaphragmatic curvature, on account of its dependent posi-
tion, contains large volumes of liquid, in which certain salts are abundant,
such as ammonio-phosphate of magnesium, especially after oat diet, and
in this localit}7 these salts are often deposited as intestinal calculi.

Digestion in the large intestine caunot, therefore, be said to take
place, although absorption is highly active, and numerous cases are on
record in which life has been preserved through the absorption by the
walls of the large intestine alone of alimentary substances introduced
into the rectum. In the large intestine complex fermentations take
place, and true decomposition frequently occurs in the contents of this
portion of the alimentary tube, especially when the reaction is alkaline.
Man}^ of the gases, such as oxygen and nitrogen, which are found here
have probably entered with the food ; others are derived from different
fermentations ; thus, for example, hydrogen is liberated in the butyric
acid fermentation, sulphuretted hydrogen and ammonia from the putre-
faction of animal substances.

XI. THE COMPARATIVE DIGESTIBILITY OF DIFFERENT FOOD-STUFFS.

The quantity and chemical composition of the faeces is of special
interest on account of the insight which it permits as to the degree of
digestibility and convertibility of the different food-stuffs, for it is evi-
dent that if we know the amount and composition of any food given to
an animal for a series of days, the loss of these materials, determined by
an analysis of the faeces, will indicate within certain limits the amount
which has been digested and absorbed in its passage through the bod}-.
In making these calculations, however, it must be remembered that a
large amount of fluid is added to the food in the form of the digestive
juices, which, to be sure, is again largely absorbed ; but we have further
seen that certain excretory ingredients have been added to the faeces,
and, further, that the different food-stuffs may undergo decompositions
other than digestive in the alimentary tract. The digestive processes,
as we have seen, are of the same nature in all our domestic animals,
simply varying in degree. This difference we have also seen to be due to

COMPARATIVE DIGESTIBILITY OF FOOD-STUFFS. 433

the different degrees of perfection with which mastication is accom-
plished, to differences of construction in the alimentary canal, different
constitutions, and the different degrees of concentration of the digestive
juices. Thus, the herbivora, through the high development of their
molar teeth, the roomy and long digestive eanal, and large amounts of
amylolytic ferments in their digestive secretions, are especially suited for
digesting carbol^drates. Their gastric juice is comparatively poor in
acid, and, as a consequence, prevents their living on a highly albuminous
diet ; while the highly alkaline nature of their intestinal contents facili-
tates putrefactive changes in albuminoids, the characteristic results of
such fermentations being met with in large amounts in their urine. In
the carnivora, on the other hand, we find a short and less capacious
intestinal canal, with a relatively voluminous stomach and an active acid
gastric secretion, thus fitting them for the digestion of albumen, while
the conditions for the digestion of carboh}rdrates are less favorable.

Omnivora naturally occupy a mean between these two classes. It
is to be remembered, however, that as long as animals are fed on their
mothers' milk there is no difference in the digestive act in the carnivora
or in the herbivora.

Not all the nutritive substances which are contained in the food are
actually digested, but a considerable proportion, under the most favorable
circumstances, is apt to remain undigested and pass unchanged into the
faeces. The cause of this is frequently to be found in the fact that the
food is taken in such quantities that the amount of digestive secretion
poured out by the alimentary tract is insufficient to act upon it. There
appears to be, again, a limit of absorbability even of the amount of food
digested. This limit, of course, varies in each group of, animals, and the
residue of food, even though it may be digested, remains unabsorbed in
the alimentary canal to undergo breaking down into various decompo-
sition products, such as leucin, tyrosin, etc. Again, another cause for
indigestibilit}' of food is to be found in the fact that in many cases,
especially in the food of the herbivora, the nutritive principles are con-
tained in resisting envelopes which are impermeable to the digestive
secretions, and which require mechanical comminution in mastication
before being accessible to the act of digestion. Imperfect mastication,
therefore, from whatever cause, will reduce the digestibility of food. By
this term, digestibility of food, is meant the amount of any food-stuff
which through digestion is rendered capable of absorption and does
actually enter the blood, in proportion to the amount which remains
undigested or which is not so absorbed. This quantity, which may be
termed the co-efficient of digestion, varies according to the composition
of food and to the mode of digestion of different classes of animals. We
will, therefore, allude to these sources of variation in turn : —

434 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

First. Vegetable fibre is capable of being digested to a more or
less degree by all herbivora and even to a certain extent by the hog, the
co-efficient of digestion lying, in green and dry fodders, between 45 and 75
per cent. In vegetable foods, such as grains, roots, and bulbs, and the
artificial nutritive substances made from such materials, all of which are
rich in cellulose, the digestibility becomes greatly reduced, and, in fact,
many such products may be said to be entirely undigestible. It is prob-
able, again, as already mentioned, that a certain amount of cellulose
which disappears in its passage through the intestinal canal may be ex-
plained as due to the development of carburetted hydrogen and carbon
dioxide and other fermentations.

Second. The non-nitrogenous extractive matters, as found in beets
and potatoes and seeds, are almost completely digested, only about
2 per cent, escaping the action of the digestive fluids, though in green
fodders the digestive co-efficient of these materials may sink from 84 to
48 per cent. In this connection the remarkable fact appears that the
amount of soluble non-nitrogenous food-constituents which undergoes
digestion, together with the amount of cellulose which is digested, almost
exactly equal the total sum of non-nitrogenous extractive matters found
in the food, and in this we have, therefore, a means of estimating the
quantity of non-nitrogenous extractive matters actually digested and
absorbed. The digestible portion of the non-nitrogenous extractive
matters in any food may be estimated in nutritive value as pure carbo-
hydrate, and therefore compared with starch.

Third. As regards fat, it may be stated that, when perfectly pure,
fat is entirely digested, but since fat in the ordinary foods is not pure
and contains other indigestible constituents, it is evident that the digest-
ive co-efficient of fat will be subject to great variation. In clover and
various oil-cakes this co-efficient varies between 80 and 90 per cent.; in
seeds, between 60 and 90 per cent. In beets and potatoes fat may be
regarded as entirely digested, while, on the other hand, the fat in green
foods, although present in smaller amount, still varies in digestibility
through very wide limits. Thus, 80 per cent, may be absorbed, or only
20 per cent. In general, in this connection, clover is more readily
digested than grasses, while straw of the hulled fruits is more digestible
than the straw of the hulled cereals.

Fourth. The nitrogenous constituents of the food are generally
regarded as albumen, although, of course, other nitrogenous materials
are often constituents of foods. In beets and potatoes albuminous
matters are, as a rule, entirely digested, in seeds a certain amount
escapes, the co-efficient of digestion varying from 60 to 90 per cent. In
green and dried fodder great variation is met with, the co-efficient of
absorption varying between 17 to 75 per cent., as a rule, the digestibility

COMPAKATIYE DIGESTIBILITY OF FOOD-STUFFS. 435

of albuminous matters being greater in the green than in the dry fodder,
even though of the same material ; while still further the statement
may be made that the larger the relative proportion of albuminous matter
and the smaller the amount of the cellulose, the greater will be the amount
of albuminous matter digested.

Fifth. The digestive co-efficient of the different food-stuffs may be
altered through the addition to the food of different nutritive substances.
Thus, it has been shown that the administration of a readily digestible
albuminous diet is without influence on the co-efficient of digestion of
the other foods; but, on the other hand, the addition of starch or sugar
will reduce the digestive co-efficient of the albuminous bodies when the
amount of carbohydrates given exceeds by 15 per cent, the solids of the
other food-stuffs. This depression of digestibility is especially marked
in the dry foods. A similar result is also manifested when beets and pota-
toes are added. The addition of oil is without influence on the digestive
co-efficient so long as it is not given in great amounts. When the amount
given exceeds the proportion of one-tenth gramme to one kilogramme of
body weight, slight disturbances of digestibility are readily produced.
When the food is composed of several nutritive substances combined,
the proportion of the nitrogenous and the non-nitrogenous constituents
of the total amount is of great influence on the digestibilit}^ This
nutritive relationship of the non-nitrogenous substances is found by
adding the amount of fat to the sum of the non-nitrogenous extractive
matters, the amount of cellulose being excluded. Ordinarily the amount
of fat is multiplied by two and four-tenths or two and five-tenths, and
this product then added to the amount of extractive matters, — a pro-
cedure which is, however, apt to give an erroneous idea as to the nutri-
tive value of the fat.

The general result may be stated that a food is readily digestible
when the proportion between nitrogenous and non-nitrogenous con-
stituents varies from 1 : 5 to 1 : 7. An increase of this proportion causes
a certain amount of the non-nitrogenous constituents to remain undi-
gested while an increase of the nitrogenous substances causes a waste.
It is evident that the above statement as to the digestibility of food may
be only regarded as in general true. Each group of animals will possess
special facilities for digesting special foods ; these will deserve considera-
tion in turn.

As might be expected, the time required for undigested food to
appear as faeces after feeding very closely corresponds in different
animals with the comparative length of the intestinal canal. Thus, it
has been found that in oxen fed with oat-straw the first traces appear in
the fneces about thirty-six hours after feeding, and disappear after seventy-
two to ninety-six hours, while in the goat seven days were required after

436 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

giving certain food for its traces to disappear from the faeces. In the calf
three days were required for the removal of traces of a previous meal of
barley, while four days 'were required for an ox under the same condi-
tions. In the sheep fed with hay, it has been determined that the food
remains 20 hours in the first three stomachs, and in the fourth stomach
1.2 hours; in small intestine, 2.3 hours; in caecum, 7 hours; and in colon,
5.5 hours; or, in all, 36 hours before appearing as faeces.

Carnivora fed on pure flesh diet produced but little faeces. A dog
weighing thirty-five kilos, and fed with a half to two and a half kilos of
meat, produces from twenty-seven to forty grammes of faeces, in which
there will be only nine to twenty-one grammes of solids ; therefore it
may be said that with a flesh diet only 1 per cent, of the amount of solids
taken with the food escapes from the body in the form of faeces.

Omnivora form considerably larger amounts of faeces. Animals
living on a mixed animal and vegetable diet, like man, will pass daily
about one hundred and thirty grammes of faeces, containing thirty-four
grammes of solids, which will represent about 5 per cent, of the solids
taken as food. When the vegetable diet is in excess, this may rise to
13 per cent., so that only seven-eighths of the solids are finally absorbed.
Hogs pass in their faeces only about 20 per cent, of mixed matter taken
in food. However, when fed on sour milk, with beans and peas, only
about 1 per cent, escapes absorption. So, also, according to Wolff, pigs
digest almost completely the residue remaining after making meat ex-
tracts. The hog is able to digest both vegetable and animal matter,
and is claimed to be capable of digesting fully 50 per cent, of cellulose.

The following table gives the percentage of constituents absorbed in
hogs fed with sour milk : —

Albumen, 96.06 percent.

Non-nitrogenous substances, . . .98.90 "
Inorganic matter, 64.46 "

So, also, of the following vegetable foods, the figures indicate the
amount digested and absorbed : —

Horse-beans,
Peas, .
Oats, .
Barley,
Rye, .

99.8 per cent.
99.7 "
98.7 "
92.7 "
90.7 "

The largest amount of faeces is formed by the herbivorous animals.
In the horse and ox, of one hundred parts of food about 40 per cent., as
a rule, escapes unchanged in the faeces, so that only three-fifths of the
food swallowed serves any nutritive purpose. This follows from the
fact that a large part of vegetable food is absolutely indigestible, and all
is very difficult of digestion. The horse, as a rule, digests a smaller pro-
portion of dry fodder than does the ox.

COMPAKATIVE DIGESTIBILITY OF FOOD-STUFFS. 437

• As a rule, it may be stated that the ox is capable of digesting the
following amounts: —

Albuminoids. Cellulose.

Oats, . 49 per cent. 55 per cent. 44 per cent.

Wheat-straw, 26 52 39

Bean-straw, 51 " 36 •" 62

Clover-straw, 51 «' 39 «« 67

Barley-hay, 60 " 60 '* 67 "

Henneberg has found that the digestibility of a fodder is altered
when a second nutritive substance is added to it. Thus, the digestibility
of any fodder is reduced by the addition of starch, while, on the other
hand, the addition of fat facilitates the digestion of albuminoids and
cellulose. In general, it may be stated that the digestibility of any dry
fodder is decreased by the addition of any readily digestible substance,
such as albumen, starch, sugar, and in ordinary fattening diet a loss of
at least 20 per cent, of nutritive substances may be calculated. This
author's experiments have further shown that at least five days are
required after the change of diet before the traces of indigestible food
are removed from the faeces, and that the removal of the residue of
prairie haj^ occurred about thirty hours before that of wheat-straw. In
the calf, experiments have been made to determine the digestibility of
cereals and grains taken whole, with the following results: —

Oats. Flaxseed. Barley. Wheat.

Digested, . .' . 91.4 58.2 94.6 36.3

. . . 91.5 57.4 94.9 36.7

In the sheep the same results have been obtained as in the ox. An
addition of starch or sugar to the food diminishes considerably the
digestibility of the albumen and, when in small amount, of the cellulose
also. Pure albumen has slight influence on the digestibility of the food.
Substances containing sugar, with the exception of beets, are almost
entirely digested, while in potato-starch 80 per cent, is digestible, and fat,
when added to fodder, is usually absorbed, though its administration
when given in large amounts interferes with the digestion of cellulose.

According to Wildt, lambs which were fed with barley-straw, and
then the residue from meat extracts, absorbed 95 per cent, of the latter.
Experiments on the horse have also proved that this animal is capable of
digesting cellulose to about 50 per cent. In comparison with the
ruminants, the horse is less capable of digesting all the constituents of
hay. The loss in the horse, as in other herbivora, is much greater than
in the carnivora. The carnivora may be said, as a rule, to absorb about
98 per cent, of albuminous matter given in the food. In a man fed on
milk and meat diet only 2J to 10 per cent, escapes in the faeces ; with
vegetable diet, rice, bread, and potatoes, the loss may amount to 30 per

438 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

cent., though the carbohydrates are almost completely absorbed, only
1 per cent, being lost, and only 5 per cent, of fats escapes absorption. In
the herbivora the loss is, however, much greater. Thus, a horse fed with
six kilos of oats and fifteen liters of water will pass about twelve kilos
of faeces, composed of three kilos of solids, containing 5 per cent, of
albuminous matter, 20 per cent, of fat, 20 per cent, of starch, and 60 per
cent, of cellulose. If the horse is fed with a mixed diet, composed, for
example, of three and a half kilos of oats, five and a half kilos of hay,
and one and three-fourths kilos of chopped straw, seventeen kilos of
faeces will be passed, in which there will be four kilos of solids, of which
30 per cent will be albuminous matter, 40 per cent, fats, 30 per cent,
starch, and 60 per cent, cellulose having escaped digestion. The loss
is, therefore, greater in a mixed diet than in a horse fed on grain
alone. In the ruminants the digestibility of hay is much greater than
in the horse. Oxen fed with ten kilos of hay will digest and absorb
about 50 per cent, of the albuminous matter, while, as already mentioned,
if more readily digestible substances are added to the hay diet, less hay
will be digested.

It has been found that in the fermentation of cellulose large quanti-
ties of COa and CH4 are formed, and, as the latter gas is constantly found
in the intestine, that its source is in the putrefaction and fermentation in
the intestinal canal is readily conceivable, and indicates a possible expla-
nation of the fact that about 40 to 60 per cent, of cellulose disappears
in the intestinal canal. This may occur in the rumen of the ruminants,
while it certainly occurs in the caecum of the horse, although in this
animal less cellulose disappears than in the ruminant.

As regards the inorganic constituents of the food, the fact that the
faeces contain but small amounts of soluble salts shows that they must
have been largely absorbed. Small amounts only of the alkalies are
found in combination with chlorine and sulphuric acid, while potassium
and sodium are found in combination as chlorides or sulphates in minute
quantities. Magnesium is also almost entirely absent. In the herbivora
less lime is absorbed than magnesium, while in the carnivora but very
small quantities of both lime and magnesium are absorbed. Another
point of contrast between carnivora and herbivora is that in the former
almost all the phosphates in the food are absorbed, while in the herbivora
they are almost entirely excreted in the faeces, unless they are fed with
meal, milk, or other readily digestible food.

Mr. E. F. Ladd has tested the relative digestibility of the different
feeding stuffs by digestion experiments performed with them, after
thorough comminution, with an artificial gastric juice, formed of 0.2
per cent, hydrochloric acid with five grammes of pepsin to the liter.
The following tables give his conclusions : —

COMPARATIVE DIGESTIBILITY OF FOOD-STUFFS.

CO CO CO tO tO to tO tO tp tO tO tOtOI— '»— >l— 'K- 'h-i|— 'I— 'I— 'I— » I— •>' I

439

3-§? -§ II i S.S.i-i-s'S

ooenoOtOtO

ooooeno
G i— H-^CO

I— ' »— ' OS i— ' I— '

00 00 00 00 OS 00 OS CO 00 OS CO

bOOli— ' t— '*'(— 'H- '1— '

Water.

tococoocccooot— 'i— coo rf^entot— '^rcoas-<rO4^co »->

H-1 o co co o as to as co bo bo bo to co ^j o bo o as '*-* co as n-1
-<r o co i— co >— o co ^r oc as to ^ en >-* 4^ en 4*. as as as co co

t~* P ~ '

^.T 4^. OO

co to o

Albuminoids,
NX 6.25.

;<r co co j-i to to j-i ps p to to • en co to co _en co co to 4^ O Cn to en en "

CO to

-OiOo

Crude Fibre.

enasasas-<r-<iasenenosas " tococoosasentoenenen co to co 4^ " * co

co -<r ~4 -<r pi co p co to co po • H- po 4s> 4^ to oo o to »4^ co -<r oo o en i— ' • • t— '

•— ' co en 'CD i— • ^<r ^<r I—1 o to to o en co
cooooit— rf^oocotoco to cc rf»- oo as

co co co
co en
-<r to bo

CO OO rfi.

Nitrogen-
free
Extract.

t-* 1— » t-J CO CO 4*- CO 4*- CO en

• to to po -<r j-1 as 4^- en co to {-• j-> *-> to to

• co h-L to en to O O *-* co bo J-* co co o o
. to co o co H- oo £ as co as cnenoooos

Fat, Ether
Extract.

co h- » j— i j— » j-j »— ' *— ' co to *— ' i— '
H— O ~J en i— ' ^i oo

as ot or i— ' »-*

• en o co en co ^r to oo co i— '
i— 'coo . Oi^rcoototo4^astoto

co co <r as co • • as h-> co
i -- 1 •— as 4^ . . H^CHO

Ash.

4*. CO CO (-* i— ' to CO k-i ^-» t-*

to »-» t— ' i-* i— ' i— 1 1— > to i— ' >— '

co CD bo to bo 4^ bo bo co t-o co ^r to co en en ^i en o bo bo bo
H-' co -<r en ^i »— ^j ^j H-I en ^ co ^- ^r o o en o as -4 i-* ^r

Albuminoids.

co »— ' co -<r to

to bo bi bo "4^. co o co en co bi
cot— 'i— *Go-<icotocooot— >cn

co o "co i— ' to 4*- !— ' O as *— '
^-ascotooocoocoooco

COtOC04^CO- • 4i-4^CO

to po en co as . . p (-1 co

4> co en J-» bo . . ^<r >-» o

ooenrf»-asco t— ' i— » to

• • o o en

Crude Fibre.

to4^coasasosenenasas
toooas4^^»4^toco

oocn4iooco o co >— '

rf*. CO 4*. O >— ' ' Oi en »-»
• • --7 CO CO

Nitrogen-
free
Extract.

4*- CO Cn en CO

CO OO 4^ tO CO CO CO •»

. en to oo oo to co i— > en 4^ co

ISD to to co co to to co

' bo

rfi. <J CD Cn 4*. 4=» OO

oienooocot— 'os

Fat, Ether
Extract.

>_i (_i j_» co to j-1 1-1 . po en en t-J to

. o 'en ^.T bs i-* en as CD en o

rf^rf5>coOOi— 'enrf^toco

en p as en en . . en 4^ 7<r

co bs to bs bo . . 4*. bo H-'
totocooco, ^ cogg

Ash.

440

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

TABLE No. II.
DIGESTED BY FLUID FROM HOG'S STOMACH (LADD).

i*8

06

12

£4

1

£>

8

|5

P|

HAY AND COARSE FODDERS.

Si

S.|

-g

*j-2

0 o

o % £*

C g

r^'3

C £>^

gg-s

c-fll

^Is

|J

«-!

|||

o||

fc

£3«

£^

£M

IW

£<*>

1

Clover-hay ^

1381

1003

3 62

73 75

63 91

2

Same, exposed, average, . .

12.19

9.38

6.20

49.23

33.90

3

Same, exposed, poorest, . . .

13.84

11.31

7.09

48.76

37.31

26

Corn-meal

1087

831

1 71

8398

7942

10

Ensilage,

731

446

2 32

68 90

47 98

TABLE No. III.
DIGESTED BY PEPSIN SOLUTION (LADD).

< <M

•d o

l^a
|2l

^&C§

44

HAY AND COARSE FODDERS.

Per Cent, of Crude
Albuminoids, N X
6.25.

Per Cent, of True
Albuminoids.

i

&

ii

g

PerCent. of Crude
Albuminoids Di-
gested.

Per Cent, of True
Albuminoids Di-
gested.

4

Clover-hay .

1453

1003

4 70

6765

53 14

5

Same, steamed, ....

1434

670

5327

6

7
8

Hay, ordinary, mixed, . .
Hay, poor, many daisies, .
Fodder-corn, .....

5.94
5.94

7.81

' 5.44
588

2.09
2.51
289

35.32
57.69
6300

53.86
5083

9

Soja-hispida

1068

956

2" 57

75 92

73 11

10

Ensilage,

731

456

282

61 35

3925

11

By-Products.
Wheat-bran,

1587

1300

265

8327

7961

13

Gluten -meal,

3287

551

8323

14

Starch-refuse .

21 06

560

7343

'*

15

Starch -feed

J250

1268

489

6080

61 36

16
17

18
19
20
21
21

Corn-feed, ground germ, . .
Corn-feed, ground hull, . . .
Linseed-meal, old process, . .
Linseed-meal, new process,
Cotton-seed rneal,
Same, cooked,
Ship-stuff

10.75
7.50
34.50
35.37
43.21
42.73
1781

33.13
32.19
40.25

1681

4.54
2.28
3.61
7.62
5.30
11.19
234

57.98
69.71
89.52
78.44
87.73
73.81
87 86

89.10
76.33
86.83

86 08

24

Grams.
Pea-rneal, .

2431

2019

275

8869

8638

25

Crushed oats

11 87

1031

2 15

81 8°

79 14

26

Corn -meal

1087

8 31

1 50

86 15

81 95

27

Corn-meal ....

1041

764

285

7258

6400

28

Same, cooked, ....

987

761

3 64

63 16

52 17

31
29

Wheat, Clawson's winter, . .
Corn-meal,

14.93
1225

8.81
8 81

1.93
357

87-07
70-85

78.09
59 48

30

Same, heated

11 81

8 81

358

69-79

5935

22

Corn-meal,

1237

941

3 87

68-63

5887

23

Same cooked ....

11 25

5 19

4 44

6053

16 37

. 32

Bean, navy or pea, ....

25.51

22.06

1.13

95.59

94.93

COMPARATIVE DIGESTIBILITY OF FOOD-STUFFS.

441

TABLE No. IV.
DIGESTIBLE CONSTITUENTS OF THE FOOD IN PERCENTAGES (KUHN).

NOX-NITBOGEN-

ALBUMEX.

FAT.

ous EXTRACT-

CELLULOSE.

IVE MATTERS.

NAME OF THE
FOOD.

3

d

|

3

|

3

3

3

d
§

|

j

3

\

.

s
§

*$

d

3 •
J

?3

.

"3

i

I

0

a

i

'3

1

§

o

'c

'*
•

2

§

3

S

i

a

3

i

A

s

§

3

s

I. Green Fodders.

Pasture-grass, .

70.6

79.3

75.0

63.4

68.1

66.0

74.5

84.4

79.0

70.3

75.2

73.0

Good meadow-

grass, .

69.0

71.7

70.Q

60.4

68.1

65.0

74.7

84.4

79.0

65.4

72.8

69.0

Clover, . . .

77.7

78.7

78.0

63.3

65.1

64.0

78.0

78.5

78.0

66.9

67.4

67.0

Lucern-clover, .

78.2

83.2

81.0

37.0

53.6

45.0

61.1

76.9

72.0

31.6

46.8

41.0

Esparcet, . . .

71.7

73.3

73.0

64.1

69.2

67.0

76.5

80.0

78.0

42.1

42.3

42.0

Lupines, . . .

73.0

75.7

74.0

15.5

45.3

30.0

57.3

65.9

62.0

67.1

79.8

73.0

Potato-stalks

(beginning of
October),

420

24.0

60.0

36.0

Aspen-leaves, .

• •

• •

56.0

• •

• •

79.0

65.0

• •

• •

35.0

II. Hay.

Prairie-hay, . .

38.9

71.0

57.0

8.5

69.7

46.0

48.0

78.8

63.0

44.6

72.4

58.0

Second-crop hay,

53.0

68.0

61.0

27.0

57.4

46.0

56.7

75.0

66.0

54.3

74.9

63.0

Clover-hay, . .

43.0

73.3

60.0

33.0

75.3

59.0

62.5

80.1

69.0

38.0

59.2

47.0

Lucern-h'ay, . .

72.1

83.0

77.0

29.7

51.0

39.0

52.6

72.0

65.0

33.1

45.7

40.0

73.0

75.7

74.0

15.5

45.3

30.0

57.3

65.9

62.0

67.1

79.8

73.0

Acidified beet-

leaves, . . .

• •

• •

65.0

• •

60.0

• •

• •

54.0

• •

54.0

III. Straw.

Wheat-straw

r

260

270

400

52.0

Rye-straw, . .

2.6

28.6

25.0

21.2

40.9

32.0

28.5

51.8

36.0

46.8

72.9

56.0

Oat-straw, . .

14.4

50.0

38.0

14.0

51.0

30.0

33.2

47.0

42.0

53.0

67.0

61.0

Barley-straw, .

12.8

16.8

15.0

32.4

42.6

38.0

50.7

51.3

51.0

49.1

55.6

52.0

Pea-straw, . .

60.3

60.6

60.5

41.6

50.1

46.0

64.0

64.8

64.0

47.2

65.9

52.0

35.4

39.7

37.0

25.4

35.0

30.0

64.5

65.4

65.0

49.2

52.0

51.0

IV. Cereals.

Oats (experi-

ments with

ruminants), .

58.0

81.3

74.0

68.4

99.0

82.0

65.0

79.7

73.0

5.5

32.1

21.0

Crushed barley

(experiments

with rumi-

nants), . . .

.

77.0

100.0

_

87.0

.

20.0

Crushed corn

(experiments

with hogs), .

83.9

88.1

85.0

74.4

78.5

76.0

9.25

96.3

94.0

17.0

57.4

34.0

442

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

TABLE No. IV.
DIGESTIBLE CONSTITUENTS OF THE FOOD IN PERCENTAGES. — (Continued.)

NON-NITROGEN-

ALBUMEN.

FAT.

OUS EXTRACT-

CELLULOSE.

IVE MATTERS.

NAME OF THE

•

.

FOOD.

EJ

a

B

S

d

a

1

a

g

a

d

1

|

j

1

£3

j

1

J

e

'2

|

«

fl

rt

&

a

1

S

a

X

•

8

§

s

i

s

s

S

1

55

Crushed beans

(experiments

with rumi-

nants), . . .

80.6

100.0

90.0

86.9

100.0

97.0

90.7

98.7

94.0

25.1

100.0

63.0

Peas (experi-

ments with

hogs), . . .

84.4

91.5

88.0

45.0

69.0

58.0

94.7

98.6

97.0

55.1

88.5

74.0

Peas (experi-

. ments with

sheep), . . .

95.5

97.6

97.0

• •

• •

100.0

77.0

100.0

90.0

! ' '

• •

• •

V. Manufactured

Products.

Rape-seed cake

(experiments

with cows and

oxen), . . .

81.3

92.4

85.4

79.7

93.6

88.0

70.2

84.9

78.0

.

34.3

11.0

Rape-seed cake

(experiments

with sheep), .

65.3

83.9

75.9

59.8

77.2

69.0

66.0

85.4

78.0

5.5

3.0

Linseed cake (ex-

periments with

oxen), . . .

80.2

89.9

87.0

86.7

93.9

91.0

85.0

96.3

91.0

.

54.5

26.0

Linseed cake (ex-

periments with
goats & sheep),

80.0

87.4

83.0

86.5

92.5

90.0

60.0

78.7

71.0

29.7

92.9

62.0

Wheat-bran (ex-

periments with

oxen), . . .

82.9

93.5

88.0

77.6

81.6

80.0

77.7

81.2

80.0

16.9

32.2

20.0

Wheat-bran (ex-

periments with

sheep), . . .

75.0

500

700

37.0

Rye-bran (ex-

periments with
pigs), . . .

65.8

66.2

66.0

57.4

57.6

57.5

74.2

74.7

74.5

6.5

10.5

9.0

Skimmed sour

milk (experi-

ments with

pigs),

96.0

.

95.0

99.0

.

p

Meat residue (ex-

periments with

ruminants), .

m

^

95.0

;

98.0

f

.

4

,

. .

. .

Meat residue (ex-
periments with
pigs), . . .

95.1

98.9

96.0

82.3

90.7

87.0

- -

COMPARATIVE DIGESTIBILITY OF FOOD-STUFFS.

443

TABLE No. V.

DIGESTIBILITY OF THE NUTRITIVE PRINCIPLES IN FOOD-STUFFS BY DIF-
FERENT ANIMALS (POTT).

NON -NITROGEN-

PKOTEIDS.

FATS.

OUS EXTRACT-

IVE MATTERS.

FODDERS.

'

•

g

|

g

|

jj

g*

|

2

53

i 2

|

{«

i

|

S3*

1

1

1

°8

1

§
«

1

1

i

S

£

S

; i

S

s

i

s

&

A. THE RUMINANTS digest the fol-

lowing percentages of nutri-

tive substances : —

1. (a) Green Foods: Prairie-grass,

clover, lucern, esparcet,

vetches, rye, lupines, corn,

beans, peas, spurry, white

mustard, rape-seed, cabbage,

beet-leaves.

(6) Hay of esparcet, vetches,
lucern, and lupines

60.0

81.0

70.0

50.0

75.0

60.0

65.0

79.0

73.0

2. (a) Green Foods, etc. : Prairie-

grass after blossoming, beet-

leaves, buckwheat.

(6) Prairie-hay, clover-hay.

(c) Straw of beans, peas, and

lentils

40.0

78.0

60.0

32.0

62.0

50.0

54.0

76.0

65.0

3. Prairie Grrummet .

58.0

70.0

64.0

45.0

68.0

54.0

62.0

74.0

67.0

50.0

72.0

60.0

46.0

76.0

60.0

53.0

67.0

60.0

5. Straw of the cereals, rape,

clover, lupines, potatoes, . .

17.0

48.0

27.0

20.0

49.0

35.0

35.0

60.0

44.0

6. (a) Roots and Bulbs: All sorts

of beets, potatoes, etc.

(6) Residue from manufacture

of spirits, starch, and sugar,

etc.,

51.0

86.0

65.0

. .

. .

• •

89.0

96.0

93.0

68.0

86.0

78.0

67.0

97.0

82.0

67.0

91.0

86.0

Malt,

81.6

49.0

87.6

Brewers' grains, . , .^ . .

73.0

*

84.0

64.0

Acorns,

83.0

87.5

91.4

8. Hulled Fruits,

81.0

95.0

91.0

66.0

100.0

86.0

84.0

99.0

92.0

9. Fodder Cakes : Rape-seed cake,

unshelled ground-nuts, un-

shelled cotton-seed and other

oil-cakes and oil-cake meals, .

74.0

90.0

81.0

69.0

91.0

88.0

46.0

85.0

70.0

444

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

TABLE No. V.

DIGESTIBILITY OP THE NUTRITIVE PRINCIPLES IN FOOD-STUFFS BY DIF-
FERENT ANIMALS. — (Continued).

FODDERS.

PROTEIDS.

FATS.

NON-NITROGEN-
OUS EXTRACT-
IVE MATTERS.

|

|

'3

i

|

g

1

1
£

|
J
1

86.0
50.0

|

1
S

|

5

3

"3

i

1

a
'*

1

10. Fodder Cakes of the various
nuts and seeds, as above,
after shelling

80.0
70.0

100.0
89.0

88.0
82.0
95.0

100.0

77.0

90.0
63.0
98.0
76.0
100.0
95.0
69.0

68.0
50.0
76.0
71 0

63.0
71.0

98.0
82.0

86.0
76.0

11 Wheat-bran

12 Meat-powder

Fish-guano

900

Blood-powder

62.0

43.0

89.0
95.0
93.0

53.0

91.0
99.0
96.0

100.0
98.0
47.0

90.0

96.0
95.0
91.0
75.0
100.0

13. Milk and dairy residues, . .
14. Brewed hops,

91.0
26.0

75.0
85.0
84.0

97.0
39.0

80.0
90.0
88.0

94.0
33.0

78.0
88.0
85.0
790

90.0
52.0

65.0
36.0
74.0

99.0
77.0

77.0
67.0
79.0

B. HOGS digest the following per-
centages of nutritive sub-
stances : —

1. Crushed barley,

2. Crushed peas,

3. Crushed corn,

4. Crushed beans,

5. Rye-bran,

91.0
99.0

81.0

66.0
90.0
95.0
72.0
77.0
960

82.0
79.0

91.0
91.0

58.0
87.0

83.0
95.0

• •

. .

880
82.0

71.0

7 Meat-powder

8. Blood-meal

- •

• •

92.0

9 Crushed beetles

10. Skimmed sour milk, ....

80.0
80.0

70.0
92.0

49.0
61.0
67.0
17.0

49.0

90.0
90.0

78.0
96.0

62.0
67.0
71.0
30.0

66.0

99.0
98.0
850
85.0

76.0
89.0
93.0
73.0
94.0
87.0
56.0
63.0
69.0
24.0
66.0
56.0
94.0
99.0

11. Potatoes

73.0

12 Oil-cake

60.0
70.0

77.0

75.0
80.0

91.0

68.0
75.0

86.0
83.0
86.0
94.0
78.0
800

75.0
60.0

71.0

85.0
70.0

81.0

42.0
31.0
30.0
100.0

80.0
65.0

78.0
70.0
80.0
37.0
63.0
42.0
23.0
29.0
26.0
84.0
13.4
22.0

13. Brewers' grains and malt, . .

C. HORSES digest the following per-
centages of nutritive sub-
stances : —

1. Oats

2. Peas,

3 Beans

84.0

90.0

6. Barley,

7 Prairie-hay .

54.0
51.0
70.0

27.0

66.0
60.0
75.0
44.0

61.0
55.0
72.0
36.0
6PO

14.0
28.0
21.0
67.0

8 Clover-hay

9 Lucern-hay

10. Wheat-straw
11 Meadow-grass

12 Prairie-grass

54.0

69.0

61.0
990

13.0

42.0

13 Carrots . .

14 Potatoes

880

COMPOSITION OF F^CES. 445

Of the feeds examined in per cent, of digestibility of the albumi-
noids, bean-meal stands the highest, linseed-meal (old process) next, and
pea-meal but little less, while the mixed hay of rather inferior quality,
but similar to much hay feed, stands lowest. The old process linseed-
meal shows a higher per cent, of digestibility than the new process ; this
difference is due, very likely, to the partial cooking of the meal by steam
during the process of oil extraction and preparation of the meal for feed.
Cotton-seed meal, much the richest substance examined, gives a high
co-efficient for digestibilit}r. A marked difference exists between the
first three hays, showing plainly the difference between well-cured hay
and that exposed to the weather.

Of the raw and cooked foods examined, in every instance the higher
digestion co-efficients were obtained from the raw foods, and an exami-
nation of the table of anatyses shows an actual loss in albuminoids by
cooking, and a change in the fat rendering it insoluble in ether, and un-
acted upon by acids or alkalies of the strength used for fibre determina-
tions.

XII. THE COMPOSITION OF F^CES.

The faeces are composed of the more or less altered residue of the
food-stuffs, to which are added the excretory products of the digestive
tract. The character of the faeces will be governed by the relative
amounts of these two groups of substances.

When no food is given, as during fasting and in the fetal state, the
faeces consist only of the excretory products of the digestive tract. This
state of affairs will also hold when the food given is entirely digested
and absorbed, as is the case with the dog fed on a not too abundant
meat diet.

The amount of matter found in the faeces which fs not derived from
the faeces may vary under different circumstances. In the fasting con-
dition, according to F. Mu'ller, the faeces contain 4 per cent, of the total
amount of nitrogen eliminated, 1.4 per cent, of the amount of carbon, and
25 per cent, of tbe inorganic matter. When, however, food is given, the
activity of the intestinal mucous membrane i* increased, and through
increased secretion and excretion the percentage of faecal constituents
not derived from the food is increased.

The faeces passed in the fasting condition furnish, therefore, no index
as to the degree of intestinal excretion. This, however, may be reached
through the examination of the faeces of eamivora fed on meat, when
the amount of nitrogen eliminated will toe- afeowt 1,2 per cent, of the total
amount, carbon 2.7 per cent., and inorganic matters 18.5 per cent.

Meconium, or the contents of the foetal intestinal canal, contains
neutral fats, free fatty acids, biliverdin,bilirubin, unchanged biliary acids,

446 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and various unknown bodies which may be extracted with ether ; on the
other hand, phenol, indol, leucin, and tyrosin are absent, indicating the
absence of putrefactive changes in ,the fetal canal. Meconium also
contains sulphur, lime, magnesium, phosphoric acid, and considerable
amounts of alkaline salts. The reaction is faintly acid.

The faeces passed by the carnivofa during fasting closely resembles
m.econium, differing from it, however, in that they contain no unchanged
biliaiy acids and hydrobilirubin is present. When fed with meat the
faeces of the dog usually have an alkaline reaction, and where the meat
has not been too freely given never contain undigested muscle-fibres.
The proof that the faeces in carnivora after meat feeding are mainly com-
posed of excretory matter is found in the facts that while increasing the
amount of meat does increase the amount of faeces, the increases are not
proportional; and that the amount of food remaining unchanged, the
amount of faeces varies. The amount of nitrogen is about 6 per cent.,
while the inorganic matter is considerably larger in amount than in meco-
nium, but contains less alkaline salts. When large amounts of fats are
given to dogs with meat, the faeces are dark-brown externally and
grayish on the inside ; the daily amount passed is also larger than where
meat alone constitutes the diet.

The faeces in herbivora always have an aspect and color closely
similar to the food with which the animals have been fed. Thus, they
are yellow when fed on hay, and green if grass has been given, since
chlorophyll is unchanged in the alimentary tube; the tint will, however,
vary according to the rapidity of their progression through the intestine
and the quantity of bile poured out. The faeces of solipedes are extruded
in rounded masses, flattened at the sides from mutual pressure, and are
yellow, green, or brownish in color. In oxen the faeces are of semi-solid
consistence, and dark-green or brown in color. The faeces of sheep and
goats are passed in the form of small, hard balls, very dark-green or
black in color. In hogs the faeces are semi-solid, very offensive in odor ;
their color depends on the nature of the food.

The consistency of the faeces depends naturally upon the quantity
of water contained in them, which even in the most solid instances is
still considerable. In carnivora the faeces have a blackish tint if meat
has been given cooked. They become fatty or cla3r-colored in cases of
obstruction to the flow of bile or in diseases of the pancreas. The odor
is characteristic of each group of animals, and is due primarily to indol
and sulphuretted hydrogen. The quantity, both absolute and relative to
the amount of food, is greater in herbivora than in carnivora; thus,
horses empty their bowels on an average every three hours, and when
fed oil 10 kilos hay and 2 kilos oats will1 pass about 17 kilos faeces, con-
taining 2.67 kilos of solids ; cattle evacuate about 30 kilos of faeces daily,

COMPOSITION OF F^CES. 447

with about 4.6 kilos of solids ; dogs, when fed on a purely meat diet,
only every two to four days, and only a few grammes in amount. The
consistency, as mentioned before, depends upon the amount of water con-
tained in them, and is naturally governed by the activity of secretion, of
absorption,. and the amount of water drunk. Thus, in man they contain,
on an average, 31 per cent, of water ; in the hog, 75 per cent. ; in the sheep,
5t> per cent. ; in the horse, 77 per cent, and in the ox, 70 to 80 per cent.

The reaction of the faeces may be either alkaline, neutral, or acid,
depending upon the character of the fermentations occurring in the con-
tents of the large intestine. Thus, when alkaline, as is usually the case
in abundant albuminous diet, the reaction is due to ammoniacal fermen-
tation, while an acid reaction is usually due to the fermentation occurring
in the carbohydrate constituents of the food.

The faeces are composed of excrementitious substances no longer of
use to the economy and which must be eliminated. They contain indi-
gestible matters, such as chlorophyll granules, gums, resin, wax, animal
and vegetable elastic tissue, cellulose, hulls of seeds, and epithelial cells.
Lactic acid, butyric acid, and various gases, such as hydrogen, oxygen,
carbonic acid, and carburetted hydrogen, are present, while in addition
various salts are found in large amounts, of which the ammonio-phosphate
of magnesium is usually in excess. As putrefactive products, leucin,
ty rosin, indol, and finally skatol and the volatile aromatic acids, such as
valerianic and caproic acids, are met with, while cholesterin and the
bile coloring-matters and glycochol are also found, taurocholic acid being
again absorbed.

The contents of the large intestine are alwa3*s in a more or less
marked degree of putrefaction, which, however, though hindered, is not
entirely prevented by the bile.

In carnivora fed on bones, the faeces are dense and gray from the
presence of lime salts. Silicious salts constitute a large percentage
of the excrement of the lower animals ; thus, in the horse and ox they
amount to from 2J to 3 per cent.; in the sheep, to 6 per cent.; while in
the hog as much as 8 per cent, of silicious salts are present. These
salts are products derived from the matters taken into the alimentary
canal of inorganic nature, and from the inorganic matter of the hulls of
the cereals. A small amount of soluble salts are present.

The following table gives the percentage of salts found in the faeces
of different animals. The percentage will, of course, vary according to
the nature of the food. It may, as a rule, be said that in the faeces of the
dog about 20 per cent, of inorganic matter is present when on a pure meat
diet, and 24 per cent, on a mixed diet ; in that of the herbivora 58 per
cent, is inorganic, though the faeces of the sucking calf will contain only
2.6 per cent, of the inorganic matter contained in the food. According

448 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to Valentin, 100 grammes of faeces of the bog contains 37.2 grammes,
ox 15.2 grammes, horse 13.3 grammes, sheep 13.5 grammes of ash: —

Sodium chloride, .

Horse.
0.03
11.30

Ox.
0.23
2.91

Hog.
0.89
3.60

Sheep.
0.14
8 32

1.98

0.98

3.44

3.28

Lime, ....
Magnesium, .
Oxide of iron,
Phosphoric acid, .
Sulphuric acid,

4.63
. 3.84
1.44
. 10.22
1.83

5.71
11.47
5.22

8.47

1.77

2.03
2.24
5.57
5.39
0.90

18.15
5.45
2.10
9.10
2.69

Carbonic acid,
Silicon, ....
Sand ....

'. 62.40

62.54

0.60
13.19
61.37

traces
50.11

Oxide of magnesium, .

2.13

. .

. .

XIII. THE MOVEMENTS OF THE INTESTINES.

The walls of both small and large intestines are supplied with un-
striped muscular fibres arranged in circular and longitudinal layers
which, through their contraction, serve to cause a slow, onward, pro-
gressive movement in the contents of the alimentary tube.

The arrangement of these muscular fibres differs in the small and large
intestine and in different animals. The longitudinal layers lie beneath
the submucous layer immediatel}' below the serous covering, and, there-
fore, give the intestine its longitudinally Striated appearance.

In the small intestine these longitudinal fibres form a thin, uniform
layer, which entirely surrounds the intestine, while in the large intestine
they are grouped into bands, and, being rather shorter than the intes-
tine, throw the intermediate parts into a series of pouches ; this con-
dition is seen in the large intestine of man, the omnivora, in the caecum
of solipedes, and in the fixed colon in these animals, while in the floating
colon their arrangement is more similar to that seen in the small intes-
tine, and, consequent^, in those portions of the alimentary tract the
sacculated appearance is wanting. Immediately below the longitudinal
fibres is found the layer of circular fibres, which are considerably more
developed than the longitudinal fibres.

The motions of the intestine have been compared to the move-
ments of a worm, and are termed peristaltic contractions. When the
abdomen of an animal is opened after death the walls of the intestine
are seen to be in active motion, and cause the intestine thus to undergo
a series of active movements of the same nature, but greatly exaggerated
in intensity, as the movements occurring during life. If the intestines
are closely examined, it will be seen that these movements consist in the
downward passage of a constriction due to the successive contractions of
the circular fibres of the small intestine from above downward, while at
the same time the longitudinal fibres contract immediately below the

MOVEMENTS OF THE INTESTINES. 449

ring of constriction so as to shorten the intestine and to cause a rolling-
motion in the intestine itself. The contractions of the circular fibres of
the small intestine, as a rule, commence immediately below the pylorus
and progress downward toward the large intestine, so tending to force
the contents of the small intestine onward toward the ileo-ctecal valve;
but while the pylorus is ordinarily the commencing point of this series
of contractions, the wave of contraction frequently may seem to com-
mence at other points, and normally invariably moves downward toward
the large intestine. It is stated that occasionally the wave of contraction
moves in both directions, the upward movement being then spoken of
as an antiperistaltic movement. Such a contraction occurs in cases of
obstruction of the intestines, but it is extremely doubtful as to whether
such an antiperistaltic movement ever occurs during health.

It is a peculiarity of unstriped muscular fibre that when stimulated
its contraction is preceded by a very long latent period and lasjbs a con-
siderable time, relaxation taking place but slowly afterward. In .such
cases as the intestine and ureter, a stimulation of any one point not only
causes contraction of the muscular fibres in that locality, but that con-
traction is transmitted to the parts below it, the contraction being prop-
agated from fibre to fibre, so producing a wave of contraction which
passes along both circular and longitudinal coats of such tubular struc-
tures.

The peristaltic movements of the intestine are, in all probability, due
to the contact of food with the interior, and yet, as in the case of the
stomach, it is probable that this stimulation is not of a purely mechanical
nature ; for while the insertion of foreign bodies into the small intestine
starts up a wave of contraction, that contraction soon passes off as the
intestine becomes accustomed to the presence of the body. So, also, the
intestinal movements are frequently more energetic when the intestine is
comparatively empty than when distended with food.

The principal cause of the movements of the muscular coat of the
bowels is without doubt to be found in the condition of the blood circu-
lating through the vessels in the walls of the alimentary tube. Closure
of the aorta causes active peristaltic motion of the intestine. If the
intestinal tube be already in motion, closure of the aorta increases the
vigor of the intestinal movement. Closure of the vena cava, or portal
vein, and dyspnoea likewise increase peristalsis. An increase in the
amount of carbon dioxide in the blood, or a decrease in the amount of
oxygen, leads to powerful peristaltic movements, and this condition will
probably explain the activity of the intestinal movements seen in animals
recently killed. In this case, however, the exposure to the cold air is
also concerned in the production of this movement. The manner in
which these changes in blood supply influence intestinal movement has

29

450 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

not been thoroughly cleared up. The closure of the aorta may act
through the intermediation of the spinal cord, either by the stimulation
of motor or the paralysis of inhibitory apparatus ; or it may act directly
on peripheral, intra-muscular, ganglionic cells ; or directly on the mus-
cular fibres themselves. That the central nervous system is not solely
concerned in the production of peristalsis is proved by its occurrence in
an intestine removed from all connection with the central nervous
system, and it has been found that ligation of the mesenteric artery pro-
duces in the main the same effects as ligation of the aorta. We have,
therefore, to look to the periphery for the mechanisms which maintain
peristalsis. It is not permissible to assume that the state of affairs here
is analogous to the connections between nerves and striped muscular fibre,
even although intestinal peristalsis may be proved to be influenced by
nerve impulses. The state of affairs is more analogous to the action of
the pneumogastric nerve on the heart ; for while the peristaltic action
may occur independently of the central nervous system, as has been
proved by its occurrence in excised intestine, it also is influenced by
nervous impulses passing along the splanchnic and pneumogastric nerves.
We have, therefore, to infer that the movements are mainly due to nervous
impulses starting in the ganglia found in the walls of the intestine. — the
ganglia of Auerbach and Meissner's plexus, — and that these ganglia may
be influenced by impressions traveling along these nerves. When the
splanchnic nerve is cut, the peristaltic contractions are temporarily
arrested, probably through the large supply of arterial blood which then
passes through the walls of the intestine. On the other hand, if the
splanchnic nerve be stimulated while active movement, is going on,
peristalsis is arrested, in this case probably through the consequent
constriction of the intestinal blood-vessels. If the pneumogastric be
stimulated, the intestinal movements are increased, especially when the
splanchnic nerve has been cut, and it is probably through the pneumo-
gastric that the movements of the intestine are reflexly influenced
through the emotions.

Temperature is also of influence on the intestinal movements.
Contact of the exterior with cold air, or the introduction of cold fluid
into the interior, accelerates peristaltic movements; so, also, the more
fluid the contents of the intestine, the more active are the intestinal move-
ments, thus perhaps explaining the action of various cathartics which
lead to the transudation of considerable quantities of fluid into the
interior of the bowels.

The movements of the large intestine are the same as occur in the
small intestine, but are less marked, owing to the modified, sacculated
shape of this portion of the alimentary canal. Just as the peristalsis of
the small intestine commences at the pylorus, the contractions of the walls

DEFECATION. 451

of the large intestine commence at the ileo-caecal valve, which is the
terminal point of the peristaltic movements of the small intestine. The
movements of the large intestine are said not to be influenced by stimu-
lation of the splanchnic nerves.

XIV. DEFECATION.

The contents of the alimentary tube, which are forced onward by
the peristaltic movements of the walls of the intestine, are arrested at the
lower extremity of the large intestine through the tonic contraction of
the sphincters of the anus.

By defecation is meant the mechanisms, partly voluntary and partly
reflex, which are concerned in the evacuation of the contents of the lower
bowel. The anus is closed by two muscles — an inner sphincter which
consists of unstriped involuntary fibres, and an external sphincter com-
posed of voluntary red striped muscles ; both of these muscles are in a
state of tonic contraction due to the constant transmission of impulses
from a special centre located in the lumbar portion of the spinal cord,
and which is only inhibited during the act of defalcation. The contact
of the faeces with the mucous membrane of the rectum leads, as it is
ordinarily described, to the desire to defaecate, and inhibits the contrac-
tion of the sphincter muscles. The peristaltic contraction of the larger
bowel is then sufficient alone to evacuate the contents of the rectum,
while a simultaneous elevation of the anus, through the contraction
of the levator ani muscles, raises the floor of the pelvis and pulls the
anus, to a certain extent, up over the descending faecal mass, at the same
time preventing distention of the pelvic fascia. "As the fibres of both
levatores converge below and become united with the fibres of the exter-
nal sphincter, they aid the latter during the energetic contractions of
the sphincter." Defalcation is partly a voluntary movement and may be
aided voluntarily through pressure produced by the contraction of the
abdominal muscles. When the contact of the faecal mass with the mu-
cous membrane of the upper portion of the rectum originates a desire to
defalcate, the impulse is transmitted to the brain and from this to the
spinal cord, inhibits the centre of defalcation in the lumbar portion of the
cord, and by this means relaxes the anal sphincter ; a deep inspiration is
then made and the glottis is closed ; powerful voluntary contractions pf
the abdominal muscles press upon the abdominal contents and force the
intestinal mass down into the pelvis, thus mechanically aiding peristalsis
in causing the downward passage of the faeces.

The contraction of the anal sphincters is kept up through the action
of a nervous centre situated in the lumbar spinal cord. If the connec-
tion of this centre with the sphincter is divided relaxation of the anus
takes place, but section of the cord in the dorsal region only temporarily

452 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

inhibits the tonic contraction of the sphincter. By the action of the will
the tonic action of the sphincter may be increased, or the action of the
sphincter may be completely inhibited. While the abdominal contrac-
tions above alluded to aid in defaecation, the sigmoid flexure serves to
ward off the pressure of the abdominal walls; therefore, the contraction
of the abdominal muscles is not sufficient alone to produce defaecation,
but must be accompanied by the peristaltic action of the. large intestine
and sigmoid flexure.

As a rule, the contraction of the abdominal muscles is voluntary,
but the contact of the faecal mass with the mucous membrane of the sig-
moid flexure is itself sufficient to inaugurate and normally complete the
act of defaecatioru Therefore, defaecation may be produced in states of
entire unconsciousness.

Evacuation of faeces occurs at various intervals in different animals —
in the horse, usually six to seven times in the twenty-four hours ; in the
sheep, four to five times ; and in the hog, once or twice.

In the act of defaecation in the horse, the loosely attached mucous
membrane of the lower part of the rectum is also extruded, forming the
so-called "rose of the anus," and is again retracted after the act is com-
plete ; the object of this is, perhaps, to reduce friction between the mu-
cous surface and the more or less hard faecal masses. The horse is able
to evacuate its rectum while in motion ; animals, as a rule, adopt a more
or less squatting position, with the back highly arched, so as to increase
the expulsive action of the abdominal muscles.

SECTION III.

ABSORPTION.

WE have already seen that the alimentary tube is developed as an
involution of the external integument. Hence, even after having under-
gone the most perfect digestion, food-stuffs are practically still outside
of the body, and can serve no nutritive purposes until they have entered
the lymph- or blood-currents. This entrance of the digestive products
into the circulation is termed absorption, and, as just indicated, sub-
stances reach the blood-current from the alimentary canal in one of two
wa}-s : either directty through the walls of the minute blood-vessels in
the mucous membrane of the stomach and intestine, or through the
mediation of the lymph-channels. Both of these modes occur in the
absorption of digestive products.

1. VENOUS ABSORPTION. — The first of these modes of absorption is
frequently termed venous absorption, as the entrance of substances into
the blood in all probability occurs through the walls of the minute
venous radicals, where there is not a sufficiently high pressure to inter-
fere with the passage of fluids from without to within the vessels under
the ordinary physical laws of nitration and osmosis. In fact, in the
very arrangement of the capillary blood-vessels in the intestine we find
the conditions at one time advantageous to the passage of fluid from
within to without the blood-vessels, and again directly the reverse hold-
ing. Thus, after undergoing subdivision into the minute arterioles, we
find the first capillary loops, where, consequently, the pressure is highest,
distributed around the deep ends of the intestinal tubules : the con-
ditions are there most favorable for the transudation of fluid from the
interior of the vessels and the consequent formation of the intestinal
secretion. The capillary loops, after leaving the deeper portions of the
intestinal mucous membrane, when the blood has been deprived of water,
then pass to the most superficial layers, and the conditions are then most
favorable to absorption. The blood is more concentrated, from the loss
of water in secretion ; it, therefore, from the affinity of the albumen of
the blood for water, favors the absorption of large quantities of water,
which may, of course, hold nutritive matters in suspension. More
than this, the blood-current is now becoming more accelerated, and the
internal pressure on the walls of the vessels reduced, both of which
conditions are favorable to absorption.

(453)

454 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The substances which enter the blood by venous absorption are
probably all those which are soluble in water, such as salts, sugar, soaps,
and peptone, as we know that all of these will more or less readily diffuse
through organic membranes outside of the body. The process of osmosis
is generally accepted as explaining the mode of entrance of soluble sub-
stances 'into the blood, but many data are still required before this view
can be acknowledged as conclusively established. In the case of grape-
sugar the author has found that the osmotic equivalent of sugar ab-
sorbed from the stomach of the frog very closely corresponds with the
equivalent of diffusion in ordinary physical experiments, and some-
what similar observations have been made for various salts and for
peptone. There is still, however, a great deal of obscurity in the matter.
We have seen that by the time the blood has left the secreting surfaces
of the alimentary tube and reached the absorbing surfaces it has lost a
good deal of its water, Now, if we assume that the absorption (of
sugar, for instance) is governed by purely physical laws, we must admit
that for every gramme of sugar that is absorbed seven and one-tenth
grammes of water (the osmotic equivalent of sugar) will leave the blood
to enter the intestine. The blood will, therefore, become progressively
concentrated and the intestinal tube filled with fluid ; consequent!}', every
substance which has a high osmotic equivalent will be apt to prove a
cathartic ; and it has, indeed, been found that the higher the osmotic
equivalent of the purgative salts, the more marked is their cathartic
action, though the relation of cause and effect between these facts has
been denied (Hay).

Consequently, though it is probable that osmosis is largely con-
cerned in the absorption of substances which are soluble in water, the
process is not a pure one, such as might occur between similar fluids
separated by a membrane outside of the body. In the living animal the
phenomena of filtration may greatty aid venous absorption. As we have
seen, the contents of the venous radicals are subjected to but low pres-
sure, and it is quite conceivable that the pressure exerted through its
contractions by the intestine on its contents may aid the passage of
fluids from the exterior to the interior of the veins. Here also we are
unable to conceive of an uncomplicated process of filtration, for a pres-
sure sufficiently great to force fluids through the walls of a blood-vessel
would undoubtedly so compress that vessel as to obliterate its lumen.

From the above it follows that although the physical processes of
osmosis and filtration underlie the absorption of salts, sugar, and peptone
from the alimentary tract, neither process is entirely analogous to similar
operations outside of the body, it being probable that the excess of pres-
sure on the intestinal contents keeps down the osmotic equivalent, and
again aids in the resorption of the transuded water ; while, further, the

ABSORPTION. 455

vital properties of the epithelial cells are in some way concerned in the
absorption not only of fat, but of sugar, peptone, and salts. Lannois
found that by the injection of alcohol into exposed loops of intestine the
epithelial cells were destroyed, and the absorption of oil, sugar, peptone,
and mineral salts was delayed. The tendency of opinion of late has
been in favor of the epithelial cell as an active factor in absorption, as
it is in secretion.

M. Leubuscher has made some experiments which seem to confirm
this view. He found in isolated loops of intestine that the absorption of
25 to 50 per cent, solutions of salt took place just as rapidly as that of

FIG. 167.— SECTION OF INTESTINE OF DOG SHOWING THE VILI-I. (Cadiat.)

The blood-vessels, r, and the lacteals, d, have been injected. The blind ending, or simple loop of the black
lacteal, is seen to be surrounded by the capillary net-work of the blood-vessels.

pure water, — a phenomenon which would not take place if the law of
diffusion were the sole factor in the process. The salts of sodium were
absorbed more rapidly than the salts of potassium, and absorption was
not hastened by the presence of bile — contrary to the general belief.

Gumelewski made a somewhat similar series of experiments, and
reached much the same conclusion. Strong solutions of sulphate of
sodium increase the rapidity of absorption.

Hofmeister, especially, has identified himself with the theor}^ that
the absorption of peptone is not a purely mechanical process of diffusion
or filtration, but that it represents a function of certain living, cells or

456

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

leucoc}Ttes, which in the assimilation of albuminoids fill a role analogous
to that of the red blood-corpuscles in respiration. He assumes that the
reason wiry peptone cannot be recognized in the blood is because it has
combined with these lymphatic cells, and is, through their mediation,
transported to different parts of the body ; and he regards the rapid pro-
liferation of the cells of the adenoid tissue of the intestinal mucous mem-
brane and of the Peyer's patches as a morphological expression of the
chemical processes of assimilation occurring in these tissues.

Thus, it seems that the process of absorption is as much a vital one
as that of secretion, and that the epithelial or lymphatic cell not only
aids the taking of fat into the blood, but also that of peptone (changing it
to albumen), and of sugar and salts.

2. ABSORPTION BY THE LYMPHATICS. — Absorption by the lymphatics is
accomplished through the instrumentality of the villi of the small intes-
tine. Each villus contains in its axis the
commencement of a chyle-vessel, which is
surrounded by a fine capillary net-work (Fig.
167). The chief purpose of this villous for-
mation is evidently to obtain an increase of
surface for absorption with economy of
space ; but each villus has, further, some
special mechanism which aids the absorption
of the intestinal contents, as is proved by
the entrance into the chyle-vessels of
globules of oil after having undergone emul-
sification by the bile and pancreatic juice.

The fat-globules first enter the proto-
plasmic caps of the epithelial cells, from
these pass into the tissue of the villus, and
thence into the central chyle-duct (Fig. 168).
After an abundant fatty diet, this absorption of fat may be so active as
to completely fill the net-work of lymphatics of the mesentery with
milk-white, emulsified oil, and even sometimes give the blood-serum a
milky-white color (Fig. 169). It further appears that the fat which is
absorbed in a state of emulsion by these chyle-vessels is greatry in
excess of the saponified fatty acids which may be absorbed by the
veins ; for, after a fat diet, nearly two-thirds of the amount of fat given
as food may be recovered from the thoracic duct.

As regards the mechanism of fat absorption, the most probable view
attributes the entrance of the oil-globules into the epithelial cells of the
villus to a true, protoplasmic, selective power exerted *by the contents
of these cells, and entirely analogous to the mechanism of feedin
sessed \>y the amoeba and other infusoria.

FIG. 168. — DIAGRAM OF THE
RELATION OF THE EPI-
THELIUM TO THE LACTEAL,
RADICAL, IN A VILLUS,
AFTER FUNKE.

The protoplasmic epithelial cells are
supposed to be connected to the absorbent
vessel by adenoid tissue.

ABSORPTION.

457

Microscopic examination of the intestinal epithelium after a full
meal which is rich in fatty elements of food will reveal the fact that the
epithelium of the villi is crowded with minute oil-globules. These

E. VEHNIORCKLH.se

FIG. 169.— LACTEALS OP A DOG DURING INTESTINAL DIGESTION. (Colin.)

A, lacteals of mesentery ; B, mesenteric glands ; C, efferent chyle-ducts ; D, receptaculum chyli.

globules may be found in the substance of the epithelial cell itself and
in its free, protoplasmic cap (Fig. 170).

When once the absorbed fat has reached the central chyle-vessel of
the villus, its onward progression through the lymphatics admits of

458 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

ready explanation. Each villus under the epithelial coat is supplied
with a layer of pale muscular fibres, and when these contract, the central
chyle- vessel being full, the effect must be to press out the contents of
the central vessel in the direction of the thoracic duct, at the same time
emptying the capillary vessels by pressure. When, now, the muscular
fibres relax, the capillaries will again become filled, and by the turgidity
of the net-work of blood-vessels cause the central vessel to become
expanded, and so exert a certain amount of suction in the interior of
the villas since the valves in the lymphatics will prevent regurgitation

FIG. 170.— SECTION OF AN INTESTINAL VILLUS OF A HORSE. (Ellcnbergcr.)

A, epithelium ; B, adenoid tissue ; C, commencement of lacteal.

from the mesenteric vessels. Each villns may therefore be regarded as a
minute lymphatic heart, which fills itself from the interior of the villus
in dilating, and in contracting forces its contents into the circulation.

In addition to the absorption of fat, it is evident that other sub-
stances contained in the intestinal contents will also mechanically be
drawn into the villus with the oil-globules. Thus, unchanged albumen
ma}^ be absorbed in this manner and has been found in the contents of
the chyle-vessels.

SECTION IV.

CHYLE.

THE chyle is the cl^me which has been absorbed by the intestinal
villi and the thoracic duct through the mesenteric lymphatics. In the
receptaculum chyli it is mixed with the lymph coming from the lower
extremities.

It may be obtained pure in the ox from the large trunk which
accompanies the anterior mesenteric artery (Fig. 171).

FIG. 171.— COLLECTION OF CHYLE IN THE Ox. (Colin.)

An incision is made in the right flank of an animal in active digestion, and one of the chyle-v«ss«1§
which accompany the mesentery artery is ligated. When it becomes distended a silver cannula termi-
nating in a rubber tube may be readily inserted.

It is a milky-white, or occasionally reddish, opaque liquid, of alka-
line reaction, saltish taste, and a specific gravity which varies between
1007 and 1022.

In a fasting animal the chyle found in the thoracic duct and mesen-
teric lymphatics is pale and transparent, or perhaps somewhat reddish
in tint. During the absorption of a meal containing fat, we have seen
that it becomes milky in appearance even in the very beginnings of the
lymphatic radicals in the villi.

In the adult herbivora, whose diet is, as a rule, comparative!}7" poor
in fatty matters, the chyle is scarcely opalescent, or may be perfectly

(459)

460 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

transparent, and of yellowish or reddish tint. In suckling lierbivora,
as in the carnivora, it is milky.

In its passage from the intestine to the thoracic duct it undergoes
important changes in composition. At first it contains albumen in solu-
tion, oil-globules in suspension, and is not spontaneously coagulable.
After it passes through the mesenteric lymphatic glands lymph-cor-
puscles are added, and it acquires the property of undergoing fibrinous
coagulation. It becomes poorer in albumen and fats in its onward
progress, and richer in corpuscles and fibrin.

When taken from the thoracic duct after a full meal of fat it is a
white, milky-looking fluid, which undergoes spontaneous coagulation on
exposure to the air. The nature 6f the coagulation of the chyle is iden-
tical with that of the blood, to be subsequently studied, and is due to
the addition in the mesenteric glands of immature blood-corpuscles and
fibrin factors.

Examined under the microscope, the coagulated chyle obtained from
the thoracic duct contains fibrin, a large number of white blood- or
lymph-corpuscles, a few immature red blood-cells, oil-globules inclosed in
albuminous envelopes, and fatty granules.

The composition of chyle differs in different animals and at dif-
ferent periods in the same animal, dependent on the rapidit}T and nature
of absorption taking place from the intestinal surface. In the chyle
obtained from horses fed with hay the fat scarcely exceeds in amount
that found in the blood, at most not more than 1 per cent., while it may
rise to 3.10 per cent, in horses fed with oats. It is made up of formed
elements (lymph-corpuscles added as the chyle passes through the
mesenteric lymphatics) suspended in a fluid medium (serum).

The serum contains the following bodies in solution in water : —

1. Globulin, alkali albuminate, serum-albumen, and peptones in
small amount, rising during digestion to 0.6-0.7 per cent.

2. Cholesterin, lecithin, and fatty soaps.

3. Dextrose, varying from a mere trace to 2 per cent., depending on
the amount of carbohydrates in the food.

4. Urea derived from the lymph, and alkaline lactates, especially in
the lierbivora, and after starchy food.

5. Inorganic salts of the alkalies and alkaline earths, iron, phos-
phoric acid, etc. (Charles).

As a result of sixteen analyses of the chyle of the horse, Gorup-
Besanez gives the following figures : —

Water, 871.0 to 967.9 in 1000 parts.

Albumen, .... 19.32 " 6053
Fat, traces " 36.01

The chyle possesses the power of converting starch into sugar,

CHYLE.

4G1

probably clue to the absorption of the amylolytic ferment of the pancreas
from the intestinal canal.

Chyle of Man (Rees).
Water 90.48 per cent.

Solids,

Fibrin, :' . . ^
Albumen, .....
Eats, lecithin, cholesterin, etc.,
Extractives, . .

Salts, . . . ». • .

Water,
Solids,

Chyle of Dog (Hoppe-SeyUr).

trace
7.08
0.92
1.0
0.44

90.67
9.02

Fibrin, . .";.-.

Albumen

Fats, lecithin, cholesterin, etc.,

Fatty acid and soaps,

Salts,

0.11
2.10
6.48
0.23
0.79

Chyle of Horse (C. Schmidt).

Serum, * * .

. 96.74

Clot, . . . *

. 3.25

Water, . . . ...

, 88.7

Solids, • . .

. 11.2

Fats, . .

. 0.15

Soaps, .-. . • . .

. 0.03

Fibrin, . . *

. 3.89

Albumen, sugar, and extractives,

. 6.59

Haematin, ......

. 0.20

Sodium chloride,

0.23

Sodium, 0.13 " "

Potassium, . . ... . . 0.07 " "

Phosphates and sulphates, . . . 0.11 " "

The following table gives the composition of the chyle from the
thoracic duct in the ruminant under different conditions (Wurtz) : —

O

X.

Cow.

Cow.

Before
Rumina-
tion.

After
Rumina-
tion.

Fed with
Hay and
Straw.

Fed with
Straw and
Clover.

Water

950.89

929.71

951.24

962.21

1.76

1.96

2.82

0.93

Albuminoids,
Fats
Salts (soluble in alcohol). .
Salts (soluble in water), .

39.74
0.81
2.47
4.33

59.64
2.55
2.50
3.61

38.84
0.72
2.77
3.59

26.48
0:49
1.92
7.97

Pure chyle from the mesenteric vessels of the ox before mixture
with the lymph has a specific gravity of 1013 and contains in 100 parts

462 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

0.0019 parts of dry fibrin. The serum contains 4.75 per cent, solids
(albumen, fats, salts, etc.), and 95.21 per cent, of water.

The amount of chyle is proportional to the activity of digestion,
after a hearty meal the mesenteric vessels and thoracic duct being dis-
tended with a milky emulsion, while during fasting they are collapsed
and are only seen with difficulty.

The movement of the chyle is dependent upon a number of causes.
In the first place, as mentioned in the description of the mechanisms of
absorption of fat, the villi may be regarded as lymphatic hearts, the con-
traction of their muscular fibres leading to an onward movement of the
contents of the mesenteric lacteals, backward flow being prevented by
the valves of these vessels.

The respiratory movements are also of influence in producing an
onward flow of the contents of the thoracic duct. With each act of ex-
piration, as may be readily determined by making a fistula of the thoracic
duct where it empties into the veins at the root of the neck, there is an
acceleration in the flow of chyle, evidently from compression of the duct,
while in inspiration this flow is retarded or may be even arrested. In-
spiration, therefore, by the production of negative pressure, favors the
flow of chyle frdm the lacteals into the thoracic duct.

Contraction of the abdominal muscles, and even intestinal peristalsis,
will further aid the forward movement of the chyle. So, also, it has
been noticed that there is a slight increase in the rapidity of the flow
of chyle coincident with each systole of the heart. While this factor is
comparatively insignificant, it acts by the compression of the thoracic
duct where it passes under the arch of the aorta.

Finally, in addition to these influences and to the vis a tergo from
continuous absorption by the villi and the propulsion due to their contrac-
tion, the most important factors, there is also a vis a f route concerned in
the circulation of the chyle. For, as Draper has pointed out, where the
thoracic duct empties into the veins, a suction force is exerted on the
contents of the lacteals by the passing current of the venous blood, upon
the well-known hydraulic principle of Venturi : " If into a tube, through
which a current of water is steadily flowing, another tube opens, its more
distant end being in communication with a reservoir of water, through
this tube a current will likewise be established, and the reservoir will be
emptied of its contents."

SECTION V.

LYMPH.

As THE blood circulates through the capillaries, it is continually
losing a portion of its fluid constituents through transudation, carrying
with the water of the blood various salts, gases, and organic matters
in solution. This fluid, which is termed the lymph, bathes all the ulti-
mate tissue elements and supplies them directly with materials necessary
for their nutrition, at the same time removing the soluble effete matters
which result from cellular activity. This fluid, thus resulting from trans-
udation from the blood-vessels, not only fills all the intercellular chinks
of the different tissues, but also finds its wajr from the extra-vascular
spaces and large lymph-spaces (as the lacunae of the connective tissue
and great serous sacs) through the minute radicals of the lymphatic
vessels to the lymphatic glands, and from there through the large lym-
phatic trunks again enters the blood-vessels (veins in the neighbor-
hood of the heart).

From its origin it is evident that the lymph must have a compo-
sition closely similar to that of the liquor sanguinis ; but since different
organs take from the lymph different substances needed by their nutri-
tive demands, and yield effete matters of varying composition, its com-
position must vary according to the region from which it is taken and
the stage of activity of the organs contributing to it. This contrast of
lymph, drawn from different localities, is most marked in the lymph
taken from the tymphatics of the mesentery during the period of diges-
tion when compared with that drawn from other localities. Lymph
drawn from the so-called lacteals during the digestion of fat is termed
chyle, and is of a milky appearance from the large quantities of minute
fat-globules which it holds in suspension. The characters of the chyle
have been already considered.

Lymph may be obtained by inserting a cannula into the thoracic duct of an
anaesthetized animal where it empties into the junction of the large veins at the
root of the neck ; or in large animals, such as the horse and ox, it maybe collected
by a similar process from the lymphatics which accompany the carotid artery.

The amount of tymph which may be obtained by such a process varies
under different circumstances. It is increased by active or passive move-
ments, by venous obstructions, and by poisoning with curare. It is
diminished by decrease in blood pressure.

(463)

464 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

When freshly drawn from the thoracic duct of fasting animals,
lymph is a transparent, slightly yellowish fluid ; when collected during
digestion, it is milky from the fat in suspension derived from the chyle.
When examined under the microscope, lymph is seen to contain color-
less corpuscles, identical with the colorless blood-corpuscles, floating in
a clear lymph-plasma: these corpuscles are much fewer in number in
lymph drawn from the lymphatic radicals, while they are comparatively
abundant in the tymph as it issues from the lymphatic glands. Although
the lymphatic glands are the principal manufacturers of the lymph-cor-
puscles, they are not their sole source. The lymph-cells also originate
wherever adenoid tissue is found, as in the mucous membrane of the
stomach and intestines, in the thymus, tonsils, and spleen.

The lymph of animals in active digestion is milky from admixture
with the fatty clryle : such lymph is said to have a molecular basis from
.the finely divided fat-globules which it holds in suspension. These par-
ticles often exhibit Brownian movements.

The amount of lymph can only be approximately estimated. It has
been reckoned that for every two hundred and twenty pounds of body
weight there is contained in the body about thirteen and a half pounds
of lymph and chyle — seven and a half pounds being chyle and six
pounds lymph. As much as six kilos of tymph have been collected in
two hours from the lymphatic trunk in the neck of the horse, wrhile in
twenty-four hours ninet3'-five kilos of lymph and chyle have been col-
lected from the thoracic duct of the ox. The amount of these two fluids
(lymph and chyle) will evidently increase during digestion. Active and
passive movements and increased blood pressure, as well as obstruction
of the veins, by facilitating transudation from the blood-vessels, will
increase the amount of lymph.

Lymph is a viscid fluid, slightly less alkaline than blood, having
a specific gravit}' that varies from 1022 to 1037, or occasionally as high
as 1045. When removed from the body it coagulates in from five to
twenty minutes, the process being analogous to the coagulation of blood-
plasma, though much slower, perhaps on account of its high alkalinity.
The coagulation of lymph may be accelerated by the addition to it of a
few drops of defibrinated blood b}^ the addition thus accomplished of
fibrin factors in larger amount. A soft, trembling jelly is first formed,
which gradually contracts, expressing out a clear lymph-serum, in which
floats a colorless contracted coagulum, composed of fibrin which is iden-
tical with that formed in blood coagulation.

From 1000 parts of the lymph of a foal, Schmidt determined that
955.17 were serum, while only 44.83 were coagulum. After death the
lymph usually remains perfectly fluid in the lymphatics, and does not
coagulate when the lymph-current is arrested during life.

LYMPH.

465

Lymph is very variable in its chemical composition. It may be
generally stated as follows : —

Water, . . . . . 93 to 98 per cent. (Charles).

Solids, . . . ... 6 " 2

Alhumen, . . " . . .3.2 " 0.3 "

Veuves, •: : : :. 55 }•**»»«•«•••

Ash, . . ; . ... .. .„ 0.7 to 0.8

Sodium chloride forms about 0.6 per cent. The proteids consist of
tibrinogen, serum-globulin, and serum-albumen. Lymph yields only 0.4
to 0.8 per one thousand of fibrin, being much less, therefore, than the
amount obtainable from blood.

In the ash of lymph sodium chloride is very abundant and phos-
phates scant}' : the lymph-cells, however, contain an excess of potassium
and phosphoric acid, as compared with the serum, the latter having an
excess of sodium. Urea is always present (0.019 per cent, in the cow),
and grape-sugar (0.16 per cent, in the dog), though it has been stated
that cli3'le does not take up sugar when animals have been fed on a
starchy or saccharine diet.

The lymph contains C02, N, and traces of 0 when pure and un-
mixed with blood. The amount of C03 is greater than in arterial but
less than in venous blood. While the quantity of N is about the same as
in the blood, the amount of O is always less than in the blood, thus
showing that the tissues rapidly appropriate the O of the blood.

The following table gives a comparison of the composition of the
lymph and blood : —

LYMPH (Wurz).

BLOOD (Nasse).

Water, .

\

Ox.
938.97
2.05
50.90
0.42
7.46

Cow.
955.38
2.20
34.76
0.24
7.41

Ox.
799.59
3.62
66.901
2.045
7.041
121.865

Calf.
826.44
5.737
56.414
1.610
8.241
102.803

Fibrin, . . . .
Albumen and extractives,
Fats, ....
Salts, ....
Blood-corpuscles, .

HESULTS OF THE QUANTITATIVE ANALYSIS OF LYMPH AND CHYLE.
I. ANALYSES OP THE LYMPH OF MAN.

CONSTITUENTS IN
100 PARTS.

Gubler and
Quevenne.

Marchand
and
Colberg.

Scherer.

Dannhardt
and
Hensen.

Odeiflus
and
Lang.

I.

It

III.

rv.

V.

98.63
1.37
0.11
0.23

0.15
0.88

VI.

Water ....

93.99
6.01
0.05
4.27
0.38
0.57
0.73

93.48
6.52
0.06
4.28
0.92
0.44
0.82

96.93
3.07
0.52
0.43
0.261
0.31./
1.54

95.76
4.24
0.04
3.47

0.73

94.36
5.64
0.16
2.12
(2.48
\ 0.16
0.72

Solid matters, . . .
Fibrin,
Albumen

Fats

Extractive matters,
Salts

466

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

II. ANALYSES OF THE LYMPH OBTAINED FROM THE LYMPHATICS OF THE

HORSE (C. SCHMIDT).

CONSTITUENTS IN 1000 PARTS.

I.

II.

Water

963.93

955.36

Solid matters, . . . . ...,,-.

36.07

44.64

Fibrin,

1

Albumen,
Fats and fatty acids, . . . .-.., . .

28.84

34.99

J

Inorganic matters, . . . . . .

7.22

7.47

NaCl . .

5^43

5.67

Na20, . . . . . . . ' .

1.50

1.27

K20, . ' .< ' ' .

0.03

0.16

S03, . . . . . . . . ...

0.03

0.09

P2O5, combined with alkalies, .....
Ca3(P04)2 - . . . .
Mg3(P04)2, .

0.02

0.22

0.02
0.26

In the serum from 1000 parts of lymph Schmidt

found : —

Albumen, . . . . ..'...
Fats and fatty acids, . . ....'. .

23.32

f 30.50
| 1.17

4.48

1.69

III. ANALYSES OF CHYLE OF THE HORSE, DOG, AND MAN (HOPPE-SEYLER).

CONSTITUENTS IN
1000 PARTS.

I
Chyle of
Horse.

II.
Chyle of
Horse.

III.
Blood-
Serum.

IV.

Chyle of
Dog.

V.
Blood-
Serum of
Dog, IV.

VI.

Chyle of
Man.

Water,

960.97

956.19

930.75

906.77

936.01

904.80

Solids

39.03

43.81

69.25

96.23

63.99

95.20

Fibrin

257

1 27

1 11

Albumen, ......

22.60

29.85

56.59

21.05

45.24 $

70.8

Fats, cholesterin, and
lecithin,
Fatty acids in the form
of soaps, ....
Other organic matters,
Hsematin,
Mineral salts, ....
Loss

Qr09

0.76
5.37
0.05
7.59

0.53

0.28
2.24
0.06
7.49

1.57 >
3.855

7.14

64.86
2.34
7.92

6.81
2.91

8.76
027

9.2
10.8
'4.4

NaCl

5.76

5.84

5.74

Na20

$ 1.17

0.87

K20

A 1.31

I 013

014

SO3 '

007

005

Oil

'

P O5

0.01

0.05

0.01

Ca3(P04)2, ....
Mg (P04)2, .

I 0.44
1.02

0.25

082

0.26
056

• •

. .

LYMPH.

467

Schmidt gives the following analysis of the lymph of a cow : —

Serum, . .''.•' 95.52

Clot, 4.42

In 100 parts
Serum.

Water, .

Fibrin, .

Other albumens,

Fats, , »

Organic matter,

Salts,

Sodic chloride,

Soda,

Potash, .

Sulphuric and phosphoric acids and

earthy phosphates, . . . . 0.04

3 20

0.12
0.17
0.74
0.56
0.13
0.01

In 100 parts
Clot.

90.73
4.86

3.43

0.96
0.60
0.06
0.10

0.23

The lymph further differs in composition according to the locality
from which it is collected. The following table gives the composition
of the lymph of the horse : —

Lymph
Collected from
the Femoral
Vessels
(Gmelin).

Lymph
Collected from
the Cervical
Vessels (Leuret
and Lassaigne).

Lvinph
Collected from
the Vessels of
the Foot
(Geiger).

Lymph from
the Vessels of
the Foot of an
Ass (Rees).

Water .

964.30

925.00

983.70

965.36

Solids,

35.70

75.00

16.30

34.64

Fibrin

1 90

330

040

1 20

Albumen, ....
Fats
Extractives, ....
Inorganic matters,

21.17
traces

10'.63

57.36
14".34

6.20
traces
2.70
7.00

12.00
traces
15.69
5.85

The Circulation of the Lymph. — The tymph is continually moving
in the lymphatic vessels in a slow stream from the lymphatic radicals to
the larger lymphatic trunks, and thence into the large veins in the neigh-
borhood of the heart, motion being due to the difference in pressures be-
tween the lymphatic capillaries and the entrance of the lymph-trunks
into the veins.

Since the lymph originates as a transudation from the blood-vessels
in the interstitial spaces, the pressure to which it is subjected will be
nearly identical to the pressure in the blood-vessels which causes its pas-
sage through the vascular walls. Each volume of lymph will, therefore,
be forced onward by the amounts which succeed it under a pressure
which is nearly equal to the blood pressure. On the other hand, the
pressure of the lymph at the points of entrance of the lymphatics into
the veins will be in all cases slight, and sometimes will be even negative :
for during inspiration the expanding thorax aspirates the blood from

468 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the large venous trunks into the veins of the thorax, and by the dilata-
tion of the right auricle from thence into the heart. As the lymphatics
empty into the veins in the neighborhood of the heart, this aspiration
will also be exerted on the lymphatics and will tend to produce a nega-
tive pressure. The lymph will, consequently, be subjected to a steadily
decreasing pressure from the periphery to the central vessels, and will,
therefore, move from the lymphatic radicals toward the venous trunks.
The onward motion of the lj*mph is also facilitated by muscular move-
ments, which, by compressing the lj mphatics, force their contents onward,
backward motion being prevented b}^ numerous valves.

The lymphatic vessels, also, possess the power of rhythmic contrac-
tion, through the contraction of their muscular fibres, and sometimes
true lymph-hearts aid the propulsion of the lymph.

In certain organs special mechanisms are concerned in the propul-
sion of the lymph. Thus, in the abdominal surface of the central tendon
of the diaphragm there are free communications between the peritoneal
cavity and the lymphatics of the diaphragm; and as the central tendon
is composed of two layers of fibrous tissue arranged in different
directions, these layers are alternate^ pressed together and pulled apart
in the respiratory movements of the diaphragm. The effect is to pump
lymph into the spaces between these layers. A similar mechanism exists
in the costal pleura and in the fascia covering the muscles. " When a
muscle contracts, lymph is forced out from between the layers of the
fascia, while, when it relaxes, the lymph from the muscle, carrying with
it some of the waste products of muscular action, passes out of the
muscle into the fascia, between the now partially separated layers"
(Landois). While the lymph-glands offer considerable resistance to the
onward passage of the lymph, this is, to a certain extent, compensated
by the non-striped muscular fibres which exist in the capsule and
trabeculse of the glands, these muscles, together with those of the
lymphatics and lymphatic hearts, when present, being directly under the
control of the nervous system.

The velocity of the lymph-current increases as the trunk increases
in size, from the decrease in sectional area. In the large lymphatic in
the neck of the horse it has been placed at two hundred and thirty to
three hundred millimeters per minute ; it must, therefore, be very slow
in the small vessels. The lateral pressure in the lymphatics in the neck
of the horse has been estimated at from ten to twenty millimeters of a
weak soda solution (Weiss).

SECTION VI.
THE BLOOD.

THE blood may be regarded as the main organ of nutrition, since, on
the one hand, the assimilated food-stuffs enter into it at the point of
their absorption to be carried to the points where they may be needed
by the economy ; and, on the other hand, the results of tissue waste are
given up to it to be removed from the economy.

The blood may be regarded as a cellular tissue with a fluid inter-
cellular substance in perpetual motion within a system of branching
tubes. The blood is not a homogeneous solution, but is composed of
an immense number of minute-formed elements, the blood-corpuscles or
cells, suspended in a colorless, transparent fluid, the blood-plasma. Of
the blood-corpuscles, the so-called red cells are greatly in excess, and it
is to the haemoglobin, or red coloring-matter, which they contain that
the red color of the blood is due.

The red hue of the blood drawn from a living animal will vary ac-
cording to the locality from which it is taken ; the blood taken from the
arteries, the left side of the heart, or the pulmonic veins being of a bright,
scarlet-red color, while that drawn from the veins, the right side of the
heart, or the pulmonic artery, is dark, brownish red. When exposed to
air or to oxygen gas, the dark venous blood becomes arterial in hue,
and this change occurs most rapidly when the blood and gas are shaken
up together.

The specific gravity of defibrinated human blood varies from 1045
to 1062, the average being 1055, though greater variations than the above
are not inconsistent with health. Again, the specimens of blood first
drawn will have a higher specific gravity than that examined after con-
siderable hemorrhage, as the water in the blood will have then increased
from the abstraction of fluid from the tissues. The cells are specifically
heavier than the plasma, and of the former the red cells are heavier than
the white. Thus, if blood is prevented by cold from coagulation — and
this is best accomplished with horse's blood — the blood will separate
into three distinct strata, the lowest being composed of red corpuscles,
the middle of white cells, and the upper layer of the clear blood-
plasma. The corpuscles have a density of 1088-1105 ; the plasma, of
1027-1028.

The reaction of the blood is always distinctly alkaline, due to sodium

(469)

470 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

bicarbonate and sodic phosphate, most marked when the blood is freshly
drawn, and decreasing rapidly in intensity until coagulation occurs.

Blood has a peculiar odor which varies in different animal species,
and in certain animals, as in the cat, dog, sheep, and goat, is charac-
teristic of the species. This odor is due to the presence of certain vola-
tile, fatty bodies contained in the blood-plasma, and may be readily
developed by treating the blood with sulphuric acid.

The temperature of the blood varies in different animals, and depends
upon the oxidation processes continually occurring in the tissues. In
man and the domestic mammals the temperature varies from 37.5° to
38° C. In birds it is always higher than in mammals, and may rise as
high as 44.03° C. even in a state of health. The arterial blood is, as a
rule, warmer than venous blood, as the conditions for radiation of heat
are more favorable in the latter than in the former. The temperature of
the blood of the hepatic and portal veins is warmer than other venous
blood, and the blood of the right side of the heart is warmer than that
of the left heart.

The quantity of blood varies in different animals and in the same
species of animal at different periods of life. Various methods have been
proposed for determining the amount of blood contained in the body.
The method which is now generall}' adopted as giving the most reliable
results is to bleed an animal to death and measure the amount of blood
collected. The blood-vessels are then washed out with dilute saline solu-
tion until the fluid which issues from the veins comes out entirely color-
less, and the various washings are collected and mixed. A known
quantity of blood is. then diluted with saline solution until it acquires
the same tint as a measured quantit}7 of the washings collected from the
veins. From the data so obtained the amount of coloring matter in the
washings m&y be estimated. The entire body is then minced, washed
free from blood with saline solution, filtered, and the amount of coloring
matter in the washings estimated as before. The quantit}* of blood in
the two washings, together with the blood first drawn, give the total
amount in the body.

Estimated in this wa}- , the total amount of blood in the human body
has been fixed at y1^ of the body weight ; in the rabbit at y1^ of the body
weight ; dog, y1^ of the body weight ; cat, ^r ; frog, TTg ; mouse, -^ ; the
guinea-pig, y1^ ; bird, yV-^a ; fishes, y^-yV No reliable estimates
exist as to the amount of blood in the larger domestic animals. Colin
states that the amount of blood in the ox amounts only to ^ of the
body weight, but this is probably a low estimate. In animals bled to death
the amount of blood retained in the bod}r depends upon the amount of
adipose tissue : the fatter the animal, the more blood remains in the bod}'
after slaughtering. In thin cattle the amount of blood which escapes

BLOOD.

471

has been estimated at 4.7 per cent, of the body weight; in fat animals,
at 3.9 per cent. In the horse the amount of blood has been estimated at
•fg of the body weight.

The following tables represent the general composition of the blood
in different domestic animals : —

In One Hundred Parts Venous Blood (Hoppe- Seyler and Fudakowski).

Horse. Dog.

Corpuscles, . ; 32.62 38.34

Plasma, ".,.-. . ..... 67.38 61.66

One Hundred Parts Plasma.

Solids, 9.16 7.87

Water,. ..'..'. . . . 90.84 92.13

Fibrin, 1.01 0.18

Albumen, . .' 7.76 6.10

Fats, 0.12 0.21

Extractives, * . . 0.40 0.39

Soluble salts, . . . . . . 0.64 0.82

Insoluble salts, ..... . .0.17 0.17

One Hundred Parts Corpuscles.

Water, 56.50 . . .

Solids, . 43.50 . . .

In One Hundred Parts Defibrinated Venous Blood of Ox (Bunge).

Corpuscles. Serum.

31.87 68.13

Water, . . .

Solids, .

Albumen,

Haemoglobin,

Other organic matters, .

Inorganic matters,

Potassium,

Sodium,

Lime,

Magnesium,

Iron oxide,

Chlorine,

Phosphoric acid,

Water, .

Fibrin, .

Fat,

Corpuscles, .

Albumen,

Alkaline phosphates,
" sulphates,
" carbonates,

Sodium chloride, .

Iron oxide, .

Calcium,

Phosphoric acid, .

Sulphuric acid,

19.12
12.75

3.42

8.94

0.24

0.15

0.0238

0.0667

6.0005

6.0521
0.0224

Ox.

799.59
3.62
2.04

121.86
66.90
0.468
1.181
1.071
4.321
0.731
0.098
0.123
0.018

62.22
5.91
4.99

0.38

0.54

0.0173

0.2964

0.0070

0.0031

0.0007

0.2532

0.0181

Calf.

826.71
5.76
1.61

102.50
56.41
0.957
0.269
1.263
4.864
0.631
0.130
0.109
0.018

1. THE RED BLOOD-CORPUSCLES. — Human red blood-corpuscles re-
semble biconcave lenses : their diameter varies between 0.0064 and
0.0086 millimeters.

472

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In man and all mammalia, with the exception of the camel tribe,
they are circular and devoid of a nucleus ; in birds, reptiles, and most
fish, they are oval, biconvex, and nucleated ; in the camel, the red
blood -cells are oval, but are not nucleated. From the fact that the
edges of the red blood-cells are convex and the centre concave, these
different parts refract light differently, and when examined under the
microscope, if the edges are sharply denned, the centres appear dark,
and vice versa (Fig. 172).

There is no constant relation between the size of an animal and the
size of its blood-disks ; thus, among mammals, although the red blood-
corpuscles of the elephant are the largest, those' of the mouse are by no
means the smallest, being, in fact, three times as large as those of the
musk-deer (Fig. 173).

FIG. 172.— RED BLOOD-CORPUSCLES. (Landois.)

A, human red blood-corpnscles: 1, seen on the flat; 2, on edge: 3, rouleaux of colored corpuscles
slightly separated. B, colored amphibian blood-corpuscles: 1, seen on the flat, and, 2, on edge. C, ideal
transverse section of a human red blood-corpuscle magnified five thousand times linear: no, diameter;
c d, thickness.

In the various domestic animals their diameter is placed as follows
in fractions of a millimeter : horse, 0.004-0.005 ; ox, 0.003-0.005 ; dog,
0.005-0.007; sheep, 0.002-0.004; goat, 0.002; hog, 0.003-0.004 milli-
meters. Frequentl}', particularly in growing animals and after profuse
hemorrhage or exhausting disease, red blood-corpuscles smaller than the
above will be found. These are probably to be regarded as young, grow-
ing blood-cells. The number of the red blood-cells is almost infinite; in
one cubic centimeter of blood in man, five million red blood-disks have
been estimated to be present ; in the goat, nine to ten millions ; in the lamb,
thirteen to fourteen millions ; in birds, one to four millions ; in the fish,
one-quarter to two millions ; in the frog, half a million ; and in the pro-
teus, thirty-six thousand. In fact, 30 to 40 per cent, of the entire mass
of the blood is composed of red blood-corpuscles ; thus, in the horse,

BLOOD.

473

63. 7 per cent, of the blood is constituted by the plasma, and 36.3 per
cent, blood-corpuscles. The red corpuscles, as already mentioned, are
heavier than the other constituents of the blood, and are the cause of

FIG. 173.— BLOOD-CORPUSCLES OF DIFFERENT ANIMALS. (Thanh offer.)

1, proteus : 2, rana esculenta : a, upper view : b, white blood-corpuscle : c., side view of red blood-cor-
puscle: 3, triton ; 4, snake: 5, camel; 6, turtle; 7, salamander: 8, carp; 9, cobitis fossilis; 10, cuckoo;
11, chicken; 12, canary-bird; 13. lion: 14, elephant; 15, man: a, upper view; 1>. crenated form; c, color-
less corpuscle ; 16, horse, the cells arranged in rouleaux ; 17, hippopotamus, upper view.

the color and opacity of the blood ; their specific gravity may be placed
at about 1090. If water is added to blood, it appears darker in reflected
light, but is more transparent. This depends upon the change in shape

FIG. 174.— RED BLOOD-CORPUSCLES, SHOWING VARIOUS CHANGES IN SHAPE. (Landois.)

«, 6, normal human red corpuscle, with the central depression more or less in focus : c, d, e, mulberry
forms: <j, h, crenated corpuscles; A% pale, decolorized corpuscles; t, stroma; /, a frog's corpuscle, partly
shriveled, owing to the action of a strong saline solution.

of the red blood-cells : as they imbibe water they swell up, and so reflect
less light, and at the same time the co-efficient of refraction differs less
than normal from that of the blood-serum. On the other hand, if salt

474

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

solution is added to blood instead of water, the corpuscles shrivel up and
therefore favor the reflection of light and prevent its transmission ;
hence the blood is now less transparent, but appears lighter in reflected
light (Fig. 174).

The red blood-corpuscles are almost fluid in consistence, and
resemble, therefore, suspended drops of jell}'. This characteristic is
frequently seen when the circulation in the capillaries, as in the mesen-
tery of the guinea-pig, is examined under the microscope. The red
blood-cells will often be observed to change their shape by pressure
from a disk to an elongated rod, and sometimes such a distorted cor-
puscle will catch at the point of
bifurcation of a capillary, where it
may hang like a pair of saddle-bags,
part in one branch of the capillary,
and the other half in the opposite.
Even in animals with nucleated red
blood-cells, like the frog, similar
change in shape may be seen ; the
red blood-cells may even be seen to
pass out through the walls of the
blood-vessels, becoming in the
process drawn out into a fine thread.
The red blood-corpuscles are
composed of the " stroma" and " hae-
moglobin."

Early observers regarded the red
blood-corpuscle as a vesicular body
in which a cell-membrane inclosed
fluid contents ; at present it is be-
lieved to be composed of a semi-fluid
net-work or frame-work, the stroma,
denser at the periphery than at the
centre, in the meshes of which are inclosed the other constituents of the
cell. The stroma may be demonstrated by alternately freezing and
thawing the blood, which then loses its opacity and becomes a clear,
lake-colored fluid, the haemoglobin having left the corpuscles to pass into
solution in the plasma, and the stromata remaining as colorless bodies,
which sometimes retain the original form of the blood-cell, but usually
are either more globular or more shriveled than normal. The stroma is
colorless and highly elastic and is albuminous in nature ; it is insoluble
in serum, dilute salt or sugar solutions, and water below 60° C., but it
is soluble in serum containing alcohol, ether, or chloroform, in caustic
alkalies, and in solutions of alkaline salts of the bile acids.

FIG. 175.— H^MOG^OBIN CRYSTALS
THE Ox. (Ellenberger.)

OF

BLOOD.

475

The most important constituent of the red blood-corpuscles, both in
quantity and function, is the " haemoglobin." Haemoglobin, or the blood
coloring-matter, is a complicated, crystallizable albuminoid body
containing iron, and forms about 90 per cent, of the red blood-cells.
When separated from the corpuscles, haemoglobin readily crystallizes out

.4, a

o

FIG. 176.— BLOOD-CRYSTALS OF MAN AND DIFFERENT ANIMALS. (Thanhoffer and Prey.)

1, haemoglobin crystals ; Mo, squirrel ; Tr, guinea-pig ; U, ground-mole : L. horse: Em, man; H,
marmot; Ma, cat; T, cow; mu, from the venous blood of a cat. 2, hsematin crystals ; E, man; V&,
sparrow ; M, cat. 3, haematoidin crystals from an old blood extravasation of man.

of its solutions in serum when concentrated. These crystals have dif-
ferent forms in different species of animals, depending, apparently, on
varying amounts of water of crystallization. In the domestic animals they
belong to the rhombic system ; those of the squirrel are hexagonal. The

476 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

crystals are doubly refractive and soluble in water and weak alkaline
solutions, those obtained from horses' blood being more soluble than the
haemoglobin of the dog or cat (Figs. 175 and 176).

Haemoglobin solutions decompose after s.tanding a few daj^s, es-
pecially when concentrated and exposed to a warm temperature, and the
red color is then replaced by a dirty-brown hue, which appears greenish
in transmitted light. Concentrated alkalies, various metallic salts, and
acids facilitate this decomposition, which consists of the breaking up of
the haemoglobin into certain albuminoids and a coloring matter, haematin,
which is often found in old blood extravasations. Haemoglobin crystals
may be obtained in various ways from the blood of the dog, horse,
guinea-pig, or cat. All the agents which deprive the red corpuscles of
their coloring matter, so rendering the blood lake-colored, may serve to
form oxyhaemoglobin crystals ; such as repeated freezing and thawing, elec-
tricity, a temperature of 60° C., powdered salts, ether in vapor or sub-
stance, chloroform, and the bile salts. The simplest way is to defibrinate
dog's blood, remove as much serum as possible, and then shake the blood
with a little ether. As soon as the ether has partially evaporated the
crystals commence to form.

The composition of haemoglobin is as follows : —

16.1^21.6^0.5.

The following has been given as its empirical formula, assuming
that the molecule contains one atom of iron : —

C60oH960N164FeS8Om.

Haemoglobin readily forms a loose chemical union with oxygen,
called - oxyhaemoglobin. It may be formed by shaking a solution of
haemoglobin with oxygen. The oxygen is again readily removed from
this compound by exposure to a vacuum or by various reducing agents,
such as ammon. sulph., iron salts, or metallic iron. That this union of
oxygen with haemoglobin is of a chemical nature is proven, in the first
place, by the constancy of the equivalent of combination : Thus, one
gramme of haemoglobin will unite with 0.0024 gramme oxygen ; this
would place the molecular weight of haemoglobin at about 13,000.

In the second place, the difference in optical characteristics of
haemoglobin and oxyhaemoglobin point to difference in chemical consti-
tution. Thus, reduced haemoglobin is characterized by an absorption-
band in the yellow portion of the spectrum, while solutions of
oxyhaemoglobin show two absorption-bands, one at the line D (sodium
line), and the other at E of the solar spectrum, while the portion of the
spectrum which with reduced haemoglobin is dark, with oxyhaemoglobin
is clear (Fig. 177).

BLOOD.

477

In the animal body haemoglobin is never saturated with oxygen,
even in arterial blood, while oxy haemoglobin is never absent from venous
blood ; consequently, physiologically, we have to deal with an association

of haemoglobin with oxy haemoglobin, the. relative proportions of each
varying in different localities and under different circumstances.
Further characteristics of these bodies will be studied in the chapter on
Respiration.

478 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Compounds similar to oxyhsemoglobin are formed between haemo-
globin and carbon monoxide and cyanogen. These two gases displace the
oxygen from oxyhaemoglobin, and form compounds which cannot again
be broken up with oxygen. These compounds, as well as those formed
with nitrous oxide and sulphuretted hydrogen, are more stable in nature
than the oxyhsemoglobin.

Haemoglobin is chemically an even more complex body than albumen,
since the latter, together with haematin, are decomposition products of
haemoglobin. This decomposition especially occurs under the action of
acids, though it also takes place when solutions of haemoglobin are
exposed to a moderately warm temperature. Out of one hundred parts
haemoglobin, about four parts haematin and ninety-six parts albumen
may be separated.

The inorganic constituents of the red blood-corpuscles differ very
essentially from those found in the blood-plasma. While the latter is
rich in chlorine and sodium, only traces are to be found in the blood-
corpuscles, where, however, potassium and phosphates are present in
large amounts, though they are almost entirely absent from the serum.
The fact that we have here such a marked separate distribution of soluble
salts, without any apparent tendency to their equal distribution, shows
that there must be some force present which interferes with the working
of the laws of diffusion and inhibition.

The following table shows the contrast between the inorganic con-
stituents of the corpuscles and blood-plasma (Schmidt) : —

1000 parts of Moist Corpuscles yield— 1000 parts of Plasma yield-

Mineral matters (exclusive Mineral matters, . . 8.550

of iron),
Chlorine,

Sulphuric anhydride,
PHOSPHORUS PENTOXIDE,
POTASSIUM, .
Sodium,

Calcium phosphate,
Magnesium, .

8.120 CHLORINE,

1.686 Sulphuric anhydride,

0.066 Phosphorus pentoxide,

1.134 Potassium,

3.328 SODIUM. .

1.052 Calcium phosphate, .

0 114 Magnesium phosphate,
0.073

3.640

0.115
0.119
0.323
3.341
0.311
0.222

Too much importance must not, however, be laid upon this peculiar
distribution of the inorganic constituents of the red blood-corpuscles
and plasma, as given above for human blood, since it does not by tiny
means hold in the case of other animals, for in most animals the sodium
salts in the corpuscles actually preponderate over the potassium salts.
The following table illustrates this : —

BLOOD-OKLL.S. LIQUOK SANGUINIS.

K.

Man,
Dog,
Cat, .
Sheep,
Goat,

K.

Na.

Cl.

K.

Na.

Cl.

40.89

9.71

21.00

5.19

37.74

40.68

6.07

36.17

24.88

3.25

39.68

37.31

7.85

35.02

27.59

5.17

37.64

41.70

14.57

38.07

27.21

6.56

38.56

40.89

37.41

14.98

31.73

^3.55

37.89

40.41

BLOOD. 479

2. THE WHITE BLOOD-CORPUSCLES. — The white blood-cells are nucle-
ated masses of free protoplasm destitute of any membrane, granular in
appearance, and of the same nature as lymph and pus, or connective-
tissue corpuscles. When in globular form these cells have a diameter
of about 0.01 millimeter ; like other forms of free protoplasm, such as
the amoeba, they are capable of assuming the most diverse shapes. Even
after being drawn from the body, if a drop of blood is kept at the body
temperature 011 a warm stage under the microscope, the white blood-

FIG. 178.— HUMAN LEUCOCYTES SHOWING AMOEBOID MOVEMENTS. (Landois.)

cells may be seen to change their shape and position, arid even take fine
granules, such as carmine, into their interior. In other words, they
behave precisely like the amreba (Fig. 178).

The white blood-cells are found in much smaller numbers in the
blood than the red cells ; their relative proportions vary according to the
nutritive condition of the animal, the locality from which the blood is
taken, and various other circumstances. As an average, it may be stated
that there are about three hundred to three hundred and fifty times as
many red cells as white.

480 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The white corpuscles are much lighter than the red, as is shown by
their being found in greatest number near the upper surface of a blood-
clot, and by the fact that when horses' blood coagulates the white blood-
cells form a distinct layer on the surface of the red corpuscles.

The white blood-cells possess great adhesiveness, even while in the
blood-current. This adhesiveness of the white cells may also be seen
in blood drawn from the body. If a drop of blood is covered with a
cover-slip and a drop of -J per cent, salt solution passed under the cover
by dropping a little of the solution at one side. and drawing it through
by placing a piece of bibulous paper at the opposite edge, the red blood-
cells may be seen by the microscope to rapidly pass from one side of the
field to the other, while the white cells remain adherent to the cover-slip.
They, therefore, have a tendency to cling to the walls of the blood-vessel
in which they may be circulating, and, since the white cells have an almost
fluid consistence, they readily pass through the walls of the capillaries
into the surrounding tissue. This especially occurs in inflamed tissues,
when the slow blood-current and high pressure favors this transudation ;
in fact, according to many pathologists, nearly all pus-cells are supposed
to originate in such a transudation of the white blood-cells.

After passing through the walls of the capillaries in normal circum-
stances the white blood-cells directly enter the lymph-spaces in which
originate the Lymphatic vessels, from which they may again enter the
blood-current. It does not, however, follow that all lymph-corpuscles
which are thrown into the venous current have originally been derived
from white blood-cells which have passed from the blood through the
walls of the capillaries into the lymph. We have already seen that
man}T lymph-cells originate in the lymphatic glands, are developed in
the blood into red blood-cells, and as such are again broken down. This
change of the white into red blood-cells appears principally to take place
in the red marrow of bones and in the spleen. In these organs capillary
arterioles do not pass directly into the venous radicals, but into large
spaces, or lacunse, from which, after passing through a sieve-like cellular
net-work, the modified blood-cells enter at once into large venous capil-
laries. The passage of the blood into these great expansions naturally
produces a great slowing of the current, and it is quite conceivable that
time will then be given for profound changes in the blood-cells ; part of
the protoplasm of the white cells is changed into haemoglobin, the
nucleus appears to be extruded and ultimately dissolved in the blood-
serum, and a red blood-cell is thus developed.

The white blood-cells have a very complex chemical composition ;
various albuminoids enter into their composition, as well as carbo-
hydrates, fats, lecithin, cholesterin, phosphates, and calcium, while the
cell-nucleus appears to consist mainly of a phosphorized bod}^, nuclein.

BLOOD. 481

Albuminoids of various sorts form the great mass of the white
blood-corpuscles. These correspond mainly to the albuminoids which
are found in the blood-plasma, which, together with the paraglobulin,
or fibrino-plastic substance, will be described in the consideration of the
coagulation of the blood.

The protoplasm of the colorless blood-cells undergoes partial coagu-
lation at 40° C. It swells and becomes transparent when treated with
acetic acid, the nuclei becoming more distinct. With 10 per cent, salt
solution the protoplasm swells and becomes dissolved (leaving the nuclei
intact), the solution being coagulable with heat and the mineral acids
and precipitated by dilution with water. The proteid constituents of
the white blood-cells are thus largely of a globulin-like nature.

Of the carbohydrates, gtycogen occupies the first rank in importance.
When treated with a solution of iodine (one gramme) in iodide of potas-
sium (two grammes in one hundred c.c. water) many of the white blood-
cells assume a reddish, mahogany color, while in others the body of the
cell stains deep j^ellow, numerous granules taking on the mahogany
tint which is characteristic of gtycogen. From the importance which
glycogen has been found to possess for muscular contraction, it may be
assumed that the contractility of the white blood-corpuscles is developed
at the expense of the glycogen.

Variable amounts of fat are also found in the protoplasm of the
white blood-corpuscles in the form of highly refractive granules. The
importance of this fat for the life processes of the blood-cells is as jret
undetermined. Whether it is formed as a result of the breaking down
of the cell-protoplasm, or whether it exists as a result of absorption
processes, is not certain, though the following experiment seems to
indicate the former origin.

If a piece of dry pith is inserted into the abdominal cavity of a liv-
ing animal, the pores of the pith are soon found to be filled with blood-
serum and white blood-cells ; the latter pass into the interior of the pith,
and if, after remaining in the abdominal cavity for twenty-four hours,
the pith is examined under the microscope, the external layers will be
found to be occupied by perfectly normal, living, white blood-cells, wrhile
those which are found in the central portions have assumed a spherical
form and undergone such extensive fatty degeneration that the pith
seems to be impregnated with fat-globules.

Lecithin. — A phosphorized body which has already been described
as a constituent of nearly all developing cells is also found as a constant
constituent of the white blood-cells. As regards the origin of this sub-
stance, there is also the greatest uncertainty, though there is some
evidence in favor of the view that it exists as a preliminary stage to
the formation of fat. Lecithin is capable of a high degree of aqueous

31

482 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

inhibition, when it becomes a very adhesive, gummy substance, to which
probably the adhesive properties of the white blood-cells are due.

Cholesterin is also a constant constituent of normal white blood-
cells. It is not known whether the cholesterin is dissolved or suspended
in the protoplasm of the white blood-corpuscles.

In addition to the above substances which are contained in the liv-
ing white blood-corpuscles, there exists in breaking up corpuscles the
fibrin ferment which originates in the death of the protoplasm. This
substance, which possesses the power of converting soluble into insoluble
fibrin, may be regarded as a complicated organic body, and possesses,
even when in most minute quantity, the power of decomposing the
peroxide of hydrogen, probably with the assistance of the elements of
water, and of producing the modified forms of fibrinogen. That this fer-
ment is set free by the breaking down of tl^e protoplasm of the white
cells, and is not contained dissolved in the plasma of the blood, is ren-
dered probable by the following experiment : —

If the mesenteiy of the guinea-pig be examined under the micro-
scope and a crystal of common salt placed near a small blood-vessel, as
the salt melts the inner wall of the vessel will be found to be gradually
covered with numerous white blood-cells until the lumen of the vessel is
finally obstructed by a plug of white blood-cells. At first the margin of
each separate cell is distinct, but soon they become indistinct and the
vessel is then filled with a mass of fibrin, white thrombus, which exactly
resembles the colorless coagulum which forms in clotting blood-plasma.

Nuclein is the most important constituent of the cell-nucleus. Nu-
clein is insoluble in water and dilute acids, but readily soluble in dilute
potash solutions ; when treated with hydrochloric acid it is changed
into a stiff jelly. Nuclein is completely indifferent to the action of the
digestive juices.

As every increase in the white blood-cells is preceded by a growth
of the nucleus, it is possible that the nuclein plays an important role
in the life of the white blood-corpuscles.

In addition to the white and red blood-corpuscles, microscopic ex-
amination of the blood will often reveal the presence of granular nucleated
bodies, which are described as blood-plates or haematoblasts. These
bodies vary considerably in size, being usually about one-third the size
of a red blood-cell, and, like them, biconcave in shape, have about the
same specific gravity as the white blood-cells, and possess the power
of amoeboid movement. They occur as pale, colorless, oval, round,
or lenticular disks, of variable size, averaging about 3 (J.. By Hayem
the}1- are supposed to represent an early stage of development of the red
blood-corpuscles. They are about forty times as numerous as the
leucocytes, and may be recognized in the circulating blood in the mesen-

BLOOD.

483

tery of the guinea-pig or in the wing of the bat. They are precipitated
in enormous numbers upon threads suspended in fresh blood. They are
believed by Bizzozero to be the agents which immediately induce coagu-
lation and take part in the formation of fibrin. They become colorless
and disintegrate during the act of coagulation (Fig. 179).

3. BLOOD-PLASMA AND BLOOD COAGULATION. — Blood-plasma is blood
less blood-corpuscles. It may readily be obtained for study by pre-
venting the coagulation of horses' blood by cold, when both the red and
white blood-corpuscles settle to the bottom and leave the pure plasma,
forming a clear, amber-colored fluid above.

Plasma is a somewhat viscid fluid of alkaline reaction. Its specific
gravity is about 1027 or 1028. It contains about 90 per cent, water,
with from 7 to 9 per cent, of various albuminoids, with small amounts

FIG. 179.— " BLOOD-PLATES " AND THEIR DERIVATIVES, AFTER BIZZOZERO
AND LAKER. (Landois.)

1, surface view of red blood-corpuscles ; 2, side view; 3, unchanged blood-plates; 4, a lymph-cor-
puscle, surrounded with blood-plates; 5, blood-plates variously altered; 6, a lymph-corpuscle with two
heaps effused blood-plates and threads of fibrin; 7, group of blood-plates fused or run together; 8, a simi-
lar heap of partially dissolved blood-plates with threads of fibrin.

of urea, kreatin, kreatinin, and other nitrogenous organic bodies, as well
as sugar, fat, cholesterin, and mineral bodies, of which compounds of
sodium with chlorine and carbon dioxide are in excess. If horses'
plasma, prepared as above, is allowed to become warmed a few degrees
above the freezing point, it completely solidifies into a solid mass : the
plasma is then said to be coagulated. This process of coagulation com-
mences at the edges, in contact with the walls of the vessel which con-
tains it, and on the free surface of the fluid, and rapidty extends through-
out the entire mass until a firm jelly results, which is quite as transparent
as the original fluid. Coagulation is due to certain albuminoids becoming
transformed from the fluid to the solid state, resulting in the formation
of fibrin. Shortly after the formation of the coagulum, a depression
forms in the upper surface of the clot, in which a clear fluid, the serum,

484 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

collects ; the clot then gradually shrinks away from the sides of the vessel
and contracts in every direction, and as the coagulum decreases in bulk
the fluid serum increases, until, finally, the now opaque, small, firm clot
swims in a large amount of clear, yellowish serum.

When horses' blood is not artificially cooled, and in blood of other
mammals, the process of coagulation follows a somewhat different course.
Here also it is only the fibrin which coagulates, and not the blood in toto;
but the process takes place so rapidly that the corpuscles do not have
time to settle, but remain entangled in the fibrin, and the coagulum,
instead of being colorless, is of a deep-red color from the contained red
blood-corpuscles, the whole forming a red, gelatinous mass, — the crassa-
mentum, or clot. Here, also, the process of coagulation commences at the
free surface of the blood and at the surfaces in contact with the walls of
the vessel by the formation of a delicate pellicle, which rapidly thickens
until in from seven to fourteen minutes the entire mass of blood is trans-
formed into a stiff jelly ; and here, also, after the formation of the clot,
there is a gradually progressive contraction, with exudation of serum,
until finally there results a small, red, firm coagulum, floating in the
yellowish serum.

Blood of different species of animals varies in the rapidity with which
coagulation takes place. In the following series coagulation occurs in
gradually increasing rapidity from the first to the last, — horse, cat,
dog, ox, pig, goat, sheep, — the time varying from twenty-five to one
and a half minutes. Normal horses' blood always clots so slowly
that the corpuscles have time partially to settle to the bottom
of the vessel which contains it. Immediately before coagulation, there-
fore, the horse's blood forms different-colored layers, the upper and
smallest being yellowish, while the lower is red. When coagulation
takes place the same arrangement holds, and the clot of horses' blood
has, therefore, a yellowish upper surface, the so-called buffy coat, forming
what used to be called an inflammatory clot (crusta phlogistic a}. Every-
thing, therefore, which accelerates the settling of the red blood-cells,
or which delays coagulation, will tend to develop the buffy coat on
the clot.

In addition to cooling, coagulation nuiy be retarded by pumping out
the oxygen from the blood, by saturation with carbon dioxide (explaining
the tardy coagulation of the blood in animals dying from suffocation, and
why coagulation occurs sooner in venous than arterial blood), addition
of certain salts, such as sulphate, borate, and carbonate of sodium,
chloride of sodium, sulphate of magnesium, nitrate, acetate, and car-
bonate of potassium, and chloride of potassium, through the addition
of small amounts of caustic potash or ammonia, sugar and gum solutions,
or by acidulation with dilute acetic or nitric acids. By exact neutraliza-

BLOOD. 485

tion of acidified blood with ammonia, or through the prolonged action of
ozone, the coagulabilit}' of the blood may be completely removed.

The intravenous injection of 0.3 gramme peptone in 0.5 per cent, salt
solution for each kilo of body weight in the dog likewise prevents the
coagulation of the blood.

Warming of the blood above its normal temperature accelerates co-
agulation : so, also, the more extensive the contact of the blood with
foreign bodies and with the atmosphere, the more rapid the coagulation.

If blood, as it escapes from a blood-vessel, is stirred or whipped
with glass rods or twigs, coagulation occurs somewhat more rapidly
than normally ; but instead of the entire blood being transformed into a
jelh', the substance — fibrin — on whose solidification blood coagulation
depends separates in the form of fibrous lumps and shreds adhering to
the body with which the blood is whipped. The blood is then said to be
defibrinated, and the fluid in which the corpuscles remain suspended is
termed serum, instead of plasma. Plasma is, consequent!}-, the fluid
constituent of blood which still contains uncoagulated fibrin elements ;
serum is plasma minus the fibrin elements. Serum may be obtained as
a clear fluid by allowing the corpuscles to settle or by separating them
with the centrifugal machine ; or, as already stated, it exudes from the
clot when blood is allowed spontaneously to coagulate.

The coagulation of the blood consists in the formation of fibrin, an
albuminous body which results from the action of a ferment-like body
on the albuminous constituents of the plasma, the process being similar
to the spontaneous conversion of soluble into coagulated casein in milk
from the action of the casein ferment.

The theory as to the formation of fibrin which has met with most
general acceptance, though we shall find that it requires some slight
modification, is that coagulation results when two albuminous bodies
contained in blood-plasma, the fibrinogen and fibrino-plastic substances,
unite under the influence of the fibrin ferment. The conditions governing
this chemical process may be made clear by the following experimental
facts (Foster): —

If the blood, as it flows from a divided vessel, is received in a beaker
containing about one-third the volume of blood of a saturated solution
of a neutral salt, such as magnesium sulphate, coagulation will be
prevented, the corpuscles will settle in time to the bottom of the vessel,
the fluid plasma — mixed, of course, with the salt solution — forming a
transparent la\^er above them. If some of this plasma be drawn off
with a pipette and diluted with eight or ten times its bulk of water,
coagulation will be produced. The neutral salt has, therefore, merely
prevented coagulation by its presence, and has not destroyed the sub-
stance or substances from which fibrin is formed. If to some of the

486 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

undiluted blood-plasma, in which coagulation has been prevented by cold
or a neutral salt, an excess of sodium chloride in bulk be added, a sticky,
white precipitate will be formed, and if it is filtered off' it will be found
that the plasma, even if warmed or diluted with water, has now lost its
power of coagulation. If the precipitate collected in the filter be
washed with a saturated solution of sodium chloride, in which it is
insoluble, and then dissolved in a small amount of distilled water
(enough salt will cling to the precipitate to make it a dilute saline
solution) and filtered, the clear filtrate will rapidly solidify in the same
manner as the blood-plasma prevented by cold from coagulation when
gently warmed. This substance is termed plasmine, and it is evident
that the coagulation of the blood is due to the conversion of plasmine
into fibrin. Plasmine is not, however, a simple body, but a mixture of
two proteids, as is shown by the following facts : —

If sodium chloride in bulk be added to the serum which separated
from clotted blood, a precipitate will be formed which in its general
characters resembles plasmine, but its solution will not coagulate spon-
taneously. This body is termed paraglobulin or fibrinoplastin.

If sodium chloride be added in bulk to some hydrocele fluid, a
similar precipitate will also be formed, which also, when in solution, will
not coagulate spontaneously. This substance is termed fibrinogen. If
a solution of fibrinogen be added to a solution of paraglobulin, coagula-
tion occurs in a manner precisely similar to that observed in blood-plasma
or in solutions of plasmine. So, also, the addition of blood-serum to
hydrocele fluid will likewise cause coagulation. These facts would seem
to indicate that plasmine is a mixture of paraglobulin and fibrinogen.
Another factor is, however, also concerned.

Both paraglobulin and fibrinogen may be precipitated from serum
and hydrocele fluid by C02, and yet the solutions of these precipitates
when mixed together will not coagulate.

If some defibrinated blood be poured into about twenty times its
volume of strong alcohol, all the proteids will be coagulated. If, after
standing some weeks in alcohol, the precipitate be filtered off and ex-
tracted with water, a few drops of this solution added to the above mix-
ture of paraglobulin and fibrinogen obtained by C02, coagulation will
rapidly result. If, however, the watery extract be first boiled, no
clotting will result. This points to the presence of a ferment. Conse-
quently we say coagulation results from the union of paraglobulin and
fibrinogen in the presence of the blood ferment.

It has, however, been found that fibrin may result from the addition
of the fibrin ferment to pure fibrinogen, without in any way requiring
the assistance or presence of fibrinoplastin. Nevertheless, the amount
of fibrin so formed is considerably less than would result from the coag-

BLOOD. 487

illation of the same amount of fibrinogen if fibrinoplastin were present.
It would, therefore, appear that the fibrinoplastin in some way assists in
converting the soluble fibrinogen into the insoluble fibrin, without itself
directly taking part in the formation of the latter. This view is sup-
ported by the fact that while blood-serum is entirely free from fibriu-
ogen it contains nearly as much fibrinoplastin as uncoagulated blood.

Fibrinoplastin perhaps acts in the same way as certain salts (NaCl,
CaCl2) and lecithin, which, when added in very small amounts to coag-
ulable fluids, appear to increase the amount of fibrin formed.

The above-mentioned fibrin factors do not exist ready formed in
the circulating blood of living animals, but originate in the breaking
down of the white blood-cells in man and other mammals, and of the red
nucleated blood-cells of birds and amphibia. As to how far the haemato-
blasts are concerned in this process is still the subject of controversy;
it is, however, absolutely certain that immense numbers of the white
blood-corpuscles disappear during coagulation.

Fibrinogen belongs to the group of globulins, i.e., albuminous bodies which
are insoluble in water, but soluble in dilute saline solutions, in which again they
are rendered insoluble through the action of acids and alkalies.

Fibrinogen may be prepared by collecting horses' blood in one-fourth its
volume of a saturated solution of magnesium sulphate, stirring and filtering,
separating the corpuscles from the plasma by the use of the centrifugal machine,
and adding to the latter an equal volume of a saturated salt solution. The pre-
cipitate is then collected, dried by pressing between layers of filter-paper, dis-
solved in an 8 per cent, salt solution, again precipitated with an equal volume of
saturated salt solution, again drying and dissolving, and repeating the process until
a precipitate is obtained, which, after drying with filter-paper, still retains enough
salt adhering to it to render it soluble in distilled water, and which should con-
tain no trace of serum-albumen or paraglobulin. The removal of the paraglobu-
lin depends upon the fact that fibrinogen is very much more readily precipitated
l>y 15-20 per cent, salt solution than is paraglobulin. So* obtained, fibrinogen, in
1-5 per cent, salt solution, coagulates at 52°-55° C. It also may be obtained,
mixed with fibrinoplastin, from hydrocele or pericardial fluid, by dilution with
10-15 volumes of water, or by the passage of a stream of CO2.

The jibrinoplastic substance, or paraglobulin, is obtained as a white precipi-
tate when perfectly clear and colorless blood-serum is faintly acidulated with
acetic acid, and then diluted with fifteen or twenty times its volume of distilled
water. The precipitate is then collected on a filter and washed with distilled
water. Out of 100 c.c. ox-serum 0.7-0.9 gramme paraglobulin may be obtained
by this process, though it is almost impossible to free it entirely from fibrin
ferment.

The freshly precipitated paraglobulin is perfectly white, is insoluble in water,
but is soluble in dilute solutions of sodium bicarbonate, sodium phosphate, sodium
chloride, and other neutral salts of the alkalies. These solutions coagulate on
heating like ordinary albumen (between 60° and 80° C.), and when diluted with
distilled water again precipitate the paraglobulin.

If paraglobulin is added to certain serous fluids, such as hydrocele fluid, peri-
cardial fluid, and serous effusions, coagulation is instantly produced through the
action of the fibrin ferment, which always contaminates it.

There is less paraglobulin in horses' blood than in oxen's blood — 0.3 to 0.5
per cent, in the serum of the former to 0.7 to 0.8 per cent, in the latter.

Paraglobulin, as well as fibrinogen, originates in the breaking down of
white blood-corpuscles.

The fibrin ferment has never been obtained pure. Its aqueous solutions may
be prepared by adding 15-20 volumes of absolute alcohol to the pure serum of

488 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

horses', oxen's, or dogs' blood, allowing the coagulated albuminoids to remain for
at least two weeks under alcohol until they become completely insoluble, filtering,
drying over sulphuric acid, and dissolving in water ; traces of albumen which
still cling to the ferment may be removed by the cautious addition of acetic acid,
or CO2. The ferment is not contained in living blood, but is a product of break-
ing down white blood-corpuscles. Its amount appears to have no influence on
the quantity of fibrin formed, but only on the rapidity of the process. Its activity
increases up to the temperature of the body, and the heat of boiling water destroys
it ; it may be preserved indefinitely, without losing its activity, at 0° C

The serous transudations, especially of the horse, since they contain both
fibrinogen and fibrinoplastin, but no ferment, coagulate at once on the addition of
a drop of ferment solution ; these fluids are, therefore, admirable tests for the pres-
ence of the ferment. The same also holds for the still fluid blood which remains
in the blood-vessels after death.

Fibrin is an albuminous body which, in its percentage, composition, and be-
havior to most reagents, does not difler from other albuminoids. It may readily
be obtained by whipping blood as it flows from a vessel, and then washing the
coagulum in water until all the red blood-corpuscles are removed. It then forms
a snow-white fibrous mass of the greatest elasticity, this latter property depend-
ing on the water contained in its molecular interspaces, for dry fibrin is as brittle
as glass.

Fresh, spontaneously coagulated fibrin contains within its meshes large quan-
tities of blood-serum, which are pressed out in the contraction of the fibrin.

The fibrin formed by the slow coagulation of the plasma of horses' blood
possesses a less marked fibrous structure than the fibrin obtained by whipping
blood, or even by the coagulation of other mammalian blood. It is rather more
of an almost amorphous jelly, which will fracture along any line.

In hydrochloric acid of from 0.1-0.5 per cent., and in dilute phosphoric,
acetic, and lactic acid solutions, fibrin swells up to a transparent jelly, but with-
out, to any great extent, passing into solution, unless kept for some time at an
elevated temperature, when it is nearly all converted into syntonin and passes into
solution. On neutralization it is precipitated, the precipitate being insoluble in
water, but readily soluble in very dilute acids and alkalies. Boiled fibrin is
entirely insoluble in dilute acids and alkalies, but is partially soluble in the con-
centrated acids.

The cause of the constant fluidity of the blood in the living organism
is found in the influence of the normal vascular wall on the blood con-
tained in the vessels. That the fibrin factors are not found in the living
blood is not a sufficient explanation, for it offers no reason why these
substances develop in blood outside of the body.

Coagulation occurs as soon as contact with the living blood-vessels
ceases, or when, through various causes, the walls of the blood-vessels
lose their normal properties, from which we might infer that something
in the vascular walls prevents the development of the fibrin factors ; for
injections of fibrinoplastin and the fibrin ferment, or transfusion of u lake-
colored" blood, have, as an immediate consequence, the abundant forma-
tion of blood-clots even in perfectly normal vessels.

It is not necessary for the blood to be in constant motion in the
vessels to prevent coagulation, for the circulation may be arrested in
any part, provided the stoppage does not entail any injury to the walls
of the vessels, and the blood still remain fluid. But if any circumscribed
injury be made to the walls of a blood-vessel, as by the application of a
ligature, even though it be subsequently removed, a deposit of fibrin
will occur at that point.

BLOOD. 489

4. THE BLOOD-SERUM. — Blood-plasma freed from fibrin constitutes
blood-serutn, and, as already stated, may be obtained by allowing blood
to coagulate in a glass cylinder, when the gradual contraction of the
fibrin in the clot presses out the serum.

Serum is an alkaline, transparent fluid, of a specific gravity of from
1026 to 1029, amber-yellow in the horse's blood, and almost colorless in
that of the other domestic animals. In carnivora and omnivora, as well
as in nursing herbivora, the serum is often milky from the contained fat-
globules, which gradually rise to the top to form a Ia3*er of cream ; this,
however, only occurs at, or shortly after, the period of fat absorption.

In round numbers the composition of serum is as follows : —

Water, ... . .-'.-. . . . 90 per cent.

Proteids, 8 to 9 " "

Fats, extractives, and salts, . . . . 2 to 1 " "

The Albuminoids of the Serum. — The following albuminoids are
found in serum : Paraglobulin, alkali albuminate, serum-albumen, and fre-
quently peptone.

Paraglobulin has already been considered under blood coagulation ;
in coagulation all the fibrinogen becomes solidified, while a considerable
amount of paraglobulin still remains in the serum. The amount remain-
ing in solution in the serum has been estimated at from 1.7 per cent, in
the rabbit to 4.5 per cent, in the horse.

Alkali albumen (sodium albumen, serum-casein) is precipitated by
exact neutralization with acetic acid. It is insoluble in distilled water,
but readily soluble in dilute acid and alkalies.

Serum-albumen exists in larger amount than all the other albumi-
noids, the serum containing from 6 to 8 per cent. As already mentioned,
it differs from egg-albumen in rotating polarized light 56° to the left,
while egg-albumen rotates it but 35.5°, and in its behavior to ether and
acids. After removing paraglobulin and alkali albuminate, serum-albu-
men may be completely coagulated after acidulation and dilution by heat
(70°-75° C.).

The quantitative proportions between serum-albumen and para-
globulin vary in different animal species. The proportion, while not
even constant in any given species, varies about as follows, paraglobulin
being represented by the numerator of the fraction, serum-albumen by
the denominator : Horse ^Vrj QX ff.A*» ^an T.sVn Dog T.J3, Rabbit 5^.

Peptone differs from other albuminoids in that it is not coagulated
by heat or acetic acid and potassium ferrocyanide, but is precipitated by
tannic acid, corrosive sublimate, absolute alcohol in great excess, phos-
phowolframic acid, phosphomolybdic acid, and iodide of mercury and
potassium.

490 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Its other characteristics have been described under the head of
Gastric Digestion.

To detect the presence of peptone in blood-serum, all the other albuminoids
must first be removed. This may readily be accomplished by adding a solution
of acetate of iron, to which a few drops of sulphate of iron solution have been
added. The serum must first be diluted with five to eight volumes of water, heated
on the water-bath, and the iron solution and then caustic soda added, until only
a faint acid reaction remains. A thick, brown precipitate then falls, and the
supernatant fluid is free from iron and all albuminoids but peptone, the presence
of which may be recognized, after filtration, by the biuret reaction.

Peptone is only found in the serum during and shortly after albu-
men absorption.

Other Organic Constituents of the Serum. — Sugar may be detected,
after removal of albuminoids, by the copper test. Sugar is a constant
constituent of the serum of blood. Its origin and importance will be
discussed later. Ox-blood contains 0.543 pro mille sugar, sheep's blood
0.521 pro mille, dogs' blood 0.787 pro mille.

Fat has already been mentioned. It is found only in scanty amount,
except after a meal, being in largest amounts in the serum from suckling
animals. Stearin, palmitin, and olein, with their respective soaps, are
the principal representatives. The odor of serum is probably due to a
volatile body of the fatty acid series. The yellow color of serum is due
to the presence of a special pigment.

Lecithin is a constant constituent of the ethereal extract of blood-
serum. A large proportion of the phosphoric acid of the serum is con-
tained in this bod}-. Its origin and uses are not well understood.
Perhaps, since it is the carrier of phosphorus, it is of special importance
in the nutritive processes of bone.

Cholesterin is also found in the ethereal extract of blood-serum, from
which it coagulates in white, pearly flakes.

Further, small amounts of urea are found in serum, as well as
kreatin, kreatinin, and other products of the retrograde metamorphosis
of tissues, which will subsequently claim attention.

The Inorganic Constituents of Blood-Serum. — Serum }^ields about
0.75 per cent, of ash, in which the following bases are found: Na, K,
Ca, Mg, Si, and Fe and P2O5H2, H2SO4, C02, and Cl. K and Fe are in
extremely minute quantit}^; Mg and Cain somewhat larger quantit}^,
though out of proportion to the richness of the organism in these bodies.

The Gases of the Blood. — Oxygen, carbon dioxide, and nitrogen are
found in the blood in conditions of loose chemical union with certain
blood constituents (haemoglobin) and in solution in the blood-plasma,
which, like other fluids, is capable of dissolving a certain amount of
different gases. Their consideration will be reserved for the chapter on
Respiration.

SECTION VII.
THE CIRCULATION OF THE BLOOD.

IT has been seen that digestion is the preparation of food for ab-
sorption ; absorption is the process by which the results of digestion
reach the interior of the blood-vessels ; but that the blood, which by
means of absorption has thus received the nutritive principles of the food,
may satisfactorily meet the nutritive wants of the different tissues of
the body, it must be in constant motion. The circulation of the blood is,
therefore, that function by means of which the nutritive materials sup-
plied by absorption are distributed to the economy after being subjected
to aeration, and by which the refuse and effete materials are carried where
they may be excreted.

1. GENERAL VIEW OF THE ORGANS OF CIRCULATION. — Circulation is an
organic function, being present in both the animal and vegetable king-
doms.

In the simplest forms of life, both animal and vegetable, in which
absorption takes place by imbibition from the entire external surface,
no special circulatory apparatus is required. It is only when certain
tissues become specialized organs for absorption and others for aeration
that a necessity arises for some apparatus by which the materials ab-
sorbed are convej-ed from the point of absorption to the respiratory
organs and to the S3'stem at large. The development of the circulatory-
organs is, therefore, proportional to the degree in which absorption and
respiration are limited to special tissues.

As might be expected from the definition of the circulation, in
the lowest animals, as in plants, in which absorption takes place from
the entire external surface, there exists no apparatus for carrying
on a circulation of fluid, the contractile vesicles seen in many of the
protozoa having, probably, rather a respiratory than a circulatory
function ; it is only when the digestive organs become highl}: specialized
that a circulator}' apparatus appears. Thus, in the coelenterata the
somatic cavity is in free communication with the digestive cavit}- and
with the exterior, and the fluid which it contains, representing the blood
of higher orders, is moved b}r the contractions of the entire body and by
the vibration of cilia lining the somatic cavity, there being no indication
of either a heart or a vascular system. In the turbellaria, trematoda,
and cestoidea the lacunae of the mesoderm and the interstitial fluid of

(491)

492

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

its tissues are the representatives of a blood-vascular system — a condi-
tion closely analogous to what occurs as the first indication of a circula-
tion in plants. In annelida, as is also the case in the rotifea, we find a
perivisceral cavity lying between the splanclmopleure and the somato-
pleure, communicating with the segmental organs, as the water-vascular
system. In the former group there is also to be found a system of canals
(the pseudo-haemal system), in some instances communicating with the
perivisceral cavity, with contractile and often ciliated walls, and con-
taining a clear, sometimes corpusculated fluid, which may be either red
or green from the presence of a substance which resembles haemoglobin
and which is evidently of a respiratory value. These canals always com-
municate at some point b}^ a tubular stem with the exterior. In the
lowest forms of the arthropoda the same general conditions noted in
the turbellaria are to be found, viz., a perivisceral cavity and an inter-

si. A

IAA

FIG. 180.— DIAGRAMS TO SHOW THE ARRANGEMENT OP THE GREAT BLOOD-
VESSELS IN WORMS AND LOWER CRUSTACEANS. (Jeffrey Bell.}

A, earthworm : D. dorsal vessel. B, crayfish: A A, anterior aorta ; PA, posterior aorta ; H, heart;
AT and HP, transverse vessels which supply the anterior regions of the body and the viscera; ST.A,
sternal artery ; SI.A and IAA, abdominal artery.

stitial fluid, in which, however, colorless cells may be detected. In the
lower Crustacea and in many insecta we find a single elongated, some-
times segmented, contractile vessel, the dorsal vessel, provided with
lateral valvular openings by which the blood enters from an inclosing
venous space or sinus (Fig.180). In the anodon (Fig. 181, C) the spaces
or sinuses are much more developed, and no traces of a ventral vessel
are now to be seen ; the dorsal is, however, shown by the heart, with its
anterior and posterior aortae, while the terminal parts of the transverse
vessels become enlarged to form the auricles of the heart. In the higher
Crustacea, as in the lobster, there is a single, well-developed, muscular,
systemic dorsal heart surrounded by a venous sinus and giving off a
number of arteries, which pass into capillaries ; but the venous system
still remains more or less lacunar. In the mollusca, also, the same gradual

CIRCULATION OF THE BLOOD.

493

differentiation of the blood-vascular system is observable. In some of
the lowest forms, as in polyzoa, neither a contractile heart nor even
vessels can be detected ; circulation in them, as in lower forms, being
carried on by mere imbibition. In the tunicata the heart, whose
position closely resembles its ventral situation in the vertebrata, has
no valves between its dilated chambers, and the blood is propelled by
opposite peristaltic movements, first in one direction and then in
another ; hence, here the heart is sometimes systemic and sometimes
respirator}'. The most perfect form of circulation found in tha
mollusca exists in the cephalopoda. In them there is a systemic
ventricle provided with valve's at its orifice, with systemic arteries, the
blood being returned into a large venous sinus, from which it passes to
the gills through contractile vesicles, the branchial hearts, which serve
to propel the blood through the gills ; from there it passes again into

H

PA

DA

BR

FIG. 181.— DIAGRAMS OF THE GREAT BLOOD-VESSELS IN THE FRESH- WATER
MUSSEL AND THE FISH. (Jeffrey Bell.)

C, fresh-water mussel : H, heart : AA. anterior, and PA. posterior aortse ; A, auricle. D, fish : H,
heart ; BR, branchial vessels ; DA, dorsal aorta.

contractile venous sinuses, which, therefore, act as auricles, and is then
driven to the heart.

Thus we find that in the invertebrata the circulatory apparatus, even
in the highest forms, contrasted with what we shall find in the vertebrata,
does not consist of a continuous series of tubes, but that the blood
passes from such vessels into spaces (lacunae or perivisceral spaces)
without distinct walls. Connected with the vessels we often find several
pulsating cavities more analogous to the lymphatic or venous hearts
found in the vertebrata than to a true respiratory or systemic heart.
When a heart is present in the invertebrates, it is single, is, as a rule,
placed on the dorsal aspect of the body, contrasted with its ventral
position in vertebrates, and is of a systemic and not respiratory function.
In the invertebrata there is no trace of a portal system, the liver being
supplied by the systemic arteries.

494

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

FIG. 182. — DIAGRAM OF THE
CIRCULATION IN THE FISH.
(Eeclard.)

A, dorsal artery, or aorta; C, sys-
temic organs ; O, auricle ; V, ventricle ;
B, branchiae.

In the vertebrata, amphioxus, the lowest form of fish, has a system
of blood-vessels with contractile walls, but no distinct heart, while in all
the other vertebrates there is a heart with, at fewest, three chambers
(sinus venosus, atrium, ventricle), arteries, capillaries, and veins, and a

system of lymphatics connected with the
veins. In many of the lower forms of verte-
brates we still find large venous sinuses, but
in the higher forms these are for the most
pavt replaced by definite vessels with mus-
cular walls. Important peculiarities, how-
ever, exist in the vascular systems of the
vertebrata dependent upon the character of
their respiration, whether pulmonated or
air-breathing, or branchiated or water-
breathing ; and further, as to whether their
blood is warm or cold. Mammalia and birds
are included in the group of warm-blooded
pulmonated vertebrata ; reptilia and amphibia

in the group of cold-blooded pulmonated animals ; and fish constitute
the group of cold-blooded branchiated vertebrata.

In all of these animals the character of the circulatory apparatus
depends upon the manner in which the blood is oxy-
genated ; therefore, in those animals (certain of the
amphibia) which commence life as branchiated ani-
mals and subsequently become pulmonated, we find
that their circulatory apparatus becomes modified
accordingly, and presents two different styles corre-
sponding to the stage of their existence. In all forms
of vertebrata a portal system is present — that is,
the liver receives a special supply of venous blood
derived from the sj'stemic capillaries of the abdominal
organs.

FIG. 184.— PLAN OF
CIRCULATION IN
THE FISH. (Car-
penter.)

A, auricle; B. ventricle;
C, branchial artery ; D,

{Pniting in FTthe^aorta"!

G, venacava.

FIG. 183.— DIAGRAM OF THE ARTERIAL CIRCULATION IN FISHES,

AFTER WlEDERSHEIM. (Jeffrey Sell.)

In fishes (see Fig. 181, Z)),the lowest forms of vertebrates, the heart
consists of a single auricle with the sinus venosus, which is always present,
and a single ventricle, the former receiving the dark venous blood from the

CIRCULATION OF THE BLOOD.

495

bod}' and transmitting it through an opening, guarded by a valve, to the
ventricle, from which the blood is propelled to the bulbus arteriosus, and
then through four or five branching vessels supported on the cartilaginous
branchial arches to the gills (Figs. 182 and 183). After being subjected to

FIG. 185.— ClRCFLATORY APPARATUS IN

THE FISH. (Owen.)

A, bulhus arteriosus: B, branchial arteries: b,
branchial veins : H, ventricle ; h, auricle ; L L, portal
vein: V V, vena cardinalis: »*, jugular veins ; I, in-
testine; A' A', aorta; K, kidney.

The lower figure shows an enlarged diagram of a
branchial arch, the lettering being the same as above,
be being the branchial cavity.

FIG. 186.— HEART OF TORTOISE. (B6clard.)

1, right auricle: 2, single ventricle: 3, left auricle:
4, right aorta ; 5, left aorta ; 6, pulmonary artery dividing
into two branches ; 7, venae cavae.

FIG. 187.— HEART OF FROG. (Livon.)

I, anterior view ; II, posterior view. A A, aortas ;
Vc, superior venae cavae : Or, auricles : V, ventricle : Ba,
aortic bulb ; SV, venous sinus : Vci, inferior venae cavae ;
Vh, hepatic veins ; Vp, pulmonary veins.

aeration in the capillaries of the gills, .the blood is then collected by the
branchial veins, which, uniting into a single arterial trunk situated on
the dorsal aspect of the alimentary canal, and corresponding to the
aorta of higher vertebrates, serves by a sj^stem of branching vessels to

496 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

distribute the arterial blood to the S3^stem at large ; whence it is again
returned by the venous system, after passing through the systemic
capillaries to the auricle (Fig. 184). In fishes, therefore, the respira-
tory apparatus forms a part of the general systemic circulation, the
heart being, therefore, a branchial and not a systemic organ, and the cir-
culation being simple instead of imperfectly double, as in the reptilia, or
perfectly double, as in the warm-blooded vertebrata. In the fish, a
portal S3rstem, composed, as in all vertebrates, of veins from the digestive
apparatus, conducts the blood from the abdominal organs through the
kidneys and liver ; hence, in the fish, both these glands receive venous
blood (Fig. 185).

In the reptilia the heart consists of two auricles and one ventricle
(Figs. 186 and 187). The right auricle receives venous blood from the

FIG. 188.— DIAGRAM OF THE CIRCULATION

IN REPTILIA. (Beclard.) FIG. 189.— DIAGRAM OF THE CIRCULATION
P, lungs; O, left auricle; V, ventricle, whence the IN THE REPTILIA. (Carpenter.}

blood is driven through the systemic circulation to enter A, ventricle; B, left auricle ; C, right auricle : D, pulmo-
the right auricle, O', after being collected by the veins. nary circulation; E, systemic circulation.

system at large; the left auricle receives arterial blood from the lungs;
both discharge their contents into the single ventricle, which thus re-
ceives a mixture of venous and arterial blood. From the ventricle the
blood is driven partly through the lungs and partly to the general
S3rstem, so both lungs and system receive a partially aerated blood,
forming an incomplete double circulation (Fig. 188 and 189). In
the reptilia, as a rule, there is a distinct arterial and distinct pul-
monary trunk arising from the ventricle, but in the amphibia there is
only a single trunk, of which the pulmonary arteries are branches, rising
from the ventricle. In the crocodile there exists a partial ventricular
septum, so placed that it serves to direct the dark venous blood entering
from the right auricle chiefly into the pulmonary arteries, whilst the
arterial blood coming from the left auricle is sent out into the systemic

CIRCULATION OF THE BLOOD.

497

arteries, thus closely approaching the double circulation of birds and
mammals (Fig. 190). A portal circulation is also present in the cold-
blooded pulmonated vertebrata, and, as in the fishes, is connected with
the renal veins.

In birds the heart, as in man, consists of four cavities, two auricles
and two ventricles, and the general distribution of the circulation
is the same, i.e., the right auricle collects the blood from the sys-
temic veins and transmits it to the right ventricle, which, by means of the
pulmonary artery, forces the blood through the lungs. From the lungs the
oxygenated blood is carried by the pulmonary veins to the left auricle,
from there to the left ventricle, and thence, by means of the aorta and its
branches, to the system at large. There is, therefore, in birds a perfect
double circulation — a pulmonary and a systemic circulation (Fig. 191).

FIG. 190. — HEART OF THE CROCODILE.

(Perrier.)

a a, venae cavae : b, right anricle ; r. right ventricle ;
<L left ventricle : e, pulmonary veins : /, left auricle ; It hf.
aortae : i. second arch of the aortae. in which arterial and
venous blood is mixed ; g, pulmonary arteries.

FIG. 191.— DIAGRAM OF THE CIRCULATION
IN BIRDS AND MAMMALS. (Carpenter.)

A, heart ; B, vena cava ; C, right auricle ; D, right
ventricle ; E, pulmonary arte^1- ; F, pnlmonic capillaries ;
G, left auricle; H, left ventricle ; i, aorta; J, systemic
capillaries.

The portal system is also present in birds, and, as in the lower verte-
brates, receives branches from the kidneys and from the lower limbs.

The circulation in mammals, of which man may be taken as a type,
deserves to be treated at somewhat greater length ;than the circulation in
inferior organisms. As in other vertebrates, with the exception of the
openings, of the larger lymphatics, the blood is contained in a com-
pletely closed S3rstem of vessels, whose course and general arrangement
we will first trace in outline.

The circulation is carried on through a S3Tstem of tubes of different
functions and different properties. These are : (1) the central organ, the
heart, a hollow muscle, which serves as both a pump and a reservoir,
divided into four cavities, two auricles or receivers of blood, and two
ventricles or pumps (Fig. 192) ; (2) the arteries, a system of muscular

32

498

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and elastic tubes coming off from the heart, which gradually subdi-
vide, like the trunk of a tree, into branches, and which serve to carry
oxygenated blood to the tissues; (3) the veins, another S3Tstem of branch-
ing tubes, also elastic and muscular, but less so than the arteries, which
conduct to the heart the blood collected from (4) the capillaries, a
system of fine tubes situated between the arteries and the veins.

In man, as in other mammals, we have to deal with a double circu-
lation— the s}^stemic circulation and the pulmonic. Their general out-
line may be given as follows : Starting from the heart, the arterial
blood leaves the left ventricle through the aorta, which immediately
gives off two vessels, the coronary arteries, for nourishing the tissues

I

FIG. 192.— DIAGRAM OF MAMMALIAN HEART. (B6clard.)

a, left ventricle; 6, right ventricle; c, left auricle; Bright auricle: /, aorta; g g, pnlmonary
arteries ; h, inferior rena cava ; i, superior vena cava; k, orifice of the superior vena cava ; I, orifice or
the inferior vena cava; m, orifice of the coronary vein ; o, left pulmonary veins; p, right pulmonary-
veins; r, orifices of the right pulmonary veins; s, orifice of the left pulmonary veins.

of the heart itself; the aorta then "divides into branches, which them-
selves become successively subdivided to supply arterial blood to the
head, trunk, limbs, and all the organs of the body, the vessels
becoming finally so minute as to allow merely the passage of a single
blood-corpuscle, forming then the so-called capillary vessels. From the
capillaries the blood is again collected by converging venous radicals,
which finally are united to form two main venous trunks — the vena
cava superior, bringing the blood from the head and upper extremities,
and the vena cava inferior, collecting the blood from the trunk and
lower limbs. Both of these large veins empty into the right auricle, com-

CIRCULATION OF THE BLOOD.

499

pleting the circuit of the greater or systemic circulation. From the right
auricle the blood is emptied into the right ventricle, from which it is
forced by the heart's contractions into a single large trunk, the pul-
monary artery. This artery, which, however, contains venous blood,
soon divides into two trunks, one going to each lung, each of which
divides and subdivides in the lung-tissue to form a second capillary net-
work, in which the dark venous blood is subjected to the influence of
the air contained in the air-cells, gives up its carbon dioxide and
certain organic impurities, and absorbs
oxygen, becoming again bright-red arterial
blood. It is then collected by the pul-
monary veins and carried to the left
auricle, thus completing the lesser or
pulmonary circulation, and bringing us
back to the point from which we started
(Fig. 194).

2. THE ACTION OF THE HEART. — The
circulation of the blood consists in the con-
tinuous movement of the blood in a series
of ramifying tubules or blood-vessels, and

FIG. 193.-HEART OF DTTGONG, SHOWING THE SKP-

A RATION OF THE RIGHT AND LEFT, OR PUL-
MONARY AND SYSTEMIC HEARTS. (Pei'rier.)

FIG. 194.— SCHEME OF THE CIRCU-
LATION IN MAMMALS. (Landois.)

a. right auricle ; A, right ventricle ; b, left
auricle : B. left ventricle : 1, pulmonary artery ;
2, aorta, with semi lunar valves ; L, area of pul-
monarv circulation ; K, area of systemic circu-

* ; < Id, i minnteric arr

q, portal vein; L, liver; h, hepatic vein.

owes its maintenance largely to the motor power derived from the
contractions of the heart. The circulatory apparatus consists, there-
fore, of the heart, the arteries, the veins, and midway between the
latter the capillaries. The conditions which govern the movement of
the blood-current in these different parts of the circulatory apparatus
will be studied in turn.

The heart is a muscular reservoir, divided, as already indicated, in

500

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

mammals into four cavities, two auricles and two ventricles. In its
function it acts as a force-pump, and by the contraction of its walls
empties the contents of its cavities into the arterial branches in connec-
tion with them, and therefore is the starting point of the circulation. Its
action as a pump is therefore mainly physical, the effect produced by its
contractions being governed by their frequency, force, and character,
and the quantity of blood ejected at each beat. Its physical properties,
as indicated by the above considerations, are governed by a number
of vital conditions, which modify the various characters of cardiac
pulsation. These will later demand attention.

The heart consists of interlacing muscular fibres, which are midway
between the striped and nnstriped muscular tissues. They are
extremely short, transversely striated, are devoid of sarcolemma, and
are usually bifurcated at their extremities and anastomose with each

FIG. 195.— ARRANGEMENT OF MUSCULAR FIBRES IN THE AURICLES AND
GREAT VEINS. (Landois.)

I, muscular fibres on the left auricle, showing the outer transverse and inner longitudinal fibres, and
the circular fibres on the pulmonary veins, v.p. V, the left ventricle (Reid).

II, arrangement of the striped muscular fibres on the superior vena cava (Elischer). a, opening of
vena azygos ; v, auricle.

other. In the tubular heart of the embryo, microscopic inspection
shows that the muscular fibres may at first be resolved into an outer
circular and an inner longitudinal layer of fibres. And, from the
fact that at first the heart consists of but one chamber, it is clear
that a part of the fibres at least must be common to the two
auricles and a part also to the two ventricles. While, however, this is
true, the muscular fibres of the auricles are completely separated from
those of the ventricles by the fibro-cartilaginous rings of the auriculo-
ventricular orifices. In adult animals the fundamental circular arrange-
ment of the embryonic fibres partly remains, while in the ventricles, as
the septum becomes formed, the fibres become twisted into the form
of spiral loops. The arrangement of the muscular fibres in the differ-
ent cavities of the heart serves to a considerable degree to explain the

CIRCULATION OF THE BLOOD.

501

physiological characteristics of the different cardiac cavities, this physio-
logical difference depending upon the anatomical structure of the different
parts of the heart, as has been clearly traced out by Landois whose
description of this subject has been mainly followed. In the auricles
the fibrous auriculo-ventricular rings serve to separate the auricular
muscular fibres from the ventricles, and, therefore, serves to explain the
fact that the auricles are enabled to contract independently of the ven-
tricles.

In the auricles the muscular fibres are arranged in an external trans-
verse layer continuous over both auricles and an internal longitudinal
layer. This double arrangement of the fibres enables them in their
contraction to produce a uniform diminution of the auricular cavities
(Fig. 195).

FIG. 196.— COURSE OF THE VENTRICULAR MUSCULAR FIBRES. {Landois.)

A, on the anterior surface ; B, view of the apex with the vortex (Henle) ; C, scheme of the course of the fibres
within the ventricular wall; D, fibres passing into a papillary muscle (C. Ludwig).

At the openings of the large veins into the auricles there is a special
development of circular bands of striped muscular fibre. The contrac-
tion of these bands enables the veins to empt}7 themselves into the
auricle and also serves to prevent, to a certain degree, backward reflux
of the blood from the auricles into the veins when the auricles contract,
even though no valves are present in these vessels. In the ventricles the
fibres are arranged in a number of separate Ia3*ers so as to form figure of
8 loops. First, there is an outer longitudinal layer which is in the
form of single bundles on the right ventricle and forms a complete layer

502 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

on the left ventricle, constituting about one-eighth of the thickness of the
ventricular wall (Fig. 196). " A second longitudinal layer of fibres lies on
the inner surface of the ventricles, distinctly visible at the orifices, and
within the vertically placed papillary muscles, while elsewhere it is
replaced by the irregularly arranged trabeculae carnse. Between these
two layers there lies the thickest la}^er, consisting of more or less trans-
versely arranged bundles, which may be broken up into single layers
more or less circularly disposed. The deep lymphatic vessels run between
the layers, while the blood-vessels lie within the substance of the layers,
and are surrounded by the primitive bundles of muscular fibres (Henle).
All three layers are not completely independent of each other : on the
contrary, the fibres which run obliquely form a gradual transition between
the transverse layers arid the inner and outer longitudinal layers. It is
not, however, quite correct to assume that the outer longitudinal layer
gradually passes into the transverse, and this again into the inner longi-
tudinal layers (as is shown schematically in 0, Fig. 196), because, as Henle
pointed out, the transverse fibres are relatively far greater in amount.
In general, the outer longitudinal fibres are so arranged as to cross the
inner longitudinal layer at an acute angle. The transverse layers, lying
between these two, form gradual transitions between these directions.
At the apex of the left ventricle the outer longitudinal fibres bend or
curve so as to meet at the so-called vortex (Wirbel), B, and where
they enter the muscular substances, and, taking an upward and inward
direction, reach the papillary muscles (Lower), D, although it is a
mistake to say that all the bundles which ascend to the papillary muscles
rise from the vertical fibres of the outer surface ; many seem to rise inde-
pendently within the ventricular walls.

"According to Henle, all the external longitudinal fibres do not rise
from the fibrous rings, but the roots of the arteries."

The Movements^/ the Heart. — The movements of the heart can be
most readily studied in their simplest form in the frog.

The batrachian heart, as seen in Fig.. 187, is an egg-shaped mass slightly flat-
tened at the sides and marked by a furrow which crosses the heart nearly at right
angles to its axis, dividing the heart (in an anterior view) into an upper globular
part, the two auricles, and a lower conical, the single ventricle ; the anterior sur-
face of the ventricle is also marked by a slight groove inclining from above down-
ward toward the right of the heart. Anteriorly, the ventricle is seen to be con-
tinuous with a cylindrical prominence, the bulbus arteriosus, which crosses over
the right auricle and divides into the right and left aortse. In viewing the pos-
terior part, the right auricle is seen to be continuous with a bulbar expansion of
the inferior vena cava, which receives the name of the sinus venosus, the line of
junction of the sinus with the auricle being marked by a slight furrow. The two
auricles are separated from each other by an antero-posterior septum, incomplete
at its lower margin, where the two auricles communicate through a crescentic
opening ; the opening of the sinus into the auricle is marked by an Eustachian
valve, which hangs downward and toward the right.

The auriculo- ventricular valve consists of an anterior and posterior segment,
each of which is continuous at its edge with the inter-auricular septum.

CIRCULATION OF THE BLOOD. 503

To expose the heart of a chloralized frog, the integument is divided over the
sternum and the anterior wall of the upper part of the visceral cavity, which is
then to be carefully opened so as to expose the pericardium, taking care not to
wound the large abdominal vein. The pericardium is then carefully slit up and
the pulsating heart exposed. A large glass rod is now thrust down the oesophagus
of the animal so as thoroughly to distend the parts and bring the heart more
prominently forward.

On directing attention to the series of movements which constitute a
cardiac revolution, taking first the anterior view alone, the wave of con-
traction is distinctly seen to commence in the auricles. The auricles be-
come distended and full of blood ; they suddenly contract and transfer
their contents into the empty and relaxed ventricle, which is now gorged
with blood, but it is not until the auricular contraction is complete that
the ventricle, in its turn, contracts and discharges the blood into the
relaxed bulbus arteriosus, which becomes distended and finally forwards,
in its turn, its contents to the arterial sj'stem. From the fact that while
the ventricle contracts the auricles are already filling, and that the ven-
tricle does not contract until the auricular contracting is complete, it
would appear, on superficial examination, as if there were a constant inter-
change of contents between the ventricle and auricles. But on lifting up
the ventricle and dividing the little band which connects its posterior sur-
face with the pericardium, so as to expose the posterior portions of the
heart, the true sequence of contraction is immediately evident. The
wave of muscular contraction distinctly originates in the sinus venosus,
extends to the auricles, and it is not until their contraction is complete
that the ventricle contracts ; but by this time the sinus is again already
full and the auricles filling. Therefore, while the ventricular contraction
is determined by that of the auricles, and the auricular by that of the
sinus, the contraction of the latter originates independently of an y previ-
ous movement.

This sequence of contraction may be graphically represented by resting a
lever of the second class on the contracting heart in such a manner that its point
will describe its movements on the
smoked surface of a revolving drum,
as show/i in the accompanying tracing
(Fig. 197) :—

In this curve the first slight ascent
represents the contraction of the
auricles, and its subsidence represents
the interval between its contraction
and that of the ventricle, thus showing
that the one is complete before the
other commences. The next more de-
cided ascent is due to the vigorous con- FlG\ I9J'TTRA^TNG DRAWN BY A LEVER

. * /» ., i * • t T *i i -/Vrx*lMEL) UIRKCTIjY TO THE APEX. OF

traction of the ventricle and the descent THE FROG'S HEART. (Sanderson. )

tO its relaxation We learn from this x contraction of auricles; B, contraction of ventricle;

that the auricles have completed their c, relaxation of ventricle,
systole before the ventricle contracts.

Passing now to the movements of the heart as seen in mammals the thorax is
to be opened in a rabbit, rendered insensible by chloral, by dividing the integu-
ment from the larynx to the end of the xiphoid cartilage and then removing the

504 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

sternum by cutting through the costal cartilages on each side with a pair of strong
scissors. If the operation is performed carefully very little hemorrhage will
occur. On dilating the opening in the thorax thus formed, and maintaining the
opening by means of hooks fastened to weighted cords, the movements of the
heart are readily followed. We have, however, by thus opening the thoracic
cavity interfered with respiration, and to permit of a reliable study of the cardiac
movements the animal's life must be prolonged by artificial respiration.

Having now the heart and great vessels well exposed, and the normal con-
ditions as regards respiration imitated as nearly as possible, the sequence of events
which make up a cardiac revolution may be readily followed.

Starting in the distended venous trunks at the base of the heart, as
seen in the mammal, the wave of contraction extends rapidly to the auri-
cles, now filled with blood, which contract with a sudden, sharp systole,
discharging their contents into the flaccid ventricles, the auricular append-
ages becoming pale and the whole auricle being drawn down toward the
auriculo-ventricular ring. During the systole of the auricles, the ventricles
become more and more gorged with blood, but when felt are still soft
and flaccid. Immediately, however, upon the completion of the auricular
contraction, the ventricles harden and become globular, or, in other words,
shorten and thicken. Examined more closely, it is seen that during
repose the ventricles form an imperfect cone, its base being a transverse
ellipse, but during systole they form a more perfect cone, shortened in
its long axis, and having a circle for a base, the greatest contraction hav-
ing taken place in its longitudinal and transverse axes, while the antero-
posterior diameter of the base of the cone has been little altered, although
the circumference of the base has been actually increased (Foster). At
the moment of ventricular systole the heart rotates on its axis to the
right, so as to expose more of the left ventricle, while the apex seems to
approach the base. The rotation of the heart is due to the contraction of
the muscular fibres which pass from the sternal surface of the auriculo-
ventricular rings obliquely downward and to the left ; when they shorten
they raise the apex and bring more of the posterior surface of the ven-
tricles in relation with the chest-walls. At this moment the aorta and
pulmonary artery are seen to expand and lengthen, thus compensating
for the shortening in the long axis of the ventricle. Then, as diastole
commences, the ventricles flatten and elongate, the great arteries con-
tract and shorten, the heart rotates back to the left, and the cardiac revo-
lution is completed.

It has been stated that in the systole the apex seemed to be drawn
up toward the base. This, however, is not exactly correct.

In the conditions in which we have been studying the heart its nor-
mal supports have been more or less interfered with, and although we
have not thereby lessened the value of the conception obtained of the
sequence of contractions, we ma}' perhaps extend our knowledge as to
the degree and character of the locomotion performed by different parts
of the heart in its contraction.

CIRCULATION OF THE BLOOD. 505

This may be accomplished by the following experiment : —

A large dog should be rendered unconscious by a subcutaneous injection of
morphine, fastened securely on his back, and a long, slender, steel needle then
passed perpendicularly through the walls of his chest into his heart at the point
of greatest intensity of the cardiac impulse. Then, following the line of the ven-
tricle up to the aorta, three more steel needles should be inserted, one in each
succeeding intercostal space above the first, and then again one on each side of
the second needle, about one inch from it and in the same interspace. -Then it will
be seen that, although each of these needles moves at each contraction of the heart,
the movements described by their free ends widely differ.

No. 1, inserted in the apex, merely quivers at each pulsation without describ-
ing any definite motion dependent upon the cardiac contraction, though it is seen
tolbllow the ascent and descent of the diaphragm.

Nos. 2, 3, 4, inserted in the intercostal spaces above, describe an instantaneous
upward movement at each contraction, the degree of excursion of their free ends
being directly dependent upon their distance from No. 1. The fulcrum on which
each needle moves is its point of transfixion of the chest-wall ; therefore, an up-
ward movement of the free end of the needle indicates a downward movement of
the body in which the other end is inserted. Finally, Nos. 5 and 6 oscillate more
or less horizontally, their free ends receding from each other as well as from
No. 1 at each contraction of the ventricle.

From these facts we learn that the apex, the point at which the car-
diac impulse is felt, is itself nearly motionless, while the base of the
heart at each ventricular systole approaches the apex, and that the other
parts of the ventricle are drawn toward the apex in a degree propor-
tionate to their distance from it, while, as seen in the exposed heart, the
shortening of the ventricles is compensated by the elongation of the
great vessels at the base. The impulse, therefore, is the hardening of the
ventricle, transmitted through the stationary portion which is in contact
with the chest-walls, through the chest-wall to the finger. It is improper
to speak of the impulse as a blow, as the apex never leaves the chest-
wall. But while this is so, there is, nevertheless, a certain amount of
motion in the apex which results in the elevation of the chest-wall at
the point of cardiac impulse. If an excised heart is placed on a hori-
zontal surface, the base of the ventricles in a state of diastole takes on
the form of an ellipse with its largest diameter horizontal, while the
apex falls until it is in contact with the supporting surface. When the
ventricle passes into systole the base of the heart passes from an ellip-
tical to a circular form, and since the apex takes a position in a line with
the central point of the base of the heart it leaves the surface on which
it rested and tilts forward, at the same time approaching the base from
the reduction in the length of the ventricles. The state of affairs is
somewhat similar while the heart is in its normal position in the
thorax. There the base of the heart takes on an elliptical form from
contact with the chest-walls, while the apex tends to fall away from the
chest. In systole, the base, assuming a circular form, must cause the apex
to move forward, and, so producing stronger pressure on the ribs, cause
the elevation which constitutes the cardiac impulse, the base descending
in systole as already described.

506

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Ludwig and Hesse have shown that the shape which the heart
assumes after death does not represent its shape during life, either during
systole or diastole. They obtained the diastolic shape of the ventricle
by making a plaster cast of the heart dilated under the pressure of a
column of defibrinated blood equal to that of the mean arterial pressure
(150 mm. of mercury in the dog). The systolic shape was obtained by
immersing the heart, immediately after death, in a hot (50°C.) saturated
solution of potassic bichromate, when the heart gives a single contraction
and remains in systole, the proteids being coagulated from heart rigor.
A plaster cast is then made as before. They found that in diastole the
shape of the ventricle is nearly hemispherical, with the posterior surface

in iv v

FIG. 198.— PROJECTIONS OF A DOG'S HEART, AFTER LUDWIG AND HESSE. (Landois.)

I, posterior surface. II. left lateral surface. Ill, anterior surface. IV, A. aorta : PA, pulmonary
arterv : M, mitral, and T, tricnspid orifices. V. projection of the base in systole and diastole: RV, right,
and LV, left ventricles. The shaded outlines represent the projections of the heart in diastole, the dotted
line the outline of the heart in systole.

flatter than the anterior, the greatest diameter being the transverse
diameter of the base, and the shortest from the apex to the base. In
systole the ventricle becomes more conical from the greater contraction
of the basal diameters, the curvatures of the anterior and posterior
surfaces being now nearly equal, and while the vertical diameter of the
right ventricle shortens the left remains unchanged. In the systole, the
area of the base of the heart is diminished nearly one-half, thus, by
diminishing the auriculo-ventricular openings, greatly assisting the ven-
tricular valves (Fig. 198).

The transmission of the ventricular contraction may be represented
graphically by the cardiograph (Fig. 199).

CIRCULATION OF THE BLOOD.

507

Sanderson's cardiograph consists of a hollow disk, the rim and back of
which are of brass, while the front is of thin rubber. To the back is fastened a
flat steel spring, bent twice at right angles in the same
direction, so that the free end, which is provided with
an ivory button, hangs directly over the centre of the
rubber membrane. The ivory button is on one extrem-
ity of a small screw which perforates the free end of the
lever, while the other end of the screw rests on the
rubber membrane, the rubber being protected from the
point of the screw by a light metal plate. The instru-
ment is further provided with three adjusting screws, by
which it rests on the chest-wall. The cavity of the
tympanum communicates by a rubber tube with the
interior of a somewhat similar drum, the rubber surface
of which is in communication with a long, light lever 'of
the second order (Fig. 200).

On placing the ivory button of the cardiograph
over the point of cardiac impulse, and regulating the
adjusting screws so that the instrument is parallel to
the chest-walls and the screw-point of the button in
contact with rubber membrane, each movement of ascent
of the button creates pressure on the rubber membrane,
with a consequent diminution of the capacity of the
tympanum. Then, since the drum is in air-tight com-
munication with a second similar one, each diminution
in the capacity of the first causes a proportionate increase
in the contents of the second, a bulging of its rubber
face, and a consequent elevation of the lever with which
it is connected. Then, on causing this lever to record
its movements on the smoked surface of a revolving
drum, an exact record of the movement of the surface is
obtained with which the button is in contact.

This instrument, applied to the study of the im-
pulse of a healthy human heart, shows that each systole
of the ventricle, when the button is precisely over the
apex, is marked by a sudden ascent of the lever, and the
end of the systole by a marked but more gradual descent
(Fig. 201).

By shifting the cardiograph toward the sternum, ^ m

so that the button is no longer over the point of im-
pulse, a tracing of an entirely different character is
obtained (Fig. 202).

Although the ventricular systole is indicated by an
elevation of the lever, this ascent is immediately followed
by a sudden fall below the position of rest of the lever, <(

FIG. 199.— SANDERSON'S CARDIOGRAPH.

FIG. 200. — M AREY'S TYM-
PANUM AND LEVER.
(Sanderson.)

A, bearings in which the steel
axis of the lever works. It may be
raised or depressed by the adjusting
lever, the long arm of which extend*
downward and backward from A;
B. tympanum : F, tube by which the
cavity of the tympanum communi-
cates with the cardiograph.

508

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

thus indicating that there has been an actual recession of the chest, and
representing graphically the condition known in clinical language as the
"negative impulse."

FIG. 201.— TRACING OBTAINED WITH THE CARDIOGRAPH WHEN THE BUTTON

is PLACED AT APEX BEAT OF THE HUMAN HEART. (/Sanderson.)

Each ascent in the curve coincides with the ventricular systole.

To recapitulate, it may be stated that a single pulsation of the heart
may be divided into three phases : — 1st. The auricles contract, while the

FIG. 202.— CARDIOGRAPH TRACING OBTAINED WHEN THE BUTTON is PLACED

TO ONE SIDE OP APEX BEAT. (Sanderson.)

The line of descent coincides with the ventricular systole.

ventricles are relaxed, con traction and relaxation occurring synchronously
on both sides of the heart. 2d. The ventricles contract, while the

«-•

FIG. 203.— HEART-BONES OF A Cow, NATURAL SIZE. (Mutter.)

a, larger, b, smaller heart-bone ; c, anterior, d, posterior extremity.

auricles are relaxed. 3d. Both auricles and ventricles are in a state of
relaxation, the auricles being near the end and the ventricles at the

commencement of their diastole ; this
phase is termed the pause, the con-
dition of ventricular contraction being
described as systole, of relaxation as
diastole. The duration of a cardiac
revolution, consisting of diastole, sys-
tole, and pause, is equal to the interval
of time ^tween two pulsations felt in

THE HEART-BONES. ONE-HALF THE nT1\r nrtprv
NATURAL SIZE. (Milller.) •> a er-> '

a, larger heart-bone ; b, smaller heart-bone : c, The ActlOH of the VdlveS OJ the
root of the aorta ; d, right coronary artery ; e, rigrht
semi-lunar valve ;/, central part of the mitral valve. Heart. The direction of tllC CUrreilt

of circulating blood through the heart is rendered possible solely
through the integrity of the cardiac valves. These A'alves, as already

CIRCULATION OF THE BLOOD.

509

mentioned, are situated between the two auricles and ventricles, and at
the origin of the pulmonary artery and aorta. Their mechanical action
is different, the two auriculo-ventricular Aralves operating upon the same
principle, and the two valves at the starting point of the large arteries
being similar in function and operation. Both the auriculo-ventricular
valves at their bases constitute complete cylinders which originate in the
auriculo-ventricular ring, which is often cartilaginous, and even, in some
animals, as in the bird, furnished with a bone.

In the heart of the ox are found two bony structures at the origin of the aorta,
to the larger of which are fastened the right leaflet of the aortic semi-lunar valve
and the central portion of the mitral valve, while the smaller is in connection with
the left semi-lunar valve of the aorta (Figs. 203 and 204).

IK-

FIG. 205.— HEART OF THE HORSE, SEEN FROM THE RIGHT SIDE, THE RIGHT
AURICLE AND RIGHT VENTRICLE BEING LAID OPEN. (Miiller.)

Hb, Hb, pericardium slit open and drawn to the sides ; r V. right auricle : rK. right ventricle : IK, left
ventricle ; 1, inferior, or posterior, vena cava, with probe inserted in it : 2, superior, or anterior, vena
cava: 3, azygos vein; 4, pulmonary veins: 5, posterior aorta; 6, anterior aorta: 7, right auricular
appendage : ft. Lower's ridge : 9, orifice of the coronary vein ; 10, oval foramen : 11, right coronary artery ;
12, longitudinal fissure, with 13, its artery, and 14, its vein: 15, columnar carnse; 16 16, papillary
muscles ; 17 17, chordae tendinae ; and 18, a leaflet of the tricuspid valve.

The cylindrical form of these valves exists only a short distance from
this ring, and then the valve divides into a number of different segments,
which, in the right ventricle, are three in number, hence the name of
tricuspid valves, and in the left are two, hence the name of mitral valves.

510

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The leaflets of these valves again subdivide into numerous tendinous
filaments which are inserted in the papillary muscles of the heart (Figs.
205 and 206). The tendinous threads which arise in the papillary muscles
and are inserted in the valve are not in connection solely with the free
border of the latter, but the entire surface of the valve, which is directed
toward the walls of the ventricle, offers points of insertion for these
tendons (Figs. 207 and 208).

Numerous theories have been proposed to explain the manner in
which the auriculo-ventricular valves prevent, in the systole of the ven-

FIG. 206.— HEART OF THE HORSE, SEEN FROM THE LEFT SIDE, THE LEFT
AURICLE AND LEFT VENTRICLE BEING LAID OPEN. (Muller.)

I V, left auricle : IK, left ventric'e; r K, right ventricle; 1, trabeculae in left auricle; 2, coronary
fissure, with its artery and vein ; 3, pulmonary artery ; 4, anterior aorta ; 5, posterior aorta : 6, left longi-
tudinal furrow ; 7. left coronary artery; 8, coronary 'vein ; 9, columnar carnae ; 10 10', papillary muscles;
11 11', chordae tendinae; 12 12', mitral valve.

tricle, regurgitation of blood into the auricles. These may be classified
into two different groups.

According to the one, the occlusion is purely passive, and is pro-
duced by the pressure of the blood behind the valves, causing their
ascent, and so occluding the orifice between the ventricles and auricles.
In this view of their action, the papillary muscles have for their sole
function the regulation of the situation of the valves, and, consequently,

CIRCULATION OF THE BLOOD.

511

the degree of occlusion, and to prevent the valves being everted into the
auricles. According to the other view, which seems to be supported by
the largest amount of proof, the papillary muscles play an active role
in the occlusion of the auriculo-ventricular orifices. This view has been
strongly supported by Ku'ss, who describes their operation as follows :
" If the finger be introduced into the auriculo-ventricular region at the
moment of the systole of the ventricle, we find that the kind of funnel

FIG. 207.— HEART OF A Cow, WITH THE RIGHT VENTRICLE LAID OPEN,
ONE-FOURTH THE NATURAL SIZE. (Miillei:)

a, posterior aorta; at, anterior aorta; b b, spaces in the lateral wall of the right ventricle ; p pt pH,
papillary muscles ; q q>, columns; carnae ; L, pulmonary artery laid open ; O, opening into right auricle;
S, ventricular septum; W, lateral wall of ventricle; 1, 2, and 3, leaflets of the tricuspid valve; 4, chorda
tendinse ; 5, 6, 7, cusps of semi-lunar valve ; 8, sinus of Valsalva.

which hangs from the auricle to the ventricle is continued ; it even
appears to lengthen itself out, and the finger, as it were, is drawn into
the interior of the ventricle. In fact, the first result of the contraction
of the papillary muscle is the lengthening of the auricular cone, the
edges of which are afterward brought near each other. While this
hollow cone descends into the ventricle, the sides of the latter contract
and approach the cone in such a manner that the auriculo-ventricular

512

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

apparatus acts as a sort of hollow piston, which penetrates the ventricle
and comes into close contact with its walls, and thus the ventricle (Figs.
207 and 208) empties itself completely, the -contact becoming perfect
between its sides and the auricular prolongation.

" The result of this mechanism, which is so simple, and tyet so gen-
erally misunderstood, is that no reflux of blood into the auricle can take
place ; the auricle, even by means of the mechanism which we have de-
scribed, exercises a sort of suction upon the venous blood, its cavity being

FIG. 208.— HEART OF A Cow, WITH LEFT AURICLE AND VENTRICLE LAID
OPEN. (Miiller.)

a, root of the aorta ; 6, spaces in the wall of the auricle : c c, orifices of the pulmonary veins : 1 1, pul-
monary veins ; p p, papillary muscles; <f ql, columnae carnae; t, auricular trabeculse : "A, orifice of the
aorta ; K, left ventricle ; S, septum ; V, left auricle ; W, lateral wall of left ventricle ; 1, 2, leaflets of the
mitral valve.

continued so far into the ventricle. We see, also, that when the ventricular
systole is complete, the lengthened tube, the hollow cone which unites
the ventricle and the auricle, is full of blood, and that a slight and rapid
contraction of the auricle is sufficient to drive this blood into the ven-
tricle and fill it.

" Nearly all the standard works admit without discussion the theory
of the occlusion of the auriculo-ventricular orifices by the simple inech-

CIRCULATION OF THE BLOOD.

513

anism of a plug or valve, just as in the case of the arterial orifices (see
farther on), but without remarking the entire difference of structure
which distinguishes the auriculo-ventricuiar valves from the semi-lunar
valves of the aorta and of the pulmonary artery. This theory has be-
come, up to a certain point, the property of Chauveau and Faivre, on
account of the interesting experiments which they have so often made
upon horses killed instantaneously by section of the bulb, and in which
artificial respiration was kept up. ' If, under these circumstances, the
finger is introduced into one of the auricles, and the auriculo-ventricuiar
orifices explored, the tricuspid valves will, at the moment that the ventricles
begin to contract, be felt to straighten, push their borders, and stretch in
such a manner as to become convex, and form a concave dome above
the ventricular cavity.' This method of proof does not always furnish

FIG. 209. — DIAGRAM OF THK AURICULO-
VENTRICULAR APPARATUS DURING
VENTRICULAR SYSTOLE, AFTER Kiiss.
(Beaunis.)

\. During the first part of systole. 2. At the com-
pletion of systole. AV, valvular cone ; O, auricle ; \t
ventricle ; A, aorta or pulmonary artery.

FIG. 210. —DIAGRAM OF THE ATJRICULO-
VENTRICUL.AR APPARATUS DURING
VENTRICULAR DIASTOLE, AFTER Kiiss.
(Beaunis.)
V, vena cava: O, auricle; V ventricle; A, artery;

1, valvular cone ; 2, arterial infundibulum.

such decided results, and many observers, among others Spring and
Onimus, have met with one entirely different. The latter found the
auriculo-ventricuiar orifices effaced by the contraction of the muscular
fibres, which, at this level, really form a sphincter (this is the case in the
heart of birds, but not of the mammalia). The papillary muscles, being
now contracted, lower the valves, and these, supporting themselves
against the sides of the ventricles, have the effect of driving the blood
ingulfed between them and the corresponding sides into the arterial
orifices. Such is, in short, the working of the auriculo-ventricuiar mem-
branes. This is the only theory which accounts for the existence and
arrangement of the papillary muscles.'7

The action of the semi-lunar valves is more simple. The semi-lunar
valves are composed of three free folds of serous membrane, which during

83

514 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the systole of the ventricle are forced back by the escaping current
of blood against the walls of the pulmonary artery and aorta; they,
therefore, offer no obstacle to the escape of blood from the cavities of the
ventricles. At the end of ,the contraction of the ventricles relaxation
commences, the ventricles dilate, and there is, therefore, a tendency for
the blood to return into their cavities from the aorta and pulmonary
artery. This backward current carries the blood behind the free margins
of these valves and, distending the pockets behind them, flattens out the
valves, causing them to come into complete contact and thus completely
obstruct the orifice of these arteries into the ventricles (Fig. 211). This
closure of the semi-lunar valves is rendered more perfect by the fact that
the three leaflets do not originate from the walls of the artery on the
same plane, but their origins form a spiral line around the base of

these arteries ; consequently, the
leaflets descend one over the
other, and, to a certain extent,
overlap each other, and thus
completely prevent regurgitation
of tlie arterial blood into the
ventricles.

The Sounds of the Heart.—
When the ear is applied to the
walls of the thorax over the
heart, two sounds are recog-

FIG. 211.-BASE OF THE HEART OF THE HORS^, ™^ ^"^ ^^ ^ intensity,

BOTH AURICLES BEING REMOVED. (Miillcr.) jn pitch, and in duration. These

rV, right auricle ; IV, left auricle; rK, right ventricle ; IK, _ Y ..

left ventricle; 1, coronary furrow ; 2, right, 3, left auricnlo-ven- SOlinClS are described aS tllC
tricular orifices; 4, origin of the aorta; 5, aortic semi-lunar

valves- 86>auriSar Vtam"1™01""7 artory; 7, its semi-lunar first and SCCOnd SOUnds of tllC

heart. The first of these sounds

is dull and prolonged, and coincides with the systole of the ventricle ; the
second sound is shorter, sharper, and of higher pitch, and occurs at the
end of the systole, or at the commencement of ventricular relaxation.
The musical interval between these two sounds corresponds about to a
fourth; the pitch of both sounds varies, but this interval is usually
preserved. The first sound is heard with greatest distinctness at the
spot where the impulse is felt, and is not dependent upon the cardiac
impulse, from the fact that it exists after the removal of the chest-walls.
As it coincides with the contraction of the ventricle, it also, of course,
coincides with the closure of the auripulo-ventricular valves, and is
largely due to the action of these valves.

The character ol the first sound of the heart is not, however, purely
valvular in nature, and is not what 'would be expected from the sudden
closure of a membranous valve. That it is, however, largely due to the

CIRCULATION OF THE BLOOD.

515

action of these valves is proved by the alteration in its character which
occurs when either the mitral or bicuspid valves are diseased, when this
sound becomes obscure, altered, or replaced by murmurs.

While the valves in their closure are the principal factors in the pro-
duction of the first sound of the heart, its characters are dependent upon
the presence of several other factors. It will be found that whenever
a muscle contracts a sound is produced which depends for its pitch upon
the number of contractions occurring per second. At the moment of
closure of the auriculo-ventricular valves the blood is forced out from
the ventricles into the great arteries. The rushing sound of this moving
column of blood is, therefore, another factor in the production of the first
sound of the heart.

To recapitulate : It may be stated that the first sound of the heart is
produced by the sudden tightening of the auriculo-ventricular valves,
whatever view be accepted as to the nature of their action, to the sound
of muscular contraction, and to the rushing of the current of blood from
the ventricles into the pulmonary artery and aorta. In support of this view,
it may be mentioned that when the muscular contraction of the heart
becomes greatly weakened from any depressing cause, as in severe fevers,
the first sound of the heart becomes distinctly sharper and more purely
valvular in nature, evidently due to the diminished intensity of the con-
traction of the cardiac muscle.

The second sound of the heart is short and sharp, and is due to the
sudden closure of the semi-lunar valves, which by their rapid increase in
tension, like every other elastic membrane, produce a sound. In living
animals, the second sound of the heart is best heard over the root of the
large vessels. When the semi-lunar valves are destroyed, as by inserting
a hook into these valves, the second sound disappears. The relative
lengths of the auricular and ventricular systole and diastole, the time of
the occurrence of the impulse, and the different sounds of the heart may
be diagrammatical^ represented by a line divided into five parts, which
represent the length of a cardiac revolution : —

1 | 2 | 3 I 4 | 5

1 1 1

Auricle . .

v Systole.

Diastole or repose.

Ventricle . .

Eepose.

Systole. Repose.

Sounds . .

Silence.

1st Sound.

2d Sound.

Shock . . .

Impulse.

We may now extend, somewhat, the sketch which has already been
given as to the movement of the blood through the pulsating heart.

516 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

During the diastole of the auricles the blood streams into them from the
large venous trunks which are in connection with the base of the heart,
the propelling force being the pressure of the blood in the veins and the
aspiration exerted by the lungs. Soon the elastic tension of the walls
of the dilated auricles becomes sufficiently great to balance the forces
which cause the entrance of blood into the auricles; but before the
entrance of blood into the auricles is entirely arrested, the ventricles,
which had, np to this point, been in systole, and thus prevented entrance
of blood from the auricles, now relax, the auriculo-ventricular valves
are forced open by the pressure of blood in the auricles, and the ven-
tricles dilate, not only through the aspiration of the lungs, but in virtue
of the elasticity of their own walls.

The auricles now pass into systole, and by the pressure of the con-
traction of their muscular walls force the blood from the auricles through
the auriculo-ventricular openings into the relaxed and dilating ventricles.
The blood passes from the auricles into the ventricles, and not back into
the veins, because this is the direction in which the moving blood-cur-
rent meets with the least resistance. We have seen that by the opening
of the auriculo-ventrieular valves the bottom falls out of the auricles and
the dilatation of the empty ventricles exerts a negative pressure on the
contents of the auricles. At the same time the contraction of the mus-
cular fibres of the auricles serves somewhat to constrict the openings of
the veins, and the pressure of the blood in the venae cavae, supported by
the valves in the inferior vena cava, offer a sufficient resistance to prevent
regurgitation into the veins.

The blood continues to flow from the auricles into the ventricles
until the propelling force of the contracting auricles is balanced by the
elastic tension of the dilated ventricles or by commencing ventricular
systole, exit of blood from the ventricles being prevented by the closed
semi-lunar valves at the openings of the aorta and pulmonary arter}^. The
ventricles now being filled, systole commences, the closure of the auriculo-
ventricular valves prevents regurgitation into the auricles, and, the force
of the ventricular contraction being greater than the pressure of the blood
in the aorta and pulmonary artery, the semi-lunar valves are forced open,
and the ventricles empty themselves completely into these vessels. The
ventricles then relax, regurgitation from the great arteries being pre-
vented by the closure of the semi-lunar valves, the ventricles fill them-
selves from the auricles, and the process goes on as before.

3. THE HYDRAULIC PRINCIPLES OF THE CIRCULATION! — The physical
principles concerned in the movements of the- blood through the arteries
of the animal body are largely governed by the purely physical laws of
hydraulics. Before, therefore, we attempt to explain the movements
of the blood, a glance at the most important of the physical principles of

CIBCULATION OF THE BLOOD. 517

hydraulics or hydrodynamics will greatly facilitate the explanation of the
circulation.

Every fluid particle under the action of the law of gravitation falls
like a solid body to the earth. When, however, a large mass of fluid is
freely acted on by gravity the slight cohesion exerted by the molecules
of liquid on each other leads to their separation one from the other.

Every fluid, therefore, in falling tends to separate into drops. This
tendency to break up into drops may be prevented either by delaying
the flow of the liquid, as by causing it to descend an inclined plane, or
permitting the liquid to flow within a vessel in which the tendency of
the particles to separate will lead to the production of a vacuum, and
atmospheric pressure will, consequently , serve to strengthen the cohesive
forces. Consequently, in a stream of liquid falling into a tube each par-
ticle is not only acted on by gravity, but also by the pressure of the mass
of fluid behind it. If, therefore, an aperture be made in the bottom of any
vessel, any particle of liquid on the surface of the fluid contained in that
vessel, if we could imagine that it would fall freely without reference to
the particles below, would have a velocity on reaching the orifice equal
to that of any other body falling through the distance between the level
of the liquid and the orifice. If the liquid in such a vessel be maintained
at the same level, the particles will follow one another with the same
velocity and will issue in the form of a stream ; while, from the principle
of transmission of pressures in liquids equally in all directions, a liquid
would issue from an orifice in the side with the same velocity as from an
aperture in the bottom of the vessel, provided the depth were the same.

The velocity of efflux, therefore, as formulated by Torricelli, is the
velocity which a freely falling body would have on reaching the orifice
after having started from a state of rest at the surface. It is expressed
by the formula —

V = l2^h, in which g = 32.16 ft.

It further follows that while the velocitj' of efflux depends on the
depth of the orifice below the surface and not on the nature of the liquid,
the velocities of the efflux, from the laws of falling bodies, are directly
proportional to the square roots of the depths of the orifices, while the
quantity of fluid which issues from the orifices of different areas is very
nearly proportional to the size of the orifice, provided the level remains
constant. It is evident, however, that the mass of liquid in such an ex-
periment at the side of the column vertically over the orifice of exit offers
by friction more or less resistance to the line of movement.

And while the molecules vertically over the centre of the orifice
pass directly down and out by the orifice, the molecules of fluid at the
side of this moving column not only offer resistance to this downward

518

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

FIG. 212.

motion through attraction, but also through their own mobility tend to
pass in an oblique line into the moving column. In fact, every particle
above the orifice endeavors to pass out of the vessel, and in so doing
exerts pressure on every particle near it. The result may be made clear
by the diagram (Fig. 212).

Every particle above A B endeavors to pass out of the vessel, and
in so doing exerts a pressure on those near it. Thosje that issue near
A and B exert pressures in the direction M M and
N N, those in the centre of the orifice in the direction
II Q, those in the intermediate parts in the directions
P Q, P Q. In consequence of the fluid in the space
P Q, P is unable to escape, and that which does escape,
instead of assuming a cylindrical form, contracts and
takes the form of a truncated cone. It is found that
the escaping jet continues to contract until at a distance
from the orifice about equal to the diameter of the orifice.
This part of the jet is called the vena contracta. It is found that the area
of its smallest section is about five-eighths or 0.62 of that of the orifice.
Accordingly, the actual value of the escape is only about 0.62 of its
theoretical amount. If a cylindrical tube (termed ajutage), with a
length two or three times its diameter, be made the channel of exit of
the fluid, the amount discharged per second may be increased to about
0.82 of the theoretical amount. A contracted vein is formed within the
tube, just as it would do if issuing freely into
the air; but from the adhesion of the water
to the interior of this tube, the section of the
column flowing from the tube is greater than
that of the contracted vein (Fig. 213). (The
contraction of the moving column of fluid
within the tube causes a partial vacuum, and if
a side tube, dipping into mercury, be connected
with the ajutage at this point the mercury will
rise in the vertical tube, demonstrating the
existence of the vacuum. This fact is made
use of in Bunsen's filter pump.) If a conical
tube be fitted to the orifice of exit, with the

smaller end in connection with the vessel, the efflux may be still further
increased, and fall very little short of the theoretical amount.

Flow of Liquids Through Rigid Tubes. — If the ajutage inserted
in the side of the vessel has more than a certain length, the amount of
fluid escaping is very considerably reduced. This fact rests upon the
hydraulic friction produced between the moving liquid and the walls of
the tube in liquids which exert a certain amount of adhesion against the

FIG. 213.

CIBCULATION OF THE BLOOD.

519

walls of the tube ; for the movement of the portion of liquid in contact
with the walls of the tube is delayed by adhesion, and the movement of
the central column is delayed by friction with the external layers. It is
evident that the resistance due to friction along the sides of the tube
will depend upon the length of the tube. This may be illustrated by
the accompanying diagram.

If a horizontal tube be connected with a reservoir of liquid and a
number of vertical side arms be connected with the horizontal tube, the
liquid will rise in the branch tubes to different heights inversely as the
distance of the vertical tube from the reservoir, for the propelling force
in the horizontal tube will diminish from point to point on account of
the uniformly acting resistance (Fig. 214). The vertical tubes will, there-
fore, enable us to measure the pressure exerted by the fluid upon the
walls of the tube through which it is flowing, and shows us that the pres-
sure at an 3^ point of such a tube will be less the greater the distance from

FIG. 214.— ESTIMATION OF PRESSURE OF LIQUID IN A HORIZONTAL, OUTFLOW-TUBE
CONNECTED WITH A CYLINDRICAL, VESSEL FILLED WITH WATER. (Landois.)

a b, outflow-tube, along which are placed at intervals vertical tubes I. II, and III to estimate the pressure. The
line D, Dl, D2, D3, D4 indicates the rapidly decreasing pressure.

the propelling force. Further, the resistance increases with the velocity
of the current ; for it is evident that, the resistance being mainly depend-
ent upon friction, if the column of fluid is at rest there is, consequent^,
no friction and no resistance, while the greater the rapidity of motion
the greater will be the friction, and, consequent!}^, the greater the resist-
ance. It follows from this that the smaller the tube the greater will be
the resistance, for the smaller the tube the greater will be the velocity
of motion. It may, therefore, be said that in a moving column of liquid
" the resistance is directly proportional to the length of the tube and is
inversely proportional to its cross-section, and increases with the speed
of the stream."

It has been mentioned that the friction of the central moving column
on the outer layer is a source of resistance, consequently increase in the
cohesive nature of the fluid will increase the retardation of the central

520

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

column and accordingly increase the resistance, while heat, by diminish-
ing the cohesion of the liquid, will lessen the resistance.

A similar state of affairs holds in tubes of varying calibre. In tubes
of unequal calibre, as already pointed out, the velocity of the current
will vary ; that is, it will be slower in the wide part of the tube and
more rapid in the narrower parts of the tube. And as the resistance
is greater in narrow tubes, the propelling force will diminish more
rapidly than in wide tubes. " When a small tube passes suddenly
into a tube of larger diameter there is a sudden increase of pressure at
the surface of junction, accompanied by a diminution in the speed of
movement through the wider tube. The molecules of which the fluid
consists cannot suddenly change the swift movement into a slower one,
and on account of their inertia the pressure exerted by them on one
another develops the increased force. On the other hand, the rapid
transition from a slow to a quick movement at a place where a wide tube

FIG. 215.— DIAGRAM ILLUSTRATING THE VARIATIONS OF PRESSURE IN AN
OUTFLOW-TUBE OF VARYING CALIBRE. (Rollet.)

passes into a narrow one diminishes the pressure. The effect, however,
in a system of tubes of a series of wider parts is to diminish the total
resistance " (Robertson) (Fig. 215).

Bending the tube adds a new resistance, the fluid pressing more
strongly on the convex than on the concave side of the bend, and, there-
fore, producing greater resistance to movement on the convex side.
Consequently, resistance is increased behind the bend and diminished
in front of it, with a consequent increase in the velocity of the current at
this point. When a tube through which liquid is passing divides into
two or more branches, still further resistance is added by not only in-
creasing the surface, but by the production of angles and bends. The
total calibre of the branches which originate from a single tube may be
either greater or less, and so the surface of contact between the walls of
the tube and the fluid are either increased or decreased.

The most interesting case corresponds to that seen in the develop-

CIRCULATION OF THE BLOOD.

521

FIG. 216. —DIAGRAM OF VARIATIONS IN
PRESSURE IN BRANCHING TUBES.
(Wundt.)

The changes in
represented

re in the tube A, B, C, D are
the broken line A, B, c, D, E.

ment of the circulatory system of animals, where a vessel divides into
several branches of greater total calibre than the parent stem, and where,
after repeated subdivision, the branches again unite to form a single tube
whose calibre is about the same as that of the original tube.

A simple representation of such a series of branching tubes is given
in Fig. 216.

In such a series the pressures are seen in the broken line A, B, c, D, E.
At B, taking into consideration only the increase in calibre, a sudden
increase in pressure occurs. On the
other hand, considering only the occur-
rence of bends and angles in the tube,
the pressure would suddenly sink.
These two causes, however, oppose
each other, and the most ordinary rep-
resentation of the case would be
indicated by a slower sinking in the
line of pressure than in the single
parent stem. The condition is, how-
ever, different where the branches again unite to form a single trunk;
here the pressure must fall, because the bed of the stream becomes
contracted, while at the same time an angle is also met with. Both
these facts, therefore, work in the same direction, and the pressure
undergoes a sudden fall which would be greater than that produced
by mere contraction of the stem.

It follows from the above that in a symmetrical system of tubes the
pressure does not symmetricall}* increase and decrease, but will be greater
in any portion in the centre of the system of the tubes (at M, Fig. 216)
than the mean of pressure at any
two points equally distant in front
or behind this point. It ma}r, there-
fore, happen that in a complicated
system of branching tubes the re-
sistance is not greater than in a single
tube, or may even be smaller, since
the increase in the diameter may

diminish the resistance more than the branching increases it. If the
resistance is the same, it is evident, also, that the rapidity is the same
in both cases, and as a consequence more fluid will flow out of such a
branching system of tubes when the resistance is smaller than would
escape from a single tube (Fig. 217).

The angle formed by the branches with the original stem seems to
produce no marked influence on the resistance and velocity of movement.

The above relationship between resistance and velocity of movement

FIG. 217.— DIAGRAM OF SYSTEM OF BRANCH-
ING TUBES. (Wundt.)

522 PHYSIOLOGY OP THE DOMESTIC ANIMALS.

and diameter of the tube only holds as long as the calibre of the tubes
does not fall below a certain diameter.

In capillary tubes the conditions are so far similar in that the resist-
ance is proportional to the length of the tube. It has been found, how-
ever, that the discharge is not proportional to the calibre of the tube, but
to the fourth power of the diameter. This is evidently to be explained by
the greater prominence attributed to the adhesion of the fluid to the
wails of the tube, and will; therefore, differ greatly in different liquids.

The, Flow of Liquids Through Elastic Tubes. — When a constant
stream passes through an elastic tube the conditions are precisely the
same as have been described as governing the movement of liquids
through rigid tubes. When, however, the current is intermittent, the
elasticity of the tube then comes into play, and decidedly modifies the
conditions of movement.

If a quantity of liquid be forcibly injected into an elastic tube
already distended with fluid, the first part of the tube suddenly dilates
to accommodate the quantity of fluid propelled into it.

This impulse communicates a movement of undulation to the par-
ticles of fluid, which is rapidly transmitted to all the particles of fluid
within the tube. In other words, a wave movement is rapidly propa-
gated throughout the entire length of the tube. If the elastic tube
be imagined to be closed at its further end, the wave will be reflected
from the point of occlusion, and will be conducted to and fro in the tube,
gradually decreasing in intensity until it at length disappears. This
propagation of the wave should not be confounded with the forward move-
ment of the fluid. For when the fluid itself moves the movement of
each particle is in the line of the axis of the tube, but in a wave move-
ment the motion of the particles is simply one of undulation at right
angles to the line of movement, and not of forward movement.

In a rigid tube, a movement of progression alone exists. In a
closed elastic tube, filled with liquid, into which more fluid is suddenly
injected, the wave movement alone exists.

If the peripheral end of the elastic tube be open and more fluid be
injected, both movements co-exist ; that is, there is a forward progression
of the particles of the liquid added to the wave movement already de-
scribed. When the wave movement passes in the same direction as the
current, it is called a positive wave; when in the opposite direction, it is
called a negative wave. The speed of propagation of the wave is pro-
portional to the elastic force/ of the walls of the tube, while the height
of the wave depends upon their extensibility.

It is evident from the above that the movement of liquids in open
tubes will vary according to whether their walls are rigid or elastic. If
in a rigid tube a definite amount of liquid be injected, no more or no less

CIKCULATION OF THE BLOOD. 523

can escape from the open end. If the calibre of a rigid tube be dimin-
ished, the increased resistance will react on the propelling power, and
will likewise prevent injection of more than can escape by the open end.

Thus, suppose a rigid tube be connected with a pump which throws
any definite quantit}', say one ounce, of water at each stroke, the rigid
tube being supposed to be already distended with liquid. At each
stroke of the pump, therefore, one ounce of liquid will escape from the
free end. Suppose, now, the free end of the rigid tube be so decreased
in calibre as to allow only one-half the previous quantity to escape, this
resistance will, therefore, react on the pump and prevent its throwing
more than one-half the quantity into the tube.

If, on the other hand, the walls of the tube be elastic, the conditions
Will vary according as the resistance is increased or diminished.

If an elastic tube of the same length and diameter as the rigid
tube already experimented with be connected with a pump throwing
the same quantity of liquid at each stroke, it is evident that the con-
ditions will be the same as in the rigid tube ; that is, the same amount
of fluid will escape from the free end as enters at the opposite end
from the pump, and the time of injection and escape of liquid will
coincide.

If, now, the distal end of the elastic tube be contracted so as to
diminish the outflow, the pump still throwing the same amount of
fluid, it is evident that if we say only one-half of the amount injected
can escape from the free end of the tube the other half will collect
in the tube and overdistend its walls.

In the intervals of action of the pump, the elasticity of the walls
of the tube will lead to their contraction, and this recoil will act as a
propelling power on the contents of the tube, and lead to its escape
from the end of the tube. The stream, now, instead of being inter-
rupted and in jerks, will tend to become continuous. Thus, elastic tubes
have the power of transforming an intermittent into a continuous flow.
The fluid thus contained in a series of elastic tubes is subjected to two
pressures, one derived from the propelling force and the other exerted
by the elastic walls, due to the overdistention of the tubes. In tubes
with elastic walls, the velocity of the current is diminished before the
quantity of fluid discharges is increased.

In the mechanics of the circulation the former of these forces is
spoken of as blood pressure upon the walls of the vessels, and is due to
the propelling power of the heart; while the second, the force exerted
by the walls of the arteries upon the blood, due to the recoil of these
vessels, is spoken of as arterial tension.

4. THE CIRCULATION IN THE ARTERIES. — The principal cause of
the movement of the blood in the arterial system is the intermittent

524 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

contraction of the ventricles. At each systole of the ventricles the heart
completely empties itself, and, consequently, throws into the blood-
vessels the amount of blood capable of being contained in its cavity,
while at the same time an equal quantity of blood enters the heart from
the veins. This injection of new amounts of blood into the arterial
system, as a consequence, occurs intermittently, as may be readily
recognized by opening the artery of an animal, when it will be found
that the blood will issue in spurts, each spurt corresponding to a con-
traction of the ventricles. It will, however, be remarked that there is
also an escape of blood during the pauses of the contractions of the
heart, and that the farther from the heart a blood-vessel be opened the
less will be the apparent effect of ventricular contraction in increas-
ing the velocity with which the blood flows from the divided vessel. In
other words, the blood within the blood-vessels is subjected to a con-
siderable tension, derived from the elasticity of the vascular walls, and
this tension itself serves partly to assist in the onward movement of the
blood. When a vessel divides, except in rare instances, the sum of the
calibre of the branches is, as a rule, greater than that of the parent stem.
In nearly all cases, however, the capacity of the branches is consider-
ably greater than the original vessels before division, even though the
sum of the diameters of the branches be but little greater than that of
the parent stem. The arterial system may thus be regarded as a cone
whose apex joins the left ventricle, and whose base is represented by the
capillary S3^stem. The venous system, on the other hand, may be repre-
sented by an inverted cone, whose base is formed by the capillaries, and
whose apex is in communication with the right auricle.

In the arteries the conditions of the movements of the blood are
largely governed by the physical characteristics of the walls of the blood-
vessels. The arteries consist of three coats — an inner serous coat or
endothelium, the middle elastic and muscular coat, and an outer fibrous
coat. It is to the middle coat that the physical characters of the circu-
lation are largely due. The proportion of muscular fibre to elastic tissue
varies considerably in different parts of the arterial system. In the
large arteries directly in the neighborhood of the heart the middle coat
is composed almost solely of yellow elastic tissue, while the muscular
fibres are present in small amount. As the capillary system is ap-
proached, or, in other words, as the arteries become smaller and smaller
by repeated subdivisions, the elastic coat diminishes in amount, while the
muscular coat increases. The relative proportions of these two elements
of the middle coat are, therefore, inversely as the diameter of the vessel.

The action of these two elements is to a certain extent antagonistic,
although they both combined serve to assist in the onward movement of
the blood.

CIRCULATION OF THE BLOOD. 525

The direction of the muscular fibres of the arteries is circular, while
longitudinal fibres are absent. As a consequence, the contraction of the
muscular coat of an artery tends to obliterate its calibre. On the other
hand, the elastic element tends to keep the artery open. When, there-
fore, an artery is reduced in calibre by contraction of its muscular fibres,
when the muscular coat becomes relaxed, the elastic coat dilates it.
There is no active dilating mechanism in the walls of the blood-vessels.
The combined action of these two forces, the expanding force of the
elastic coat and the contracting force of the muscular coat, would serve
to cause the arteries to assume the form of hollow ribbons with flattened
sides, or flattened cylinders. This shape is found in the arteries of an
animal when examined after death. In the act of dying the arteries
empty themselves by the contraction of the muscular coat, forcing their
entire contents over into the venous system ; they, therefore, become
completely emptied, and are then flattened cylinders ; this condition
holds until one of the larger arteries be opened; air then enters the
arteries, the muscular force having been lost through death; the arteries
then dilate through the action of the elastic tissue which is longer pre-
served, and they now become hollow C3Tlinders filled with air. It is thus
seen that the larger arteries are highly elastic tubes, and the influence of
the elasticity of the walls of a tube on a moving column of fluid has been
already alluded to. In other words, the elastic tissue in the walls of the
large arteries tends to overcome the intermittent action of the heart and
to render the flow of blood in the arteries continuous. In the smaller
arteries the elastic tissue is reduced in amount and often becomes en-
tirely absent, but, on the other hand, the proportion of muscular tissue is
increased. Muscular tissue is itself a highly elastic tissue, consequently
the smaller arteries are not only elastic but are also supplied with con-
tractile walls, and as a consequence their calibre may be reduced, thus
permitting variations in the supply of blood to different localities.

The conditions for permitting a satisfactory interchange between
the blood and different organs are, therefore, fulfilled. For we have not
only a constant flow of blood through all parts of the body, but this flow
is susceptible of general and local alterations ; general alterations, be-
cause the heart itself is capable, as already indicated, of being modified
in its activity ; and, second, because we see that the smaller arteries are
supplied with tissue which, by regulating the calibre of the blood-vessels,
is capable of regulating the amount of blood supplied to different organs.
The mechanism by which this supply is governed will be alluded to
directly.

Blood Pressure. — In the arteries in their normal state the elastic
coat is in a condition of distention beyond its point of equilibrium. In
other words, the arteries are vessels overfilled with fluid. The contents

526 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of the vessels must, consequently, produce pressure on the walls of the
blood-vessels to a sufficient degree to prevent the regaining by tM elastic
tissue of its position of equilibrium. Such a tension as already described
is one of the important factors in blood pressure. By blood pressure is
meant the pressure which the blood exerts on the walls of the vessels.
By arterial tension is meant the pressure which the walls of the vessels
exert on their contents. It is thus seen that these two terms are mutually
convertible. The pressure which the blood exerts on the walls of the
vessels is, of course, dependent upon the energy of the contraction of the
heart and the resistance which the capillaries offer to the onward motion
of the blood. The pressure which the elastic walls of the arteries exert
on their contents will, of course, again depend upon the amount of blood
contained in the arteries and their consequent distention, and while this,
again, as we shall see, is capable of being modified by different causes, it
is mainty dependent upon the activity of the heart. Blood pressure is
measured by estimating the pressure which the blood exerts on the vas-
cular walls.

It has been mentioned that when an opening is made in the walls of an
artery the blood escapes therefrom in jets,, and it is found that the larger
the artery, and, consequently, the nearer the opening is to the heart, the
higher will be the jet of blood and the more intermittent will be the
flow ; this indicates that the blood pressure is, therefore, greater in the
large vessels than in the small arterioles, and is only what is to be
expected from the conditions which are necessary for the maintenance of
the circulation. It has been stated that the arteries subdivided into
smaller and smaller vessels', and, consequently, the friction proportionally
increases with the minuteness of the vessel. It is, therefore, evident,
further, that the pressure in the large arteries must be higher than in the
arterioles, and in all arteries higher than in the veins.

The hlood pressure may be directly measured in any accessible artery by
directly connecting a manometer with the interior of the vessel (Fig. 218). Such
an instrument, in its simplest form, consists of a U -shaped tube containing mercury *
in its lower part, the distal end being free to the atmosphere, and the proximal
end connected directly with the interior of the blood-vessel. If the pressure in
the blood-vessel is greater than the atmospheric pressure, it is evident that the
mercury will be depressed in the proximal arm and rise in the distal arm, until
the difference in height between the columns of mercury in the two arms equals
the pressure exerted by the fluid. Such an experiment is termed a blood-pressure
experiment, and is readily performed on any of our domestic animals.

To make a blood-pressure experiment, the animal should be securely
fastened and the artery exposed through an incision. In the dog, in which such
experiments may be most conveniently performed, the arteries usually experi-
mented on are the carotid or the femoral. To expose the carotid artery, the' hair
is removed from the front part of the neck, and an incision, about two inches in
length, made in the middle of the neck, at the anterior border of the sterno-mas-
toid muscle : the platysma and subcutaneous fascia are then broken through with
forceps or blunt hooks, and the sterno-mastoid muscle pushed to the outside, and
the artery is readily found lying beneath it, the pneumogastric nerve running in
the same sheath. The bundle containing the pneumogastric, the sympathetic, and

CIRCULATION OF THE BLOOD.

527

carotid arteries is then raised on a blunt hook, the connective tissue gently torn
away with two pairs of forceps, and the artery freed from the surrounding nerves
and fibrous tissue. After the blood-vessel is so isolated for a distance of about
an inch, it is firmly ligated at the extremity of the free portion nearest to the
head, and a thread is then tied in a loop-knot around the artery at the end of its
freed extremity nearest to the heart. A small cut is then made in the interme-
diate portion with a pair of scissors, and a slightly constricted glass tube inserted
into the interior of the artery and bound fast with a thread. This glass tube is
then to be filled by a pipette with a saturated solution of sodium bicarbonate, to
prevent coagulation of the blood, and the cannula then connected by thick rubber
tubing, also filled with the same solution, with the proximal arm of the manome-
ter. Care should be taken that all air-bubbles are removed from the cannula,
rubber tube, and proximal arm of the manometer, so that the entire tubing, from
the level of the mercury to the interior of the carotid, is completely filled with
soda solution. If, now, the slip-knot previously tied around the carotid is

FIG. 218.— MERCURIAL MANOMETER FOR MEASURING AND RECORDING THE
BLOCTO PRESSURE. (Yeo.)

a, proximate limb of the manometer; b, union of the two limbs of the manometer: e, the rod floating
in the mercury carries the writing point; d, stop-cock through which the sodium bicarbonate can be
introduced between the blood and the mercury of the manometer.

loosened, thus establishing communication between the interior of the artery and
the manometer, the blood at once rushes from the artery into the connecting tube,
and so causes the level of mercury to be depressed in the proximal arm and rise
in the distal arm. This rise of mercury occurs very rapidly, in jerks correspond-
ing to the beats of the heart, and soon reaches its maximum. When this point is
attained, the mercury does not remain level, but undergoes rapid oscillations,
each rise corresponding to the systole of the ventricle, each fall correspond-
ing to the diastole. If a float, swimming on the top of the mercury, in the
distal arm of the manometer be allowed to record its up-and-down movements
on a moving surface, as, for example, the revolving drum of the kymographion
(Fig. 219), a series of curves will be produced, in which each ascent cor-
responds to the contraction of the ventricle, each descent to its diastole (Fig.
220). In the experiment, as above described, it is evident that a considerable
quantity of blood will leave the arterial system and fill the tube of the manometer.

528

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

To avoid this loss of blood, it is therefore advisable to inject the sodium carbo-
nate solution into the tube of the manometer until the column of mercury has
been elevated to the height which will probably correspond to that of the mean
arterial pressure.

Comparative experiments made in the above-described manner will
show that the blood pressure is considerably higher in the arteries than
in the veins, and greater in the large arteries than in the arterial
branches (Fig. 221) ; so, also, the pressure may be demonstrated to be
higher in the small veins than in the large veins at their opening into
the heart. Experiment will further show that in the veins the pressure is
almost constant, overlooking the insignificant variations which are due to
respiration ; so, also, the pressure will be found to be almost constant in

FIG. 219.— LUDWIG'S KYMOGRAPHION, AFTER HERMANN. (Yco.)

The ordinary form of rotating, blackened cylinder (R), which is moved by the clock-work in the box
(A) by means of the disk (D) pressing on the wheel (•»), which can be raised or lowered by the screw (L)
BO as to rub on a part of the disk more or less near the centre, and 'thus rotate at different rates. The
cylinder may be raised by the screw (») which is turned by the handle (U).

the small arteries, while in the large arteries considerable variations,
corresponding in their increase to the systole and their decrease to the
diastole, are invariably found. It is evident that the mean between the
maximum and minimum pressures in the arteries, as indicated by these
oscillations, will represent the force which is concerned in the propul-
sion of the blood. Although theoretically and practically the pressure
decreases as the distance increases from the heart, yet in any artery
which is not too small to be subjected to such manometrical experiments
it will be found that the pressure will be slightly affected, not more than
one-tenth lower than the mean pressure in the aorta. This fact indicates
that the blood in moving through the arteries has to overcome but slight

CIRCULATION OF THE BLOOD.

529

FIG. 220.— BLOOD-PRESSURE CURVE, DRAWN BY MERCURIAL MANOMETER. (Yeo.)

0to x = zero line, y to yl = curve with large respiratory waves and small waves of heart impulse. A scale
is introduced to show height of pressure in millimeters of mercury.

FIG. 221.— DIAGRAM SHOWING THE RELATIVE HEIGHTS OF BLOOD PRESSURE
IN THE DIFFERENT REGIONS OF THE VESSELS. ( Yeo.)

H, heart; A. arteries: a. arterioles : r, capillaries: V. small veins; r, large veins: H V, being the
zero line, the pressure is indicated bv the elevation of the curve. The numbers to the left give the
pressures (approximately) in millimeters of mercury.

34

530

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

resistance, evidently to be* explained by the fact that as the arteries
divide their total calibre increases. If the mean pressure in the artery
is measured at different times it will be found to be subject to very great
variations, from causes which will subsequently receive attention.

The average blood pressure of mammals is by no means dependent
upon the animal's size. In all cases the arterial blood pressure may be
stated as exceeding the atmospheric pressure and varying between one
hundred and two hundred millimeters of mercury.

The following table gives various estimates of the mean arterial
pressure in different animals (Volkmann) : —

Animal. Mean Pressure in mm. of Mercury.

Horse, .

321 mm. (Ludwig) in the carotid artery

Horse, .

214

"

"

Horse, .

150

(Spengler)

brachial

Horse (old),

140

"

"

Sheep, .

206

(Ludwig)

carotid

Sheep, .

169

"

"

Sheep, .

156

(Blake)

brachial

Sheep (old),

86

"

*<

Calf, .

177

(Ludwig)

carotid

Calf, .

165

(Spengler)

"

Calf, .

153

«

brachial

Calf, .

133

(Ludwig)

"

Dog (large),

172

< n

carotid

Dog, ,

157

(Blake)

brachial

Dog, .

166

(Spengler)

carotid

Dog, .

143

(Ludwig)

brachial

Dog (young)

104

"

Goat, .

135

"

Cat,

150

"

Rabbit, .

90

"

Goose, .

162

(Blake)

carotid

Stork, .

161

M

Pigeon,

157

brachial

The facts thus reached experimentally as to the gradual decrease in
pressure from the arteries to the commencement of the veins and from
there to the larger venous trunks completely explains the constant cur-
rent of blood from the arteries to the veins. The blood, therefore, moves
in a circle from the heart to the arteries, through the capillaries to the
veins, and from the veins to the heart, to again enter the arterial system.

The Velocity of the Blood. — From the fact that the arteries as they
pass into the capillaries increase immensely in area, and as the capillaries
pass into the veins a corresponding decrease is found, it is to be expected
that the velocity of the blood-current will be greatest in the vessels near
the heart. As the blood leaves the heart to pass into the aorta the
velocity of the current is at its maximum ; it then gradually decreases as
the capillaries are reached, then undergoes a sudden retardation, and again,
as the blood is collected from the capillaries in the veins, the current
moves with an increasing velocity as the right side of the heart is ap-
proached. No absolute figures can be given as representing the normal

CIRCULATION OF THE BLOOD. 531

velocity at any point in the blood-vessel system, since measurements
show that at any one point the velocity is subject to very great varia-
tions.

The velocit}* and pressure of the blood at any given point do not
correspond, and may even be in inverse ratio ; thus many causes, such
as obstruction of any part of the vascular system, will increase the blood
pressure at that point and decrease the velocity. As a rule, the pressure
at any point depends upon the distance of that point from the heart,
whether in the arterial or venous S3rstem, while the velocity depends upon
the capacity of the vessels at that point.

Where the area of the circulatory system is very large, as in the
capillaries, the blood circulates slowly, just as the current of a stream
becomes retarded as it widens into a lake.

Various methods have been employed for calculating the rapidity of
the circulation in different blood-vessels. The following represents the
estimations as to the flow in the arteries, capillaries, and veins of the
horse (Volkmann): —

Carotid artery, 300 mm. per second

Maxillary artery, 165

Metatarsal artery, . . . . .56

Capillaries, 0.5 to 0.8

Jugular vein, ...... 100

Vena cava, . . . . . .110

Chauveau estimates the velocity of the blood-flow in the carotid of
the horse as varying from 520 to 150 mm. per second, the highest velocity
coexisting with the systole of the ventricle and the lowest with its dias-
tole. In the larger veins respiration also produces considerable varia-
tion in the velocity of the flow, the velocity being increased in inspira-
tion and decreased in expiration. The velocity of the circulation through
any one vessel may be modified by a number of causes ; provided the
artery maintains its calibre unchanged, the velocity would evidently be
dependent upon the propelling force. Therefore, an increase in the
energy of the heart's contraction, the calibre of the arteries remaining
unchanged, will produce an accelerated flow through those vessels, while
a decrease in the heart's energy will correspondingly retard the arterial
current. On the other hand, the heart's energy remaining the same, a
dilatation of the artery will cause a slowing of the current, and a reduc-
tion in the calibre of the artery will cause the current to become acceler-
ated. So, also, if the resistance to be overcome in the circulation of the
blood be reduced, as by the relaxation of the capillaries, the energy of the
heart's contraction and the calibre of the artery remaining the same, the
velocity of the blood-current will be increased ; while, again, an increase
in the resistance, the other conditions being unchanged, will retard the
blood-flow.

532 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Various attempts have been made to calculate the time required by
the blood for making one complete circuit of the body. The method
which is generally accepted as giving reliable results is what is known
as the " transfusion method " of Hering, and consists in injecting into
one of the jugular veins toward the heart a solution of some salt, the
presence of which in the blood may be readily recognized by chemical
tests, and in finding how soon after the injection the salt appears in
the blood coming from the head in the corresponding vein on the
opposite side of the neck. As determined by Vierordt, the duration of
the circulation in different animals is as follows : —

Horse, . 31.5 seconds. Goose, . 10.86 seconds.

Dog. . 16.7 " Duck, . 10.64 "

Rabbit, . 7.79 " Buzzard, . 6.73 "

Hedgehog, 7.61 " Fowl, . 5.17
Cat, .

By comparing these numbers with the frequency of the pulse in
these animals, the deduction has been made that the circulation is
accomplished in 21 heart-beats. From this the amount of blood thrown
out at each contraction of the ventricle may be calculated : for if the
entire amount of blood passes through the heart in 27 pulsations, one
pulsation will throw out gV the total amount of blood in the body, and
placing this amount at, for example, ^ of the body weight in a man
weighing 65.8 kilos, the ventricles at each pulsation will discharge 187.5
grammes, the amount, of course, being the same for both ventricles.. If
we assume that these data are approximately correct, the work done by
the heart may be calculated. One kilogramme-meter is a force which in
the unit of time can raise one kilo one meter high. If, therefore, the
left ventricle expels 0.188 gramme of blood against the pressure of blood
in the aorta (250 milligrammes of mercury or 3.21 meters of blood), the
work done at each systole is 0.188 X 3.21 = 0.604 kilogramme-meter.
If the number of beats is 75 per minute, then the work done in twenty-
four hours = (0.604 X 75 X 60 X 24) = 65,230. kilogramme-meters,
while the work done by the right ventricle, since the pressure in the
pulmonary artery is only one-third that of the aorta, will be one-third
this amount, or 21,740. kilogramme-meters: and both ventricles together
will do a work of 86,907. kilogramme-meters in the twenty -four hours.
Since part of this work is converted into heat, the contractions of the
heart assist in maintaining the body temperature.

In the case of the ox it has been estimated that 0.75 liter of blood
is driven from the left ventricle at each systole, and since the pulse
in this animal averages 50 per minute 37.50 liters of blood will pass
through the heart in each minute, or 900 liters in twenty-four hours.
The specific gravity of the blood being 1045, 18,810 pounds of blood, or

CIRCULATION OF THE BLOOD. 533

fifteen times the body weight, will be set in motion b}^ the contractions
of each ventricle, or 37,620 pounds in all, Jf it be admitted that the
amount of blood in the ox is ^ of the body weight, or 52.18 pounds,
and each systole propels 0.75 liter, or 1J pounds of blood, thirty-five con-
tractions of the heart would be needed to drive the entire amount once
around the body ; or, the pulse-rate being 50 per minute, the circulation
would be completed in forty-two seconds. It is evident that these figures
are in opposition to the estimates obtained by Bering's method, which,
according to Vierordt, places the duration of the circulation as equal to
the time required by the heart for making twenty-seven pulsations.*

The Pulse. — As the left ventricle empties itself into the aorta it is
compelled to overcome the pressure of the blood already contained in
the arterial system and two phenomena result — an acceleration of the
current of blood toward the capillaries and the dilatation of the aorta to
accommodate the additional amount of blood thrown in by the ventricle.

In the description of the physical principles concerned in the pas-
sage of fluid through an overfilled system of tubes with elastic walls,
it was stated that at each introduction of fluid a wave was produced
which rapidly traversed the walls of the tube, its velocity of movement
being proportional to the tension of the walls of the tube, while its cause
was found not in the passage of the fluid, but in an up-and-down oscilla-
tion of the walls of the vessels. Such a wave of oscillation as seen in
the arterial system is described as the pulse. The pulse is, therefore,
the diastole of the arteries. In the arteries which are close to the heart
this diastole is almost synchronous to the systole of the ventricle, but as
the distance from the heart increases a sensible interval may be recog-
nized between the contraction of the ventricle and the appearance of the
pulse-wave. This time is required for the transmission of the wave
through the walls of the vessels. To determine the time required for the
transmission of this wave it is only necessary to estimate the interval of
time elapsing between the contraction of the heart and the appearance of
the pulse-wave in any locality. This time, together with the distance
of the point examined from the heart, will enable us to calculate the rate
of movement of the pulse-wave. It has been found that the transmission

*It is probable that the data on which the above calculations are made are not even
approximately correct, though they may perhaps serve to give a general idea of the subject.
For experimental proof as to the different sources of error in Bering's method and the
mode of calculating the amount of blood thrown out in the contractions of the ventricles,
see papers by the author— "A New Method for Determining the Amount of Blood Thrown
Into the Arterial System by Each Ventricular Systole," Philadelphia Medical Times,
Jan. 26, 1884, and "The Time Required by the Blood for Making One Complete Circuit of
the Body," Transactions of the College of Physicians, Philadelphia, 1884, and American
Journal of the. Medical Sciences, April, 1884. Also W. H. Howell and F. Donaldson,
" Proceedings of the Royal Society," No. 226, 1883 and 1884, p. 139, and Stolnikow, Archiv
fur Anat. u. Physiologic, 1886.

534 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of the undulation is not uniform in all segments of the arterial system.
It progressively diminishes from the centre to the periphery, and in-
creases with the resistance and thickness of the arterial walls. It is,
therefore, more rapid in the arteries of the inferior extremities.

It has been found that in man in the arterial system of the upper
extremities the pulse-wave travels with a velocity of 5.8 meters per sec-
ond. In the arterial system of the leg the velocity of movement is about
6.4 per second. In }roung individuals before maturity, and when, there-
fore, the arteries are more extensible and, consequently, less elastic, the
velocity of the pulse-wave is diminished, it then being only about four
meters per second. So, also, the causes which reduced the blood-pres-
sure will also reduce the rapidity of movement of the pulse-wave. It
must not be forgotten that the time of appearance of the pulse-wave in
any point of the arterial system by no means indicates that the blood
thrown out from the left ventricle would in that interval reach the point
at which the pulse-wave is perceived ; for by comparing the velocities
of movement of the blood, even in the vessels where the velocity of
movement is highest, and the velocity of movement of the pulse-wave, it
will be found that the latter moves with many times the higher velocity.
The onward current of the blood in the arteries at points at a distance
removed from the heart is due to the blood being mechanically pushed
forward by the increased quantities thrown into the vascular system by
the contraction of the ventricle.

When the finger is applied over a superficial artery resting upon
some firm surface, as on a bone, a series of impulses are felt which coin-
cide in number with the contractions of the heart. They are not, how-
ever, synchronous with the heart's contraction, but each dilatation of
the artery will occur at an appreciable interval after the heart's con-
traction, the length of that interval corresponding with the distance
of the point examined from the heart. This intermittent expansion is
called the pulse, and corresponds to the intermittent outflow of the blood
from a severed artery, and is present in the arteries only, being absent,
except under certain circumstances, from the capillaries and veins.

The practical phenomena concerned in the production of the different
degrees of the pulse-wave may be reproduced by forcing fluid intermit-
tent^ through a tube with elastic walls, in which a variable resistance
may be introduced, and by so arranging movable levers in contact with
the walls of the tube as to enable them to record their movements on a
revolving surface.

The following diagram, after Marey (Fig. 222), represents the curves produced
by a series of levers placed at intervals of twenty centimeters along an elastic
tube, into which fluid is forced by the intermittent strokes of a pump. With each
stroke of the pump each lever rises and then falls, thus describing a curve and
indicating an expansion of the tube, which travels along its walls in the form of

CIRCULATION OF THE BLOOD.

535

a wave. The rise of each lever is abrupt ; its fall is more gradual, and usually
marked by secondary fluctuations.

If two levers, separated by a considerable length of tube, be allowed to
record their movements on a rapidly traveling surface, it will be found that on
working the pump the movements described by the levers will not be synchronous ;
in other words, an appreciable interval of time will be required for the trans-
mission of the wave through the length of tube separating the two levers. In

,WV\AA/W\A/\/VWW

50V

FIG. 222.— PULSE- WAVES DESCRIBED BY LEVERS PLACED AT INTERVALS OF
TWENTY CENTIMETERS ON AN ELASTIC TUBE, INTO WHICH FLUID is
FORCED BY THE SUDDEN STROKE OF A PUMP, (foster.)

The pulse-wave is traveling from left to right; A, primary, and B C secondary waves. The intervals
between the dotted lines each correspond to 1-50 second, determined by the tuning-fork curve V, and
permit measurement of the velocity of the wave. A'A' are reflected waves from the closed end of the tube.

such an apparatus the statement already made as to the conditions governing the
rapidity of transmission of the wave-impulse may be readily demonstrated. The
more rigid the tube, the more rapid the movement of the wave ; the more exten-
sible the tube, the slower the wave travels. It will also be noticed that the
nearer the levers are to the pump, the greater will be their excursion, indicating a
greater expansion of the tube at that point, while in very long tubes the wave
gradually decreases in intensity until it often becomes scarcely distinguishable.

536

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The same condition applies in the arterial system of animals : the nearer the artery
to the heart, the greater will be its expansion on the systole of the ventricle and
the stronger will be the pulse, while the greater the distance the less will be the
expansion and the weaker, consequently, will be the pulse.

It has been mentioned that the descending limb of the curve described by
such levers is ordinarily broken into a number of secondary undulations. These
may be due to various causes. When by the injection of a mass of fluid the
walls of the tube are distended, as they regain their position of equilibrium inertia
carries them still farther, until the point of equilibrium has been passed ; a recoil
then takes place, and so on. In other words, each point of the tube is the seat of
a series of oscillations following each succeeding wave, and which are due simply
to the inertia of the walls of the tube.

FIG. 223.— MAREY'S SPHYGMOQRAPH. (Yeo.)

The frame B, B, B, is fastened to the wrist by the straps at B, B, and the rest of the instrument lies on
the forearm. The end of the screw, V, rests on the spring, R, the button of which liee on the radial artery.
Any motion of the button at R is communicated to V, which moves the lever L up and down. When in
position, the blackened slip of glass is made to move evenly by the clock-work, H, so that the writing
point draws a record of the movements of the lever.

Again, in the artificial scheme of the circulation, if the resistance be consider-
able, or if the end of the tube be completely obstructed, the wave will be
reflected from the distal end of the tube, and will again cause a secondary wave.
If a lever (the sphygrnograph, Fig. 223) be so placed on an artery in a living
animal as to record the movements of its walls, various breaks will also be seen
in the descending limb of the pulse-curve (Fig. 224). The most important of
these is the so-called dicrotic wave, which is more or less marked in every pulse r
although it may be so exaggerated as to produce the impression of a double
impulse, or may, on the other hand, be scarcely perceptible. Anything which
reduces the tension in the arterial system will facilitate the development of the
dicrotic wave. Anything which increases the rigidity of the arteries reduces the
degree of the dicrotic wave. It is, therefore, evident that the dicrotic wave is

FIG. 224.— TRACING DRAWN BY MAREY'S SPHYGMOGRAPH. (Yeo.)

mainly a wave of oscillation, due to the inertia of the walls of the vessels, possibly
being reinforced by a wave of expansion reflected from the closure of the aortic
valves. When the conditions are especially favorable for producing such waves
of oscillation, or, in other words, when the walls of the arteries are especially
relaxed, we will then sometimes find that the pulse-curve in its descent will be
marked by two breaks, the first of which is then spoken of as the pre-dicrotic
and the second as the dicrotic wave.

5. THE CIRCULATION IN THE CAPILLARIES. — The capillaries consist
of minute tubules whose walls are constituted by a single layer of trans-
parent, thin, nucleated, endothelial cells joined to each other by their

CIRCULATION OF THE BLOOD.

537

margins. These tubules divide and reunite to form net-works which
differ in shape and arrangement in different organs and tissues. Their
diameter varies considerably, but is as a rule about that of the single red
blood-corpuscle. In the lungs and brain, the capillaries are smaller than
those of the skin ; in the retina and muscle, are smaller than in bone,

FIG. 225.— SMALL PORTION OF FROG'S LIVER, VERY HIGHLY MAGNIFIED,
AFTER HUXLEY. (Yeo.)

A, wall of capillary vessels ; B, tissue lying between the capillaries ; C, epithelial cells of the skin,
only shown in part of specimen where the surface is in focus ; D, nuclei of the epithelial cells ; E, pigment-
cells, contracted ; F, red blood-corpuscles : G, H, red corpuscles squeezing their way through a narrow
capillary, showing their elasticity ; I, white blood-cells.

marrow, river, and the choroid tunic of the eye. In all probability the
walls of the capillaries are not contractile, although they are capable of
undergoing variations in diameter, this change in all probability being
of a passive nature, owing to similar phenomena taking place in the
small arteries and veins. Thus, the pulse which is evident in inflamed

538 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

organs is not due to rhythmic contractions of the walls of the capillaries,
but to the paralysis of the walls of the minute arterioles and the conse-
quent conduction of the impulse from the heart.

The circulation of the blood through the capillaries admits of ready
study in the transparent tissues of different organs, such as the web of a
frog's foot, the lung of the frog, or the mesentery of the guinea-pig.
When such tissue is subjected to microscopic examination in an animal
rendered motionless by the injection of curare, the blood may be seen
passing in a continuous stream from the smaller arterioles through the
capillaries to the veins (Fig. 225). The arterioles are readily recognized
by the greater velocity of the flow within them and by the fact that
occasionally faint pulsations synchronous with the contractions of the
heart may be recognized. Under ordinary circumstances when the
circulation through the capillaries is examined it will be found that the
corpuscles pass in single file with a velocity usually of about 0.5T mm.
a second. The calibre of the capillaries is, however, the seat of frequent
changes whose mechanism will be subsequently studied. Often we shall
find that the capillaries dilate, and we have then a stream of corpuscles
moving several abreast through them, and even while undergoing
inspection the capillaries may be seen to become smaller in diameter
and occasionally in certain places so narrow as to refuse the passage
of a single corpuscle; the blood then becomes blocked up behind this
contraction, and then we have channels dilating behind this obstruction
and carrying off the stagnated blood.

The mean blood pressure in the capillaries has been placed at about
thirty-five millimeters of mercury, but it is evident that this pressure
must be subject to very great variations.

When a microscopic examination is made of a frog's foot it is seen
that the file of nucleated corpuscles move with their axes parallel with
the stream, rotating sometimes on their axes, and occasionally we find
an evidence of the flexibility of the red blood-cells by noticing that
sometimes one of these cells, striking the bifurcation of a capillary,
will become doubled on itself, part lying in one branch and part in
another, until finally driven along by the cells coming behind it.

The white blood-cells will be found to be moving with a much lower
velocity than the red blood-corpuscles (one-tenth or one-twelfth as fast),
rolling slowly along in contact with the walls of the capillaries outside
of the central, rapidly moving blood-current. Such a layer is termed the
inert layer, and in nearly all cases it will be found that, while the red
blood-cells move in a rapid stream through the centre of the vessel, a
clear space between this central column and the walls of the capillaries
may be recognized, in which inert layer, as already mentioned, the white
cells may be nearly always found. The presence of the white blood-cells

CIKCULATION OF THE BLOOD. 539

in this peripheral layer is due to two causes. The white blood-cells are
much more adhesive than the red, and therefore tend to cling to the
sides of the capillaries. In addition to this, the white blood-cells are
lighter in specific gravity than the red, and it has been noticed that when
a fluid holding particles in suspension of two different densities is forced
through a capillary tube, the heavier particles will always pass through
the rapidly moving axial current, while the lighter particles will be in a
current by the sides of the tube, where the friction is greatest and where
motion is therefore slowest.

When the circulation is studied in the vessels of the mesentery of
a warm-blooded animal, or where inflammation is produced in the tissues
of the web of a frog's foot by mechanical irritation, the corpuscles may
frequently be observed to pass through the walls of the vessel in great
numbers (diapedesis). At first the colorless cells are found to move
more and more slowly; several accumulate and adhere to the wall and
ultimately pass out through it, during the act of passing being finely
drawn out into slender, protoplasmic threads. It is doubtful whether
actual stomata or openings exist between the cells which compose the
vascular walls, or whether they simply pass through the cement substance
between the endothelial cells.

6. THE CIRCULATION IN THE VEINS. — The veins are much less elastic
than the arteries, and so do not remain open, even in a dead body, after
the blood has been withdrawn; otherwise they resemble the arteries in
structure, although the muscular element in them is unequally distributed.
The veins are, nevertheless, contractile, although unequally so, and may
often be noticed to reduce in diameter when the part is exposed to the
cold or to various other irritations. The veins are very dilatable, and
are in capacity much greater than that of the arterial system : the veins
are, in fact, capable of containing the entire blood of the body.

When a vein is cut the flow from the divided extremity occurs
usually from the distal end; that is, the one nearest the capillaries, alone.
It is continuous and of comparatively slight velocity. The pressure of
the blood within the veins, as determined by connecting a manometer
with them, is always much lower than in the arteries, and decreases as
the heart is approached, where during inspiration even a negative
pressure may be noticed. This is proved by the constant entrance of
the lymph, which is itself moved under an extremely low pressure, into
the large, venous trunks at the root of the neck. In the sheep the mean
pressure in the brachial vein has been found to be four millimeters of
mercury ; in the crural, eleven and four-tenths millimeters ; in the axillary
the pressure is usually negative, becoming one millimeter negative
during inspiration, and three to five millimeters during strong inspira-
tion, and becoming positive only during forced expiration. No pulse is

540 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to be detected in the veins, except in cases where the small arterioles
and capillaries are greatly dilated, as in the case of the secreting glands,
and where the arterial pulse may be directly transmitted to the veins.
The forces which occasion the movement of the blood in the veins con-
sist in the propulsion of the blood by the heart through the capillaries,
a vis a tergo ; a vis a f route, found in the aspiratory power of the lungs
in inspiration and of the heart in diastole, aided by the compression of
the venous trunks in the contraction of various muscular masses, by
which the blood is forced on toward the heart.

The velocity of movement in the veins is much less than in the
arteries, and it is greater in the large veins than in the small, from the
reduction in the total capacity of the venous system.

In the dog the velocity of movement has been stated to be about
two hundred millimeters per second. The veins are generally furnished
with valves arranged in such a manner that when any increase of pres-
sure takes place they become closed and obliterate the lumen of the ves-
sel and prevent the blood from returning to the capillaries. The valves
are formed by free folds of the inner endothelial coat arranged in the
form of either single, double, or triple cusps. They serve to support the
blood-column in the large veins, and here these vessels are furnished
with especially thick coats. Where local pressures are not apt to un-
dergo sudden modification, we find that valves are not present ; they are,,
therefore, absent in the veins of the brain and lungs.

The portal vein differs from other venous trunks in that the blood
circulating in it passes, not into a larger trunk or directly into the heart,
but through a second capillary net-work in the liver. The forces, how-
ever, which move the blood in the portal vein are the same as in other
veins.

7. THE INFLUENCE OF THE NERVOUS SYSTEM ON THE CIRCULATION. —
The quantity of blood supplied to any organ is not a fixed quantity, but
is governed by the demands of the organ. To accomplish this, it isr
evidently, necessary that the influence which produces and maintains the
circulation cannot be a fixed and constant force, but must be capable of
modification. The modifications in the organs of circulation may be of
two different kinds — modifications in the force and frequency of the
heart's pulsation or modifications in the calibre of the peripheral vessels,
which latter, evidently, may be either general or local. Both of these
variations are dependent upon the influence of the nervous system.

The Intrinsic Nervous System of the Heart. — The conditions upon
which the action of the heart depends, and the means by which it may
be modified, will now be considered. That the heart contains within
itself the conditions necessary for its rhythmical movement was known
to Galen, but that the main factor of its motor apparatus consists of

CIRCULATION OF THE BLOOD. 541

small automatic nervous centres situated in the walls of the heart was
first pointed out by Remak. These cardiac ganglia are three in number
and are of different functions ; two are motor ganglia, one an inhibitory
ganglion. The motor ganglia are the ganglia of Remak, situated at the
opening of the inferior vena cava; the ganglion of Bidder is situated in
the left auriculo-ventricular septum. These ganglia are entirely independ-
ent of the will, and, under the excitation of the temperature and chemical
composition of the blood, communicate to the muscular fibres of the
heart their motor impulse. The inhibitory ganglion is that of Ludwig,
situated in the inter-auricular septum. The function of this ganglion is
to regulate the transmission of motor impulses, produced by the motor
ganglia, to the fibres of the heart. It fulfills this end, however, not by
acting directly on the muscular structure of the heart, but through the
mediation of the motor ganglia ; by this means it compels the motor
ganglia to dispense the power which they develop during excitation
rhythmically and moderately. As regards the manner in which these
ganglia produce the rhythmical contraction of the heart, little is known,
but that they are the prime factors in producing the rhythm of the car-
diac revolutions, with its various modifications, is capable of experimental
demonstration.

If the heart be removed from a frog and placed in a watch-glass
containing a dilute saline solution, it will be seen that it still continues
to pulsate in as exact rhythm and as vigorously as when in its normal
condition. Under favorable circumstances it might be kept pulsating
for many hours. This is not, however, the case with the frog alone ; the
heart of almost any cold-blooded animal will beat outside of the body,
and a similar observation has even been made on the heart of man. But,
to return to the share of the motor ganglia in producing cardiac pulsa-
tion : As before stated, one motor ganglion is situated at the opening of
the inferior vena cava, and the other in the auriculo-ventricular septum.
If the apex of the ventricle be cut off from the base of the heart with a
pair of sharp scissors, dividing the ventricle at about its lower third,
instantly the apex ceases to pulsate, while the remainder of the heart
still goes on contracting as before. The apex has been cut off from its
motor ganglia. It may be said that the section of the heart has destroyed
the irritability of the muscular fibres of the apex, but if the apex be
irritated with a weak induction current it responds ; it will again pulsate,
to again, however, become quiescent on removal of the irritation. It
has, however, been stated by Meruncowicz that the apex fragment will
again commence to pulsate if kept supplied with defibrinated blood or
artificial serum ; so, also, after an hour or more the apex will usually
again spontaneous^ commence to pulsate.

Further, if in a narcotized frog the ventricle is compressed trans-

542 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

versely with the blades of a pair of forceps in the line of incision of
the former experiment, the apex will cease to pulsate, though still
supplied with its normal excitant and nutriment ; it has been separated
from its motor ganglion. If the apex be irritated it will beat, to again
become motionless on removal of the irritation. This condition of
affairs will remain for an indefinite length of time, even for as much as
three weeks — the apex of the ventricle motionless and gorged with
blood and the rest of the heart contracting normally. If, however, the
intra-cardiac pressure be increased by clamping the aorta, the apex will
commence to beat, but independently of the rest of the heart and at a
slower rate. This being so, if we can be positive that there are no
ganglia present in the apex, it must be concluded that the heart-muscle
may contract independently of any nervous mechanism. It must not
be forgotten, however, that it has not been definitely proved that there
are no ganglia in the apex, only they have never been found. The posi-
tion then is this : —

A fragment of cardiac muscle containing a motor ganglion will
pulsate when removed from the body, and without any artificial stimulus.
A fragment of muscular fibre unconnected with a motor ganglion will
remain quiescent until it receives some external stimulus. By cutting a
heart in halves it will be seen that one part pulsates while the other does
not. If this subdivision be carried still further, gradually cutting the
heart into fragments until they become microscopic in size, and some of
them be placed under the microscope, it will be seen that some fragments
are rhythmically contracting and others are motionless ; if the sub-
division be carried still further, until the ultimate fibres of the heart are
isolated, in nearly all the contracting fibres will be found ganglionic
nerve-cells, while none are to be found in those which are motionless.

The action of the inhibitory ganglion may be seen by exposing the
heart of a frog in the usual way, and distending the oesophagus with a
short glass rod in order to bring the parts exposed into more prominent
view.

The apex of the ventricle should be seized with a pair of forceps
and drawn forward and to the right, after dividing the little connecting
band between the posterior surface of the ventricle and the pericardium.
With the aid of a delicate aneurism needle, a silk ligature is to be passed
between the vena cava inferior and the ventricle and between the vena
cava superior and the right auricle in such a position that when tight-
ened it will grasp the line of junction, which is marked by a slight
groove, of the sinus venosus and right auricle. After seeing that the
heart is pulsating rhythmically, the ligature should be suddenly tightened,
and it will be found that after a few beats the heart will stop in diastole,
while the sinus will continue to pulsate as before. After a few moments

CIRCULATION OF THE BLOOD. 543

the ventricle will again pulsate, but its rhythm will be no longer syn-
chronous with that of the sinus.

In another frog, prepared in the same manner, the heart may be
separated from the sinus venosus with a pair of scissors, following the
line of the ligature in the preceding experiment, and the result will be the
same. Cut off the ventricle, including the auriculo-ventricular groove,
from the auricle be fore it starts spontaneously to pulsate, the ventricle
immediately begins to beat ; the same result might have been obtained
after ligature as in the first experiment.

Or, if this line be irritated with an induction current, taking care to
include the sinus in the current, the same result will follow. But in a
frog in which T^Tr of a grain of atropine has been injected irritation with
the electric current will have no effect ; while if the first experiment is
repeated, by ligating this line, the heart will stop as before.

What inference can be drawn from these experiments ? It has been
stated that the ganglion of Remak, a motor ganglion, is situated at the
opening of the inferior vena cava, that is, in the sinus venosus ; also that
the inhibitory ganglion of Ludwig is in the interauricular septum, and the
motor ganglion of Bidder in the left auriculo-ventricular septum. We
may assume that Remak's ganglion is an automatic motor centre, i.e.,
"a ganglionic centre in which energy tends to accumulate and discharge
itself in the form of motion at regular intervals, the length of which varies
with the resistance to the discharge and with the rapidity of the accumu-
lation," the physiological grounds for this assumption being as follows:
The succession of acts which make up a cardiac revolution distinctly
start in the sinus ; this is the only portion of the heart that contracts
independently, and electric excitation of this centre induces increased
frequency of contraction of the whole organ. By separating the heart
from the sinus venosus, either by ligature or by amputation with the
scissors, we not only remove the heart from its main motor centre, but
also irritate the inhibitory centre, and so cause arrest of the pulsation
of the heart, while the sinus containing the motor centre goes on con-
tracting as before. After a few minutes, however, the inhibitory effect
induced through irritation passes off, and then the motor ganglion at the
base of the ventricle starts the heart again. So, when, without waiting
for the inhibition to pass off, we remove the ventricle from the auricles,
the motor ventricular ganglion is released from its inhibition and starts
the heart again. The effect is somewhat different, however, when we
irritate this line with electricity ; then the stoppage is due alone to the
inhibitory action of the ganglion, and when this passes off the heart
pulsates. So, when this inhibitory ganglion is paralyzed with atropine,
electric irritation is powerless to stop the heart, while ligature by re-
moval of the heart from its main motor centre prevents pulsation.

544

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

From these experiments it has been found that a heart will contract
rhythmically outside of the body, that this function is probably due to

FIG. 226.— SIMPLEST FORM OP MANOMETER FOR FROG'S HEART. (Sanderson.)

(For description, see text.)

the presence of motor ganglia, and that the heart may be slowed or
stopped either through inhibition from irritation of the inhibitory

CIRCULATION OF THE BLOOD.

545

SM — -

GP-Y-i

ganglion or removal of the heart from the influence of the main motor
ganglion.

To carry this subject still further, a more delicate means of experimentation
must he used. Poisons must be employed as instruments of investigation.
Pharmacology has indeed in this line almost run ahead of physiology, for it has
been through the study of the action of poisons on the heart that our complete ideas
of cardiac physiology have been derived.

Fig. 226 represents an apparatus devised by Dr. Coats, of Glasgow, and
Professor Ludwig, of Leipsic. It consists of a reservoir, A, with a stop-cock,
15, containing fresh serum ; a rubber tube, C, leading from this, and acannula, D,
which is to be inserted into the vena cava inferior ; another cannula, D', to be
inserted in the aorta, connected by tubing with a mercurial manometer, E, i.e., a
fine U -shaped tube partly filled
with mercury, and supporting on
one limb of the column a piston
with a long, delicate wire rod, G,
above it.

The brain and spinal cord of
a frog should be destroyed by
introducing a needle into the cere-
bro-spinal canal, the heart freely
exposed, and one of the pneumo-
gastric nerves carefully dissected
out. To find the vagus nerve,
follow up the diverging aortae to
where they cross the cartilaginous
tips of the posterior horns of the
hyoid bone : from each of these tips
the petro-hyoid muscles are seen
passing upward and backward to-
ward the occipital region. The
lower border of these nearly par-
allel fibres is the guide to the vagus,
which is found lying beneath its
inner edge. Following these
muscles back from their insertion
in the hyoid bone to their origin in
the petrous bone, they are seen to
be crossed first by the hypoglossal
nerve, ascending inward to the
muscles of the tongue Nearer FlQ ^.-DIAGRAM OP THE COURSE OF THE
the middle line and following the VAGUS NERVE IN THE FROG. (Stirling.)

same course as the hypoglossal
is seen the glosso-pharyngeal, and
crossing over the top of the in-
ferior horn of the hyoid bone is
the laryngeal nerve (Fig. 227).

Place a thread loosely around the nerve, so that it can be easily found when
required. The next step is to insert the cannula, D, into the inferior vena cava,
and secure it with a thread ; the cannula, D', is then inserted into one aorta, the
other being ligated. All the other organs may be removed, leaving only the
thorax, heart, and a large fragment of skin, S, to cover the heart and nerve, to pre-
vent drying. The oesophagus is now distended with a large glass rod, firmly
clamped to an upright stand. The next step is to connect the vena cava by
means of its cannula with the reservoir containing serum. Open the stop-cock
for a moment, and allow the serum to pass through the heart and apex of the
arterial cannula, to wash out all the blood from the heart. The arterial cannula
is then connected with the manometer, and the serum allowed to flow through the
heart into the manometer until the air in the proximal is entirely expelled through
at F. Then the apparatus is ready for use. The heart should be filled so full that
a little tension exists, even during the diastole. It will be noticed that at each

35

H, heart; LU, lung; BR, brachial plextis; HY, hypoglossal
nerve ; V, vagus ; L, laryngeal nerve ; GP, glosso-pharyngeal
nerve ; SM, submental muscle ; GH, genio-hyoid muscle ; HG,
hyoglossal muscle ; HB, hyoid bone ; PH, petro-hyoid muscle :
OH, omo-hyoid muscle ; SH, sterno-hyoid muscle.

546

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

FIG. 228.— PULSE TRACING OF THE FROG'S
HEART. (Sanderson.)

pulsation of the heart the column of mercury sinks in one arm of the manometer,
while it rises a corresponding distance in the other, carrying with it the piston,
which by means of its pen traces a line composed of a succession of curves on
the smoked surface of the revolving drum. The ascending limb of each curve
corresponds to the systole of the ventricle, and the descending curve to its
diastole (Fig. 228). By irritating the vagus with a weak induction current the
heart stops in diastole, a result similar to that obtained in the previous experiment
when the line of junction of the auricle and sinus venosus was irritated. This
identical result, however, has not been produced by the same mechanism, as may

be seen if to the serum in the reservoir
a few drops of dilute solution of nico-
tine be added ; if the vagus now be
irritated, no arrest of the heart occurs.
The vagus has been paralyzed by nico-
tine ; it no longer is able to restrain
the heart, which beats faster than be-
fore. (When the nicotine is first given
the heart is slowed, and then quick-
ened, the slowing being due to the first
effects of the nicotine on the vagus,
irritating it before it paralyzes it.)

It would seem that nicotine and atropine have the same action. But it will
be remembered that after atropine poisoning it is impossible to stop the heart
through electric irritation of the sinus venosus.

But if the sinus venosus be irritated in the heart which has received the
nicotine, it will stop. Therefore, nicotine and atropine must act on different
inhibitory organisms.

If in a frog which has been placed under the influence of nicotine the heart
be removed and placed on a watch-glass, it will pulsate regularly. If a drop of
saline solution containing a little of the alkaloid muscarine be placed on the heart,

it ceases to beat entirely, and will remain motion-
less. But if while at rest a drop of a solution of
atropine be placed in the heart, it will commence
to beat again.

If in two fresh frogs a drop of muscarine
solution be placed on the "hearts, immediately they
begin to beat more and more slowly, and at last
stop in diastole. If into one frog nicotine be in-
jected no effect will be observed ; the heart still
remains motionless in diastole ; but the injection
of atropine into the other frog whose heart was
stopped by muscarine will cause it to commence
to beat, and it will pulsate as strongly and rhythm-
ically as before the operation. If, however, the
atropine be injected first, and then the muscarine
be applied, the heart will not be stopped.

It has now been stated that both nicotine
and atropine render the heart insusceptible to
irritation of the vagus, but that irritation of the
sinus venosus will stop the heart in nicotine
poisoning, but not in atropine poisoning There-
fore some part of the cardiac inhibitory apparatus
escapes in nicotine poisoning which is paralyzed
by atropine.

In the above diagrammatic sketch of the arrangement of the cardiac
ganglionic apparatus, proposed by Schmiedeberg (Fig. 229, M), is the main motor
ganglion acting on the muscular fibres of the heart by means of radiating fibres.
It is regulated by an intermediate apparatus represented by the dotted lines, on
the one side by the inhibitory ganglion, I, connected again with an intermediate
apparatus with the vagus nerve, and on the other side by the accelerator ganglion,
Q, connected in the same manner with the accelerator nerves. According ro
this arrangement, nicotine is supposed to paralyze the fibres intermediate between
the inhibitory ganglion and the vagus nerve, while atropine paralyzes this portion.

FIG. 229. — DIAGRAM OF THE
HYPOTHETICAL, NERVOUS
APPARATUS OF THE H.EART.
(Lauder-Brunton. )

M, motor ganglio

I, inhibitory

ganglion ; Q, accelerator ganglion ; V, in-
hibitory extra-cardiac nerves : S, acceler-
ator extra-cardiac nerves. The interme-
diate apparatus of Schmiedeberg is
represented by the dotted lines.

CIRCULATION OF THE BLOOD. 547

the inhibitory ganglion and the apparatus intermediate between the ganglion, I,
and the motor ganglion. On the other hand, muscarine slows the heart or stops
it in diastole, similar to irritation of the vagus, while its effects are not interfered
with by either the previous or subsequent injection of nicotine : therefore, mus-
carine must act on some apparatus more central than that affected by nicotine,
and as the effects are gradually developed, it is supposed to act by irritating the
ganglion, I. Again, we have seen that muscarine will have no effect after the in-
jection of atropine, and that atropine will cause a heart stopped by muscarine to
recommence beating ; therefore, atropine acts on a more central apparatus than
muscarine: in other words, on the apparatus intermediate between I and M. The
effects of atropine may be removed by physostygma and is antagonistic to
nicotine. These points are valuable in determining the antidotal effects of
poisons.

The action of the accelerator apparatus has not been so thoroughly well
worked up, but the action of poisons, as of veratrine, renders it necessary to
assume a similar arrangement.

There is one more point in the action of these cardiac ganglia ; that
is, the influence of heat and cold on the heart.

The simplest method of studying the action of heat on the cardiac
pulse is that of Lauder-Brunton (Fig. 230). His arrangement consists
of a plate of glass about three inches by four inches, at one end of
which a cork is cemented projecting about half an inch beyond the edge

7

FIG. 230.— LAUDER-BRUNTON'S ARRANGEMENT FOR STUDYING THE EFFECT
OF HEAT AND COLD ON THE HEART OF THE FROG.

of the glass plate. To this is fastened a long, light lever freely moving
on a pivot, and projecting about one and one-half inches beyond one end
of the plate and about four inches beyond the other end ; the lever is
counterpoised by fastening a small pair of forceps on the short end of
the lever ; by altering the angle of the forceps, the lever can be balanced
to a nicety. A frog's heart may be placed on the plate close up to the
pivot and lying so that the lever is lifted at each pulsation of the ven-
tricle, the lever being balanced so as to make slight pressure by altering
the position of the pair of forceps. If the glass plate is placed on some
pounded ice the heart will beat gradually more and more slowly, until at
length it will come to rest in diastole, thus indicating irritation of some
portion of, the inhibitory apparatus. If the plate be removed from the
ice, the heart will commence again, and by gradually heating it over a
spirit-lamp the heart will pulsate faster and faster, the extent of the
contractions increasing up to 20° C., until at length it will stand at rest
in what is called u heat-tetanus ; " if, however, the temperature is lowered
the heart will again commence to beat, but if the temperature is raised

548

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

still higher than before when the heart stopped from heat, the condition
of heat-tetanus will pass into that of " heat-rigor," and no application
of cold will have the slightest effect toward again starting the heart.

The influence of heat and cold on the amount of work done by the
heart is an extremely complicated subject. We can only state here that
within certain limits the mechanical work done by the heart increases
with an increase of temperature, but that very soon the contractions
increase in number in much greater proportion than the mechanical
effect ; hence, though the amount of work done at a comparatively high
temperature is greater than can be accomplished at a low temperature,
the effect of each individual contraction is much less.

The frequency of the normal rate of contraction of the heart varies
greatly in different animals, as shown in the following table compiled by

Colin :—

Frequency of the Pulse per Minute.
In the elephant,
camel,

25 to

28 to

28
32

giraffe, .

horse, . . i . 86 to 40

ox, . . 45 to 50

mule, . . . 46 to 50

tapir, . . 44

ass, . . . . . . . . 46 to 50

pig, . . . . . - . . . 70 to 80

lion, . . . . . . . .40

lioness, . . 68

tiger, 64

sheep, 70 to 80

goat . 70 to 80

leopard, 60

female wolf, 96

hyena, 55

dog, . . 90 to 100

cat, . - . • . . . . » . 120 to 140

rabbit, 120 to 150

marmot, 90 to 175

mouse, ......... 120

goose, ........ 110

chicken, ....... 140

pigeon, . 136 to 138

snake, 24

carp, . 20

frog 80

salamander, 77

The following table shows the variation and frequency of the pulse
per minute in the horse and ox at different ages : —

Horse. Ox.

Newborn, .... 100-120 Newborn, .... 92-132

Fourteen days old, . 80- 96 Fourteen days old, . 68

One-fourth year old, 68- 76 One-fourth year old, . .

One-half year old, . 64- 72 One-half year old, . 50- 68

One year old, ... 48- 56 One year old, . . 50-68

Two to three years, . 40- 48 Young cow, ... 64

Four years of age, . 38-50 Four-year-old ox, . 56

Aged, 32-40 Aged, 45-50

CIRCULATION OF THE BLOOD.

549

The frequency of the pulse in man and animals depends upon the
age, sex. state of nutrition, size, and various other conditions.

In man the normal rate of the pulsations of the heart is about 72
per minute ; in the female, about 80, though great variations may be met
with in perfectly normal individuals. Up to fifty years of age the rate
of the pulse is in inverse ratio to the age, as is shown in the following

table :—

Beats per Minute.
Newly born infant,
One year, .
Two years,
Three "
Four "
Five "
Ten '"

The pulse-rate is increased by muscular exercise in creating a
greater demand for arterial blood, by increasing blood pressure, by in-
creased temperature (fever), in digestion, by various mental disturbances,
and in extreme debility. It is more frequent in the erect than in the
recumbent position, and varies inversely with the barometric pressure.

ant

, 130-140
120-130
105
100
97

Ten to fifteen years,
Fifteen to twenty,
Twenty to twenty-f
Twenty-five to fifty,
Sixty

. . 78
. . 70
ve, . 70
. . 70

74

90- 94
about 90

Eighty, ....
Eighty to ninety, .

. . 79

over 80

FIG. 231.— TRACING OBTAINED FROM THE FROG'S HEART ON STIMULATION
OF THE PNEUMOGASTRIC NERVE. (Foster.)

The current entered the nerve at a, and was shut off at b. The latent period is indicated by the fact
that one pulsation occurred after the stimulation entered the nerve. It is further evident that the inhi-
bition persisted some time after the stimulation ceased.

In addition to the intrinsic nervous system of the heart, the pulsa-
tions of this organ are also governed by impulses coming from the
central nervous system. These are of two different kinds, — inhibitory
and accelerating.

The Inhibitory Nerves of the Heart. — It was discovered in 1848
that stimulation of the pneumogastric nerve or of its divided periph-
eral extremity had the effect, in the dog, of retarding the pulsations
of the heart, and, when the stimulation was sufficiently strong, of entirely
arresting the heart in diastole. This effect is not produced immedi-
ately on the application of the electric current to the nerve, but is pre-
ceded by a latent period amounting to about one-tenth of a second ; so,
also, the effect lasts a certain time after the shutting off of the current,
if the application has not been too prolonged (Fig. 231). On the other

550

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

hand, if the current is very strong, the heart may be completely arrested
and yet start again during the passage of the current. With weak cur-
rents no actual arrest of the heart takes place, but the pauses between
the beats are prolonged during the earlier part of the application of the
current, and the pulse is thus rendered slow. If the pneumogastric be
stimulated in a dog during a blood-pressure experiment some such curve
as represented in the diagram will be produced (Fig. 232).

The blood pressure is seen to undergo a rapid fall shortly after the
application of the current, from the fact that on the cessation of the
pulsation of the heart the arteries, through their contractility, empty
themselves into the venous system. As the heart again commences to
pulsate it throws its contents into the arterial system, which has been
already largely depleted of blood, and, as a consequence, the walls of the
arteries are rapidly stretched, and we have a correspondingly rapid

FIG. 232.— MANOMETER TRACING FROM THE CAROTID OF A RABBIT ON STIM-
ULATION OF THE PNEUMOGASTRIC NERVE. (Foster.)

The current entered the nerve at a and was shut off at b.

increase in pressure, and therefore a rapid rise in the mercury in the
manometer. When the heart is only slowed b}^ stimulation of the
pneumogastric, and not completely arrested, the mercury in the manom-
eter undergoes extensive oscillations, partly due to inertia, which
exaggerates these movements, and partly due to the same cause already
mentioned. In other words, between the pulsations of the heart, which
succeed each other slowly, the arterial system has time to partially empty
itself into the veins.

Inhibition of the heart may not only be produced by direct stimu-
lation of the pneumogastric, but also may be produced reflexly. If one
pneumogastric nerve be divided, and the central end, in connection with
the brain, be stimulated with the induction current, the heart will be
arrested or slowed as before. If the abdomen of a frog be opened, and
the intestine struck sharply, as with the handle of a scalpel, the heart

CIRCULATION OF THE BLOOD. 551

will be likewise arrested in diastole. If the mesenteric nerve be stimu-
lated by an induction current the heart will also be brought to a sudden
standstill. If both pneumogastric nerves be divided, the anterior roots
of both spinal accessory nerves be torn out, or the medulla oblongata
destroyed, the preceding experiments will all fail. This indicates that in
the first case the impulse was conducted through the central stump of
the divided pneumogastric to the brain, and there, from a collection of
nerve-cells in the medulla oblongata, which is termed the cardio-inhibi-
tory centre, is transmitted through the spinal accessory nerve to the
pneumogastric plexus, and through the undivided vagus to the heart.
If the spinal accessory nerve be pulled out by the roots, the cardio-
inhibitory fibres of the pneumogastric undergo degeneration, and four or
five days after the operation stimulation of the vagus fails to slow the
heart. In the other instance, where irritation of the intestinal surface
or mesenteric nerves produces inhibition, the impulse is conducted
through the mesenteric and s^^mpathetic chain to the spinal cord, from
there to the cardio-inhibitory centre, and from there to the heart. It is
probable that the syncope occasionally produced by severe pain, emotions,
or sometimes from drinking ice-water when overheated is produced in
the same manner, the heart being arrested or slowed through reflex
inhibition.

It is thus observed that the pneumogastric nerve possesses a function
directly opposed to that of most other nerves. When a motor nerve is
stimulated it produces contraction of the muscles to which it is dis-
tributed. Stimulation of the pneumogastric, on the other hand, produces
relaxation of the heart-muscle. The manner by which this effect is
produced is in all probability through the inhibition of the motor ganglia
of the heart.

The cardio-inhibitory centre in the medulla is in constant action,
through reflex stimuli conducted to it through the abdominal and cervical
sympathetic, and might be compared to the action of a brake on a
moving machine. When both pneumogastric nerves are divided, the
heart in the dog, and to a less extent in the rabbit, beats very much
faster, so that this inhibitory centre is constantly restraining the action
of the motor ganglia. The cardio-inhibitory centre may be directly
stimulated by sudden anaemia of the medulla, as by sudden ligation of
both carotids; by sudden venous hyperaemia, as by ligation of all the
veins of -the neck; or by increased venosity of the blood, as by dyspnoea
or causing an animal to inhale CO,. It may also be reflexly stimulated,
as already indicated.

The Accelerator Nerves of the Heart. — The action of the heart
may not only be retarded or arrested through the stimulation of the
pneumogastric, but in the mammal, even after division of both pneumo-

552

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

gastrics, it may be accelerated by stimulation of the cervical sympathetic,
stimulation of the cervical spinal cord, or in a more marked degree by
stimulation of the communicating filament between the spinal cord and
the inferior cervical and the first dorsal ganglia of the S3rmpathetic.
These latter fibres are described as the accelerator nerves of the heart,
and when stimulated produce an increase in the rate of the heart's pulse,
but with a decreased force, the loss in power being, however, compensated
by the increase in rapidity. As a consequence, after stimulation of these

nerves the blood pressure remains unchanged.
The course of these nerves is different in the
rabbit and the dog.

The diagrams (Figs. 233 and 234) indicate
their most usual course.

These accelerator fibres originate from
centres in the medulla oblongata and spinal
cord, though their exact location has not been
determined. It is by means of stimulation of
these fibres, therefore, that stimulation of either
the cervical spinal cord or cervical sympa-
thetic produces increase in the rate of the
heart's pulsation. When the cervical spinal
cord is stimulated a great increase in blood
pressure follows from stimulation of vaso-motor
nerves, but that the increased rate of the
heart's contractions is not due to the high
blood pressure alone is proved by the occur-
rence of acceleration of the pulse when the
cervical cord is stimulated, even after section
of the splanchnic nerves, when increased blood
pressure is prevented. These nerves are not
in constant activity ; in other words, they do
not antagonize the pneumogastrics, and when
divided the heart does not beat slower. A
long latent period also characterizes these
nerves, and it takes considerable time, as much as ten seconds, from
the commencement of stimulation before the maximum acceleration of
the heart is reached ; while, again, it is only slowly and gradually that
the normal heart-rate is regained even at the cessation of stimulation.

8. THE INFLUENCE OF THE NERVOUS SYSTEM ON THE ARTERIES. —
Anatomical examination of the walls of the minute arteries shows that
these vessels are not only supplied with circular muscular fibres, but are
also supplied with nerve-fibres which come both from the sympathetic and
cerebro-spinal nervous system, and numerous ganglia have also been

FIG. 233. — SCHEME OF THE
COURSE OF THE CARDIAC
ACCELERATOR FIBRES.
(Landois. )

P, pens ; MO, medulla oblongata ;
V, inhibitory centre for heart ; A, accel-
erator centre : VAG, vagus ; SL, supe-
rior, IL inferior laryngeal nerves ; SC,
superior cardiac fibres ; H, heart ; C, cere-
bral impulse; S, cervical sympathetic;
a, a, accelerator fibres.

CIRCULATION OF THE BLOOD. 553

detected. Anatomical data, therefore, support the view — which would
otherwise be rendered probable, as, for example, in the production of
blushing from emotions — that the calibre of the minute arterioles is under
the control of the central nervous system. Numerous experiments still
further demonstrate the truth of this statement. When the web of a
frog's foot is examined under the microscope it will be found that the
smaller arterioles are constant!}' varying in calibre, sometimes being so
contracted — evidently due to the contraction of their muscular fibres —
as to almost shut off blood from the part supplied by the contracted

FIG. 234.— CARDIAC PLEXUS AND STELLATE GANGLION OF THE CAT. (Landois.)

R. right; L. left: X 1^- 1. vagus: 2'. cervical sympathetic, and in the annulus of vieussens ; 2,
communicating branches from the middle cervical ganglion and the stellate ganglion ; 2", thoracic sym-
pathetic; 3, recurrent laryngeal ; 4, depressor nerve: 5, middle cervical ganglion; 5', communication
between 5 and the vagus : 6, stellate (first thoracic) ganglion ; 7, communicating branches with the vagus ;
8, accelerator nerve ; 8, 8', 8", roots of the accelerator nerve; 9, branch of the stellate ganglion.

vessel, at other times so dilated as to cause the tissues supplied by the-
vessel to become gorged with arterial blood. If the web of the frog's
foot be examined and an arteriole picked out which appears to be midway
between the states of extreme relaxation and extreme dilatation, and a
weak induction current be then applied to the sciatic nerve, the arterioles
will all, as a rule, be found to become immediately contracted. If the
effects of stimulation be allowed to pass off, and then, instead of stimu-
lating the sciatic, this nerve be divided, directly opposite results will

554 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

ensue. The arterioles will now all dilate, and, as a consequence, the parts
will become filled with blood.

Similar effects may be seen in warm-blooded animals. If the sympa-
thetic nerve be divided in the neck of a rabbit, it will be found that the
vessels in the lobe of the ear on that side will have greatly increased in
calibre, will appear not only larger, but numerous vessels which before
were invisible will now be readily seen. The entire tissue of the ear will
be much redder than before, much warmer in temperature, and distinct
throbbing of the pulse may be readity perceived. Here division of the
sympathetic has produced dilatation of the auricular arterioles. If, on
the other hand, the cervical sympathetic be stimulated with an induction
current in the rabbit, directly opposite results will be produced. The
auricular vessels will now all contract, and the tissues of the ear will
become pale and free from blood.

So, also, if the sciatic nerve be divided in a mammal, a corresponding
dilatation occurs in the small arterioles of the foot and leg, and may be
readily determined through inspection of the balls of the toes, especially
as seen in the cat, where they are hairless and not pigmented. So, also,
the temperature of the foot on the side on which division of the sciatic
nerve has been performed will be considerably elevated. Further, if the
splanchnic nerves be divided, the vessels of the abdomen all undergo
extensive dilatation. If the lingual nerve be divided, the vessels on the
corresponding side of the tongue dilate, while in all cases in which
a nerve supplying a muscle is cut a great increase in the flow of blood
from the muscle may be made out. It is, therefore, evident that the
blood-vessels of certain parts of the body are kept in a state of tonic
contraction through impulses traveling along certain nerves. Section of
these nerves has been found to produce dilatation in the corresponding
vascular areas : therefore it is evident that the arteries before the division
of their vascular nerves were in a state of constriction through contraction
of their muscular fibres, and that this state of contraction was due to
impulses coming along the vascular nerves or vaso-motor nerves of that
part. Section of these nerves, therefore, produces paralysis of the
muscular fibres, and the muscular tissue is no longer able to resist the
pressure of the blood, and, as a consequence, these vessels passively
dilate.

It has been found that the vascular condition of the specific parts
of the body are governed by impulses coining along specific nerves, and
that these nerves may be either of the sympathetic or cerebro-spinal
systems. If the spinal cord is divided in the lumbar region it will be
found that the blood-vessels of all the parts below will be paralyzed and
gorged with blood. If the spinal cord, or even the lateral columns alone,
be divided in the cervical region, the blood-vessels of the entire body

CIRCULATION OF THE BLOOD. 555

become dilated. This, therefore, indicates that some portion of the
brain higher up than the cervical spinal cord is the centre from which
originate all the impulses which travel along the different vaso-motor
nerves to innervate the muscular fibres of the different arterioles of the
body. When the path of communication between any vascular area and
•the medulla oblongata is broken, the vessels of that part are deprived of
the nervous impulse coming from the medulla, they lose tone, their mus-
cular fibres relax, and their arteries dilate. When the entire body is cut
off from the medulla all the vessels, therefore, dilate. It has been stated
that stimulation of one of the vaso-motor nerves — such an example being
the sympathetic, the sciatic, or splanchnic — leads to contraction of the
arterioles in the corresponding vascular area. In other words, the
electric stimulation has been added to that coming constantly from the
medulla, and has therefore increased the contraction of the muscular
fibres of the arteries. So, also, if the spinal cord be itself stimulated,
the blood-vessels in all the parts below become still further contracted,
while by directly stimulating the medulla oblongata all the blood-vessels
of the body contract. These facts indicate that the normal degree of
constriction of the arterioles of the body, or what is termed vascular
tonus, is maintained by a series of impulses constantly coming from
a collection of cells in the medulla oblongata, called the vaso-motor
centre. These impulses reach the arteries after passing through the
lateral columns of the cord, during which passage they make connection
with the subordinate vaso-motor centres of the cord, either through the
anterior spinal roots directly or by passing through the rami commu-
nicantes to the sympathetic.

The vaso-motor centre has been located in the floor of the fourth
ventricle, its lower limit being a horizontal line about four or five milli-
meters above the point of the calamus scriptorius and the upper limit
about four millimeters higher up, or one or two millimeters below the
corpora quadrigemina. The vaso-motor centre, as already stated, may
be directly stimulated, and so lead to increased vascular contraction
throughout the entire body. Increased venosity of the blood and vari-
ous poisons, such as strychnine, likewise directly stimulate the vaso-
motor centre, and so cause increased blood pressure ; so, after death, the
venous character of the blood, through stimulation of the vaso-motor
centre, leads to firm contraction of the arteries and a consequent empty-
ing of these vessels into the veins. It nmy also be reflexly stimulated.
Irritation of any sensory nerve will reflexly act on the vaso-motor centre
and lead to arterial contraction, especially of the vessels of the abdomen.
On the other hand, the vaso-motor centre may be inhibited.

If the small nervous filament which is formed in the rabbit by the
union of branches from the pneumogastric and superior laryngeal nerves

556

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

be stimulated, it will be found that the blood pressure will steadily fall
until it may be not more than one-third of the normal height (Fig. 235;.
During the production of this decrease of blood pressure no change
occurs in the rate of pulsation of the heart. It must be, therefore, due to
the diminution of the resistance in the peripheral vascular system. If the
splanchnic nerves be divided previous to this experiment, no subsequent
decrease in pressure will take place. The conclusion from this is evi-
dent. When this nerve, which has been termed the " depressor of Lud-
wig and Cyon " (the superior cardiac branch of the vagus), is stimulated
the impulses pass to the vaso-motor centre in the medulla, and there so
alter the impulses coming from it that it is unable to maintain the nor-
mal degree of contraction of the abdominal vessels, through the failure of
the influence which it normally exerts on these vessels through the
splanchnic nerves. The abdominal vessels, consequently, dilate and

JUUUUUUUUUUUUUUU^

FIG. 235.— BLOOD-PRESSURE TRACING OBTAINED BY STIMULATING THE DE-
PRESSOR NERVE IN A BABBIT. (Foster.)

The current entered the nerve at C and was shut off at O. The intervals on the line T represent seconds.

draw off so much blood from the general arterial system that the
blood pressure may be reduced two-thirds or more. On the other hand,
if in an animal placed under curare the central end of the divided
sciatic nerve be stimulated, directly opposite effects will be produced.
Without any change in the heart's rate of pulsation the pressure will
gradually rise until it may be one-third higher than before the experi-
ment : here, again, the increased pressure being, evidently, due to constric-
tion of the local arterioles, for previous division of the splanchnic nerves
will largely interfere with the production of an increased blood pressure.
These variations in blood pressure are of the greatest importance in
governing the general character of the circulation.

The effects of local and general variations in vascular tone have
been admirably formulated by Foster : —

Let us suppose that any artery, A, is in a condition of normal tone —

CIRCULATION OF THE BLOOD. 557

is midway between extreme constriction and dilation. The flow through
A is determined by the resistance in A and in the vascular tract which it
supplies, in relation to the mean arterial pressure, which again is depend-
ent on the way in which the heart is beating and on the peripheral re-
sistance of all the small arteries and capillaries, A included. If, while
the heart and the rest of the arteries remain unchanged, A be constricted,
the peripheral resistance in A will increase, and this increase of resist-
ance will lead to an increase of the general arterial pressure. This in-
crease of pressure will tend to cause the blood in the body at large to
flow more rapidly from the arteries into the veins. The constriction of
A, however, will prevent any increase of the flow through it — in fact, will
make the flow through it less than before. Hence, the whole increase of
the discharge from the arterial into the venous system must take place
through channels other than A. Thus, as the result of the constriction
of any artery there occur (1) diminished flow through the artery itself,
(2) increased general arterial pressure, leading to (3) increased flow
through the other arteries. If, on the other hand, A be dilated, while
the heart and other arteries remain unchanged, the peripheral resistance
in A is diminished. This leads to a lowering of the general arterial pres-
sure, which, in turn, causes the blood to flow less rapidly from the arteries
into the veins. The dilation of A, however, permits, even with the low-
ered pressure, more blood to pass through it than before. Hence, the
diminished flow tells all the more on the rest of the arteries. Thus, as
the result of the dilation of any artery, there occur (1) increased flow of
blood through the artery itself, (2) diminished general pressure, and (3)
diminished flow through the other arteries. Where the artery thus con-
stricted or dilated is small, the local effect, the diminution or increase of
flow through itself, is much more marked than the general effects, the
change in blood pressure and the flow through other arteries. When,
however, the area the arteries of which are affected is large, the general
effects are very striking. Thus, if while a tracing of the blood pressure
is being taken by means of a manometer connected with the carotid
artery the splanchnic nerve be divided, a conspicuous but steady fall of
pressure is observed very similar to that which is seen in Fig. 235. The
section of the splanchnic nerves causes the mesenteric and other abdomi-
nal arteries to dilate, and these being very numerous a large amount of
peripheral resistance is taken away, and the blood pressure falls accord-
ingly ; a large increase of flow into the portal veins takes place, and the
supply of blood to the face, arms, and legs is proportionally diminished.
It will be observed that the dilation of the arteries is not instantaneous,
but somewhat gradual, the pressure sinking, not abruptly, but with a
gentle curve.

Arterial tone, then, both general and local, is a powerful instrument

558 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

for determining the flow of blood to the various organs and tissues of
the body, and thus becomes a means of indirectly influencing their func-
tional activity.

In certain instances stimulation of spinal nerves will not only pro-
duce contraction of the arterioles of different parts of the bod}^ through
reflex stimulation of the vaso-motor centre, but will also produce dilata-
tion of the arterioles in the vascular area supplied by that nerve ; thus,
for example, if in a rabbit under the influence of curare the central stump
of the great auricular nerve be stimulated with an induction current, the
blood pressure will be increased through constriction of the general vas-
cular areas, while inspection of the ear will show that its vessels have
become largely dilated. So, also, as already described under the section
on Digestion, when the chorda tympani nerve is stimulated, we not only
have increased secretion of saliva, but we have, also, an increase of the
supply of blood to the glands. Such nerves as the chorda tympani and
the great auricular, with numerous others, are spoken of as vaso-dilator
nerves, from the fact that their stimulation leads not to contraction of
arterioles, but to an increase in their calibre ; they, therefore, are of op-
posite function to the vaso-motor nerves. The vaso-dilator nerves, as a
rule, come from the cerebro-spinal system; the vaso-constrictor nerves
are, as a rule, branches of the sympathetic S3^stem. The explanation of
the functions of the vaso-dilator system of nerves is somewhat simplified
by the following observation : It has been stated that when the sciatic
nerve of a frog is divided, the vessels of the parts supplied by that nerve
dilate. Such dilatation is, however, usually transient. Twenty-four hours
after the section of the nerve the vessels ma}' be found to have quite
regained their normal calibre, even if still cut off from the central nerv-
ous sj'stem. Such a fact, which must, of course, be due to the regained
power of contraction of the circular muscular fibres, can only be ex-
plained through the assumption that the walls of the vessels are supplied
with nervous ganglia which are themselves capable of originating im-
pulses sufficient to produce varying degrees of contraction of the circular
muscular fibres of the arterioles. Normally, the impulses originated by
these peripheral ganglionic cells are dominated by the influences coming
from the central vaso-motor centre. When the vaso-motor nerve of a
part is divided these centres are suddenly deprived of this dominating
influence, the muscular fibres are paralyzed, and the arteries dilate. When
the shock of the operation has passed off, the peripheral ganglionic cells
themselves acquire the power of governing the degree of contraction of
the muscular fibres of the arteries and the vessels then regain their nor-
mal tone. When stimulation of the auricular nerve or of the chorda
tympani produces dilatation of the vessels of the parts supplied by these
nerves, the effect may be explained by assuming that the impulses com-

CIRCULATION OF THE BLOOD. 559

ing along these vaso-dilator nerves inhibit the local ganglia in the walls
of these vessels and thus lead to relaxation of the muscular fibres of the
vessels and to their consequent dilatation. Their modus operandi may
thus be regarded as similar to that of the pneumogastric nerves, since
r in both cases the motor ganglia are inhibited and the muscular fibres in
the walls of the organs of circulation relax (Fig. 236).

FIG. 236.— DIAGRAMMATIC PLAN OF THE CARDIAC-NERVE MECHANISM, AFTER
CARPENTER. (Yeo.)

The direction of the impulses is indicated by the arrows. Both right and left sides of the cut are used
to show one complete lateral half of the fibres.

Finally, to recapitulate, the pulse and blood pressure may be modi-
fied \)y the following causes ( Laud er-B run ton) : —

We have now to follow the blood in its course through the body and
consider the changes which it undergoes in the different organs and tis-
sues. It was seen that the circulation might be divided into two sys-
tems, the greater and lesser. The changes which the blood undergoes in
the latter, the pulmonary system, will be considered first.

560

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

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SECTION VIII.

RESPIRATION.

IT has been seen that through absorption the products of digestion
enter into the blood and are carried by means of the circulation to the
various organs and tissues of the body. Jn spite, however, of the con-
stant addition of these substances to the blood its general composition
remains almost uniform, for the income from the alimentary tract is
balanced by the outgo through the different tissues. The blood in its
passage through the capillaries of the body nevertheless undergoes
great alterations in its composition. It gives up to the tissues the
substances brought from the alimentary tract which are destined to
nourish the different tissues of the body. Every function of a cell is
accompanied by chemical change in its composition, the resulting prod-
ucts in the majority of cases being no longer of use to the economy.
The blood is charged to remove these substances from the tissues.

Again, it has been found that the vital functions of every cell
necessitated a supply of oxygen. It is the function of the blood to act
as carrier of this gas and to remove as well the gaseous products of cell
decomposition. We thus find that the blood acts not only as an organ
of nutrition, but as an organ of excretion ; in fact, as a common carrier
of the several substances essential to cell life, and the carrier of the
deleterious substances resulting from the breaking down of cells, and it
bears them to different parts of the body where special organs are set
aside for their removal. The removal of these deleterious substances
constitutes excretion, the mode of removal depending upon the nature
of the substances to be eliminated.

One of the most striking changes which occur in the blood in
passing through active organs is the 3rielding up of oxygen and the
overloading of the blood with carbon dioxide. It has been stated that
the difference between the arterial and venous blood is that the
former contains an excess of oxygen, the latter an excess of carbon
dioxide, the oxygen of the arterial blood being derived from the atmos-
phere and entering into composition with the haemoglobin as the blood
passes through the capillaries of the lungs. The carbon dioxide is
derived from the breaking down of the cell-constituents, and is likewise
removed from the blood while passing through the pulmonary capillaries.
The process by which these gases enter and leave the blood is almost

36 (561)

562 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

purely physical, and is termed respiration. Respiration may therefore
be defined as that function by means of which oxygen is taken into the
system and carbon dioxide eliminated. Oxygen passes into the blood
from the air, mainly by a process of gaseous diffusion ; the same process
is also largely concerned in the giving up of oxygen by the blood to the
different tissues and the absorption of carbon dioxide from the different
tissues by the blood, and the yielding of this gas to the air within the
lungs.

1. GENERAL VIEW OF THE ORGANS OF RESPIRATION. — The function of
respiration is an organic function, existing in the vegetable as well as in
the animal, the products of respiration being the same in both. In the
vegetable the introduction of oxygen and elimination of carbon dioxide
takes place both during da}T and night, but during the day the function
of respiration is masked by the processes of nutrition in which the
reverse change takes place, carbon dioxide being appropriated by the
plant and oxygen set free.

In examining the different forms of respiratory apparatus peculiar
to different kinds of organic beings it is readily determined that in all
the main respiratory tissue is that part of the respiratory apparatus
which is concerned in the absorption of oxygen and in the elimination
of carbon dioxide, and, like the digestive tube, is simply a modification
of the external tegumentary surface.

In the simplest forms of plant life the external tegumentary covering
constitutes the entire respirator}7 apparatus, and it is through this that
oxygen is absorbed and carbon dioxide eliminated. But in the more
highly organized forms of plants a system of tubes, known as the spiral
vessels, are found ramifying through their stems and leaves, and even in
their most perfect form seldom contain other than gaseous matters.
These spiral vessels in the endogenous plants are universally distributed
through the stem, and form a part of every bundle of nbro-vascular
tissue; but in the exogenous plants they are usually confined to the
medullary sheath immediately surrounding the pith. In each case, how-
ever, they traverse the stems in such a manner as to enter the leaves
through the foot-stalks. These vessels carry air from the exterior to the
interior, and it is an especial fact to be noted that the atmospheric air
contained in them possesses a larger amount of oxygen than the free
atmosphere. On the under surfaces of leaves are also to be found
distinct openings, or stomata, which, although apparently for the admis-
sion of materials necessary for nutrition, also seem to have the power
of admitting air into the cavities existing in the leaves, especially beneath
the inferior cuticle. Thus, it is the external surface of the plant through
which respiration is practical!}' performed.

So, also, in animals, respiration always takes place through an

BESPIKATION. 563

external membrane, or some extension of such membrane, outward pro-
longations constituting gills, inward prolongations constituting the lungs ;
so that all animals may be classed as air-breathers or water-breathers,
the latter breathing the air dissolved in water. To the former class
belong nryriapods, spiders, insects, reptiles, birds, and mammals, while
all other animals, with few exceptions, are water-breathers ; in the first
class the organs of respiration are internal ; in the latter class more or
less external, but in all are to be regarded as modifications of the external
integument (Fig. 237).

In the lowest forms of animal life, all of which are inhabitants of
water, there are no prolongations of this membranous surface — aeration
of the fluids being accomplished by their exposure to the surrounding
medium containing oxygen in solution. No distinct respiratory organs
are present in these forms of life, unless the contractile vesicles described
as being constantly found in such organisms are of this character. In
animals belonging to the group of protozoa the surface of the body is

FIG. 237.— DIAGRAM ILLUSTRATING DIFFERENT FORMS OF RESPIRATORY
APPARATUS. (Carpenter.)

A, simple leaf-like gill ; B, simple respiratory sac ; C. divided gill ; D, divided sac ; E, pulmonary
branchia of spider.

usually more or less provided with cilia, which serve by their vibrations
to continually change the stratum of water immediatel}7 in contact with
the external surface. The presence of a fluid containing ox}*gen in
solution in contact with the respiratory surface is thus alwa}Ts insured.

In sponges, as in infusoria and polyps, we find that the respiratory
surface exists in the form of tubulary passages through the body, pro-
vided at certain points with cilia, the air being absorbed from the currents
of water passing through them.

In the ccelenterata, which are all aquatic, no circulatory organs are
present, and, as a consequence, no respiratory apparatus; for we find
that while organs of circulation are dependent upon the complexity of
the alimentary apparatus, so the presence of distinct circulatory organs
governs the presence of organs of respiration.

In the coelenterata any part of the body surface appears to be capable
of accomplishing the interchange of oxygen and carbon dioxide. In some
the body cavity also, doubtless, fulfills this function. This would seem to

564 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

indicate a step higher in organization and a beginning of a specialization
of certain tissues for carrying on the functions of respiration. This is
the case in the polyps and in the sea-anemone, while in the bryozoa
there is a marked dilatation of the pharynx, which seems to be particu-
larly intended to provide for the aeration of fluids.

In certain members of the group of annuloida a still higher special-
ization of the respiratory apparatus is met with. Thus, in many there
exist peculiar ramified contractile vessels, the trunks of which open
upon the surface of the body, and are in part ciliated in their interior.
These are the so-called water-vessels, and are supposed to be subservient
to the respiratory process.

In various of the echinoderms, in addition to numerous gill-like
fringes, two sets of canals are found, the one carrying the nutritive fluid,

and the other radiating from a ring
around the mouth, and distributing
aerated water.

In worms, especially in the
silk-worm, a system of spiral vessels
analogous to those of the plant and
permeating the structure in every
direction is often to be detected.
These are called tracheae, and com-
municate directly with the atmos-
phere by open breathing orifices on
different portions of the body of the

insect, and may be readily noticed
FIG. 238.— TRACHEAE OF INSECT, SHOWING J

THE SPIRAL FIBRE. (Jeffrey Bell.) in the caterpillar as dark spots upon

the sides. In fresh-water worms,

like the leech and earth-worm, the body is covered externally by a viscid
fluid which has the power of absorbing air; so such animals breathe by
the skin, beneath which lies a dense net-work of blood-vessels. In
insects one of these spiracles, as they are also named, traverses the
body on either side along its whole length, sending out ramifications, as
referred to above. The tracheae are prevented from having their cavities
obliterated by spiral elastic fibres which seem an analogue of the carti-
laginous rings in the tracheae and bronchise of the air-breathing verte-
brates (Fig. 238).

Thus, in insects, as in mammals, the air is carried to the fluids to be
aerated.

In marine worms, which are water-breathing animals, the simplest
form of gill is seen ; it consists of delicate veins projecting through
the skin along the side of the body in a series of arborescent tufts. As
these float in the water the blood is purified (Figs. 239 and 240).

RESPIKATION.

565

In the spider the respiratory apparatus consists of a series of sacs,
less numerous than the tracheas of the silk-worm, and not communicat-
ing with each other ; yet additional space is obtained by arranging the
lining membrane into a series of folds, which lie in close relation to each
other like the leaves of a book, thus forming the first indication of a lung.
From the extensive surface thus produced, in which lies a net-work of
vessels, the blood is brought into immediate relation
with the air, which enters through the breathing parts
referred to. The exchange of air in the sacs is accom-
plished by the movements of the body of the insect,
which empty the sacs by compression and allow them
to refill by the elasticity of their walls. These respira-
tor}- cavities are called pulmonary branchiae from their
resemblance on the one hand to the lungs of the higher
animals, and on the other hand to the branchiae or gill-
sacs (Fig. 241).

In the oyster and mollusk we have an approach to
the respiratory apparatus of the fish. On opening an
oyster a delicate membrane, known as the mantle, is
seen lining the edge of the cell. The gill is constituted
by a double fold of the mantle covered with cilia ; upon
the gill ramify the blood-vessels, wrhich are bathed by
the water which passes over them. From this water
the blood receives oxygen and gives carbon oxide to it,

FIG. 239. —THE
LOB-WORM (Are-
nicola). (Carpen-
ter.)

The arborescent gills
are situated on certain
segments only.

FIG. 240.— TRANSVERSE SECTION OF ARENICOLA, AFTER GEGENBAUR.
(Jeffrey Bell.)

D, dorsal, V, ventral sides : N, ganglionic chain : I, intestine ; BR, gills : v, ventral vessels ; D,
dorsal vessel; v', visceral vessel ; P, vessel around intestine; A B, vessels of gills.

— an exchange which is just as essential to the oyster as for breathing
mammals (Fig. 242).

In the clam the gills are inclosed in the mantle, forming a tube, the
siphon, through which the water is forced b}' cilia.

In the lowest forms of crustaceans, as in the branchiopods, the
respiratory appendages are nothing more than thin plates, within which

566

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the blood circulates, and outside of which is the oxygenated water in
which they are bathed (Fig. 243). In the higher orders, as exemplified
by the crab, we find external gills like those of the oyster, and attached
to movable parts of the body, as the legs, exemplifying the association
of locomotor with respiratory activity. They are kept in motion to
bring the respiratory apparatus in contact with fresh portions of water.
In the crab the gills are inclosed within a cavity formed by a doubling
of the horny integument, and the stream of water is kept up through

FIG. 241.— RKSPIRATORY APPARATUS OF INSECT. (Carpenter.)

A, first pair of legs ; B, first segment of thorax ; C, origin of wing ; D, second pair of legs ; E, third
pair of legs ; F, tracheae ; G, stigmata ; H, air-sacs.

these by means of a valve in the exit-pipe worked by the jaws. The
constant movement causes a regular stream of water to issue from the
gill-chamber.

In the fish the respiratory apparatus in all essentials corresponds
with that of the mollusk, the branchial element onl^y being modified and
multiplied in accordance with the higher grade of life. The gills are
formed of folds of membrane, between which are distributed the blood-
vessels, and which are suspended from two bony or cartilaginous arches

KESPIKATION.

567

(Fig. 244). The water is taken in by a process of swallowing, the mouth
being first distended, and, as the muscles contract, the water is expelled
through the aperture on either side of the pharynx into a cavity called
the gill-cavit}T, and, as it passes over the gills, the oxygen of the atmos-
phere held in solution is absorbed by the blood.

Fish are thus admirably fitted for aquatic respiration, but die on
removal from the water from the fact that, as the gills dry, absorption
of oxygen is impaired, and the gills cling together, and so prevent ex-
posure of their greater portion to the air. Under such circumstances
fish then die from asphyxia. In some cases there is provided in addition
an air-bladder or swimming-bladder, like a rudimentary sac of the air-
breathing apparatus of the higher animals. In its simplest condition
it is entirely closed, and can, therefore, serve no purpose except to

C

FIG. 242.— DIAGRAMMATIC SECTION OF A LAMEI/LTBRANCH (FRESH-WATER
MUSSEL, Anodon) THROUGH THE HEART. (Huxley.)

F, ventricle ; G, auricles ; C, rectum ; P, pericardium : H, inner gill ; I, outer gill ; O Q, organ of Bojanus :
B, foot; A A, mantle-lobes.

regulate the specific gravity during swimming. In others this bladder
is connected with the alimentary canal by a short, wide tube, called the
ductus pneumaticus, and is filled by the process of swallowing.

If we admit, as seems perfectly reasonable, that the air-bladder of the
fish is a rudimentary lung, it may be stated that all vertebrates in the
course of their life have two different kinds of respiratory apparatus.
Every form of vertebrate breathes through gills during embryonic life;
in the fish and a few reptiles the gills are permanent, but in others they
disappear, and, while traces of a lung are seen in all vertebrates, they
acquire full development only in reptiles, birds, and mammals : while,
again, certain amphibians, as the Proteus and Siren, retain both gills and
lungs to adult life, and thus form a link between fishes and reptiles.

568

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

BR'

FIG. 243. — TRANSVERSE SEC-
TION OF A BRANCHIOPOD,
SHOWING THE LEAF-LIKE
GILLS. AFTER GRUBE. ( Jef-
frey Bell.)

C, heart; I, intestine; N, ventral
nerve-cord; D, fold of the integument:
BR BR', gills, which are appendages of
the body.

Vertebrates are the only animals that breathe through the nostrils or
mouth. Fishes inspire only, and all vertebrate animals in whom the ribs

are absent or solidly fastened together
swallow air.

In reptiles we first meet with a complete
adaptation of a pulmonary structure for the
direct aeration of the blood through the
influence of the atmosphere. In them there
is an internal prolongation of the external
integument, constituting the lungs, though
they exhibit great simplicity, being, for the
most part, capacious sacs, occupying con-
siderable bulk, .but being but slightly sub-
divided, so that the amount of surface
exposed is really very small, the blood being
exposed on one surface only to aeration.
The greatest diversity is met with in these animals as regards the
structure and mobility of the thorax. In the saurians, the thorax
resembles that of mammals, with movable ribs; in the chelonia, the

thoracic walls are rigid and immovable ; in the
ophidians, the ribs are very numerous and
movable, the sternum being absent. A dia-
phragm is met with only in the higher sau-
rians. In reptiles inspiration is not accom-
plished by inhalation, but by deglutition, air
being drawn into the pharynx by depression
of the hyoid apparatus, and the nares then
being closed, the air is forced into the trachea.
Expiration is accomplished mainly by the
elasticity of the lungs, aided by the abdom-
inal muscles, and in saurians and ophidians
by the intercostal muscles and the elasticity
of the chest-walls. In snakes, as a rule,
there is a single, long, c}rlindrical lung,
while the left lung is rudimentary.

In birds, though the diaphragm is still
absent or rudimentary, the respiratory appa-
ratus is more complicated than any yet
considered, so that the energy of the respira-
tory process is much increased, and yet
the general plan of the apparatus is much more closely allied to that of
reptiles than of mammals. For each lung may be considered to be sub-
divided into lobules, each of which resembles the rudimentary lung of

FIG. 244.— GILL OF THE PERCH.

(Jeffrey Sell.)

A, branchial artery ; B, branchial arch
(seen in cross-section) ; C, branches of the
branchial vein, V; D, branches of the
branchial artery.

KESPIRATION. 569

the frog, flattened and fixed to the back of the thorax. In addition to
the elementary lungs numerous large air-sacs, distributed in various
parts of the body, as the abdomen, the muscular interspaces, interior
of the bones, etc., are found communicating with the lungs. And
as the lining membrane of the bones, as well as of all these cavities, is
extremely vascular, it also, in these localities, serves to assist in the aera-
tion of the blood by exposure to the air. In fact, if the wind-pipe be tied
and an opening be made in the wing-bone, respiration may still go on.
This large increase of respiratory surface serves as well as store-room for
atmosphere and is well adapted to the purposes of flight, during which
the respiratory movements are less free. The lungs and the accessory
apparatus of birds is filled with air by the process of suction through
the trachea, in consequence of the permanent distended condition of the
whole cavity of the trunk from the nature of its bony encasement. Such
is the natural condition of this bony frame-work that when no pressure
is made upon it it is completely distended ; as a consequence, the lung-
tissue permanently attached to the ribs possesses such a degree of elas-
ticity as to enable it to spontaneously dilate. Hence, the disposition of
the air to fill the distended cavities until, by the action of the external
muscles upon the bony frame-work, a portion of the air is expelled and its
place again immediately taken by a fresh supply of air on relaxation of
these muscles. Inspiration, therefore, in birds, in opposition to what
we shall find to be the case in mammals, is passive, while expiration is
active and is accomplished by drawing the sternum toward the backbone
by muscular contraction, thus compressing the lung and expelling the air.

The organs of respiration in man and mammals generally consist of,
first, the bony frame-work of the chest ; second, the diaphragm and other
muscles ; and, third, the trachea, bronchial tubes, and air-vessels. • In
mammals alone is there a perfect thorax, i.e., a closed cavity for the
heart and lungs, with movable walls and a muscular partition, the
diaphragm, separating the thoracic from the abdominal cavitj*.

The trachea is a cylindrical tube consisting of a varying number of
cartilaginous rings, imperfect posteriorly in man and most animals.
These posterior imperfect spaces are occupied by the muscles which
control the calibre of the tube. The use of these cartilaginous rings is
to keep the tube patulous, so as to permit the entrance and free egress
of air, subserving the same function as the spiral fibres in the interior
of the air-vessels of the plant and insect already described. Immediately
within the' cartilaginous rings, which are bound together by fibrous
tissue, is found a fibrous connecting membrane ; within that is a mucous
membrane continuous with that of the mouth and the pharynx, supplied
with cylindrical, ciliated, epithelial cells, the cilia of which vibrate toward
the pharynx and serve the purpose of facilitating the discharge of the

570

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

secretions or of any foreign substance which may lodge upon it. When
the trachea reaches the second or third dorsal vertebra it bifurcates into
two principal bronchi, passing one to each lung, and subsequently these
again divide and subdivide in various directions until they have attained
the size of the most minute bronchial tubes.

The larynx, which is placed at the laryngeal extremity of the
trachea, may be considered as corresponding to the base of a tree, the
trachea to its trunk, and the bronchi to its different branches ; while the
ultimate bronchi terminating in the air-vesicles of the lung may be
regarded as representing the leaves of the tree. The bronchi have the
same anatomical constituents as the trachea, and are composed of carti-
laginous rings, musculo-fibrous membrane,
and a lining mucous membrane (Fig. 245).
The cartilaginous rings are also imperfect,
but the imperfect spaces are irregularly dis-
tributed, sometimes in front and sometimes
at the side. The object of the rings is, of
course, the same as those of the trachea.
The tubes are thus mere gaseous conduits
kept patulous by their cartilaginous constit-
uents. In the bronchi a fibrous basement
membrane is found, as well as unstriped
muscular fibres, and in the bronchi the
muscular fibres do not merely connect the
ends of the rings, but completely encircle the
tubes in the form of annular fibres. These
muscular fibres are unstriped and involun-
tary, and therefore possess the same char-
acteristics as the unstriped muscular fibre
found elsewhere, and serve to regulate the
calibre of the tubes. The lining mucous
membrane of the bronchi is also a ciliated membrane and extends down
to the commencement of the finest bronchi. In the mucous membrane
are found tubular glands forming a mucous secretion. In the minute
bronchi the cartilaginous rings disappear and the bronchioles are then
constituted of a la}rer of circular muscular fibres with an inner epithelial
membrane, the cartilaginous rings disappearing when the bronchi have
been reduced to about one-thirtieth to one-fiftieth of an inch in diameter.
The bronchi ultimately terminate in a dilated portion, termed lobules or in-
fundibula, which consist simply of a homogeneous membrane abundantly
supplied with blood-vessels. This dilatation is formed by the same
material as constitutes the fibrous wall of the tube thrown up into folds,
between which ramify the blood-vessels. The contained blood is, there-

FIG. 245.— BRANCHIAL TREE OF
A MAMMAL (HORSE), AFTER
AEBY. (Jeffrey Bell.)

A, eparterial, B, hyparterial ventral
(V), and, D, hyparterial dorsal bronchi ;
PA, pulmonary artery; PV~, pulmonary
vein.

KESPIEATION. 571

fore, exposed on both sides to the atmosphere. As the capillary net-
work is spread over several cells, aeration of the blood is thus
thoroughly secured, and in this locality the venous blood is converted
into arterial. The calibre of these capillaries is extremely small, being
only in diameter equal to the thickness of a red blood-corpuscle. It has
been estimated, nevertheless, that the pulmonary capillaries in man are
capable of containing about two liters of blood, and it has been further
calculated that this amount is renewed ten thousand times in twenty-four
hours. And, even making allowances for error in these calculations, it
is evident how large is the surface for the interchange of gases between
the air and blood.

The diameter of the air-vesicles is from one two-hundredth to one-
seventieth of an inch. Their number is almost infinite. It has been
calculated that about the termination of each bronchus in a mammal are
collected seventeen thousand seven hundred and ninety air-cells, and
their total number has been computed to be at least six hundred millions.
It has been further calculated by Lieberkiihn that the whole extent of
respiratory surface of both lungs in man is fourteen thousand square
feet, or two hundred square meters, and this surface is attained through
the reduplications of the membrane, so occupying the least possible
bulk. The air-vesicles gradually increase in number from infancy to
adult life, when they remain stationary for a time, after which they
decline, so that there is less respiratory surface in infancy and old age
than in adult life.

The walls of the air-vesicles are highly elastic, from the presence of
elastic fibres, which form a close net-work with very fine meshes. Through
the presence of this elastic tissue the air-vesicles, therefore, tend contin-
ually to contract, — a phenomenon which, as will be later demonstrated,
is of the greatest importance for the process of expiration. All the
different parts of the lungs are held together by delicate elastic tissue,
and outside of this by a serous membrane, termed the pleura, which
covers the external surface of the lungs and is reflected on to the internal
surface of the thorax. The pleural membrane thus forms a shut sac,
and the lung lies on the outside of it.

The thorax is composed of a closed cavity in the form of a truncated
cone, of which the sides, back, and a portion of the interior surfaces
are formed by the ribs and costal cartilages with their intervening
muscles. Its base is oblong, more or less flattened laterally in quad-
rupeds and antero-posteriorly in man. The ribs are always more or less
curved, with their concavity directed internally. In general, the first rib
is the shortest, is less curved, and less inclined to the vertebral column.
As a rule, it may be stated that in animals in whom the thorax is short
the ribs are more curved than in those where the thorax is longer.

572 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The backbone forms a part of the posterior boundary of the chest,
the sternum the anterior boundary. Below, the thorax is shut off from
the abdominal cavity in mammals by the diaphragm ; above, it is closed
by the muscles of the neck. The lungs are suspended in a semi-distended
state in the cavity of the thorax, and with Uie heart and great blood-
vessels completely fill it. Since the thorax forms an air-tight cavity
there is through the elasticity of the lungs a constant tendency to the
production of a vacuum between the pleural surfaces. This tendency to
contraction, due to the elastic fibres of the lungs, is of great importance
in assisting respiration. If an opening be made into the pleural cavity
the atmosphere at once enters, and the lungs then through their elasticity
collapse. Atmospheric pressure being the same within and without the
lungs, the resistance of the walls of the thorax is the only factor which
prevents the collapse of the thorax from the elasticity of the lungs.

This tendency to retraction of the thoracic walls is readily seen in
the intercostal spaces, particularly if the outer muscular Ia3-ers be
removed. Distinct depressions may then be recognized between each
rib, and indicate the negative pressure produced upon the walls of the
thorax by the constant tendency to contraction of the lungs. This
negative pressure is likewise exerted on the upper and lower extremities
of the thorax. There is, therefore, a constant depression of the soft
tissues of the neck toward the thoracic cavity, until the increased
tension so produced results in equilibrium. So, also, there is a constant
tendency to the ascent of the diaphragm in the thoracic cavity by the
same means. In the passive state of the thorax there is, therefore, a
constant equilibrium produced, which results from the balance between
this negative pressure exerted by the lungs and the resistance of the
walls of the thorax.

The walls of the thorax, in so far as they are constituted by the ribs
and diaphragm, are not, however, rigid, but are capable of undergoing
change in position.

The ribs are acted on by various muscles whose contraction results
in an increase in the lateral and antero-posterior diameters of the thorax.
The diaphragm is also capable of changing its position, but when it
contracts tends to depart from its concave, dome-like position, and
become more horizontal. The contraction of the diaphragm, therefore,
serves to increase the vertical diameter of the thorax.

As the thorax is increased in its dimensions the lungs are compelled
to follow its movements, from the fkct that otherwise there would be a
production of a vacuum in the pleural cavity. As, however, the lungs
likewise become increased in volume, the air in them becomes rarefied,
and since the air within the lungs is in direct communication with the
atmosphere the air streams in from without to the interior of the lungs,

KESPIKATION.

573

until equilibrium is produced (Fig. 246). On the other hand, if the forces
which produce enlargement of the thorax cease to act, the elasticity of
the lungs, together with that of the cartilages of the ribs, is now sufficient
to produce a return of the thorax to its original volume. The lungs,
therefore, now decrease in volume, and as a consequence the air within
them tends to become compressed, and, as a result, a portion of the air
is expelled through the air-passages to the external atmosphere. The
expansion of the thorax constitutes inspiration ; the contraction of the
thorax constitutes expiration.

As the tension of air in the lungs becomes decreased through
inspiration, fresh air enters the lungs which is less charged with the
carbon dioxide than that previously present in the lungs, while it is also

FIG. 246.— DIAGRAMMATIC REPRESENTATION OF THE RELATIONS BETWEEN
THE LUNGS AND THE THORACIC CAVITY, AFTER FUNKE. (BeaUHlS.)

The bell-jar, 1, represents the thorax ; the rubber membrane, 4, the diaphragm ; the membrane, 6, the
soft parts of an intercostal space ; 2, the trachea, terminating in two rubber bulbs representing the lungs ;
3, a manometer for measuring the pressure within the bell-jar.

In the figure to the left the atmospheric pressure within the bell-jar is the same as on the outside, and
the mercury in the manometer stands at the same level in both arms. If the rubber membrane, 4, ia
drawn downward by the button, 5, the cavity of the bell-jar is increased and the atmospheric pressure
diminished, as shown by the manometer and the depressed space, 6. The negative pressure thus produced
leads to the entrance of air through the tube, 2, into the rubber bulbs, which consequently expand. The
action of the diaphragm in producing inspiration is precisely similar.

richer in oxygen. By diffusion, from the inequality of these gaseous
tensions, we have oxygen brought to the lowermost strata of air in the
lungs and carbon dioxide diffusing from them, and when the air again
leaves the lungs in expiration it has been the means of introducing
oxygen into the lungs and removing carbon dioxide from them.

The amount of air which ordinarily enters the lungs in inspiration
and is dispelled in expiration is spoken of as the tidal volume. By
forcible muscular contractions the capacity of the thorax may be both
increased and decreased beyond the dimensions present in gentle respi-
ration. The amount of air so drawn in by a forced inspiration is spoken
of as complemental air; that expelled from the lungs in violent expiration
is spoken of as supplemental air; while, even after forced expiration, a

574 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

considerable amount of air remains in the lungs, and this quantity is
spoken of as the residual volume.

2. THE MECHANICAL PROCESSES OF RESPIRATION. — The Mechanism of
Inspiration. — Every increase in the diameters of the thorax produces, as
a consequence, for the reasons already referred to, an expansion of the
lungs ; hence, air enters the lungs from the difference in atmospheric
pressures. Such a movement is termed an inspiration. It is clear that
in the production of inspiration the natural elasticity of the lungs and
the thoracic walls must be overcome. Inspiration is, therefore, an active
movement and requires the exertion of muscular force. The diameters
of the thorax may be increased either through the elevation of the ribs
or through the descent of the diaphragm. It is through the latter that
in quiet respiration inspiration is produced. The diaphragm may, there-
fore, be regarded as the principal muscle
of inspiration. In its condition of relax-
ation the muscular fibres of the diaphragm
together form a curved surface whose con-
cavity extends far up into the thorax.
When the muscular fibres of the diaphragm
shorten they tend to form a straight line
between their origins and insertions, and,
therefore, the diaphragm in its condition
of extreme contraction tends to form an
almost plane surface across the lower
P01>tion of the thorax. The origins and
THE DIAPHRAGM. (Xtciard.) insertions of the muscular fibres of the

If A represent a plane extending in expi-
ration from the sternum to the vertebra, and diaphragm may be regarded as compara-

D the position of the diaphragm, in inspiration J

^npdeLeendWto1rovet°tt'whilethediaphragm tively fixed. The central tendon is,

moreover, but slightly movable, since it is

firmly connected with the organs occupying the mediastinum above, and
below is more or less supported by the liver and stomach. It is, there-
fore, evident that the diaphragm in inspiration cannot become completely
flattened, since its curvature corresponds with that of the curvature of
the abdominal organs. When the diaphragm, then, contracts, the curve
is slightly flattened out, and this muscle may, therefore, be regarded as
acting as a curved piston which descends in the cavity of the thorax, and
so increases its long diameter ; at the moment in which the diaphragm
contracts, the ribs in which it is inserted anteriorly are actively elevated.
Thus, while the diaphragm in descending tends to lengthen the vertical
diameter of the chest, the elevation of the inferior ribs would appear to
diminish this diameter.

The ascent of the lower ribs is, nevertheless, much less extensive
than the descent of the diaphragm. It is further to be noticed that every

RESPIRATION. 575

ascent of the ribs produces an increase in the antero-posterior diameter
of the thorax ; or, in other words, increases the distance between the
sternum and vertebral column. Therefore, this ascent of the ribs, so
far from diminishing the inspiratory effect of the diaphragm, tends even
to increase it. This may be rendered clear by the diagram (Fig. 247).

At the same time the diaphragm contracts the abdominal organs are
pressed downward, and so cause a projection of the abdominal walls.

In forced inspiration the power exerted on the ribs through the dia-
phragm is greater than that which tends to elevate the lower ribs. This
is especially the case when there is any obstruction to the entrance of
air into the lungs. In such cases there is a distinct constriction of the
thorax at the points of insertion of the fibres of the diaphragm. This
reduction in the circumference of the chest at these points is, however,
of but slight importance, since the increase of the thoracic cavity by the
greater descent of the diaphragm more than compensates for the decrease
in its circumference. It is probable that in all circumstances this de-
pression of the lower ribs would be more marked in strong contraction
of the diaphragm were it not for the fact that the descent of the ab-
dominal organs produces an increased tension in the abdominal walls,
and, therefore, offers a certain resistance to the production of this
constriction.

Colin has estimated that in the horse the diaphragm in inspiration
descends from ten to twelve centimeters in the abdominal cavity, thus,
to this extent, increasing the long diameter of the thorax, while the
transverse diameter at the same time increases from three to four centi-
meters.

The movements of the ribs in producing inspiration are much more
complicated. Each rib articulates by two facets with a costal cavity
formed by the junction of the ribs and two contiguous dorsal vertebrae.
The only movement possible in the ribs, therefore, must occur around a
line which passes between these two points of articulation ; or, in other
words, nearly coincides with the axis of the neck of the rib. If the ribs
were straight they would be only able to turn around on their own axes ;
since, however, the ribs are all curved in different degrees, the turning of
the rib around the axis of its neck causes every point of the rib to
describe an arc of a circle (Fig. 248).

Further, the point of articulation of each rib with the vertebral
column is on a higher plane than its articulation with the sternum and
costal cartilages, the degree of inclination being greatest in the first rib,
least in the second, and then gradually increasing until the last rib forms
almost the same angle as the first. From this arrangement it is evident
that every elevation of the ribs will increase the distance between the
sternum and the vertebral column, while the rotation of the ribs will

576

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

increase the lateral diameters of the thorax ; for, since the ribs form
arches, each increasing in its radius from above downward, it is evident
that when the lower rib is so elevated as to occupy the position pre-
viously held by an upper rib the lateral diameter of the thorax at
that point will be greater than before. Still further, the articulations of
the ribs with the sternum are more or less fixed, and the resistance,
therefore, which these articulations offer to the movement of the ribs

FIG. 248.— THE ACTION OF THE RIBS OF MAN IN INSPIRATION. (Btclard.)

The shaded parts represent the positions of the ribs in repose. The line A B represents a horizontal
plane passing through the sternal extremity of the seventh rib ; the line C D represents a horizontal plane
touching the superior extremity of the sternum ; the line H G indicates the linear direction of the sternum.
When the ribs are elevated, as indicated by the dotted lines, the line A B becomes the plane a b, the line C D
the line c d, and the line H G becomes the line h g, the projection of the sternum being the more marked
inferiorly. The distance which separates the line M N from the line m n measures the increase in the
antero-posterior diameter of the thorax.

will in the elevation of the ribs tend to open out the angles between the
ribs and their cartilages.

By the elevation, consequently, of the ribs, the diameters of the
thorax are increased both laterally and in an antero-posterior direction.
Hence, everything that tends to elevate the ribs will produce an inspira-
tory movement; everything which depresses the ribs will produce an
expiration. All muscles, therefore, which in any way may produce
elevations of the ribs are inspiratory muscles.

EESPIKATION.

577

The most important muscles of inspiration, which act by elevating
the ribs, are the levatores costarum. These are small muscles which
rise from the upper sides of the cervical and dorsal vertebrae, and are
inserted in the posterior surfaces of the ribs. Although these are small
muscles, they are inserted near to the axis of rotation of the ribs, and,
consequently, but a slight degree of contraction, the lever being so long,
will produce considerable elevation of the anterior extremity of the ribs.
At the anterior extremity of the upper two ribs are inserted the scalene
muscles, wrhich rise from the cervical vertebra, and which in their con-

i

_o k f

FIG. 249.— SCHEME OF ACTION OF THE INTERCOSTAL MUSCLES. (Lantlois.)

I. When the rods a and ft, which represent the ribs, are raised the intercostal space mnst be widened
(«/><"0- On the opposite side, when the rods are raised, the line a h is shortened (/ A-<</ h, the direc-
tion of the external intercostals) ; I m is lengthened (lm<.on, the direction of the internal intercostals,'.

II. When the ribs are raised the intercartilaginei, indicated by g h, and the external intercostals, in-
dicated by I k, are shortened. When the ribs are raised the position of the muscular fibres is indicated by
the diagonals of the rhombs becoming shorter.

traction serve to elevate the first ribs, and so also tend to elevate the
entire thoracic wall.

Between the ribs are found the intercostal muscles, which form two
layers, the external and internal. The external intercostal muscles are
attached to the adjacent margins of each pair of ribs, and extend from
the tubercles of the ribs, behind, to the commencement of the cartilages
of the ribs, in front, where they terminate into a thin, membranous aponeu-
rosis, which is continued forward to the sternum. They arise from the
outer lip of the groove on the lower border of each rib, and are inserted
into the upper border of the rib below. Their fibres are directed obliquely

37

578 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

downward and forward (Fig. 249). When the external intercostal
muscles, therefore, shorten, they tend, of course, to approximate their
origins and insertions, and so bring the ribs into a position in which
the distance between their point of origin and insertion will be the
shortest possible. This condition is, of course, fulfilled when the ribs
are horizontal; therefore, the contraction of the external intercostal
muscles serves to elevate the ribs, and these muscles are, therefore, to
that extent inspiratory.

In quiet inspiration the cavity of the thorax is increased by the
contractions of the scalene muscles, the levatores costarnm, and external
intercostal muscles, which all serve to elevate the ribs. The diaphragm
also, by its contraction, is perhaps the most important inspiratory
muscle.

If the head be fixed, the sterno-mastoid muscle, by its contraction,
serves to elevate the sternum, and, as a consequence, elevates all the
ribs. It, therefore, may be regarded as an accessory muscle of inspiration,
which is, however, only employed in forced inspiration. If the scapula
be fixed, the pectoralis minor muscle, which rises from the coracoid
process of this bone to be inserted into the anterior extremities of the
upper ribs, will by its contraction also serve to elevate the ribs ; so,
also, the seratus posticus superior muscle may also, in forced inspiration,
serve to elevate the ribs, and so act as an auxiliary muscle of inspiration.

The Mechanism of Expiration. — In the production of the enlarge-
ment of the chest, such as is essential to the accomplishment of inspira-
tion, it has been mentioned that the elasticity of the lungs and thoracic
walls has to be overcome by exertion of muscular force ; when the
inspiratory muscles relax, the elasticity of the lungs and thorax is alone
sufficient to cause the lungs to return to their original volume. This
contraction of the lungs, of course, occasions the expulsion of a quantity
of air from their interior, and expiration is therefore produced. It is
thus seen that expiration is mainly a passive movement, due to the
reaction of the forces which have to be overcome in the production
of inspiration.

It has been stated that when the diaphragm descends in inspiration,
by forcing the abdominal contents downward the abdominal walls are
put upon the stretch ; when the diaphragm relaxes the abdominal walls
tend to regain their original position, the abdominal organs are forced
upward into the thoracic cavity, and the borders of the ribs, which had
been slightly elevated, are now depressed. It is probable that the
elasticity of these different organs is in quiet expiration entirely
sufficient to balance the displacement produced in quiet inspiration.
The thorax may, nevertheless, be also reduced in volume to a greater
degree than is possible by the means already described. The muscles

RESPIRATION.

579

which by their contraction lead to a decrease in the thoracic capacity,
and which thus act as muscles of expiration, are mainly the muscles of
the abdomen. When the abdominal muscles contract, they not only
serve to still further force the abdominal organs up into the thoracic
cavity, and thus lessen its vertical diameter, but they further serve to
pull down the sternum and the middle and lower ribs. By so doing they
lessen the antero-posterior and transverse diameters of the thorax. The
internal intercostal muscles also probably assist in producing expiration
by depressing the ribs. When expiration becomes extremely violent all
the muscles are brought into play, which, through their contraction, may
either depress the ribs, press on the abdominal viscera, or offer fixed
support to muscles having those actions.

The movements of the thorax in respiration are accompanied by
movements of the nostrils and glottis.

In inspiration the current of air enters through the nostrils, and not
by the mouth, and by exposure to the vascular mucous membrane of the

FIG. 250.— THE HUMAN GLOTTIS IN A
GENTLE INSPIRATION, AFTER MANDL.
(Beaunis.)

I, tongue ; e, epiglottis ; pe, pharyngc-epiglottic fold ;
o«, aryteno-epiglottic fold : ph, posterior wall of the
pharynx ; c, cartilage of Wnsberg ; th, superior thyro-
arytenoid fold ; ti, inferior fold ; o, glottis.

FIG. 251.— THE HUMAN GLOTTIS IN A
FORCED INSPIRATION, AFTER MANDL.
(Beaunis.)

b, tip of the epiglottis ; g, pharyngo-laryngeal pouch ;
I, tongue; rap, aryteno-epiglottie fold; or, arytenoid
cartilage; c, cuneiform cartilage; tr, interarytenoid
fold ; rs, false vocal cords ; ri, true vocal cords.

nasal passages becomes warmed up to the temperature of the body. At
each inspiration the external nares expand by the contraction of their
dilator muscles ; this movement is especially marked in labored breathing.
The horse is incapable of breathing through the mouth, and if the dila-
tors of the nostrils be paralyzed, as by section of the facial nerve,
asphyxia may be produced. In expiration, the elasticity of the carti-
lages of the nostrils is sufficient to cause these parts to return to their
usual position. The current of air entering through the nose passes
over the passive soft palate to enter the larynx, after passing through
the pharynx. At each inspiration the vocal cords are separated and the
glottis is thus widely opened (Figs. 250 and 251). At each expiration
the arytenoid cartilages approach each other, so approximating the vocal
cords, and the glottis is thus narrowed.

3. THE RHYTHM OF RESPIRATION. — The movements of the column of

580

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

RESPIRATION.

581

air in respiration in the smaller mammals may be recorded by connecting
the trachea by means of a tube with Marey's tambour: —

This instrument consists of a cylindrical box, the upper surface of which is
formed by a sheet of rubber membrane, the interior being connected by tubing
with the trachea, and a lever so adjusted to the rubber membrane as to record.
its movements (Fig. 252). If air is forced into this box it will, of course, produce
bulging of the rubber membrane, and thus cause the ascent of the lever, while,
on the other hand, if the air be rarefied in the interior of the box the membrane
will be depressed and the lever descend. By allowing such a lever to record its
movements on some revolving surface, as, for example, on the smoked paper
of a kyinographion, if the interior of the box be connected with the trachea of an
animal, namely, in the dog or rabbit, a curve somewhat similar to the following
will be produced (Fig. 253).

The descents in this curve represent the inspirations, the ascents the
expirations. It is seen that the curve of inspiration begins suddenly
and advances rapidly, and is then succeeded by an expiratory movement,
which at first is more rapid than inspiration, but gradually becomes
slower. No pause is present between the end of inspiration and the
beginning of expiration, but a short pause is noted at the end of expi-

FIG. 253.— TRACING OF THORACIC RESPIRATORY MOVEMENTS. (Foster.)

(To be read from left to right.)

A whole respiratory phase is comprised between a and a, inspiration extending from a to b, and ex-
piration from b to a. The undulations at c are caused by the heart's beats.

ration, the undulations in the curve at this point being caused by the
heart's beats.

The duration of inspiration is, as a rule, shorter than expiration, the
proportion being from ten to fourteen, although this is not invariable.
The pause which is noted at the end of expiration will average in dura-
tion about one-fifth to one-third the time occupied by the entire respira-
tory movement.

The number of respirations in most animals may be placed, as a
rule, as one respiratory movement to four pulsations of the heart. Ex-
ercise and a large number of other conditions will greatly increase the
number of respiratory movements by increasing the amount of tissue
change, and, therefore, increasing the amount of carbon dioxide in the
blood which has to be eliminated in respiration.

In cattle the rate of respiration is higher in cows than in bulls or
steers. During sleep the average rate in the cow is twenty-two in the

582

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

minute ; during rumination it varies from twenty-four to thirty -six, the
position appearing to be without influence. In bulls and oxen the rate
of respiration averages twenty in the minute. The frequent eructation
of gas and pauses caused by rumination render the rhythm of respiration
more irregular in ruminant than in other mammals.

In the horse the normal respiratory movements ma}r be placed at
about ten in a minute ; after only the slight exercise of walking two
hundred yards, respiration in the horse may be increased to twenty -eight

FIG. 254.— GRAPHIC REPRESENTATION OF THE RESPIRATORY MOVEMENTS OF
A HORSE WHILE AT REST AND AFTER MOVEMENT. (Thanhoffer.)

1, standing at rest ; 3, after a few minutes' walk : 7-8. after trotting ; 9, after a short rest : 11. after
several minutes' trotting and running ; 17, after a short rest from the trot and run ; 51, curve at the end of
the experiment. I = inspiration ; E = expiration ; i = time in seconds.

in the minute, while after trotting five minutes the respirations were
found by Colin to be fifty-two to the minute, falling to forty in the fol-
lowing three minutes, and were fifty-two, likewise, in a minute after five
minutes' gallop (Fig. 254).

In all animals similar facts may be noticed. Thus, in the sheep the
normal rate of respiration is fifteen in the minute, and after running may
be raised to one hundred or one hundred and forty in the minute ; or

RESPIRATION.

583

even when frightened be raised from fourteen to forty-five, thus showing
the effect of mental impressions. So, also, the lion has a normal respira-

FIG. 255.— GRAPHIC REPRESENTATION OP THE RATES OF RESPIRATION IN DIF-
FERENT ANIMALS. (Thanhoffer.)

1, fish; 2, tortoise:- 3, adder (in winterl : 4, boa-constrictor (in summer); 5, frog: 6, alligator; 7,
lizard; 8, canary-bird ; 9, adult dog; 10, rabbit : 11, man; 12, dog; 13, horse. I = inspiration : E = ex-
piration; m/ = deep, n/= superficial respiration; A = abscissse; Coordinates.

tory rate of twelve to fourteen movements in the minute, and when
excited has been found to breathe seventy times a minute. In insects

584

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the rate of respiration is very much more rapid, being one hundred and
sixty in the beetle, and in some other insects as high as two hundred
and forty.

The following table, which is taken from that compiled by Paul Bert,
represents the number of respiratory movements in different animals : —

Tiger,

Lion,

Cat,

Dog,

Ox,

Rabbit,

Rat,

Rhinoceros, .
Hippopotamus,

Horse, .
Condor,
Pigeon,
Canary,

6 in the minute.
10 "
24 "
15 "
15-18 "
55 "
C 100 asleep.
< 210 awake.
( 320 excited.

6 in the minute,
f 1 in the water.
( 10 out of water.
10-12 in the minute.
6 "
30 "
18 "

The rate of respiration varies also according to the age of different
animals. This is shown in the following tables : —

Newborn infant,

5 years,

15 to 20,

20 to 25,

25 to 30,

30 to 50,

In the foal,
Adult horse.
Young ox, .
Adult ox, .
Lamb,
Sheep,
Puppy,
Dog, .

44 per minute.

26

20

18.7

16

18.1

10 to 12

9 to 20

18 to 20

15 to 18

16 to 17
13 to 16
18 to 20
15 to 18

It is thus seen that young animals, as a rule, respire more frequently
in the minute than adult animals ; so, also, small animals breathe faster
than large animals. Thus, the giraffe, camel, horse, rhinoceros, and
hippopotamus breathe about ten times in the minute; the llama and
deer, sixteen to twenty times a minute ; the whale, four to five times a
minute ; the guinea-pig, thirty-five times a minute ; the larger birds,
twenty to thirty times, and the smaller birds, thirty to fifty times a
minute.

As already described, the respiratory movements may vary in
intensity. In other words, inspiration and expiration may be either
shallow or deep. It is self-evident that the quantity of air taken in in
a deep inspiration and expelled from the lungs in forced expiration

KESPIKATION. 585

will be greater than the volume of air displaced in gentle respiration ;
and, of course, the deeper the inspiration or the more forced the expira-
tion the more air will be displaced. There is a limit present in both
cases beyond which the quantitj^ of inspired and expired air cannot be
increased. In the case of the domestic animals it has not as yet been
established what is the average quantity of air displaced in respiration,
but that it depends upon the size of the animal and the size and mode
of structure of the thorax is self-evident. From the few experiments
which have been made on this subject it may be assumed that in a quiet
respiration about one-sixth of the total quantity of air capable of being
contained within the lungs is displaced. It would follow from this that
every six or seven respiratory movements would serve to completely
renew the air within the lungs. In man, the volume of air changed in
different respiratory movements has been subjected to close study. It
was found that in an ordinary respiratory effort about thirty cubic inches
of air enter the lungs. With this accepted as a fact, and placing the
average number of respiratory movements at twenty in a minute, the
whole amount of air passing through the lungs in a minute will amount
to six hundred cubic inches ; in an hour, to thirty-six thousand cubic
inches; and in a day, to eight hundred and sixty-four thousand cubic
inches, or five hundred cubic feet. Extending these periods, one
hundred and eight}^-two thousand five hundred cubic feet of air may be
estimated to pass through the lungs of an adult man in a year, and to
produce this displacement nine million respiratory movements are
required. This quantity of air is employed in the aeration of about
three thousand five hundred tons of blood sent out by the heart to the
lungs in the same period. With these facts before us, we may obtain
valuable suggestions upon the subject of ventilation. Though about
five hundred cubic feet of air passes through the lungs in twenty-four
hours, yet this amount of atmosphere is insufficient to sustain life for
that period, for after the introduction of carbon dioxide into the air
the liberation of gases in the lungs is to a certain degree rendered more
difficult. There must be at least five hundred cubic feet of pure air sup-
plied, and it has been found that to attain this at least eight hundred
cubic feet of air should be provided for each individual.

The amount of air taken into the lungs at each gentle inspiration
and displaced by the reverse movement constitutes the so-called pressure
or tidal volume, and has been placed at about thirty cubic inches in man.
At the end of every gentle inspiratory effort the lungs may be capable of
still further inflation, and the additional quantity of air so inspired
amounts to about one hundred and ten cubic inches (complemental
volume). At the end of every gentle expiratory effort the lungs may be
still further compressed ; the amount of air so displaced by this

586

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

additional effort is termed the reserve volume, and also amounts to about
one hundred and ten cubic inches. After a forced expiration there is
still a certain amount of air which cannot possibly be forced out of the
lungs ; this constitutes what is termed the residual volume, and also
equals about one hundred and ten cubic inches.

The vital capacity volume is the amount of air which man is
capable of expiring by the greatest expiratory effort after the greatest
inspiratory effort. It includes the complemental volume, the breathing
volume, and the reserve volume, and is, therefore, the amount of air
which may be displaced in respiration. It has been shown by Dr.
Hutchinson that this volume bears a relation to the height of the
individual, which is especially remarkable when we recollect that the
height of individuals depends upon the length of the legs, and not upon
the trunk, the same persons who may vary greatly in height while
standing exhibiting but slight difference in height when sitting. It is
curious, also, to observe that the vital capacity does not depend upon
the capacity of the chest so much as upon the degree of mobility. Thus,
a man of greater girth may have less amount of vital capacity than
another with less girth but greater mobility of the walls of the chest.
Mr. Hutchinson has constructed an instrument for measuring this vital
capacity volume. It consists of a bell-jar so mounted as to be readily
displaced by the power which is exerted by the air in passing from the
mouth and air-passages. With the interior of the bell-jar communicates
a tube and attached mouth-piece. The person to be experimented upon
takes a deep inspiration, and then breathes out by the tube by a forced
expiration, which causes the bell-jar to rise, and the number of cubic
inches thrown out is measured by a graduated scale, suitably placed to
indicate the rise and fall of the bell-jar. As a result of these experi-
ments it was found that every inch added to the height of an individual
increases about eight cubic inches the vital capacity. This appears upon
examination of the following table : —

Height. Vital Capacity.

5 feet 0 inches to 5 feet 1 inch, .

174 cubic inches.

5

1 inch

5

2 inches,

182

5

2 inches

5

3

190

5

3

5

4

198

5

4

5

5

206

5

5

5

6

214

5

6

5

7

222

5

7

5

8

230

5

8

5

9

238

5

9

5

10

246

5

10

5

11

254

5

11

5

12

262

The age has a marked effect upon the vital capacity volume ; the
volume increases from 15 to 30, remains about stationary from 40 to 45,

KESPIEATION. 587

and above this age diminishes. In females it is about half that of males,
although it may amount to almost as much. Weight also exerts a great
influence. It has been shown that there is an average weight to every
average height. If the weight increase above this amount by 7 per
cent., the vital capacity decreases one cubic inch for every pound for
the next thirty-five pounds above this weight. For every pound thus
gained, an inch of vital capacity volume is lost for the next thirty-five
pounds.

4. THE CHEMICAL PHENOMENA IN RESPIRATION. — The phenomena in
respiration so far studied have been purely mechanical in nature, and
have had for their object simply the introduction of air into the lungs
for oxidizing the blood, and for expelling air from the lungs after its
object has been served.

We have now to study the chemical changes which occur in respira-
tion. We find that these are of two kinds, — the respiratory changes
occurring in the air in the lungs and the respiratory changes occurring
in the blood.

The atmosphere consists of a mechanical mixture of oxygen and
nitrogen in the proportion of about twenty-one of the former to seventy-
nine of the latter. Watery vapor is usually present in small but variable
amount, while carbon dioxide is present in extremely small quantity,
varying from about 0.03 to 0.05 per cent. During inspiration a certain
quantity of this gaseous mixture, in man about thirty cubic inches in
amount, is drawn into the trachea and upper air-passages. These air-
passages, as well as the more deeply located portions of the lungs, are
already occupied by a gaseous mixture, in which these gases are present
in different proportions. It has been found that expiration immediately
follows inspiration without any pause, and a certain amount of this
inspired air is, consequently, at once again expelled. It has been calcu-
lated that about two-thirds which remain after expiration at once
commences to mix by diffusion with the air already in the lungs. It has
been found that when gases are placed in contact with each other at the
same temperature and pressure they mix rapidly, until the one gas is
uniformly diffused throughout the other. It has been stated in a
previous section that this diffusion is independent of gravity, but is
inversely as the square root of the densities of the gases. Mixtures of
gases behave precisely like single gases, and diffusion will take place
from one gas into another, precisely as if into a vacuum.

It has been stated that the object of respiration was to supply
oxygen to the blood and to remove carbon dioxide from it. Without
discussing, at present, the process by which this change takes place, it is
evident that if this be a fact the air in the deepest portions of the lungs
will have lost oxygen to the blood and will have taken up carbon dioxide-

588 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The air in the air cells will, therefore, be richer in carbon dioxide and
poorer in oxygen than fresh air taken in in inspiration ; as a consequence^
we have the phenomena of diffusion at once taking place, the oxygen of
the inspired air diffusing down into the deepest portions of the lungs,
while the carbon dioxide diffuses up from the air-cells into the atmos-
phere through the larger bronchi and trachea. As the air penetrates,
therefore, by diffusion deeper and deeper in the bronchial tubes it loses
oxygen and receives more and more carbon dioxide, but the rate of
diffusion is not interfered with : for in the deeper portions of the lungs
the descending atmosphere is meeting with an increasing tension of
carbon dioxide and a decreasing oxygen tension, so that, although the
atmosphere now is poorer in oxygen than the external air, it is yet richer
than the air in the air-cells, and diffusion, therefore, continues. This
difference in tensions remains constant, for we have continually fresh air
taken in in inspiration, and just as continually the removal of the oxygen
from the air in the lower portions of the lungs and the addition to it of
carbon dioxide.

The changes which the air undergoes in respiration may be recog-
nized by a comparison of the composition and the physical character-
istics of the expelled air as contrasted with the inspired air.

The temperature of the expelled air is, as a rule, higher than that of
the inspired air, from the fact that the temperature of the body is almost
invariably higher than that of the surrounding medium. The expired
air is, as a rule, saturated with watery vapor, the water coming directly
from the blood and the mucous membrane, the quantity being estimated
in man as about one and one-half pounds. The watery vapor of the
expired air becomes readily perceptible through its condensation in cold
weather.

Expired air contains, further, numerous organic substances derived
from the blood, resulting partly from the decomposition of the materials
entering into the composition of the tissues, and partly from matters
taken into the blood from without by absorption. Thus, various drugsy
such as turpentine, are excreted by the pulmonary mucous membrane,
readily revealing this in the odor of the expired air. Ammonia, also, is
contained in small amount in the air leaving the lungs, the amount given
off in ordinary respiration in twenty-four hours being calculated at 0.014
per cent. The presence of organic matter in the expired air may be
readily proved by breathing into a vessel, stopping it tightly, and allowing
it to stand a short time ; the odor of putrefaction will develop itself, and it
is, without doubt, to these organic substances in the inspired air that the
odor of the breath is due. It has been estimated that in man about three
and one-half grains of organic matter are so removed in the twenty-four
hours in expired air. Many of these substances which are organic in

RESPIRATION. 589

nature, and find their way into the expired air, are probably of a poisonous
nature. For it has been found that expired air is much more poisonous
to animal life than air which has not passed through the lungs of an
animal, but which contains the same amount of carbon dioxide and the
same degree of decrease of oxygen. It is, therefore, probable that these
organic substances which are removed from the lungs are poisonous,
rather than the carbon dioxide which accompanies them.

The air which passes through the lungs actually decreases in volume
about one-fortieth or one-fiftieth of the amount taken in in inspiration,
this falling off being probably due to the fact that all the oxygen inspired
does not reappear as carbon dioxide, but enters into other compositions
in the body.

The most striking contrast between expired and inspired air is in
the relative proportions of oxygen and carbon dioxide, while the nitrogen
undergoes but little change. The following represents this change: —

Oxygen. Nitrogen. Carbon Dioxide.

Inspired air contains . . 20.81 79.15 .04

Expired " . . .16.033 79.557 4.380

The expired air, therefore, contains from 4 to 5 per cent, less
oxygen and 4 to 5 per cent, more carbon dioxide than the inspired
air. Taking thirty cubic inches as the amount of air taken in in each
inspiration in man, this will represent about one and one-half cubic
inches of oxygen. Supposing five hundred cubic feet to be taken in per
diem, the oxygen absorbed would amount to twenty-three cubic feet, or
one and one-third pounds, avoirdupois, oxygen. The amount of oxygen
varies according to different circumstances.

The following conclusions give at a glance some principal sources
of variations. They will be studied more in detail under the subject of
Nutrition : —

A man in repose and fasting, with an external temperature of 90° F.,
consumes 1465 cubic inches of oxj^gen per hour.

A man in repose, fasting, with an external temperature of 59° F.,
consumes 1627 cubic inches of oxygen per hour.

A man during digestion consumes 2300 cubic inches of oxygen per
hour.

A man, fasting, while he accomplishes the labor necessary to raise in
fifteen minutes a weight of seven thousand three hundred and forty-three
kilos to the height of six hundred and fifty-six feet, consumes 3814
cubic inches of oxygen per hour.

A man, during digestion, accomplishing the labor necessary to raise
in fifteen minutes a weight of seven thousand three hundred and forty-
three kilos to the height of seven hundred feet, consumes 5568 cubic
inches of oxygen per hour.

590 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

As already mentioned, the quantity of oxygen taken in at each
inspiration does not all appear as carbonic acid ; a certain quantity of
the oxygen disappears, varying with the nature of the food

If a dog be fed upon animal food, only 75 per cent, of the 0x3^ gen
of inspiration returns in the form of carbon dioxide. If it be fed on
vegetable food, 90 to 95 per cent, returns in the carbonic acid.

There is no absolute relation between the amount of oxygen inspired
and the carbon dioxide expired, but a certain amount of oxygen always
remains behind, the surplus quantity going to oxidize certain materials,
such as sulphur, phosphorus, and, perhaps, certain food-constituents.

The expired air also contains a notable quantity of carbon dioxide,
amounting to about 4 per cent.

If we take thirty cubic inches as the volume of each expiration, the
average of carbon dioxide in each will be 1.29, or about twenty -three
cubic inches per minute, about one thousand three hundred and ninety-
three per hour, or twenty-seven thousand eight hundred and sixty-four
cubic inches per day, or what is equivalent to about seven and one-half
ounces of solid carbon.

The quantity of carbon dioxide thrown off by the lungs is notably
diminished by the presence of a certain amount of carbon dioxide in the
atmosphere we breathe.

To throw off the full amount, the surrounding atmosphere must be
devoid of this gas. If we breathe the same air over and over again, so
as to permit the accumulation of carbon dioxide, the difference in tension
between the amount of carbon dioxide in the inspired air and the air in
the lungs will be decreased, and diffusion interfered with.

It has been found that if 5 per cent, of carbon dioxide be allowed to
remain in the air we breathe a fatal result ensues in consequence of the
difficulty of elimination of the carbon dioxide from the blood. Even when
carbon dioxide accumulates in the air below 2J per cent, it soon begins
to produce depressing influences, and this, together with the accumula-
tion of other deleterious matters which are normally thrown off from the
lungs, is the common cause of the languor which comes on in crowded
rooms. When gradually subjected to these influences we do not appre-
ciate them so much as when suddenly subjected to them, for when grad-
ually brought under their influence the vital powers become depressed
to such a degree that they do not require the same amount of oxygen as
under ordinary circumstances. A person passing from the open air to a
room which has been occupied for some time by a large number of per-
sons at once experiences a depression, but after remaining there a little
while the vital powers become similarly depressed and the inconvenience
resulting from the presence of carbon dioxide in the atmosphere is no
longer appreciated.

RESPIRATION. 591

An experiment first performed by Bernard, showing how an indi-
vidual may become accustomed to bad air, fully confirms this statement.
He placed under a bell-jar a living sparrow, and, having allowed it to
remain there for a certain period, he removed it but slightly influenced
by the accumulated carbon dioxide: without replenishing the air, he
placed a second sparrow, which had been breathing pure air, under the
bell-jar, and death rapidly ensued. He then replaced the first sparrow
in the same air, and it also died.

The influence of age in varying the quantity of carbon dioxide in the
expired air is very striking. It has been shown that there is a notable
increase in the quantity of carbon dioxide exhaled from infancy to
puberty. In the male this quantity- continues to increase after puberty
until the age of thirty ; from thirty to forty, it remains about stationary ;
at forty, it begins to decrease and continues decreasing until the age of
sixty, when but little more carbon dioxide is exhaled than by a child of
eight years. The same applies, also, to the female.

Not only does age, but time of day, amount of exercise, character
of food, and the temperature also influence the quantity of carbon
dioxide exhaled. More carbon dioxide is thrown off in winter than in
summer, partly because more food is consumed in winter, and partly,
also, because a cubic foot of atmosphere contains a larger quantity of
oxygen in winter than in summer, when it has a lower density. During
the day more carbon dioxide is thrown off than at night. Alcohol and
other articles of the so-called accessory diet diminish the quantity of this
gas removed through the lungs, probably by diminishing the waste of the
tissues. This matter will be again referred to under the consideration
of nutrition.

The quantity of carbon dioxide eliminated with each expiration is
diminished after rapidly repeated inspirations, though the whole quantity
exhaled is increased.

The Respiratory Changes in the Blood. — As has been already indi-
cated, the main points of contrast between the arterial and venous blood
consists, in the former in the presence of an excess of oxygen, in the
latter of an excess of carbon dioxide, while as the venous blood circulates
through the capillaries of the lungs it larg'ely gives up its carbon dioxide
and absorbs oxygen. We have now to consider the way in which the
gases are held within the blood and the manner in which they enter
and leave the blood in the pulmonary and systemic capillaries, and to
trace a relationship between these changes in the blood and the changes
in the air in respiration.

When blood is exposed to a vacuum produced by a mercurial air-
pump, it will be found to yield about sixty volumes of gas to each one
hundred volumes of blood, the temperature being zero C., and the

592 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

height of the barometer seven hundred and sixty millimeters. If the
gas so collected be analyzed it will be found that in the gaseous mixture
so obtained from the arterial blood there will be more oxygen than can
be obtained from the venous blood ; while, on the other hand, the gases
so abstracted from the venous blood will contain more carbon dioxide
than those obtained from the arterial blood. Further, it may be repeated
that if venous blood be agitated with air or with oxygen, it will at once
assume the arterial hue. It may, therefore, be concluded that the differ-
ence in the relative amounts of these gases present in the blood consti-
tutes the real difference between arterial and venous blood, and all other
differences, such as difference in color, are dependent upon this funda-
mental fact. The amount of gas which may be abstracted from blood
has been placed at sixty volumes for each one hundred volumes of blood.
The following table represents the proportions of these gases which
may be obtained from one hundred volumes of arterial and venous
blood : —

Oxygen. Carbon Dioxide. Nitrogen.

Arterial blood, . 20 volumes. 36 volumes. 1 to 2 volumes.

Venous blood, . 8 to 12 " 46 " 1 to 2

All measured at 760 millimeters and 0° C.

The question is now raised as to the manner in which these gases
are held in the blood. In the chapter on the diffusion of gases it was
pointed out that every liquid possesses the power of absorbing gases,
and that the co-efficient of absorption varies with the nature of the
liquid, the nature of the gas, pressure of the gas, and the temperature
to which it was subjected. Blood, therefore, like every other liquid,
possesses the power of absorbing gases. When, however, we measure
the quantity of oxygen which may be extracted from the blood loy
exposing it to a vacuum, we are struck by the fact that the amount so
removed is greatly in excess of that which may be held in solution in
the blood, regarding it merely as a fluid, by exposure to a gaseous
medium in which the oxygen is in no higher tension than it is in the
atmosphere.

Again, the fact is worthy of notice that the absorption of oxygen
by the blood and its release from the blood are not governed by
variations of pressure. If we expose blood containing little* oxygen to
a successive series of atmospheres in which the oxygen tension gradually
increases, we shall find that at first there is a very rapid absorption of
oxygen, and that this suddenly ceases; while if we submit blood highly
charged with oxygen to an atmosphere containing decreasing amounts of
oxygen, we shall find that at first but little oxygen will diffuse out from
the blood until the pressure has been reduced almost to that of a vacuum.
Oxygen then suddenly almost totally escapes from the blood. Again, if

RESPIRATION.

593

we expose blood-serum to an atmosphere of oxygen it will absorb no
more oxygen than water under the same conditions of pressure, and the
amount so absorbed will be far less than that which is capable of being

absorbed by the blood. The absorption, then, of oxygen by the blood
is not due to its plasma. If, however, a solution be prepared of haemo-
globin, or the coloring matter which forms 90 per cent, of the dried red
corpuscles, and it be exposed to oxygen, it will be found capable of

594 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

absorbing nearly the total amount which may.be absorbed by the blood.
It, therefore, would appear that oxygen is absorbed by the blood through
the mediation of the red coloring matter. The general characteristics of
haemoglobin have been already described under the subject of the blood.
They, however, deserve more especial attention in their relationship to
the respirator}7 functions of the blood.

When a tolerably dilute solution of haemoglobin, which possesses
the bright-red color of arterial blood, is placed before the spectroscope,
it is found that a portion of the red end of the spectrum is absorbed,
together with a portion of the blue end, while two absorption bands are
found between the lines D and E ; the line toward the red side of the spec-
trum is the narrowest, but is the most distinct, and with very dilute
solutions is the only one visible. The other toward the blue side is much
broader, but less distinct. These absorption bands are characteristic of
solutions of haemoglobin. When stronger solutions of haemoglobin are
used the bands broaden and become darker, while more and more light is
shut out from each end of the spectrum, until finally the two bands
become fused together, and only the green and red rays are now visible :
with still stronger solutions the red rays alone pass, and finally they
also may disappear, thus indicating the cause of the natural color of
solutions of haemoglobin in transmitted light (Fig. 256).

If crystals of haemoglobin are subjected to a vacuum, oxygen is
given up and the crystals become darker and more of a purple color.
The quantity of oxygen which is given off is a fixed quantity, each
gramme of haemoglobin giving off 1.76 cubic centimeters of oxygen,
measured at a pressure of seven hundred and sixty millimeters and at
zero temperature. The haemoglobin is then spoken of as reduced
haemoglobin. It also is soluble in water and forms a purplish solution.
When examined under the spectroscope, instead of the two absorption
bands, a single, less distinct, but much broader band is found, whose
position lies about midway between that of the two absorption bands of
the unreduced haemoglobin.

In strong solutions of reduced haemoglobin less of the blue than of
the red end of the spectrum is absorbed, and with concentrated solutions
the blue rays may still pass, thus accounting for the difference in color
between the arterial and venous blood, the former allowing the red and
orange-yellow rays to pass, the latter the red and bluish-green rays ;
hence arterial blood appears scarlet, venous blood purple.

The oxygen which is removed from venous blood or from oxyhaemo-
globin by exposure to a vacuum, or by the use of reducing agents, is not
the oxygen which enters into the molecular constitution of haemoglobin,
but is a definite volume which is capable of entering into loose chemical
combination with it.

KESPIKATION. 595

If, now, such a solution of reduced haemoglobin, or the crystals of
reduced haemoglobin, be exposed to the atmosphere, the}' then again
absorb oxygen and now change to a reddish color, the amount of oxygen
absorbed being again precisely similar to that which was given off to the
vacuum.

The above phenomena serve to explain what occurs in the process
of respiration. As the venous blood leaves the right ventricle, its haemo-
globin has already largely lost its oxygen by passing through the 83*8-
temic capillaries, and is now mainly reduced haemoglobin. It absorbs
oxygen from the atmosphere through the walls of the pulmonary vesicles
while passing through the pulmonary capillaries, and now becomes oxy-
haemoglobin and is now arterial blood.

As the arterial blood passes through the S3*stemic capillaries, the
oxj^gen of the oxyhaemoglobin is largel}7 yielded up and haemoglobin
becomes reduced.

The mode in which the carbon dioxide is held in the blood does not
admit of as ready demonstration as is the case with the oxygen. It is,
however, clear that almost the total amount of carbon dioxide which may
be extracted by the vacuum pump from the blood is held, in some way or
other, in the blood-serum, for almost quite as much of this gas may be
extracted from the serum as from the blood itself. The carbon dioxide
is not, however, simply dissolved, for here also the degree of absorption
of this gas by the blood is not governed by the same laws as would apply
to its absorption by water.

When blood-serum is exposed to a vacuum, about 25 volumes per
cent, of this gas is extracted, and this amount is spoken of ns the loose
carbon dioxide. If, now, an acid be added to the serum, about 5 volumes
per cent, more are released, and it may therefore be concluded that this
latter amount exists, in all probability, in the serum in the form of car-
bonates, and probably united with sodium.

The corpuscles also contain about 5 volumes per cent, of carbon
dioxide ; for, if the corpuscles separated from the serum be exposed to a
vacuum, the}' also will yield this amount of carbon dioxide.

If, now, corpuscles and serum, from both of which gas has been
separately removed by pumping, be together exposed to a vacuum, 5 per
cent, again of carbon dioxide is given up, from which it would appear
that the corpuscles in this experiment play the r61e of an acid ; and it
may be assumed that perhaps the haemoglobin in its decomposition
liberates aii acid, which again sets free the combined carbon dioxide from
the serum.

It is not by any means established as to in what manner the free
carbon dioxide is held in the blood-serum. A certain portion of it is,
without doubt, held in solution under the simple laws of absorption 0f

596 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

gases by liquids, and increases with the gaseous tension; while, on the
other hand, a larger amount must be held in some form of chemical com-
bination, since blood is capable of absorbing under equal pressures much
more carbon dioxide than water.

On the other hand, it is also clear that this chemical combination
must be a very loose one, since it is broken up by exposure to a vacuum.
It is probable that part of this carbon dioxide is present in the serum as
a bicarbonate of sodium, — a combination which, by reduced pressure, is
readily broken up into sodium carbonate and free carbon dioxide. It is
further possible that another part of this carbon dioxide may be loosely
combined with a sodium biphosphate, — a salt which is likewise present
in the blood-serum, and which has been shown to readily combine with
carbon dioxide. It is, however, to be noted that this salt, sodium biphos-
phate, is solely present in considerable amounts in the blood of carnivora
and omnivora, while only traces of it are present in the blood of her-
bivora, so that in the latter this combination cannot exist. It, in any
case, seems evident that the red blood-corpuscles in some way govern
the presence of this gas in the serum.

The nitrogen, which may be removed from the blood by exposure to
a vacuum in from 1 to 3 volumes per cent., is without doubt simply
held in solution by the serum, since water likewise is capable of absorb-
ing this gas to the same amount.

The exchange which takes place between these gases in the blood
and the atmospheric air in the lungs is governed almost purely by the
simple physical laws of gaseous diffusion. As already mentioned, the
air within the pulmonary vesicles is separated from the blood in the
capillaries only by the delicate epithelial walls of the vesicles and the
structureless walls of the capillaries. The oxygen of the blood? as
already indicated, is loosely combined with the haemoglobin. When re-
duced haemoglobin is exposed to an atmosphere of oxygen it readily
absorbs that gas, provided the tension of the oxygen in the surrounding
medium be greater than the tension of the oxygen in combination with
the haemoglobin. When, therefore, the blood from the pulmonary arter-
ies reaches the capillaries of the lungs a large part of the haemoglobin
there present exists in the form of reduced haemoglobin, while the atmos-
phere within the pulmonary alveoli contains oxygen, perhaps in a lower
tension than in the atmosphere, but at any rate in a higher tension than
is present in the haemoglobin. As a consequence, diffusion phenomena
set in, the oxygen passing from the interior of the alveoli through the
moist walls of the alveoli and blood-capillaries into the interior of
the latter vessels, and there combining with the haemoglobin. It may
be assumed that the oxygen tension in the alveoli of the lungs amounts
to about 10 per cent. The oxygen tension in the venous blood will,

KESPIBATION. 597

as a rule, amount to about 3 per cent. This difference in pressure is,
therefore, sufficient to explain the entrance of oxygen from the air in
the pulmonary alveoli to the blood in the pulmonary capillaries. The
laws of absorption of oxygen by the blood-corpuscles are, while partially
dependent upon the differences in oxygen tension in the blood and in the
capillaries, not solely dependent upon them ; otherwise an increase in the
oxygen tension in the atmosphere would cause a proportionate increase
in the amount of oxygen absorbed, a decrease in the oxygen tension a
diminution of the amount of this gas which enters in the blood. This is
not, however, the fact, for it has been determined, as already stated, that
but a limited quantity of oxygen is capable of combining with haemo-
globin. If the oxygen of the atmosphere be decreased the tension of
this gas in the lungs will also be decreased, and, therefore, to a certain
extent the blood will be insufficiently aerated ; this will perhaps explain
the dyspnoea which is so often noted in ascending to great heights, as to
the tops of mountains, and in balloons.

As regards the escape of carbon dioxide from the blood in the capil-
laries of the pulmonary artery, we are perhaps warranted in assuming
that they are governed purely by the laws of gaseous tensions ; since
we may assume that even although we do not know exactly what the
tension of carbon dioxide in the pulmonary alveoli is, and although it
must be greater than that in the expired air, it is, nevertheless, less than
that of the venous blood.

The tension of carbon dioxide in the air of the alveoli has been
placed at twenty-seven millimeters of mercury.

The tension of carbon dioxide in the blood in the right side of the
heart has been placed at forty-one millimeters of mercury, or, in other
words, fourteen millimeters higher than the tension in the alveoli. This
difference will, in all probability, be sufficient to inaugurate phenomena
of diffusion.

Thus, in passing through the pulmonary capillaries the venous blood
yields up carbon dioxide and absorbs oxygen, and becomes converted
fr-om a dark-red venous blood into the bright red arterial blood.

The characteristics of arterial blood are preserved throughout the
entire arterial system until the capillaries are reached, and when the
capillaries have been traversed we find that again the arterial blood loses
its characteristic properties and now becomes venous. In other words, in
the capillaries a part of the oxygen disappears and is replaced by carbon
dioxide. In the tissues, therefore, a process takes place which is exactly
the reverse of that which has been described as occurring in the lungs.
It may be assumed that the oxygen leaves the blood in the same manner
as it enters in the pulmonary capillaries ; in other words, in the tissues it
becomes exposed to a surrounding medium whose gaseous tension in

598 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

oxygen is less than that of the arterial blood. As a consequence, the
oxyhaemoglobin is broken up and yields a large part of its oxygen to the
tissues, passing through the walls of the capillaries by diffusion, to be
used up in the tissues in the processes of oxidation which are there con-
tinually taking place. One of the principal results of such oxidation
processes is the formation of carbon dioxide, and here, again, we have
phenomena of diffusion taking place between the tissues and capillaries.
In the tissues tthe gaseous tension of carbon dioxide is higher than in the
capillaries, and, as a consequence, by diffusion this gas leaves the tissues
to enter the blood-serum. This process of gaseous interchange in the
systemic capillaries may, therefore, be spoken of as internal respiration,
and varies in intensity in different conditions of the system. Thus the
interchange is more rapid and extensive in muscles during contraction
than in muscles at rest. It is more active in secreting glands than in
quiescent glands.

As to the subsequent fate of the oxygen after leaving the blood-
vessels, but little can be positively said. It is probable that processes of
oxidation occur in the tissues, and that these result in the formation of
carbon dioxide, but it does not follow that the oxygen as it leaves the
blood directly unites with the organic tissue-constituents, and is thus
directly returned to the blood as carbon dioxide; for we know that
various tissues removed from the body and placed in an atmosphere
entirely devoid of oxygen will still produce carbon dioxide. It is, there-
fore, possible that the oxygen that leaves the blood-vessels is stored up
in some combination or other in the tissues, and is then drawn upon as
the needs of the tissues demand, finally to be returned to the blood as
carbon dioxide.

5. THE NERVOUS MECHANISM OF RESPIRATION. — Although the muscles
of respiration are red, striped, voluntary muscles, and although through
an effort of will the rhythm, number, and depth of the respiratory move-
ments may be greatly modified and changed, the act of respiration is to be
regarded as an involuntarjr action. Although the breath may for a cer-
tain time be held and. the movement of respiration completely interrupted,
after but a very short interval, probably not more than between two and
three minutes, in spite of the strongest effort'of the will, an inspiration must
be made. The fact that respiration persists in the absence of mental
effort points further to the fact of the independence of respiration of the
will. Thus, during sleep and in states of unconsciousness, in various
diseases and as an effect of various drugs, respiration may be perfectly
performed. So, also, in the lower animals the brain may be exposed and
may be gradually removed from the cerebrum down to the base of the
brain, and still respiration be unaffected, provided loss of blood or some
other accident does not interfere with the lower portions of the central

KESPIKATION. 599

nervous system. It has been pointed out that the mechanical operations
of respiration require the associated action of a large number of different
muscles, different in function and in locality. It has been mentioned
that during respiration muscular movements occur in the face, neck,
thorax, and abdomen, and it is found that the character of the contrac-
tion of these muscles is the same in each group. Thus, in gentle inspi-
ration we notice a gentle contraction of the diaphragm, of the scalene
muscles, the external intercostals, and the elevators of the ribs. In
gentle expiration we notice but a gentle contraction of the abdominal
muscles. The degree of contraction of each of these muscles in such a
respiratory movement is identical. When any one muscle or group of
muscles is the seat of an especially violent contraction, the normal
rhythm of respiration is departed from. Again, in forced expiration the
same state of affairs holds; the degree of contraction of each muscle is
proportionate to that of all the other muscles concerned in producing
the respiratory movement. These facts indicate, as in the case of other
complex associated muscular movements, the domination of some part
of the central nervous s3Tstem. In the case of respiration such a state
of affairs will also be noted. In other words, the movements of respira-
tion are controlled by a single co-ordinating centre, located in the me-
dulla oblongata. The proof of this statement may be reached in quite a
number of ways.

If one of the phrenic nerves is divided, the corresponding half of the
diaphragm is paratyzed, and, although motions of inspiration still are
possible, it will be noticed that the excursions of the non-paralyzed half
of the diaphragm will be greater than when the phrenic nerve has not
been cut, and that the share in inspiration borne by the other respiratory
muscles will be more marked than is normally the case.

Section of both phrenic nerves emphasizes this point still further ;
the diaphragm is then completely paralyzed, but inspiration is accom-
plished solely by the muscles which elevate the ribs.

Again, if one or more of the intercostal nerves be divided the mus-
cles supplied by those nerves will be paralyzed, and the act of inspira-
tion will then be produced by calling in the aid of an increased degree of
contraction of other inspiratory muscles.

If the spinal cord be divided below the level of the seventh cervical
nerve, consequently below the origin of the phrenic nerves, all thoracic
and abdominal movement will cease, but respiration will still be possible,
and inspiration will be accomplished solely by the contraction of the
diaphragm, while expiration will be dependent entirel3r upon the recoil
of the elastic tissue of the lungs and thorax. In this state of affairs the
transmission of impulses to the muscles of respiration, with the excep-
tion of the diaphragm, has been interrupted. The thorax will then be

600 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

quiescent, but that the respiratory centre, whose location we have
assumed to be in the medulla, is still sending out its motor impulses
is evidenced by the increased movements of the nostrils and glottis. If,
now, the facial and laryngeal nerves be cut this movement will also
cease.

These facts indicate that in some part of the central nervous system
arise the motor impulses which are conducted to the muscles of respi-
ration. As one after the other of the paths of communication between
these centres and the muscles are interrupted, we find that one after the
other these muscles become paralyzed.

It has been found, as already mentioned, that the brain may be
removed down to the level of the medulla oblongata and still respiration
take place, thus marking the upper limit of this centre. On the other
hand, the spinal cord may be divided up to the calamus scriptorius, and
through the movements of the face the evidence of the activity of the
respiratory centre may still be made out. The respiratory centre, there-
fore, lies some place between these two points. Its exact locality has
not been determined, but it is clear that it lies in the floor of the fourth
ventricle, somewhat lower down than the vaso-motor centre, and nearer
the tip of the calamus scriptorius. When this locality is injured, as by
puncturing with a sharp-pointed instrument, all respiratory movements
at once cease. The motions of the heart are, also, at once arrested from
a simultaneous irritation of the cardio-inhibitory centre. This point,
therefore, when injured causes instantaneous death, and was, conse-
quently, termed by Flourens the vital centre, the nceud vital.

The action of this centre is automatic and is not reflex, though it
may be influenced by afferent impulses coming through various sensory
nerves. Thus, for example, a dash of cold water on the skin causes a
deep inspiration by exalting the action of this centre through the con-
duction of impulses to it from the external integument.

Again, the activity of the respiratory centre may be influenced by
impressions coming from above. Thus, the various emotions, which may
be regarded as impulses originating in the cerebrum, also, are capable of
modifying its activity. The respiratory centre, while not dependent,
however, upon impulses coming through afferent nerves, is especially
modified in activity by impulses traveling through the pneumogastric
nerves; and though the pneumogastric nerves ma}^ be regarded as the
principal paths of conduction of afferent impulses, modifying the activitj^
of the respiratory centres, their integrity is not essential for the mani-
festation of the peculiar action of this ganglionic centre. This fact is
demonstrated by the modifications produced in respiration by section of
these nerves.

If one pneumogastric nerve be cut respiration becomes slower and

KESPIKATION.

601

deeper, while the pauses between the respiratory movements are more
prolonged. If both pneumogastric nerves are divided the respirations
are still further slowed, the pauses are prolonged, and each respiratory
movement is deeper than normal. If the quantity of air displaced in any
given number of respiratory movements before and after section of these
nerves be estimated, it will be found to be almost unchanged; in other
words, the increased depth of the respiratory movements after section of
the pneumogastric compensates for their decrease in frequency. The
amount of carbon dioxide exhaled and oxygen absorbed from the pul-
monary surfaces, therefore, remains unchanged.

If after section of the pneumogastrics the central end of one of the
divided nerves be irritated, the rapidity of respiration
will be increased. By carefully graduating the strength
of stimulation the normal rhythm of respiration may be
again almost exactly restored. If the irritation be
gradually increased, the movements of respiration will
increase in vigor until, finally, they
will apparently run into each other,
and respiration will then be arrested
with the diaphragm in a condition of
tetanic contraction. Respiration is
thus stopped in the phase of extreme
inspiration.

If the central end of the superior
larj-ngeal nerve be stimulated with the
faradic current the respiratory move-
ments will be slowed, and with a
powerful irritation will be arrested,
the diaphragm being completely re-
laxed, and the thorax and lungs being
in the condition seen in forced expira-
tion. It would therefore appear that pXagi

i n ,1 . laryngeal; CX. pulmonary fibres of vagus that excite

the trunks Of the pneUmOgaStriC inspiratory centre; CX/. pulmonary fibres that excite

. expiratory centre; CX", fibres of superior laryngeal

nerves are the pathS OI impulses traV- *hat excite expiratory centre ; IKK, fibres of superior

laryngeal that inhibit the inspiratory centre.

eling from the lungs, which, reaching

the respiratory centre, tend to exalt its activity. The vagus may,
therefore, be regarded as a stimulating nerve for this centre. The laryn-
geal nerves, on the other hand, may be regarded as inhibitory nerves
of the respiratory centre, and, when stimulated, arrest respiration, the
diaphragm being in a state of relaxation and the thorax contracted
(Fig. 257).

While the respiratory centre is thus capable of being modified by
impulses coming from these nerves, its degree of activity is, above all,

FIG. 257.— SCHEME OF THE CHIEF RE-
SPIRATORY NERVES, AFTER RUTHER-
FORD. (Landois.)

INS, inspiratory, and EXP, expiratory centres—

602 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

mainly dependent upon the character of blood supplied to it. Deficient
oxygenation of the blood acts as a stimulus to this centre and causes
the respiratory movements to become quicker as well as deeper, while
expiration becomes especially increased in power. In a greater degree the
deprivation of oxygen from the blood appears to cause the extension of
the stimulus from the respiratory centre to other adjoining motor centres,
and we then find that not only the ordinary muscles of respiration are
thrown into violent action, but that every muscle in the body which is
connected with respiration is thrown into forced contraction. Such a
state is described as dyspnoea.

On the other hand, the blood may become overcharged with oxygen,
as by causing an animal to breathe an atmosphere overcharged with this
gas, or by making forced artificial respiration in one of the lower animals.
The blood then becomes saturated with oxyhiemoglobin. The stimulus
of the respiratory centre is thus removed, and, as a consequence, we find
that in such an animal the motions of respiration cease, and the animal
may remain perfectly quiescent without breathing for a number of
minutes until the blood has • freed itself from the excess of oxygen.
These facts show that a want of oxygen in the blood is a natural stimu-
'lus to the respiratory centre. Blood which is poor in oxygen is also
to be regarded as rich in carbon dioxide. That it is the poverty of oxygen
and not the excess of carbon dioxide which brings this centre into
activity is shown by the fact that if an animal be caused to breathe an
atmosphere deprived of oxygen, or one which will not interfere with the
removal of carbon dioxide, the phenomena of dyspnoea will still appear.
Thus, an animal placed in an atmosphere of hydrogen will not be
prevented from removing carbon dioxide from its venous blood, but will,
of course, be shut off from all supply of fresh oxygen. In such an
animal the phenomena of dyspnoea rapidly appear. This action on the
respiratory centre is produced directly, and not through the mediation
of any nerves, for even when the spinal cord is cut and the supply of
oxygen from the medulla shut off the phenomena of dyspnoea are
evidenced in the spasmodic contractions of the nostrils and glottis, even
though their expression through the muscles of respiration is rendered
impossible. So,also,ligating the vertebral and carotid arteries produces
the same result by decreasing the Supply of oxygenated blood brought to
this centre. Again, if the blood distributed to the respiratory centre be
heated above normal, dyspnoea is also produced, from the fact that the
increased temperature of the blood leads to an increased activity of the
chemical processes in the body, and so to the more rapid exhaustion of
oxygen. Here, also, we find dyspnoea produced through the shutting off
of the supply of oxygen from this centre.

As has been mentioned, if the supply of oxygen be interfered with,

• RESPIRATION. 603

either through some mechanical obstruction of the air-passages or
through the reduction of the amount of oxygen in the air, as by breathing
in a confined space, normal respiration gradually is replaced by dyspnoea,
in which simply all the accessory muscles of respiration are brought into
play, and respiration then, instead of being an almost imperceptible
involuntary movement, now becomes convulsive. If this interference
with the normal ox3^genation of the blood continues, the animal then
passes into a state of asphyxia, which proves rapidly fatal.

When the reduction of oxygen in the blood supplied to the respira-
tory centre becomes decreased, the overexcitation of the respiratory
centre becomes evident in the increased violence of the respiratory
movements; expiration becomes gradually convulsive, until often every
muscle which may react on the thorax is brought into play. Very
soon almost all of the muscles of the body are implicated and the animal
is then in a state of active convulsions. It would appear that these con-
vulsions are due simply to the extension of the activity of the respira-
tory centre to other closely associated centres in the medulla. For we
notice that first the ordinary respiratory muscles contract with greater
vigor, we then have the accessory muscles brought into play, and event-
ually the entire muscular sj^stem of the body ; and although a con-
vulsive centre in the medulla is sometimes spoken of, it is evident
that this centre must be closely connected with the respiratory centre.
After a variable period the violent muscular contractions suddenly
disappear, from the exhaustion of the nervous 83- stem, the pupils are
then found to be dilated to their utmost and are unaffected by light,
and the cornea insensible to the touch. All the muscles of the body
are now in a condition of relaxation ; and although the respiratory
movements have not entirely ceased, they are, however, far between,
are gasping, accompanied by twitching of other muscles, especially of
the face, and the intervals between them become gradually increased ; the
rhythm of the respiratory movements becoming irregular, each inspira-
tion shallower and shallower, again implicating the other muscles of the
body, with the head thrown back and the mouth open, the face drawn
and the nostrils dilated, the last breath is taken in.

It is thus evident that the phenomena resulting from the deprivation
of ox}Tgen ma}' be divided into three different stages : —

First, a stage of dyspnoea, characterized by an extraordinary mus-
cular effort in the muscles of respiration, expiration being especially con-
vulsive. Second, an extension of the convulsive muscular contractions
to all the other muscles of the body, and therefore characterized by
general convulsions, while the final stage is one of exhaustion, in which
the inspirations become slower and slower, more and more shallow,
and are finalty arrested.

604 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The duration of asphyxia varies considerably in different animals
and in the same animal under different circumstances. As a rule, young
animals will bear a longer deprivation of fresh air than adults. It has
thus been stated that while a full-grown dog will rarely recover from an
immersion in water over one and one-half minutes, a puppy has been
known to recover after an immersion of fifty minutes. This is evidently
to be explained by the fact that in younger animals the processes of
tissue change are less active than in adults, and, as a consequence, the
demand on. the oxygen in the blood is less.

During asphyxia the circulation is the seat of various departures
from normal.

In the stage of dyspnoea and convulsions the blood pressure is
reduced, while in the final stage it rapidly falls far below normal, until
at the period of death the blood pressure does not exceed the atmos-
pheric pressure.

The heart also is modified in ^its activity. At first it beats more
rapidly than normal and then is slowed, but each pulsation is greatly
increased in force. As a rule, the heart continues to beat for some
time after the final cessation of respiration. During the first and
second stages of asphyxia, the great increase in blood pressure from the
contraction of the arterioles leads to great increase in the resistance
met with by the heart in emptying itself. We find, therefore, if the
chest of an animal is opened during asphyxia, that the right side of the
heart especially is gorged with blood. The lungs and the pulmonary ves-
sels are overfilled and distended, and, as a consequence, blood collects
in the venous system, so accounting for the cyanosed appearance seen
on all external surfaces, and so characteristic of asphyxia.

Modified Respiratory Movements. — In addition to the normal respira-
tory rhythm, various modifications of the respiratory movement are often
noticed. Many are involuntary, and yet nearly all of them may be repro-
duced by a direct effort of the will.

Sighing is produced by a long, deep inspiration, air being inhaled
through the nose and the inspiration followed by a number of shorter
expirations.

Yawning is accomplished by a deep inspiration through the mouth,
and is accompanied by a depression of the lower jaw and elevation of
the shoulders.

Hiccough is produced by a sudden contraction of the diaphragm
and a sudden closure of the glottis, so arresting the entrance of air into
the lungs, and, by the striking of the column of air against the closed
vocal cords, producing the sound characteristic of this phenomenon.
Hiccough is, as a rule, due to the stimulation of the gastric branches of
the pneumogastric, especially in some disturbance of digestion.

KESPIKATION. 605

Sobbing is produced by a series of similar convulsive inspirations,
in which the glottis is closed earlier than in hiccoughing, and no air, con-
sequently, enters the chest.

The foregoing are the principal modifications of the inspiratory
phase of the respiratory rhythm.

The following owe their characteristics mostly to some modification
of expiration : —

Coughing is produced by a long, deep inspiration, after which the
glottis becomes firmly closed. A forced expiration is then made through
the violent contraction of the abdominal muscles and serves to force
open the glottis, the vibration of the vocal cords producing the charac-
teristic sound. The starting point of the act of coughing may be found
in the contact of any foreign body with the mucous membrane of the
air-passages, the impression being conducted through the superior laryn-
geal nerve. Other parts of the body may, however, also serve as the
starting point to the act of coughing. Thus, stimulation of the auricular
branch of the pneumogastric, as is often the case in numerous ear dis-
eases, may produce coughing, as may the stimulation of other nerves.

Sneezing is produced by a mechanism closely similar to that of
coughing, with the exception that the expelled column of air passes
through the nose instead of the mouth.

The point of origin of the afferent impulses is usually found in the
mucous membrane of the nose and is conducted through the fifth pair of
nerves. In certain individuals the optic nerve may also be the path over
which the afferent impulses travel to originate the act of sneezing.

Laughing consists of a long inspiration followed by a series of short
expirations, during which the glottis is open and the vocal cords thrown
into vibration by the movement of the column of air.

Crying is produced by the same mechanism as laughing, the only
difference being in the facial expression. As a consequence, laughing
frequently verges into crying, and the reverse, and the two are frequently
indistinguishable.

6. INFLUENCE OF THE RESPIRATION ON THE CIRCULATION. — In the exami-
nation of a tracing obtained in a blood-pressure experiment, in addition
to the undulations caused by the variations in the blood pressure due to
each individual heart contraction, a larger series of waves, each com-
posed of a number of cardiac pulsations, may be noticed. These undula-
tions have already been referred to as being due to the influence of the
respiratory movements on arterial blood pressure. Their mode of pro-
duction is now to be considered. Roughly speaking, it may be stated
that during every inspiration the blood pressure falls, and during every
expiration it rises. This statement is, however, not absolutely correct,
but requires some slight modification.

606 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The large vessels of the thoracic cavity vary in capacity according
to the degree of pressure to which their walls are subjected. Naturally,
the veins, possessing thinner and less rigid walls, are more influenced by
external pressure than are the arteries. When the thorax becomes ex-
panded in inspiration, naturally a negative pressure is likewise exerted
on the walls of the veins, and tliey consequently tend to expand. As a
consequence the flow of blood toward the heart is accelerated, and, as
has been already indicated, the pressure within the veins in the neighbor-
hood of the great vessels at the base of the heart becomes negative dur-
ing inspiration. If an opening be made in a vein, as, for example, at the
root of the neck, at each inspiratory movement there is a tendency for
air to enter the venous trunks, forming one of the serious sources of
danger in wounds of the large veins. As a consequence of the greater
increase in the venous blood-current during inspiration a larger quantity
of blood enters the right auricle.

Further, if an opening be made in the skull of an animal, a distinct
rate of pulsation, which is synchronous with the respiratory movements,
may be noticed, in addition to that due to the arterial pulsation. At
each inspiration the brain sinks, and at each expiration it rises. The
production of this phenomenon is evidently due, in the first place, to
facilitation of the flow of blood from the brain in inspiration and, in the
second place, to retardation in expiration, since it disappears on ligature
of the large arteries going to the brain or when a free opening is made
in the venous sinuses. During inspiration, therefore, a larger quantity
of blood enters the right side of the heart, and, as a consequence, a larger
quantity escapes from the left ventricle, more blood escapes into the
aorta, and the blood pressure is increased.

During expiration opposite conditions obtain. The pressure on the
walls of the great veins of the thorax is now increased by the reduction
in the volume of the thorax, and entrance of blood into the thorax is
hindered, less blood enters the heart, less is thrown out by the left ven-
tricle, and, as a consequence, arterial pressure falls.

This state of affairs is, however, not quite so simple as this would
seem to indicate. In the first place, the effect of the respiratory move-
ments on the arteries must be different from that on the veins, for
while inspiration tends to facilitate the flow of blood in the veins toward
the thorax, it likewise tends to hinder the escape of blood in the arteries
from the thorax ; while at the same time a negative pressure is exerted
not only on the veins but on the arteries, and, therefore, tends to produce
expansion of the arterial trunks in the same way as expansion of the
veins is produced. Therefore, the effect of inspiration on the great arte-
rial trunks would be to reduce blood pressure. But from the fact that, as
already indicated, the walls of the arteries are less yielding than those

KESPIKATION. 607

of the veins, the effect of inspiration in producing expansion of the blood-
vessels is less marked on the arteries than on the veins, and, as a conse-
quence, the reduction of blood pressure from arterial expansion is less
marked than the increase of blood pressure from venous expansion.
During expiration, on the other hand, increase of pressure without the
aortic arch acts, of course, in a similar manner to reduction of the calibre
of the aorta, and so would lead to an increase in the blood pressure. This
reduction is, however, likewise less than the compensating reduction in
the volume of the veins ; so that although expiration would therefore tend
to increase arterial pressure, it is more than compensated for by the
reduced amount of blood brought to the heart through the veins.

If, however, a simultaneous tracing be made of the blood pressure
and of the respiratory movements, it will be seen that the increase of
blood pressure does not exactly coincide with the commencement of
inspiration, nor is the fall of blood pressure synchronous exactly with
expiration ; but it will be found that at the commencement of inspira-
tion blood pressure is falling, while it begins to rise before inspiration
is completed, and does not attain its maximum until after expiration has
commenced. Then, before expiration is completed, the fall again com-
mences, and continues during the first part of the succeeding inspiration.
These facts show that, in addition to the mere mechanical changes in the
blood supply produced by the va^ing pressure in inspiration and expira-
tion, some other causes are at work.

The respiratory undulations in the blood pressure are due, in part,
to var}Ting degrees of stimulation of the vaso-motor centre. In other
words, the degree of tonicity of the blood-vessel walls is subject to
rhythmical variations, these variations depending upon coincident
changes in the degree of stimulation of the vaso-motor centre, to which
are added the changes produced in a purely mechanical way by altera-
tions in the intra-thoracic pressure.

If the pulsations be counted in the ascending and descending phases
of the blood pressure, it will be noticed that the pulse beats faster dur-
ing increase of pressure than where it is decreasing. This variation in
the pulse-rate is especially marked in the dog, and is due to changes in
the activity of the cardio-inhibitory centre in the medulla oblongata, as
is proven b}^ the fact that section of both vagi causes the difference in
pulsation to disappear.

It is therefore evident that the vaso-motor, the respiratory, and the
cardio-inhibitory centres to a certain extent act in unison.

The state of affairs is different in cases where artificial respiration is
carried on, as in curarized dogs, when the mechanical causes at work
must necessarily be reversed. If a dog be curarized and subjected to
artificial respiration, and tracings of the intra-thoracic pressure and of

608 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the blood pressure be simultaneously made, the respiratory undulations,
although in a modified form, will still be present. In this case the con-
ditions are exactly reversed, for in inspiration air is forced into the lungs
instead of being aspirated, so that the pressure in the thorax is increased
during inspiration instead of being decreased, as in normal inspiration.
So that we are compelled to attribute the greatest influence in the pro-
duction of these respiratory undulations to varying changes in the vaso-
motor centres rather than to the mechanical causes producing changes in
the intra-thoracic pressure.

Another cause which may be concerned in the production of these
respiratory undulations is also, to a certain extent, mechanical, and
depends upon varying pressures within the abdomen. As the diaphragm
descends in inspiration, the abdominal contents, including the abdominal
vessels, are pressed upon, and, as a consequence, the blood pressure must
be increased. The reverse naturally obtains during expiration, and it is
found that section of both phrenic nerves and opening of the abdominal
cavity causes an almost entire disappearance of the respiratory undu-
lations ; so that, therefore, the mechanical changes in the abdominal
pressure are likewise, to a certain extent, concerned in the production of
the respiratory undulations.

SECTION IX.

THE MAMMARY SECRETION.

THE milk is the secretion of the mammary glands of the females of
the mammalian group, and is poured out, as a rule, only in the last
stages of pregnancy and after the birth. Sometimes, especially in
goats, the secretion of milk is formed by the rudimentary glands of the
male.. In many cases the mammary glands of newly-born infants of both
sexes also pour out a scanty secretion, which is, probably , closely similar
in composition to milk, although it has been but slightly investigated.
This secretion commences usually three or four days after the birth,
increases np to the eighth day, remains a few days stationary, and then
commences to decrease, and by the end of the first month has usually
entirely disappeared.

The mammary glands of various animals of the mammalian type
also frequently pour out a secretion immediately after birth. These
facts, as well as the morphological characters of the mammary gland,
indicate that they are exceptionally developed sebaceous glands ; the
close similarity in composition of the milk and the secretion of the
sebaceous glands of the skin also supports this view.

The following table represents the composition of this secretion
from the rudimentary mammary gland : —

Water,
Solids,

Casein,
Albumen,

Newly-Born Five-weeks-
infant, old FoaL

95.705 93.10

4.295 6.90

0.557 0.50

0.490 1.02

1.456 (?)

Fat,

Milk-sugar, 0.956 3.67

Inorganic salts, . , " . . . . 0.826 0.44

Before and shortly after delivery pregnant females secrete a fluid
from their mammary glands which differs considerably from that of the
later secretion. It is termed colostrum.

Colostrum is an opaque, yellowish fluid, containing a large amount
of the so-called colostrum cells (true glandular cells in different stages
of fatty degeneration), few milk-globules, a large amount of albumen,
little or no casein, and but little fat, milk-sugar, and salts. On account
of its large percentage of albumen, it coagulates when heated, differing
in this respect from milk ; in fact, colostrum when first secreted closely

39 (609)

610

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

resembles blood-serum, with the addition of colostrum corpuscles.
Gradually, however, the colostrum secretion passes into a milk secretion,
albumen and colostrum corpuscles become reduced in amount, fat, casein,
sugar, and milk-globules increase. The specific gravity of colostrum
varies from 1040 to 1060, being higher immediately after delivery and
falling as it gives place to a true milk secretion. Thus, according to
Quevenne, the specific gravity of colostrum of the Cow on the first day
after calving is 1060; on the second, 1053; on the third, 1035; on the
fourth, 1040 ; on the fifth, 102T. The reaction of colostrum is ordinarily
alkaline and becomes acid on standing. Immediately after calving the
colostrum of the cow contains 8.5 per cent, albumen, after one day 6.4
per cent., after three days 3.4 per cent., after seven days 1.9 per cent.,
and after twentj^-one days 0.6 per cent. On an average, colostrum may
be said to have the following composition : —

Water,

Casein,

Albumen,

Fats,

Sugar,

Salts,

78.7 per cent.
7.3
7.5
4.0
1.5
1.0

The so-called uterine milk is a white or rose-colored, creamy, alkaline
fluid, with specific gravity of 1030 to 1040, and is obtained by compres-
sion of the placenta! cotyledons of ruminant animals. It rapidly
becomes acid and undergoes spontaneous coagulation. It contains fatty
particles, free nuclei, and epithelial cells. The following table represents
its composition in the cow : —

Water, . . . ' , ,, »• '-.- t . 87.91 per cent.

Solids, . . . .•• ...'"' . o"". . 12.09
Fats, . . . . ' . . . > 1 23

Albumen cells, . . *. . . . 10.40

Albuminates, 0.16

Ash, 0.37

1. THE PHYSICAL AND CHEMICAL PROPERTIES OP MILK. — Milk is an
opaque fluid, with a sweetish taste and an opalescent bluish tint, in thin
layers, and a characteristic odor due to the volatile substances derived
from the secretions of the cutaneous glands.

Milk is not a homogeneous fluid, but is an emulsion, which consists
of the so-called milk-globules suspended in milk-plasma, the latter con-
sisting of a solution of albumen, sugar, and salts. Examined under the
microscope the milk-globules appear as highly refractive drops of oil
floating in the clear fluid (Figs. 258 and 259).

-The size of these globules varies from 0.01 to 0.03 millimeter.

In colostrum the corpuscles are much larger than in milk, and are
capable .of amoeboid movements. The milk-corpuscles consist almost

MAMMARY SECRETION.

611

entirely of fat, and are composed of combinations of gtycerin with
oleic, palmitic, and stearic acids. They are surrounded by a thin layer of
casein, not in the form of a solid deposition, but the casein probably
exists in a condition of high imbibition rather than in a state of solidity
or of true solution. The laj'er of casein cannot be regarded as consti-
tuting a membrane, although it, to a certain extent, fulfills the same
function. If acetic acid is added to a preparation of milk, under the
microscope it will be seen that the caseous envelope is dissolved and the
oil-globules run together and form irregular masses of oil.

When cows' milk is shaken up with caustic potash and then
agitated with ether the oil passes into solution in the ether. The
previous subjection to the action of caustic potash is, however, essential,
since ether will not dissolve the oil from cows' milk unless the casein
envelopes be previously dissolved by acetic acid or potash.

FIG. 258.— MICROSCOPIC APPEARANCE OP MILK AND COL,OSTRTTM. (Landois.)

The upper half of the figure represents milk ; the lower half colostrum.

If milk be allowed to stand for some time the oil-globules, which in
freshly secreted milk are uniformly distributed through the milk, now
rise to the surface and form a layer largely composed of fat, or the
so-called cream.

The reaction of freshly secreted milk is alkaline in the herbivora and
in the human female, while that of the carnivora is acid.

The milk of herbivora frequently will exhibit both an alkaline and
an acid reaction, due to the presence of an acid sodium phosphate
(H2NAP04) and of an alkaline disodic phosphate (NAaHP04). Such
a reaction is spoken of as amphioter.

When milk is allowed to stand, the alkaline reaction, when present,
gives place to an acid reaction, which is due to the fermentation of the
milk-sugar and its conversion into lactic acid. When the cream is

612

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

removed from milk the skimmed milk is less opaque and white, while
the edges in contact with the vessel have a distinct bluish tint.

The specific gravity of milk varies from 1018 to 1040. Cows' milk,
when pure, may vary between sp. gr. 1028 and 1034, usually increasing
from the first to the eighth month of lactation from 1031 to 1039.

In composition milk consists of solids partly dissolved and partly
suspended in a fluid plasma, the amount varying from 12 to 13 per cent.
Of these solids, 3 to 6 per cent, is represented by the fats, 9.25 per cent,
by the other solids.

In composition, milk is composed of 85 to 90 per cent, water,
casein, albumen, fat, milk-sugar, lecithin, and salts, with carbon dioxide,

FIG. 259.— MICROSCOPIC APPEARANCES OF MILK, I; CREAM, II; BUTTER, HI; COLOS-
TRUM OF MARE, IV; AND COLOSTRUM OF Cow, V. (Thanhoffer.)

oxygen arfd nitrogen gases, urea, and various accidental constituents,
such as lactic acid after milk fermentation, haematin, bile coloring-
matters, and mucin. It often serves to eliminate various substances such
as drugs, among which may be mentioned potassium iodide, iodine, salts
of various metals, the oil of garlic, and various other bodies. When
filtered through animal membrane or porous-clay filters, the milk-plasma
is obtained as a clear, slightly opalescent fluid, which contains casein,
serum-albumen, peptone, milk-sugar, salts — in fact, all the constituents
of milk, with the exception of the oil-globules and a considerable portion
of the casein, the amount of the latter which is kept back being greatly
•- increased when a fresh animal membrane is used as a filter.

MAMMARY SECRETION.

613

The following tables represent various analyses of this secretion
in different animals : —

I. COMPOSITION OP THE MILK OF DIFFERENT ANIMALS. (AFTER GORUP-
BESANEZ, LIEBERMANN, GAUTIER, ETC.)

Woman.

CONSTITUENTS.

Ass.

Cow.

Goat,

Sheep.

Mare.

Colos-

truin.

Water,

86 27

8891

8777

84.08

90 70

8656

86.76

83.30

8284

Solids,

13.72

11.09

12.23

15.92

19.30

13.44

13.24

16.69

17.16

Casein, >
Albumen, $

2.95

3.92

2.34

3.23

1.70

C 3.50
{ 0.58

2.92?
1.31$

5.73

1.64

Butter, ....

5.37

2.67

3.68

5.78

1.55

4.03

4.48

6.05

6.87

Milk-sugar, . .
Inorganic salts,

5.13
0.22

4.36
0.14

5.55
0.23

6.51
0.35

5.80
0.50

4.60
0.73

3.91
0.62

3.96 >
0.68 $

8.65

II.

In 100 Parts.

Cow.

Goat.

Sheep.

Ass.

Mare.

Sow.

"Woman.

Water

85 7

864

840

91 0

828

824

888

Solids,

14.3

13^6

16.0

9.0

17.2

17.6

11.2

Casein,
Albumen,.

4.8
06

3.3)
12S

5.3

2.0

1.6

6.1

3.5

Fats,

4.3

4.4

5.4

1.3

6.9

6.4

3.5

Sugar,
Salts

4.0

0.6

4.0
0.7

4.1)

0.7$

5.7

8.7

$ 4.0

I 1.1

4.0
0.2

Asses' milk is nearest in composition to women's milk ; cows' milk
has one-half more fat and almost one-half more albuminoids.

III. THE ASH OF MILK IN 100 PARTS.

WOMEN'S MILK.

Cows'

MILK.

(Wildenstein.)

(Weber.)

(Haidlen.)

Sodium,

4.21

6.38

8.27

Potassium

3159

2471

15.42

Chlorine .

1906

1439

16.96

Calcium

18 78

17.311

Magnesium, ....

0.87

1.90 I

56.52

Phosphoric acid,

19.00
2.64

29.13 J
1.15

Ferric oxide ... .

0.10

0.33

0.62

Silica,

trace

0.09

614 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

IV. THE RELATIVE VALUE OF DIFFERENT KINDS OF MILK.

Water.

Casein and
Albumen.

Butter.

Sugar and
Walts.

Mares' milk, . . .

91.15

1.03

1.27

6.12

Asses' " . .

89.01

3.57

1.85

5.57

Women's milk, .

87.24

2.88

3.68

5.78

Goats'

86.85

3.79

4.34

3.78

Cows' " .

84.28

4.35

6.47

4.34

Sheep's " .

83.30

5.73

6.05

O G£J

o.t/O

V. SOLIDS IN A PINT OF MILK.

Nitrogenous constituents, 23.9 grammes.

Fatty 22.7

Saccharine " . . . . .80.3 "
Salts, 4.0

2. CASEIN AND MILK COAGULATION. — Casein is a proteid body of an
acid reaction which is scarcely soluble in water but soluble in dilute acids
and alkalies. In milk its solution is rendered possible by its combina-
tion with soluble alkali albuminates and through the presence of calcium
phosphate. In amount it varies from 3 to 5 per cent., the relative pro-
portions of casein and albumen being from 1.87 per cent, to 4.68 per
cent, of the former and from 0.60 per cent, to 1.77 per cent, of the latter.

Casein, although closely similar in composition to alkali albumen, is
not identical with it, but is probabty to be regarded as a combination of
alkali albuminate and nuclein. Casein may be obtained from milk by
dilution with four times its volume of water, the addition of dilute acetic
acid (0.1 per cent.) until a precipitate begins to appear, th.en passing a
current of carbonic acid gas, filtering, and washing the precipitate with
water, alcohol, and ether.

Casein may also be obtained from milk by the addition of magnesium
sulphate to saturation.

When freed by ether from fats after its preparation by the latter
process and dissolved in water, casein is a snow-white powder and in
solution rotates yellow light eighty degrees to the left; in dilute alkaline
solution, seventy-six degrees to the left; in strong alkaline solution,
ninety-one degrees to the left ; and in dilute hydrochloric acid, eighty-
seven degrees to the left. It leaves no ash on incineration.

When milk is boiled the serum-albumen of milk becomes coagulated,
while the skim formed is due to the deposition of a thin pellicle of casein
due to evaporation, and which is renewed as fast as it is removed.

The coagulation of milk depends upon the precipitation of casein.
Everything, therefore, which causes casein to become insoluble causes
coagulation of milk. Such agents are acids, rennet, tannin, alcohol, and
mineral salts.

MAMMARY SECRETION. 615

Milk is coagulated by all acids. Several, especially acetic acid in
excess, again dissolve the precipitate of casein. Casein is precipitated
by acids only when a certain degree of acidity is reached, since alkaline
phosphates must be first neutralized ; if the alkaline phosphates are
removed, even carbon dioxide is then capable of precipitating casein.
The spontaneous coagulation of milk is produced by the development of
lactic acid, which is formed from milk-sugar in the milk by the action
of bacteria introduced from without or by the action of the lactic acid
ferment which appears to be present in milk. In this process the neutral
alkaline phosphate is converted into acid phosphate. The casein is sepa-
rated from its combination with calcium phosphate and is precipitated,
the sugar being decomposed into lactic acid and carbon dioxide.' When
milk coagulates spontaneously, or, in other words, curdles, it separates
into a tough, jelly-like substance or curd, which consists of the insoluble
casein and fat, floating in an opalescent acid fluid, or whey. The whey
contains the greater part of the salts of the milk, the lactic acid, the
undecomposed milk-sugar, and certain amounts of fat and the albumi-
noids. That the spontaneous curdling of milk is due to the action of the
ferment contained itself in milk (which decomposes the milk-sugar into
lactic acid)- is proved by the fact that boiling greatly retards the spon-
taneous coagulation, evidently through the destruction of this ferment.
This lactic acid ferment may be precipitated from milk by the addition of
an excess of alcohol. If the ferment is then dissolved in water and added
to solutions of milk-sugar it will produce rapid fermentation. The action
of the milk-curdling ferment, as pointed out in the chapters on Digestion,
is very different. Here, the casein is rendered insoluble by the action of
the rennet ferment, even in alkaline fluids and without at all calling in
the aid of lactic acid. The salts in milk, especially the calcic phosphate,
are essential to the action of milk-curdling ferment ; for, when milk is
subjected to dialysis, rennet is then rendered incapable of producing
coagulation.

Spontaneous coagulation of milk may be prevented by the addition
of sodic carbonate, boracic or salicylic acids. So, also, the addition of
one drop of the ethereal oil of mustard to twenty cubic centimeters of
milk will likewise preserve its fluid condition.

Colostrum, sows' milk, and the milk of carnivora coagulate when
heated. Boiled milk coagulates spontaneously only with difficulty, and
is also more difficult to coagulate with rennet, but when acidulated the
casein coagulates even more readily than in fresh milk.

A high temperature facilitates both forms of coagulation. Milk
which has become acid, but which is still fluid, will coagulate when
heated. '

In addition to casein, milk contains other albuminoids, one of which

616 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in all of its characteristics closely resembles serum-albumen. It is
present in about 0.5 per cent., though in colostrum it is in much larger
percentage. It is there present in about 15 per cent., but rapidly de-
creases for about four weeks, when it reaches its average percentage of
0.5 per cent.

When the plasma of milk is slightly acidulated and boiled it coagu-
lates between 10° and 80° C. Peptone is also present in small amounts
as a trans udat ion from the blood.

3. MILK-SUGAR. — Milk-sugar is an animal carbohydrate found only
in milk ; its average percentage is 4.5 per cent., varying from 3 to 7 per
cent. Of all the constituents of the milk the milk-sugar is least influ-
enced by external conditions. It is found dissolved in milk-serum and in
whey, whether after the spontaneous coagulation of the milk (acid whey)
or after the action of rennet (sweet whey). It may be obtained by coag-
ulating milk and evaporating the whey until Crystals form. It occurs
with one molecule of water in rhombic prisms soluble in from five to six
parts of cold water and in three- parts of boiling water. It is, therefore,
very insoluble in comparison with the other forms of sugar. It is only
slightly soluble in alcohol and water, and is not readily crystallizable.

Its formula may be placed at C6H12O6. Heated up to 100° C. it
loses some of its water, and may thus be represented by the formula
C12H220U.

The specific rotation of milk-sugar containing water of crystalliza-
tion is -f- 52.53° at 20° C. ; anhydrous milk-sugar = -\- 81.3°. When
warmed with alkalies it becomes brown, like dextrose (Moore's test), and
likewise reduces Fehling's solution.

The milk-sugar of the human female, the cow, and the goat agree in
their chemical characteristics, their form of crystallization, and their
action on polarized light.

The spontaneous coagulation of milk is due to the formation of
lactic acid from milk-sugar, one molecule of milk-sugar forming foui*
molecules of lactic acid. The formula may be represented as follows : —

When lactic acid forms, it unites with the alkaline phosphates to
form lactates of the alkalies and acid salts, and coagulation only occurs
when all the alkaline phosphates have been converted into acid salts. A
slight further development of lactic acid is then sufficient to cause coag-
ulation.

If two glasses, one containing milk and the other a pure solution of
milk-sugar, are subjected to the same conditions, after a fewtla}^ the
former will contain so much lactic acid that the milk will be coagulated;
while not the slightest trace of acidity will be found in the milk-sugar

MAMMAKY SECRETION. 617

solution. This proves that the milk contains a ferment which is capable
of splitting up milk-sugar into lactic acid. Such a ferment is widely
distributed in the animal body. It may be often extracted from the
gastric mucous membrane, and is entirely distinct from pepsin or the
milk-curdling ferment, since it preserves its action even after the other
ferments are destroyed by dilute caustic soda. The ferment may be
obtained from milk after dialysis by precipitation with alcohol, and,
after drying, dissolving the precipitate in water. Such a precipitate will
coagulate milk and will cause the development of lactic acid in solu-
tions of milk-sugar.

This ferment has a neutral reaction and is soluble in glycerin. It is
destroyed by boiling, and appears to regain its activity when treated
with oxygen. This would indicate that it is a ferment generator and
not a true ferment, and explains why boiled milk may be kept longer
than unboiled ; while the fact that even boiled milk will ultimately coag-
ulate is to be attributed to the subsequent development of the ferment
through the action of the air.

Increase of temperature increases the activity of the ferment. Milk-
sugar is not directly fermentable; that is, it cannot be directly converted
into alcohol, though by the action of dilute sulphuric or hydrochloric
acids it ma}^ be partly transformed into a fermentable lactic acid. This
process is concerned in the manufacture of koumiss from mares' milk,
which contains a large amount of sugar. A similar fermented liquid
may be obtained from cows' milk through the action of the yeast-plant.

4. FAT AND CREAM. — Fat is present in milk in the form of minute
globules, the average percentage being 3 to 3| per cent., although it
may vary from 2^ to 5J per cent.

The following fatty acids have been found in milk : But}'ric, caproic,
caprylic, caprinic, myristic, palmitic, stearic, and oleic. The percentages
of palmitic, oleic, and stearic acids vary. So the melting point of butter
also varies, as does, also, its specific gravity. Normally, the melting point
varies from 32° to 37.5° C.

Cows' butter contains about 68 per cent, palmitin, 30 per cent,
olein, and 2 per cent, other fats, the solid fats apparently being more
abundant in winter than in summer. The butter may be separated from
milk by mechanical agitation (churning), the enveloping layers of casein
being thus ruptured. It was formerly supposed that the fatty globule
of milk had a solid envelope, because the fat does not pass into solution
in ether unless caustic potash had been previously added. At most,
however, we may assume that the fat is surrounded by an envelope of
fluid casein, rendered more consistent here than elsewhere by the mo-
lecular attraction exerted by the fat-globules. Casein is not present in
the milk in the form of a true solution, but rather in a high degree of

618 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

imbibition ; so the effect of caustic potash is to enable the casein to pass
into solution, and so render the oil accessible to ether. The absence of
any solid envelope of the oil-globule is proved by the absence of any
such formation after mechanically breaking up the oil-globules, while the
proof of the fact of non-solution of casein in the milk is found in the
fact that when milk is filtered through porous earthenware scarcely any
casein passes through, while the other albuminoids which are really in
solution do so pass. Casein, therefore, in milk acts like the gum around
the oil-globules in an artificial mucilage emulsion.

On account of the lighter specific gravity, when milk stands the oil-
globules rise to the top and, accompanied by varying amounts of the
other constituents of the milk, constitute the cream ; the largest rise
first, while the smaller ones remain suspended in the body of the milk.
The ascent of the cream is the more rapid the smaller the distance the
fat-globules have to traverse. Hence, cream is formed more rapidly in
broad, shallow vessels than in tall, narrow ones. Unless the temperature
of the milk is constant, currents are set up in the milk from the differ-
ences of temperature, and the formation of cream is delayed until the
entire volume of milk and the external medium are of the same tempera-
ture. Hence, shallow metal pans, by leading to a rapid equalization of
temperatures, are usually employed for the separation of the cream. As
the milk has a greater volume when warm than when cold, the cream will
contain less serum when the molecules of the fluid are further separated
from each other. So cream formed from warm milk has a higher per-
centage of fat in a small volume than cream formed from cold milk, and
the higher the temperature at which the formation of cream takes place
the smaller the amount of fat left in the skimmed milk.

If the cream has been removed from milk by means of the centri-
fugal machine the separation is much more complete (often only O.L
per cent, of fat remaining in the milk), while the milk remains sweet
instead of becoming sour, as ordinarily occurs in the usual method of
separating the cream. Skimmed milk so obtained is, therefore, a more
valuable food, since it still contains all the sugar and is less apt to pro-
duce disturbances of digestion.

The addition of a small amount of water facilitates, the addition of
salt interferes with, the separation of the cream.

The following table represents the composition of cream : —

Water, . . . . . •*,.,% . 61.67

Fat, . . . . . .... . . 33.43

Casein, . " . . . 2.62

Sugar, ... 1 56

Salts, . 0.72

By the process of churning, which is only effective after the milk
has become slightly acid, only about two thirds of the fat are removed ;

MAMMARY SECRETION. 619

the other third remains in suspension in the buttermilk. Churning is
best accomplished at about 14° C., with thirty to forty strokes of the
churn per minute.

The average composition of buttermilk may be placed as follows :
Fat, 0.50 to 0.75 per cent. ; casein, 3.60 per cent. ; albumen, 3.7 per cent. ;
sugar, 0.52 per cent. ; ash, 0.52 per cent. ; water, 91.7 per cent.

The amount of cream which may be obtained from milk varies very
considerably in different animals and under different conditions, and will
be subsequently referred to.

Usually about 80 per cent, of the entire amount of fat contained in the
milk passes into the cream, and if the average percentage of fat in milk
be placed at 3.5 per cent., the fat in cream would amount to 2.7 per cent.

When butter becomes rancid the volatile fatty acids are set free and
acrolein and formic acid are formed from the glycerin.

Skimmed milk has a higher specific gravity than unskimmed milk,
from the fact that the lighter constituents, that is, the oils, have been
largely removed. The specific gravity of skimmed milk may rise to
1037, or even higher. Its composition may be placed as follows : —

Water, 89.65

Fat, 0.79

Casein 3.01

Sugar, 5.72

Salts, . 0.83

5. THE INORGANIC CONSTITUENTS OF MILK. — In addition to the albu-
minoids, fats, and carbohydrates contained in milk, the mineral constitu-
ents necessary for the support of the animal body are also present,
their average amount being about as follows : —

Phosphoric acid, . . 28.31

Chlorine, 16.34

Calcium oxide, 27.00

Potassium, . . . . . . . . .17.34

Sodium, 10.00

Magnesium, 4.07

Ferric oxide, 0.62

Oxygen, nitrogen, and carbon dioxide are also present; and since
these gases may be entirely removed by pumping, they are, therefore, in a
condition of solution in the milk.

Nitrogen is present in 0.7 volumes per cent. ; oxygen, 0.1 per cent. ;
carbon dioxide, 7.7 per cent.

6. VARIATIONS IN THE QUANTITY AND COMPOSITION OF MILK. — The
variations which occur in the quantity and composition of milk are
largety dependent on the quantity and composition of the food; in-
sufficient food leads to a reduction in both the absolute quantity and
solid constituents of the milk. In addition to these conditions, to be

620

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

studied in detail directly, the amount and character of the milk depends
largely upon the period of pregnancy and suckling, as there is a close
sympathy between the secretion of the mammary glands and the genital
organs. The period of activity of the mammary gland is inaugurated
shortly before the first birth, and shortly thereafter yields the largest
amount of secretion, which in the best Dutch cattle may be as large as
30-35 liters each day. This maximum persists for several weeks, and
then commences gradually to decline, there being a continual and gradual
relative increase in the albuminoids and a decrease in the fats and sugar,
and at the end of the tenth month only one-quarter or one-sixth as much
milk is secreted as at first. During the first ten months of lactation in
the best cows more than 6000 liters may be secreted ; fairly good cows
will form 3000 liters, and poor cows not more than 1000 liters of milk in
the same time

Quite frequently good cows will yield as much milk, nearly, after ten
months as in the first week after birth.

Colostrum is far richer in solids than the later secretions of milk.

Immediately aftei
1st day after cal
2d "
3d " "
4th "
5th " "
6th " "
14th "
28th " "

r calving,
ving, .

9

Solids.
. 38.4
. 30.1
. 23.1
. 15.3
. 14.9
. 13.7
12 9

Water.
61.6
69.9
76.9

84.7
85.1
86.3

87.1
87.4
87.6

. ::•'

. 12.6
. 12.4

The solids contain the following constituents : —

Immediately after calving,

1st day after calving,

2d

3d

4th

5th

6th
14th
28th "

Fat.

8.4

5.9

6.2

4.0

4.5

3.7

3.0

25

2.6

Sugar. Albuminoids.

0.0
0.2
0.9
2.5
3.6
3.9
4.3
4.3
4.4

15.5

13.7

10.9

8.6

5.1

3.4

2.0

1.6

0.7

Colostrum contains 3.3 per cent, salts, and it therefore follows that
the percentage of casein must be 11.2 per cent.

The quantity of milk depends upon the breed of cow. Some races
are good milkers, while others are better as meat producers and beasts of
burden. Nevertheless, the quantity of milk is directly proportionate to
the degree of development of the mammary gland. Even in two cows
of the same breed, and on precisely the same food, the amount of milk
secretion will depend upon the degree of development of the glandular
tissue.

MAMMARY SECEETION.

621

The following table gives the average milk grven by different breeds
of Irish and English cattle (Schmidt-Mulheim): —

English Cattle.

Breed.

f'SSSffin. Total Milk.

1. Shorthorns (Wiltshire), .

2. " ...

3. " ...

4. Cross-bred (Cheshire),

5. Yorkshire, ......

6. Half-bred and Shorthorns (Cheshire),

7. North-bred and South Devon, Jer-

seys and Shorthorns (Devon),

8. Yorkshire (Hunts), ....

9. Half-bred Yorkshire (Hunts), .

10. Hereford,

11. Yorkshire (Surrey), ....

12. Shorthorns (Yorkshire), .

Average,

Irish Cattle.
Breed.

1. Cross-bred, Durham, and Ayrshire

(Kerry)

2. Cross-bred, Irish, and Shorthorns

(Limerick), . . . . .270

3. Half-bred, Shorthorns (Cork), . . 270

4. Cross-bred (Cork), . . . .270

Average, 274

270 days. 2160 quarts.

240

2520

•

255

3060

t

240

2880

t

270

3465

«

240

2640

'

320

3840

<

240

1440

<

180

2520

(

240

1920

<

270

3240

'

235

2142

t

250

2652

Duration Tntal \fi11r

of Lactation. «*»«•*

285 days. 1995 quarts.

2430
2700
2970

2524

As the milk-glands in the cow weigh only about five kilos, with 24 per
cent., or 1.2 kilos, solids, it is evident that each gland produces two and
a half times its own weight in solids.

Goats give one-half to one liter of milk daity.

Women produce one to one and one-third liters of milk daily.

The milk of different breeds of cattle varies not only in quantit3T,
but also in quality. As a rule, the milk of the Dutch cattle contains the
largest percentage of fat and albumen ; then come the Swiss and Tyro-
lean cows and Normandy cows with greatest percentage of solids.

The composition of milk also varies according to the stage of lacta-
tion, casein and fat increasing in women up to the second month, while
sugar decreases even in the first month.

In five to seven months fat decreases. Casein decreases after the
ninth to tenth month. Salts increase in first five months and then
decrease.

In goats casein first sinks, then remains constant, and then increases.
Fat gradually decreases.

So, in dogs, albuminous diet increases the fat in milk. This influ-
ence is less marked in cows. Fat in food appears to decrease the fat in

622 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

milk if there is an insufficient amount of albumen given at the same
time.

Carbohydrates in food of carnivora appear to be without influence
on amount of milk-sugar. Also, in herbivora, milk-sugar depends for its
origin principally on the albumen of the food.

The mode of living is of the greatest influence on the milk secretion.
When a large quantity of milk is desired, the animals must remain per-
fectly at rest, as every excitement or movement, even of the animals'
body muscles, decreases the milk secretion. When the animals are per-
fectly motionless the, greater part of the blood-stream passes through
the glands, and vice versa. So a much smaller quantity of milk is pro-
duced by grazing than by stall-fed animals, and it has been found that
even leading cows out to drink decreases the amount of milk.

The feeding has also a certain influence on the composition of the
milk ; to produce a large quantity of good milk, the animal, naturally,
must receive enough food to maintain a good condition. If a poor food
is given the milk will not be very seriously influenced, nor will a rich
food increase the quantity of milk to any great extent. The milk secre-
tion is far more closely dependent on the breed of cattle than on the
feeding ; a certain maximum which is peculiar to each individual cannot
by any artificial means be increased:

Water, of all foods, seems -to have the greatest influence on the
composition of milk. When large quantities of water have been drunk,
the milk contains a higher percentage of water. The amount of
albuminoid constituents of the food exerts great influence on both
the composition and quantity of the milk. An increase in the pro-
teids in the food increases the total quantity and solids of the milk,
the fats being relatively more increased than the albuminoids. As an
illustration of these facts, Weiske has found that a goat which on a
diet of one thousand five hundred grammes potatoes and three hundred
and sevent}T-five grammes chopped straw secreted seven hundred and
thirty-nine grammes milk, secreted one thousand and fifty-four grammes
milk when two hundred and fi/ty grammes of meat residue was added
to the ration, the fat in the milk increasing from 2.71 per cent, to 3.14
per cent. In carnivora, also, a rich proteid diet leads to the production
of a copious secretion, which may be almost completely arrested by
confinement to a carbohydrate diet. In the human female, a rich
albuminous diet leads not only to an increase in the amount of milk,
but also of its solid constituents, as is seen in the following table : —

Water. Solids. Fats. Casein.

On scanty diet, . . . 914.0 86.0 8.0 35.5 39.5
One week later, after abun-
dant meat diet, . . 880.6 119.4 34.0 37.5 45.4

MAMMAKY SECRETION. 623

In herbivora, carnivora, and omnivora, therefore, the same general
rule holds, that an increase in the albuminous constituents of the food
increases both the total amount of milk and its percentage in fats. In
cows, however, it is to be noted that the relative percentages of casein
and fat are not dependent so much on the amount of albumen of the
food as on the breed and individual characteristics. The influence of the
fatty constituents of the food on the composition of the milk is less
marked.

It will be shown, under the subject of Nutrition, that the addition
of fat to the food serves to reduce the waste of tissue-albumen, and
therefore permits the deposition of nitrogenous tissue-constituents. To
this extent, by yielding a greater supply of albuminous bodies to the
glandular epithelium, a fatty diet may help the milk secretion, but not,
as will be shown directly, by an immediate transfer of the fat of the food
to the milk. In fact, the addition of fat to the food even seems to reduce
the amount of butter in the milk if the amounts of albuminoids in the
food are not amply sufficient for the nutritive needs of the economy.
When, however, the albuminoids and other constituents of the food are
ample for preserving nutritive equilibrium, the further addition of fat
will increase the percentage of butter in the milk.

The milk secreted at different hours of the day shows certain con-
stant, though small, variations in composition.

Morning milk has the largest percentage of water; midday milk the
smallest.

In 100 Parts. - Morning. Noon. Evening.

Water,

88.46

88.16

88 30

Solids,
Butter,

11.54
2.69

11.84
2 94

11.70
2 82

Milk-sugar,

4.87

4.90

4 87

Casein,

3.15

3.27

3 21

Salts,

0.828

0.725

0.802

So/also, the first- and last-drawn portions of milk have different com-
positions. The last portions have more solids, and especially more fat,
than the earlier portions. A difference of four hours in time of milking
makes this most apparent. It has been attempted to attribute this differ-
ence to the rising of the cream in the udder of the cow, just as occurs in
milk standing in a vessel outside the body. The same differences may,
however, be made out in human milk, where this mechanical explanation
can have but little force. It must not be forgotten that in milking not
only ready-formed milk is withdrawn, but during the act new milk is
secreted, and it is quite warrantable to suppose the cell processes which
result in the production of the solids of the milk are less active in the
pauses than during the act of milking or suckling, when the process is
stimulated from the irritation of the nipples.

624

PHYSIOLOGY OF THE DOMESTIC ANIMALS.
QUANTITATIVE COMPOSITION OP MILK.

•d

4

^

S3

d

a

3

g

^

fl •

J

a

In 1000 Parts.

i

c3

s

8

1

£

tc'Sc

|

5

1

's
S

'5

£*

'o

§

o

•tJ

"35

^

d

"3

I

GC

H

>

OQ

ft

w

W <

Q

P

W

Water, .

851.98

817.40

849.90

853.15

871.80

837.48

803.20

845.62

839.72

857.70

841.80

Solids, .

148.02

182.60

1.50.10

146.85

128.20

162.52

196.80

154.38

160.28

142.30

158.20

Casein,

22.56

41.98

37.64

22.63

42.18

46.50

45.62

32.46

34.87

31.50

28.52

Albumen

3.08

7.60

8.00

8.82

5.15

7.24

7.90

11.14

7.32

9.10

10.20

Butter,

70.88

79.60

51.40

62.80

32.40

57.04

98.80

64.10

68.46

62.20

63.40

Sugar.

45.90

48.42

46.26

46.20

42.12

45.54

37.26

39.70

43.50

32.92

49.68

Salts, .

5.60

5.00

6.80

6.40

6.00

6.20

7.22

6.82

6.14

6.78

6.40

7. THE SECRETION OF MILK. — The mammary glands belong to the
t}Tpe of compound acinous glands, and are constructed on a similar plan
to the salivary glands. The alveoli are lateral expansions at the termi-
nations of the excretory ducts and are formed of a closed membrane
covered, as is also the case with the ducts, with a single layer of cells,
whose appearances vary according to the stage of activity of the glands.
The secretory cells are composed of polyhedral cellular structures
containing a round nucleus and usually a varying number of oily
globules. During the stage of greatest activity the secretory cells
increase in size, the nucleus often is apparently reduplicated, and the
number of oil-globules greatly increased. In active secretion, during
which the oil-globules and cell-contents appear to be extruded, the
remaining cells are much smaller and only contain a single nucleus. The
excretory ducts, which are short, are likewise supplied with flat epithelial
cells and terminate in a canal which in each part of the gland becomes
enlarged, especially at the base of the nipple, where it becomes dilated
to form the so-called milk-cistern, which is connected at the exterior by
several canals which open at the end of the nipple (Fig. 260). This
cistern is lined with a mucous membrane composed of cylindrical epi-
thelial cells (Fig. 261). In the canals and in the nipple the epithelial
coat becomes converted into pavement epithelium. The excretory
canals are abundantly supplied with unstriped muscular fibres, which at
the opening into the nipple become developed into strong circular layers.

It is evident from the composition of milk that its most important
constituents must result from a special cell activity, since neither casein
nor milk-sugar are found in the blood, and, although fat is a constant
constituent of the blood, the amount in comparison with that found in
the milk is almost infinitesimal. It follows, therefore, that the milk, like
the other secretions, cannot be regarded as a transudation, but is a result
of the protoplasmic activity of the epithelial cells of the mammary glands.
But, further, good cows may yield as much as twenty-five kilos of milk
daily, containing as much as 2.5 kilos of albuminoids, fats, and sugar.

MAMMAEY SECEETION.

625

The weight of the milk-gland is not more than 4.8 kilos, with 24.2 per
cent, solids, including all the glandular tissue (vessels, capsule, connective
tissue, etc.), or 1.16 kilos solids. Consequently, the gland must renew
itself 2.09 times dail}* to furnish this amount of organic matter if derived

M

•ms

FIG. 260.— SECTION OP THE UDDER AND NIPPLE OF THE Cow. (ThanTicffer.)

Ma, gland-substance : B, nipple; ms, acini of gland; tj, milk-ducts ; C, milk-cistern ; r, folds in wide
milk-ducts ; z, section of sphincter muscle ; kb, external skin ; ki, narrow milk-duct in the nipple.

solety from the secreting cells. This would, however, require an incred-
ibly rapid cell growth, and we are compelled to assume that although the
growth and disappearance of the secreting cells is of the greatest im-
portance in furnishing the organic constituents of the milk, these sub-
stances are not derived solely from the breaking down of the cells, but

40

626

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

that in their functional activity they, to a certain extent, simply modify
certain substances already existing in the blood and lymph.

As regards the production of the fat of milk, oil-globules may be
seen to collect in the epithelial cells and escape into the excretory ducts,
either by a breaking up of the epithelial cells or by a process of contrac-
tion similar to that observed in the amoeba in the process of ejecting
the residue from digestion. The origin of the fat is, without doubt, in a
process of fatty degeneration of the protoplasmic cell-contents, for the

cw

cw

cw cw

FIG. 261.— DIAGRAM OF THE FORMATION OF THE NIPPLE, AFTER KLAATSH.

(Ellenberger.)

I, cat ; II, mare ; III, woman ; IV, cow. DR, milk-cistern ; CW, cutaneous surface.

amount of fat contained in milk, so far from being increased, is actually
diminished by an increase of fat in the food ; while, further, the fats in
milk do not necessarily coincide in nature with the fats of the food. On
the other hand, an increase in proteid diet increases the amount of fat in
the milk. In microscopic examination of the epithelial cells of the
mammary glands, oil-globules may be actually seen to increase in size
and number until often the protoplasmic contents become almost entirely

MAMMAKY SECKETION. 627

replaced by oil-globules, which entirely agree in their characteristics with
the oil-globules found in milk. So, also, in feeding animals on highly
albuminous diet they may even be seen to increase in weight, while at
the same time more fat is removed in the milk than could be taken in the
food, while the increase in weight indicates that the origin of fat is not
from the adipose tissue of the bod}^. On the other hand, it is impossible
that in the herbivora the fat of the milk should be derived from the break-
ing up of albuminoids in the gland, for the total amount of albuminoids
breaking up in the body is insufficient to furnish the fat removed in the
mammary secretion. Part must, therefore, be derived from the blood.

As regards the casein, this substance is, without doubt, developed
at the expense of the albuminous cell-contents, since it is absent from the
blood, the alkali albuminate being directly derived from the breaking
down of the protoplasm, while the nuclein, which is to be regarded as a
constant component part of the casein, is, without doubt, derived from
the nucleus which disappears in the process of secretion. This con-
version of the albuminous contents into casein is still further evidenced
by the fact that the proportion of casein in the milk depends upon the
degree of perfection of cell activity. Thus, in the earlier stages of
lactation, in the formation of colostrum, the amount of albuminoid
matter contained in the milk is greatly in excess of the amount contained
in milk after lactation has become thoroughly established, while coinci-
dently with the decrease in albumen there is a proportionate increase
in the percentage of casein. A ferment has even been extracted from
the mammary gland which possesses the power of converting albumen
into casein.

The origin of milk-sugar is less clearly established, although it also
seems, without doubt, to originate in changes occurring in the proto-
plasmic contents of the epithelial cells of the mammary gland. For the
amount of sugar in the milk is entirely independent of the amount of
carbohydrate constituents of the food, and remains unchanged even
when animals are fed on a purely meat diet. It would, therefore, appear
that the milk-sugar, casein, and fats are all formed by the direct activitv
of the epithelial cells as a result of the decomposition of their proto-
plasmic contents or their action on the food-constituents in the blood.

The other constituents of the milk, the water and salts, evidently
result from a direct process of transudation from the blood, with the
exception that, without doubt, a certain percentage of the potassium
salts and phosphates, like the specific milk-constituents, originate in the
metamorphosis of the protoplasm of the secretory cells.

The process of secretion of milk may, therefore, be regarded as a
process of molting of the epithelial cells, which undergo decomposition
and discharge the resulting products into the excretory ducts.

628

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

According to the results of Heidenhain, the histological appearance
of the cells of the mammary glands differs according as they are examined
at the commencement or termination of secretion or while the secretion
is at its height.

In the first stage of secretion the cells are flattened and lie against
the walls of the alveoli, of which they may be regarded as forming a
protoplasmic boundary. Their nuclei are at this period spindle-formed,
lying close to the contours of the cells, scarcely detectable on examina-

FIG. 262.— MAMMARY GLAND OP THE DOG IN FIRST STAGE OF SECRETION.

(Heidenhain.)

a, b, section through the centre of two alveoli of the mammary gland of the dog, the epithelial cells seen
in profile ; c, surface view of the epithelial cells.

tion in transverse section. Seen from above, however, the epithelial
cells are found to be polygonal, and each containing a round nucleus.
In the terminal period of secretion the cells may be found to have greatly
increased in size, possess one to three nuclei, and contain in the portions
directed toward the alveoli large numbers of fat-globules. Often the
cells may be seen to undergo subdivision, a part falling free into the
alveolus (Figs. 262, 263, and 264). Between these two extreme periods

FIG. 203.— MAMMARY GLAND OF THE DOG IN SECOND
STAGE OF SECRETION. (Heidenhain.)

FIG. 264.— MAMMARY GLAND OF
THE DOG IN MIDDLE STAGE
OF SECRETION. (Heidenhain.)

various intermediary stages may be recognized. From these histological
changes Heidenhain concludes that in the formation of colostrum the
epithelial cells are not dissolved, and that, therefore, the colostrum
corpuscles are not fatty, degenerated epithelial cells, but that only the
free end of the epithelial cells with their contained oil-globules is liber-
ated ; that the broken-down protoplasm becomes dissolved in the milk,
and the fat-globules are thus set free.

MAMMARY SECEETION. 629

As regards the influence on the mammary secretion of the nervous
system, while certain data have been clearly established (thus, the
influence of the emotions on the mammary secretion is well known), the
process is by no means so thoroughly understood as is the case as regards
the salivary secretion.

It is well known that the maintenance of the milk secretion is closely
dependent upon periodic emptying, whether by suckling or milking, of
the milk-gland, and the question arises, What connection is there between
this emptying of the gland and the act of secretion? Does the reduced
internal pressure which follows emptying the gland start the secretion
anew, or does the act of suckling or milking stimulate the secretion
reflexly ? It is clear that when the milk-ducts and cistern are filled with
fluid the activity of secretion must be reduced, and when the gland is
emptied by milking it again fills itself, at first rapidly, and then more
and more slowly ; but that this augmented secretion is not due solely to
decreased internal pressure is evident from the following facts : The
cavities of the milk-gland of the cow are capable of containing about
three thousand cubic centimeters of fluid, — a quantity very much less
than may be withdrawn from the milk-gland in a single milking, so that
evidentty during milking renewed secretion is excited even before the
gland is emptied, and, as is well known, frequent milking increases the
total milk secreted. It would, therefore, appear that this renewed
secretion is produced reflexly from stimulation of the nipple in a manner
to be described directly.

The first stimulus to the activity of the mammary glands is found
usually coincident with the birth of young, although the gland even for
several days before birth is the seat of a more or less active secretion.
In this way the connection between the generative organs and the
mammary glands is clearly indicated.

The influence of the nervous system on the secretion of milk has
been especially studied by Rohrig.

The mammary gland is innervated in quadrupeds (in addition to
the ileo-inguinal nerve distributed to the skin) by the external spermatic
nerve. This nerve originates from the lumbar portion of the spinal cord
and passes out between the greater and lesser psoas muscles, dividing
in the pelvis into three branches, of which one is distributed to the
abdominal muscles, while the other two leave the abdominal cavity
through the femoral ring accompanying the crural artery, and then,
following the course of the external pudic artery, are distributed to the
mammary gland. These nerves may be spoken of as the middle and
inferior branches of the external spermatic nerve. The middle branch
divides at the base of the gland into three twigs: first, a small filament
which follows the course of the pudic artery and is lost in its walls ;

630 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

second, a much larger branch, termed the papillary branch, which is
distributed to the nipple; third, one, or occasionally two, glandular
branches, which are supplied to the walls of the milk-ducts and the
cistern.

According to Rohrig, section of the papillary branch produces no
change in the milk secretion, but simply causes relaxation of the nipple.
Irritation of the peripheral end of this nerve causes erection of the
nipple without change of glandular secretion, while irritation of the cen-
tral end of this nerve produces considerable increase in the secretion.

Section of the glandular branch, on the other hand, produces slow-
ing of the amount of secretion by causing relaxation of the walls of the
duct, while stimulation of this nerve may increase twenty-fold the secre-
tion of milk by causing contraction of the milk-ducts and consequent
discharge of their contents.

Section of the inferior branch produces great increase in the amount
of milk secreted, while the stimulation of the peripheral end of this
nerve produces arrest of secretion.

The explanation of these two classes of phenomena are understood
through a study of the character of this nerve. The median branch is
a compound nerve composed of both sensory and motor fibres, the latter
being especially found in the papillary branch distributed to the nipple,
while the glandular branch is almost solely motor. When the papillary
branch is stimulated it produces, by a reflex action, the contraction of
the muscular fibres of the excretory ducts, and so causes discharge of
their contents, while it also, in all probability, acts through the inferior
branch, and by it also increases the amount of milk formed in a manner
to be referred to directly.

When the glandular branch is stimulated the muscular fibres of the
ducts contract, and, although no more milk may be actually formed,
there is, nevertheless, an increase in the amount poured out through
the contraction of the walls of the milk-ducts.

On the other hand, the inferior branch is a vaso-motor nerve. When
its peripheral termination is stimulated, the milk secretion is arrested
through the constriction of the blood-vessels supplied to this gland.

On the other hand, when it is divided, the blood-vessels become
greatly relaxed, more blood passes through the organ, and its activity is
largely increased.

Whether any of these processes are associated with the action of
true secretoiy nerves is not known, but from analogy, from what we have
seen in the case of the salivary gland, it may be assumed that such is the
case.

The explanation of the connection long known between the mechan-
ical irritation of the nipple, as in suckling and milking, and the increased

MAMMAKY SECEETION. 631

secretion of the gland is thus evidently to be found in reflex action, the
afferent impulses passing through the sensory nerves of the nipple, the
secretory impulses passing through the inferior branch and the glandular
branch of this nerve.

It is thus seen that, as far as we know, the mammary secretion is
dependent upon the amount of blood passing through the glands.
Changes in the general blood pressure, by modifying the blood supply
of the mammary gland, also influence the amount of milk secreted.

Thus, various substances which act as stimuli to the vaso-motor
centre, and so produce increase of blood pressure, produce likewise an
increase in the amount of milk secreted. Strychnine in small amount,
digitalis, caffeine, and pilocarpine are all galactagogues and probably act
in this way, while through reduction of blood pressure, as by means of
chloral, the milk secretion may be considerably reduced.

8. MILK INSPECTION AND ANALYSIS. — Good cows' milk is white, with a faint
yellowish tint, and only bluish when diluted. If a drop of good milk is placed on
the thumb-nail it retains its shape instead of spreading gut, as occurs when diluted
or unhealthy. Milk is most apt to be adulterated with water, which within cer-
tain limits may be detected by determination of the specific gravity. Unskimmed
milk possesses a higher specific gravity than that of the skimmed milk from the
effect of the removal of the fats, so that a milk from which all the cream has been
removed might, if dependence be placed upon the specific gravity alone, be con-
sidered as a better specimen than the pure milk. The average specific gravity of
normal cows' milk may be placed at about 1030 at 60° F. ; if diluted with half its
volume of water the specific gravity will fall to about 1014 or 1016. As a conse-
quence, by the determination of specific gravity a general idea may be obtained
as to how much water has been added to diluted milk. The following table may
serve to assist in this determination : —

With With

Skimtned Milk. Unskimmed Milk.
A specific gravity of 1087 to 1033 or 1033 to 1029 indicates a pure milk.

1033 to 1029 or 1029 to 1026 " milk with 10 per cent, water.

" " 1029 to 1026 or 1026 to 1023 " " " 20 " "

" " 1026 to 1023 or 1023 to 1020 " " " 30 " "

" 1023 to 1020 or 1020 to 1017 " " " 40 " "

The instrument by which the specific gravity of milk is determined is usually
termed the lactometer, and simply consists of a hydrometer with a scale running
from 1000, which is the specific gravity of distilled water and is marked zero on
the scale, to 1034, marked 120, which is the specific gravity of a rich sample of
milk. In using the lactometer special attention must be paid to the physical
characteristics of the milk, since a little attention would readily detect skimmed
inilk from unskimmed, although their specific gravity might be the same. In
milk rich in cream where the specific gravity might be abnormally low, its
physical appearance and the fact that it clings to the instrument would enable it
to be recognized, while watered or skimmed milk is bluish and does not cling to
the lactometer ; so, if a sample of milk should read above 110 on the lactometer
without manifestly being full-bodied, it would be only fair to presume that a
portion of the cream had been removed. Milk diluted with spring-water may be
recognized by the detection of nitrates in the milk. Sulphuric acid is added to
the milk, the precipitate filtered off, the filtrate distilled, and nitric acid looked for
in the distillate. This may be readily accomplished by converting, through milk-
sugar, the nitric into nitrous acid. A few drops of pure H2SO4, potassium iodide
solution, and boiled starch solution are then added to the distillate; if nitrous acid
is present iodine is liberated from the potassium iodide solution and the starch is
colored blue.

632

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The cream maybe roughly determined in milk by placing it in a tall cylindrical
glass, graduated into one hundred parts The milk should be allowed to stand in
this creamometer for twenty -four hours and the volume of cream separated on the
surface may then be determined, one gramme of cream equaling about 0.2
grammes of fat. Good cows' milk should separate from ten to fifteen volumes of
cream. This method is, however, not thorouhgly reliable, since different speci-
mens of milk will throw up their cream with different degrees of readiness. The
second method, and a much more reliable one, of determining the amount of fat
or cream present is by means of the lactoscope. This instrument consists of a
little cup with two of its sides formed of two parallel plates of glass, distant from
each other half a centimeter. For applying this test, in addition to such a glass,
a jar graduated to one hundred cubic centimeters and a pipette of three cubic
centimeters are needed. Three cubic centimeters of milk are taken and shaken
up well with one hundred cubic centimeters water, and the mixture then placed
in the glass cup with the parallel sides and a lighted stearin candle placed one meter
from it in a dark room. If at the first experiment the contour of the flame can be
seen, the milk is poured back into the large measure and a further measured quantity
of undiluted milk added until the contour of the candle-flame is entirely obscured.
The percentage of fat is then determined by the following formula : If x equal
the percentage of fat and n the number of cubic centimeters of milk required, then

»).» o

x equals _ "^ -f- 0.23. Thus, if three cubic centimeters of milk were required to

obscure the light, the formula would read : x =

23.2

1.23, or x = 1. 96, the per

cent, of fat in the milk. Six cubic centimeters of pure cows' milk with one hun-
dred cubic centimeters water should form a mixture which will obscure the candle-
flame ; if more milk is required, then the milk has been diluted. Thus, twelve
cubic centimeters indicate 50 per cent, water, and eight cubic centimeters about
30 per cent, water. The following table gives the percentages of fat in the milk
when the candle-flame is obscured by different amounts of milk in Vogel's galacto-
scope : —

3 cubic centimeters of milk indicate 7.96 per cent, of fat.

3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
11.0
12.0
13.0
14.0

6.03

5.38 "

4.87

4.-15

4.09

S.fcO

3.54

3.32

3.13

296

2.80

2.77

2.55

2.43

2.16

2.01

1.86

Another ready method of estimating the fat in milk is by means of Marchand's
lactobutyrometer. As improved by Caldwell and Parr (Amer. Chem. Journ., Nov.
1885), this method is performed as follows : —

The instrument employed consists of a thick glass tube, open at each end,
with a stem six cubic centimeters in diameter and twenty-three centimeters long,
graduated in ^ cubic centimeter, and a bulb about eight centimeters in length,
and of such a capacity that in passing from the lowest graduation on the stem
to the inner end of the stopper in the lower mouth one passes from five to thirty-
three cubic centimeters. Then the ether-fat solution will always come within the
range of the graduation on the stem. Closing the lower mouth with a good cork,
ten cubic centimeters of the well-mixed sample of milk are delivered into the
well-dried tube from a pipette, then eight cubic centimeters of ether (Squibb's
stronger) and two cubic centimeters of 80 per cent, alcohol. Close the smaller
mouth of the tube with a cork and mix the liquids by thorough shaking (not
violently nor prolonged). Both corks should be held in place by the fingers
during this operation, and the upper one should be once or twice carefully

MAMMARY SECRETION. 633

removed to relieve the pressure within, otherwise it is apt to be forced out, with
consequent loss of material. Lay the tube on its side for a few minutes and then
shake it again ; add one cubic centimeter of ordinary ammonia diluted with about
its volume of water, and mix as before by shaking ; then add ten cubic centimeters
of 80 per cent, alcohol and mix again thoroughly by moderate shaking, holding
the tube from time to time in an inverted position.

Now, put the tube in water kept at 40° to 45° until the ether-fat solution sepa-
rates ; this separation may be hastened by transferring the tube to cold water
after it has stood in the warm water for a few minutes, and then returning it to
the warm water. Finally, transfer the tube to water at 20° C., and as the level of
the liquid falls in the stem by contraction of the main body of it in the bulb,
gently tap the side of the tube below the ether-fat solution to dislodge any flakes
of solid matter that may adhere to the side. The readings are to be taken from
the lowest part of the surface meniscus to the line of separation between the ether-
fat solution and the liquid below it.

The following table gives the percentages of fat corresponding to each tenth
of a cubic centimeter of ether-fat solution down to one cubic centimeter, and for
each twentieth of a cubic centimeter thereafter : —

Reading. Per Cent, of Fat. Reading. Per Cent, of Fat.

3.0 1. 13.5 3.51

4.0 1.23 14.0 3.63

50 . 1.47 14.5 3.75

6.0. ... . 1.71 15.0. . . . 3.87

7.0 1.95 15.5 4.00

8.0 2.19 16.0 4.13

9.0 2.43 16.5 4.26

10.0 2.67 17.0. . . . . .4.39

10.5 2.79 17.5. . . . 4.52

11.0 2.91 18.0 4.65

11.5 3.03 18.5 . 4.78

12.0 3.15 19.0. . 5.01

125 3.27 19.5 5.14

13.0 3.39 20.0 5.27

This method has been applied with fairly satisfactory results to the milk of a
herd of cows receiving bran and cotton-seed meal in their rations, the objection
to the unreliability of this method under these circumstances being overcome by
the use of the ammonia. Various other forms of lactoscope are used, depending
on the property that the opacity of milk varies with and is proportional to the
amounts of fats present. Skimmed milk contains smaller fat-globules than intact
milk, and this causes a greater cloudiness in proportion to the amount of fat pres-
ent than the large ones, and, hence, the application of this test to skimmed milk
would give a higher percentage of fat than is actually present.

For the quantitative estimation of the different milk-constituents the following
methods, taken from Charles's "Physiological and Pathological Chemistry," are
the simplest and require the least apparatus : —

1. The Solids. — (j.) To ten grammes dry sand or powdered gypsum add five
cubic centimeters milk, then dry the mixture for a long time at 100° until the
weight is constant. The increase in weight is equal to the solids in five cubic
centimeters milk. Suppose this to be =05 gramme, then one hundred cubic
centimeters rnilk contain ten grammes, or 10 per cent, solids (Baumhauer).

Instead of five cubic centimeters, ten grammes of milk and twenty grammes
of dry sea-sand may be weighed in a tared capsule of about fifty cubic centimeters,
and evaporated at 100° until the weight is constant. When quite cold, the cap-
sule, with its contents, is weighed in a desiccator over sulphuric acid.

(ij.) Place a little milk in a platinum capsule, and, having weighed it, add a
few drops of alcohol or acetic acid ; evaporate over a water-bath, dividing the
coagulum against the sides of the dish, and dry it at 100° to 110° until the weight
is constant. It is generally completed in six hours (Gerber). Cover carefully
before weighing, as the residue is very hygroscopic.

The total solids should not, as a rule, be much less than 11.5 per cent.; cows'
milk, for example, varies between 10.5 and 15 per cent.; less than this indicates
dilution.

2. The Butter.— (j.) Shake the milk well, and to twenty cubic centimeters of
it add twenty cubic centimeters of a 10 per cent, caustic potash solution and
then some ether (sixty to one hundred cubic centimeters), and agitate vigorously

634: PHYSIOLOGY OF THE DOMESTIC ANIMALS.

for some time ; on standing, the ethereal solution of the liberated fat rises to the
surface and is to be carefully decanted into a weighed porcelain dish. Some more
ether is to be added to the alkaline milk, and after vigorous agitation it also is to
be transferred, as before, to the capsule. The same process may be repeated
several times if necessary. The ethereal extract is now evaporated over a water-
bath, and after having been dried in an air-bath at 110° the weight of the residue
is to be ascertained ; this multiplied by 5 gives the percentage. With cows' milk
it varies between 2 and 5 per cent., but the normal minimum for fats is about 2.75
(Cameron).

3. The Casein and Albumen. — (j.) (a) Dilute twenty cubic centimeters milk
with four hundred cubic centimeters water, and treat the mixture with very dilute
acetic acid, added drop by drop, until a flocculent precipitate begins to appear.
Now pass a current of carbonic acid gas through the fluid for fifteen to thirty
minutes and lay aside for one or two days. Collect the precipitated casein on a
weighed filter, wash it with spirit, and then with ether until a drop of the wash-
ings leaves no fatty stain on paper ; dry at 100° and weigh. Subtract the weight
of the filter, and the difference multiplied by 5 gives the percentage of casein. In
human milk, precipitate the casein by saturating with magnesic sulphate.

(6) The filtrate from the casein precipitate is to be concentrated to a small
bulk over a water-bath and an acetic acid tannin solution added so long as any
precipitate occurs ; after the precipitate has settled, collect it on a weighed filter,
where it is to be washed with dilute spirit until the filtrate gives no blue coloration
with ferric chloride (indicating absence of tannin) ; dry now at 100° and weigh.
The weight multiplied by 5 gives the percentage of albumen.

In cows' milk the casein varies between 3.3 and 6 per cent., and the other
albumens from 0.3 to 0.4 per cent. In diseased milk the casein may be as low as
0.2 per cent., and the other albumens as high as 10 per cent.

(ij.) (#) Ten cubic centimeters milk are diluted with one hundred cubic cen-
timeters distilled water and well mixed ; a copper solution, made by dissolving
sixty-three and five-tenths grammes of cupric sulphate in one liter of water, is
then added slowly with stirring until the coagulum begins to settle quickly. The
whole mixture, together with half the cupric sulphate solution already employed,
is then added to some potash solution (fifty grammes of potash to the liter), and
after a short interval the clear fluid is filtered off through a filter dried at 110° C.;
the precipitate is washed until the washings amount to two hundred and fifty
cubic centimeters, and the sugar is to be estimated in this subsequently.

(&) The coagulum on the filter is next treated with absolute alcohol, slowly
dried, and extracted with ether; the ethereal and alcoholic extracts are then to be
distilled, and the fatty residue dried and weighed. The coagulum, after having
been dried at 125°, is weighed, then ignited, the ash deducted, and the difference
taken as pure albuminoid (Ritthausen).

4. The Sugar. — (j) Take twenty-five grammes of milk, acidify with hydro-
chloric acid, boil, and filter, washing the coagulum with water; to convert the
milk-sugar into glucose, boil the filtrate and washings for an hour or so in a flask,
to the mouth of which a long tube has been attached. When the liquid cools,
make its volume up to two hundred cubic centimeters and determine the sugar
by Fehling's method, measuring twenty cubic centimeters Fehling's solution into
a flask, diluting with eighty cubic centimeters water, and to the boiling mixture
add the diluted filtrate from a Mohr's burette until the copper is entirely reduced.

(ij.) This sugar determination may be readily effected by the polariscope.
Measure forty cubic centimeters milk into a flask of one hundred cubic centimeters
capacity, add some carbonate of sodium if the milk is not alkaline, and then
twenty cubic centimeters moderately concentrated solution of neutral acetate of
lead, and shake well ; having next fitted the neck of the flask to a long glass tube
or to the condenser of a Liebig's still, boil it over a small flame ; then filter, and
test the filtrate with the polariscope. With a one-decimeter tube the percentage
of sugar is obtained by multiplying the rotation by 1.44.

*For other ready methods of milk analysis and for the detection of foreign substances

f. J. ft-tCf /«-tM /V«//f'U/C, -IOCXJ, i i i j wj M U.. U, c». -ntr , I . ^ * . K7UW1 i<. -*i »fir, i . \^ ri/orr*tisic<(, ,/ i rrr i /&., .rVMl 11. 1OOI5 U. J.W ,

Morse APigott, Jft., April, 1887, p. 108 ; F. A. Woll, /&., February, 1887. p. 60 ; Morse and Burton,
J6., June, 1887, p. 222 ; A, July, 1888, p. 322.

SECTION X.

THE RENAL SECRETION.

THE blood not only bears to the different tissues the substances
required for their nutrition, but also removes from the tissues the
different waste products which result from their Ararious metabolic
processes. In the lungs, part of these oxidation products, especially of
the carbon compounds, are removed, while the results of nitrogenous
waste largely pass through the lungs to be carried through the aorta
from the left ventricle to the kidneys, whose function is to remove these
nitrogenous excrementitious substances, together with the carbon com-
pounds which have passed the lungs, with various salts and water. The
product of this functional activity of the kidneys is the urine, which is
a pure excretion, since all its constituents are waste products which
must be removed from the organism.

1. THE PHYSICAL AND CHEMICAL PROPERTIES OF URINE. — Urine is
in general a thin, yellowish colored, transparent fluid (the depth of color
depending on the concentration) of a salty taste and peculiar aromatic
odor, due to the presence of various volatile acids. Its reaction may
be faintly acid, neutral, or alkaline : it rotates the plane of polarized
light to the left. The reaction in the carnivora and in fasting or
suckling herbivora is acid ; in the herbivora and omnivora, when on
vegetable diet, it is alkaline. The explanation of the production of an
acid renal secretion from the alkaline blood is to be attributed to a
specific property of the renal epithelium similar to that possessed by the
gastric mucous membrane. The more alkaline the blood, the less acid
the urine ; hence the great alkalinity of the blood of herbivora causes
the urine to have an alkaline reaction. For although sulphuric acid is
formed from the decomposition of vegetable just as it is from animal
albumen, vegetable foods contain large amounts of organic salts which
break up into alkaline carbonates, and so neutralize the sulphuric acid.
These salts are absent from the food of carnivora, hence the acids are
less perfectly neutralized. It is, therefore, the form of diet which, by
modifying the alkalinity of the blood, determines the reaction of
the urine. The specific gravity of urine varies between 1005 and 1050.
When exposed to the air, the urea undergoes decomposition and is
transformed into ammonium carbonate ; a part of the ammonia then
combines with magnesium phosphate, and ammonium-magnesium phos-

(635)

636

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

phates, together with calcium phosphate, are deposited as a crystalline
precipitate. This process is known as ammoniacal fermentation, and is
due to the action of ferments derived from the atmosphere. In some
animals the urine always deposits mucus derived from the membranes
over which it passes. Its quantity is subject to great variations.

The most important constituents of the urine are water, salts, gases,
and certain specific constituents. Among the salts, potassium com-
pounds are more abundant than sodium. Lime and magnesium are in
varying amounts. Of the acids H2SO4 and P206 are most abundant.
C02 in combination is found in the urine of the herbivora. When
NaCi forms part of the diet, this salt is also a large constituent of
urine.

The following are the specific constituents of urine : —

1. The decomposition products of the albuminoids, as urea, uric
acid, hippuric acid, kreatin and kreatinin, and the combinations of
H2S04 with indol and phenol.

2. Coloring matters, of which urobilin is the best known.

3. Aromatic bodies which give the urine its peculiar odor.
The gases C02, N, and O are found free in the urine.

As regards quantitative composition there is great inconstancy.

Water, .
Organic matter,
Inorganic matter, .

Horse.
90.
5.5
4.5

Ox.
91.

5.

4.

Sheep.

89.

8.

3.

Hog.

98.
0.5
1.5

COMPOSITION OF THE URINE (BOUSSINGAULT).

Urea, .

Horse (1).
. 31 0

Cow (2).
18 5

Pig (3).
4 9

Potass, hippurate,
Alkaline lactates,
Potass, bicarb.,
Mag. carb.,

. 4.7
. 20.1
. 15.5
. 4.2

16.5
17.2
16.1
4.7

0.0

10.7
09

Calcium carb.,
Potass, sul ph.,
Sodium chloride,
Silica, .
Phosphates,
Water and undetermined
stances, .

. 10.8
. 1.2
. 0.7
. 1.0
. 0.0
sub-
. 910.0

0.6
3.6
1.5
traces
0.0

921.3

traces
2.0
1.3

0.1
1.0

979.1

1000.0 1000.0

(1) Diet of oats and clover-grass.

(2) Diet of hay and potatoes.

(3) Diet of cooked potatoes.

1000.0

The water, K, Na, Ca, and Mg compounds are derived directly
from the blood, and in greater part directly from the food and drink, and
in fasting animals from waste of tissues. H2SO4 originates in oxidation
of the sulphur compounds in food ; the phosphates from the oxidation
of albuminoids of food and tissues ; carbonates, partly directly from

KENAL SECRETION. 637

food and drink, partly from modifications of the vegetable acid com-
pounds in vegetable foods.

The urea and uric acid are the nitrogenous end products of the
decomposition of the albuminoids of food and of the tissues.

Kreatin and kreatinin are closely dependent on the animal matter
taken as food, since, even in muscle, kreat in is formed as a modification
of its own albuminoid constituents.

Hippuric acid is a combination of glycochol with benzoic acid, and
originates, to a great extent, in the constituents of vegetable foods, the
cuticular substance of which develops the benzoic acid.

Phenol is derived from the decomposition of albuminoids in the
intestine, and in the excretory ducts of the kidney unites with H3S04.

Indican originates in indol.

Many other substances are accidentally present in urine, such as
aromatic constituents of food, alkaloids, metals, bile coloring-matter, etc.

The quantity of the urine is dependent on the amount of water
taken in food and drink, on the diminution of excretion of water by
other organs, especially the skin, on the amount of excretory products,
especially urea, and on the amount of substances taken in food, e.g.,
salts, which must be excreted.

It is to be noted that all the water taken as food is not excreted
through the kidneys, but that part is removed by the lungs, skin, and
intestinal canal. The proportion of water removed through these
different organs varies in different species : —

In the Urine. Through the Lungs.
In herbivora, 20 per cent, of water is removed; 80 per cent.

In omnivora, 60 " " " 40 "

In carnivora, 85 " " " 15 "

Various conditions maj^, however, modify these proportions.

In fasting and suckling animals of both the herbivora and carnivora
the urine has the same characters, since in them the tissues alone are
undergoing waste.

There is the greatest difference between the urine of carnivora and
herbivora.

In carnivora the urine is smaller in amount, is acid, clear, and richer
in solids, especially urea, uric acid, and kreatin; sodium salts, sulphates,
and phosphates are in excess, and the urine has a higher specific gravit}'.
Phenol and sulphuric acid only are present in small amount and hippuric
acid absent when on a purely flesh diet.

In herbivora it is larger in amount, is turbidr contains few solids,
hippuric acid replaces uric acid, and the reaction is alkaline; urea is
present only in small amount. Potassium salts are in excess unless
sodium chloride is given with the food. Lime and magnesium, united
with C0a, are in abundance, phosphates often absent , sulphates abundant.

638

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

That this difference is dependent only on differences in diet is proved
by the fact that during fasting the urine of the herbivora agrees in all
its characteristics with the urine of the carnivora. Under such circum-
stances the herbivora are not consuming vegetable matters, but living at
the expense of their own tissues, are then practically carnivorous, and
their urine becomes acid, clear, and rich in urea and phosphatic salts.

The Urine of the Horse is cloudy and has an alkaline reaction. Its
specific gravity varies from 1016 to 1060, 1050 being about the average.
It contains a large percentage of mucin, and is therefore viscid and may
be drawn into threads. It becomes brown on exposure to the air, deposits
CaC02, and a pellicle forms on it, showing iridescent colors.

The characteristics of normal horses' urine depend largely on the
mode of feeding. When fed exclusively on hay and straw the urine is
always alkaline, while when oats constitute the principal food it is
secreted in small quantity, is turbid, and of acid reaction, and more
viscid than alkaline. The influence of the diet on the amount of solids
in the urine is shown in the following table : —

SOLIDS IN URINE.

In 100 C. C.

Total.

Hay.

Oats.

Wheat-
Straw.

Kilos.

Kilos.

Grammes.

Grammes.

8 kilos.

2 kilos.

22.31

5.04

11.2

566.6

7

2

1 kilo.

26.33

4.72

11.2

529.4

6

4

21.36

4.99

10.3

511.8

4

4

2 kilos.

27.55

4.66

10.2

477.0

4

6

.

23.73

4.53

10.4

460.7

1

6

2.6"

24.60

6.03

5.7

346.1

A high percentage of calcium salts is characteristic of horses' urine.
Of the amount contained in the food, from one-third to one-half passes
into the urine, while in the ruminant, especially in the sheep, not more
than 5 per cent, passes. In the case of potassium the conditions are
just reversed. In the sheep 95 per cent, of the potassium in the food
passes into the urine, while in the horse at most 66 per cent, appears.
The following table gives the percentage of inorganic constituents in
one hundred parts of the ash of horses' urine : —

Potassium, «. , « . . . .36.85 per cent.

Sodium, 3.71

Calcium, 21.92

Magnesium, . 4.41

Phosphoric acid, . . . . . ....

Sulphuric acid, . . . . . .17.16

Chlorine 15.36

Silicic acid, 0.32

KENAL SECKETION. 639

Horses' urine contains urea and hippuric acid in inverse proportions.
When one increases the other decreases, the amount of the latter depend-
ing on the amount of green forage or hay or straw, the former on the
amount of oats, grains, roots, etc. The percentage of urea in ordinary
feeding varies from 2.5 to 4.0 per cent.

Very large amounts of aromatic sulphur compounds are present,
especially of phenol and indican. The former, with hippuric acid, causes
the peculiar odor ; the latter, the colors seen in the film which forms
when exposed to the atmosphere. Brenzcatechin is also present and is
the cause of the brown color which forms on standing.

CaC03 is the principal salt, and is rapidly deposited as a sediment.
Sulphur compounds are found in varying amounts. Phosphates, except
in abundant feeding with grains, are only present in traces. The amount
of urine is only about five to six liters daily, evacuated in three to four
portions, since a large amount of water is lost through the skin in
perspiration.

The Urine of the Ox. — The amount of urine depends not only upon
the amount of water taken, but especially on the amount of nitrogenous
food. Thus, when the diet has been poor in nitrogen, the amount of
urine passed daily will vary from 9.7 to 12.6 kilos, and when a richer
nitrogenous diet is given the amount will be increased to from 16.3 to
16.8 kilos. This is, without doubt, partly to be attributed to the larger
amount of water required in a rich, nitrogenous diet. The evacuation
of the urine occurs from eight to ten times daily, averaging about one
kilo each time. The character of the food exerts the greatest influence
on the reaction of the urine. Fodder rich in alkaline carbonates or com-
pounds of the organic vegetable acids occasions an alkaline reaction of
the urine. The amount of carbonates in the solids of the urine is
directly in proportion to its alkalinity. Carbon dioxide is especially
abundant when fed on beets, clover, hay, or bean-straw, when it may
amount to 10 or 12 per cent. When fed with oat-straw or barle3T-straw,
the carbon dioxide sinks to from 3 to 6 per cent. Exclusive feeding with
wheat-straw is said to cause an acid reaction of the urine on account of
the poverty of carbonates and vegetable acids. The total amount of
solids in the urine averages about 6.8 per cent., composed of —

C, . . . ... . . 27.8 to 53.1 per cent.

H, . . •„•*•. . . . 3.5 to 6.9

N, . . . . . . . . 8.9 to 33.6

O, . . . < . . . . . 15.6 to 50.2 "

The quantity and quality of the organic matter in the urine varies
greatly according to the food, varying between 4.2 to 11.3 per cent., and
is especially dependent upon the digestible, nitrogenous food-stuffs. The
non-nitrogenous food-stuffs are without influence on the organic urine

640 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

constituents. Uric and hippuric acids are the representatives of the
nitrogenous organic constituents. Uric acid and hippuric acid are found
in proportions which are governed by the character of the diet in the
same way as in the case of the horse. The mineral constituents are like-
wise dependent on the food, potassium and lime combinations being
especially abundant. The urine of the ox is clear, yellowish, or greenish,
and possesses a peculiar, musky odor. Its specific gravity varies from
1020 to 1030, depending on the amount of water in the food. It is
always poorer in solids than the urine of the horse. It also contains less
sulphuric acid compounds, especially of the aromatic group, than horses'
urine. The phosphates are entirely absent, or present only in traces.

The Urine of the Sheep and Goat is similar to that of the ox, but
shows great variation in the salts derived from the food. Its specific
gravity varies from 1006 to 1015 ; the amount from five hundred to eight
hundred and fifty cubic centimeters daily. Urea and hippuric acid are
present in the proportion of about two to three, the hippuric, contrary
to what is the case in the horse, being more abundant when on a diet of
young hay rich in proteids.

The Urine of the Pig is clear, yellowish, with a faint alkaline reac-
tion; specific gravity, 1010 to 1015. It contains urea, but rarely uric or
hippuric acids. The salts depend on the character of food. In general,
the urine resembles that of carnivora.

The Urine of the Dog is deep yellow in color, acid reaction ; specific
gravity, 1050 when fed on meat. It is rich in urea, but contains but little
uric acid. Kreatin and indican are present, but no phenol. Mg salts are
in larger amount than Ca salts, while the chlorides are scanty ; sulphates
and phosphates abundant. It readily undergoes ammoniacal fermenta-
tions (from urea) and deposits phosphates. Its composition and character
likewise vaiy greatly with the nature of the food.*

2. THE MECHANISM OF RENAL SECRETION. — The substances which
exist in the urine in a state of solution also exist in the blood, and the
process of secretion of the urine is, therefore, largely a process of
mere infiltration. Nevertheless, certain constituents of the urine are
evidently manufactured in the kidney, since their presence has not yet
been detected in the blood. Renal secretion is thus possessed of two
factors, — a phjTsical process of filtration and a process of true secretion
dependent upon the activity of the renal epithelium.

The mechanism of the renal secretion is, to a certain extent, capable
of explanation by the study of the structure of the kidney. The kidney
is composed of a series of fine tubules, which, starting from the hilum

*For further detail s as to the composition of the urine of the domestic animals under
different forms of diet the reader is referred to the " Encyclopaedic der Gesammten Thier-
heilkunde," Bd. iv, p. 202.

EEXAL SECRETION.

641

in the medullary portion of the kidney, form, by frequent subdivisions,
a series of straight, branching canals, the so-called urinary tubules.
After frequent subdivision each branch terminates in a looped tubule,
which, after undergoing various convolutions in the cortical portion of
the kidney, terminates in a bladder-like expansion. In each of these
expansions enters a small branch of the renal artery, the vas afferens,
which undergoes division into a bunch of capillaries which is so placed
as to be surrounded by a double layer of the bladder-like expansion of

FIG. 265.— NAKED-EYE APPEARANCES OP THE KIDNEY OF MAN, AFTER
TYSON AND HENLE. (Landois.)

1, cortex; If, medullary rays; 1", labyrinth; 2, medulla; 2f, papillary portion of the medulla; 2'f,
boundary layer of the medulla; 3, transverse section of tubules in boundary layer; 4, fat of renal sinus;
5, artery : *, transversely coursing medullary rays ; A, branch of renal artery ; C, renal calyx ; U, ureter.

the tubules. The relation between this bunch of vessels and the expan-
sion of the tubules is similar to what would be expected if a tip of the
finger of a glove was inverted from the outside. The collection of capil-
laries is, therefore, in contact with the external layer of the tubule, and
is surrounded by a space which is in direct communication with the in-
terior of these tubes. After having undergone subdivision into capilla-
ries in this expansion of the tubules, the efferent vessel, which collects

41

642

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the blood which has passed through this series of capillaries, again un-
dergoes subdivision into a second net-work of capillaries distributed
around the urinary tubules. In the glomerulus is represented the filtra-
tion apparatus, in which, through the influence of blood pressure, the
substances held in solution in the blood-serum may be removed from the
blood and forced into the interior of the commencement of the urinary
tubules. The conditions are, therefore, evidently different here, where
transudations directly enter into the excretory ducts, from what holds in
the case of other glands, where the transudations simply pass into lymph
and require some other force for their transference to the secretion.

Cortex.

Boundary or
marginal zone.

Papillary zone.

FIG. 266.— LONGITUDINAL SECTION ov A MAI/PIGHIAN PYRAMID. (Landois.)

PF, pyramids of Ferrein ; RA, branch of renal artery ; RV, lumen of a renal vein receiving an inter-
lobular vein ; VR, vasa recta; PA, apex of a renal papilla; b b embrace the bases of the renal lobules.

That this separation of the constituents of the blood through the glom-
eruli of the kidney is actually dependent upon the blood pressure is
shown by the fact that if the blood pressure be reduced below fifty milli-
meters of mercury secretion ceases, while if it be increased the secretion
is correspondingly augmented. The contrast between this fact and the
secretion of saliva is, therefore, very striking.

If, however, pressure is increased by venous obstruction, then, in-
stead of an increased secretion, the reverse takes place. That this does
not contradict the filtration hypothesis is explainable by the fact that ob-
struction of the veins increases the pressure in the capillaries, and these

RENAL SECRETION.

643

so expand in the unyielding capsule of the kidney that the urinary
tubules are completely compressed, and nitration is, of course, at once
arrested.

Various conditions may modify the blood pressure in the kidneys.
Thus, for example, the local blood pressure may be increased by- general

Sub-capsul ar layer
without Malpi-
ghian corpuscles.

12. First part of col-
lecting tube.

11. Distal convoluted
tubule.

A. CORTEX.

10. Irregular tubule.

4. Spiral tube

13. Straight part of
collecting tube.

9. Wavy part of as-
cending limb of
Henle's loop.

Inner stratum of cor-
tex without Mal-
pighian corpuscles

7 and 8. Ascending
limb of Henle's
loop tube.

3. Proximal convo-
luted tubule.

9. Wavy part of as-
cending limb.

2. Constriction or
neck.

4. Spiral tubule.

1. Malpighian tuft
surrounded by
Bowman's capsule.

8. Spiral part of as-
cending limb of
Henle's loop.

B. BOUNDARY ZONE.
5. Descending limb
of Henle's loop
tube.

I

6. Henle's loop.

C. PAPILLARY ZONE.

FIG. 267.— DIAGRAM OF THE COURSE OF Two URINIFEROUS TUBULES,
AFTER KLEIN AND NOBLE-SMITH. (Landois.)

increase of blood pressure or by a relaxation of the renal arter}7, accom-
panied by the constriction of other vascular areas, which, while dimin-
ishing the pressure in the renal artery itself, increases the pressure in its
capillaries. Of course, pressure w&y be reduced in the kidney by the
reverse causes.

644

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The principal constituent of the urine which is removed by a process
of filtration is, of course, water. Therefore, in the quantity of urine,

FIG. 268.— BLOOD-VESSELS AND URINIFEROUS TUBULES OF THE KIDNEY

(SEMI-DIAGRAMMATIC). (LandOtS.)

A, capillaries of the cortex ; B, of the medulla ; a, interlobular artery ; 1, vas afferens ; 2, vas
efferens ; r e, vasa recta ; c, venae rectae ; v v, interlobular vein ; S, origin of a vena stellata ; i i, Bow-
man's capsule and glomerulus; X X, convoluted tubules; 1 1, Henle's loop; n n, junctional piece; o o,
collecting tubes ; O, excretory tube.

which, of course, means quantity of water, the variations in the activity
of the process of filtration may be mainly made out. Wherever the

KENAL SECKETION.

645

renal secretion is diminished, it may almost invariably be concluded that
the process of filtration has been interfered with by some means or
other ; and, conversely and as a consequence, the so-called diuretics are,
as a rule, substances which directly increase blood pressure and thus
facilitate transudation. So, anything which reduces blood pressure in
the kidneys will reduce the secretion. Section of the spinal cord acts in
this way. By the universal vascular relaxation produced, the blood
pressure is reduced in the kidney, as elsewhere, and filtration rendered
almost impossible.

Stimulation of the spinal cord acts in the opposite direction by con-
stricting the general vascular areas, together with the renal artery, and
yet produces the same result ; for the increase of general pressure does
not compensate for the increased resistance in the renal artery. As a

v

FIG. 269.— THE SECRETING PORTIONS OF THE KIDNEY. (Landois.)

II, Bowman's capsule and glomerulus: a, vas afferens ; «, vas efferens; c, capillary network of the
cortex; k, endothelium of the capsule; h, origin of a convoluted tubule. Ill, "rodde'd" cells from a
convoluted tubule ; 2. seen from the side, with g, inner granular zone ; 1, from the surface. IV, cells
lining Henle's loop. V, cells of a collecting tube. VI, section of an excretory tube.

consequence, the flow of blood in the latter is reduced and filtration pre-
vented.

If the local pressure in the kidney be increased, as by section of the
renal nerves or by section of the splanchnics, both of which lead to the
dilatation of the renal arteries, and hence an increased pressure in the
glomeruli, an increased secretion is produced. Conversely, stimulation
of the splanchnic or renal nerves arrests filtration by reducing the blood
supply to the kidney.

The correlation between the action of the kidneys and skin is
explainable on these data : It is known that in cold weather the kidneys
are more active than in warm weather, while the reverse holds with the
skin. In cold weather the capillaries of the external integument are con-
stricted and the blood pressure in the internal organs is, therefore,

646 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

increased and nitration through the kidneys facilitated. As a conse-
quence, the urine in cold weather is of low specific gravity from the large
amount of water forced through the glomeruli. In warm weather, on the
other hand, the capillaries of the skin are relaxed, general blood pressure
is, therefore, reduced and filtration to that extent interfered with, and
the urine is now scanty and of a higher specific gravity from the decrease
in its percentage of water.

Filtration is not, however, the only process concerned in the forma-
tion of urine. This is evident from the examination of the composition
of urine ; for if it were merely a filtrate from the blood it could con-
tain no soluble constituent in greater proportion than it exists in the
blood ; for a solution cannot by filtration through a moist animal mem-
brane become more concentrated. Yet the urine contains many sub-
stances, especially urea, in much larger amount than in the blood, and it
must, therefore, be assumed that the fluid which is removed from the
blood by filtration through the glomeruli differs in important respects
from the urine. It must be almost identical with transudations from
the blood in other localities. It is, however, probable that it is free from
albumen. For the fluids which leave the blood must traverse not only
the walls of the capillaries of the glomeruli, but also the walls of the
capsule, and it is well known that such relatively thick membranes offer
difficulty to the filtration of albumen.

It is well known that normal urine is free from albumen, and this is to
be explained either by the statement above mentioned, or by the assump-
tion that albumen does pass through the glomeruli into the interior of
the urinary tubules, but is again absorbed by the epithelial cells lining the
looped portion of the tubules. This, however, is perhaps supported by the
fact that in kidney diseases, where the epithelium of the tubules is
diseased or absent, and absorption, presumably, thus interfered with,
albumen is then constant^ found in the urine.

It is readily conceivable that various constituents may be added to
the urine in its passage through the different portions of the uriniferous
tubules. That such is the case is rendered probable by the histological
structure of the kidney. The fluid removed by the glomeruli from the
blood passes through a series of convoluted tubules lined with epithelial
cells similar to those found in other secreting organs and surrounded by
a second net-work of capillaries. The epithelial cells lining the tubules
may be regarded as specific secretory cells which are concerned in
removing the specific constituents of the urine from the blood. That
they are capable of removing substances from the blood circulating in
the capillaries may be demonstrated by the injection into the blood-cur-
rent of indigo carmine, after previous section of the spinal cord, thus
preventing the formation of the urinary secretion by filtration. If ani-

KENAL SECRETION. 647

mals are killed at various periods after such an injection, indigo carmine
may be traced from the blood into the interior of the epithelial cells and
from there into the interior of the uriniferous tubules. No trace of this
pigment passes through the glonaeruli.

This experiment demonstrates that even when the blood pressure is
greatly reduced the epithelial cells of the kidney do not lose their
activity, but are still able to remove substances from the blood and
transfer them into the interior of the tubules.

Certain substances which belong to the group of diuretics produce
a flow of urine without at all increasing the blood pressure ; such sub-
stances are urea, urates, etc. It follows that if the blood pressure has
not been increased, or, in fact, may even have been decreased, and yet
the flow of urine not be interfered with, some other portion of the
kidney besides the glomeruli is concerned in the separation of the water
together with the other constituents of the urine.

It is capable of demonstration that urea passes from the. blood into
the renal secretion through the activity of the renal cells.

In amphibious animals the kidney receives a suppty of blood from
the renal artery and also from the renal portal system, which is formed
by a branch of the femoral vein which joins its fellow from the opposite
side to form the anterior abdominal vein.

The renal artery alone supplies the glomerulus ; the renal portal
vein alone supplies the uriniferous tubules. If the renal artery be tied,
the blood is, of course, shut off from the glomeruli, and all filtration is
thus prevented. Urea, nevertheless, is still a constituent of the secre-
tion formed by such a kidney, and when urea is injected into the blood
it likewise causes a secretion of urine.

On the other hand, substances which are presumably removed from
the blood by a process solely of filtration, viz., sugar, peptones, and vari-
ous salts, do not appear in the urine after the renal artery has been tied.

It is thus evident that the secretion of urine is a double process,
partty a process of filtration, in which water and crystalline substances
are removed from the blood by a process of transudation occurring in
the glomeruli. Everything, therefore, which increases blood pressure in
the renal arteries will lead to transudation and to an increase in the
watery constituents of the urine.

The renal secretion is also an active secretory process in which the
epithelial cells lining the convoluted portions of the uriniferous tubules
are concerned in removing the specific constituents of the urine from the
blood, while perhaps completing the process of transformation of some of
the antecedents of urea into that substance. This subject will again be
referred to from this point of view when we consider the problems of
nutrition which occur in the animal body.

648 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

3. THE MECHANISM OF MICTURITION. — The secretion of urine, like
the bile, is constant, and if the ureters be divided it will be found that
there will be a steady flow of urine, drop by drop. The urine has been
described as a pure excretion — that is, it is composed solely of sub-
stances which no longer have any office to fulfill in the economy, and
which are deleterious and must be removed. Arrest of the renal secre-
tion, or so-called suppression of urine, by preventing the elimination of
these substances invariably leads to a fatal result.

The urinary constituents eliminated from the blood through the
action of the glomeruli and epithelial cells of the uriniferous tubules pass
drop by drop through the straight canals into the pelvis of the kidney,
and from there through the peristaltic contractions of the muscular walls
of the ureters into the bladder.

The bladder is a muscular organ composed of an internal mucous
coat and double muscular coat. The fibres, which are of the unstriped
variety, are arranged in oblique and circular layers, the latter being es-
pecially developed at the neck of the bladder. Externally situated is a
fibrous membrane, while the upper portion of the bladder is covered by
the peritoneum. The ureters pierce the vesical walls obliquely, and at the
orifice of entrance of the ureters into the bladder is located a valvular
fold of mucous membrane. As the bladder fills the increased pressure
on its walls tends to obliterate the orifice of entrance of the ureters,
and so prevent regurgitation through the ureters back to the kidneys.
Sometimes, as a consequence of obstruction to the flow of urine from the
bladder, it will be found that the ureters are then the seat of considera-
ble distention. Such distention is not, however, caused by a reflux from
the bladder, but is only produced when, the bladder becoming distended
to its full capacity, the constant secretion of urine still continues to
collect in the ureters behind the bladder. As the urine accumulates in
the bladder it rises from the c&vity of the pelvis to occupy the lower
portion of the abdominal region, where in man, when fully distended, it
may be recognized by percussion, and extends from eight to ten centi-
meters above the symphysis of the pubes.

The urine is retained in the bladder by the normal tonic contraction
of the circular sphincter of the bladder, aided by the tonic contraction
of the sphincter urethras and the elastic fibres surrounding the urethrse.
As the bladder becomes distended the sphincter becomes relaxed, and
the contact of the escaping urine with the upper part of the membranous
portion of the urethra causes the desire to urinate. Escape of urine may
at this time be prevented by the contraction of the sphincter urethra
muscle, which is a red, striped, voluntary muscle.

In animals and infants this contact of the urine with the mucous
membrane of the urethrse starts the process of micturition, which, in

BENAL SECKETION. 649

such circumstances, is a purely reflex action, and may be carried on
without the assistance of the will.

The state of contraction of the vesical muscular fibres, as was
found to be the case as regards the rectum, is governed by a spinal centre
located in the lumbar portion of the spinal cord. When the spinal cord
is divided in the dorsal region in a dog, after the shock of the operation
has passed off the bladder may fill with urine, and, when distended,
empties itself in a perfectly normal manner.

The distention of the bladder starts sensory impulses, which are
conducted to the spinal cord through the posterior roots of the third,
fourth, and fifth sacral nerves. The centre of micturition, which in dogs
is situated opposite the fifth and in rabbits opposite the seventh lumbar

c

FIG. 270.— DIAGRAM OF THE NERVOUS MECHANISM OF MICTURITION. ( Yeo.)

B, bladder ; M, abdominal muscles ; C, cerebral centres ; R represents impulses which pass from the
bladder to the centre in the spinal cord, whence tonic impulses are reflected and pass along T to the
sphincter which retains the urine. When the bladder is distended, impulses pass to the brain by 1, and
when we will, the tonus of the spinal centre stimulating the sphincter is checked, and the abdominal
muscles are made by 2 to force some urine into the neck of the bladder, whence impulses pass by 3 to
inhibit the sphincter centre and excite the detrusor through 4.

vertebra, is then called into play, and the muscular fibres of the sphinc-
ter of the bladder relax, while contractions of the longitudinal fibres, or
the so-called detrusor urinae muscle, are called forth.

The contraction of this muscle serves to contract the capacity of
the bladder in all directions, its contents are thus forced out through
the relaxed sphincter muscle through the urethras, and urination is ter-
minated by the rhythmical contraction of the bulbo cavernosus, or
ejaculator nrinae muscle.

Ordinarily the emptying of the bladder is assisted by the co-
operation of the abdominal muscles in the same way as their contraction
aids in defsecation. A deep inspiration is made as the bladder becomes

650 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

almost totally emptied, the glottis closes, and the abdominal muscles,
contracting, serve to force down the abdominal contents into the pelvis,
and so by pressure from above aid the emptying of the bladder. Section
of the spinal cord above the level of this centre first causes retention of
urine by increasing the reflex activitjr of the urethral sphincter and by
interfering with the conduction of inhibitory impulses from the brain.
As soon as the bladder becomes distended the sphincter becomes mechan-
ically dilated, and the urine trickles away in drops, but less rapidly than
it enters from the kidney ; so the bladder becomes enormously dilated
and the retained urine is apt to undergo ammoniacal fermentation.
Goltz, however, has seen dogs micturate in a perfectly normal manner
after complete division of the spinal cord above the lumbar region.

While urination is thus originally a purely reflex action, it is pos-
sible by education to bring it, to a very considerable extent, under the
control of the will. The contact of the first few drops of urine with the
mucous membrane of the urethrse, instead of inaugurating the act of
micturition, may by an exertion of the will lead to an increase of
the tonic contraction of the sphincter of the bladder instead of to its
inhibition. The act of micturition is thus voluntarily postponed
(Fig. 270).

In addition to this voluntary control of the act of micturition, this
process is also largely governed by the emotions, and the starting point
of the act may originate not only in the distention of the bladder, but
in various forms of irritation of the genital apparatus. Such a cause
will frequently be found to explain the urinary incontinence of children.

SECTION XL
THE CUTANEOUS FUNCTIONS.

ANOTHER source of loss to the blood occurs in its passage through
the capillaries of the external integument by means of the sweat and
the sebaceous glands. As already indicated, the waste products of the
animal economy are mainly urea and its antecedents, carbon dioxide,
salts, and water. In the study of respiration we found that the pul-
monary mucous membrane constituted the organ whose function as an
excretory organ was mainly concerned in the removal of carbon dioxide,
water, and certain organic products from the blood. The kidney we
found to be especially active in removing urea, various salts, and water.
These two organs constitute the main paths of elimination of substances
no longer of use to the economy, and, as a consequence, constitute the
most important excretory organs of the body.

The skin may be regarded as an organ supplemental in its action
to the lungs and kidneys, since the skin by its secretion is capable of
removing a considerable quantity of water from the blood, small amounts
of carbon dioxide, and small amounts of salts, and in certain instances
during suppression of renal secretion a small amount of urea.

The skin is thus an excretory organ, serving to remove gaseous,
liquid, and solid waste products. The skin is also the chief organ for the
regulation of animal heat, by, on the one hand, through conduction,
radiation, and evaporation of water, permitting of loss of heat, while it
also, through mechanisms to be considered directly, is able to regulate
the amount of heat lost. Since the skin is more permeable to gases
than a dry membrane, a certain amount of gaseous interchange takes
place through the skin. The skin further, through the various forms
which the epidermal organs may take on, whether hoofs, horns, claws,
fur, or feathers, furnishes means of protection and offensive organs.
Thus, the hairs (fur or feathers) furnish protection against extreme and
sudden variations of temperature by the fact that they are poor con-
ductors of heat, and inclose between them a still layer of air, itself a
poor conductor of heat. The hairs are also furnished with an apparatus
by which the loss of heat may be regulated ; thus, in cold weather, through
the contraction of the unstriped muscular fibres of the skin (the erectores
pili}, the hairs become erect and the external coat thus becomes thicker.
Further, cold acts as a stimulus to the growth of hair, and we find, as a

(651) '

652 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

consequence, a thicker coat in winter than in summer. This is not only
seen in the thicker fur in animals which inhabit a cold climate, as con-
trasted with the same species in warmer latitudes, but also in the periodic
growth and shedding of hair seen in the horse and ox in the change of
the seasons. The hairs also furnish protection against wet, from the fact
that they are always more or less oily, from the secretions of the sebaceous
glands, and thus shed water. The hairs, through their elasticity, furnish
mechanical protection, and through the thickness of the coat, to a certain
degree, resist the attacks of insects ; thus the external auditory meati,
the external nares, and the eyes are protected by hairs. Finally, the hairs
assist the sense of touch.

1. THE SWEAT SECRETION. — The sweat-glands, which are found only
in mammals, occur in their simplest form in the domestic animals in the
ox, where they are simply oval sacs, which in man and the horse and in
the feet of the dog and cat and snout of the hog become developed into
long, convoluted tubes, passing through the entire thickness of the skin.

In the horse the sweat-glands are comparatively highly developed,
especially in the inguinal region, where they are also abundant in the
sheep. In the ox the sweat-glands, as alread}r mentioned, are rudimentary,
and, as a consequence, this animal sweats but very little. Cats, rabbits,
and rats do not sweat at all, the carnivora generally sweating only in the
soles of their feet.

The sweat is a transparent, colorless liquid with a characteristic
odor, varying as to its source from different parts of the skin, with a
salty taste. Its specific gravity is about 1004. Its reaction may be
said to be normally alkaline or neutral. The frequent acid reaction is to
be attributed to the development of fatty acids in the decomposition of
fatty matters formed by the sebaceous glands, and which are ordinarily
mixed with the perspiration. Its quantity is very variable, governed by
conditions to be referred to directly. It may be stated in a general way
that, as a rule, twice as much water is given off* by the skin as by the
lungs, while, as a rule, in man eleven grains of solids are eliminated by
the skin in twenty-four hours, in contrast to seven grains removed by
the lungs. The sweat contains no structural elements with the exception
of epithelial scales, which may be accidentally removed from the
epidermis.

The sweat in its composition contains about 1.8 per cent, of solids,
of which two-thirds are inorganic and mainly constituted by alkaline
chlorides. The nitrogenous constituents of the sweat consist almost
solely of urea, which by its decomposition may give rise to ammonia.
The non-nitrogenous constituents of the sweat are composed of volatile
fatty acids, such as formic, acetic, butyric, proprionic, and caproic, which
give to the sweat its characteristic odor. Cholesterin and neutral fats

CUTANEOUS FUNCTIONS. 653

coming from the sebaceous glands are also frequently found in it. The
mineral matters are composed mainly of sodium chloride, potassium
chloride, phosphates, and alkaline sulphates, phosphatic earths, and
traces of iron. The sweat, in addition, contains traces of free carbon
dioxide and small amounts of nitrogen.

The following table represents the different anatyses of the sweat: —

In 1000 Parts.

Favre.

Schottin.

Funke.

Water

995.573

977.40

988.40

4.427

22.60

11.60

4.427

4.20

2.49

Fats, .

0.013

4.20

2.49

Lactates, .

0.317

4.20

2.49

Chlorine sudorates,

1.562

4.20

2.49

Extractive matters,

0.005

11.30

2.49

Urea, .

0.044

11.30

1.55

Sodium chloride,

2.230

3.60

1.55

Potassium chloride,

0.024

3.60

1.55

Sodium phosphate,

traces

3.60

1.55

Alkaline phosphates
Phosphatic earths,

0.011
traces

1.31
0.39

1.55
1.55

Other salts,.

traces

7.00

4.36

The quantity of sweat is very variable. In man its amount has been
placed at five hundred to nine hundred grammes daily, although under
different conditions it may be increased to fifteen hundred or two thou-
sand grammes, or even more. Under all conditions in which the activity
of the skin is not absolutely prevented a considerable quantity of perspi-
ration is formed by the skin, the water of which evaporates as rapidly as
it is poured out. The secretion of sweat is then spoken of as insen-
sible perspiration. Under other circumstances fluid may be noticed
to collect on the surface of the skin, and is then spoken of as sensible
perspiration. The proportion of the sensible to the insensible perspi-
ration will depend upon a number of external conditions. Thus, sup-
posing the rate of secretion to remain constant, the drj-er and hotter the
air and the more rapid the circulation of air in contact with the body, the
greater will be the amount of sensible perspiration which undergoes
evaporation and is thus converted into insensible perspiration. On the
other hand, when the air is cool, and especially when saturated with
moisture, evaporation from the surface of the body is prevented, and,
even although the rate of secretion by the skin be no greater than in the
previous condition, the amount of sweat which remains on the surface of
the body as sensible perspiration will be greatly increased.

The total amount of secretion poured out by the skin is not only
modified by the condition of the atmosphere, but also by the character
and quantit}*- of the food and by the amount of exercise, and especially
by the amount of fluid drunk. It is also influenced by the mental con-
ditions, by medicines, poisons, and, as pointed out under the heading of

654 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Renal Secretion, the activity of the skin as a secreting organ is, as a rule,
inverse to that of the kidnej^. As a consequence, in warm weather the
cutaneous blood-vessels relax, more blood circulates through the skin,
and the perspiration is, therefore, increased, while the amount of water
eliminated by the kidnej's is decreased. Hence, in warm weather the
urine is scanty and of high specific gravity. On the other hand, in cold
weather the cutaneous capillaries are contracted, the activity of the sweat-
glands diminished, while from the increased blood pressure in the internal
organs the activity of the kidney, especially of the glomeruli, is increased,
and the urine is now more abundant in quantity and of lower specific
gravity.

The formation of sweat is a true secretion and is dependent upon
the secretory activity of the epithelial cells of the sweat-glands. The
relation between the activity of the sweat-glands and of the blood supply
has been very clearty made out. Nearly all conditions which increase
the blood supply to a part will lead to an increased secretion of sweat.
This, as already mentioned, will probably explain the increased secretion
when the skin is subjected to a high temperature.

Bernard also succeeded in producing secretion by the skin by
division of the vaso-motor nerves supplying the part. Thus, division of
the cervical sympathetic in the horse will cause an abundant secretion of
sweat on the corresponding side of the face.

The sweat-glands are further governed by special secretory nerves.
This statement is supported not only by the production of sweat in
various pathological conditions and in the evident influence of the
emotions on the sweat secretion, even in the absence of increased circu-
lation, but also has been demonstrated by direct experiment.

If in a dog or cat the peripheral end of the sciatic nerve be stimu-
lated with an interrupted current, a profuse secretion of perspiration is
produced on the balls of the toes. Such a secretion is evidently not
produced by modifications of the blood supply ; for stimulation of the
sciatic nerve, as a rule, may be said to lead to the constriction of the
blood-vessels in this part, and the secretion may even be produced after
ligation of the blood-vessels of the limb or even after its amputation.
Moreover, the vaso-motor effects may be produced, as in the case of the
secretion of the saliva, and the secretory effects prevented by the injection
of atropine. The analogy, therefore, between the secretion of sweat and
that of saliva is clearly established, and we are warranted in stating that
the sciatic nerve, like the chorda tympani, contains special secretory
fibres whose stimulation leads to an increased activity of the secretory
epithelium.

Moreover, experiment enables us to determine that the sweating
produced by exposure to high temperature is not solely due to the

CUTANEOUS FUNCTIONS. 655

increased blood supply of the part, but to direct action on the nervous
system. For if the sciatic nerve be divided in a cat, on exposure to
high temperature the part removed from the central nervous system will
form no secretion, while the other surfaces of the body will form an
abundant secretion of sweat, thus clearly showing that heat acts mainly
as a stimulant to the secretion of sweat by calling into play the activity
of the central nervous S3^stem.

Sweat may also be produced by stimulating the central end of the
divided sciatic nerve, where, of course, its production is clearly of a
reflex nature, and is attributed to the stimulation of the so-called sweat
centres located in the spinal cord. The sweat secretion may also be
called forth by various drugs, especialty by pilocarpine, the alkaloid of
jaborandi, which appears to act as a local stimulant to the sweat-glands,
although it may also have some stimulating action on the sweat centres.
As in the case of the secretion of saliva, it may be antagonized by atro-
pine. The function of the sweat-glands in the formation of sweat is
mainly that of an excretoty organ, while, added to this, by the evapora-
tion of the perspiration from the external surfaces of the bod}7 it exerts
a considerable influence as a regulator of the temperature of the body.
As a consequence, therefore, when, as in warm weather, the secretion of
the skin is increased, the corresponding increase in evaporation tends to
prevent the overheating of the body.

2. THE SEBACEOUS SECRETION OF THE SKIN. — In the derm are found
a large number of racemose glands whose excretory ducts, as a rule,
open into the hair-follicles. The excretory ducts are lined with pave-
ment epithelium, which in the deeper portions gives place to true secretory
cells in which a nucleus is present, although only capable of being
detected with difficulty, its presence being usually obscured by the large
number of fatty globules surrounding it. Such sebaceous glands are
not uniformly distributed over the animal body, but are especially
developed in points most abundantly supplied with hair. During foetal
life the external body surface is covered with a thick layer of sebaceous
matter, the so-called vernix caseosa, which protects it from maceration
in the amniotic fluid. The secretion formed by these glands is a soft,
crumbling, fatty mass, suspended in a tolerably small amount of water,
and contains a small amount of albuminous matter and considerable
amounts of potassium salts and of cholesterin. The secretion is formed
by the activity of the protoplasmic secretory cells, which remove certain
substances from the transudations from the blood-vessels, and whose
protoplasm itself undergoes fatty degeneration. The secretion, there-
fore, consists mainly of the breaking down of the cell-contents. It is
composed of about 31 per cent, water, 61 per cent, of albuminous matter
and epithelium, 5 per cent, of neutral fat and soaps, and 1 per cent, of

656 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

inorganic salts. Olein and palmatin are the principal representative
fatty bodies, phosphatic earths and chlorides, and salts. The wool of
the sheep contains a fatty potassium salt which is soluble in water, and
which constitutes at least one-third in weight of raw merino wool.

The function of the sebaceous secretion is to act as a lubricant to
the skin and epidermal appendages.

3. CUTANEOUS ABSORPTION. — When the body is plunged in a liquid
medium, as into a bath, a considerable amount of water is absorbed by
imbibition through the epithelium. From there it is able to pass by
absorption into the vessels which circulate through the superficial layers
of the derm, and from there into the general blood-current. This state-
ment may be demonstrated b^y the increase in weight which, as a general
rule, follows immersion in fluid. The result of such an immersion will,
however, vary according to the temperature of the fluid. When the
temperature of the bath is above that of the body, the increased secretion
from the skin will more than counterbalance the gain in absorption, and,
as a consequence, the weight of the body may be decreased. If, on the
other hand, the temperature of the bath is lower than that of the body,
the body may gain in weight through the absorption of water. The
epidermis is, nevertheless, not equally permeable by substances brought
into contact with it. And this interference with absorption is also
increased by the sebaceous secretion of the skin. Substances held in
solution in water are accordingly absorbed but to an extremely slight
extent, unless this immersion be so prolonged as to permit of softening
of the epidermis.

Absorption through friction of the skin surface with different sub-
stances, especially when suspended in a fatty excipient, is to be explained
by the mechanical forcing of such substances into the sebaceous glands,
and. it may be, even into the interstices of the epidermal cells. Thus,
friction with tartar emetic suspended in oils may produce vomiting,
with mercury may produce salivation, and with belladonna dilatation
of the pupil.

Abrasion of the skin leads to a marked increase in its facility for
absorption.

4. CUTANEOUS RESPIRATION. — The skin of man and animals in whom
the skin is bare offers a certain analogy to the lungs in that it is abun-
dantly supplied with blood-vessels which are nearty in contact with the
external atmosphere. It is, therefore, conceivable that through the skin
there may be an interchange between the gases of the atmosphere and
blood. Experiments show this to be a fact. If the body be inclosed in
an air-tight chamber extending to the neck, and after a time the air
within this chamber be analyzed, it will be found that it will have
decreased in the amount of oxygen and gained in carbonic acid. The

CUTANEOUS FUNCTIONS.

657

skin is, however, of considerable density, and from its structure, as
compared with that of the pulmonary mucous membrane, must offer
great resistance to the diffusion of gases. As a consequence, the
amount of such interchange which occurs through the skin must be
slight. In animals, however, in which the skin is not only bare, but
thin and moist, gaseous interchange through the skin may be of much
greater importance ; thus, for example, it has been found that if the
entrance of air ?nto the lungs of the frog be entirely prevented by sur-
rounding the head with a rubber membrane, life may be preserved in
contact with the air for several da3~s, and b}~ examining the composition
of the atmosphere, if the frog be placed in a confined space, it will be
found that the frog has absorbed oxygen and set free carbonic acid. In
other words, the frog is able to breathe without lungs, the respiration
carried on through its skin being sufficient for its needs.

In cold-blooded animals this degree of cutaneous respiration is much
more extensive than in warm-blooded animals, while the function is
least developed in warm-blooded animals whose skin is covered with fur,
hair, or feathers. In fact, it is probable that whatever gaseous inter-
change does occur takes place from the capillary net-work surrounding
the sweat-glands. The exhalation of carbon dioxide may be readily
demonstrated by placing the arm in a vessel containing distilled water
and which is closed from the external atmosphere ; after an hour's im-
mersion only in the water the addition of lime-water, by the character-
istic precipitate of carbonate of lime, will demonstrate its transudation
through the skin.

The amount of carbon dioxide eliminated by the skin may be readily
determined by collecting the total amount of carbon dioxide liberated
both by the skin and lungs and then deducting the latter amount from
the total. Or it may be directly measured by closing the bod}7" in an air-
tight chamber and preventing entrance of the expelled air by breathing
through a tube. It has been found in this way that the amount elimi-
nated by the lungs is, in man, about one hundred and thirty times as
much as passes through the skin. The following experiments by Reg-
nault and Reiset indicate this amount in the rabbit and dog: —

ANIMAL.

Body Weight
in Grammes.

Duration of Experiment in
Hours.

CO2 Exhaled in Grammes.

Through the
Skin in One
Hour.

Through the
L unks in
One Hour.

Rabbit, . .
Dog,. . .

2425
4159

( 8 hours 25 minutes
( 7 hours 25 minutes
f 7 hours 33 minutes
( 8 hours 50 minutes

0.358
0.197
0.136
0.176

20.63
19.38
39.15
42.50

658 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

It was long ago noticed that if the skin be covered with a thick
varnish death will be rapidly produced. The most probable explanation
is that in addition to the rapid cooling of the body by the dilatation of
the cutaneous capillaries the suppression of perspiration causes the
retention in the economy of some poisonous principle, for the general
symptoms closely resemble those of poisoning — the respiration becomes
slow and disturbed, the pulsation of the heart reduced in frequency,
and convulsions frequently accompany the final stages.

5. THE LACHRYMAL SECRETION. — The lachrymal glands belong to
the group of compound racemose glands, and secrete a fluid which is
tolerably rich in albuminous constituents. The tears are a colorless
liquid of salty taste and alkaline reaction. They contain about 1 per
cent, of solids, which consist of a small amount of mucus and albumen,
coagulable by heat, and traces of fat and mineral salts. Of the latter
sodium chloride is the principal representative, with a small quantity of
alkaline and earthy salts.

The following table represents their analyses : —

Water, 982.00

Albumen and traces of mucus, ..... 5.00

Sodium chloride, 13.00

Other inorganic salts, 0.2

The lachrymal secretion is continuous and is produced by the direct
protoplasmic activity of the secretory cells of this gland : the blood
pressure is of special influence, and it is probable that the lachrymation
which accompanies laughing, coughing, vomiting, etc., is produced by
local increase of pressure through the arrest of the venous circulation.

The lachrymal secretion, like that formed by the other glands, is
under the control of the nervous system. Normally the lachrymal secre-
tion is of reflex origin, the afferent impulse being conducted either from
the conjunctiva or nasal fossae, over the first and second branches of the
trigeminal nerve, from a retinal stimulation, as by intense light, or through
some mental impression. As a rule, such stimuli lead to an increased
secretion of the glands on both sides, with the exception of stimuli
originating in the nasal fossae or conjunctiva, in which case the secretion
is unilateral. The secretory nerve is the lachrymal nerve. Its stimula-
tion is followed by an abundant secretion of tears, while its section is
followed after a time by a continuous secretion corresponding to the
paralytic secretion which follows section of the chorda tympani.

Normally the tears, after passing over the anterior surface of the
eyeball, partially evaporate and partially are conducted through the
lachrymal passages to the nose, only when in excess overflowing the
lower eyelid and running over the cheeks. The function of the tears is
to protect the eye by keeping its surface moist and to wash away foreign
bodies.

SECTION XII.

NUTRITION.

IT has been found that the blood is constantly losing portions
of its constituents in the formation of the different secretions and
excretions of the body and in supplying nutritive substances to the
different tissues. The excretions and the substances removed from the
blood in supplying the tissues with nutriment are to be regarded as
permanent losses to the blood, since in the former case the substances
so separated are conducted directly without the body, while in the latter
case they undergo modifications in the tissues which deprive them of all
nutritive value. In the case of secretions, on the other hand, it has
been found that the losses which the blood undergoes in their formation
are temporary, the matters removed from the blood in these processes
being again returned to it after the secretions have fulfilled their function.
The milk alone is an exception to this statement.

On the other hand, we have seen that in absorption from the
alimentary canal the blood is constantly receiving additions. The
balance between this income and outgo of the blood constitutes nutrition.
If the income exceed the outgo the body increases in weight ; if the
latter predominates, the body loses weight.

Two methods are open to us for studying the processes which are
concerned in the maintenance of nutritive equilibrium. We have found
that the income of the body or the substances which enter the blood and
lymph in the form of peptone, sugar, albumen, salts, and fats are con-
stituted of the elements of carbon, hydrogen, oxygen, and nitrogen in
various proportions. It has been seen that the waste products of the
animal body are urea, carbon dioxide, water, and salts.

We know that nearly all the carbon taken in the food is removed by
the lungs and skin in the form of carbon dioxide; we know that nearly
all the nitrogen taken in with the food is excreted in the form of urea.
Alt the h\'drogen is excreted in the form of water, while the oxj-gen
leaves the animal economy in combination with carbon as carbon dioxide,
or with hydrogen as H20.

The attempt to trace the intermediary stages through which the
constituents of the food pass before reaching these final excretory
products is accompanied by the greatest difficulty. But little is known
as to the way in which these substances are transformed one into the

(659)

660 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

other, or as to the manner in which energy is set free and made use of.
Certain of these processes of conversion nuiy, however, be followed, and
the fact that these processes may in certain instances be located in
special tissues, in the continuation of the plan of specialization of
function, we are, perhaps, warranted in speaking of certain tissues as
set aside to elaborate the raw materials which result from the absorption
of digestive products and to so modify the waste products as to permit
of their ready removal from the body. Such tissues are spoken of as
metabolic tissues, and the study of the chemical changes which occur in
these tissues furnishes us with one method of tracing the conversion of
the substances absorbed into the matters excreted.

The other method of stud3Ting the nutritive phenomena of the
animal body is what is knowrn as the statistical method.

We may, by chemically examining the composition of the food-
stuffs, ascertain the total quantity of each constituent. By chemical
analysis we may also determine the total amount of these different con-
stituents removed from the body in the excretions. By the comparison
of the results obtained in these two examinations valuable conclusions
may be drawn as to the changes which occur in the body in the con-
version of the income into the outgo. These methods will be referred
to in turn.

I. THE FATE OF THE ALBUMINOUS FOOD-CONSTITUENTS.

It has been seen that the albuminous food-constituents in digestion,
through a process of hydration by the action of ferments, are converted
into peptone, which enters through absorption into the radicals of the por-
tal vein, but an insignificant portion being absorbed by means of the lac-
teals. When once within the blood-current, possibly in the process of
absorption itself, the peptone must apparently be reconverted to the form
of albumen, for the amount of peptone capable of detection in the portal
vein, even after an abundant albuminous diet, is too insignificant to repre-
sent the amount of albuminous matters absorbed. We may, therefore, state
that almost immediately on entering the blood-current the albuminous
food-constituents are converted mainly into serum-albumen. It has
further been stated that urea represents the end product in the series of
decompositions which the albuminous bodies of the tissues undergo.
The attempt to trace the changes, commencing with albumen and termi-
nating in the production of urea, is, however, shrouded with the greatest
obscurit}r. It is known that the amount of urea removed gives an index
of the amount of albuminous destruction occurring in the animal body.
Numerous experiments have proved that with the withdrawal of all food
the excretion of urea decreases, and that a small amount continues to be
removed through the urine until the occurrence of death through starva-

FATE OF THE ALBUMINOUS FOOD-CONSTITUENTS. 661

tion, this evidently being formed at the expense of the albuminous con-
stituents of the tissues. It is further clear that tshe excretion of urea may
be increased by an albuminous food, and that the amount of urea elimi-
nated increases proportionately to the increase in the albumen given in
the food. Urea is not, however, a simple product of oxidation of albu-
minous bodies, but is a product of complicated decompositions which
are peculiar to the animal body, and which are accompanied by the pro-
duction of such bodies as kreatin, allantoin, guanin, xanthin, and uric
acid. It is not improbable that the albumen, like many of these inter-
mediary products, retains the nitrogen in the form of a cyanogen radical,
and that it is only in its conversion into urea that by the re-arrangement
of the nitrogen it becomes converted into a member of the amide group.

In the sketch which we have given of the chemical processes occurring
in the animal body it was mentioned that uric acid might be regarded as
an antecedent of urea, since the administration of uric acid to animals
is followed by an increase in the amount of urea removed by the kidne3Ts.
This, however, applies only to the case of mammals, for the reverse is
noticed in birds, where the administration of urea increases the uric acid
of the urine, indicating in the latter case a process of synthesis rather
than of destruction. It cannot be assumed, however, that urea is invari-
ably preceded by the production of uric acid, or, in other words, that it
results from a further oxidation of the latter.

From an examination of the constituents of the different tissues,
such as the muscles, the liver, the spleen, and all organs in which it is
known that the destruction of albuminoids takes place, the detection of
nitrogenous crystalline bodies, such as kreatin, xanthin, hypo-xanthin,
etc., would indicate that they are also products of the destruction of
albumen and perhaps antecedents of urea. In the case of kreatin it
has been found that muscular tissue, under nearly all circumstances, will
contain from two-tenths to four-tenths of 1 per cent, of this body ; and
since kreatin is a diffusible, crystalline body, it must further be assumed
that large quantities of it are continually entering the blood-current from
the muscular tissue. An examination of the urine again shows that
kreatin and kreatinin, into which the former is readily converted, are
constant constituents, and the supposition might at first appear warrant-
able that the kreatin formed in the activity of muscular tissue after
entering the blood is at once removed without change by the kidneys.
This hypothesis is, however, negatived by the fact that increased
muscular activity, which leads to the increase in the formation of kreatin,
does not lead to increase in the kreatin eliminated by the kidneys. On
the other hand, during starvation the kreatin entirely disappears from
the urine; so that it would, therefore, appear that the kreatin eliminated
through the kidneys does not represent tissue waste, but a product of

662 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the breaking down of the albuminous food-constituents which has com-
menced in the intestinal canal, perhaps through the formation of leucin
and tyrosin. Again, it seems clearly established that increase in mus-
cular exercise leads to an increase in the elimination of urea. Since, as
has been stated, the amount of kreatin formed by the muscles increases
with exercise, and the amount of urea eliminated by the kidneys
increases under the same circumstances, it would appear warrantable to
assume that the kreatin resulting from the breaking down of the albu-
minous tissue-constituents of muscles and nerves represents the main
source of urea. As to where this conversion — which, it should be stated,
can only be acknowledged to have a certain degree of probability — takes
place, but little positive information can be given.

It does not occur solely in the kidney, for the suppression of urine
is followed by an accumulation in the system of a large amount of urea.
Again, the urea, under all circumstances, is a constant constituent of the
blood, indicating that even if a part of the urea be formed in the
kidneys the renal epithelium is not the sole source of the manufacture of
this body. As to where kreatin becomes converted into urea no data
can be given.

Another possible source of urea may be found in the products of
the decomposition of albuminous matter in the intestine. It has been
seen that the introduction of a large amount of proteid in the alimentary
canal is followed by a corresponding increase in the amount of urea
eliminated. It is further known that the excess of proteid over and
above that needed for nutrition in the alimentary canal breaks down
under the influence of pancreatic digestion into leucin and t3Trosin. If .
leucin be itself introduced into the intestinal tube the amount of urea
eliminated will be proportionately increased. Leucin, therefore, may
represent a step in the processes of conversion of albumen into urea. In
the latter case we can probably locate the conversion of leucin into urea
in the liver, for the liver, unlike other glands, normally contains large
quantities of urea; and if we again assume, as perhaps seems warranted,
that the leucin is absorbed by the portal vein, the formation of urea out
of leucin would be a natural conclusion.

Uric acid has also been found to be a constant constituent of the
urine of carnivora and of suckling herbivora. It is never met with in
the free condition, but in the form of uric acid salts. In the urine of
birds and reptiles it replaces urea. It also evidently results from the
decomposition of proteids, and, perhaps, under certain circumstances, is
an antecedent of urea, since by oxidation one molecule of uric acid may
be split up into two molecules of urea and one molecule of mesoxalic
acid. This is not, however, to be regarded as invariably taking place,
but the majority of evidence would, perhaps, point to the formation of

FATE OF THE ALBUMINOUS FOOD-CONSTITUENTS. 663

uric acid by a process of decomposition of albuminous matters, differing
slightly from that which results in the production of urea. Sarkin and
xanthin, by progressive oxidation, might perhaps be converted into uric
acid, and, since they are usually found accompanying each other, will,
perhaps, indicate one source of uric acid.

Sarkin, xanthin, and uric acid differ from each other only in one
atom of oxygen, thus : —

Sarkin = C5H4N4O.

Xanthin = C5H4N4O2.

Uric acid =C5H4N403.

As to where this conversion takes place we have no data to fall back
on, except that it does not occur in the kidneys, for the excision of the
kidneys or the ligation of the renal vessels leads to an accumulation of
uric acid in the economy. Of the different localities where uric acid
is especially met with the spleen occupies the first position. In the
spleen uric acid is constantly found in large quantities, even in the her-
bivora, whose urine is free from uric acid ; and conditions which lead to
an increased blood supply to the spleen, as in its enlargement in malarial
diseases, lead also to an increased excretion of uric acid. The spleen
may therefore be looked upon both as the place of origin of uric acid in
the carnivora and of its destruction in the herbivora.

In the herbivora uric acid is represented by hippuric acid, which
differs from uric acid in containing three atoms less of nitrogen, one
atom more of carbon, and five atoms more of hydrogen.

Its formula is, therefore, C6H9N08.

In the herbivora the hippuric acid of the urine represents a peculiar
decomposition occurring in their food. Hippuric acid is a compound of
benzoic acid and glycochol, and the administration of benzoic acid to
any animal, whether carnivorous or herbivorous, will result in the elimi-
nation of hippuric acid through the kidneys.

This process of synthesis may be represented as follows : —

Hippuric acid has, therefore, its origin in the food. As long as the
herbivora are being suckled, or when fasting, it is absent from the urine,
but appears whenever vegetable matter is added in sufficient quantity to
the food. Certain forms of vegetable food are not, however, followed by
the elimination of hippuric acid. Hippuric acid is absent from the urine
of animals fed on peas, wheat, oats, or potatoes, but nearly all grasses
are, however, followed by its appearance in the urine.

When benzoic acid is given to animals, hippuric acid is invariably
found in the urine, and an examination of the vegetable matters whose use
as food is followed by the formation of hippuric acid will nearly always
indicate the presence in such foods of benzoic acid or some allied body.

664 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Glycochol, through whose union with benzoic acid hippuric acid is
formed, is manufactured in the liver, the formation of hippuric acid
occurring probably both in the liver and kidneys.

II. THE FATE OF THE FATTY CONSTITUENTS OF FOOD.

It has been found that the fats contained in the food are largely
absorbed unchanged in the form of an emulsion, a small fraction only
being converted into fatty soaps. Such absorption was, moreover, found
to occur mainly b}' means of the chyle-ducts and only partially through
the blood-vessels. It may, therefore, be stated that fats are absorbed
unchanged in the forms in which they enter the alimentary canal. The
attempt to trace the progress of the fats through the animal body will
be aided by the study of the changes which occur in the adipose tissue.
This, of all the tissues of the body, varies most rapidly and in widest
extremes. Within a short space of time, as in starvation, the adipose
tissue of the body may almost totally disappear ; while, on the other hand,
it may, under exceptional circumstances, accumulate with the greatest
rapidity. In describing the histology of adipose tissue it was stated that
the oil-globules appeared in the centre of the connective-tissue corpuscles
and at their expense, and the process was likened to the nutritive pre-
hension of food in a small mass of undifferentiated protoplasm, such as
the amoeba.

The fat, we have seen, enters the blood in all important respects
unchanged, and the simplest explanation of the development of the adi-
pose tissue would be to suppose that the connective-tissue corpuscles,
by a process, of vital appropriation, pick out the oil-globules from the
fluid in which they are bathed. Several difficulties, however, oppose
this simple theory. In the first place, it is well known that but a small
amount of fat deposited in adipose tissue can come directly from the fat
of the food : for, as is well known, the butter in cream is far in excess of
the fat contained in the food, and it has been shown that in a fattening
hog for every one hundred parts of fat in the food four hundred and
seventy-two parts are stored up as adipose tissue. Again, if animals are
fed on a meat diet and soaps the}7 accumulate adipose tissue — a process
which is scarcely capable of being explained by the re-transformation of
the fats by taking up glycerin and giving up alkali.

On the other hand, the fats of different animals differ in composition,
and if two animals of different species are fed with the same fat the
chemical composition of their adipose tissue will vary. Thus, for ex-
ample, if a dog be fed with meat, palmitin, stearin, and soap, the fat
of its adipose tissue will be found to contain olein fat as well as palmitin
and stearin. So it is, therefore, clear that the latter neutral fat must have
been manufactured by the organism.

FATE OF THE FATTY CONSTITUENTS OF FOOD. 665

If a lean dog be fed on a diet of meat and spermaceti, a large amount
of adipose tissue may be accumulated, in which, however, but a trace of
spermaceti may be found. Again, fat alone, as we know, is incapable, as
a food, of sustaining life, although it, to a certain extent, saves the wast-
ing of tissue ; so, as a consequence, when fat alone is given as a food,
the amount of urea excreted by the kidneys is less than would be
excreted by a starving animal. This, evidently, is to be explained by the
fact that fat, being readily oxidized, is rapidly converted into carbon
dioxide, which is, of course, eliminated in the expired air and serves to
a certain extent to spare the elimination of the proteids in oxidation.

It is, then, clear that in the animal body fats are made from some-
thing which is not fat. Two possible sources of fat suggest themselves.
It is known that the nitrogen of urea represents the total amount of
nitrogen passing through the body, and that a certain quantity of urea
(one hundred grammes) represents a certain quantity of proteids (three
hundred grammes). If, however, we estimate the quantity of carbon in
one hundred grammes of urea, we will find that a large amount of carbon
remains unaccounted for. Part of this evidently goes off as carbon
dioxide. It is probable that the remainder is fixed in the body as fat.
It may, therefore, be assumed that proteids split up into non-nitrogenous
and nitrogenous compounds, the former, when not completely oxidized
into carbon dioxide and water, being deposited as fat, the latter leaving
the body oxidized as urea. Other illustrations as to the development of
fats from proteids may be readily given. Thus, in the pancreatic diges-
tion of proteids fatt}r acids may be developed. The fatty degeneration
of muscle is evidently due to the decomposition of proteids, while
animals fed on a pure diet of lean meat with a small amount of fat will
deposit in their tissues more fat than is contained in the food.

Still other lines of study point to the development of ftit from
proteids. It is known that in poisoning with phosphorus various organs
rich in proteids undergo fatty degeneration, and that the fat so formed
is produced at the expense of the tissue-albumen, the fat being formed
from the non-nitrogenous residue of the proteids after the formation of
urea. The following experiment proves this : —

A large dog was allowed to fast for twelve days, so freeing
its tissues almost entirely from fat, and was then slowly poisoned
with phosphorus. Death occurred on the twentieth day of fasting.
Before poisoning, from the fifth to the twelfth day of fasting, the
elimination of urea in the urine was about constant, and amounted
to 7.8 grammes daily; as a consequence of the phosphorus poisoning
the elimination of urea was greatly increased, amounting at last to 23.9
grammes daity, or more than three times the normal amount removed
during fasting. The post-mortem examination showed extensive fatty

666 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

degeneration of various organs, the increase in urea elimination proving
that the fat was derived from the albumen.

As regards the carbohydrates, which may also be regarded as a
possible source of fat, considerable doubt exists as to the manner in
which they act. As is well known, carbohydrates are always an
important constituent of fattening foods, and it may be assumed either
that the carbohydrates, being themselves readily oxidized, save the
non-nitrogenous bodies derived from the proteids, and so enable them to
be converted into fat, or that they may be directly concerned in the
formation of fats. It is clear that carbohydrates may undergo the
butyric acid fermentation, and other ferment actions might likewise
serve to manufacture other fats. Thus, Pasteur claims that glycerin,
which is the basis of neutral fats, may be formed from pure carbo-
hydrates. It is probable, therefore, that in both of these ways the
carbohydrates serve to increase the adipose tissue of the body both
directly and by enabling the non-nitrogenous matters derived from the
proteids to be converted into fat and stored up as such.

The following experiments recently made in Vienna with a hog
thirteen months old and weighing one hundred and forty kilos are of
special interest in this connection : Two kilos of soft-boiled rice were
given daily as fodder, and a comparison of the income and outgo
demonstrated the daily deposit in the tissues of thirty-eight grammes of
albumen and 351.8 grammes of fat. For the development of the latter
at most only 65.4 grammes of proteid in the food, corresponding to 33.6
grammes fat and 7.9 grammes fodder fat can be reckoned on. The
excess (351.8 — 41.5 = 310.3 grammes), or 88.2 per cent, of the entire
amount of fat deposited in the body, can only have been derived from
the carbohydrates of the food.

So, also, in the case of geese and bees, the development of fat from
carbohydrates admits of proof. The dog, however, like other carnivora,
seems incapable of developing fat from carbohydrates.

III. THE FATE OF THE CARBOHYDRATE FOOD-CONSTITUENTS.

The metamorphosis of the carbohydrate food-constituents may be
somewhat more readity followed. It has been seen that under the influence
of the salivary, pancreatic, and intestinal ferments, starch and dextrin
are turned into maltose and cane-sugar into invert-sugar, the sugar as
such entering the blood by absorption ; or, in a rich amylaceous diet,
splitting up in the intestine into lactic and but}7ric acids. In the blood,
the sugar is either reconverted to a member of the starch group
(glycogen) in a process to be considered directly, or is rapidly oxidized
into C02 and H20, the intermediary products being, however, unknown.
That sugar is directly oxidized would seem probable from the fact that

FATE OF THE CAKBOHYDKATE FOOD-CONSTITUENTS. 667

when on an amylaceous diet a larger proportion of the inspired oxygen
is returned to the atmosphere as CO2 than when on animal diet. It
would appear, however, from the fattening which occurs on excessive
carbohydrate diet, that this oxidation is not complete, but that part of
the carbohyd rates remain in the body. It has been already mentioned that
albuminoids may split up into fat, and it will be shown under the
statistical consideration of nutrition that the addition of carbohydrates
to a rich albuminous diet spares a certain amount of albumen from
destructive oxidation, and in this way carbohydrates may lead to the
deposit of fat. On the other hand, the connection between the carbo-
hydrates and fat must be closer than this, for bees on a pure diet of sugar
are able to manufacture wax, — a substance closely allied to the fats.
Besides, it has been shown that in the putrefaction of car bo hyd rates, in
addition to lactic, butyric, and caproic acids, fixed fatty acids are also
developed; and, since a similar fermentation occurs in the alimentary
canal, it is possible that these fatty acids are in the body converted into
neutral fats.

The seat of the oxidation of the carbohydrates is to be found
mainly in the muscles, as evidenced by the shortness of breath produced
by excessive muscular exertion, for it is only natural to suppose that the
more rapid breathing is to enable the body to get rid of the decom-
position products normally removed through the lungs, i.e., C0a, and to
introduce larger amounts of oxygen. The fact may, however, be proved
directl}' by estimating the C02 in the venous blood coming from a con-
tracting and resting muscle. That the CO2 thus formed in muscular
action is from oxidation of the carbohydrate, and not albuminoid
muscle constituents, is proved by the following facts : An animal
in a given time accomplishes a certain amount of muscular work, and by
the estimation of the urinary constituents it may be determined how
much albumen has undergone oxidation. The comparison of the amount
of work represented by the combustion of this amount of albumen and
the amount actually accomplished shows that the latter must have been
at the expense of the combustion of some other substance than albumen.
This substance, in all probability, consists of carbohydrate material.

In addition to the changes already sketched, the carbohydrates are
closety concerned in the function of glycogenesis, or the formation of
glycogen in the liver, — one of the processes of metabolic change which
has been most clearly localized. When comparative estimates are made
as to the amount of sugar contained in the hepatic and portal veins,
contrary to what would be expected, it will be found that in the hepatic
vein sugar is constantly found, even though none may be present in the
blood of the portal vein. So far, therefore, from destroying sugar, as was
formerly supposed, the liver is evidently concerned in the manufacture

668 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of sugar. Even after death, if the blood be removed from the liver by
injecting water through the portal vein, it will be found that after every
trace of sugar has disappeared, if the liver be allowed to stand for a
time in a warm place, the repetition of these injections will again remove
sugar from the liver.

If the liver be removed from an animal immediately after death and
divided into two portions, if one of these is thrown immediately, after
rapid mincing, into a large quantity of previously prepared boiling water,
an opalescent decoction will be obtained which will contain barely a
trace of sugar. If a decoction be made of the other portion of the
liver, after allowing it to remain for several hours in a warm place, the
decoction will be clear, and not opalescent, and will contain large quan-
tities of reducing sugar.

On the other hand, if to a small quantity of the opalescent decoction
which was free from sugar be added a few drops of saliva, or of the
diastatic ferments of the pancreatic juice, sugar will be abundantly
formed.

It is evident, therefore, that the liver contains something which is
capable of being converted into sugar through the influence of some
ferment contained either in the liver-cells or in the blood.

If the opalescent infusion be tested with iodine, a mahogany-red
color will be formed ; it is evident, therefore, that this substance is some-
what of the nature of dextrin or starch, and Bernard, its discoverer,
gave to it the name of glycogen.

Glycogen may be obtained from such a decoction, after rapidly cooling by
surrounding it by a freezing mixture of snow and salt, by the alternate addition
of hydrochloric acid and the potasso-mercuric iodide solution* until no further
precipitate occurs. By this means the albuminous constituents are removed.
This precipitate should be filtered off, and glycogen may be precipitated from the
filtrate by the addition of alcohol until about 60 per cent, of absolute alcohol is
present in the mixture. The glycogen is then to be collected on a filter and
washed with 60 per cent, alcohol until the washings give no cloudiness with a
mixture of dilute caustic potash, ammonia, and ammonium chloride. It is then
to be washed with alcohol and ether. The glycogen remaining should then be
dried on a piece of porous earthenware at a moderate temperature. It may be
further purified, if necessary, by dissolving in hot water and precipitating with
alcohol containing a little ammonia, redissolving as before, and precipitating with
spirit containing a little acetic acid.

This last precipitate should then be washed with alcohol and ether, and then
dried.

As obtained by this method, glycogen is a white, amorphous, non-
nitrogenous substance, which, with water, forms an opalescent solution
and rotates the plane of polarized light strongly to the right to about

*The potasso-mercuric iodide solution is prepared by precipitating a saturated
solution of potassic iodide with a saturated solution of mercuric chloride, and, after
washing the precipitate, making a saturated solution of it in a hot solution of potassic
iodide.

FATE OF THE CAEBOHYDEATE FOOD-CONSTITUENTS. 669

three times the degree possessed by grape-sugar ; it is inodarless and
insoluble in alcohol or ether. Under the action of the salivary or pan-
creatic ferments, namely, diastase, or the action of dilute mineral acids,
it is converted, like other carbohydrates, into a mixture of maltose and
dextrin. Its formula may be given as a multiple of C6H1006.

Glycogen is not confined to the liver-cells, although its presence may
be recognized there by treating a section of hepatic tissue with iodine,
when it may be recognized by the characteristic red staining with iodine
in the neighborhood of the cell-nucleus. It is present, also, in the pla-
centa, in muscular tissue, white blood-cells, the brain, and in various
embryonic tissues. From the fact that it is found in largest amount
in growing tissue it would appear to be especially concerned in the
phenomena of development.

The amount of glycogen which may be present in the liver varies in
very wide amount, from a maximum to an absolute absence, the amount
being dependent upon the state of the nutrition of the animal. If a
rabbit is allowed to starve to death, and its liver be treated as described
above, it will be found that the decoction of the liver will be absolutely
free from glycogen. In other words, it would appear that the glycogen
is derived from the food-stuffs which are absorbed by the walls of the
alimentary tract and are carried by the portal vein to the liver. If it
be determined by experiment how long starvation must be continued to
remove all traces of glycogen from the liver, and after the lapse of such
an interval the animal be abundantly supplied with carbohydrate food
and then killed, it will be found now that the liver has regained its
store of glycogen, and that the decoction now made will show the maxi-
mum quantity of glycogen present. If after starving for the same length
of time the animal be fed with a meat diet, a certain amount of gtycogen
will also be detected in the liver, but in much less amount than after the
carbolmlrate diet.

The question arises at this point as to whether the glycogen so
developed originates from the albuminous constituents of the meat diet,
as it is known that meat, especially the meat of the horse, which is em-
ployed in such experiments, contains representatives of the carbohydrate
group. This question may be settled by substituting a pure albuminous
substance as diet, and it will then be found that although the amount of
glycogen obtainable from the liver is larger than that obtained from a
starving animal, it still falls below the amount obtained after feeding
with meat. It would, therefore, appear that the development of glycogen
on the meat diet is only partially due to the conversion of the albuminous
constituents of the food into gtycogen, but mainly to the carbolrydrate
constituents.

If a starving animal be fed on a fat diet, even though abundant, no

670 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

more glycogen will be found in the liver than would be obtainable from
this organ in a starving animal. It would, therefore, appear that while
the amount of glycogen in the liver is dependent upon the food, it is
especially the carbohydrates which are the sources of this substance.

As already stated, the digestible carbolrydrates in the alimentary
canal are converted into some form of sugar, are absorbed by the
intestinal walls, and enter the blood of the portal vein, and are thus carried
to the liver. As is well known, the food of herbivora is constituted
largely of carbohydrates, and these substances can only be absorbed after
being converted into sugar. On the other hand, it is well known that the
presence of sugar in the blood above a very small percentage at once
leads to its elimination through the kidneys, constituting gtycosuria.
Admitting, therefore, that large quantities of sugar in these animals
enter the blood through the walls of the alimentary canal, two possibil-
ities arise — either it is eliminated as rapidly as absorbed, or it at once,
through combustion, serves in the development of heat.

Neither of these possibilities are, however, actual^ the case, since
even after the richest carbohydrate diet but traces of sugar are to
be found in the urine, and it is not conceivable that the large amount of
sugar which may be absorbed in the food at once is converted into
carbon dioxide and water.

The onl}7 remaining conclusion is that the sugar at once, after its
absorption, is carried by the portal vein to the liver, and is there con-
verted into some less diffusible form by which its immediate excretion by
the kidne3rs is avoided. Such a substance is evident!}7 found in glycogen,
and the liver may, therefore, be regarded as a storehouse for one of the
most important food-stuffs, which is again reconverted into sugar, as the
needs of the economy demand.

Bernard believed that there is a continual conversion of glycogen
into sugar going on in the liver, and that the sugar so formed is carried
by the hepatic vein to the general circulation to be oxidized in the lungs
and muscles.

It is evident that this hypothesis necessitates the presence of a
larger amount of sugar in the hepatic than in the portal vein, and such
a state of affairs is claimed by Bernard to be a fact, although his state-
ments have met with a certain amount of contradiction. It may, however,
be concluded that even if the estimates made by Bernard as to the
comparative amount of sugar in the hepatic and portal veins are not
absolutely conclusive, the statements of his opponents are no more
trustworthy.

As to the ultimate end of the sugar derived from the conversion of
the glycogen, but little can be accurately stated. It is known that
normal blood contains always a definite amount of sugar. If this

FATE OF THE CAEBOHYDKATE FOOD-CONSTITUENTS. 671

amount be increased, sugar appears in the urine, and it appears that the
sugar in the blood is largely made use of in the chemical processes
occurring in contracting muscles. It would seem, therefore, that the
object of the ghrcogenic function of the liver is to store up in a non-
diffusible form the excess of carbohydrate matter taken into the blood
during a meal rich in carbohydrates, and then to distribute it, little by
little, to the economy as occasion may demand.

The liver converts glycogen into sugar through the action of its
own peculiar diastatic ferment.

If a fragment of liver be washed with water and then with spirit to
remove the blood, and then cut up into small pieces and immersed in
absolute alcohol for twenty -four hours, if the alcohol be removed and a
gtycerin extract made of the residue, a solution will be obtained which
will be capable of rapidly converting glycogen infusion into sugar.

In the process of making the decoction of gtycogen this hepatic fer-
ment is destro^yed by heat, while in the experiment above alluded to, in
which the liver was exposed to a warm temperature after removal from
the body before making an infusion, the absence of gtycogen from such
infusion and the presence of sugar indicate the conversion by this
hepatic ferment of the glycogen into sugar. Such a conversion also
undoubtedly takes place during life. As to why, during life, all the gly-
cogen of the liver is not rapidly converted into sugar, it being admitted
that such a ferment is present, it can only be stated that this problem
belongs to the same group of phenomena as to why the blood does not
coagulate in the living blood-vessels, why the active and living pancreas
and stomach do not digest themselves, and wh}- the living muscle does
not become rigid. That this process of conversion is, however, capable
of occurring in the living liver, and that this ferment is not, as has been
claimed, simply a post-mortem development, is proven by the various
conditions which lead to the abnormal conversion of gtycogen into sugar
in greater amounts than the system can use, and the consequent elimina-
tion of the excess of sugar from the blood b}- the kidneys, constituting
the disease glycosuria, or diabetes mellitus.

Bernard discovered that if the medulla oblongata be punctured in
the neighborhood of the vaso-motor centre in a rabbit, after abundant
feeding with carbohydrates, in an hour or less a considerable quantity
of sugar may be detected in the urine, which, after a day or two, will
disappear.

If a similar operation be performed on a rabbit which has been
deprived of food for several days, no such glycosuria will result, and it
therefore seems clear that this diabetic puncture produced the gtycosuria
through the rapid conversion of the glycogen of the liver into sugar.
It therefore appears that the glycogenic function of the liver is under

672 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the control of the nervous system, and the path of this influence, which
originates in the neighborhood of the vaso-motor centre, may be traced
along the spinal cord, and then, by means of the vagi, to the third and
fourth dorsal ganglia, from this to the thoracic ganglia, and from there
to the liver by some path not yet absolutely determined.

The production of diabetes by such an operation is probably to be
regarded as of a vaso-motor nature. It seems clear that through this
operation the small branches of the hepatic artery are largely dilated, and
the liver, consequently, receives a larger amount of arterial blood, and
that simple division of any part of this nervous path, such, for example,
as removal of the first thoracic ganglion, will likewise produce diabetes.

If the splanchnic nerves be divided previous to this operation g\y-
cosuria will not result, evidently by withdrawing a large quantity of
blood into the abdominal organs and so preventing relatively any dilata-
tion of the hepatic artery.

IV. THE STATISTICS OF NUTBITION.

The preceding sketch as to the fate of the different organic food-
constituents gives but an imperfect idea as to the metabolic processes
occurring within the animal body. By a close comparison of the income
and outgo of the economy statistics of nutrition may be formed which
are of great value for obtaining an idea of the nutritive processes of the
economy under different forms of diet, and thus assist in the formation
of scientific methods of feeding.

When we compare the income with the outgo, the ingesta with the
excreta, we learn not only what part of the ingesta is retained in the
body, but by the detection of substances in the excreta not present in
the food we may extend our idea of the changes which the body has
undergone under the influence of the food.

In determining the true income of the body the constituents of the
faeces must be subtracted, for, as already noted, the faeces consist almost
solely of food-stuffs which have escaped digestion and absorption, the
amount of excretory matter in the fasces being so small as to be dis-
regarded. From the study of the composition of the food we know
that in certain amounts of proteids, fats, carbohyd rates, salts, water, and
inspired air, the animal body takes in definite quantities of nitrogen,
oxygen, carbon, hydrogen, sulphur, phosphorus, salts, and water.

The determination of statistics of nutrition is based upon the
following facts : —

1. With the exception of wool- and milk-producing animals, all the
nitrogen is excreted in the urine ; that found in the faeces may be
regarded as derived almost solely from undigested food.

2. From the difference between the amounts of nitrogen in the food

STATISTICS OF NUTEITION. 673

and in the urine and faeces it may be determined whether there is an
increase or a waste of the nitrogenous matter (albuminoids) of the
economy.

3. The nitrogen in the urine is a measure of the decomposition of
albuminoids in the body, while from the sum of the amounts of nitrogen
in urine and faeces may be deduced the amount of albuminoids which
become fixed in the body.

4. The difference in amount of carbon in income and outgo (including
that which is given off by lungs and skin), taking into account the
carbon derived from decomposition of albuminoids, gives us a means of
estimating the changes in the fat of the animal body, since with the
exception of fat there is not, in any important amount, tiny other carbon
compound in the body.

5. Differences in the amount of water in the economy are readily
calculated. It is only necessary to compare the increase or decrease of
body weight with the data determined as to the decomposition of albumen
and fat. •

For making the above estimates the composition of albumen is
placed as follows : —

C. H. N. O. 8.

53.6 per cent. 7.0 per cent. 16.0 per cent. 23.0 per cent. 1.0 per cent.

Albumen thus consisting of 16 per cent, of nitrogen, if the amount
of nitrogen in the urine is multiplied by 6.25 (= Iffi) we are able to
determine the amount of albumen represented by the nitrogen in the
urine.

As regards the fats, all the animal fats are remarkably constant in.
their composition ; they possess in mean 76.50 per cent, carbon.

From the difference in carbon in income and outgo the amount of
carbon of the decomposed albumen is first deducted (53.6 per cent.),
and from the remainder by multiplication by the factor 1.307 (— j£j$) the
amount of fat may be calculated.

The behavior of the mineral constituents is calculated from the
mineral constituents of the food and that of the urine and faeces. So,
also, for water in a like manner.

The following example (quoted by Schmidt-Mulheim, who has been
largely followed in this chapter) makes clear the method by which such
statistics of nutrition are reached : —

Henneberg fed a full-grown ox, weight 712.5 kilos, for twent}^-eight
clays with 5 kilos clover-ha}-, 6 kilos oat-straw, 3.7 kilos crushed beans,
0.06 kilo salt, and 56.1 kilos water. During the experiment the animal
increased daily 1.035 kilos in weight.

From the analysis of the food, faeces, and nvrine, and from the esti-

43

674

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

mate of the excretion of C02 by means of Pettenkofer.'s apparatus and
car b u retted hydrogen of the intestinal canal, the following data were
obtained : —

A. Daily Income.

70.975 kilos food,

Water.
58.200

Mineral
Matter.

0.890

c.

5.825

H.

7.500

N.
0.310

o.

4.900

B

. Daily (

)utgo.

Water."

Mineral
Matter.

C.

H.

N.

O.

40.65 kilos faeces,

. 35.075

0.575

2.585

0.310

0.105

2.00

13.9 kilos urine,

. 13.075

0.305

0.22

0.025

0.170

0.105

9.795 kilos CO2,

. ...

2.67

0.03 kilo CH2,

002

0.01

Total,

48.150 0.880 5.495 0.345 0.275 0.230

In addition to the above, 9.5025 kilos water in the form of aqueous
vapor were removed through the lungs and skin.

The total of amounts daily appropriated and kept in the body, con-
sequently, were : —

Water.
0.525

Mineral
Matter.

0.010

C.
0.330

H.

0.050

N.
0.035

O.
0.850

These figures corresponded to a daily increase of —

Albumen, 0.220 kilo.

Fat, 0.280 "

Salts, ..-.-. 0.010 «'

Water, 0.525 "

The calculation of the statistics of nitrogen in milk- and wool-pro-
ducing animals is somewhat more complicated than the above, as the
amount of the above productions have also to be taken into account.

1. TISSUE CHANGES IN STARVATION. — Before attempting to study in
detail the influence of food on tissue change, the changes which occur in
the animal body when all food is withheld must first be studied. And
here it should, in the first place, be recollected that the skeletal muscles
form nearly one-half the body, and about one-quarter of all the blood in
the body is contained within them, while another fourth of the blood is
contained in the liver. These two facts are sufficient to indicate that $
large part of the metabolism of the body is carried on in the muscles
and liver.

In fasting animals there is a steady waste of the various tissues and
an excretion of those waste products ; and since this waste is not sup-
plied by new matter, there is a progressive loss of body weight.

STATISTICS OF NUTKITION.

675

Thus, in a dog weighing one thousand and twelve grammes and fast-
ing for fourteen days there was a daily loss of body weight as follows-:— ^

1st day of fasting,

2cl

3d

4th

5th

6th

7th

8th

9th
10th
llth
12th
13th
14th

82 grammes.
44

40
32
27
31
25
26
26
22
23
21
19

From this table it is seen that the loss is far greater on the first day
of starvation than on any other, and that after the first day the loss
gradually becomes less and less marked.

It has also been found that age is of marked influence on the degree
of loss of body weight in starvation. The younger the animal, the
greater the loss.

It is also noticed that birds can stand a greater relative loss of body-
weight from starvation before death occurs than mammals and other
warm-blooded animals ; in the latter death only occurs when 40 per cent,
of the bod}'" weight has been lost.

It has been found that if water is freely given, a horse may stand a
complete fast for from eight to fifteen days without any serious conse-
quences. If this time is, however, passed, even feeding will then be
unable to prevent death.

Herbivora stand starvation worse than carnivora, even although they
lose only one-half as much tissue-albumen ; it is stated that death from
starvation in the horse does not occur until the twentieth to the thirtieth
day, while a dog may live from forty to sixty days without food before
death takes place.

If the body of an animal dead of starvation is examined there will
be found the greatest difference in the loss which the different tissues
have undergone. Adipose tissue suffers most, muscles and viscera less,
and nervous system least of all, and this latter fact is worthy of especial
notice, since fat forms a large constituent of the nervous system. The
body is greatly emaciated ; all subcutaneous and perivisceral fat has
disappeared ; the muscles and other organs are atrophied ; and with the
exception of the alimentary canal, in which fluid is generally found, all
the tissues are markedly 'dry and free from water. In the stomach the
fluid has an acid reaction ; in the intestine there is a slim}' fluid matter
which is evidently decomposed bile.

676

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Since fat and muscle have disappeared in largest amount, it is evi-
dent the starving animal feeds on its own flesh, and, under such circum-
stances, the urine of the herbivora and carnivora are identical.

Of the diiferent organs the percentage of loss of original weight is
as follows : —

Bones

Muscles,

Liver, .

Kidneys,

Spleen,

Pancreas, .

Testicle,

Lungs,

Heart,

Intestine, .

Brain and Cord,

Skin, .

Fat, .

Blood,

Other organs,

13.4 per cent, or 5.4 per cent, of total loss.

30.5
537
25.9
66.7
17.0
40.0
17.7

2.6
18.0

3.2
20.6
97.0
27.0

42.2
4.8
0.6
0.6
0.1
0.1
0.3
0.02
2.0
0.1
8.8

26.2
3.7
5.0

Since in fasting all the nitrogen leaves the body in the form of
urea, the amount of urea in the urine gives a means of measuring the
waste of the albuminoid constituents of the body. Even up to the time
of death the body continues to eliminate urea without, of course, any
new albuminoid matter entering the economy, thus showing that there is
a gradual and constant waste of proteids in the body. The amount of
urea eliminated progressively decreases, as, of course, there is no repair
of the stock of proteids from which it is drawn. Thus, a dog, which
during feeding eliminates daily 63.96 grammes of urea, during the first
day of starvation removes only 14.91 grammes, and there is then a
gradual diminution in the amount up to the time of death. Thus, on the
fifty-ninth day of starvation the dog alluded to above only eliminated
3.50 grammes of urea.

Of course, the richer the tissues are in proteids, the greater will be
the difference between the amount of urea eliminated in the first and sub-
sequent days of starvation. If before the commencement of the starva-
tion experiment the animal has been on a spare diet, less urea will be
eliminated in the first daj-s of fasting, and then the decrease in amount
will be more gradual than if it had been well fed.

The destruction of albumen in starvation is, however, by no means
parallel to the amount of proteids in the entire body ; or, in other words,
an animal which on the first day of starvation destroys five times as
much albumen as on the tenth does not have on the first day five times
as much proteid in the body as on the tenth.

Yoit has found that the excretion of urea on the first day after full
feeding is so much greater than under other circumstances that he con-
cluded that the amount of proteids in the body is of less importance

STATISTICS OF XUTEITION. 677

than the amount of albumen in the preceding diet in determining the
degree of albumen destruction in the first days of starvation, and that
the albumen destruction from starvation is dependent upon two
causes : —

1. A very variable one, which only acts in the first days and which
is dependent on the preceding diet and the general condition of the
body.

2. A constant cause, which alone remains in force after the cessa-
tion of action of the first.

The following table shows how the amount of urea excreted
increases with the amount of nitrogenous matter in the preceding
meals : —

Food given Before Ui
Starvation.

2500 grammes meat, .

:ea in Last Day Urea in First Day
of Feeding. of Fasting.

180.8 601
142.9 33.6
110.8 29.7
51.8 19.8

26.2 . 16.9
16.1 15.4

2000 •• " . ..'.'.

1500 " " ....
800 " " and 200 grammes fat,
Decreasing amount of meat on last clay
176 grammes, .....
Abundance of fat after starvation,

Yoit concludes that animals possess, first, a considerable available
" store " of albumen, which is capable of being increased by a previous
meal rich in albuminoids and which is again rapidly removed in any
drain on the economy ; and, second, a much larger amount of proteid
matter, which represents all the proteids of the animal body and
which he terms " tissue-albumen." Of this latter but a small portion
comes under the conditions of decomposition. The rapid fall in elimi-
nation of urea in starvation depends upon the using up of the " stored r'
albumen; when, however, this is all consumed, then the tissue-albumen
in its turn undergoes destruction. Of course, the stored-up albumen is
also located in the various tissues.

Herbivora contain in their tissues a lesser amount of this stored-
up or reserve albumen than do the carnivora ; even the tissue-albumen
is present in relatively smaller amount. Thus, it has been found that a
full-grown ox during starvation will only use up 1.27 kilos of proteids,
while, measured by the albuminoid waste in carnivora, at least double the
amount of nitrogenous excretion products might be expected.

In addition to the influence of these amounts of albumen on the
proteid waste of fasting animals, the amount of fat in the animal body
is also of moment; the greater the amount of fat, the less the nitrogenous
waste, and this holds whether the fat is already stored up in the economy
or is given to thin animals in the food.

Voit, by giving one thousand five hundred grammes of meat daily
to a dog, brought it to a nutritive condition in which the excretion of

678

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Last da
1st day
2d
3d
4th
5th
6th
7th
8th
9th

y of fee
of fasti

ding,
ng,

i

A.

Urea in

Grrammes.

110.8
26.5
18.6
15.7
14.9
14.8
12.8
12.9
12.1

11.9

urea remained constant. He was then allowed to fast for ten daj'S and
the urea estimated (A). He was then fed with the same food, and then
for ten days received nothing but one hundred grammes of fat (B).
The following results were obtained : —

B.

Urea in
Grammes.

111.8
27.2
16.3
14.1
12.9
12.4
10.8
10.5
10.7
10.2

Through the administration of the fat 14.1 grammes of albumen
escaped destruction, or, as Yoit expresses it, was " saved."

Water also exerts a considerable influence on the destructive
processes in starvation, a large consumption of water always increasing
the excretion of urea. This evidently points to an increased decom-
position of proteids, and not a mere increase in the amount of urea
washed out, since it has been proved that when water is withheld there
is no accumulation of urea in the economy.

On the other hand, the most violent muscular movements during
starvation produce but little appreciable increase in the amount of urea
eliminated, thus showing that the combustion of albuminoids is not the
source of muscular force.

In earlier times, with the exception of the lime salts in the bones,
the inorganic substances found in the animal body were regarded as
secondary in importance and, in fact, almost as accidental constituents.
Liebig and his scholars first recognized the importance of these bodies;
especially Na, Cl, Ca, K, Mg, Fe, and P2O6 are absolutely essential for
the health of the animal body. If these bodies are removed from the
food, or even reduced in amount, the animals rapidly perish, even though
supplied with an abundance of organic food.

This disturbance of nutrition is not, as was first supposed, because
the removal of salts interferes .with the activity of the digestive secre-
tions, since digestion and absorption, even under such circumstances, is
perfectly carried out, but because salts are removed constantly from the
body, and if they are not supplied in food the animal rapidly perishes, as
these salts are essential to the various functions of the economy.

Forster fed a dog with food which was as much as possible freed
from salts; as proteids, he used the residue from the manufacture of
beef extracts, butter freed from salts, potato-starch washed with HC1,
and distilled water.

STATISTICS OF NUTRITION. 679

A dog weighing thirt}'-two kilos, which experience showed could
be kept in constant weight by receiving six hundred to seven hundred
grammes meat and one hundred and fifty grammes fat, was allowed to
eat as much as he would take of the above foods, and 3ret he rapidly
commenced to fail, and in fourteen days was unable to stand from his
great weakness. After three weeks disturbance of digestion appeared —
indigestion, diarrhoea, and finally vomiting.

The comparison of the inorganic income and outgo showed that, as
regards phosphoric acid, 21.9 grammes were taken in while 51. 7 grammes
were excreted; consequently, the dog had lost 29.8 grammes of phos-
phoric acid, or ten times the amount which is normally contained in the
blood ; 7.24 grammes of NaCl were lost.

These results show that the body cannot be sustained by organic
substances alone, but must also receive a certain amount of inorganic
salts. If the amount of salts in the food sinks below a certain figure
or is entirely suspended, salts are excreted by the economy, and the
body passes into such a state of malnutrition that death speedily results.

As regards the amount of inorganic salts required by different
animals in order to preserve perfect nutrition, it appears that the
amount of NaCl in meat, which amounts to 0.11 per cent., is sufficient
for the needs of the carnivorous animal. As a consequence, these ani-
mals prefer unsalted to artificially salted foods.

It is quite different with the herbivora, for, although these animals,
as a rule, receive proportionately quite as much salt in their food as the
carnivora, they will, nevertheless, always greedily devour salt.

As regards the relative proportion of these salts required by different
animals, it appears that all animals require relatively similar propor-
tions of chlorine and sodium, but that herbivora take in their daily
food at least double as much potassium as carnivora.

Thus: One kilogramme cat, fed with mice, takes daily 0.1434
gramme K, 0.0743 Na, 0.0652 Cl! One kilo ox, fed solely with clover-
hay, 0.3575 gramme K, 0.0266 Na, 0.0433 Cl ; when fed with beet-roots
and oat-straw, 0.2923 gramme K, 0.0674 Na, and 0.0603 Cl.

The following table gives the amounts of K, Na, and Cl in various
foods : —

Oat -straw, .

K.

. 1040

Na.
1.36

Cl.
2.97

Clover,

. 21.96

1.39

2.66

Sweet grasses, .
Prairie-grass,
Acid grasses,
Vetches,

. 20.80
. 15.28
. 20.60
. 33 93

2.57
2.65
5.74

6 77

3.67
4.35
4.52
3.65

Beet (roots),
Beet (tops),
Carrot (roots), .
Sugar-beet (tops),

. 34.79
. 46.68
. 19.65
. 50.07

10.24
30.80
12.32
25.76

5.40
22.56
2.90
20.16

680

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Bunge has stated that it is this large amount of K in the food of
the herbivora that causes them to require so much NaCl. For when
potassium salts, the electro-negative constituent of which is other than
chlorine, such as carbonate, phosphate, or sulphate of potassium, come
into watery solution with NaCl at the body temperature they are partly
decomposed, both salts give up their acids, and, in addition to potassium
chloride, the carbonate, phosphate, and sulphate of sodium result through
double decomposition. If these K salts enter the alimentary canal they
are rapidly absorbed and meet with NaCl in the blood. As the above
interchange then takes place, the blood in attempting to preserve its
normal composition allows the new substances rapidly to diffuse away
through the kidneys. Consequently, through the taking in of potassium
sulphate, carbonate, or phosphate, the blood loses both Na and 01, and
this loss must be replaced by the ingestion of extra amounts of NaCl.
Consequently, herbivora, whose diet is rich in K salts, require more
XaCl than the carnivora.

It is thus seen that the character and extent of the tissue changes
in starvation will be largely governed by the previous nutritive condition
of the animal. The following table, after Lawes & Gilbert, shows the
percentage of albumen, fat, salts, and water in the tissue of animals in
different conditions : —

IN 100 PARTS.

THE SOLJDS CONTAIN.

Solids.

Water.

Inorganic
Matter.

Fat.

Albumen.

1. Fattened oxen, .

51.4

48.6

4.1

31.9

15.0

2. Half-fattened oxen,

43.9

56.1

5.1

20.7

18.0

3. Fattened sheep, .

53.8

46.2

2.9

37.9

13.1

4. Thin sheep,

39.0

61.0

3.4

19.9

15.9

5. Fattened hogs, . ' 'M

57.1

42.9

1.7

44.0

11.9

6. Thin hogs, . . .

41.8

58.2

2.8

24.6

14.1

2. THE NUTRITIVE PROCESSES IN FEEDING. — (a) Feeding with Meat. —
When animals are fed exclusively with fats or carbohydrates there is but
little difference in the metamorphosis of proteids other than is seen in star-
vation. So, also, exercise, water, and various other conditions are of little
influence. When, however, proteids are given with the food there is an
immediate increase in the amount of urea eliminated, for the albumen of
the food after being absorbed almost at once undergoes decomposition.

Bischoff and Yoit found that a fasting dog which eliminated daily
twelve grammes of urea, when fed with twent3^-five hundred grammes of
meat eliminated one hundred and eighty-four grammes of urea daily ;
the destruction of albumen, therefore, increased more than fifteen fold.

It would at first appear that if the same amount of albumen is

STATISTICS OF NUTKITION. 681

given to an animal as is lost during starvation, the destruction of the
proteids of the tissues would cease. But since the administration of
albumen increases the tissue waste this is not the case, and at least
two and a half times as much albumen must be given as the body loses
in starvation in order to preserve the balance. If enough of albumen is
given to an animal to prevent its drawing on the albuminoids of its tis-
sues, then the amount of nitrogen eliminated will just equal the amount
contained in the food, and a nitrogenous balance is thus preserved.

If, now, to such an animal a larger amount of meat is given, the
eliminated nitrogen does not at first increase, and a certain amount of
the nitrogen remains in the body to increase the albuminoids of the
tissues. Soon, however, the nitrogen eliminated increases until finally a
nitrogenous balance is again regained. Every increase in the albumen
of the food has the same result — first, an increase in the store of pro-
teids of the body, and then an increase of urea, until the nitrogen of the
latter equals the nitrogen of the food. A maximum is soon, however,
reached in which the limit of albumen which can be digested and ab-
sorbed is attained.

A similar state of affairs holds in animals in a condition of nitro-
genous balance when the albumen of the food is diminished. At first
there is no decrease in the amount of urea eliminated, so the albuminoids
of the tissues must have been drawn upon to make up the excess of
nitrogen in the urine over that of the food. Then in a few days the
elimination of nitrogen becomes reduced, until again a nitrogenous bal-
ance is regained. Every further decrease in the ration of albumen has
the same effect — first, decrease of the store of tissue-albumen, and then
nitrogenous balance. The minimum limit is then reached. When too
small an amount of albumen is given in food to balance the tissue waste
inanition then commences.

These facts show that the requisite amount of albumen in the food
to prevent excess of tissue waste is dependent on the store of albumen
in the body, and that the better the body is nourished by previous feed-
ing the more food must be given to preserve a nutritive balance. Con-
sequently, well-nourished animals require more food, badly-nourished
animals less food, to preserve an equilibrium.

The amount of albumen in the food has, also, an influence on the
body fat. If a small amount of albumen undergoes destruction, fat
must be given up by the body in order to supply the amount of carbon
necessary to form C0a. If the body is rich in fat, and in consequence of
abundant albuminous food a large amount of albumen undergoes de-
struction, the fat decreases ; but if only a little fat is stored up and still
a large amount of albumen is given in food, and there is, consequently,
a large destruction of albumen, all the nitrogen is eliminated in the urine,

682 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

while a part of the carbon remains behind to be stored up as fat. Con-
sequently, the body may be kept stationary as regards its store of albumen
and fat through the administration of meat alone, but then a large
quantity is required. An increase in tissue-fat and albumen may also,
to a slight degree, take place from the administration of albumen alone,
but only in illy-nourished individuals.

If peptone is given as food it is entirely destro3Ted, and the destruc-
tion of the tissue-albumen is completely prevented ; but there is no
increase in the body albumen, thus showing that peptone is earlier
destroyed than albumen and can only partially replace the albumen of
the food.

If gelatin and gelatinous tissue (bones, tendons, etc.) are given
exclusively the destruction of albumen does not cease, thus showing
that gelatin cannot replace albumen. But if gelatin and albumen are
given together the destruction of albumen is greatly reduced.

(b) Feeding with Fat. — The influence of fat on the destruction of
albumen is seen in the fact that in fasting animals the destruction of
albumen is less in fat than in thin animals ; this action is also seen in the
administration of proteid foods alone, where the destruction of albumen
is less in fat than in thin animals. Indeed, we have seen that in an
abundant albuminous diet, whereby the excretion of urea is increased, in
fat animals there may even be an increase in the body fat.

If fat is given alone as food to a carnivorous animal the destruction
of albumen is reduced but not prevented ;• when large amounts of fat are
given the fat of the body may even increase and yet the animals pass
into a state of starvation, for the tissue-albumen is gradually being
reduced.

If enough albumen is given to cause a nitrogenous balance and then
fat is added to the food, the nitrogenous elimination is reduced and all
the carbon of the fat does not appear in the C02; carbon is, therefore,
kept back in the body and stored up in the form of fat, while a certain
amount of nitrogen also being retained indicates, an increase of the
body albumen. So, the addition of fat to the food leads to both an
increase of tissue-fat and albumen, though this only occurs when a large
amount of fat is added to a moderately small amount of albumen.

If the amount of albumen is increased the elimination of urea also
increases, and, as a consequence of the great destruction of albumen, a
certain amount of the fat is spared and is stored up in the body. But
if the amount of albumen is reduced more fat is used up, and fat may
even be taken awa}r from the body.

The amount of fat in the body in feeding with albumen and fat is
also of influence on the metabolism of the body ; a body poor in fat,
which needs and destroys more albumen, more readil}- stores up fat;

STATISTICS OF NUTRITION. 683

while a body rich in fat, since, it needs and destroys less albumen, must
draw on its store of fat. Young animals, since they are thin, therefore
need more albumen and fat than older ones, while young animals, to
fatten, require more food than older ones. It is also easier to fatten thin
animals than to make tolerably fat animals still fatter.

(c) Feeding with Carbohydrates. — The action of the carb.ol^drates
in nutrition is especially seen in the herbivora, which are incapable of
being supported with albumen alone or with albumen and fat. Experi-
ment has shown that in so far as they are digestible all carbohydrates
have the same influence on the metabolism of the body. This applies to
starch, cane-, grape-, and milk-sugar, dextrin, and, to a certain extent, to
cellulose.

It is generally assumed that all the carbohydrates which enter the
animal body unite with the oxygen obtained in inspiration to form C02
and H20, so that an increase in carbohydrate diet means an increase in the
CO3 of the expired air. This is not, however, universally true, since
under many circumstances the carbohydrates may be retained in the
body as fat; on the other hand, it cannot be positively stated whether
the carbohydrates which are converted into sugar in digestion are
directly oxidized as sugar, or are all first converted into glycogen.

Feeding dogs exclusively with carbohydrates has proven that the
destruction of tissue-albumen and fat is under such circumstances less
than when the animal is deprived of all food, but that the destruction
of albumen is constant, and that such animals finally perish from
inanition. If albumen is given together with the carbohydrates in
increasing quantities, the excretion of nitrogen increases correspond-
ingly, but in a much less degree than when albumen alone or albumen
and fat constitute the diet ; therefore the carbohydrates in food serve to
spare the tissue change in proteids to a greater extent even than fat.
Hence, to keep the body in a state of nutritive balance a moderately
small amount of albumen is required with a large amount of carbo-
hydrates, and, as a consequence, the herbivora are kept in good nutrition
with the small amount of albumen found in their food. If the smallest
amount of albumen is given with the corresponding amount of carbo-
hydrates under which the body weight may be maintained without losing
albumen or fat, and then the albumen of the food is increased, the
elimination of nitrogen is also increased, but to a less degree than if
albumen was given alone ; there is, therefore, now an increase in the
albumen and fat of the bod}'. If, now, the amount of carbohydrates
is increased without diminishing the quantity of albumen in the food,
fat then accumulates in the body; and if the albumen is also increased
both albumen and fat accumulate.

It is not yet quite clear whether this fat is formed from the carbon

684 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of the albumen, as is generally acknowledged to be the case in the car-
nivora, or whether fat may not also be formed from the carbohydrates
directly. It thus seems clear that the addition of carbohydrates to the
diet spares the waste of tissue-albumen and body fat, and the attempt
has been made to determine the amount of carbohydrates which in their
nutritive value are equivalent to a given amount of fat. This has been
fixed by Yoit at the ratio of one hundred and seventy-five to one hun-
dred ; in other words, one hundred and seventy-five grammes of starch
are equivalent to one hundred grammes of fat.

V. THE FOOD KEQUIKED BY THE HERBIVORA UNDER DIFFERENT

CONDITIONS.

The nutritive processes in the herbivora differ in many respects from
those of the carnivora. In the first place, less albumen is destroyed
during fasting by the herbivora than is the case in the carnivora. Thus,
while in the example given above a dog weighing thirty-five kilos de-
stroys daily one hundred and sixty-eight grammes of albumen, an ox
weighing five hundred and twenty-two kilos only destroys twelve hundred
and seventy grammes. So, also, the herbivora on feeding with carbo-
hydrates and fat show much less tissue waste than the carnivora. In
other respects, with allowances for the different digestive peculiarities of
carnivora and herbivora, the nutritive process may be said to be similar.

It has been already stated that foods must not only contain repre-
sentatives of the proteid, carbohydrate, and fat groups, with salts and
water, but the different constituents must be present in definite propor-
tions, which may, however, vary according to the demands on the animal.
The proportion of albuminous to non-nitrogenous matter in food, i.e., the
proportion of albumen to starch and fat, is spoken of as the nutritive
proportion. The average nutritive proportion is attained when the food
contains one part proteid to from five to eight parts of non-nitrogenous
matter, it being remembered that one hundred parts fat may be replaced
by one hundred and seventy-five parts carbohydrates ; 1 : 2-4 is spoken
of as a narrower nutritive proportion, and 1:8-12 as a wider nutritive
proportion.

The natural food of the domesticated herbivora has a nutritive pro-
portion of 1:4-1:7; thus, ordinary hay has a proportion of 1:5-1:Y,
and, although it may be regarded as the normal food of ruminants, is not
suitable when there is a demand for rapid fat, milk, or work production.
In grass the proportion is only 1 :4-6, and on such foods cattle produce
the most milk ; young cattle thrive on it and rapidly put on flesh. Clover
has a proportion of 1:5-6, but on account of its large percentage of
cellulose is not completely digested, so it is usually combined with some
more concentrated food. Before blossoming clover has a proportion of

FOOD KEQUIKED BY THE HEKBIVOEA. 685

1 :4, or even 1:3, and its use then entails a waste of valuable proteids
unless combined with chopped straw so as to bring the proportion down
to 1:5. In the cereals the proportion on an average is 1:5-7, being
broader in barle}r and corn than in oats, r}re, and wheat ; in the hulled
fruits, malt, brewers' grains, and distillery residues the proportion is 1:3,
and in rape-seed ca-ke 1 : 1-2. These latter fodders are, therefore, only
applicable under special conditions. After this recapitulation we may
consider the principles of feeding somewhat more in detail.

Animals which have no work to do besides growing and keeping up
their nutrition are nourished perfectly well b}^ grazing if the grass
is abundant and of proper composition ; .this is the case for sheep, two-
to three-year-old horses, and }*oung cattle. If these animals are stall-
fed, instead of being put to grass, on account of the perfect quiet and
even temperature, the nutritive demands are reduced ; so now feeding
with hay or straw with some nitrogenous food suffices. A similar state
of affairs holds in animals which are stall-fed without being worked, such
as oxen in winter months, and the amount of food may here, also, be con-
siderably reduced. The data showing the amount of food required are
about as follows : —

For unworked animals, for ever}- one hundred kilos body weight,
2.5 kilos of solids in the grasses (green fodder) is sufficient ; therefore,
for the herbivora, for every one hundred kilos body weight, ten kilos of
grass, containing 2.5 kilos of solids, and of this 1.3 kilos of digestible
matters, is sufficient. In this amount 0.25 kilo is represented by albu-
men, non-nitrogenous extractive one kilo, and fat 0.05 kilo ; so the ratio
of the amount of food to the amount of digestible matter is 1 :4.2.

Thus, a horse weighing five hundred kilos may preserve a nutritive
equilibrium on a daily ration of seven hundred grammes albumen, two
hundred and ten grammes fat, three thousand seven hundred and fifty
grammes starch and cellulose, and about twenty kilos of water ; the ratio
of nitrogenous to non-nitrogenous food being thus 1:5.5. Starch and
fat may replace each other, seventeen parts of starch being equivalent to
ten parts of fat. In the horse, the carbohydrates are more important
heat-producing foods than is the case in man. Wolff has found tliat of
the heat produced, 76 per cent, is due to carbohydrates, 13.5 per cent,
to proteids, and 10.1 per cent, to fats.

In a general way it may be said that for each kilo of body weight
the herJbivora requires daily one hundred and fifty grammes albumen,
fifty grammes fat, and seven hundred and fifty grammes carbohydrates.
Smaller animals require proportionately larger amounts, since the de-
structive processes are more active in them. In fattening animals the
carbohydrates must be increased ; in milking animals the albuminous
food-constituents.

686 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Experiment has proved that cattle preserve a nutritive equilibrium
when the}- receive a daily ration calculated for ten hundred kilos of
body weight, as follows :—

19.5 kilos clover-hay.

3.7 " " " 13.0 kilos oat-straw, and 0.6 kilos rape-seed cake.

2.6 " " " 14.2 " " " " 0.5 "

3.2 " " " 13.3 " barley " " 0.6 "

25.6 " fodder-beets, 12.6 " oat " " 1.0

In the above feeding the animals digested and absorbed for ten hun-
dred kilos body weight on an average 0.57 kilo albumen and 7.4 kilos non-
nitrogenous matter; hence, the nutritive proportion was 1:13. The
above fodder contains on an average 0.05 kilo phosphoric acid, 0.1 kilo
lime, and 0.2 kilo alkalies; in addition, for ten hundred kilos body
weight, fifty -five kilos water were given.

For pregnant animals which are not worked, as brood mares, pas-
ture is sufficient; or if stall-fed, hay and straw, the latter with some
nitrogenous food, will answer if the total composition is made to cor-
respond with that of grass. If the grass and hay are not of the proper
composition some accessory food must be added. Especial reference
must be paid to the amount of albumen and salts in the food, such as
lime and phosphates, as of special importance for the development of the
osseous system of the young. In such cases some albuminous food rich
in salts is necessary, such as grains.

Male breeding animals which do not work must have their food so
adjusted that they do not put on fat; not that the amount of organic
matter may be reduced, but the food must be concentrated, have a small
percentage of indigestible matter, and little water and much albumen. Es-
pecially in the coupling season must the food be rich in albumen to make
up for the losses through copulation. Fat stallions and bulls are not
fruitful.

Animals for labor require more than pasture ; they require a large
amount of albumen, for by it the muscles are enabled to appropriate a
larger amount of oxygen ; so, also, fat and carboln'drates must be increased,
since they give to the muscles the substance which is consumed in muscular
activity. If the work is constant the carbon of muscles must always be
in excess. Voluminous and watery food must be avoided. The former
distends the alimentary canal, and so interferes with respiration, and the
latter leads to an accumulation of water in the tissues, and reduces the
tension and elasticity of the muscles. So the food must be concentrated,
as oats and barley, which are especially valuable on account of their fat.

Cattle on moderate work require per thousand kilos body weight,
from 0.7 kilo to 1.6 kilos albumen, non-nitrogenous matters from 8.4 to
12 kilos ; the nutritive proportion should thus be 1 : 7.5.

FOOD REQUIRED BY THE HERBIVORA. 687

This proportion may be reached in the administration of suitable
amounts of hay with some concentrated food, or clover-hay with chopped
straw. When severe work is required it is advisable to increase the
quantity of fat given (as by adding some oil-cake), the nutritive propor-
tion being brought to 1:6.

Working oxen can stand a larger amount of raw food (hay, etc.)
than horses. If rapid work is required of horses, a rich albuminous food
such as oats must be given ; if prolonged work is demanded, one richer
in fat, as corn, is better.

If animals are fed for food purposes an increase in the solids and
digestible matter of the food is requisite ; so the appetite must be
stimulated, and yet overloading of the alimenta^ canal avoided. It is,
therefore, advisable gradually to increase the amount of the usual food,
to stimulate the secretion by small quantities of salt, if possible, to aid
digestion by a previous preparation of the food, such as b}* giving ground
meal, and so to choose the foods that the waste of the organism will be
at a minimum.

At the commencement of such fattening, the organism must be made
rich with albumen : so thin animals must receive a large amount of
digestible food, with an extra proportion of fat and carbohydrates, since
we have found that under such circumstances there will be least waste of
albuminoids. This is accomplished by feeding for about two weeks with
2.5 kilos albumen and 12.5 kilos non-nitrogenous matters per thousand
kilos body weight, thus giving a nutritive proportion of 1:5. Then the
non-nitrogenous matters must be increased to from 12.5 to 16.25 kilos per
thousand kilos body weight, so making the proportion 1 :6.5. When the
economy becomes rich in albumen and then commences to put on fat, the
albumen of the food may be increased to 3.0 kilos, making a proportion
of 1 :5.5; when it becomes very fat, the solids, especially the indigestible
solids, must be reduced, and some oil-cake added to the food.

In fattening oxen the water given should be in the proportion of
4-5 :1 of the solids given, in sheep 2-3 : 1.

In fattening sheep it has been proved that highty albuminous foods
are especially valuable. Ground beans ma}^ be used for this purpose
(0.5 kilo daily) combined with hay, In fattening sheep the preparatory
treatment necessary with cattle may be usually dispensed with, and the
diet more rapidly changed from one poor in nitrogenous matters (1:5.5)
to one rich in proteids (1 : 4.5). The diet for sheep must not be too rich
in water, so beets are not as valuable as with cattle ; the best results are
obtained from feeding with good hay and a corresponding amount of
crushed beans or cereals. Sheep fatten more rapidly after shearing than
before, for then the appetite is better and the thirst lees.

Young animals which are designed for food purposes will slowly take

688 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

on flesh in a good pasture ; if an accumulation of fat is desired, additional
carbohydrates and fatty food must be given.

As a rule, the hog is more readily fattened than the sheep, and the
latter than the ox. Race is also of influence. Thin, full-grown hogs at
the commencement of fattening require large amounts of food, forty kilos
of solids per thousand kilos body weight. Good results are obtained by
feeding with crushed barley, corn, or peas, the latter especially, if mixed
with steamed potatoes. The use of buttermilk or sour milk enables the
amount of food to be reduced and still give satisfactory results.

For milk animals the conditions of food have been already consid-
ered, and a good pasture is all that is required.

When stall-fed, nutritive change is reduced ; when food corre-
sponding to pasture is given the quantity of milk and butter is increased.

In wool-producing animals a larger percentage of proteids is required
in the food than in cattle, goats requiring less than sheep. Experiment
has proven that sheep (ninety-six kilos in weight) on feeding with hay
for one thousand kilos body weight require daily twenty-six kilos, and
of this digest 1.32 kilos albumen and 10.53 kilos non-nitrogenous matters
(with 0.322 kilo fat). On such feeding the weight increased somewhat,
0.181 kilo albumen and 0.299 fat (reckoned for one thousand kilos body
weight) being deposited. The nutritive proportion, therefore, for sheep
should be 1 : 9.3. It has further been determined by Wendee and Hohen-
heim that slight loss of weight, within limits, does not interfere with
wool production, especially if the food be rich in proteids.

By chopping food mastication is, to a certain extent, facilitated, but
it cannot be regarded as a substitute for mastication, since the mixing
with saliva can only be perfectly performed when the food is thorough^
masticated. The principal object in chopping food is to enable it to be
mixed with other materials so as to increase its tastefulness and digesti-
bility, or to assist in the administration of other substances. Chopping
should never be carried so far as to permit of the food being swallowed
without undergoing a certain amount of mastication. The cereals are
especially suited for administration under the forms of meals and may
be readily mixed with other foods. The readily digestible grains, of
course, do not need to be ground, but in the form of meal they may be
mixed with less digestible, bulky substances, such as chopped straw.
Thorough mastication of the latter is so attained and the grain gives
taste to the mixture, without which, probably, the food would be rejected.
To horses and sheep all grains the hulls of which are not too hard and
thick may be given uncrushed by mixing with chopped straw and the like
as long as their organs of mastication are in good condition. Barley is
best given to sheep when roughly ground, while the seeds of the legu-
minous plants and corn may likewise be ground for sheep and horses.

FOOD REQUIRED BY THE HERBIVORA. 689

Grinding of oats is only necessary for old horses or those in which the
teeth are changing. Oxen and hogs, as a rule, digest the ground cereals
better than the whole grains. According to Lehinann, of the entire
grains in a fourteen-months-old ox 48.2 barley and 19.6 per cent, oats
remained undigested. In a five-months-old ox 33.0 barley and 6.5 per
cent, oats remained undigested.

Even after mixing with chopped straw a large part of the entire
grains escape digestion and pass through the faeces almost entirely
unchanged, and still possess the power of germination. Of one hundred
kilogrammes of the unground grains fed to hogs Lehmann found in the
faeces 50.6 kilos of oats, 49.8 kilos of rye, 54.8 kilos of barley, and 4.8
kilos of peas. The experiment, therefore, points in the most emphatic
manner to the administration to the ox and hog of all the cereal grains
mealed and mixed with other foods. About the only exception to this
statement is found in the case of oats. The chopping of dry fodder
enables it to be mixed readily with large amounts of more tasty sub-
stances. So, also, the j^oung, tender, highly albuminous green foods
may be chopped and mixed with less nutritious substances, such as straw.
The transition of dry to green feeding and the reverse is facilitated by
the mixture of the green fodder with dry, chopped straw. Horses should
always receive good hay unchopped, but the straws of the cereals should
always1 be given in a chopped state, since horses will only take the hard
straw in small amounts. Chopped food for horses should not be shorter
than from one and one-third to two centimeters in length of each piece,
since smaller pieces readily lead to obstructive colic, especially if given
with meal in a moist condition. For the ox, straw may be chopped into
pieces two and one-half to three centimeters long, and mixed well with
corn-meal or chopped beets or potatoes in order to make it more tasty.

The duration of the interval between different times of feeding of
the domestic animals is a matter of considerable importance. Too fre-
quent feeding should be avoided on account of the shortening of the
necessary pauses between the digestive processes. The ruminants, espe-
cially, should not receive more than at most three meals in the day, so as
to allow time for rumination. Horses likewise should receive three meals
and hogs from three to four meals a day. On the other hand, the inter-
vals between feeding should not be too long, on account of the great
increase of hunger so produced leading to faulty mastication and imper-
fect insalivation of the food. This state of affairs may produce much
more serious disturbance in the non-ruminants than in the ruminants.
In young cattle from four to six meals may be given a day on account
of the relatively smaller size of their stomachs, since three meals scarcely
furnish enough to sustain them. So, also, when the fodder is especially
fluid the meals may succeed each other every two or three hours, for in

44

690

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

NORMAL AMOUNTS OF FOOD FOR CATTLE, HORSES, SHEEP, AND SWINE.

For every kilogramme of body weight the following amounts of digestible
food-stuffs must be contained in the daily ration: —

N I T R 0-

NON-NlTRO-

.

SOLIDS.

GENOUS
M A T -

G E N O IT S

EXTRA c T-

FAT.

1

•1

TERS.

IVE MAT-
TERS.

|

CLASS OP ANIMAL.

a

a

g

S

£

a

a

a

a

5|

£
f

'2

1

1

P

a

'3

3

i

a
I

a
S

c:
1

J

|

i

o

f

f

§

s

*

§

%

3

%

^

*

Kilogrammes.

1. Young Cattle.

2-3 months old, 75 kg.

weight,

21.0

26.0

23.5

3.0

5.0

4.0

9.5

12.5

11.0 1.5

2.5

2.0

17.0

1:4.0

3-6 months old, 150

1

kg. weight, . . .

23.5

27.0

25.0

3.0

3.5

3.0

9.5

12.0

11.0 0.75

1.25

1.0

15.0

1:4.2

6-12 months old, 250

kg. weight, . . .

25.0

30.0

26.0

2.0

3.0

2.5

9.5

12.0

11.0 0.4

0.8

0.6

14.1

1:5.0

12-18 months old, 350

kg. weight, . . .

25.0

30.0

26.0

1.8

2.5

2.0

9.5

11.0

10.5,0.3

0.5

0.4

12.9

1:5.7

18-24 months old, 425

1

kg. weight, . . .

25.0

30.0

26.0

1.4

1.8

1.5

9.0

10.5

9.5

0.2

0.4

0.3

11.3

1:6.8

2. Oxen.

At rest

15.0

20.0

18.0

0.6

09

0.7

5.5

7.0

6.5

0.1

0.2

0.15

7.35

1:1.0

Working, . . . . .

24.0

28.0 26.0

1.4

1.8

1.6

8.0

10.0

9.0

0.2

0.4

0.3

10.9

1:6.0

Severe working, . .

24.0

32.0

28.0

2.0

2.8

2.4

10.0

12.0

11.0

0.4

0.6

0.5

13.9

1:5.1

S, Fattening Cattle.

1st period, ....
2d "

27.0
260

30.0

9,90

28.5

9,7 5

2.3

9, 8

3.0
35

2.5
30

11.0

11 0

12.5
1?0

12.0
11 5

0.5

06

0.7
1 0

0.6

0 7

15.1
152

1:5.4
1-4 5

3d "

250 '-2RO 9,«5

95

3 3

97

11 0

11 5

05

08

06

14 8

1-48

4. Milk Cows.

21.0

32.0

26.0

2.2

2.8

2.5

9.5

12.0

10.0

0.35

0.6

0.4

12.9

1:4.4

5. Horses.

Working

21.0

27.0

24.0

1.6

2.0

1 8

80

100

90

05

08

06

11.4

1:5.8

Heavy work, . . .

23.0

30.0

26.5

2.5

3.0

2.8

9.0

12.0

10.5

0.6

1.0

0.8

14.1

1:4.5

6. Young Sheep.

5 -6 months old, 28 kg.

weight,

28.0

32,0

30.0

2.5

3.5

3.2

9.5

11.5

10.5

0.7

1.0

0.8

14.5

1:4.0

6-8 months old, 33-34

kg. weight, . . .

26.0

28.027.0

2.5

2.8

2.7

8.5

10.5

9.5

0.5

0.8

0.6

12.8

1:4.0

8-11 months old, 37-

38 kg. weight, . .

23.5

26.0

25.0

2.0

2.5

2:1

7.5

9.5

8.5

0.4

0.8

0.5

11.1

1:4.7

11-15 months old, 41

kg. weight, . . .

23.5

25.0

24.5

1.5

2.0

1.7

6.5

8.5

7.5

0.3

0.5

0.4

9.6

1:5.0

15-20 months old, 42-

43 kg. weight, . .

21.5

25.0 23.5

1.2

i.r,

1.4

6.5

8.5

7.5

0.25

0.4

0.3

9.2

1:6.0

FOOD REQUIRED BY THE HERBIVORA.

691

NORMAL AMOUNTS OP FOOD FOR CATTLE, HORSES, SHEEP, AND SWINE.

(Continued.)

N I T R O-

NON-NlTRO-

SOLIDS.

GENOUS !
M A T -

GE NOUS

EXTRA c T-

FAT.

3

|

TERS.

IVE MAT-
TERS.

1

1

CLASS OF ANIMAL.

d

|

Q

3

d

a

g

g

q

£

3

|

eg

1

3
1

a
_§

1

p
I

1

g

i

V

1

a

1

3

i

f

E

1

3

1

S

§

B

Kilogrammes.

7. Wool Sheep.

Coarse-wooled sheep, .

19.0

24.0

22.0

1.0

1,5

1.2

6.5

8.5

7.5

0.1

0.3

0.2

8.9

1:6.7

Fine-wooled sheep, .

21.5

27.0

24.5

1.1

1.7

1.5

7.5

9.0

8.5

0.2

0.4

0.3

10.3

1:6.2

8. Rams.

23.5

27.0

25.0

2.0

2,5

2.2

9.0

12.0

10.5

0.4

0.6

0.5

13.2

1:5.3

9. Fattening Sheep.

27.0

32.0

29.0

2.5

3,5

3.0

11.0

13.0

12.0

0.4

0.6

0.5

15.5

1:4.5

2d " .....

25.0

30.0

27.0

3.0

4.0

3.5

11.012.0

11.0

0.5

0.7

0.6

15.1

1:3.5

Non-Nitro-

genous Ex-

tractive

10. Young Pigs.

Matters and
Fats.

2-3 months old, 25 kg.

weight,

50.0

58.0

54.0

,7.0

8.0

7.5

26.6 31.0

28.5

3-5 months old, 33-50

kg. weight, . . .

41.0

47.0

44.0

5.0

7.0

6.0

22.0

26.0

24.0

5-6 months old, 62-63

kg. weight, . . .

39.0

43.0

41.0

4.0

5.0

4.5

20.0

24.0

22.0

6-8 months old, 85 kg.

weight,

32.0

38.0

35.0

3.0

4.0

3.5.

18.020.0

19.0

8-12 months old, 125

kg. weight, . . .

24.0

30.0

27.0

2.5

3.5

3.0

15.018.0

16.5

11. Fattening Pigs.

1st period, ....

45.0

48.0

46.0

4.5

6.0

5.0

24.5

26.5

26.0

31.0

1:5.2

2d "

37.0

45.0 40 0

3.5'45

4.5

21.0

24.5

230

27.0

1:5.8

3d "

26.0

33.0

30.0

2.5

3.5

3.0

17.0

19.0

18.0

21.0

1:6.0

12. Breeding Pigs.

(Sows and Boars), . .

26.0

32.0

32.0

1.5 2.0

1.8

1.25

15.0

14*

15.8

1:7.8

this condition the stomach rapidly empties itself and the feeling of
hunger again appears. So, also, when feeding with dry fodder is com-
menced it is better at the beginning to give at least four different meals,
so as to avoid overdistention and filling of the stomach with this more
bulky food. At the end of fattening the meals may be increased in
number and reduced in amount, digestion of small amounts of readily
digestible foods being now more readily accomplished.

692 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

VI. HUNGER AND THIEST.

The sensations which lead to the prehension of solid and liquid
foods are known as hunger and thirst. It was previously supposed that
hunger was a local sensation which was produced by the absence of food
in the stomach. Evidently this is a mistaken idea, else would the rumi-
nants never experience this sensation, for in them the stomach is never
free from food, even when death occurs from starvation. The appear-
ance of hunger coincides with absorption of the matters digested at the
previous meal. Although the sensation is apparently referred to the
abdomen, it cannot be regarded as a localized sensation, but rather as a
peculiar modification of the general system similar to that produced in
dyspnoea; nor, indeed, is the stomach even the starting point of hunger,
for the pneumogastrics, the sensory nerves of this organ, may be divided,
and if the animals be deprived of food the clearest evidences of hunger
are, nevertheless, capable of detection. In spite of this fact, the sensation
of hunger is, nevertheless, to a certain extent dependent upon the con-
dition of the stomach, as is indicated by the temporary relief of hunger
which follows introduction into the stomach of matter which is not in
the slightest respect nutritious. So, again, even when the stomach is
filled with food, if through any disease digestion or absorption or the
passage of food into the small intestine are interfered with the hunger
may, nevertheless, be intensely felt; and, again, even after a hearty meal
digestion may be complete, and the stomach empty for some time before
the sensation of hunger appears.

In the case of thirst the state of affairs is somewhat similar, except
that there the sensation is more distinctly localized in the fauces and
may be relieved by the application of moisture to that part. When an
animal is deprived of liquid, the blood, from the continued formation of
secretions and excretions, rapidly loses its normal percentage of water.
The sensation of thirst is evidently due to the irritation of the sensory
nerves of the mucous membrane of the pharynx produced by the drying
of the mucous membrane, and while it may be relieved, as already
mentioned, b}T moistening this part, the arrest of thirst is only temporary.
But, on the other hand, the thirst may be permanently relieved by the
injection of water into the veins and even by enemata of water, and
while thirst, therefore, has a local expression, like hunger, it represents
the needs of the econom}*- for water ; thirst may thus be abolished, even
although no water enter the mouth. Every cause, therefore, which
diminishes the proportion of fluid in the blood, whether intense heat or
exercise which favor cutaneous and pulmonary evaporation, dropsies,
abundant hemorrhages, or diabetes, all lead to thirst ; so, also, salts
occasion thirst by withdrawing water from the blood.

SECTION XIII.
ANIMAL HEAT.

IT has been seen that the income of the animal body is represented
by complex combinations of carbon, hydrogen, nitrogen, and oxygen, and
the introduction of free oxygen in respiration ; the outgo of the body,
on the other hand, is represented by similar combinations of the same
elements in t;lie form of carbon dioxide, water, and urea.

The conclusion is thus evident that the absorbed ox^ygen has within
the body undergone combination with carbon and hydrogen with the
production of carbon dioxide and water, and that the substances intro-
duced as food have all in different degrees united with oxygen. In other
words, the nutritive processes in the animal body are represented by a
series of oxidations by which the organic food-products are restored to
the inorganic form. Oxidation of any kind will invariably be accom-
panied by a production of heat, and we thus see that one of the principal
sources of the heat of the animal body is to be looked for in such pro-
cesses of oxidation. It is a well-established fact that the combustion of
any body, whether rapidly or slowly produced, is accompanied by the
evolution of a fixed quantity of heat, provided the energy be not other-
wise employed. Thus, the complete combustion of one gramme of sugar
invariably corresponds to the development of four heat-units.*

If this combustion takes place in the animal body, it is evident that
the same amount of heat must be developed, no matter what may be the
character of the substances developed between the starting point and the
final termination of the process of oxidation.

In the animal body, however, such processes of combustion are
rarely as complete as would occur in the incineration of food-stuffs
outside of the body. Thus, for example, in albumen the process of
oxidation results in the formation of urea, which itself is capable of
still further oxidation. ' Nevertheless, it ma}T be stated with a tolerable
degree of accuracy how much heat is set -free in such processes of
oxidation of the food-stuffs in the animal body. Knowing the amount
of heat developed in the oxidation of one gramme of albumen and
the amount developed in the oxidation of a proportionate quantity of
urea, deducting the latter from the former will evidently represent the

* By this term, heat-unit, is meant that amount of heat which is required to raise one
kilogramme of water from 0° C. to 1° C.

(693)

694 PHYSIOLOGY OF THE DOMESTIC ANIMALS

degree of oxidation occurring in the animal body. This factor has been
estimated as corresponding to five heat-units. With these data the
amount of heat developed in twenty-four hours may be readily calculated.
Thus, taking the example given by Fick, the income of the body was
represented in round numbers by one hundred and twenty grammes of
fat, two hundred and sixty-three grammes of carbohydrates, and one
hundred and seventeen grammes of albumen, with the excretion of
thirty-nine grammes of urea. The combustion of one gramme of fat is
represented by the development of nine and six-tenths heat-units, and, as
already seen, one gramme of carbohydrates by four heat-units, and one
gramme of albumen by five heat-units. The total amount of heat, there-
fore, developed is represented by 120 X 9.6 -f 263 X 4 -f 1 17 X 5, or, in
round numbers, two thousand eight hundred heat-units. The confirma-
tion of these figures and their influence in maintaining the heat of the
animal body is determined by calorimetric experiments. To accomplish
such an experiment, first, the tissue change in twenty-four hours must be
calculated ; second, the amount of heat liberated by the body in that
time ; third, the average temperature of the animal body at the com-
mencement and end of the experiment; and, fourth, the average heat
capacity of the body. Asa rule, the difference between the body tem-
perature at the commencement and end of such experiments is so slight
as not to deserve attention, and the amount of heat set free in twenty-
four hours may be regarded as indicating the amount of heat developed
in the body.

Such experiments do not, however, serve with absolute accuracy to
confirm the theoretical figures deduced from the co-efficient of heat
production represented above as belonging to the different food-stuffs.
In nearly all cases there is an apparent loss of heat over what should be
expected from these data. It is to be recollected, in the explanation of
this discrepancy, that the energy set free in such oxidations ma}7 take
on the form either of heat or of mechanical work. In the animal body
all these sources of loss of energy occur. All forms of muscular move-
ment are accompanied by liberation of energy, and a continual loss of
heat is taking place through radiation from the surface of the body, by
conduction, by the evaporation from the skin and mucous surfaces, and
by the warming of the ingesta. The amount of heat dissipated by the
animal body in a condition of health is in close dependence upon the
amount produced, upon the difference in temperature between the animal
body and the surrounding medium, and especially upon the relationship
between the external surface of the body and the body weight. Thus,
small animals for each kilogramme of the body weight set free more heat
than large animals. It has been estimated that for each kilogramme of
body weight the horse in each hour sets free two and one-tenth heat-

ANIMAL HEAT. 695

units ; sheep, two and six-tenths heat-units ; the dog, four heat-units ;
and the sparrow, thirty-two heat-units. The cause of this difference may
be found in the fact that the smaller a sphere the greater is its superficial
area in comparison to its cubic contents. The same rule applies, also, to
the irregular form of the animal body, in which the smaller it is in pro-
portion to the weight of the animal the greater will be its superficial area.
It is, however, from the external surfaces that the greatest amount of
body heat is dissipated, and it is, therefore, seen why small animals lose
proportionately more heat than larger animals.

Two different conditions are noted in reference to the heat which is
retained in the animal body, and which, therefore, causes the body tem-
perature. In the cold-blooded animal the temperature of the body is
not constant, but varies with that of the surrounding medium, rarely
being more than a few tenths of a degree above it. In the warm-blooded
animals, as in mammals and birds, on the other hand, the body tempera-
ture is, as a rule, higher than that of the surrounding medium, and is
independent of variations in the latter. The cause of this difference of
body heat lies in the difference in energy of the tissue changes. In the
cold-blooded animals the development of heat is so slight that this
amount of heat is at once given up to the cold atmosphere. If the ex-
ternal temperature be increased, this dissipation of heat is accordingly
diminished, and as a consequence part of the heat produced is retained
in the body and increases its temperature. On the other hand, if the
external temperature falls, the amount of heat dissipated is increased
and the body temperature falls. In animals with a constant body tem-
perature the amount of heat, on account of the greater energy of tissue
change, is so much greater that but a part alone is given up to the sur-
rounding medium. From the fact that the source of temperature is
found in the chemical changes occurring in the tissues, it is evident that the
development of heat will be greater in tissues in which such processes are
active than where they are sluggish. The temperature of the animal body
will, therefore, vary in different localities ; it will be greater in secreting
glands and contracting muscles ; it will be less where loss of heat is
favored, and, as a consequence, the exterior surfaces of the body will
possess a lower temperature than the inner cavities.

In the lungs the blood gives up so much heat to the air that the
temperature of the blood in the left side of the heart is cooler than that
of the right, in spite of the development of heat which accompanies the
oxidation of haemoglobin. With this exception the arterial blood, as
being less exposed to loss of heat, ma}', as a rule, be stated to be warmer
than venous blood.

The temperature of an organ will, therefore, depend upon the amount
of blood circulating through it. Under certain circumstances the venous

696 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

blood may increase in temperature over that of the arterial blood ; such
a state of affairs is seen in the blood coining from the contracting muscles
or from a secreting gland. The blood by its continuous circulation
through the body tends to equalize the body temperature, giving up
heat to tissues which are cooler than itself and withdrawing heat from
those which are warmer. The mean between the highest and lowest
temperature of the animal body is spoken of as the body temperature,
and is generally represented by the temperature taken in the mouth or in
the rectum.

The following figures represent the mean average temperatures of
the different domestic animals : —

Horse,
Ox, .

37.50 to 380 C.
. 380 to 38.50 C.

Dog,

38.50 c.

Sheep,
Chicken,

390 to 400 C.

420 C.

Hog,

390 to 400 c.

Ass,
Rabbit,
Mouse,
Cat,
Goose,
Pigeon,

39.50 to 38° C.
390 to 39.50 C.
41.10 C.
38.50 to 390 C.
41.50 C.
420 C.

While these figures represent the average body temperature, varia-
tions within narrow limits may often be observed even in perfectly
healthy individuals. A variation of one degree or more indicates some
failure in the organism or some departure from the natural process of
metabolism. It is, therefore, evident that the mechanisms which regulate
the balance between the production and loss of heat must be extremely
sensitive. Such a regulating mechanism will prevent an increase of the
body temperature either by diminishing the production or increasing
dissipation of heat, or, in the other case, by increasing the production
and diminishing the loss.

Heat, as already indicated, is lost to the body by conduction to the
ingesta and egesta, to the expired air, and by conduction and radiation
from the skin and through the evaporation of fluid from the surface of
the body. The relative amounts of heat lost by these different channels
have been calculated by Helmholtz as follows : through the expired air,
5.2 per cent.; through the water of respiration, 14.7 per cent. ; through
the skin, 77.5 per cent. The chief means, therefore, of heat dissipation
are through the lungs and skin. The more rapid the respiration the
greater will be the loss of heat, and in animals which do not perspire the
lungs will represent the main source of heat dissipation. In other
animals the skin is, no doubt, the great regulator of the body temper-
ture. The more blood passes through the cutaneous vessels, the greater
will be the loss of heat through radiation, the greater will be the cuta-

ANIMAL HEAT. 697

neous secretion, and, as a consequence, the greater will be the loss of
heat through evaporation. Everything, therefore, which dilates the
cutaneous blood-vessels will increase the heat dissipation. The working
of the mechanism of heat regulation through increasing heat dissipation
is well seen in the case of exercise. Every muscular contraction, as
already pointed out, leads to an increase of heat production, and, as a
consequence, the blood coming from a contracting muscle may be several
degrees warmer than the arterial blood supplied to it. Nevertheless, the
body temperature, even in severe exercise, is but little elevated above the
average, for the increased exercise leads to an increased demand of
oxygen in the inspired air, and, as a consequence, respiration is increased
and the amount of heat eliminated through the expired air thereby aug-
mented. The action of the heart is likewise accelerated, the circulation
through the skin is augmented, perspiration is increased, and a greater
amount of heat is given up from the skin by radiation and by the evapo-
ration of the perspiration. By this means enough heat is lost to the
animal body to balance the increased production.

Increase of external temperature likewise prevents an increase in
the body temperature by increasing the circulation through the skin
and the cutaneous perspiration, and so also increases the loss of heat.
On the other hand, if the external temperature is reduced the cutaneous
vessels contract, the evaporation of perspiration is prevented, and again
a balance is struck between the production and the heat dissipation.

The influence of the nervous system on the temperature of the
animal body is both directly and indirectly exerted. It has been men-
tioned in a previous section that division of the cervical sympathetic
nerve is followed not only by contraction of the pupil, but also by an
increased temperature of the corresponding side of the head and neck.
If this experiment be performed upon a rabbit the increase of tempera-
ture is so great as to be readily perceptible to the touch ; and if the ears
of the rabbit be examined in transmitted light the blood-vessels of the
auricle on the side of section of the sympathetic will be found to be
greatly dilated. Section of the sympathetic, therefore, by paralysis of
the vaso-motor nerves, has occasioned dilatation of the blood-vessels, and
the consequent increased vascularity facilitates radiation of heat and so
causes a perceptible increase in the temperature of the part. But the
increased radiation of heat is also attended with increased heat produc-
tion ; for the hypersemia produced by vaso-motor paralysis is accom-
panied by increased nutritive activity, and heat production is thereby
augmented. Thus, it has been shown by Bidder that excision of a part
of the cervical sympathetic in the rabbit is followed within two weeks by
a marked increase in the size of the ear on the side of operation ; and
excision of the cceliac plexus has been said to produce intense hyperaemia

698 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of the stomach. Numerous instances of pathological increase of nutri-
tive activity from increased blood supply and consequent increased tem-
perature will doubtless suggest themselves.

In addition to this indirect influence of the nervous system through
the vaso-motor nerves on calorification, the central nervous system is
stated to both directly and reflexly govern the development of heat,
though much of the evidence brought forward as to a special nervous
mechanism for regulating animal heat is imperfect. Experiments have
chiefly been directed toward locating special heat-centres in various
parts of the brain. Ott claims that there are four localities in the brain
irritation of which increases bodily temperature by from 2.2° to 3.3° C.
These heat-centres are said to be located as follows: 1. In front of and
beneath the corpus striatum. 2. The median portion of the corpora
striata. 3. Between the corpus striatum and the optic thalamus. 4. The
anterior inner end of the optic thalamus. A heat-centre is also claimed
to be present in the dog, in the cortex of the anterior portion of the
upper surface of the brain, near the median line, the locality agreeing
with that of the motor centres of the hind limbs, and for the movements
of flexion and rotation of the fore limbs. According to Wood, section
of the brain between the pons and medulla oblongata causes increased
radiation of heat and diminished heat production, due to the cutting of
the paths of communication with the cerebral heat-regulating centre.
There seems to be little doubt but that irritation of various parts of the
brain does lead to modifications in the heat-producing mechanisms
of the body, arid that fibres in connection with these centres decussate
in the medulla; but as to whether the effects produced are stimulating
or inhibitory, whether they act through the production of change in
circulation, or whether they directly influence the chemical operations
concerned in the production of heat, is quite unknown.

BOOK II.

THE ANIMAL FUNCTIONS.

(699)

SECTION I.
PHYSIOLOGY OF MOVEMENT.

1. THE CONTRACTILE TISSUES. — It was stated that the function of
contractility represents one of the fundamental properties of protoplasm,
and in the simplest forms of life, consisting of undifferentiated proto-
plasm, as in the structureless amoeba, the contractilit}^ of protoplasm
renders locomotion possible. The first attempt at localization of this
function of contractility, in the general specialization of function in the
development of the animal kingdom, was noted in the development of
protoplasmic prolongations of cells, so-called cilia, which in numerous
infusoria constitute organs of locomotion ; in various shell-fish, organs
for aiding the prehension of food and the functions of respiration, and in
the higher animals for producing motion of particles brought in contact
with them. The first attempt, therefore, at the development of organs
in which the function of contractility is specialized is seen in the develop-
ment of vibratile cilia. In a step higher in the progress of specialization,
contractility reaches its highest degree in the muscular tissue, which may
be regarded as a mass of protoplasm inclosed within a cylindrical or
polygonal cell. In the higher animals each of these three different
representations of contractile substances are met with : undifferentiated
protoplasm, as found in the lymph-corpuscles, white blood-corpuscles,
connective-tissue corpuscles, mucus- and pus-cells ; ciliated cells, lining
various mucous cavities in the body ; and muscular tissues of the striped
and unstriped varieties.

The characteristics of motion as occurring in undifferentiated proto-
plasm and ciliated cells have already been studied. The conditions of
muscular contractility now deserve attention. In muscular tissue the
contractile substance is inclosed in a tubular sheath, constituting a mus-
cular fibre. Muscular fibres may be either striped or voluntary fibres, or
unstriped or involuntary fibres. The striped or voluntary muscles, which
have a red appearance, constitute the great mass of contractile tissues
of the body. They are ordinarily connected with the bones, and are
therefore spoken of as skeletal muscles ; their contractions, as* a rule, are
under the control of the will. Each muscle-fibre is more or less cylin-
drical, varies in length from one one-hundredth to one six-hundredth of
an inch, and consists of the sarcolemma, an elastic sheath, probably of the
nature of connective -tissue, with transverse partitions which stretch

(701)

702

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

across the fibre at regular intervals (membrane of Krause). Within this
is inclosed the sarcous substance, or the contractile tissue of the muscu-
lar fibre, which is a broad, highly refractive, doubly refractive disk, and
the nuclei or muscle-corpuscles. The muscle-corpuscles are thus within
the sarcolemma, and it is at the expense of their protoplasm that

FIG. 271.— MUSCULAR TISSUE, AFTER GERLACH. '(Ellenberger.)

1, scheme of the different parts of striped muscular fibre; S, sarcolemma: K, nucleus: 2, striation;
F, fibrillae ; N, nerve ; E, nucleated nerve-plate ; 2, part of a cross-section : 3, isolated fibrillae ; 4, highly
magnified fibril of insect muscle : A, Krause- Amici's line; B, anisotropic substance ; C, central disk ; D,
isotropic substance ; 5, separation of disks ; 6. cell of heart-muscle of frog ; 7, embryonal development of
muscular fibre; 8, cells of heart-muscle; 9, cross-section of heart-muscle; 10, unstriped muscle-cells; 11,
cross-seqtion of unstriped muscle-cells; 12, muscular fibre with tendon; 13, interfibrillar muscular
n«rvos.

muscular tissue is formed. Between the contractile disks and Krause 's
membrane is a transparent, isotropic, semifluid laj'er (the lateral disk
of Engelnrann), which is composed of prismatic, rod-shaped elements,
the sarcous elements of Bowman.

PHYSIOLOGY OF MOVEMENT.

703

The striated appearance of muscular tissue is due to the arrange-
ment of the sarcous substance in alternate light and dark layers or disks.

Each muscular fibre is made up of a large number of primitive
fibrillse placed side by side and united by a semi-fluid cement substance,
the fibrillse being so arranged that the transverse markings lie at the
same level.

The muscular corpuscles in the muscular fibres of man and most

B

B

FIG. 272.— UNSTRIPED MUSCULAR TISSUE.

(Ellenberger. )

A and B, foetal cells: C, H. fullv formed fibre; I,
bundle of fibres ; K, cross-section of bundle of pale muscular
fibres.

FIG. 273.— MUSCULAR CELLS FROM THE
MUSCULAR COAT OP THE STOMACH,
ENLARGED Two HUNDRED AND FIFTY
DIAMETERS. (Ellenberger.)

A, elongated nucleus ; B, pointed ends of the cells.

vertebrates, with the exception of the tissue of the heart, are situated on
the surface of the muscular substance, but in invertebrates they are
usually found in the central part of the fibres. The muscular fibres are
united in bundles by connective tissue and terminate in tendons which
are composed of connective-tissue fibrillee.

The unstriped muscular fibres are composed of elongated spindle-
shaped nucleated cells, which are contractile in one direction. These

704

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

•""mil HI'-.

'it'UNUII II III"!

j-Wftti 3«|M

>»wiii 9 nm

^mifi

cells are arranged in bundles connected by a cement substance ; they do
not terminate in tendons, but are arranged in groups, usually in the form
of a membrane ; such muscular fibres are found in the walls of the ali-
mentary canal, in the walls of the genito-urinary passages, in the bronchi,
and in various other localities.

(a) The Chemical Composition of Muscle. — The chemical constit-
uents found in muscles differ greatly according as the examination is
made on fresh, living tissue, or after rigor mortis has set in. All mus-
cles after death lose their irritability, and pass from their flexible, trans-
parent condition into a state of rigidity and opacity, which is described
under the general term of rigor mortis. Analogy
may be traced in this respect between the living
and dead muscle and blood.

Blood in the process of coagulation produces
the proteid fibrin ; muscle, in the act of dying,
produces the proteid myosin.

Before taking up the characteristics of these
bodies, further comparison of the characteristics
of living and dead muscle deserves attention.

In the first place, in a state of rest, living
muscle has an alkaline reaction ; in dead muscle,
and in muscle in contraction, the reaction is acid,
due to the development of paralactic acid, as well
as acid potassium phosphate, and carbonic acid.

Living muscle is to a certain extent trans-
lucent, extensible, and elastic ; dead muscle is
opaque, rigid, inextensible, and has lost its elas-
ticity. The main difference, however, between
living and dead muscle is found in the coagulation
of nvyosin in the latter. If a living muscle be
freed from blood by repeated washing and injec-
tion of saline solution through its blood-vessels, be then frozen, chopped
up, and rubbed up in a mortar with four times its weight of powdered
ice, containing 1 per cent, of sodium chloride, a mixture is obtained
which, below the freezing point, is sufficiently fluid to be filtered. This
opalescent filtrate is known as muscle-plasma, and remains fluid only
while kept at 0° C. If allowed to be heated above this point it is
gradually transformed into a solid jelly, which subsequently separates
into a clot and serum. The clot is myosin, and originates in the doubly
refractive substance ; the serum contains serum-albumen and various
extractives.

If a muscle which has already passed into the condition of rigor
mortis be washed with water so as to remove the albumen and the dif-

i, Ulllllllll

FIG. 274. — PRIMITIVE
BUNDLE FROM THE BI-
CEPS BRACHII OF THE
HORSE. (Tereg.)

A, intermediary disks : B, cen-
tral disks ; C, dark striation ; D,
light striatiou.

PHYSIOLOGY OF MOVEMENT. 705

ferent extractive matters, and then be extracted with 10 per cent, solu-
tion of sodium chloride, a large portion of the muscular tissue will be
dissolved and will form a viscid fluid. If this fluid be allowed to fall
drop by drop into distilled water a flocculent precipitate will be pro-
duced ; this precipitate is likewise myosin. As is seen from its method
of preparation, myosin is a globulin which is soluble in strong solution
of sodium chloride, and which may be precipitated therefrom by dilution
with water. Myosin, like other globulins, may be coagulated by heat,
although it coagulates at a lower temperature than does serum-albumen,
its point of coagulation being from 55° to 60° C. It is coagulated by
alcohol and ma}' be precipitated by an excess of sodium chloride. It is
through the action of dilute acids converted into syntonin, or acid albu-
men. Myosin is, therefore, the result of coagulation of the proteid of
muscle-plasma.

In addition to myosin, dead muscle contains serum-albumen and
various extractive matters, and bodies belonging to the gelatin group.

In living muscle, on the other hand, myosin is not present, but some
substances or substance which in the death of the muscle become con-
verted into myosin, just as the fibrin factors present in living blood in
the act of coagulation become converted into fibrin.

The differences already alluded to between living and dead muscle
are, without doubt, caused by the appearance of n^osm. The process
of coagulation of muscle, however, is not directly comparable to that of
the coagulation of the blood, for, while in the latter case the alkalinity is
preserved, in the former case the alkaline reaction of living muscle
gives place to a strongly acid reaction.

Dr. W. D. Halliburton has found that the muscle-plasma of warm-
blooded animals is a j^ellowish, viscid fluid of alkaline reaction, which
remains uncoagulated at 0° C., and at the temperature of the air sets
into a jelly-like clot, on the subsequent contraction of which muscle-serum
of an acid reaction is squeezed out.

It was found, however, that cold is not the only agent which will
prevent the formation of myosin, but that, as in the case of the blood,
solutions of certain neutral salts will act similarly. The solutions found
most convenient to use were a 10 per cent, solution of sodium chloride,
a 5 per cent, solution of magnesium sulphate, or a half-saturated solution
of sodium sulphate. The salted muscle-plasma was prepared either by
receiving the expressed muscle-juice into excess of one of these solutions,
or else by extracting the finely divided pieces of frozen muscle with the
solution in question.

A further resemblance between salted muscle-plasma and salted
blood-plasma must be noticed, namely, that on dilution of the mixture
of muscle-plasma and salt-solution with water the influence of the latter

45

706 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in preventing coagulation is removed and a clot of myosin forms. This
is first a jellying through the whole liquid ; the clot subsequently con-
tracts, squeezing out a colorless fluid or salted muscle-serum ; this does
not occur if the temperature is kept about 0° C., and it occurs much
more quickly at the temperature of the body than at that of the air.
The formation of the clot at 36° C. takes, as a rule, five or ten minutes;
at the temperature of the air, several hours. The formation of the clot
is accompanied by the development of an acid reaction due to sarco-
lactic acid ; in this the formation of myosin contrasts with that of fibrin.
The resemblances between the coagulation in muscle and in blood is,
however, so striking as to suggest that the cause is similar; namely, a
ferment in both cases. The theory most generally accepted regarding
the formation of fibrin is that it is the result of a ferment action on a
previously soluble proteid of the globulin class occurring in blood-
plasma, called fibrinogen ; and the theory Dr. Halliburton now puts
forward is that myosin is also the result of a ferment action on a
previously soluble globulin occurring in a muscle-plasma, for which he
proposes the name myosinogen. This ferment can be prepared from
muscle in the same way as Schmidt's fibrin ferment is prepared from
blood ; muscle is kept for some months under alcohol, dried, and
* extracted with water. This aqueous extract contains the ferment, and
on adding it to the salted muscle-plasma coagulation occurs much more
quickly than if water alone be added. Myosin ferment is not identical
with fibrin ferment, as it does not hasten the coagulation of salted blood-
plasma, nor does the fibrin ferment hasten the coagulation of muscle-
plasma. The aqueous solution of the n^osin ferment gives the reaction
of a proteid of the albumose class, and especially of that variety of
albumose to which Kiihne and Chittenden have given the name deutero-
albumose. This is the same albumose as will be shown presently to
exist normally in the muscle-plasma.

The proteids of muscle-plasma can be separated by fractional heat
coagulation, by fractional saturation with neutral salts, and by the
occurrence of spontaneous coagulation and the separation of the plasma
into clot and serum. The proteids were found to be five in number; the
names Dr. Halliburton proposes for them and their chief properties are
as follow : —

1. Paramyosinogen. — This forms a flocculent heat coagulum at 47° C.
It is precipitated from its solutions in an uncoagulated condition (that
is, it can be redissolved in weak saline solutions) by magnesium sulphate
or sodium chloride ; by the former, when the percentage of salt present
reaches 37 to 50 ; by the latter, when the percentage reaches 15 to 26.
The precipitate so obtained occurs in white, curd-like flocculi. It is
precipitated also by dialyzing out the salts from its solutions.

PHYSIOLOGY OF MOVEMENT. 707

2. Myosinogen. — This is coagulated by heat ut 56° C., and the
coagulum so formed is a sticky one. It is precipitated by dialyzing out
the salt from its solutions ; and it is also insoluble in magnesium sulphate
solutions of the strength of 60 to 94 per cent, and in saturated solutions
of sodium chloride. Weak acetic acid added to its saline solutions gives
a characteristic stringy precipitate.

3. Myoglobulin. — This resembles serum-globulin in most of its
properties. It is coagulated by heat at 63° C., and thus differs from
serum-globulin, which is coagulated at 75° C. It is completely precipi-
tated by saturating its solutions with magnesium sulphate, sodium
chloride, or by dialyzing the salts out.

4. Albumen. — This appears to be identical with serum-albumen.

5. Myo-albumose. — This is not precipitated by heat, by copper sul-
phate, by magnesium sulphate, or sodium chloride. It is precipitated
by saturation with ammonium sulphate; \)y nitric acid in the cold. The
precipitate produced by nitric acid disappears on heating and reappears
on cooling. It also gives the biuret reaction — that is, a pink color — -
with copper sulphate and caustic potash. This proteid is closely
associated with the myosin ferment.

Peptones and alkali albumen do not occur in -muscle-plasma.

In coagulation of the muscle-plasma the first two proteids go to form
the clot, and the three latter remain in the muscle-serum. The name
paramyosinogen is given to the first on the list, because, although it
forms part of the clot, it seems rather to be accidentally carried down
than to form an essential part of the m}'osin. If pure solutions of para-
myosinogen and myosinogen respectively be prepared and ferment added
to each, in the former no coagulation occurs, but in the latter myosin is
formed. Moreover, paramyosinogen is sometimes absent, or only present
in exceedingly minute quantities in the muscle-plasma.

Saline extracts of rigid muscle, or of muscle from which rigor has
passed off, differ from the salted muscle-plasma in being of an acid reac-
tion, but otherwise very closely resemble it. Such an extract contains
the same five proteids, and, on dilution, myosin separates as it does from
muscle-plasma; pure myosin, also, if redissolved in a 10 per cent, magne-
sium sulphate or sodium chloride solution can similarly be made to
undergo a recoagulation on dilution and addition of the ferment. More-
over, this recoagulation resembles in all particulars the coagulation which
takes place in muscle-plasma ; it is first a jelly ; the jelly contracts, squeez-
ing out a colorless fluid ; it is inhibited by cold, occurs most readily at
the temperature of the body, is accompanied by the formation of sarco-
lactic acid, and is hastened by the addition of myosin ferment. In this
particular we have, also, an important difference between the coagulation
of blood and of muscle. Fibrin cannot be reconverted into fibrinogen in

708 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the same way as myosin can be converted into myosinogen, which will
again coagulate with the formation of myosin. The ease with which
myosin can thus be made to clot and unclot outside the body might
seem to be a confirmation of Hermann's view that a similar clotting and
re-solution of myosin accompanies the contraction and relaxation of
muscle during life ; in other words, that each contraction is the partial
death of a muscle. We must remember that the most important simi-
larity between rigor mortis and contraction is the formation of sarcolactic
acid, and not the development of a clot of nryosin ; in fact, as a muscle
becomes more extensible during contraction, it becomes in a sense more
liquid, not more solid, as it does when myosin is formed post-mortem.

Dr. Halliburton further suggests that the passing off' of rigor mortis
is due to the reconversion of myosin into myosinogen, brought about by
the pepsin present in muscle. For when muscle becomes acid in rigor
mortis the pepsin which it contains is enabled to act, and at the suitable
temperature (35°-40° C.) albumoses and peptones are formed by a
process of self-digestion. This is a more satisfactory explanation of the
disappearance of rigor mortis than putrefaction, for rigor mortis occa-
sionally persists after putrefaction has set in, and at other times disap-
pears within an hour after death.

The chemical processes continually occurring in living muscle also
undergo change on the death of the muscle. It has been found that liv-
ing muscle is continually appropriating oxygen from the arterial blood
and setting free carbon dioxide. In the death of the muscle the absorp-
tion of oxygen ceases, while the exhalation of carbonic acid may continue
for a certain time, even if the dead muscle be placed in an atmosphere
free from oxygen ; it is, therefore, evident that in the act of death or in
the production of rigor mortis some complex compound is split up and
carbon dioxide set free.

Living muscle is, then, alkaline and contains in solution in the sub-
stance of its fibres a coagulable proteid in the muscle-plasma.

Dead muscle, on the other hand, is acid in reaction from the devel-
opment of sarcolactic acid, and the coagulable plasma has become con-
verted into a solid myosin in muscle-serum. When muscles are sub-
jected to the vacuum of a mercurial air-pump, a certain amount of gas,
which is almost solely CO8, is extracted, which has been in part dissolved
in the muscle-plasma and in part combined with its salts. In muscles in
which rigor mortis has not taken place, 2.74 volumes per cent, of CO2
represent the free gas, 1.95 per cent, the fixed gas. If, however, rigor
mortis be produced, then 15 volumes per cent, of CO2 may be obtained.
Therefore, in rigor mortis a large amount of C0a becomes free, but this
is not due to the decomposition of carbonates by the acid formed in the
same process. So also in muscular contractions there is an increase in

PHYSIOLOGY OF MOVEMENT.

709

the amount of CO2 in muscles capable of withdrawal by the air-pump
amounting to 12.08 per cent, by volume of the muscle. The other con-
stituents of the muscle are represented in the following table (Charles) : —

ANALYSES OP MUSCLE.

COMPONENTS IN 100 PARTS.

Mean of
Human
Muscle.

Mean of
Muscle
of Mam-
mals.

Muscle
of
Birds.

Muscle
of Fish.

Muscle
of

Frogs.

Water,

73.50

72.87

73.00

74.08

80.43

Solids coagulated,

26.50

27.13

27.00

25.92

19.57 .

Albumen (rnyosin, etc.) and other

derivatives, sarcolemma, vessels,

nerves, etc., insoluble in water.

Soluble albumens or albuminates :

Haemoglobin, . ...

1.84

2.17

3.13

3.61

1.86

Fat,

3.27

3.71

1.94

4.59

0.10

Gelatin,

1.99

3.16

1.40

4.34

2.48

Kreatin

0.22

0.18

0.33

0.28

'Ash,

3.12

1.14

1.30

1.49

The constituents of muscle are, therefore, nitrogenous, non-nitroge-
nous, and inorganic. Under the former group occur myosin, alkali
albuminate, and serum-albumen, with extractives such as kreatin, sarkosin,
sarkin, xanthin, and carnin.

Of the non-nitrogenous bodies, inosite, fat, and glycogen are the most
important, while phosphoric acid, potassium, sodium, magnesium, and
lime are the principal inorganic constituents.

(b) Muscular Irritability. — The principal physiological difference
between living and dead muscle is that the former, under the action of
various stimuli, is thrown into contraction. This property of contraction
results from what is termed irritability of the muscle.

If the spinal cord and brain of a frog be destroyed the animal remains
perfectly passive, without any contraction occurring in any of its muscles.
If, however, an}' stimulus, mechanical, electrical, or thermal, be applied to
its muscles they at once shorten, and it is only on the onset of rigor
mortis that this power disappears. If the stimulus be applied to a motor
nerve-trunk a similar state of contraction is produced.

In the destruction of the central nervous system the peripheral
nerve-branches have, of course, not been destroyed, and yet the contrac-
tility of muscle is not dependent upon the stimulation of nerve-fibres
distributed to it, for muscle, like other forms of protoplasm, possesses
an independent excitability. This may be demonstrated by a number of
different methods. In the first place, various chemical stimuli, such as
ammonia^ lime-water, etc., do not produce muscular contraction when
applied to motor nerves, but do evoke contraction when directly applied
to muscle. Again, in various muscles it is impossible to recognize the

710 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

presence of nerve-filaments, as in the extremes of the sartorius muscle of
the frog, and yet in them stimulation applied directly to a muscle pro-
duces contraction. The most conclusive evidence, however, of the inde-
pendent irritability of muscles is found through the use of the poison,
curare.

This substance, a South American arrow -poison, possesses the prop-
erty of entirely paralyzing the terminal filaments of the motor nerves.
If an animal, such as the frog, be poisoned with this drug, stimuli ap-
plied to the motor nerves will be entirely incapable of producing muscular
contraction. The same stimulus, however, applied direct^ to the muscle
still produces a characteristic normal contraction. This poison acts, not
on the nerve-trunks, but on the intra-muscular terminations of the nerves.
This fact may be demonstrated by ligating the sciatic artery in one hind
leg of the frog and injecting curare into the dorsal lymph-sac. The
poisoned blood will then, of course, circulate in every part of the body
with the exception of the limb in which the circulation has been arrested.
If a stimulus be then applied to the sciatic nerve of the non-poisoned
limb it will still succeed in calling forth a contraction, even although the
sciatic trunk has been exposed to the action of curare. Stimulation of
the sciatic, on the other hand, in the limb in which the circulation has
been maintained, and in which, of course, the poison has had access to
the nerve-filaments produces no contraction, while local stimulation of
the muscle does.

Muscular contraction may be produced by various stimuli, acting
either indirectly upon the muscle through its motor nerve, or directl}-
by being immediately applied to the muscle substance.

Muscular stimuli may be either chemical, thermal, mechanical, or
electrical. All chemical substances, such as acids and various metallic
salts, which alter the composition of muscle are muscular stimuli.
Variations of temperature also produce muscular contraction. Thus, if
an excised frog's muscle be heated rapidly to about 28° C., contraction
commences and reaches its maximum at 45° C. If the temperature be
raised above this point the muscle passes into a condition of heat-rigor,
due to the coagulation of the proteids of muscle. Sudden mechanical
stimuli, whether applied directly to the muscle or indirectly to the nerve,
if repeated with sufficient rapidity, also produce contraction of muscle.
Strong local irritation, as by a blow, produces a long-continued, weal-
like contraction of the part stimulated.

(c) Th,e Phenomena of Muscular Contraction. — Muscular contraction
consists in the shortening of muscle-fibres in the direction of their long
axes, with a proportionate and simultaneous increase in their transverse
diameter. Such a contraction is accompanied by a number of phenomena,
of which the most evident is the change in form.

PHYSIOLOGY OF MOVEMENT.

711

When a single induction shock is allowed to pass through the motor
nerve of a muscle, the muscle at once gives a single short contraction.
The phenomena of such a muscular contraction may be best studied on

IF

FIG. 275.— THE NERVE-MUSCLE PREPARATION. (Stirling.)
F, lower third of femur ; S, sciatic nerve ; I, tendon of gastrocnemius muscle.

the gastrocnemius muscle of the frog. Various contrivances have been
devised for graphically representing the results of the muscular
contraction. The simplest method is to support the knee-joint of
a frog's leg in a clamp, connecting the tendon of the gastrocnemius by

Pro. 276.— ARRANGEMENT OF APPARATUS IN CONDUCTING EXPERIMENTS ON
NERVE AND MUSCLE. (Stirling.)

B, galvanic battery; K, electric key in primary circuit ; P, primary coil of induction machine;
S, secondary coil of induction machine from which the current is conducted, when the key, K', is open, to
the electrode, E, on which rests the nerve, n ; the muscle, M, is supported by a clamp, under a glass shade,
its tendon being connected by a thread with a lever, L. writing on the smoked surface of a revolving
drum. The time-marker, TM, is included in the primary circuit, so that when the current passes through
P, by closing the key, K, it also traverses the electro-magnet of the time-marker and causes a record of
the instant of stimulation to be made on the surface of the drum. S, stand supporting moist chamber ;
W, weight by which muscle is extended, and which is lifted in the contraction.

means of a thread to a lever, which records its movements on a rapidly
moving surface. If a single induction shock is then passed through the
sciatic nerve or directly applied to the muscle the so-called muscle
curve will be obtained (Figs. 275 and 276).

FIG. 277.— THE PENDULUM MYOGRAPH. (Foster.)

The figure is diagrammatic, the essentials only of the instrument being shown. The smoked-glass plate. A. swings
on the "seconds" pendulum, B, by means of carefully adjusted bearings at C. Before commencing an experiment the
pendulum is raised up to the right, and is kept in that position by the tooth, a. catching on the spring-catch, h. On depress-
ing the catch, ft, the glass plate is set free, swings into the new position indicated by the dotted lines, and is held in that
position by the tooth, at, catching on the catch, bt. In the course of its swing the tooth, n>, coming into contact with the pro-
jecting steel rod, c, knocks it on one side into the position indicated by the dotted line, ct. The rod, c, is in electric con-
tinuity with the wire, x, of the primary coil of an induction machine. The screw, d, is similarly in electric continuity
with the wire, y, of the same primary coil, both rod and screw being insulated by the ebonite block,' e. As long as r. and d
are in contact, the circuit of the primary coil is closed. When in its swing the tooth, a>, breaks this contact, the circuit
is broken, and a " breaking " induction shock is sent through the electrodes connected with the secondary coil of the induc-
tion machine to the nerve. The lever, I, is connected with the tendon of the muscle, and is brought to bear on the glass
plate, and when no muscular contraction is produced in the swing of the pendulum traces a straight line, or rather an
arc of a circle. When the muscle is stimulated during the swing of the pendulum, the muscle curve is produced. The
tuning-fork, only partly shown, serves to mark the rapidity of motion of the pendulum.

(712)

PHYSIOLOGY OF MOVEMENT.

715

Such a curve (as produced by the pendulum myograph, Fig. 277)
is represented in Fig. 278. To study the characteristics of such a curve
more fully certain additional apparatus is necessary. In the first place,
it is necessary to know the rate of motion of the recording surface.
This 'may be accomplished by means of a recording tuning-fork writing
on the traveling surface. It is further necessary to indicate the instant
at which the nerve or muscle receives the stimulus. This may be done
by including an electro-magnet writing on the traveling surface in the
current through which the stimulus to the muscle passes. If the curve
be examined, it will be noticed that the muscle does not commence to
shorten instantaneously with the entrance of the stimulus into the nerve,
but an appreciable interval elapses after the application of the stimulus
before contraction commences. This interval is termed the latent period r
and is usually about one-seventieth part of a second. The duration of
the latent period will depend upon the distance through which the stimulus

FIG. 278.— MUSCLE CURVE OBTAINED BY MEANS OP THE PENDULUM MYO-

GKAPH. (Foster.)
(To be read from left to right.)

o indicates the moment at which the induction shock is sent into the nerve ; b, the commencement ; c,
the maximum ; and d, the close of the contraction. The two smaller curves are due to oscillations of the
lever. Below the muscle curve is the curve drawn by a tuning-fork, making one hundred and eighty
double vibrations a second, each complete curve, therefore, representing 1-180 of a second.

has to pass through the nerve before entering the muscle. If the elec-
trodes be moved along the sciatic nerve farther from the muscle, the
latent period will be increased. If moved down closer to the muscle,
or applied directly upon the muscle, although not absent, the "duration
of the latent period will be greatly reduced (Fig. 279). It is, therefore,
evident that while part of the latent period is consumed in the conduc-
tion of the stimulus through the nerve, yet a considerable fraction of
it is taken up in changes in the muscle itself which precede active con-
traction, and this process occupies the greater portion of the latent
period.

When the stimulus or induction shock is applied to the nerve
the latent period is partly due, in the first place, to the production
of a nerve impulse in the nerve; and, second, the progression of that
impulse through the nerve to the muscle ; and, third, the changes already
alluded to which occur in the muscle itself.

714

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In the second case the rate of transmission of the nerve impulse has
been placed about twenty-eight meters per second. After the latent
period has been completed the muscle then commences to shorten, at first
slowly and then more rapidly, and then again more slowly until the
maximum shortening is reached, the duration of active contraction occu-
pying about the one-twentieth part of a second. As soon as the maxi-

FIG. 279.— DIAGRAMMATIC CUKVES ILLUSTRATING THE MEASUREMENT OF THE

VELOCITY OF A NERVOUS IMPULSE. (Foster.)

(To be read from left to right.)

The same nerve-muscle preparation is stimulated (1) as far as possible from the muscle, i'2) as near as
possible to the muscle, both contractions being registered in the same manner on the pendulum myograph

In (1) the stimulus enters the nerve at the time indicated by the line, a ; the contraction, shown by the
dotted line, begins at b> ; the whole latent period is, therefore, indicated by the distance from a to bl.

In (2) the stimulus also enters the nerve at a, the contraction begins at b, and is shown in the un-
broken line ; the latent period, therefore, is indicated by the distance from a to b. The time taken up in
the passage of the nerve impulse in the length of nerve between 1 and 2 is indicated by the distance be-
tween b and bt, and may be measured by the tuning-fork curve below. The distance between these
curves is exaggerated for the sake of simplicity, no value being given for the rate of vibration of the
tuning-fork.

mum contraction is reached relaxation commences, following the same
general course as in shortening, relaxing first slowly then more rapidty,
and then more slowly again, the general duration of the active relaxation
being somewhat longer than that of contraction. Such are the general
characteristics of the curve of a single muscular contraction produced
by a single stimulus.

If a single stimulus be allowed to follow the first it will be followed,

FIG. 280.— TRACING OF A DOUBLE MUSCLE CURVE.

(To be read from left to right.)

(Foster.)

While the muscle was engaged in the first contraction (whose complete course, had nothing intervened.
is indicated by the lower line in the muscle-curve) a second induction shock was thrown in at such a time
that the second contraction began just as the first was beginning to decline. The second curve is seen to
start from the first, as does the first from the base line.

like the first, by a single muscular contraction. If the interval between
the second and first muscular contraction be gradually reduced, a point
will ultimately be reached in which the second stimulus enters the nerve
before the contraction produced by the first has passed off. The result
will be that the muscle will undergo a second shortening, and such a

PHYSIOLOGY OF MOVEMENT.

715

curve will be produced as is represented by Fig. 279. The two con-
tractions are thus added together and the total shortening may be nearly
double that produced by a single contraction (Fig. 280).

If a third stimulus is then allowed to pass into the nerve before the
second contraction has passed off, a third contraction will be added to
the second, and so on in the case of the fourth, fifth, or more. It will
be, however, noticed that while the second contraction may be nearl}7 or
quite as extensive as the first, the third and fourth progressively decrease
in extent, until finally simply a broken line without any extensive increase
in contraction will indicate the entrance of the separate stimuli, the
stimuli merely serving to keep up the contraction already produced.

When the stimulation ceases the muscle then rapidly passes into a
condition of rest, relaxation occurring very rapidly.

^ I

FIG. 281.— MUSCLE THROWN INTO TETANUS WHEN THE PRIMARY CURRENT OF
AN INDUCTION MACHINE is REPEATEDLY BROKEN AT INTERVALS OF SIX-
TEEN IN A SECOND. (Foster.)

(To be read from left to right.)

The upper line is that described by the muscle. The lower marks time, the intervals between the ele-
vation indicating seconds. The intermediate line shows when the shocks were sent in, each mark corre-
sponding to a shock. The lever, which describes a straight line before the shocks are allowed to fall into
the nerve, rises almost vertically (the recording surface moving slowly) as soon as the first shock enters the
nerve at a. Having risen to a certain height it begins to fall again, but in its fall is raised once more by
the second shock, and that to a greater height than before. The third and succeeding shocks have similar
effects, the muscle continuing to become shorter, though the shortening at each shock is less. After a
while the increase in the total shortening of the muscle, though the individual contractions are still visible,
almost ceases. At b the shocks cease to be sent into the muscle, the contractions almost immediately disap-
pear, and the lever forthwith commences to descend. The muscle being only slightly loaded, the relaxa-
tion is very slow.

When the separate stimuli do not follow each other more rapidly
than sixteen in a second, the contraction produced by one stimulus has
had time to undergo partial relaxation before the following stimulus
enters ; as a consequence, the point of the lever traces a broken line on
the traveling surface (Fig. 281).

If, however, the stimuli follow each other more rapidly than this, an
apparently constant shortening is produced, in which no variation what-
ever in length can be made out. The gradual production of this state
of affairs indicates that this apparent^ constant and uniform contraction
is, nevertheless, made up of a large number of individual contractions
added to each other. Such a condition is spoken of as tetanus, and the

716 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

curve produced in such a tetanic muscular contraction is represented ira
Fig. 282.

Tetanic contraction requires for its production at least a greater
number than sixteen stimuli per second. It may thus be most readily
produced by the employment of a rapidly interrupted induction current..

Tetanus may, however, also be produced by mechanical stimulation,,
provided the impulses succeed each other with sufficient rapidity. In the
case of chemical stimulation tetanus is the ordinary expression of mus-
cular contraction.

It is thus evident that the tetanic contraction is composed of a series
of vibrations of the muscular fibre, and, as would be expected from this
statement, is accompanied by the production of a musical note, the pitch
of the note depending upon the number of vibrations of the muscular
fibre. Wherever the muscle is artificially thrown into tetanus, as by the
action of an interrupted induced current, the number of vibrations,
of course, corresponds to the number of contractions, these depending

a-

FIG. 282.— TETANUS PRODUCED WITH THE ORDINARY MAGNETIC INTERRUPTER
OF AN INDUCTION MACHINE, THE RECORDING SURFACE MOVING SLOWLY.
(Foster.)

(To be read from left to right.)

The interrupted current being thrown in at a, the lever rises rapidly, but at b the muscle reaches the
maximum of contraction. This is continued until at c, when the current is shut off and relaxation
commences.

upon the number of interruptions of the current, and, as a consequence,,
the number of vibrations of the muscle and the corresponding note pro-
duced have a pitch which corresponds in vibration to these data.

When the ear is placed over a muscle which is thrown into contrac-
tion by means of the will a musical tone is likewise appreciated. This
serves to indicate that even in a single sharp contraction of a muscle
through the action of the will, that apparent single contraction is made
up of a number of contractions, and every single muscular movement
of the animal body is, therefore, of the nature of a tetanus.

The musical note heard indicates that the rate of vibration is 19.5
per second.

We may now study the changes which occur in contracting muscle
in somewhat more detail. The most obvious is, of course, the change of
form. Such a change of form is represented by a decrease in the long
axis of a muscle, the shortening, perhaps amounting to three-fifths, of the
length of the muscle, with a corresponding increase in the cross diameter.

PHYSIOLOGY OF MOVEMENT.

717

There is no actual change in bulk in muscular contraction, the increase in
thickening being almost precisely proportionate to the decrease in length.

This fact may be demonstrated by connecting the sciatic nerve of a frog's leg
with the poles of an induction machine and then placing the leg in a bottle filled
with dilute saline solution, in the stopper of which is inserted a capillary tube,
pare should be taken that no air-bubbles are present in the bottle, that the bottle
is filled, and that the fluid ascends up a certain distance in the capillary tube. If
the leg is then thrown into contraction by passing a current through the wires,

718 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the level of the fluid in the capillary tube will remain almost constant, thus indi-
cating an absence of change in the bulk of muscle, for a decrease would, of course,
be indicated by a fall of fluid, and increase of bulk would raise the fluid in the
capillary tube. By extremely accurate measurements a slight actual decrease in
volume may be made out. Thus, Valentine has determined that a muscle with a
volume of two thousand seven hundred and six cubic centimeters in contraction
in tetanus is reduced to two thousand seven hundred and four cubic centimeters,
while its specific gravity increases from 1061 to 1062.

When a muscle is thrown into contraction, it does not occur sim-
ultaneously in all the muscle-fibres. If a muscle-fibre be placed under a
microscope and then thrown into contraction a wave of undulation may
be seen to be rapidly propagated from one end of the fibre to the other.
This wave is especially sensible if the muscular fibre is fixed at each
extremity. If a long muscle, such as the sartorius of the frog, have
its motor nerve-filaments paralyzed by curare, and the muscle then
thrown into contraction by stimulating one extremity with an induction
current, the wave of contraction travels so slowly as almost to be
capable of being seen by the eye. If such a muscle be supported

FIG. 284.— CURVE ILLUSTRATING THE PROPAGATION OF THE WAVE OF
MUSCULAR CONTRACTION. (Marcy.)

The lower of the two straight lines represents the point of the lever resting on the muscle nearest the
point of stimulation. If the time between the moment of commencing contraction at this spot and that of
commencing contraction at the spot on which the second lever rests be measured by counting the vibra-
tions of the tuning-fork, the rate of progression of the contraction may be determined.

horizontally and two light levers be placed at a distance from each other
bearing on the muscle and writing over each other on a recording sur-
face (Fig. 283), if the muscle be then thrown into contraction by direct
stimulation the levers will not be elevated simultaneously, but a curve
similar to that represented in Fig. 284 will be produced. By measur-
ing the distance between the commencement of these two contractions
and knowing the rate of movement of the recording surface, the rate
of progression of the wave ma}^ be calculated. If, instead of stimulating
the muscle, the nerve (in such an experiment) be stimulated, if no curare
have been given both levers will be simultaneously elevated.

According to Bernstein, the rate of progression in the muscles of
cold-blooded animals of the wave of contraction is about two to three
meters per second. Its rate of progression is much more rapid in the
case of warm-blooded animals.

PHYSIOLOGY OF MOVEMENT.

719

The irritability of muscle is subject to great variation, and a single
irritant is, under different circumstances, capable of producing different
results. In an excised muscle the irritability rapidly disappears, although
it persists much longer in the muscles of cold-blooded animals than in
warm-blooded. In the latter case the irritability of warm-blooded
muscles may be somewhat prolonged if the animal be artificially cooled
before death.

Temperature is of great influence on the irritability of muscle, both
an increase or decrease above the normal temperature of the muscle being
followed by a decrease in irritability. Again, through repeated contrac-
tion the muscle loses its power of being thrown
into contraction ; it is then said to be in a con-
dition of fatigue, due either to the insufficient
supply of nutritive substances or to the accumu-
lation of the products of decomposition, which,
as has been experimentally demonstrated, pro-
duce a hurtful action upon the muscle-fibres.
In all probability both of these factors are
concerned in fatigue.

When a contracting muscle is examined
under the microscope marked changes in
structure may be made out. If a living mus-
cular fibre of an insect, for example, which is
especialty fitted for such study, be examined
under the microscope while contracting, a wave
of contraction, as already mentioned, may be
seen traveling along the surface of the fibre,
while at the same time the transverse striations
approach each other. In the contracted portion
each disk has become shorter and broader, while
the band which in a relaxed muscle is light,
in a contracted muscle becomes dark, and the
band which in a relaxed muscle was dark in the
contracted muscle becomes light (Fig. 285).

In the process of contraction chemical changes occur ; these have
been already to a certain extent indicated. The muscle in which reaction
was alkaline, in contraction becomes acid through the development of
sarcolactic acid, which may even be excreted by the kidneys. During its
contraction the muscle absorbs more oxygen from the blood than during
its stage of rest, and, as a consequence, venous blood from a resting
muscle contains 8.5 per cent., that from a contracting muscle 12.8 per
cent, less oxygen than the arterial blood ; while the venous blood
from a resting muscle contains, as an average, 6.7 per cent., that from a

FIG. 285.— MUSCULAR FIBRE
UNDERGOING CONTRAC-
TION, AFTER ENGL.E-
MANN. (Foster.)

The muscle is that of Telephorus
melanurus treated with osmie acid.
The fibre at c is at rest, at a the con-
traction begins, at b it has reached its
maximum. The right-hand side of
the figure shows the same fibre as
seen in polarized light.

720 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

contracting muscle 10.8 per cent, more carbon dioxide than arterial blood.
The amount of oxygen consumed, as may be noticed from these figures,
bears no relationship to the amount of carbon dioxide liberated ; whence
it follows, as already stated, that the formation of carbon dioxide in a
contracting muscle is not a simple process of oxidation, but rather the
splitting up of some complex compound.

During contraction the glycogen of " the muscles becomes reduced,
while, on the other hand, there is an increase in the amount of kreatin
obtainable from the contracted over that found in the resting muscle.

The question, What is the source of the carbon dioxide and lactic
acid developed by a contracting muscle? may, perhaps, be answered by
the statement that they are derived neither from the albuminous nor fatty
constituents of the muscle, but from the carbohydrates, especially from
the glycogen, which may even entirely disappear during the stage of
•contraction of a muscle, even although the amount of nitrogenous decom-
position products in the muscle is not increased and the amount of fat
not diminished. From the greater demand of oxygen by a contracting
muscle we find, as a consequence, a greater increase in the supply of the
arterial blood furnished to a muscle in contraction.

When a muscle contracts, its arterioles dilate, more blood passes
through the muscle, and, as a consequence, the removal of the increased
carbon dioxide formed is facilitated. It would appear from this that
the source of muscular force is found, not, as was formerly supposed, in
the breaking up of albuminoids, but in the chemical changes occurring
in muscle which are evidenced by the breaking up of the carbohydrates.

This statement may appear contradictory to common experience,
which teaches that animals fed with albuminoids do more work than
those fed on a diet less rich in albuminoids. Our studies on nutrition
have, however, indicated that a large supply of albuminous matter
renders possible the use of the larger amount of carbohydrates. This
will, perhaps, explain the fact that well-nourished herbivora are able
to develop more force than the apparently much more powerful carnivora,
and that the activity of muscle does not increase the breaking up of
albuminates but increases the elimination of carbon dioxide. The few
examples in which muscular work is accompanied by an increased
excretion of urea, such, for example, as may be occasionally seen in the
horse, are only to be accounted for by the insufficiency of the quantity
of carbohydrates administered in the food, this insufficiency necessi-
tating a destruction of the proteids for the development of force.

As might be supposed from the above, every muscular contraction is
accompanied by an elevation of temperature. Such a heat production
may be determined experimentally by a thermometer, and, in a general
way, it may be stated that within certain limits the greater the work

PHYSIOLOGY OF MOVEMENT. 721

demanded of a muscle, in other words, the greater the resistance to be
overcome, the greater will be the amount of heat production ; and, as a
consequence, in a contracting muscle, not only is energy liberated but
heat is developed, which is capable of being converted into actual energy.
The heat development of a contracting muscle is not only dependent
upon the amount of work done, but also on the tension of the muscle,
and the heat production reaches its maximum when the tension exerted
on the muscle is so great that it is not able to contract.

Since a muscle in contracting is capable of lifting a weight, it is,
therefore, likewise capable of accomplishing work. The amount of
work will depend upon the size of the weight, upon the distance to which
the weight is lifted, and upon the time during which this lifting con-
tinues. It was found that the degree of contraction was proportionate
to the degree of stimulation. Therefore, the maximum amount of work
capable of being produced by a muscle is accomplished when the
maximum weight is lifted. The amount of work which a muscle may
perform is, therefore, equal to the product of the weight lifted and the
height to which it is lifted : thus, if a muscle contracts where no load is
present, it accomplishes no work; or, if it be loaded beyond the point at
which the load may be lifted, again no work is accomplished. If
the weight be gradually increased, even although it may be lifted, the
height to which that lift is accomplished becomes reduced, and, as
a consequence, the work diminishes.

The amount of work which a muscle may accomplish is greater in
proportion to the transverse section of the muscle, for the longer
the muscle the greater is the shortening, and, accordingly, the higher the
lift. In muscles within the animal body the amount of shortening
which they may attain is never capable of reaching the maximum
obtained in a similar excised muscle. The force with which a muscle
contracts is greater at the commencement of contraction, and, when
a muscle begins to contract, it can, therefore, lift the largest load. If a
muscle loaded with a weight be stimulated with a rapidly interrupted
induction current, after the muscle has once contracted no further
lift is produced and no external work is evident; but if the muscle
sustain a weight at the height to which it raised it, the amount of work,
in this case the amount of energy developed by the prolonged contrac-
tion of the muscle, is converted into heat.

When a muscle is stimulated with a feeble induced current and the
current then gradually increased in strength, it will be found that
the height to which the load may be lifted increases with the strength
of the stimulus.

(d) TKe Electrical Phenomena in Muscle. — If the gastrocnemius
muscle of the frog be excised and its tendinous insertions cut off, and two

46

722 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

points of this surface, or the longitudinal surface of the muscle and the
transverse section, be connected by non-polarizable electrodes with a sen-
sitive galvanometer, at the moment of making the contact a deflection
of the galvanometer needle will take place, indicating the presence of a
galvanic current. The strongest effect is produced when one point of
the transverse section and one point of the longitudinal surface are con-
nected with a galvanometer; even single fibres, nevertheless, if brought
into connection with a galvanometer also develop galvanic currents. The
direction of the current is from the longitudinal section through the con-
ducting wires to the transverse section ; within the muscle itself the
current passes from the transverse to the longitudinal section. The
nearer the one electrode is to the equator and the other to the centre of
the transverse section the stronger will be the current, while the current
becomes more feeble when one electrode is approached to the outer sur-
face and the other to the edge of the transverse section.

The existence of a muscle current may further be proved by an
experiment which is termed the rheoscopic frog. If the gastrocnemius
muscle of a frog be prepared with a long piece of sciatic nerve still in
connection with it, and the end of the nerve be placed over another
excised, fresh gastrocnemius muscle, so as to be in contact with its trans-
verse and longitudinal surfaces, contraction of the muscle connected with
the nerve occurs at the moment of contact. A single contraction is,
however, only produced, but if the nerve be removed from the muscle a
second contraction occurs ; thus pointing out that the current circulating
through the muscle is a constant current and may serve to stimulate other
muscles or nerves at the moment of breaking and making the contact.
If a muscle be prepared as before, connected with a galvanometer, and be
found to yield a strong galvanic current, if the muscle be then thrown
into tetanus by electrical stimulation of.the muscle itself, or of its motor
nerve, the needle of the galvanometer will be found to swing back to
zero, indicating the disappearance of the muscle current; such a state
of affairs is spoken of as the negative variation of the muscle current.

2. THE APPLICATIONS OF MUSCULAR CONTRACTILITY. — The contractility
of muscles serves especially to produce changes in form of the animal
body by which single members are thrown out of their condition of
equilibrium and changes of location in the animal parts thus produced ;
or in the case of the unstriped muscles to diminish the capacity of the
various cavities of the animal body. Hence, muscles may be classified
into two different groups : those without a definite origin and insertion,
and those in which definite origin and insertion are present. To the first
group belong the hollow muscles surrounding the urinary bladder, gall-
bladder, uterus, heart; intestinal canal, blood-vessels, ureters, etc. In
such instances the muscular fibres are unstriped and involuntary and are

PHYSIOLOGY OF MOVEMENT. 723

arranged in several layers, an oblique, circular, and longitudinal layer
being in nearly all cases distinguishable ; all these sets of fibres acting
simultaneously, the result is to diminish the capacity of the cavity which
they inclose. They thus aid in various motions of animal life, such as
the propulsion of the blood from the heart and in assisting its onward
passage through the arteries, the evacuation of the bladder and rectum,
the emptying of the pregnant uterus, and various other operations which
have been already alluded to. In addition to this group of muscles, the
sphincters likewise have no definite origin or insertion, but are found at
the various openings of the body, whether the anus, urethra, or mouth,
and several other localities. The muscular fibres of the sphincters are
circular, and by their contraction serve to close the orifices of these
several openings.

Of the muscJes with definite origin and insertion, either the origin is
fixed or both origin and insertion may be movable. In many cases be-
longing to the former of these groups the origin is only fixed during
muscular action; thus, in the case of the palato-pharyngeal muscles their
characteristic action is only rendered possible by the fixation of their
origin through the contraction of the levator palati muscle.

Again, both origin and insertion may be movable, the part moved
being usually under the control of the will. Thus, in the case of the
sterno-mastoid muscle, through its contraction the head may be depressed
or the chest elevated.

Movement of the animal parts or of the entire animal body is ren-
dered possible through the manner in which the skeletal muscles are
inserted in the long bones by which lever motion is possible, the bones
being regarded as levers, the joint as the fulcrum, the insertion of the
muscle the point of application of the power, and the centre of gravity
of the bone with the resistances overcome by its motion as the load.

Thus, muscles arising in one bone and inserted in another will, in
their contraction, either move both bones toward each other, or, if one be
fixed, will approach the movable to the fixed bone. From the definition
of the power-arm of a lever, it is evident that in general the direction of
muscles relative to the levers on which they act is very disadvantageous,
since their course is almost always more or less parallel to the bony levers.
This parallelism is diminished by the swelling of the articular extremi-
ties and by the development of more or less marked eminences, such as
the olecranon or the trocanters, or by the presence of sesamoid bones.
In movements of flexion, however, this parallelism becomes diminished
according to the degree of flexion, so that, therefore, at the termination
of the act of flexion the muscles are more favorably situated for the de-
velopment of power. Certain muscles, however, such as the muscles of
mastication, the flexors of the head, the psoas muscles, and the abductors

724

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and adductors of the arm have their insertion almost perpendicular to
the bones on which they act.

Although all three classes of levers are
met with, in general the lever of the first class
comes into play in movements of extension, and
that of the third class in movements of flexion.

A lever may be defined as an inflexible bar
capable of being freely moved about a fixed point or
line, which is called the fulcrum. In the first class
of lever the fulcrum lies between the weight and the
power, and may be illustrated by a common crowbar
or a pair of scissors. In levers of the second class
the weight lies between the fulcrum and the power,
and may be illustrated by the wheelbarrow or nut-
cracker. In the third class of lever the power falls
between the fulcrum and the weight, and may be
illustrated by a pair of fire-tongs or sheep-shears
CFig. 286.)

F

A

A

A

(l)

(2)

(3)

FIG. 286.— THREE CLASSES OF LEVERS. (Landois.)

W, weight; F, fulcrum; P, power; l,in levers of first class the fulcrnm
is between the power and the weight ; 2, in levers of second class the weight
falls between the power and fulcrum ; 3, in levers of third class the power is
applied between the fulcrum and weight. The index shows the direction in
which the power acts.

FIG. 287.— DIAGRAMS SHOW-
ING THE MODE OF AC-
TION OP THE THRKE
ORDERS OF LEVERS,
NUMBERED FROM ABOVE
DOWNWARD, ILLUS-
TRATED BY THE ACTION
OF THE ELBOW-JOINT.
(Yeo.)

In considering the development of power by the use of levers, the relation-
ship between the power- and the weight-arm has to be considered. The power-

FIG. 288.— PARTIAL COHTSACTIOIC or BICEPS. (Perrier.)

arm of the lever may be defined as the perpendicular distance from the line in
which the power acts to the fulcrum ; the weight-arm, the perpendicular distance

PHYSIOLOGY OF MOVEMENT.

725

from the line in which the weight acts to the fulcrum. The law of the lever may
be expressed as follows : A power will support a weight as many times as great as
itself as the power-arm is times longer
than the weight-arm. Thus, for ex-
ample, in a lever of the first class, if we
suppose that the power-arm be ten
times as long as the weight-arm, a
weight of one pound at the extremity
of the power-arm will support a weight
of ten pounds at the extremity of the
weight-arm. It must be recollected,
however, in the case of the lever, as in
every other machine, what is gained in

FIG. 289.— COMPLETE CONTRACTION OF
BICEPS. (Perrier.)

FIG. 290.— MOTION OP HEAD AS ILLUSTRA-
TING ACTION OF LEVER OF FIRST CLASS.
( Beclar d.)

a, fulcrum of the lever, c b ; a b is the weight-arm, for
the head tends to fall forward by its own weight acting ia
the line, r. This U prevented by the contraction of the
muscles of the baelt of the neck acting on the power-arm, c a,
in the line, F.

power is lost in velocity, artd vice versa. Thus, in the case of the third class of
lever, power is exchanged for velocity. This may be well represented in the
movement of flexion of the human forearm (Figs. 288 and 289). The fulcrum
is there found in the elbow-joint, the power is the insertion
of the biceps muscles in the bone of the forearm in front of
the joint, the weight is carried by the hand. In this arrange-
ment it is evident that slight motion at the insertion of the
biceps will be greatly multiplied in the case of the hand.
Thus, say that the distance from the elbow-joint to the tip of
the hand is eighteen inches, the dis-
tance from the elbow-joint to the
point of insertion of the biceps one
inch, motion of one inch at the inser-
tion of the biceps will produce motion
at the hand of an arc of a circle whose
cord is eighteen inches The forearm
is, therefore, in this action an example
of the third class of lever.

In general, in the animal body,
the point of application of the power
developed by muscular contraction
lies near the fulcrum : hence the
conditions favor the production of velocity of movement at the expense of power,
for the power-arm is always shorter than the weight-arm.

The conditions are, however, reversed in the case of the extensor muscles of
the limbs when in contact with the ground. Here the joint nearest to which the
muscle is inserted is the point of application of the weight, and the fulcrum is the

FIG. 291.— MOTION ILLUSTRATING ACTION OF
LEVERS OF THE THIRD CLASS. (Btclard.)

The fulcrum is at a, the power from contraction of gastroc-
nemhu muscle, acting in the line, d e, la applied at c, while the
weight (of the body) aete in the line, o b. acia thus the power-
arm, a b the weight-arm.

726 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

joint above, far from the insertion of the muscle. Hence, the power-arm is
greatly increased. Thus, in the horse, while the foot is on the ground in the con-
traction of the extensors the point of application of the weight is in the hock-
joint, the point of application of the power in the caleaneum, where the extensors
are inserted, and the pastern -joint the fulcrum ; hence the power-arm is long, and,
although motion is slow, it is accompanied by a corresponding increase in power.
If, however, the hind foot is not on the ground, but is extended as in kicking, then
the fulcrum is in the hock-joint, and the power-arm is now short and power is
exchanged for velocity.

The first class of levers may be represented in such movements as in nodding
the head, where the fulcrum is the articular surface of the atlas, the weight being
found in the back of the head when the throat muscles contract, in the front of
the head when the posterior neck muscles contract (Fig. 290). Movement due to
the action of levers of the second class is seen when the body is raised up on tiptoe
by the muscles of the calf (Fig. 291).

All three orders of levers may come into play in the action of the human
elbow-joint. Thus, the first class is illustrated when the forearm is extended on
the arm through the contraction of the triceps muscles ; in this instance, the hand
is the weight, the elbow -joint the fulcrum, and the insertion of the triceps in the
olecranon the power (see upper diagram Fig. 287).

If the hand rest on the table and the body be raised on it, then the hand
is the fulcrum, the triceps is the power, and the humerus, at its articulation in
the elbow-joint, the weight, thus illustrating the action of a lever of the second
class (see middle diagram 287). The third order, as already mentioned, comes
into play when the forearm is flexed on the arm.

In the horse the extensors of the forearm (A Z>, B D, and G D, Fig.
292) act as levers of the first class, the power-arm being the distance
between the summit of the olecranon and the centre of the humero-
radial articulation, which forms the fulcrum, while the weight-arm is
represented by the length of the radius. In man the triceps brachialis
(B, Fig. 293), which is the analogue of the olecranon muscles of quad-
rupeds, acts also as a lever of the first class, the power-arm, however,
being much shorter in man. In the posterior extremity of the horse
(Fig. 294), the glutens medius, the fascia lata, the triceps cruralis, the
Mfemero-calcaneus, the vastus externus, etc., are also examples of the
first class of levers. In the case of the gluteus medius (A B, Fig. 294)
the power-arm is the distance from the trochanter to the centre of the
acetabular articulation, which is the fulcrum, while the weight-arm is the
length of the femur. For the gastrocnemius the power-arm is the
distance from the summit of the caleaneum to the centre of the hock-
joint, which is the fulcrum, while the weight-arm is the length of the
metatarsus. The first class of levers is thus mainly represented by the
extensors.

Levers of the third class are mainly represented by the flexors. In
the anterior extremity of the horse (Fig. 295) the infraspinatus, the
biceps flexor, the metacarpal flexor, and the flexor pedis are all examples
of muscles whose action operates through levers of the third class, in
each instance the power acting between the fulcrum and the weight. In
operations of levers of the third class power is exchanged for velocity
of motion, from the fact that tlie power-arm is alwa}~s shorter than the

PHYSIOLOGY OF MOVEMENT.

727

weight-arm. In the posterior extremity of the horse (Fig. 296) the
superficial gluteus muscle and the ischio-tibial muscles are levers of the
third class.

Levers of the second class are more rarely met with. In the horse

FIG. 292.— ANTERIOR Ex- FIG. 293.— SUPERIOR EX-

TREMITY OF THE HORSE
IN EXTENSION. (Colin.)

AD, BD, and CD. lines of action
of the triceps extensor brachii, scapulo-
•ulnaris, and aconeus muscles. E F,
flexor brachii. G II, line of action of
flexor pedis muscles.

TREMITY OF MAN. (Colin.)

A C, line of action of the biceps
flexor. B, triceps extensor.

FIG. 294.— POSTERIOR EX-
TREMITY OF THE HORSE
IN EXTENSION. (Colin.)

AB, line of action of gluteus
medius. C D, line of action of triceps
extensor. E F, line of action of gas-
trocnemius. Gil, line of action of

metatarsal flexor.

the gastrocnemius acts through a lever of the second class when the foot
is in contact with the ground. Then the fulcrum is at the point of con-
tact of the foot with the ground, the power-arm is the distance from
the calcaneum to the ground, the weight-arm the distance from the

728

PHYSIOLOGY OP THE DOMESTIC ANIMALS.

astragalo-tibial articulation to the ground, and the resistance is the weight
of the body. This mode of action of the gastrocnemius is more evident
in man (Fig. 297) when the weight of the body is raised on the toes
through the action of this muscle. In the anterior extremity of quad-
rupeds the extensors of the forearm (A D, B D, and C D, Fig. 292) also
act through levers of the second class when the foot is on the ground,

FIQ. 295.— THE ANTERIOR EXTREMITY
OF THE HORSE IN: FLEXION. (Colin.)

A B, line of action of infraspinatus. C D, line
of action of biceps flexor. E F, line of action of
metacarpal flexor. G II, line of. action of flexor
pedis.

FIG. 296.— POSTERIOR EXTKEBIITY OF
THE HORSE IN FLEXION. (Colin.)

A B, line of action of superficial gluteus
muscle. C D, line of action of ischio-tibial
muscles. E F, line of action of metatarsal
flexor. G H, lines of action of flexors of foot.

their action serving then to flex the humero-radial articulation, instead
of extending it, as occurs when they act with the foot in the air.

The movements of the different parts of the animal body depend
upon the union of the different parts of the skeleton with each other and
the mode of insertion of the muscles. The movable parts of the skeleton
are designated as joints, the relative positions of the bones forming a

PHYSIOLOGY OF MOVEMENT.

729

joint being determined by muscular action ; for when by the action of
muscular force the positions of the bones are changed, the original
position is not regained in the cessation of that force.

The form of the joint, in which two bones are united end to end, is
subject to considerable variation, depending on
and governing the direction in which the move-
ment may take place. The articular extremities
of the bone are covered with articular cartilage,
surrounded by closed serous sacs containing
a serous fluid, the synovia, which tends to
diminish friction between the movable parts.
Since the space between articular surfaces con-
tains only the synovial fluid, it ma}^ be regarded
as a vacuum, and atmospheric pressure is itself
sufficient to keep the articular surfaces in con-
tact, even sustaining the entire weight of the
limbs and thus sparing muscular action. The
movement between the joint ends is not only
governed by the character of the joint, which
we will find may be resolved into several differ-
ent types, but is further restricted by the cap
sular ligament which holds the joints in appo-
sition and by the tendinous bands which
surround them, in all cases only those move-
ments being possible in which the articular
surfaces remain in contact.

The articulations are divided into three
classes : the immovable articulations, or the
synarthroses ; the mixed, or amphiarthroses ;
and the movable, or diarthroses.

To the first class belong the sutures and
other articulations where the surfaces of the
bones are in almost direct contact, not sepa-
rated by a synovial cavity, and immovably
connected with each other. In the second class
the osseous surfaces are connected together ^
by disks of fibro-cartilage, as between the bodies

AB C, line of action of biceps flexor.

of the vertebrae, or the articulating surfaces are (A !eyer of third class.) E, gastroc-

nemius.

covered with fibro-cartilage, partly lined by

synovial membrane, and bound together by external ligaments, as in the

sacro-iliac and pubic symphyses.

The third class includes the greatest number of joints in the animal
bod}', and as mobility is their distinguishing characteristic they are the

ITY OF MAN.

EXTREM-

(Colin.)

730 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

only ones with which we are concerned. Four different varieties of this
form of joint have been described, according to the kind of motion
permitted in each.

a. The Rotatory Joint, or Diartlirosis Eotatoria. — In this class of
joint the movement is limited to rotation, the joint being formed by a
pivot-like process turning within a ring or the ring on the pivot, the ring
being formed partly of bone and partly of ligament. The articulation
of the atlas and the occiput is an example of such a joint. In the elbow-
joint a similar rotatory articulation is met with, where in the radio-ulnar
articulation the ring is formed by the lesser sigmoid cavity and the orbicular
ligament while the head of the radius rotates within the ring. Only in
animals in whom pronation and supination of the hand are possible does
this movement occur ; it is, therefore, absent in the horse and ox. In
general, it may be said that in animals provided with the clavicle this
motion of supination and pronation is usually present.

b. The Ball and Socket Joint, or the Enarthrosis. — In this joint motion
in all directions is possible, and it is formed by the reception of the
globular head of a long bone, into a deep, cup-like cavity, hence called
ball and socket, the parts being kept in apposition by a capsular ligament
and accessory ligamentous bands. The hip- and shoulder- joints are
examples of this class.

c. The Hinged or Ginglymous Joint. — In this form motion is only
possible in one plane and only in two directions, forward and backward,
the articular surfaces being moulded to each other in such a way that a
solid cylinder moves within a greater or lesser segment of a hollow
cylinder. The joint between the ulna and the humerus is a most perfect
example of a ginglymous joint, while the joints between the phalanges
and between the inferior and superior maxillary bones of the carnivora
are other examples. The pastern-joint of the horse is a modified form
of this joint and is often spoken of as a screw-joint.

d. The Gliding Joints, or the Arthrodia. — In this class motion of a
gliding character takes place. Such joints are formed by the approxima-
tion of plane surfaces, or one slightly concave, the other slightly convex,
movement between them being limited by the ligaments or the osseous
processes surrounding the articulation. Such articulations are seen
between the vertebra, metatarsal and tar sal bones, and others.

The forces which move the joints are found in the contraction of
striped muscular fibres. The extent of contraction for which the muscle
is capable depends upon its length, and therefore we speak of long and
short muscles. A muscle whose function it is to bring its points of
origin and insertion nearer to each other must necessarily be a long
muscle, while the muscles whose contraction only leads to slight change
of place are usually short muscles. It will always be found that the

PHYSIOLOGY OF MOVEMENT. 731

length of the muscle-fibre corresponds to the degree of movement which
the muscle has to produce. It does not necessarily follow that a muscle
whose points of origin and insertion are widely separated should be a
long muscle, since the interval between these two points may be largely
taken up by tendons.

3. ANIMAL LOCOMOTION. — The essential factor for animal locomotion
consists in the movement of the centre of gravity of the body. By the
term " the centre of gravity " is understood the point about which all
the matter composing the body may be balanced. The attraction of
gravit}' tends to draw every particle of matter downward in a vertical
line. The factors of this force may be, therefore, regarded as the sum of
an almost infinite number of parallel forces, each of which is acting upon
one of the molecules of which that body is composed. Just as the
resultant of the force exerted by two horses harnessed to a swingle-tree
is equal to the sum of the forces exerted by the horses but applied at a
single point at or near the centre of the swingle-tree, so, also, the sum
of the forces of gravity may be regarded as acting upon a single point
which is near the centre of gravity of that body. In other words, the
weight of the body may be considered as concentrated at the centre of
gravity. When the centre of gravity is supported the whole body will
be in a state of equilibrium ; or when the line of direction of the force
of gravity, which is thus a vertical line passing through the centre of
gravity, falls within the base of the bod}', or base on which the body
stands, it is then said to be stable.

In all regular bodies the centre of gravity will coincide with the
central point, while in irregular bodies it will be nearest to that part in
which the greatest weight is concentrated. As the centre of gravity of
the animal body is within the body it can be directly supported. The
stability of the body will be greater the broader the base and the nearer
the centre of gravity to the support. The animal body when standing is,
however, only at best in a state of unstable equilibrium ; for when slightly
displaced from its position of equilibrium, it tends to fall still farther
from that position, owing to the fact that the disturbance has lowered
the centre of gravity, and equilibrium is not restored until it reaches its
lowest possible point. An animal in a recumbent position is in a state
of neutral equilibrium ; when its position is changed it tends neither to
return to its former position nor to fall farther from it. Stable equi-
librium is when a bod}' is so supported that when slightly displaced from
its position of equilibrium it tends to return to that position. Such a
condition can only occur when displacement raises the centre of gravity.
The pendulum is an example of stable equilibrium.

Standing is thus a condition of unstable equilibrium in which the
centre of gravity is supported from the fact that the line of direction

732 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

falls within the base of the figure. The mechanism of standing differs in
bipeds and quadrupeds. In man the centre of gravity lies within the
pelvis, about one and a half millimeters in front of the promontory of the
sacrum. In the erect attitude of man the feet are directed outward
(forming an angle of about fifty degrees), so increasing the base of
support, the heels touching, the knees extended, the thighs rotated
externally, and the pelvis and trunk bent slightly backward, the arms
hanging at the side.

In the act of standing, the body not being rigid, balancing must
be aided by the assistance of the contraction of various muscles. In a
certain number of joints the action of ligaments in the erect position
assists the maintenance of the upright posture ; thus, in the attitude
already described, where the knees are extended to the utmost, the
trunk thrown back, and the head balanced, the anterior hip-ligaments
are rendered tense, and the knee- and hip-joint remained fixed without
&i\y etfort upon the part of the joint-muscles. In the position known as
" standing at ease" the weight of the body rests mainly on one leg, the
other forming simply a support to assist the muscles around the support-
ing ankle. In this position the joints are not kept locked by the tension
of the ligaments, for the pelvis is now somewhat oblique, so as to bring
it directly over the head of the femur. Varying tension in the muscles
serves to preserve the balance and prevent fatigue. In the erect posture
the ankle supports the weight of the body; the line of gravity falling
slightly in front of the axis of rotation of the ankle-joint, the tendency
is thus for the body to fall forward at the ankles; this is, however,
checked by the calf-muscles, which keep the parts nearly in position of
exact equilibrium. In the erect position, the ankle-joint being neither
flexed nor extended to the utmost forward or backward, motion must be
prevented by muscular contraction. Lateral motion at the ankle-joint
is prevented by the malleoli. When the knee-joint is completely ex-
tended no muscular action is required to prevent it from bending, be-
cause the line of gravity then passes in front of the axis of rotation and
the weight of the body tends to bend the knee backward. Although the
ligaments which exert their contraction behind the axis of rotation tend
to render this impossible, ordinarily the position is maintained by mus-
cular action so exerted that the line of gravity passes slightly behind
the axis of the knee, the tendency thus produced of the knee to bend
being checked by the extensor muscles of the thigh.

In the hip-joint the line of gravity falls behind the line uniting the
joint. When the person is erect, the tendency thus produced of the
body to fall backward is prevented by the ileo-femoral ligament. If,
however, the knee is not extended to the full extent the line of gravity
passes a little behind the axis of rotation of that joint, and the pelvis

PHYSIOLOGY OF MOVEMENT. 733

being slightly flexed on the femora, the axis of the joint lies a little
behind the line of gravity, and the inclination thus produced to fall
forward is prevented by the glutei muscles, which are likewise concerned
in regaining the erect posture after bending the trunk forward. The
motions between the pelvis and vertebrae are practical^ so slight as to be
disregarded, and the vertebral column, with the exception of the motions
existing between the head and the upper cervical vertebrae, may be re-
garded as a rigid column. Between the occiput and atlas lateral and
rotatory motions are "possible to a considerable extent, so that balancing
the head is rendered possible only by co-ordinated muscular contractions,
since no ligaments are present which can fix the occipito-atlantoid artic-
ulation.

Sitting is that position of equilibrium where the body is supported
on the tubera ischii. The line of gravity may pass either in front of the
tubera ischii, in which the body must be supported by some fixed object,
or the line of gravity may fall behind the tubera in the backward pos-
ture, in which case falling backward may be prevented by leaning upon
a support or by the counter-weight of the extended legs. In sitting
erect the line of gravity falls between the tubera themselves, and but
slight muscular action, such as is required in the balancing of the head,
is sufficient to maintain equilibrium.

In quadrupeds the four limbs act like four columns, as in a chair or
table, in supporting the centre of gravity of the body, so that the base
of support is a parallelogram whose corners are represented by the point
of contact of the feet with the ground, and which is about four times as
long as it is broad. In consequence of the greater base of support, equi-
librium is more readily preserved in quadrupeds than in bipeds. The
centre of gravity in the large quadrupeds, such as the horse, ox, etc., lies
at the intersection of a line passing vertically behind the xyphoid carti-
lage and one passing horizontally through the end of the second third
of the sterno-vertebral diameter. In the small quadrupeds, such as the
dog, the centre of gravity is located somewhat more anteriorly. From
the fact that the centre of gravity lies below the vertebrae in quadrupeds,
in the erect position the tendency of the weight at the centre of gravity
is to curve the vertebral column inward. This is prevented by both mus-
cular action and ligamentous support. The fore extremities and scapula
are only attached to the trunk through muscular and ligamentous con-
nections which are continually on a stretch and so serve to render the
shoulder-blade immovable, while by means of the greater serrati muscles
the trunk is supported as in a sling, so that it cannot be pushed forward
against the shoulder-blade. In the posterior extremities the relationships
differ in that the single bones are not, as in the fore extremities, verti-
cally over each other. Here, also, the erect oosition is maintained through

734 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

muscular action. When the body is uniformly supported on all four
extremities, in the fore limbs the line of direction passes from the shoulder
through the centre of the elbow-joint in the axis of the forearm, through
the centre of the knee-joint in the axis of the ulna, through the centre
of the pastern-joint perpendicular to the ground behind the ball of the
foot. Three principal angles are thus formed whose degree depends
partly on the angle between the scapula and vertebrae and partly on the
relative lengths of the different bones.

In the case of the anterior extremity the line of direction of the
lower bones is almost vertical, but in the case of the upper bones becomes
considerably inclined ; thus, the scapulo-humeral angle tends constantly
to become smaller and smaller on account of the depression of the
superior extremity of the scapula and by the projection anteriorly of
the scapulo-humeral articulation. This depression and projection are
hindered by the action of numerous muscles. The most important
muscle concerned in the fixation of the upper extremity is the serratus
magnus, which, arising in numerous fan-shaped bundles from the five
posterior cervical vertebrae and the first eight ribs, converges to be
inserted in the ventral surface of the scapula. This muscle, with its
fellow, serves as a muscular sling in which the body is supported
between the fore limbs, the axis of motion of the shoulder-blade pass-
ing through its insertion in the scapula.

The superior extremity of the scapula is sustained by the rhomboid
muscles, which draw it upward, as well as by the trapezius, which tend to
elevate and advance this bone, so opposing the depression of the scapula
through the weight of the trunk. These muscles thus give fixity to the
scapula. Further, the anterior projection of the scapulo-humeral angle
is prevented by the greater and lesser pectoral muscles, which by their
contraction tend to retract this angle. The obliquity of the humerus
tends to become exaggerated during standing as well as at each act of
striking the foot upon the ground. The pectoralis major and the infra-
spinalis muscles, as well as the coraco-radii, tend to prevent this, the latter
muscle being especially efficacious, acting not only as a muscle, but a
band of unyielding tendinous material running through it enables it to
act as a ligament preventing exaggerated flexion of the humerus on the
shoulder. That the coraco radii should fulfill this function it is neces-
sary that its insertion in the inferior extremit}7 should be fixed. This
fixity is accomplished by the five olecranon muscles. At the elbow-joint
the lower end of the humerus is fixed by the strong lateral ligaments ;
reduction of the elbow angle being prevented by the fixation of the
olecranon through the contraction of the extensors of the forearm,
and anterior deviation by the tendinous expansion of the long flexor of
the forearm, its tension increasing with the weight on the shoulder.

PHYSIOLOGY OF MOVEMENT.

735

Below the humerus the bones lie, with the exception of the phalanges,
in an almost vertical line, flexion being prevented by the five extensors
of the forearm. The metacarpus continues the vertical column of which
the forearm forms the superior segment, its flexion being prevented by

Q

FIG. 298.— ANTERIOR EXTREMITY OF THE
HORSE IN EXTENSION. (Colin.)

AD, BD, and C D, lines of action of the triceps exten-
sor brachii, scapulo-ulnaris, and aconeus muscles. E F,
flexor brachii. G H, line of action of flexor pedia mus-
cles.

FIG. 209.— POSTERIOR EXTREMITY OF THE
HORSE IN EXTENSION. (Colin.)

AB, line of action of glutens medius. CD, line of
action of triceps extensor. E F, line of action of gas-
trocnemius. G If, line of action of metatarsal flexor.

the extensor inserted in its carpal extremity, and which receives in about
the middle of its fleshy belly an aponeurotic cord fixed superiorly to the
external tuberosity of the humerus. In the phalangeal region the direc-
tion of the bony support now becomes oblique, and, while its obliquity

736 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

constantly tends to become exaggerated by the weight which the upper
extremity supports, it never passes certain limits on account of the pres-
ence of the spiral ligament of the pastern-joint. Without this ligamentous
support muscular action would be insufficient to prevent extreme flexion,
but by means of the ligament, which in the horse and ruminant is composed
of powerful non-elastic tendinous fibres, represented in the carnivora by
muscular fibre, the support of the body is rendered possible without
fatigue.

In the case of the posterior limbs great deviation from the vertical
is met with, and that their obliquity should be restrained within certain
limits considerable muscular effort is required and the mechanical dispo-
sitions of the power is more complex (Fig. 298) than in the case of the
thoracic members. In the hind leg four angles are met with, viz. : in
the hip-joint, the knee-joint, the hock-joint, and the pastern-joint, the
degree of these angles being governed by the angle which the axis of the
femur makes with the vertebrae and the position in which the hind foot
is placed. In the resting position of the hind extremity the line of direc-
tion of the body weight passes from the centre of the hip-joint vertically
downward to the centre of the hock-joint, and then, deviating about 10°
from the direction of the metatarsus, passes behind the pastern-joint
to the ground. The pelvis is very oblique relatively to the trunk in the
horse, ox, and most ruminants and carnivora. The femur is obliquely
connected with the pelvis, downward motion of the pelvis and backward
motion of the femur from the body weight being prevented by the
abdominal recti muscles, whose tendons, being inserted in the pelvis, by
their tension tend to draw the hip-joint anteriorly. The gluteal muscles,
arising from the ilium and passing over the hip-joint to the femur, act
in the same direction, not only preventing forcing backward of the hip-
joint, but in its contraction pressing the hip-joint forward. The leg is,
like the femur, flexed, its obliquity being limited by the tension of the
tendons of the extensor muscles, which pass over the anterior surface of
the knee-joint, by the ligaments of the knee-joint, and by the tibio-tarsal
muscle, which in the solipedes throughout its entire length consists of a
strong aponeurotic band, thus being analogous in its action to the coraco-
radial muscle of the anterior extremity. The flexion of the metatarsus
on the leg is limited especially by the gastrocnemius muscles and: by the
superficial flexor of the phalanges, which in the suspensory ligament
becomes reduced to a cylindrical cord and flattened out at its passage
over the summit of the calcaneum. The inclination of the phalanges on
the metatarsus is prevented by a ligamentous suspensory apparatus
similar to that of the anterior extremity.

From the above it is seen that the extremities in standing support
the body only by muscular effort, principally that of the extensors.

PHYSIOLOGY OF MOVEMENT. 737

Although the flexors participate in many joints, as an example of which
it is only necessary to mention the coraco-radial, which, as already stated,
offers resistance to the flexion of the arm on the forearm, this action is
only rendered possible when the radius is fixed by the olecranon muscles.
The support of the head in standing in the case of quadrupeds is accom-
plished mainly by the ligamentum nucae, which, originating in the spinous
processes of the dorsal vertebrae, terminates in the occipital protuber-
ance, being connected at the same time with all the cervical vertebrae.

While standing quietly the weight of the horse is supported by both
of the fore legs and only one hind leg, the other hind leg being flexed and
only the tip of the toe touching the ground. By this means the muscles
of the posterior extremity which are concerned in the act of standing
are enabled to rest, the weight being borne alternately at varying inter-
vals by the opposite hind legs. From the fact that the centre of gravity
in quadrupeds lies nearer to the anterior than the posterior extremities,
the fore limbs sustain the greater part of the weight of the body. In
riding two-thirds of the weight of the rider are borne by the anterior
extremities and one-third by the posterior.

In every form of animal locomotion the position of the centre of
gravity of the body in space is changed, inertia tending to continue the
motion inaugurated by the muscular contraction until friction, resistance
of the atmosphere, or opposed muscular action arrests it.

In man, movements of locomotion are much simpler than in quad-
rupeds, and will, therefore, be first analyzed. The movements in man
consist in walking, running, and jumping. In the act of walking in man,
by the alternate action of each leg the centre of gravit3r is advanced so
that at each step there is a moment in which the body rests vertically on
the foot of one leg (say the right), while the other (the left) is inclined
obliquely behind with the heel raised and the toe resting on the ground.
Then the latter, slightly flexed to avoid touching the ground, is swung
forward like a pendulum, and the toe of the moving leg (the left)
then brought to the ground. On this point, as a fulcrum, the body is
moved forward by a propulsive act of the supporting leg (the right), the
centre of gravity becoming thus advanced until it lies vertically over the
leg (the left) which has last touched the ground. The body then rests
vertically on the left foot, the right now being directed obliquely back-
ward. The propulsive movement of the active leg, the one concerned in
pushing the body off the ground, gives sufficient impetus to the centre
of gravity to carry it by inertia beyond the vertical line on the passive
or supporting leg, so that this movement from inertia assists in swinging
forward the active leg until it advances a step beyond the passive sup-
porting leg (Fig. 299). Hence, after the act of walking is once started,
inertia is largely instrumental is maintaining the motion, and but slight

47

738

PHYSIOLOGY OF THE DOMESTIC ANIMALS..

muscular exertion is required in walking on level ground. In ascending
an incline, however, the active limb has at each step to elevate the weight
of the body by extending the knee- and ankle-joint by the thigh-exten-
sors and calf-muscles, therefore greatly increasing the muscular power
required. During walking the trunk leans toward the active leg, owing
to the contraction of the glutei muscles and the tensor fascia lata, and is
inclined slightly forward to overcome the resistance of the air. The
more anteriorly the trunk is advanced the more the centre of gravity of
the body tends to lie in the line of the active leg, and, consequently, the
stronger is the forward propulsion of the body. Hence, in rapid walk-
ing the body is more bent forward than in slow walking. During the
advancing of the passive leg the trunk rotates on the head of the active
femur and is compensated by the arm of the side of the oscillating leg

FIG. 300.— THE DIFFERENT POSITIONS OF THE LEGS OF MAN IN WALKING,

AFTER WEBEK.

A, the propelling le£ ; B, the " pendulum " leg.

swinging in the opposite direction, while that on the other side swings
in the same direction as the oscillating leg.

Running is distinguished from walking by the fact that at a certain
moment the body is raised in the air, neither leg touching the ground.
In walking, on the other hand, both feet rest on the ground for the
greater part of the step. In running the active leg, as it is forcibly ex-
tended from a flexed position, gives the body the necessary impetus, the
active leg leaving the ground before the swinging foot has reached the
ground. There is thus an interval during which both feet are off the
ground, and as each foot comes to the ground it executes a new swing
without waiting for the pendulous swing which occurs in walking.

In jumping the propulsion of the bod}' takes place from both feet

PHYSIOLOGY OF MOVEMENT. 739

simultaneously. A running jump ma}' be made higher or broader than
a standing jump from the additional impetus acquired through inertia.

4. THE GAITS OF THE HORSE. — Although the acts of locomotion in
quadrupeds are much more complicated than in man, they may be all
reduced to variations of three main t}7pes — the walk, the trot, and the
gallop.* Since in quadrupeds the centre of gravity lies in front of the
centre of the trunk, it can only be advanced by power acting from the hind
extremities, the fore legs being concerned simply in supporting the trunk.
In the horse the posterior extremities are especialty fitted for this act by
the angular character of their joints, so that in the action of the extensor
muscles the hind legs become considerably longer, and the foot remain-
ing in contact with the ground, through the contraction of the extensors
the result must be to advance the upper extremity of the leg forward ;
and the greater the angles of the posterior extremity, the farther the
trunk will be advanced in the straightening of the hind leg. The
extremity, which in the commencement of the extension of the hind
leg was behind, will now be advanced so as to support the trunk, exactly
as has been found to be the case with the swinging leg of the walking
man, which, immediately after the impulse of the active leg, swings for-
ward, and then on its part assumes the role of the propulsive leg, while
the previously active leg now becomes passive. The force of the shock
communicated to the trunk by the hind legs will be somewhat diminished
by the oblique insertions of the extremities and by the angles between
the single bones of the hind leg, while in the fore extremities the shock
of the foot striking the ground will be diminished by the soft parts,
muscles and fascia, which connect the shoulder-blade to the trunk.

Before taking up the consideration of the different gaits of the
horse the characters and mode of production of the different movements
in the individual limbs first deserve attention, taking up, first, the move-
ments of the fore leg and then of the hind leg : —

The animal being supposed to be in the erect position, before move-
ment of the fore leg takes place the body weight is first shifted, through
the contraction of the pectoral muscles, aided b}^ the latissimus dorsi, to
the opposite extremity. The shoulder being elevated by the rhomboid
and trapezius muscles, flexion commences with the contraction of the
levator humeri, approximating the humerus to the scapula and diminish-
ing the shoulder angle. The principal reduction in the length of the

* In the account of the different movements in the gaits of the horse the author has
mainly followed the analysis published by Bruchmiiller, " Lehrbuchder Physiologie," Oes-
terreicher Vierteljahresschrift fur Veterinarkunde , liii, 1880, pp. 97-120, based on instan-
taneous photography. Acknowledgment is also due to Colin, " Traite de Physiologie
Comparee ;•" Munk, " Physiologie des Menschen und der Saugethiere ;" Boehm, Archiv
fur Wissenschaftliche und Praktische Thierheilkunde, Bd. xiii and xiv ; and Schmidt-
Miilheim, " Physiologie der Haussaugethiere."

740

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

axis of the fore leg occurs through the flexion of the knee-joint, which is
elevated and advanced by the action of the coraco-radial and humero-
radial muscles ; then by the action of the flexors of the carpus and digit
the fetlock and pastern-joints are flexed.

FIG. 301.— POSTERIOR EXTREMITY OF THE
HORSE IN EXTENSION. (Colin).

A B, line of action of gluteus medius. C D, line of
action of triceps extensor. E F, line of action of gas-
trocnemius. G H, line of action of metatarsal flexor.

FIG. 302.— ANTERIOR EXTREMITY OF THE
HORSE IN EXTENSION. (Colin).

AD, BD, and CD. lines of action of the triceps exten-
sor brachii, scapulo-ulnaris, and aconeus muscles. E f.
flexor brachii. G H, line of action of flexor pedis mus-
cles.

Extension of the fore leg is the reverse of the preceding motions
and serves to open out the angles reduced in flexion and so increase the
length of the axis of the limb. Extension is still further the reverse of
flexion in that the motion commences in the pastern-joint, instead of in

PHYSIOLOGY OF MOVEMENT. 741

the shoulder, through the action of the extensor pedis, which, with the
metacarpal extensors, converts the angle of the pastern-joints into
a straight line, the axis of the phalanges forming an angle anteriorly
with the axis of the metacarpus. Simultaneously with this movement
the knee becomes extended, the axis of the metacarpus forming a
straight line with that of the radius, this movement also being accom-
plished by the contraction of the metacarpal extensors. Finally, the fore-
nnn returns to its extended position in a line with the upper arm, partly
through the action of the ligaments of the elbow-joint and partly from
the contraction of the five olecranon muscles. During this forward
motion of the foot in extension the humerus leaves its position of flexion,
and the foot striking the ground, the fore limb again becomes vertical,
and by the action of the pectoral latissimus dorsi muscles the body weight
is again transferred to it. The lever motion of the muscles producing
these movements is seen in Figs. 301 and 302. Instead, however, of the
simple motions of flexion and extension above described, which
occur when one forefoot is simply raised from the ground and again
returned to the same spot, the flexed forearm and carpus may be carried
beyond the vertical line through the extension of the humerus by the
contraction of the various extensors, aided by the abductors of the
humerus, while at the same time the posterior angle of the scapula
is drawn backward and downward by the contraction of the rhomboid
and trapezius muscles. At first, in the forward motion of the lower end
of the humerus flexion is increased, but the farther it advances forward
and the more the scapula rotates backward the more the shoulder angle
becomes opened, and, under the action of the adductors of the humerus,
directed outward and upward, so that the extensors of the lower joints
are put on the stretch and their contraction converts the flexion of the
limb into extension, the fore leg thus describing a pendulum-like
motion, and in its extended position is directed forward and downward
and strikes the ground in front of its previous position (Fig. 303). Then,
from the impulse communicated to the trunk from the hind legs, the
weight of the body is gradually transferred to the fore leg, which,
the foot remaining on the ground, gradually becomes more and
more vertical from the forward motion on it of the trunk (Fig. 304).
As, however, the inertia of the moving body carries the shoulder beyond
the vertical, the axis of the fore limb is then directed downward
and backward, the assumption of this position being aided by the
forward rotation of the scapula, while the extensors of the forearm (the
foot being fixed on the ground) not only sustain the elbow- and shoulder-
joints, but, by their contractions, give an additional forward impetus to
the body. The extreme extended position of the limb puts the flexors
of the lower joints on the stretch and so leads to their contraction, and

742 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the limb, passing now into flexion, again describes its forward pendulum
motion, the point of support of the scapula being the centre of rotation,
while the hoof describes an arc of a circle. On the other hand, while

FIG. 303.— OSCILLATION OF THE FLEXED FORE LEG. (Colin.)
The hoof describes an arc of a circle, C B A, the cord, C A, being a measure of the extent of oscillation.

the foot is on the ground the shoulder describes the arc of a circle and
the centre of rotation is in the foot. The combination of these two
movements in both fore legs is seen in Fig. 305.

J)

F-io. 304.— OSCILLATION OF THE EXTENDED FORE LEG. (Colin.)

The foot being on the ground at I), the shoulder describes an arc of a circle, ABC.

In the case of the hind leg flexion likewise results in a shortening
of the axis of the leg and the reduction of the angles between the dif-
ferent bones. The weight being thrown on the opposite extremity by

PHYSIOLOGY OF MOVEMENT.

743

the contraction of the adductors, the femur is approached to the ilium
by the contraction of the rectus and lumbar and iliac psoas muscles, the
knee being elevated anteriorly by the ischio-tibial muscle and the hock-
joint flexed by the contraction of the metatarsal flexor, whose tendinous
portion, when the stifle-joint is flexed, becomes tensed and mechanically
repeats the action on the joint below, the digital region being flexed on
the metatarsus. As a consequence of these flexions, produced almost
simultaneously, the axis of the limb becomes shorter, is raised from the
ground, and advanced in a more or less oblique line. That the foot may
again be placed on the ground the above muscles must relax and their
antagonists contract. First the femur is extended on the pelvis by the
action of the glutens maximus, whose principal trochanteric branch acts
as a lever of the first class. The leg is then extended on the thigh by

FIG. 305.— OSCILLATION OF THE ANTERIOR EXTREMITIES. -(Colin.)

The figure shows that while one fore leg is describing the pendulum motion the other is acting as a

e gure sows tat we one ore eg s escrng te penuum moton te oter is acting as a
support, while the right fore foot describes the arc, </ /(, the left shoulder describes the arc, at hi <•!, from the

on of the hind legs. Then the right
in one complete step are shown at

,

impulse given to the centre of gravity of the body through the extension of the hind legs. Then the right
shoulder describes the arc, df eJ ft. The six positions of the left leg i

abed e/, the centre of gravity having been advanced from m to n.

the rotuleus muscles, the metatarsus in its turn regaining its position on
extension through the contraction of the gastrocnemius, the digital region
being extended by the phalangeal extensors. The lever action of the
muscles which produce these motions is seen in Figs. 249 and 251.

In movements of progression each hind limb alternately serves to
give an impetus to the body by passing into a condition of extreme ex-
tension, the foot being on the ground, and then, passing into a condition
of flexion, describes a pendulum motion through the air until the foot
again strikes the ground in front of the position which it left. The pen-
dulum motion commences with flexion of the hip-joint and forward motion
of the lower end of the femur followed by flexion of the other joints.
The greater the advance of the knee the greater the tension of the ex-
tensors, until the limb becomes extended and its increased length brings

744 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the foot to the ground, the axis of the limb being now directed obliquety
downward and forward. The body weight is then shifted to this limb
through the action of the adductors, the limb again passing into a more
or less marked position of flexion. The croup muscles then contracting,
the pelvis is advanced, assisted by the extensors of the femur, which find
a fixed point in the knee, while at the same time the gastrocnemius
muscle, contracting, opens the angle of the hock-joint and elevates the
pelvis from the increase in the length of the axis of the limb. Through
these motions the line of the hind leg gradually becomes vertical, passes
the perpendicular, and is then directed downward and backward from
the advance communicated to the body (Fig. 306). When the highest

FIG. 306.— OSCILLATION OF THE EXTENDED HIND LEG. (Colin.)

The foot being on the ground at D, the hip-joint describes an arc of a circle, ABC, the lines A D,
B D, and C D representing the changing axis of the hind leg.

degree of extension is reached the weight is shifted to the opposite limb,
and after complete flexion the pendulum motion is repeated.

In these motions the hind leg does not move in the plane of the line
of direction ; in rapid movement the knee and tip of the foot are some-
what everted through the action of the iliacus muscle until the foot
strikes the ground. In slow motions, on the other hand, especially when
bearing heavy weights, the knee is directed inward from the action of
•the adductors and tension of the femoral fascia, while the hock is everted,
thus turning the toe toward the median line.

(a) The Walk. — In walking the body is supported by two legs while
the other two are describing the pendulum motion, the support being
alternately on diagonal feet and then on the two feet of the same side ;

PHYSIOLOGY OF MOVEMENT. 745

but as the impulse of the supporting feet is not simultaneously pro-
duced, four strokes of the hoof are heard with each step, but at unequal
intervals ; for when the support comes from the two feet on the same
side the preservation of equilibrium compels a more rapid shifting of
the body weight to the opposite side than when the diagonal limbs are
in action.

If we commence the consideration of the act of walking in quadru-
peds at the moment in which the one hind leg after completing its pen-
dulum motion comes again to the ground, then it occupies a position in
which the axis of the limb is directed from behind forward and from
above downward. The centre of gravity in consequence of the propul-
sive movement advances, the leg and trunk describe an arc of a circle
around the foot as a centre, so that the axis of the leg gradually
becomes vertical and then advances, and the axis now tends to become

FIG. 307.— THE WALK. (Colin.)

directed from before backward and from above downward. At this
moment active contraction of the extensor muscles occurs and the leg
which was the supporting member now becomes an active propulsive
member. It leaves the ground, becomes flexed, and swings forward,
the femoral articulation now being the centre of movement and the foot
describing an arc of a circle until it becomes advanced in front of
its point of support. It then strikes the ground and the movements
are repeated (Fig. 307). At the moment when the hind leg is thus
swinging forward the fore leg of the opposite side is likewise advanced,
the movement commencing as soon as the propulsive hind leg is in a
vertical line. Through the forward movement of the trunk the line of

746 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

direction of the fore extremity becomes changed, so that instead of being
vertical it is directed from above downward and from before backward.
The foot must, therefore, be raised from the ground and advanced in the
direction in which the trunk is moving, and, striking the ground, again
becomes vertical at the moment when the pendulous hind leg strikes the
ground. At the moment, then, when the fore leg becomes vertical, the
propulsive movement in the opposite hind leg occurs. Then the motion
commences in the opposite hind leg and fore leg, the alternation of the
limbs being perfectly regular. Thus, suppose the right hind foot to be the
propulsive foot, the left fore foot is extended on the ground, the left
hind leg is swinging forward, and the right fore foot is just leaving the
ground, the body thus being supported on a diagonal pair of feet. Then
the right hind foot leaves the ground, the left fore foot is on the ground,
the limb having passed the vertical line, the left hind leg is giving the
impulse to the body, while the right fore foot is swinging forward. The
body is then supported on unilateral feet, the support being of shorter
duration than in the first case. Hence, in walking, there is always at
any one time an anterior and a posterior limb in the air and an anterior
and posterior limb acting as a support, the limbs being raised and replaced
in such an order that of the two limbs in the air one is alwaj^s in advance
the half of its course over the other, while of the supporting limbs in
one the line of the support is vertical when the other first reaches the
ground. •

In quadrupeds the length of the step is measured by the distance
between the track formed by each separate foot, so that it is, therefore,
twice as extensive as in man. When the hind feet reach the foot-prints
of the fore feet it is twice as long as the base of support, i.e., the dis-
tance between the pairs of feet at rest. As the motion in walking in
quadrupeds is produced by the action of the diagonal extremities, the
centre of gravity is first moved to one side and then returned to the
centre and then cast to the opposite side. The duration of the step is
dependent upon the duration of the swinging of the leg. The higher an
animal raises its leg, the shorter is the pendulum and the more rapidly it
swings.

The rapidity of motion in the walk in the horse varies front one to
two meters in the second. In drawing heavy weights or in a very slow
walk the relative movement of the feet is somewhat different from that
detailed above. Then the elevation of each foot is delayed until the sup-
porting feet are firmly on the ground ; the body is then always supported
on three limbs, by which equilibrium is better preserved. The same
sequence of movement is, however, preserved.

(6) The Amble. — The amble is a modification of the walk, and is
seen in the dromedary, giraffe, and occasionally in ruminants, and more

PHYSIOLOGY OF MOVEMENT. 747

seldom still in the horse. It is characterized by the fact that the eleva-
tion of the second leg on the same side occurs sooner than in the walk.

The walk merges into the amble when, the body being supported by
the two legs on the same side, the two opposite legs are elevated simul-
taneonsty instead of separately, as in the walk (Fig. 308).

In the walk the fore leg is alwa}Ts one-half the extent of its move-
ment behind the hind leg on the same side, while in the amble both legs
on one side move together, so that, therefore, there is a regular change
between the feet on each side of the body. Consequently, in the amble
the centre of gravity is first shifted to the one side and then to the
other, the length of the step in the amble and walk being the same. But
from the fact that the supporting limbs are on the same side of the body,
to preserve equilibrium the movements must be more rapidly performed

FIG. 308.— THE AMBLE. (Colin.)

than in the walk. The gait is, therefore, a faster one, the greater rapidity
of the pace being accomplished by the reduction of the time, which cor-
responds to the half of the duration of the movement of one leg, since on
each side one-fourth of the time is saved. The rate of movement in
pacing may approach that of the trot, the velocity often rising to three
meters per second. Since the two unilateral propulsive and the two
swinging feet always move together, and are always at one time in the
same phase of motion, the swinging feet strike the ground together, so
that after one pace but two strokes of the feet have been heard.

In the rack, which is simply a modification of pacing, the uni-
lateral feet act together, but the hind leg in propulsion is somewhat
later than the fore foot of the same side in leaving the ground. Four
strokes of the feet are heard in this gait, two rapidly following sounds
when the feet of one side strike the ground, separated by a longer interval

748 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

from the two rapid sounds when the feet of the opposite side strike the
ground.

It has been seen that in the movement of locomotion in man there
are two periods of time in which both feet are on the ground and only
one interval in which only one foot is in contact with the earth. In
running, on the other hand, there is a moment in which one of the legs
is raised up while the other is still performing the pendulum motion, and,
consequently, both legs are at one time in the air. This interval is, how-
ever, much shorter than that in which both feet are on the ground.

(c) The Trot. — The form of locomotion seen in the horse and more
seldom in the ox and other quadrupeds which corresponds to the act of
running in man is termed the trot, in which the fore leg completes its
movement with the diagonal hind leg ; so that in the trot the diagonal feet
and hind limbs at the same moment leave the ground and at the same

FIG. 309.— THE TROT. (Colin.)

moment again reach it. Therefore, in the trot two strokes of the feet
on the ground are heard at each step. In the fast trot an interval occurs
between this double stroke of the feet against the ground in which the
body is moving through the air with all four feet raised from the ground.
This interval is variable, usually being about half the time that the
feet are in contact with the ground.

In the trot the impulse is communicated to the pelvis from each hind
leg alternately, so tending to strain the articulation between the sacrum
and vertebrae. This is, however, reduced to a minimum by the contrac-
tion of the ilio-spinalis of the opposite side.

In a very fast trot the second pair of feet leave the ground as soon
as the first pair have reached the vertical position. Each step in the trot
is twice as long as the step in the walk, in rapid trotting the hind feet

PHYSIOLOGY OF MOVEMENT. 749

striking the ground considerably in front of the track of the fore feet and
the velocity of motion rising to from eight to twelve meters per second.
The walk turns into the trot when, the body being supported on two
diagonal feet, the opposite hind foot rapidly leaves the ground and
swings forward so that it strikes the ground simultaneously with the
diagonal fore foot, or by one hind foot, as soon as it strikes the ground,
rapidly passing into extension simultaneously with the diagonal fore
foot.

(d) The Gallop. — The more the long axis of the body coincides
with the axis of the propelling hind legs, the greater is the propulsive
power of the legs. The angle between the hind legs and the body may
be increased by elevation by means of the fore legs, and in the act of
galloping the fore legs are raised up, while the main propulsive power
comes from the hind legs, so that the gallop is a series of jumps: Accord-
ing to the rapidity of the gallop or run of quadrupeds, four strokes of
the feet on the ground are heard in a slow gait or canter, three in the
ordinary run, and two in running at full speed. Ordinarily, the legs of
the two sides of the body do not act simultaneously, and, according
as the right or the left hind leg is extended farthest behind, one speaks
of a right- or a left-handed gallop. Thus, in the right-handed run, the
left hind leg, stretched far under the body, first in its extension gives the
impulse to the body, the right hind leg at this moment swinging forward
to add the impulse of its extension a moment later, while both fore feet are
off the ground, swinging forward, the left being the farthest advanced in
commencing extension, while the right fore leg is still flexed. Then, while
the left hind leg is still on the ground, though extended far behind the
body, the right hind leg strikes the ground and adds its impulse in
extension, while the extended left fore foot approaches the ground and
the swinging right fore foot passes into extension. Then the left fore
foot, reaching the ground, acts as a support on which the weight of the
body is sustained, both hind legs being extended behind the body, the left
being farthest extended, while the extended right fore foot is just about
to touch the ground. Finally, the right fore leg reaches the ground and
receives the weight of the body, while flexion commences in the left fore
leg, both hind legs being now flexed under the body, the left hind foot
being somewhat the farthest advanced.

At this moment the left fore foot is raised and the right fore leg,
which alone sustains the weight of the body, leaves the ground after
having passed the vertical, the body being then entirely free from all
support, the fore legs flexed, and the hind legs drawn under the body,
the left first reaching the ground.

Thus, there is a moment, in which, alternately, each limb alone sus-
tains the weight of the body, and a moment in which both hind legs are

750 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

propelling the body, and one in which both fore legs are supporting it.
In the analysis of the movements of the limbs in the run the greatest
confusion has existed as to the functions of the fore limbs ; this has now,
thanks to instantaneous photography, been cleared up. In the first
place, it is seen that at one time the body is entirely clear from the
ground, and that the weight of the body is not received on one or both
of the fore legs, but on one hind leg, advanced under the body so that
the foot is nearly under the centre of gravity. In the second place, the
fore legs do not serve merely as " props or stilts " for the support of the
body in motion, but are themselves also propelling organs. At first
sight this might seem impossible, for the insertion of the fore limbs,
acting on the body at rest, and being inserted in front of the centre of
gravity, could not advance, but only elevate it, as in rearing. In the
running animal, however, the propulsion from the hind legs advances the
centre of gravity, but at the same time tends to lower it, and if the fore
feet were immovable, the animal would tend to fall forward on its head.
This is prevented by the shifting of the fore feet, while at the same
time a distinct upward impulse is communicated to the centre of gravity.
This may be seen in Mr. Muybridge's photographs, where there is a
distinct elevation of the body at each time the fore legs leave the ground.
The centre of gravity of the body is thus acted on \)y two forces, one
from the hind legs tending to advance and lower it, the other from the fore
legs tending to elevate it ; the resultant of these two forces will evidently
be a diagonal between the two ; and the upward lift from the fore feet
will more than compensate the downward tendency, and the bod}- will
be lifted and advanced.

In this gait but two strokes of the feet are heard, the first pro-
duced by the contact of the left hind leg, lengthened by the fall of the
right hind foot, the second by the contact of the left fore foot with the
ground, lengthened by the fall of the right fore foot. The interval
between the first and second sounds is very short, that between the
second and first, while the hind legs are swinging through the air, some-
what longer. The length of the strides in the full run may amount to
six or seven meters, and a velocity of nearly fifteen meters per second
be attained.

In a slower run or gallop three strokes of the feet are heard, the
body, as in the trot, being supported on the diagonal limbs. The differ-
ence of this gait from the trot consists in the fact that in the latter the
support on the diagonal limbs is equally prolonged, while in the gallop
the support on one pair is longer than on the other. A conception of
this gait is obtained if it is imagined that one pair of feet are acting as
in the trot, the other as in the movement of jumping.

1. In this gait, when right-handed, the left hind leg is extended on

PHYSIOLOGY OF MOVEMENT. 751

the ground and gives the forward impetus to the bod}1 ; the right hind
leg and left fore leg are swinging forward, while the flexed right fore leg
is being advanced. 2. The right hind foot and left fore foot then strike
the ground and receive the weight of the body ; the left hind leg is
extended behind the body and about to leave the ground, while the fully
extended right fore leg is advanced. 3. Then the right fore leg reaches
the ground and sustains the weight of the body until the limb is vertical ;
the left hind leg leaves the ground, and the flexed right hind leg and left
fore leg are swinging forward. Finally, the right fore foot leaves the
ground, the leg being strongly flexed, and the bod}T moves through the
air from the impetus from the left, aided by the right, hind leg. The
three strokes of the hoof correspond to the three actions described
above as 1,2, and 3. The pause between the first and second sounds is
short, that between the second and third still shorter, while between the
third and first, and while the body is moving through the air, the pause
is considerably longer.

In this gait, as in the run and long jump, and occasionally in the
high jump, the weight of the body when it first reaches the ground is
not received on the fore legs, but through rapid flexion the hind legs
first touch the ground.

In the canter the action of all the limbs is much slower, the verte-
bral column being more raised, the gait, therefore, more resembling the
high than the long jump. The fall of the diagonal feet is separated by a
short interval ; so in the canter four strokes of the hoofs are heard.

The plates following page 921, through the kind permission of Pro-
vost Pepper, of the University of Pennsylvania, and Mr. Muybridge, are
reproduced from the elaborate series of instantaneous photographs made
by Mr. Muybridge in the University of Pennsylvania.

5. OTHER MOVEMENTS IN THE HORSE. — (a) Rearing. — In the act of rear-
ing the fore part of the body becomes raised up on the hind extremities,
so that the vertebral column leaves the horizontal direction and becomes
nearly vertical. The first stage of rearing consists in the fixation of the
hind legs, the elevation of the neck and head, and the contraction of the
back and lumbar muscles, by which the vertebral column becomes rigid ;
then the elevation of the fore legs commences with a slight bowing of
the extremities and subsequent powerful extension, by which the feet are
raised up from the ground and become flexed. Then there is a powerful
contraction of the back muscles (the ilio-spinal, the gluteal muscles, and
the ischio-tibial muscles), the anterior extremit}7 of the vertebral column
is somewhat raised up, its elevation being assisted by the drawing down
of the pelvis by means of the lumbar muscles, so that the weight of the
body is now borne by the flexed hind legs (Fig. 310). The vertebral
column ordinarily does not quite reach the vertical line, but yet the line of

752

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

direction of the centre of gravity may fall behind the hind legs, and then
the animal falls over backward. In rearing, the fore legs and hind legs
are parallel to each other and always somewhat diagonal ; likewise, both
fore legs are not elevated simultaneously, but one somewhat precedes the

FIG. 310.— REARING. (Colin.)

A B, line of action of ilio-spinal muscles : F G, glutens maximus ; D C, ischio-tibial
pyramidal prolongation of the vastus.

luscles; DE,

other. The return to the normal condition is accomplished by the drop-
ping of the head and neck, the return of the fore legs from their flexed
to the extended condition, so that gravitation alone is sufficient to cause

PHYSIOLOGY OF MOVEMENT.

753

the body to return to its natural position supported on all four of its
extremities.

(6) Kicking. — By this term is understood the elevation and violent ex-
tension of the hind legs, with raising of the posterior part of the vertebral

column. The first stage of this act consists in the extension of the neck
and the dropping of the head toward the ground between the firmly ex-
tended fore legs, while the hind legs are flexed by the powerful contrac-
tion of the back muscles, which find a fixed point of support in the last

48

754 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

cervical vertebrae. The pelvis and posterior part of the vertebral column
is raised, this elevation being assisted by and coinciding with the sudden
extension of the hind legs, the feet leaving the ground and being ex-
tended by the muscles of the upper joint of the leg, the lower joints
likewise being subsequently extended. Here, also, both fore feet are not
parallel on the ground, but one is somewhat advanced in front of the
other. The hind foot on the diagonal side is somewhat sooner raised,
and, therefore, further extended than the other (Fig. 311). In this act
the centre of gravity never nearly approaches the line of direction of the
fore legs, so that this position can be maintained but for an instant, the
trunk sinking again by its own weight, and is supported by the hind
legs, which are now flexed and drawn under the body.

(c) Lying Down and Rising Up. — The first stage of lying down in
the horse consists in the backward motion of the fore feet and the for-
ward motion of the hind feet, thus greatly reducing the base of support.
A sudden flexion of the fore legs then occurs, so that the animal falls on
its knees ; then the hind legs become flexed, so that the posterior surface
of the tibiae touches the ground. The act of lying down, therefore, in
the horse is practically falling down. While lying one side of the
body completely touches the ground, the limbs being extended from the
body either in slight flexion or in complete extension. In rising up the
extended extremities are drawn to the body, and by the unilateral action
of the trunk muscles the body is brought in such a position that the
chest and abdomen are in contact with the ground, the fore feet are then
extended on the ground, and a fixed point for the back muscles thus being
acquired, the contraction of these muscles draws the pelvis forward, so
that the hind legs are now enabled to bring the feet against the ground,
and by sudden extension of all the legs the bod}' is raised up.

(d) Walking Backward. — In walking backward in the horse the head
and neck are elevated, the spinal column, through the contraction of its
muscles, rendered rigid, and the fore legs in a somewhat flexed condition
are directed from above backward and downward, and then, in contact
with the ground, gradually extended, being assisted by the contraction
of the pectoralis major and latissimus dorsi, serve to push the body back-
ward from the flexed hind legs. The backward movement occurs by the
alternate movement of the diagonal feet ; thus, it may commence with
the fixation and extension of the right fore foot, then the left hind foot,
then the left fore foot, and then the right hind foot. The foot which is
raised up is, however, again placed on the ground and commences to act
as a supporting member before the foot which is next elevated has left
the ground. Consequently, support continues on three feet at one time,
and the period of support lasts much longer than that of forward move-
ment. Walking backward in quadrupeds is, therefore, an extremely slow

PHYSIOLOGY OF MOVEMENT. 755

gait. In this act the centre of gravity is not moved directly forward,
but oscillates from side to side.

(e) Swimming. — In swimming the trunk is almost entirely immersed
in the water, the neck extended, and the head held high. The horse
swims readily, since its lungs contain a large amount of air, and the rapid
movement of the limbs gives to the body an impulse in a horizontal
direction, the weight of the body being largely overcome by the buoy-
ancy of the water. The movement of the feet consists in rapid pen-
dulum-like motions from before backward, and the forward motion of
the body results from the resistance which the water offers to the back-
ward movement of the feet. The swimming motions in the horse occur
regularly in the same direction on each side of the body.

The power developed by any mechanical contrivance is estimated
by the weight multiplied by the height to which it may be raised in one
second ; this is described as a kilogram meter. Animals, therefore, may
be regarded as machines, since they possess the power of raising a weight
to a certain height. Likewise, the motion of a weight on a level surface
is to be regarded as a production of work, and whose movement equals
the sum of all the resistances which have to be overcome by the animal
and the velocity produced. The power of a horse is placed, as an average,
at sixty kilogram meters, an ox at sixty kilogram meters, and an ass at
thirty -six kilogram meters. The average velocity communicated to the
weight in work continued for several hours each day has been placed in
the horse at 1.25 meters, the ox 0.8 meter, and the ass 0.8 ; consequently
the unit of power in the horse has been placed at sevent3r-five kilogram
meters, in the ox forty-seven, and ass twenty -nine: so that, therefore, one
horse-power would mean a power which would be able to raise seventy-
five kilograms one meter high in one second. In referring these figures
to the body of animals, it has been calculated that the development of
power in animals in one hour, reckoned for each kilogram of body
weight, is —

In the horse, . . . . .940 kilogram meters.

" " mule, 800

" " ass; 640 "

" " ox, t . , . . . .620

" " man, 560 " "

In the application of animal power in' hauling, or in employing the
horse as a draught animal, resistance has to be overcome, since the centre
of gravity must be advanced by the power exerted by the hind extremi-
ties (Fig. 312). In general, the hauling power of an animal, as in all
motors, is governed by the mass moved, therefore through the weight
of the animal and through the velocity communicated. The power thus
acts in two relationships, through the overcoming of the resistance of the

756

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

weight and the transference of the velocity of the animal to the moving
mass. All the arrangements of the hind extremities are especial!}' favor-
able for the production of power; thus, reduction of the anterior pelvic
angle, accompanied by powerful development of the hips and lumbar
muscles. In animals, therefore, with short bones, slight angularity, and
short muscles the conditions are most favorable for drawing heavy
weights, while animals with long bones, long muscles, and highly
angular joints are especially adapted for speed. The position of the
centre of gravit}* in the animal body is especially of influence in the
developing power. Since the body weight is the moving force its

FIG. 312.— HAULING FROM A COLLAR. (Colin.)

The line, A B, indicates the direction of the resultant of the propelling forces through the lines, A D

and B C.

action will be the more developed the farther forward the centre of
gravity, since in this way the power-arm of the lever will be increased.
Consequently, draught animals sink the head and neck. The power
developed by horses has been estimated by raising a certain weight
to a certain height by a rope passing over a pulley. Experiments so
made have shown that a moderately strong horse may raise a weight
of ninety-five kilos in one second to 0.8 meter high, from whence horse-
power of seventy-six kilogram meters has been deduced. In the same
way the power 'of an ox has been found to be forty-seven and an ass
twenty-nine kilogram meters. In drawing a weight, the full power of an

PHYSIOLOGY OF MOVEMENT.

757

animal is never employed, but there is always a certain amount of loss
from friction and other causes. As most of the contrivances which are
employed to enable horses to draw weight consist of attachments which
applies the weight to the horse's shoulders, the weight falls in front of the
centre of gravity of the body, and the animal may thus be regarded as
pushing the weight ; and as the mass moved is the animal's body plus the
applied weight, the greater the latter the more the centre of gravity of the
common mass will be advanced. Hence, in drawing heavy weights the
fore limbs will be behind the common centre of gravity, and they, also,
in their extension will aid in propelling the body.

6. SPECIAL MUSCULAR MECHANISMS. — The Voice. — By the term voice
is meant the sound produced in man and the higher animals through the
vibration of the column of air forced by the contraction of the thorax
between the vibrating vocal cords of the larynx. Speech, of which man

FIG. 313.— THE HUMAN LARYNX, AS SEEN FIG. 314.— POSITION OF THE HUMAN VOCAL

WITH THE LARYNGOSCOPE. (Landois.) CORDS ON UTTERING A HIGH NOTE.

L., tongue : £., epiglottis: V., valleculla; R., glottis; (LandoiS.)

L. i\, true vocal cords ; S. M., sinus Morgagni : L. r>. s.,
false vocal cords : P., position of pharynx : S., cartilage
of Santorini; W., cartilage of Wrisberg ; S. p., sinus
pyriformes.

alone is capable, consists in certain modifications of the vocal sounds
by the parts situated above the larynx; that is, the pharynx, mouth, soft
palate, nasal fossae, tongue, teeth, and lips. Speech may, therefore, be
described as articulate voice.

Voice is produced by the imparting of the vibrations of the vocal cords
to the column of air within the respiratory organs. The means by which
this is accomplished is entirely analogous to that by which sound is
produced in reed instruments. The vocal cords consist of free rims of
highly elastic membrane whose tension may be varied by muscular action
and whose edges may be approximated or separated (Figs. 313 and 314).
When the edges of the vocal cords are in close contact, through a strong
muscular expiratory motion the air below the vocal cords becomes
greatly condensed and finally its tension is sufficient to overcome the
resistance of the closed vocal cords; when the vocal cords are thus

758 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

separated air passes between them, and, consequently, rarefaction of the
air below takes place, while the cords being elastic, their tension serves
to again readily overcome the propulsion of the air from the contraction
of the thorax. As a consequence, the edges of the vocal cords are set
into rapid vibration and these vibrations are communicated to the column
of air both below and above the vocal cords, and as a result a sound
which is due to these vibrations is produced ; the vibrations of condensa-
tion and rarefaction of the air are the principal causes of the tone, while
the cavities above the vocal cords fulfill the part of resonators.

Sounds produced in this way, like other musical sounds, may vary
in regard to their pitch, intensity, and quality. The pitch of the sound
will depend upon the length of the vocal cords, the shorter the vocal
cords, the more rapid are the vibrations and the higher the pitch of the
note produced. The pitch of the note is further dependent upon the
degree of tension of the vocal membrane. As in the case of musical
instruments of a similar nature, stringed instruments, or reed instru-
ments, the pitch of the note is proportionate to the square root of the
tension. In man and other mammals in whom vocal cords are present,
the pitch of the note may, therefore, be modified by varying degrees of
tension of the vocal cords through the action of different muscles.

The intensity of the sound depends primarily upon the strength of
the blast of air, so that, therefore, the more vigorous the expiration, the
greater will be the amplitude of the vibration of the vocal cords and the
greater will be the intensity of the sound, while the action of the dif-
ferent resonators of the vocal organs, through the sympathetic vibrations
induced in their cavities by the vibration of the column of air set into
motion by the swaying vocal cords, is added to the fundamental tone
that is produced and its intensity is modified.

The timbre, or quality of the vocal sounds, as in other musical in-
struments, depends upon the over-tones or harmonics which accompany
the fundamental note. Changes in the shape of the different resonating
cavities of the vocal organs will, by modifying the prominence of dif-
ferent over-tones, account for the difference in the voice of different
animals.

The mode of production and the character of the voice differ very
greatly in different members of the animal kingdom. Voice may be pro-
duced in all vertebrates possessed of lungs and la^nges, while in fishes,
where the respiration is branchial and not pulmonary, the production of
voice is impossible. In invertebrates the sounds produced in such great
variet}^ are in no respect analogous to the voice, since they are produced
by entirety different mechanisms. Thus, insects produce sounds (which
are especially distinguished for their acuteness) either by the rapid
movement of their wings, as in flies and bees, or by rubbing their legs

PHYSIOLOGY OF MOVEMENT.

759

on their wing-cases, or their wing-cases on each other or on the thorax
or abdomen. In humming insects sound may be produced by forcing
the expired air from their stigmata, which are provided with muscular
rods and which are thus thrown into vibration, so that in this group of
insects, represented by the humming-bees and many dioptera, the closest
analogy exists between the production of sound and the production of
voice in the vertebrates.

IB

Libr

L.ibr

FIG. 315.— INFERIOR LARYNX OF THK TURKEY. (Griitzner.)

A, during voice production : B, in free respiration. (In At and J5' the anterior wall is removed.)
m.st.tr., sterno-tracheal muscles in contracted condition in A and A> ; Tr., trachea; v, Tr. R.,
united tracheal rings, forming the tympanum with its antero-posterior bridge, S. ; B. Sp., bronchi ; m. t. «.,
external tympanic membrane ; m. 1. 1.. internal tympanic membrane stretched out flat in B and Bf, in A
and Al forming sharp folds in the lumen of the bronchi; L. ibr., interbronchial ligament; b., band run-
ning to the dorsal wall of the trachea.

Animals below insects, as radiates and mollusks, are all entirely
incapable of sound. Among reptiles, certain of them, such as frogs,
lizards, and other batrachians, possess true vocal organs. Among am-
phibians the frog has a larynx provided with muscles, which produces a
sound of varying pitch, dependent upon the strength of the muscular
contraction and the force of the expiratory blast. The range of such
vibrations is, however, extremely limited. In the Rana esculenta there
is on each side of the angle of the mouth a membranous bag which may

760 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

be inflated with air, and whose wralls, being thin and membranous, are
thrown into vibration, and, together with the column of air contained in
the oral chamber, aid in producing the characteristic resonance of the
croaking of the frog (Fig. 315).

In birds the vocal organs are double, a larynx situated at the upper
termination of the trachea and a syrinx at its bifurcation constituting
a true vocal organ. Two folds of mucous membrane, or three in the case
of song-birds, project into each bronchus, and are so acted on by muscles
as to vary their tension and adapt them to the production of voice. The
superior larynx acts only as an accessory in the production of sound.
The number and complexity of the muscular fibres acting on these
membranes varies in proportion to the range of voice. In the gallinacea
simply a trace of muscular fibre can be recognized ; but one pair of
muscles is found in the eagle, three pairs in the paroquet, while five
pairs are found in song-birds. These muscles have a common origin in
the trachea, and their other extremities are inserted into the first ring of
the bronchus. In addition to these intrinsic muscles there are others
concerned in varying the length of the trachea, so as to alter the length
of the vocal tube and, therefore, the pitch of the note produced. The
superior organ, -or the larynx, is entirely negative in the production of
sound, and the performance of tracheotomy below the larynx produces
but slight modification in the character of the sound produced.

In mammals, as is well known, the greatest variation exists in the
character of the sounds produced. The organs for the production of
sound are here the larynx and the upper resonating chambers, varying in
shape and general character among each other, although in all built on
the same general plan as in man. The variations in the voice are
dependent upon modifications in the larynx, in the depth of the nasal
chambers, the shape of the pharynx, of the various sinuses, and the
formation of the mouth and of the laryngeal ventricles. Sound is, how-
ever, primarily due in all cases to the vibrations transmitted to the
column of air by the swaying to and fro of the vocal cords. The superior
or false vocal cords of man are absent in many species of mammals.
The glottis of the horse is distinguished by the formation of a semi-lunar
fold of mucous membrane below the epiglottis, which serves to form a
funnel-shaped cavity. The laryngeal ventricles are also well developed.
The voice in the horse is produced by a succession of interrupted expira-
tory movements, the tension of the vocal cords gradually diminishing
during each complete expiration, so that, therefore, the first sounds
produced have a higher pitch than the last; the superior ventricles are
wanting (Fig. 316).

The larynx of the ass differs but slightly from that of the horse.
Here, also, there are two vocal cords, the ventricles are well developed,

PHYSIOLOGY OF MOVEMENT.

761

but the opening to them is narrow. The voice of the ass is characterized
by the fact that it commences in an inspiratory movement in the produc-
tion of a sound of high-pitch and it terminates in expiration in the
production of a deeper sound.

The larynx of ruminants offers considerable differences to that of
solipedes. The glottis is short, and the vocal cords can scarcely be dis-
tinguished from the lining membrane of the larynx, and there are no
ventricles. The voice in ruminants is, therefore, more imperfect than in
the horse, and consists of a

sound of low pitch capable of ifljFmafr t 5'

but little variation (Fig. 317).

In the hog below the epi-
glottis is found a large, mem-
branous sack, which fulfills the
purpose of a resonator, greatly

Fia. 316.— LARYNX OF THE HORSE
FROM ABOVE AND BEHIND. (Muller.)

a at, thyroid cartilage; b b, arytenoid car-
tilages; cc', arytenoid muscles; d dt, aryepiglottic
folds; e, epiglottis. 1 V, posterior crico-arytenoid
muscles; 2 I', oblique arytenoid muscles; 33f,
superior thyro-arytenoid muscles; 44', true vocal
cords ; 5, glottis ; 6, ventricles of larynx.

FIG. 317.— LARYNX AND HYOID BONE OF Ox.

(Milller.)

1, 2, 3, arms of the hyoid bone : 4. thyroid cartilage ; 5, body
of the hyoid bone; 5' and 5", fork of the hyoid bone; 6, arytenoid
cartilages ; 7, epiglottis ; 8, cricoid cartilage ; 9, posterior crico-
arytenoid muscles ; 10, trachea.

strengthening the intensity of the voice and giving to it its peculiar
character. In the hog the inferior vocal cords are inserted into the
tracheal border of the thyroid cartilage and the arytenoid cartilages
are fused together, the vocal cords are rudimentary, the ventricles are
deep and communicate with the interior of the larynx only by a narrow
slit. Two characters of sound may be produced by the hog, the one
of low pitch, a grunt, which is the habitual sound, while another of very
high pitch is only produced when the animal is maltreated or excited.
In the dog the vocal cords are well developed, while the false vocal

762 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

cords are scarcely perceptible; the ventricles are ample, but their
openings are very narrow. The voice in dogs is capable of greater scope
than in other of the domestic animals, with the exception, perhaps, of
the cat, which is characterized by an almost equal development of the
upper and lower vocal cords.

The mechanism of the production of the voice, therefore, depends
upon the expulsion of a blast of air between two free membranous rims,
which are thus thrown into vibration and whose tension and position are
capable of modification. The change in the position and tension of the
vocal cords is accomplished through the action of the laryngeal muscles.
The laryngeal muscles fulfill a double function. In respiration, as has
been already mentioned, the glottis is widened during inspiration and
the vocal cords tend to approach each other during expiration. In the
production of voice the vocal cords are almost always in close contact.

The glottis may be dilated by the action of the crico-arytenoid
muscles. When they contract the arytenoid cartilages are drawn back-
ward, downward, and toward the middle line, so that, therefore, the
vocal processes in which the vocal cords are inserted must be separated.
A large triangular space is thus formed between the vocal cords
as in inspiration.

The glottis is constricted by the contraction of the transverse
arytenoid muscles, which extend from both outer surfaces of the
arytenoid cartilages along their entire length. When these muscles,
together with the oblique arytenoid, contract, the arytenoid cartilages
are approximated and the glottis closed. During the production of
voice the vocal processes of the arytenoid cartilages must be closely
approximated, and to accomplish this it is necessary that they be rotated
inward and downward. This result is brought about through the
contraction of the thyro-arytenoid muscles, which are imbedded in the
substance of the vocal cords, and when they contract they so rotate the
arytenoid cartilages that the vocal processes turn inward. The glottis
is, therefore, narrowed to a mere slit in the anterior part, while a
triangular space through which respiration takes place remains open
posteriorly.

The vocal cords vary in tension according to the degree of con-
traction of the crico-thyroid muscles, which pull the thyroid cartilage
downward and forward. At the same time the crico-arytenoid muscles
act upon the arytenoid cartilages, drawing them slightly backward and
maintaining them in that position.

In the production of voice, not only must the vocal cords be thrown
into tension in the manner above described, but the triangular space of
the respiratory part of the glottis between the arytenoid cartilages must
likewise be closed. This is accomplished by the contraction of the

PHYSIOLOGY OF MOVEMENT.

763

transverse and oblique arytenoid muscles, added to the contraction of
the internal thyro-arytenoids. At the same time a concave margin
is produced in the vocal cords through the action of the crico-tl^roid
and the posterior crico-arytenoids (Figs. 318, 319, and 320).

FIG. 318.— ACTION OF THE MUSCLES OF
THE LARYNX. (Beaunis.)

The dotted lines indicate the new positions as-
sumed by the thyroid cartilage in the action of the
crico-thyroid muscles.

1, cricoid cartilage: 2, arytenoid cartilage: 3,
thyroid cartilage ; 4, true vocal cord ; 5, new position
of the thyroid cartilage ; 6, new position of the vocal
cords. '

FIG. 319.— SCHEMATIC HORIZONTAL SECTION OF
THE LARYNX. (Landois.)

I, position of the horizontally divided arytenoid cartilages
during respiration ; from their anterior processes run the con-
verging vocal cords. The arrows show the line of action of the
posterior crico-arytenoid muscles, resulting in the assumption of
the positions indicated by the dotted Hues, II, H.

FIG. 320.— SCHEME OF THE CLOSURE OF THE GLOTTIS BY THE THYRO-
ARYTENOID MUSCLES. (Landois,)

II, II, position of the arytenoid cartilages during quiet respiration ; the arrows indicate the direction
of muscular traction. 1 1, the position of the arytenoid cartilages after the muscles contract.

The thyro-arytenoid muscle is the one which principally causes
variations in the tension of the vocal cords and, consequently, variations
in the pitch of the sounds.

When the muscles acting on the vocal cords relax the vocal cords
themselves likewise relax from the reduction of the extending force, and

764 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the elasticity of the displaced thyroid and arytenoid cartilages corner
into play and causes them to assume their original position. The thyro-
arytenoid and the lateral crico-arytenoids may likewise serve to produce
relaxation of the vocal cords.

To recapitulate : the tension of the vocal cords is principally due to
the crico-thyroid and the posterior crico-arytenoids ; the narrowing of
the respiratory part of the glottis is accomplished by the transverse and
oblique arytenoids ; and the narrowing of the vocal glottis is accom-
plished by the contraction of the thyro-arytenoid and the lateral crico-
arytenoids, the former muscle likewise increasing the tension of the
vocal cords.

With the exception of the crico-thyroid all the intrinsic muscles of
the larynx are supplied by the inferior laryngeal nerve. The superior
laryngeal nerve supplies the crico-thyroid, and is at the same time
the sensory nerve of the mucous membrane of the larynx.

For the mechanism of articulated speech the reader is referred to
text-books on human physiology.

SECTION II.
THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

THE different functions of the animal body have been found to
require for their fulfillment divers structures different in location and in
mode of action. In any one of the single functions of the animal body,
such, for example, as the contraction of a muscle, a number of processes
are concerned ; thus, the inauguration of the muscular contraction
requires the conduction to a muscle of a stimulus. The muscle in con-
tracting uses up a large supply of oxygen and liberates more carbon
dioxide and other retrograde products. Increased muscular contraction,
therefore, necessitates a supply to the muscle of a larger amount of
arterial blood and the removal from the body through the lungs and kid-
neys of the products of the waste of muscular tissue. Muscular activity,
therefore, implies accelerated circulation, accelerated respiration, and
increased excretion. A similar complexity may be traced in all the other
different functions of the animal body. Each modification or even mani-
festation of function implies a reflection upon the activity of other asso-
ciated processes. This co-ordination of operations, which may be widely
different in character and yet closely interdependent, is accomplished by
means of the nervous system. The primaiy object of the nervous system
is, therefore, to link together different and widely distant organs, and
thus act as the regulator of the actions of the animal body.

In animals where specialization of function has not yet appeared no
such communication between different parts of the body is required, and,
as a consequence, in such no nervous system is present. As we found
that the organs of circulation were largely dependent for their degree of
development on the complexity of the alimentary apparatus, so it may
be found that in a general way the nervous system is developed in pro-
portion to the muscular system. This indicates one of the main func-
tions possessed by the nervous apparatus for controlling and modifying
movement. This is, however, but one side of the importance of the
nervous system.

In the nervous system is developed in the highest degree the func-
tion of automatism. By this term is meant the power possessed by the
lowest forms of protoplasm of receiving impulses from without and modi-
fying them into efferent impulses, which may take on the form of motion
as their most usual manifestation. It is thus seen that automatism

(765)

766 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

implies at least four different operations — the conduction of afferent
impulses, the reception and conversion of these afferent into efferent
impulses, and the liberation again and conduction of efferent impulses.

In the scheme of specialization of function it would only be expected
that for the division of labor we should also find that these operations
become separated and located in different structures. We find, therefore,
the nervous system, in accordance with this purpose, divided into organs
of conduction and organs of receiving and liberating nervous impulses.

The organs for transmitting nerve impulses constitute the nerves.
The organs for modifying and liberating nerve impulses are found in the
ganglia or nerve-cells of the nervous system.

The scheme of the nervous system, therefore, implies the presence
on the periphery of a receptive organ for receiving external impressions.
Such an organ is represented by the terminal filaments of the sensory
nerves, or, rather, the nerves of general or special sense. It implies a
means of communication between this external receptive organ and the
nervous ganglia at a distance, the latter possessing the power of receiv-
ing the impressions transmitted from the exterior through the afferent
sensory nerves. Such a receptive ganglion is again in connection with a
cell or collection of cells in which the automatic powers are especially
developed, and which, therefore, modify the impressions coming from
without and convert them into efferent impressions. The latter are con-
ducted from the centre through the efferent or motor nerves to various
peripheral organs, whether to the terminal plates in the muscular tissue
or to glands, blood-vessels, or the other structures of the animal body'.

Like all other organic systems, the nervous system becomes more
complicated and diversified, reaching a higher stage of perfection in pass-
ing from the lowest forms of animal life, in which it first appears, to the
higher examples of the animal series.

In the protozoa, the lowest subdivision of the animal kingdom, a
nervous system in the sense in which we have described it, as constituted
of nerve-cells and nerve-fibres, is entirely absent. The undifferentiatecl
protoplasm fulfills all the purposes of the nervous system as demanded
by the needs of such an organization.

In the animals belonging to the group of infusoria, where we find the
first appearance of the development of organs as seen in the contractile
cilia as organs of locomotion, the nervous system has not appeared, the
movement of such organs being dependent simply upon the automatic
properties of the undifferentiated protoplasm ; and we find as an illus-
tration of this that even in animals higher" in the scale, where ciliated
organs are commonly found, that such are independent of the nervous
system.

In the star-fish is found the first clear evidence of nerve fibres and

PHYSIOLOGY OF THE NEKVOUS SYSTEM.

767

cells connected together to receive and convey impression (Fig. 321).
It consists of a ring around the mouth composed of five ganglia of equal
size with radiating nerves. From this circle delicate fibres may be traced
into the different rays. In lower zoophytes all traces of the nervous
system is wanting, and in them the functions of nutrition are accom-
plished through the operations of undifferentiated protoplasm.

In the mollusks the nervous system has reached a somewhat higher
form of development, and two or more ganglia are found located around
the gullet and communicating by nerve-fibres with other ganglia in dif-
ferent regions of the body, sending off nerves to the different organs.
Usually in the mollusks there is a cir-
cular ganglion located in the cephalic
side of the animal and two abdominal
ganglia placed below the oesophagus

FIG. 322.— NERVOUS SYSTEM OF A GAS-

TEKOPOD MOLLUSK. (Perrier.)
c, cerebroid ganglia ; p, pedal ganglia ; o, otocysts ;

FIG. 321.— NERVOUS SYSTEM OF THE STAR- v> vl'vll, ganglia of second oesophageal collar ; f, ten-
FISH. (Carus.) tacles ; y, eyes ; x, excrement.

and united to the cephalic ganglion and the cesophageal ring (Fig. 322).
These ganglia are frequently connected with others whose locations will
vary in different species.

In the articulata, represented by the insects, annelida, and crusta-
ceans, the nervous system has become symmetrical (Fig. 323).

The ganglia which compose the nervous system may be arranged
in pairs on each side of the median line of the bod}*, each pair corre-
sponding to a segment of the body, extending throughout its entire
length and united to each other so as to form a longitudinal chain
of ganglia, which are connected further by transverse commissures.
Sometimes the ganglia consist of a single median row. Usually one of
the ganglia is more voluminous than the others, and being, as a rule,
located in the anterior extremity of the animal, might be compared to

768 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

the brain of vertebrates. Such a comparison is warranted by the fact
that when nerves of special sense are present they invariably originate
from this collection of nerve-cells. Where a distinct cephalic gan-
glion is present it is situated above the oesophagus, while all the other
portions of the ganglionic chain lie on the ventral side of the body, the
commencement of the chain being connected with the cephalic ganglion

FIG. 323.— NERVOUS SYSTEM OP AN ARTICULATE. (Perrier.)

by a collection of circular fibres around the gullet and spoken of as the
oesophageal collar.

The number of ganglia in the articulata is very variable ; there may
be twelve or fifteen pairs or but three. The larger the number of
ganglia, the greater their tendency to fusion along the middle line.

In all invertebrates the nervous system is composed of such a series
of separate and distinct ganglia,.

PHYSIOLOGY OF THE NEKVOUS SYSTEM.

769

In vertebrates the nervous system has reached a much higher stage
of development, and here is placed above the digestive canal, in contra-
distinction to the position which it occupies when present in the inverte-
brates, and is usually inclosed within a bony or cartilaginous cavity ; it
is divided into a cephalic portion, confined within the cranium, connected
to a long trunk of nerve-cells inclosed within the vertebral canal, con-
stituting the spinal cord (Fig. 324). From this central nervous system,

B

FIG. 325.— BRAIN OF PERCH, AFTER CUVIER. (Rymer
Jones. )

A, cerebellum; B, cerebrum : C. olfactory ganglion; i, olfactory nerves;
D, optic ganglion; G, supplementary lobe; H, transverse fibres in the walls of
the cerebral ventricle; N, commissure of the optic nerves; P, Q, R, S, T, U,
the third, fourth, fifth, sixth, seventh, and eighth pair of cerebral nerves.

RH.

VIII.

FIG. 324. — BRAIN AND
SPINAL CORD OF MAN.
(Carpenter.)

FIG. 326.— BRAIN OF FROG SEEN FROM ABOVE. (JVv/w.)

L. OLF, olfactory lobes ; L.H, hemispherical lobe (fore-brain) ; VIII, lobe
of the third ventricle; L.O, optic lobes (mid-brain) ; CELL, cerebellum (hind-
brain) ; OBL, medulla oblongata ; RH, rhomboidal sinus.

both from the brain and spinal cord, originate series of fibres which
fulfill the functions of conduction of both motor and sensory impulses
and which extend to all parts of the body. In connection with this sys-
tem, which is spoken of as the cerebro-spinal system, there is usually found
a more or less independent series of ganglia, which constitutes the
sympathetic system.

While such a cerebro-spinal system characterizes all vertebrates, it is

49

770 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

capable of great variations in development in different members of this
group. In fishes and reptiles the brain is less developed than in higher
members, no convolutions are found on its surface, and, while the cere-
bral hemispheres are not highly marked, the optic and olfactory lobules
are usually comparatively voluminous, while the cerebellum of reptiles
and fishes is reduced to a single lobe (Figs. 325 and 326).

In birds the hemispheres or cerebral lobes are still, as in the mam-
mals, the most voluminous portions of the brain, but here, also, no con-
volutions are found and the}^ are not closely united to each other, since
the corpus callosnm, as well as the pons varolii, is absent (Fig. 327).

In birds the analogue of the tubercula quadrigemina, which are four
in number in the mammals, are here reduced to two, and, therefore, receive
the name of the tubercula bigemina or optic lobes, and are visible at each
side of the brain when looked at from above.

T-
-cM

I. II.

FIG. 327.— BRAIN OF BIRD (Falco buteo). (Nuhn.)

I, view of upper surface. II, view of lower surface : cbr, cerebrum ; </, corpora quadrigemina, or
bigemina; cbll, cerebellum; nbl, medulla oblongata; //, hypophysis; opt, optic nerve.

In birds the cerebellum is likewise reduced to a single median lobe,
and is entirely uncovered \)j the cerebrum, and being single it possesses
no lateral hemispheres; the pons varolii, or the transverse fibres which
serve as a commissure for the cerebellar hemispheres, as in mammals, is
likewise absent.

The characteristics of the mammalian brain will be subsequently
alluded to.

The nervous system is composed of central masses which are in
constant communication with different parts of the body by means of
peripheral prolongations which act as organs of conduction. The
nervous system exists, therefore, under two forms — the central, composed
largely of the so-called nervous ganglia, or nerve-cells, and the organs of
conduction, or nerve-fibres. As already indicated, the peripheral termi-
nations of the nerves are likewise in connection with corpuscular bodies,

PHYSIOLOGY OF THE NEKVOUS SYSTEM.

771

which vary in accordance with the character of the nerves with which
they are in communication. The nerves or nerve-fibres are simply

FIG. 328.— BRAIN AND NERVOUS SYSTEM OF DIFFERENT ANIMALS, NATURAL
SIZE. (Thanhoffer.)

1, brain of ape: 2. domestic cat; 3. squirrel : 4. water-rat: 5. mole: 6. fox : 7. qnail : 8, nervous sys-
tem of horned beetle ; 9, perch ; />/, suprapharyngeal ganglion : h<l. abdominal ganglion : vd, end ganglion ;
b, oesophagus: e. nervous cord connecting the pharyngeal ganglion: Crh, cerebrum: <-bl. cerebellum;
mobl, medulla oblongata; olf, olfactory tract; /«. optic lobes: Ch, hemispherical lobes: I-IX (in Fig. 9),
cerebral nerves : wl, vagus ganglion ; br. branchial nerves : 10, nervous system of the snail ; Jy, supra-
pharyngeal ganglion ; ag, infrapharyngeal ganglion.

772 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

organs of conduction, and the nerve-cells, in which each nerve at each
end terminates, are for receiving and liberating impulses.

Nerves may be of two kinds: afferent or centripetal nerves, which
are concerned in the carrying of impulses from the exterior to the cen-
tral organs ; such nerves are frequently spoken of as sensory nerves :
and efferent or centrifugal, which carry impulses from the central
portions of the nervous system to the exterior ; such nerves are motor
nerves.

These two distinctions between nerves are not based on an}- differ-
ence in anatomical structure, but are simply functional differences, since
it has been found by experiment that nerves ma}T carry impulses in
either direction, and by dividing a motor and sensory nerve and con-
necting the divided extremities of the one with the other the sensory
nerve, after union has taken place, may now carry motor impulses and
the motor sensory impulses.

The essential part of the nerve-trunk is the so-called axis cylinder,
which is composed of a thin filament of undifferentiated protoplasm in
no way different, as far as ma}' be determined, from that found in other
examples of free protoplasm. This protoplasmic centre, which is com-
posed of a number of fine fibrils and constitutes the axis cylinder, is
always covered by a thin, transparent membrane, which is termed the
primitive sheath. In many instances this is the only covering to the
ultimate fibrils of the nerve, such nerves being called non-medullated
nerve-fibres; in others, which are called medullated nerves, within this
primitive sheath, and surrounding directly the fibrils of the axis cjdin-
der, is found a thick layer of double refractive substance, which is termed
the medullary sheath or white substance of Schwann (Fig. 329).

Each nerve-trunk consists of bundles of nerve-fibres held together
by fibrous connective tissue called the epineurium, in which are the
blood-vessels with which the nerve-trunk is supplied, lymphatics, and
numerous fatty cells. The neurilemma closely resembles sarcolemma in
its character; when subjected to long boiling botli yield gelatin.

Ganglioiiic cells or nerve-corpuscles vary greatly in size. They may
be spherical, ovoid, pyramidal, or of other shapes, and send off usually
numerous branched processes, which serve to characterize the cells as
multipolar nerve-cells. No cell-membrane is to be detected, but the gan-
glia are of soft consistence, containing numerous granules and pigment
matter.

The nucleus is ordinarily well developed and is disproportionate^
large to the size of the cell. Two nucleoli are nearly always present.
One of the processes of the ganglion is always unbranched and forms the
axis cylinder of the nerve originating or terminating in such a nerve-cell.
A nerve, therefore, may be regarded simply as a process of the nerve-

PHYSIOLOGY OF THE NERVOUS SYSTEM.

773

cell, the white substance of Schwann being added after the separation of
the nerve-filament from the ganglion.

FIG. 329.— THE STRUCTURE OF NERVOUS TISSUE. (Landois.)

1, primitive fibrilla ; 2, axis cylinder ; 3. Remak's fibres : 4, medullated varicose fibre ; 5, 6, medul-
lated fibre, with Schwann's sheath : C. neurilemma ; t, t, Ranvier's nodes ; h, white substance of
Schwann; d, cells of the endoneurium ; a, axis cylinder : x, myelin drops; 7, transverse section of nerve-
fibre ; 8, nerve-fibre acted on with silver nitrate : I. nvultipolar nerve-cell from spinal cord ; z, axial
cylinder process : y, protoplasmic processes — to the right of it a bipolar cell : II, peripheral ganglionic cell,
with a connective-tissue capsule ; III, ganglionic cell, with, o, a spiral, and, w, straight process ; m, sheath.

The branched processes of nerve-cells are not, as a rule, concerned
in the formation of other nerve-trunks except in the bipolar or multi-
polar cells, but are concerned in bringing in communication other

774: PHYSIOLOGY OF THE DOMESTIC ANIMALS.

adjacent cells, so that impulses may be conducted from one to the other.
In the peripheral ganglia connective-tissue corpuscles surround the
nerve-cells.

I. CHEMICAL AND PHYSICAL CHAKACTEKISTICS OF NERVOUS

TISSUES.

The composition of nervous tissue varies according as the examina-
tion is made of the white matter of the cerebrum or of the spinal cord,
or of the gray matter. The following table represents their average
composition : —

CHEMICAL COMPOSITION OP NERVOUS TISSUE.

Gray Matter. White Matter.
Water, . .' . . . . 81.6 68.4

Solids, . ... . . . 18.4 31.6

Proteids, 55.4 24.7

Lecithin, .

Cholesterin and fats,

Cerebrin, .

Substances insoluble in ether,

Salts, .'...,

17.2 9.9

18.7 52.1

0.5 9.5

6.7 3.3

1.5 0.5

When brain-matter is incinerated the greater part of the phosphorus
of the lecithin becomes phosphoric acid, and the ash, hence, has an acid
reaction. The following is the composition of the ash of one hundred
grammes brain after removing lecithin : —

SO4K2, 0.411

KC1 2.524

K2HPO4, 0.266

Ca3P208, 0.013

MgHP04, 0.084

Na2HP04, 1.752

Na2CO3 1.148

Excess CO2, 0.082

FeP2O8, 0.010

6.290

The reaction of the gray matter during life is said to be acid from
the presence in the ganglionic masses of lactic acid. The reaction of
the white matter is neutral or alkaline.

From the above table it is seen that more than half the solids in the
gray matter and about one-fourth the solids in the white matter of the
nerve-centres consist of proteids, and yet our knowledge of these bodies
is very imperfect.

The proteids consist of albumen, which is found in the axis cylinder
and in nerve-cells; it is soluble in water and coagulates at 75° C.; a
globulin-like substance, which may' be extracted by means of a 10 per
cent, solution of common salt, and which is precipitated by dilution with
water and by saturation with salt; and alkali albuminate, which remains

CHARACTERISTICS OF NERVOUS TISSUES. 775

in solution when a 10 per cent, salt solution of brain is boiled; it may
be precipitated after filtering by the addition of acetic acid.

Nuclein, also, is found, especially in the gray matter; while in the
sheath of nerve-fibres after the removal of the fatty matters by boiling
alcohol and ether a nitrogenous body is found which is termed neuro-
keratin, and which in its composition appears closety related to keratin
and is especially characterized by the sulphur (2.93 per cent.) which it
contains.

Neurokeratin is not affected in gastric or pancreatic digestion ; it
swells in caustic potash and strong sulphuric acid, but only dissolves in
these liquids when boiled.

Gelatiu is likewise found in nerves, but is evidently derived simply
from the connective tissue of their sheaths.

Fats are present in large amounts, especially in the white matter and
in the white substance of Schwann, which appears to be almost solely of
a fatty nature.

The specific constituents of the brain and nerves are of a highly
complex character and may be divided into two groups — those which
contain phosphorus in combination and those which are free from phos-
phorus. As an example of the first of these, protagon may be mentioned,
which, discovered by Liebreich, has been regarded by many chemists,
not as a distinct body, but as a mixture of lecithin, a phosphorized fat,
with cerebrin, a nitrogenous, non-phosphorized body. Experiments by
Gamgee have, however, apparently proven that protagon is a definite
chemical body, soluble in cold alcohol with difficulty, readily soluble in
warm alcohol and ether. To this substance Gamgee attributes the em-
pirical formula C160H308X5P035. It forms a clear solution with glacial
acetic acid.

Cerebrin is. an example of the special brain-constituents which are
free from phosphorus; it appears, however, that cerebrin, as described
by Mu'ller, is not a distinct body, but a mixture of cerebrin, homocere-
brin, and encephalin.

The entire subject of the organic constituents of the nervous sj'stem
needs to be re-examined, since on any matter where such diametrically
opposite opinions are held the error on both sides must be considerable.

Like the muscular tissue, nervous substance when passive has a
neutral or even faintly alkaline reaction ; after prolonged stimulation or
functional activit}T, produced in any wa}T, the reaction becomes acid.

After death the reaction likewise becomes acid and the nerves become
more solid, thus resembling the similar changes which occur in muscle,
and, although not thoroughly investigated, in all probability are due to a
similar process.

Nerve-fibres are free from elasticit}', and if divided do not retract :

776 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

their cohesion, due to their connective-tissue constituents, is consider-
able. It has been found that a weight of one hundred and ten to one
hundred and twenty pounds was required to rupture the sciatic nerve of
a man at the popliteal space. The nerves lengthen very considerably
before breaking ; they, therefore, are extensible.

II. NERVOUS IRRITABILITY.

As in the case of muscle, nerves are capable of having their func-
tional activity called into play by various stimuli ; they are, therefore,
said, like muscles, to possess the power of irritability.

Stimuli which call nervous activity into existence, like muscular
stimuli, may be either mechanical, thermal, chemical, electrical, or physi-
ological, by which is meant the normal stimuli which excite the nervous
system in living bodies.

In the case of the nervous system the influence of various stimuli
may be made evident, either by allowing them to act upon motor
nerves, when the contraction of the muscles evoked will indicate the
stimulation of the nerve ; or, in the case of sensory nerves, by the pain
produced on their application.

A mechanical irritant produces stimulation of the nerves by pro-
ducing change in the molecular arrangement of the nerve-particles. If
the mechanical stimulus, which may be of the nature of a blow, pressure,
pinching, and stretching, be sufficiently severe the nerve may then become
completely and permanently destroyed, and then lose its power at that
point of conducting impressions. A single mechanical stimulation of a
motor nerve will produce a single contraction of a muscle. If the stimuli
be repeated rapidly at short intervals the contractions may, as in the
case of electrical stimulation, be blended together, and when the stimuli
succeed each other more frequently than sixteen in the second a prolonged
tetanic contraction is produced.

The action of variations in temperature on nerve-trunks is somewhat
similar to that exerted on muscles.

If the nerve of a frog be heated to 45° C. its excitability is first
increased and then diminished, and the higher the temperature the
greater the excitability and the shorter its duration. If the temperature
be raised above 60° the medullary substance becomes disorganized and
the nerve loses its excitability. Sudden application of cold or heat acts
as a stimulus, and may cause muscular contraction. Increase of tempera-
ture above 45° produces tetanus with rapid exhaustion of the nerve.

Anything which will rapidly change the chemical composition of a
nerve-trunk may act as a nerve stimulus, and, although such stimuli may
at first increase a nerve's excitability, they rapidly diminish its irrita-
bility and often result in complete nervous paralysis.

NERVOUS IRRITABILITY. 777

Rapid desiccation of nerves by abstracting the water comes under
the head of a chemical stimulus. Sugar, urea, glycerin, and many metallic
salts likewise act as stimuli and often produce paralysis.

Nerves may likewise be thrown into activity by the application of
the electrical current, whether on employing the constant or induced
current. When a constant current is allowed to enter a nerve a single
contraction is produced at the moment of application of the current,
and no other apparent effect is evident until the current is broken. The
breaking of the current again causes a contraction to occur. So, also, in
sudden increase or decrease in the strength of a constant current
passing through a nerve the same effect will be produced as on making
or breaking the current.

When a constant current which is too feeble to produce a contraction
is allowed to pass into a nerve, and the strength of a current then
gradually increased, the degree at which the contraction is produced is
spoken of as the minimal stimulus. As the current increases in strength
the degree of contractions produced, at first rapidly and then more
slowly, increases until a maximum is reached ; such a stimulus is spoken
of as the maximal stimulus. As a rule, the effect produced by making
the current is more powerful than when the current is broken.

Nerves are more sensitive to electrical stimuli than muscles, and a
current which, applied directly to a muscle, may be too feeble to produce
contraction may throw the muscle into contraction when allowed to pass
through its motor nerve. When a strong current is allowed to pass
through a motor nerve for some time and the circuit then suddenly
broken, instead of a single contraction the muscle will be thrown into
tetanus ; such a condition is especially produced when the positive pole,
or anode, is nearest to the muscle, while, when the negative pole, or
cathode, is nearest to the muscle, tetanus occasionally follows the making
of the current. This effect is to be explained by the production of
a condition which is known as electrotonus, which will be alluded to
directly.

When a stimulus is applied to any part of a motor nerve a
condition of increased excitation is produced and the impulse travels
along the nerve, the direction of the motion depending upon the
character of the terminal organs with which the nerve is in communica-
tion. When, therefore, a motor nerve is stimulated the impulse travels
to the periphery ; when the nerve terminates on a cutaneous surface it
travels toward the centre, although it must be understood that nerves
maj^ conduct impulses in either direction and even carry impulses
simultaneously in different directions without interfering with each
other.

The rate of conduction of nerve impulses is about twenty-seven

778 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and a quarter meters, or ninety feet, per second, in both motor and
sensory nerves, and is influenced by various conditions. Reduced
temperature or a great increase in temperature reduces the velocity of
nerve impulse. Anelectrotonus decreases the velocity of conduction,
while kathelectrotonus increases it.

The conduction of nerve impulse is destroyed by all conditions
which injure the nerve, as \yy section, ligature, compression, or the use
of chemical agents which destroy its excitability at any part of its
course, by the removal of blood, or by the action of certain poisons, as
curare, which destroys the conductivity of the terminal motor-nerve
filaments.

When a nerve is subjected to continued stimulation the irritability
of the nerve rapidly diminishes ; such a nerve is said to be exhausted or
to be in a condition of fatigue. A nerve in which exhaustion has
occurred may again regain its activity, provided the stimulation has not
been too excessive or too greatly prolonged.

In cold-blooded animals stimulation may be much more severe and
protracted without producing exhaustion than in warm-blooded animalsr
and, while nerves are more slowly affected than muscles, the recovery of
the former is more slowly accomplished than in the latter.

When a nerve-fibre is separated by section from the central nervous
system the condition of the nerve will vary according as to the function
of the nerve. Provided a nerve be in connection with the nerve-centres
which govern its nutritive processes, it may be divided at any part of its
course and degeneration of the nerve will only occur in those parts which
have been separated from the nutritive centre. Thus, for example, if a
motor nerve be divided the peripheral extremity of the nerve will
become disorganized, while the part still in connection with the spinal
cord will remain intact.

If a purely sensory nerve be divided it would at first appear that
the same condition prevailed ; and if, again, a mixed nerve be divided
the peripheral part of the nerve, including all its branches, will degenerate,
while the central parts will remain intact.

The centres governing the nutrition of motor and sensory nerves
are not, however, as might appear from the above statements, the same.

If the anterior root of a spinal nerve be divided before it joins the
posterior root the motor fibres in the spinal nerve formed by the union
of this anterior and posterior root will degenerate, while the portion
remaining in connection with the cord will remain intact. If the pos-
terior root be divided between the spinal cord and its ganglion the part
of the nerve lying between the point of division and the spinal cord will
degenerate, while the peripheral portions of the part between the point
of section and the posterior ganglion will remain intact. This indicates

ELECTBICAL PHENOMENA IN NEKVES.

779

that the nutrition of motor nerves is controlled by the ganglia in the
spinal cord, while the ganglion on the posterior root controls the nutri-
tion of the sensory fibres. Such ganglia controlling nutrition are spoken
of as trophic centres, and nerves, therefore, which are separated from
their trophic centres undergo permanent degeneration. The nature of
the influence exerted by trophic centres is, however, entirely unknown
(Fig. 330).

If a nerve be divided and the divided ends again brought into con-
tact Ity means of sutures, regeneration takes place, and after a varying
time the nerve is again capable of conducting impulses.

A B C D

FIG. 830.— DIAGRAM OF THE ROOTS OF A SPINAL NERVE SHOWING THE
EFFECTS OF SECTION. (Landois.)

The black parts represent the degenerated parts. A, section of the nerve-trunk beyond the ganglion ; .

B, of the anterior root, and C, of the posterior root ; D, excision of the ganglion ; a, anterior, p, posterior
roots ; g, ganglion.

III. THE ELECTRICAL PHENOMENA IN NERVES.

As in muscles, evidence of the presence of a constant electrical
current rna3r be found in nerves. If a section of a nerve be removed
from the body and placed upon non-polar izable electrodes in connection
with a sensitive galvanometer, a strong electrical current may be observed
when the transverse section of the nerve is placed in contact with one
of the electrodes and the surface in connection with the other. The
current will then pass from the longitudinal section to the transverse
section; or, in other words, the natural surface will be positive and the
artificial surface negative. The nearer one electrode is to the equator,
and the other to the centre of the transverse section, the stronger will be
the current produced, and when two points on the surface at equal
distance from the equator are connected with the galvanometer no
current is obtained. The electro-motor force of the strongest nerve-
current has been placed at 0.02 of the Daniells' element.

Like muscle, again, the natural current of nerve undergoes a
negative variation when the nerve is artificially stimulated. If a section
of nerve be so connected with a galvanometer as to develop a strong
current, and it then be stimulated either by the application of electricity
or a chemical or mechanical stimulus, the nerve-current will be found to

780 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

disappear. This negative variation travels toward both ends of the
nerve, and, like the production of the negative variation of muscle-
current, is due to the rapid succession of interruptions of the origin of
the current.

The statement as regards the negative variation of the nerve-
current when the nerve is stimulated by an electrical current requires
some modification. The statement holds when the induced current,
either in single or rapid shocks, is employed. If the constant current
be applied to a nerve which is in connection with the galvanometer the
effect on the nerve-current will depend upon the direction of the stimu-
lating current.

If the constant current be passed through a nerve outside of the
part in connection with the electrodes of the galvanometer, so that its
current coincides in direction with that of the nerve-current (descending
current), the deflection of the galvanometer needle will be increased
instead of decreased ; such a state of affairs is spoken of as the positive
phase of electrotonus, and is directly proportional in its intensity to the
length of nerve, the strength of the galvanic current, and the nearness
of application of the stimulus to the section of the nerve in connection
with the galvanometer. If, now, the direction of the constant current
be reversed, so as to cause the constant current to pass in the opposite
direction to the nerve-current, the latter will be diminished ; such a
condition is spoken of as the negative phase of electrotonus. By the
production of electrotonus by means of such a constant polarizing
current the excitability of the nerve is greatly modified, not only in the
part through which the current is passing, but throughout the entire
extent of the nerve. It has been found that at the positive pole the
excitability is diminished; this condition is spoken of as anelectro-
tonus ; at the negative pole the excitability is increased and forms the
region of kathelectrotonus, the variation in irritability being most
marked in the neighborhood of the poles and decreasing in proportion
to the distance from the poles.

Between the poles of the polarizing current a point exists where the
region of over-stimulation and under-stimulation meet, and where, con-
sequently, the excitability of the nerve is unchanged ; such a point is
spoken of as the neutral point, and with a weak current lies nearer the
anode and with a strong current nearer the kathode.

The production of this condition serves to explain the character of con-
tractions produced on making and breaking a constant current in a motor
nerve. When a constant current is allowed to pass through a motor
nerve, or, in other words, when a current is closed, the point of greatest
stimulation is located at the negative pole and spreads from this point
throughout the remainder of the nerve. As a consequence, when the

GENERAL PHYSIOLOGY OF NERVE-CENTRES. 781

current is closed the stimulation occurs only at the negative pole at the
moment when electrotonus takes place. On the other hand, with the
breaking shock, or when the current is opened, the point of greatest
stimulation is at the anode and coincides with the disappearance of the
electrotonus.

The contraction which is produced on opening and closing a constant
current varies not only with the direction but with the strength of the
current. Very feeble currents produce a contraction only on the closing
of the current, both with an ascending and descending current, from the
fact that the occurrence of kathelectrotonus produces a greater effect on
the irritability of the nerve than the disappearance of anelectrotonus.
When the current is increased in strength contractions are produced
both on opening and on closing the current with either an ascending or
descending current. If, again, the current is greatly increased, contrac-
tion is only produced on closing the descending current and on opening
an ascending current. This is to be explained by the fact that with very
strong currents the entire intra-polar portion of the electrotonic nerve is
incapable of conducting an impulse, and, as a consequence, ascending
currents can cause only an opening contraction. These results may be
expressed in the following table, in which R = rest, C = contraction : —

Ascending. Descending.

On On On On

Closing. Opening. Closing. Opening.

Weak, . C R C R

Medium, . C C C C

Strong, . R C C R

IV. GENERAL PHYSIOLOGY OF THE NERVE-CENTRES.

The nervous system, as already indicated, consists of a combination
of ganglion cells united together by nerve-fibres. The second element
of the nervous tissue, or nerve-cell, is a mass of protoplasm supplied
with a nujleus and nucleolus, from which originate at least two proto-
plasmic strands or nerve-fibres, which serve to bind the different elements
of the nervous system together. Unfortunately, it is not possible to ob-
tain as decisive results by experimentation as to the functions of the
nerve-centres as may be determined as regards the nerve-fibres.

The properties of the central organs of the nervous S37stem can,
therefore, be only indirectly determined. The nerve-centres, by which is
meant simply a collection of nervous ganglia, may be divided into two
general classes ; one group is located on the surface of the body, and it
is adapted to the reception of stimuli originating in various external
influences brought to bear on the body surface ; the other group of
nerve-centres is located in the central nervous system, so-called, — in other
words, the spinal cord and brain, or the cerebro-spinal axis. In addition

782 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

to these two groups various so-called sporadic ganglia are also to be
found in different parts of the body, whose functions, while in the main
of the same character as all nerve-cells wherever found, differ according
to the functions of the organs with which they are in connection ; they
will subsequently receive attention.

The external ganglia, or the so-called nerve-corpuscles, vary in char-
acter according to the nature of the stimulus which it is their function
to receive. They may be distributed over the skin surface and are
litted for recognition of tactile and thermic changes, or they may be
specialized for receiving special sensations ; in such cases they constitute
the organs of special sense.

In addition to these terminals of nerves, which, it will be recog-
nized, are simply in connection with afferent nerves, another set of nerve-
corpuscles is in connection with the peripheral terminations of the motor
nerves and act as organs of distribution for motor impulses. In this
group fall the nerve-plates on the voluntary muscles and the ganglionic
cells in the walls of the intestinal tube.

The central nervous ganglia, located in the cerebro-spinal axis, pos-
sess the power of developing, first, reflex action ; second, automatism ;
third, inhibition ; fourth, augmentation ; fifth, co-ordination. These will
be alluded to in detail.

Nervous centres are capable of receiving impulses brought to them
through afferent nerves, multiplying them, and reflecting the impulses so
changed through an efferent nerve. A reflex action, therefore, requires
for its expression an afferent nerve, starting from some receptive sur-
face, some stimulus applied to that receptive surface, a nervous centre,
and an efferent nerve.

1. REFLEX ACTION. — Reflex actions may occur in a number of dif-
ferent ways. The impulse reaching the centre through a sensory nerve may
be reflected through a motor nerve and produce muscular contraction.
Such muscular movements, occurring reflexty as the result of stimuli, are
entirely involuntary and independent of the will. Such reflex actions are
almost innumerable and form an important part of the organic acts of a
living animal. As examples may be mentioned the involuntary weep-
ing which almost instantly follows the applications of a stimulus to the
conjunctiva, the movements of the limbs which occur on tickling the
soles of the feet during sleep, movements of vomiting which occur when
the soft palate or pharynx are mechanically irritated, coughing following
irritation of the larj'ngeal or trachea 1 mucous membrane, and a large
number of other movements (Fig. 331).

The spinal cord offers the best example of the production of reflex
motor actions, and, in fact, reflex action may be said to be the main
function of the spinal cord and its ganglionic cells may be regarded as

GENEKAL PHYSIOLOGY OF NERVE-CENTRES. 783

collections of reflex centres. The special characters of reflex action as
produced by the conduction of a stimulus through the spinal cord will
subsequently receive attention more in detail. At present a general
outline of the production of such reflex action is all that is needed.

If in an animal the cerebrum be removed by section from the
spinal cord, — and such an experiment may be best performed on a cold-
blooded animal, — stimuli applied to varying parts of the body surface
will result in the production of muscular movement. If in a frog the
cerebrum be removed by a section forming a tangent to the anterior
part of the t}'mpanic membrane, the frog will apparently be in a normal
condition, as far as its posture is concerned. If after the shock of the
operation has passed away the toe of such a frog be pinched, the animal
will jump; or, in other words, conduction of the sensory impulse to the
spinal cord is reflected in the complicated co-ordinated movement of
jumping. It is evident, therefore, that the sensory impulse is not simply
reflected from the nerve-cell, but that, reaching the nerve-cell, it may
there be converted into afferent impulses
which may be of the most complex character.

Coughing and sneezing, also, are illustra-
tions of this statement, where the slightest
mechanical irritation of various parts of the
respiratory mucous membrane may produce
complex muscular movements which are out
of all proportion in their complexity and

vigor to the afferent impulses which inaugu- FlG- 331.— SCHEME OF A RE-
FLEX ARC. (Landois.)

rate them. While this 1S, hOWeVer, tO a S, skin; M, muscle; N, nerve-cell, with

aj\ afferent, and ef, efferent, fibres.

certain degree true, within limits the nature

of the efferent impulse is dependent upon the nature of the afferent

impulse.

If after removing the cerebrum from a frog the flank of the animal
be gently stroked, muscular movement will occur simply as feeble
twitching of the muscles at the point of stimulation. If the stimulus
be increased in intensity the neighboring muscles are also implicated,
and a still further increase in severity in irritation may lead to the
implication of nearly all the muscles of the bod}r.

A connection may also be recognized between the locality of stimu-
lation and the nature of the resulting movement; thus, stimulation of
the larynx will invariably cause coughing ; of the mucous membrane of
the nostril, sneezing; of the mucous membrane of the eye, weeping and
lachrymation,or, to go back to the lower animals, reflex action following
from a stimulus applied to the skin of the brainless frog will be so
adapted as to remove the irritating body. Thus, if a scrap of paper
moistened with acid be placed on the right flank of such a frog, the

784 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

right foot will be gradually drawn up and swept over the point of
stimulation to remove the stimulus. The apparently purposeful char-
acter of such an action is still more strongly manifested if in such an
experiment the right foot be firmly held ; after a few ineffectual con-
tractions of the muscles of the right leg the left leg will then be drawn
up to remove the offending body. In all cases, therefore, except in those
of the very simplest character, the resulting motion produced reflectively
from a stimulus is out of all proportion in complexity to the nature of
the stimulation. This complexity is much more marked when the
stimulus is applied to the terminal corpuscles of sensory nerves, as in
the case above alluded to.

If the stimulation be applied to a sensory nerve-trunk the character
of the resultant reflex action is, as a rule, of simpler character ; or, at
least, is to a certain extent free from the apparent purposeful character
noticed above. Thus, for example, if an induced current be applied to
the central end of a divided sciatic nerve general convulsive movements
are produced, but no apparently co-ordinate attempt to remove the
stimulus can be detected, even with the employment of the weakest cur-
rent. It, therefore, is evident that the character of the reflex action
depends upon the nature of the locality of application and intensity of
the afferent impulses.

2. AUTOMATISM. — By automatism is meant the power possessed by
nerve-centres of apparently originating nervous impulses. It is, how-
ever, difficult to draw a line between so-called automatic action and
reflex action. Thus, the act of respiration, which is a favorable example
of the so-called automatic action, is in all probability due to, or, at any
rate, largely governed by, the character of the impulses brought to that
centre through the various afferent nerves. So, again, the regulation of
the calibre of the blood-vessels, which is controlled by the automatic
power of the vaso-motor centre, is again largely modified by the nature
of the afferent impulses brought to it.

The clearest example of pure automatic action is to be found in the
pulsations of the excised heart. As was seen in the chapter on circula-
tion, the heart might be removed from a cold-blooded animal and yet
preserve for many hours its power of rhythmical contraction, and it
was demonstrated that such automatic action was the result of the
function of the nervous ganglia found in the heart.

So, also, the movements of the alimentary canal were described as
of an automatic character, for although their character is influenced by
the contents of the intestinal tube, just as the movements of the heart
might be influenced by various afferent impulses, the movements of the
intestine may occur in an empty condition of the bowel or they may be
absent when the canal is filled. In the spinal cord, therefore, centres

GENERAL PHYSIOLOGY OF NERVE-CEXTBES. 785

are found which are capable of regularly and rhythmically governing
complex movements, and, to that extent, it is automatic : the brain,
however, as the seat of mental activity, perception, volition, thought,
and memory, is the highest expression of the automatic functions of
nervous centres. The automatic functions of the cerebrum will sub-
sequently receive consideration in detail.

3. INHIBITION. — In a number of examples which were given as
illustrations of reflex action, as is well known, the will by its exertion
may prevent the appearance of the ordinary reflex result of the stimulus.
Thus, for example, touching the e3'eball tends to result in the pro-
duction of winking ; touching the throat, movements of vomiting and
coughing ; tickling the soles of the feet, contractions of the muscles of
the legs. All of these, as is well known, may be controlled by a volun-
tary impulse.

One of the clearest illustrations of such inhibition of reflex action
and of its development by education is seen in the mechanism of defae-
cation. In the lower animals defaecation is a purety reflex action and, as
was described, results from the contact of the faecal mass with the
mucous membrane of the rectum.

In infants, likewise, the same state of affairs occurs. By education
the will-power is capable of inhibiting the operations which result in
defaecation, or, in other words, checking the action of the nerve-cells
which control the co-ordinated movements in this process.

A number of other illustrations might be given, of which, perhaps,
the clearest instance is seen in the action of the heart.

If the pneumogastric nerve be stimulated in an animal in whom the
heart is beating in a normal manner with an interrupted current, the
heart is almost immediately slowed and may even be brought to a stand-
still ; such a result is explained by the statement that the pneumogas-
tric contains cardio-inhibitory fibres whose stimulation arrests the
automatic action of the motor ganglia of the heart.

4. AUGMENTATION. — In contradistinction to inhibition an afferent
impulse may increase action of nerve-centres. Thus, for example, the
vaso-motor centre located in the floor of the fourth ventricle controls
the calibre of the blood-vessels and keeps their walls in a state of con-
traction. The action of the vaso-motor centre may, however, be aug-
mented through various afferent impulses, the most striking of which is
seen in the great increase of blood pressure which follows stimulation
of sensory nerves in curarized animals.

5. CO-ORDINATION. — By this term is meant the power possessed b}'
the cells of the central nervous system of combining complex muscular
movements ordinarily of a reflex nature. Thus, for example, the act of
deglutition necessitates co-ordinate action of a large number of different

50

786

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

groups of muscles, which must in their contraction follow each other in a
certain definite sequence; so, also, the act of coughing requires the associa-
tion of a number of different muscular movements. Numerous other illus-
trations might be given of the combination of complex movements which
are governed by so-termed co-ordinating centres ; that is, a collection of
ganglia located, usually, in the spinal cord or medulla oblongata which
govern certain specific movements.

V. THE FUNCTIONS OF THE SPINAL COED.

The spinal cord is contained within the vertebral canal and is com-
posed of white matter externally and gray matter internally, inclosed in
membranous sheaths of which the pia mater is adherent to the white

A A
1

L —

... L

p

FIG. 332.— TRANSVERSE SECTION OP THE SPINAL CORD. (Landois.)

In the centre is the butterfly-form of the gray matter surrounded by white matter, p, posterior, and
nterior horns of the gray matter ; PR posterior roots, A
the white anterior, L L the lateral, P P the posterior columns.

matter ; externally is found the dura mater, which lines the vertebral
canal and forms a protective coat for the cord, while between the two is
found the arachnoid membrane.

The white matter of the spinal cord is composed of nerve-fibres
arranged longitudinally and divided into the so-called anterior, lateral,
and posterior columns by the passage of the roots of the spinal nerves.
The anterior fissure is a depression which separates the two anterior
columns of the cord, which are bounded, therefore, on one side by the
fissure and on the other by the points of origin of the anterior spinal
nerve-roots.

The anterior fissure does not extend down to the gray matter, which
composes the centre of the cord, but is separated from it by the white
commissure.

FUNCTIONS OF THE SPINAL COED. 787

Between the origins of the anterior and posterior nerve-roots are
found the lateral columns, while the posterior columns are found between
the origin of the posterior nerve-roots and the posterior fissure, which is
deeper than the anterior, extending completely down to the gray matter,
and filled up by an inner layer of pia mater (Fig. 332).

In certain regions of the cord each posterior column may be subdi-
vided into an inner part lying next the fissure, the poster o-median, or
column of Goll, and a larger part next the posterior nerve-roots, the
postero-external or column of Burdach.

or

FIG. 333.— TRANSVERSE SECTION OF THE SPINAL, CORD IN THE CERVICAL
REGION, AFTER BE VAN LEWIS. (Yeo.)

A, anterior gray column ; a, anterior white column ; I, lateral white column; ac, anterior commis-
sure : ar. anterior roots ; of, anterior median fissure ; il, intermedio-lateral gray column ; vc, vesicular
column of Clarke : P, posterior gray column ; p, posterior white column : ptn, posterior median column ;
pc, posterior commissure : cc, central canal ; pr, posterior roots ; pf, posterior median fissure ; ae and ai,
external and internal anterior vesicular columns ; *y, substantia gelatinosa,

The white matter of the spinal cord is composed of medullated fibres,
in which the sheath of Schwann is absent, arranged for the most part
longitudinally. The nerve-fibres of the nerve-roots have an oblique
course, passing from the gray matter through the columns to form spinal
nerves ; transverse fibres, also, are found, which unite the different col-
umns of the spinal cord and connect the gray matter with the columns
of the cord.

The gray matter is composed of collections of nerve-cells arranged
in the form of two crescents, the convex surfaces of which are united by
the graj7 commissure. In the centre of the graj7" commissure runs the

788

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

central canal, which passes from the floor of the fourth ventricle
downward and is lined by a layer of cylindrical epithelial cells.

The cells of the gray matter of the spinal cord differ greatly in size,
those in the anterior horn being much the largest. The gray matter is,
also, like the white matter, arranged in columns, although the distinc-
tion between these columns may be less readily demonstrated. Thus,
the anterior and posterior horns form the anterior and posterior gray
columns, while between the two lies the lateral column.

The distribution of white and gray matter varies in shape in differ-
ent portions of the spinal cord. In the cervical region the lateral white
columns are large, the anterior horn of the gray matter is wide and

&• —

FIG. 334.— TRANSVERSE SECTION OF THE SPINAL CORD IN THE LUMBAR
REGION, AFTER BEVAN LEWIS. ( Tco.)

(For references see description under Fig. 333.)

large, while the posterior horn is narrow and the transverse diameter of
the cord is the longest (Figs. 333, 334 and 335). In the dorsal region both
cornua are narrow and of nearly equal breadth, while the cord is smaller
and C3'lindrical.

In the lumbar region the gray matter is largest in amount, while the
lateral columns are small and the central canal is nearly in the middle of
the cord.

As a rule, the anterior horn of gra3^ matter is shorter and broader,
and does not extend so near to the surface of the cord as does the pos-
terior horn, which is more pointed, longer, and narrower, and usually
extends nearer to the surface.

FUNCTIONS OF THE SPINAL COED.

789

The spinal cord is not only the path of conduction of nerve impres-
sions from the periphery of the brain and the reverse, but is also the
seat of a large number of nervous centres which are capable of acting
as reflex centres, or even of
originating impulses.

The functions of the spinal
cord are, therefore, to be con-
sidered— first, as a collection
of nerve-centres, and, second,
as a conductor of afferent and
efferent impulses.

(a) The Spinal Cord as a
Collection of Nerve- Centres.—
It has been already stated that
reflex action requires for its
performance afferent and effer-
ent nerve-fibres and a nerve-
centre, and the spinal cord has
been mentioned as the main
seat of the centres of reflex
action.

When the spinal cord is
divided in an animal, the ap-
plication of a stimulus to its skin produces muscular movements of
the most diverse kinds, depending, as already indicated, upon the
nature, intensit}', and the locality of the stimulus.

The histology of the spinal A

cord indicates that, from the
direct communication of the
posterior roots (which have
been found to be paths of con-
duction of sensation) through
the gray commissure with the
anterior roots (which have been
found to be the paths of motor
impulses), afferent impulses
reach the spinal cord through
the sensory nerves and are
directty conducted to nerve-
centres, which again are in communication with motor nerves. It is,
therefore, evident that afferent impulses are brought directly to nerve-
cells, which again communicate the modified nerve impulse to motor
nerves (Fig. 336). In the spinal cord such centres of reflex action. may be

FIG. 385.— TRANSVERSE SECTION OF THE SPINAL
CORD IN THE DORSAL, REGION. AFTER
BEVAN LEWIS. (Yeo.)

(For references see description under Fig. 333.)

M

FIG. 336.— SECTION OF A SPINAL SEGMENT,
SHOWING A UNILATERAL AND CROSSED
REFLEX ACTION. (Landois.)

A, anterior, and P, posterior surfaces ; M, muscle ; S, skin ; G,
ganglion.

790 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

readily proved by the entire failure to evoke reflex movements after
destruction of the cord. Thus, while reflex movements are produced
with the greatest readiness in frogs in whom the cerebrum has been
removed, if the spinal cord be then disorganized by passing an instrument
down the vertebral canal all reflex movements are then impossible, even
although the nerves possess their power of conductivity and the muscles
their power of contraction.

To appreciate the functions of the spinal cord as a collection of
centres for producing reflex action we have only to recall the statements
made on the nervous system as met with in the lowest articulata, in
which we have a collection of nervous matter, ganglionic in its nature
and comparable to the medulla spinalis of vertebrates, with afferent
fibres running to and efferent fibres running from these ganglia. Such a
type of nervous system is seen in the star-fish. If an irritation be ap-
plied to an extremity of the limb of a star-fish a sentient impression is
conducted along the sensory nerve to the ganglionic centres, and a motor
impulse goes out along the motor nerve and contraction of the muscles
supplying the body results. Sovif a decapitated centipede be placed
upon the ground it begins to make forward locomotive efforts as soon as
the impression is made upon the sentient extremities of the nerves dis-
tributed to its feet ; this impression is conveyed to the spinal ganglia,
and motor impulses are sent out along each one of the legs and loco-
motion results. If it comes in contact with an obstacle, however, as
high as itself it will mount over it, but if higher it will butt against it
its decapitated extremity until all nervous force is exhausted, when it
becomes quiet. Still more striking phenomena are present when, after
decapitation, the remainder of the body be cut in two ; if then the
halves of the body be placed upon the ground locomotive efforts will
continue in each, but they will not be harmonious. All these movements
depend upon physical excitation, and in some instances they require to
be excited by the elements in which the animal naturally moves. Thus,
if we take a decapitated water-beetle and place it upon the floor no
motion results, but place it in water and it begins to move with vigor.
The above are examples of reflex action, and result from excitation of
sentient surfaces and the conduction of that irritation to a nervous
ganglion, and the reflection of that stimulation through a motor nerve.

It has been mentioned that the impulses reaching the cord through
a single sensory nerve may spread to the adjacent receptive ganglia,
and so lead to the transmission of motor impulses through a number
of different motor nerves. Ordinarily the degree of reflex action is in
proportion to the stimulus.

Under certain conditions the irritability of the spinal cord may be
so modified that a gentle stimulus may produce excessive stimulation of

FUNCTIONS OF THE SPINAL COED. 791

the motor ganglia of the cord, and so produce violent convulsive move-
ments; or the receptivity of the cord may be obtunded through disease
or through the action of various poisons, and the most violent stimulus
now fail to evoke any reflex action. As an example of the first condition
strychnine furnishes a most striking illustration.

If a frog be poisoned with strychnine and the cerebrum removed, a
degree of stimulation which otherwise would produce but a feeble or
perhaps even no reflex action now produces tetanic contractions. Such
a result indicates that in the spinal cord every sensible fibre is in direct
communication through the gray substance with every motor fibre.

In the frog at breeding seasons the spinal cord is in a physiological
state of overexcitation ; the frog is found at this time clinging obstinately
to pieces of bark or stone, just as it does to the body of the female in
the act of copulation. Such a condition may be produced by gentle
stimulations of the skin of the sternum and of the thumb of the frog, in
which an increase of sensibility exists. Here the result is to be attributed
not only to the increased receptivity of the spinal cord, but also to the
increased sensitiveness of the receptive surfaces.

In the normal condition of animals, whether mammals or cold-
blooded animals, in whom the brain has been separated from the spinal
cord, reflex action only takes place through the application of irritants
of a certain intensity and a certain duration.

Single electric shocks as a rule produce no result, but if repeated
sufficiently often produce a reflex action ; such single impulses are con-
ducted to the spinal cord and there become added to each other by what
is known as a process of summation until a maximum result is attained.
If, then, the number of stimulations per second be increased or the de-
gree of stimulation be made more severe no further increase in the reflex
action is possible.

Pfliiger has formulated the following laws of reflex action : —

1. The reflex movement occurs on the same side on which the sen-
sory nerve is stimulated, while only those muscles contract whose nerves
arise from the same segment of the spinal cord.

2. If the reflex occur on the other side only the corresponding
muscles contract.

3. If the contractions be unequal upon two sides, then the most
vigorous contractions always occur on the side which is stimulated.

4. If the reflex excitement extend to the other motor nerves, those
nerves are also affected which lie in the direction of the medulla oblon-
gata.

5. All the muscles of the body may be thrown into contraction.
(Landois.)

In the human body are found mechanisms which may inhibit or

792 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

control reflex action, before mentioned, as produced after a mechanical .
irritation of the conjunctiva. Tickling of the feet leads to an inclination
to movement; this also is a reflex action, and, as is well known, such a
movement may, by an exertion of the will, be suppressed, such a sup-
pression being an inhibition of reflex action. This voluntary control of
reflex action may be educated to a certain extent, but only within certain
limits.

If the stimulus be severe and frequently repeated reflex action
occurs in spite of the effort of the will to prevent it. On the other hand,
numerous reflex actions are entirely beyond the control of the will ; thus
the contraction of the iris and parturition are reflex actions over which
the will has no control.

It may be demonstrated by experiment that a spinal nervous mech-
anism exists for the purpose of keeping reflex action in control. If the
cerebrum be removed from a frog on a line with the anterior edges of the
tympanic membrane reflex action may be readily produced.

The best method of studying the influence of different agents on the
production of reflex action is that of Tiirck, of Vienna.

The frog, from which the cerebrum has been removed, should be
suspended vertically by the nose, and if after the shock of the operation
has passed away the tip of one toe be dipped in a solution of sulphuric
acid it will be rapidly withdrawn ; the duration of immersion before the
foot is withdrawn may be taken as indicating the degree of reflex
activity of the spinal cord. After each immersion the foot should be
dipped into distilled water, so as to wash off the excess of acid and pre-
vent constant corrosion of the skin. If the time be determined which
elapses before the foot is withdrawn from the acid in the frog from whom
the cerebrum has been removed, and the cerebro-spinal axis be then again
divided on a line tangent to the posterior borders of the tympanic
membranes and the toe be again immersed in acid, it will now be found
that the foot is withdrawn after a much shorter interval than in the
previous experiment. This result would indicate that in some portion
of the cerebro-spinal axis between the lines of the two incisions is located
a mechanism which has for its function the controlling of reflex action.

If in another frog the cerebrum be removed and the time of immer-
sion in the acid determined before reflex action takes place, and now one
of the optic lobes be exposed and irritated, as by placing a crystal of com-
mon salt in contact with it, it will be found that the frog will retain its
foot in the acid for a much longer time than before, or may even entirely
fail to remove it. That this result is due to the stimulation of the
inhibitory apparatus and not to a paralysis of reflex mechanism is
proved by the fact that if the spinal cord be now divided below the
med.ulla oblongata the foot will be as promptly withdrawn, or even more

FUNCTIONS OF THE SPINAL COED. 793

rapidly, from the acid than before ; such a mechanism is spoken of as
Setschenow's inhibitory centre.

Reflex action may, likewise, be inhibited by stimulation of sensory
nerves. As an example of this may be mentioned the familiar experi-
ence of our ability to arrest a sneeze by compressing the skin of the nose
over the exit of the nasal nerve.

Reflex action does not take place when strong electrical irritation is
applied to the trunk of a sensory nerve, but tetanus results; while, on the
other hand, a much weaker stimulation of the skin, either chemical or
mechanical, will readily produce reflex movement. This would, perhaps,
indicate that, together with the sensitive fibres, inhibitoiy nerves pass in
the trunks of the nerve to the spinal cord.

The reflex functions of the spinal cord may be looked upon as one
of the preservative influences of the animal body, guarding all the inlets
and outlets of the economy. Through it the movements of respiration
are permitted to occur during the hours of sleep and waking. Let this
reflex action be lost in the medulla, and respiration ceases, the contents
of the rectum are involuntarily evacuated, the useful operation of wink-
ing, by which the conjunctiva is kept moist and the eye is protected, is
lost, and the acts of coughing and sneezing, so important for removing
foreign substances, would be alike impossible.

The movements of the intestinal canal, although not entirely de-
pendent upon reflex action, are in a certain degree due to it. Many of
the phenomena which we consider as voluntary may be classed among
those which are reflex m their nature, as when, in walking, we may
unconsciously pass around an obstacle in our path, or unconsciously
perform many acts which are apparently purely voluntary in nature.

As already mentioned, reflex actions are not solel}7 motor in nature,
but may result in the production of changes in secretion, in the distribu-
tion of blood to a part, or in changes in nutrition. Illustrations of
excito-secretory phenomena are very numerous.

If we touch the tongue with irritating or sapid substances the secre-
tion of saliva begins to flow through the instrumentality of the lingual
nerve ; the impression is conveyed to the medulla oblongata, whence an
efferent impulse is emitted through the chorda t3'inpani, as a result of
which the blood-vessels supplying the submaxillaiy gland are dilated and
an increased flow of saliva is produced. It has also been found that if
we stimulate the oral cavity the gastric secretion is poured out in large
quantities, indicating the action of condiments and spices in conditions
of feeble digestion.

The reflex vaso-motor results are clearly evident as examples of
reflex action. If a sensory nerve is stimulated the tonic action of the
vaso-motor centre is increased, and the blood-vessels of the body are

794 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

contracted through the reflection of that impulse from the spinal' cord
through the efferent vaso-motor nerves to the muscles composing the
walls of the arterioles. In vaso-motor reflex action phenomena of inhibi-
tion are likewise capable of demonstration. Thus, the vaso-motor centre
in the bod\^, which is a purely reflex centre, may be inhibited by stimuli
passing through certain nerves. If the so-called depressor nerve be
stimulated the vaso-motor centre in the medulla is inhibited and dilata-
tion of the blood-vessels ensues, as is evidenced by the great fall of blood
pressure. So, also, certain nerves when stimulated lead to a dilatation
of the blood-vessels by inhibition, in all probability, of the ganglia con-
tained within their walls. Such a reflex inhibition of vaso-motor action
is seen in the case of the chorda tympani, already referred to, in the reflex
stimulation of the nervi errigentes, and a number of other instances.

As an example of changes in nutrition clue to reflex action, illustra-
tions are not as readily found ; what is spoken of as sympathy is an
example, however, of changes in nutrition of reflex nature. Surgeons
are well aware that when disease of an inflammatory character exists in
one eye it is not unusual to find the eye of the other side becoming
affected in a similar manner, purely in a reflex manner ; as a proof of this
ma3T be mentioned that extirpation of the diseased eye is almost invariably
followed by a cure of the disease in the remaining one. So, also, section of
the supraorbital branch of the fifth pair of nerves leads to disturbances in
the cornea which are of a nutritive character and which are probably
due to some disturbances of the reflex control of nutrition.

It has been already mentioned that in the spinal cord are located a
number of collections of cells which have for their function the control
of certain complicated co-ordinate movements ; such centres exert their
action in a reflex manner by the modification which they produce on the
afferent impulses brought to them. These centres retain their activity
even after the spinal cord has been removed from the medulla by section,
but all are to a certain extent controlled by the action of higher reflex
centres found in the medulla oblongata and cerebrum.

The following represents the most important of these collections of
nerve-centres : —

First, vaso-motor centres which control the calibre of the blood-
vessels are found in the floor of the fourth ventricle of the medulla
oblongata and distributed throughout the entire spinal axis, as is
evidenced by the fact that the dilatation of the blood-vessels which
follows division of the spinal cord below the medulla is only transitory,
the blood-vessels regaining their normal tone as the shock of the opera-
tion passes off. If, however, the spinal cord be entirely destroyed, the
blood-vessels become then permanently paralyzed.

It is probable that in the cerebro-spinal axis are likewise found

FUNCTIONS OF THE SPINAL COED. 795

vasodilator centres. It thus appears that the calibre of the blood-
vessels in the bod}' is regulated by a collection of centres located in the
central nervous system.

Second, the cilio-spinal centre; this collection of nerve-cells is
located in the lower cervical portion of the cord ; its functions will be
again alluded to. The other centres, as of defalcation, micturition, etc.,
have been already mentioned.

(b) The Spinal Cord as an Organ of Conduction. — It has been seen
in the consideration of reflex action that modes of communication exist
between the different nerve-cells in the spinal cord. It is also evident
that in the spinal cord must exist paths of conduction of sensory im-
pulses reaching the cord through the posterior roots of the spinal
nerves to the brain, and of the conduction of motor impulses from the
brain through the anterior spinal roots to the muscles. For when the
spinal cord is divided, or when it is altered by disease or injury, the
parts which receive their nerves from the portion of the spinal cord
situated below that part are paralyzed, both as regards sensation and
motion. Impressions made upon these parts are no longer appreciated
and voluntary movements can no longer occur in them, even although
reflex action may still be present. When the spinal cord is divided
above the points of origin of the nerves coming to the muscles of respi-
ration, respiration is interfered with ; thus, if the spinal cord is divided
between the last cervical and the first dorsal vertebrae, all the respiratory
muscles, with the exception of the diaphragm, are paralyzed. If the
spinal cord is divided above the origin of the phrenic nerve, then the
diaphragm is likewise paralyzed and death occurs from asphyxia. From
these facts it is evident that the spinal cord is the means of communica-
tion between the exterior and the brain, and we haAre now to consider
the paths which different impulses follow in passing from the centre to
the peripherj' and the reverse.

In the first place, it would be scarcely conceivable that the irritation
from any localized portion of the skin surface could communicate
a definite localized sensation to the brain if the afferent impulse was
compelled to travel through the lab}Trinthine communications of the
gray cells of the spinal cord. Nor, again, could we suppose that
a single muscle could be thrown into contraction by the will by passing
through the same complicated net-work of cells and fibres. It would be
much more natural to look for the paths of communication between the
voluntary muscles and the brain on the one side and the sensory end
organs and the brain on the other in the white columns of the cord. It
does not follow from this fact that the spinal cord may be regarded as a
bundle of white fibres connecting the periphery with the brain. Were
this the case we should expect that the spinal cord would increase in

796 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

size in proportion to the number of nerves entering into it ; and that>
therefore, the spinal cord should be largest in the cervical portion and
gradually taper down to a point in the lumbar region, as if each spinal
nerve were a direct loss to the fibres of the spinal cord. Such is not,
however, the fact.

Sections of the spinal cord taken at different parts of its length
indicate that the gray matter of the cord increases with the amount of
nerve-fibre passing into each part of the cord, and that, therefore, the
largest amounts of gray matter are found in the lumbar and cervical
regions at the points of origin of the nerves for the lower and upper
extremities ; while, if the proportionate area of the lateral columns is com-
pared, it will be found that there is a steady increase in the sectional area
of this portion of the cord from the lumbar to the cervical region. This
fact would indicate that the latter regions are the main paths of con-
duction between the brain and the periphery. The proportion between

FIG. 337.— DIAGRAM OF THE ABSOLUTE AND RELATIVE EXTENT OF THE
GRAY MATTER AND OF THE WHITE COLUMNS, IN SUCCESSIVE SEC-
TIONAL, AREAS, AS WELL AS THE SECTIONAL AREAS OF THE NERVE-
ROOTS. (Landois. )
N B, nerve-roots; A C, L C, P C, anterior, lateral, and posterior columns; Gr, gray matter.

different parts of the spinal cord in the different regions and the different
areas of the spinal nerves are indicated in the diagram (Fig. 337).

In addition to the anatomical division, already alluded to, into
anterior, lateral, and posterior columns, the white fibres of the spinal
cord have been divided into several secondary columns, according to
their functions. In addition to the experimental method, to be alluded
to directly, this grouping of the longitudinal fibres of the spinal cord
into different systems has been reached through facts acquired through
the study of the degeneration of certain parts after specific injury and
through the developmental history of the cord in the embryo. Thus,
injury of certain parts of the brain is followed by a secondary descending
degeneration of certain nerve-fibres (Tiirck) ; section of the cord causes
ascending degeneration of certain fibres (Schieferdecker) ; and Flechsig
showed that the fibres of the brain and cord in the embryo became

FUNCTIONS OF THE SPINAL COED.

797

covered with myelin at different periods of development, those receiving
their myelin last which had the longest course. On the data obtained by
this method Flechsig mapped out the following system (Landois) : —

1. In the anterior column lie the (a) uncrossed, or direct pyramidal
tract (a in Fig. 338), and, external to it, (6) the anterior ground-bundle,
or anterior radicular zone.

2. In the posterior column he distinguishes (c) (roll's column, or the
postero-median column, and (d) Burdach's funiculiis cuneatus, the pos-
terior radicular zone, or the postero-external column.

3. In the lateral columns are
(e) the anterior and (/) the lateral -

mixed paths, (g) the lateral or Mlllllill!!llll'===^^^ ,. <z*

crossed pyramidal tract, and (h) the
direct cerebellar tract. The rela-
tions of these fibres in the cervical
region are shown in Fig. 339.

FIG. 338.— SCHEME OF THE CONDUCTING
PATHS IN THE SPINAL AT THE THIRD
DORSAL NERVE, AFTER FLECHSIG.
(Landois.)

The

posterior

*, anterior column ground-bundle; c, Go'll's column;
postero-external column ; e and /, mixed lateral paths ;
h, direct cerebellar tracts.

e black part is the gray matter, v, anterior, hw,
or roots ; a, direct, and g, crossed pyramidal tracts ;

FIG. 339.— SECTION OF THE CERVICAL, POR-
TION OF THE SPINAL, CORD, SHOWING
BY DIFFERENCES OF SHADING THE
WHITE TRACTS SUPPOSED TO BE
FUNCTIONALLY DISTINCT. (Yeo.)

A, anterior, P, posterior median fissures : dp, direct
pyramidal, cp, crossed pyramidal tracts ; dc, direct cere-
bellar, pm, posterior median column (Goll) ; az, anterior,
pz, posterior root-zones.

Of these columns, as we shall find directly, the pyramidal tracts may
be traced to the anterior pyramids of the medulla oblongata, where each
lateral pyramidal tract crosses to the opposite side, through the pons to
the middle third of the crusta, thence to the internal capsule, where
they diverge like the rays of a fan through the white matter of the
cerebrum to the central convolutions.

The direct cerebellar fibres may be traced to the cerebellum, reaching
it through the restiform body from Clarke's column of gray cells, thus
directly connecting part of the fibres of the posterior roots with the
cerebellum.

798

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The other systems of fibres terminate in the medulla oblongata, the
column of Goll serving to connect part of the fibres of the posterior
roots with the gray nuclei of the funiculi graciles of the medulla
oblongata; and the column of .Burdach the posterior roots through the
restiform body with the vermiform process of the cerebellum, while the
anterior and lateral mixed columns communicate with the formatio
reticularis of the medulla oblongata.

Of these columns the pyramidal tract, the cerebellar tract, and the
column of Goll are the only ones which steadily increase in size as the
medulla oblongata is approached.

eaop

FIG. 340.— COURSE OF THE FIBRES IN THE SPINAL, CORD, AFTER F. FLESCII.

(Thanhoffcr.)

Ms, anterior horn ; ffn, posterior horn ; my, anterior root ; m(j, 1, 2, 3, fibrous bundles of the anterior
root; kg, posterior root; hy, 1, 2, fibrous bundles of the posterior root: mlp, direct pyramidal tract; olp,
crossed pyramidal tract ; oak, lateral ground-bundle ; eaop, direct cerebellar tract ; nmk, anterior ground-
bundle ; he, central canal: Co, intermedio-lateral column of Clarke ; G, funiculus gracilis of Goll ; B,
funiculus cuneatus of Burdach ; x, oblique bundles of fibres.

If we trace by means of the microscope the origins and terminations
of the spinal nerves it will be found that the posterior roots of the
spinal nerves pass through the white substance of the cord to reach the
posterior gray column, in which they break up into fine twigs, uniting
with the ganglia of the cord, although their mode of connection with
the cells is not capable of ready detection. Having entered the cord.
the fibres of the posterior nerve-roots are seen to divide into three
different bundles.

The fibres of the anterior roots may likewise be divided into three

FUNCTIONS OF THE SPINAL CORD.

799

pm.f

different bundles: 1. The median bundle, represented by the black line
in the figure (Fig. 340), partly enters into direct union with the cells of
the anterior horn, while part passes through the gray matter to enter the
anterior commissure and pass to the opposite side of the cord, to termi-
nate, in part, in the cells of the anterior horn on this side and partly to
pass directly into the anterior white columns. 2. The central bundle of
motor fibres passes in part through the anterior horn without forming
any connection with its cells, to be lost in the posterior horn, where, in
all probability, through union with ganglionic cells it is in communica-
tion with the fibres of the posterior roots ; the other part of this bundle
directly unites with the cells
of the anterior horn. 3. The
lateral bundle is likewise
partly in direct communica-
tion with the gray matter of
the anterior horn and partly
runs up in the lateral columns
of the cord (Fig. 341).

Further examinations of
sections of the cord (right
half of above figure) show
that the direct and crossed
pyramidal tracts of opposite
sides of the cord are in com-
munication by means of fibres
passing through the gray sub-
stance into the anterior com-
missure, and that the direct
cerebellar column communi-
cates with Clarke's gray col-
umn and the latter with the
column of Goll on the same
side of the cord.

Some of the fibres of the posterior roots pass upward in the posterior
column. The}' thus form longitudinal commissures between the different
ganglia and make up the greater part of the posterior columns. These
commissural fibres are evidently concerned in upward conduction of sen-
sations, for when the cord is divided they undergo ascending degeneration.

The lateral fibres from the posterior root ascend obliquely and divide
in the posterior horn, with whose cells they, in all probability, communi-
cate, though part of these fibres may be traced as far as the anterior
horns. The inner bundle has been traced to the posterior commissure ;
its further course or termination is unknown.

FIG. 341.— DIAGRAM ILLUSTRATING THE PATHS
PROBABLY TAKEN BY THE FIBRES OF THE
NERVE-ROOTS ON ENTERING THE SPINAL
CORD, AFTER SCHAFER. (YeO.)

a.m./, anterior median fissure ; p.m./, posterior median fissure ;
c.c, central canal ; SR, substantia gelatinosa of Rolando ; a a, fu-
niculi of anterior root of a nerve ; p, funiculus of posterior root of a
nerve. By following the fibres 1, 2, 3, etc., their course through the
gray matter of the spinal cord may be traced.

800

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

It is thus seen that the white fibres of the spinal cord are not in
direct communication with the nerve-roots, but only connect different
segments of the spinal cord. In each segment of the spinal cord are to be
found nerve-centres for the afferent and efferent nerves of definite regions
of the bod}r, and commissural fibres connecting that segment with other
segments of the cord and with the brain (Fig. 342).

Leaving these anatomical considerations of the moment, we have
now to examine the data as to the paths of conduction of motor and
sensory impulses through the spinal cord attained through experiments
performed upon the spinal cord. The method of such experiments con-
sists in attempting to make isolated sections of different parts of the
cord and determine the interference of function which results from such
mutilations. The difficulty of such experiments is twofold : In the first

FIG. 342.— DIAGRAM ILLUSTRATING THE VARIOUS CHANNELS THROUGH
WHICH A MOTOR CELL OF THE CORD MAY BE CALLED INTO ACTION.
(Ranney.)

A.H, anterior horn ; C.P.C, crossed pyramidal column : P, posterior horn ; B, column of Burdach ;
G, column of Goll ; 1, fibre for painful sensations ; 2, fibre for tactile sensations ; 3, motor cell ; 4, motor
fibres ; 5, fibre from opposite cerebral hemisphere going to cell, 3 ; 6, ganglion on posterior nerve-root ;
7, fibre from cerebral hemisphere of same side going to motor cell, 3.

place, it is difficult to separate the temporary result, due to the shock of
the operation, and the permanent results ; and, in the case of sensation in
the lower animals, to distinguish between reflex action and purely volun-
tary movements. In the second place, it is almost impossible to make a
section of any isolated portion of the spinal cord without more or less
damaging the adjacent portions. Thus, for example, it is almost impos-
sible to cut tran sversety the posterior white columns of the cord without
at the same time more or less injuring the gray matter. This difficulty
applies to isolated sections attempted on all parts of the spinal cord.
Nevertheless, a number of valuable results have been obtained by this
method.

In the first place, it has been found that section of the cord causes
immediate loss of both sensation and motion in all parts supplied by

FUNCTIONS OF THE SPINAL COED. 801

nerves which arise behind the point of injury, with temporary vaso-motor
paralysis. The remote effects are secondary descending degeneration in
the crossed and direct pyramidal tracts and ascending degeneration in
the postero-internal columns. If the section is made on one lateral half
of the spinal cord (hemisection) paralysis of voluntary movement and
vaso-motor paralysis occur on the side of the operation in the parts
below, with loss of sensation on the side opposite to the injury and
increased sensitiveness on the side of operation, with the exception of
a limited area of anaesthesia in the part supplied by the sensory nerves
destroyed in the operation. There is also the usual ascending and
descending degeneration, the former also appearing in the column of
Goll on the opposite side.

If a longitudinal section is made through the posterior fissure of the
cord in the median line, little if any loss of motion results (some fibres
of the p3rramidal tract cross in the anterior commissure), but a consider-
able reduction of sensibil^. If the posterior white columns are di-
vided there is considerable loss of the tactile, temperature, and muscle
senses, although the sensation of pain may still be felt; no loss of motion
results. If the antero-lateral columns of white fibres be divided there is
a loss of voluntary motion in a corresponding part of the same side of
the body. Such a loss of motion, provided the gray matter be not inter-
fered with, is temporary, and indicates that the gray matter may take on
the function of conduction, ordinarily carried on by the white columns,
past the seat of injury.

The respiratory and vaso-motor fibres also pass through the antero-
lateral white columns. If the' gray matter and the posterior white
columns be divided sensory or tactile impulses no longer reach the
brain, showing that sensory impulses travel in these parts.

These facts would indicate that sensory impulses entering the
posterior roots of the spinal nerves pass for a certain distance in the
posterior columns and then cross over to the gray matter of the
opposite side to ascend to the cerebrum in the lateral column in front of
the pyramidal tract, while some may pass into the posterior column and
others ascend in the gray matter; the fibres concerned in the conduc-
tion of " muscular sense " apparently do not decussate until the medulla
is reached : or the}7 may pass to the cerebellum by the direct cerebellar
tract and posterior columns to the restiform body and thence to the
cerebellum.

On the other hand, voluntary motor impulses after having crossed
in the pons varolii and medulla oblongata descend in the antero-lateral
columns of white fibres (crossed pyramidal tracts) to leave the cord
through the anterior roots of the spinal nerves, after forming communi-
cation with the motor cells of the anterior cornua. The direct pyramidal

51

802

PHYSIOLOGY OF THE DOMESTIC ANIMALS,

FIG. 343.— DIAGRAM OF A SPINAL SEGMENT AS A SPINAL CENTRE AND CON-
DUCTING MEDIUM, AFTER BRAMWELL. (Landois.)

B, right, Bl, left cerebral hemispheres: M O, medulla oblongata: 1, motor tract from right hemi-
sphere, largely decussating at M O. and passing down the lateral column of the cord on the opposite side
to the muscles M and Ml ; 2, motor tract from left hemisphere : S. Si, sensitive areas 011 the left side of
the hody ; 3, 31, the main sensory tract from the left side of the body : it decussates shortly after enter-
ing the cord : 82. S3, sensitive arena, and 41, 4, tracts from the right side of the body. The arrows
indicate the direction of the impulses.

FUNCTIONS OF THE BRAIN.

803

tract descending in the anterior column may either supply the muscles
which always act. together on both sides of the body; or, according to
other observers, they cross in the anterior commissure to join the lateral
pyramidal tract (Fig. 343).

The paths of conduction of motion and sensation will again receive
attention when the upward connections of the different columns of the
cord have been traced.

VI. THE FUNCTIONS OF THE BKAIN.

In its earliest stage of development the l/rain simply consists of the
dilated extremity of the medullary tube formed by the turning in of the
medullary folds of the ectoderm. Almost immediately after the closure
of the medullary canal its anterior termination is seen to become differ-
entiated into three bilateral symmetrical vesicular dilatations, which are
the starting points of the fore-, mid-, and hind-
brain. From the fore-brain the cerebral lobes

ETmfi

PH.

FIG. 344.— DIAGRAM OF
THE CEREBRAL VES-
ICLES OF THE BRAIN
OF A CHICK AT THE
SECOND DAY OF IN-
CUBATION, AFTER CA-
DIAT. ( Yeo.)

1, 2, 3, cerebral vesicles; 0,
optic vesicles.

FIG. 345.— DIAGRAM OF A VERTICAL LONGITUDINAL SECTION
OF A DEVELOPING BRAIN OF A VERTEBRATE ANIMAL,

SHOWING THE RELATIONS OF THE THREE CEREBRAL

VESICLES TO THE DIFFERENT PARTS OF THE ADULT
BRAIN, AFTER HUXLEY. ( Yeo.)

OJf, olfactory lobes; F.M, the foramen of Monro; C.S, corpus striatnm ; T7i,
optic thalamus; Pn, pineal glands; M b, mid-brain; Cb, cerebellum; J/.O, medulla
oblongata; Jimp, cerebral hemispheres; ThE, thalamencephalon ; Py, pituitary
body; C.Q, corpora quadrigemina; C.C, crura cerebri ; P.V, pons varo'lii ; I-YII,
regions from which spring the cranial nerves; 1, olfactory ventricle; 2. lateral ven-
tricle; 3, third ventricle; 4, fourth ventricle.

develop as two hemispherical vesicles (prosencephalori), which, in the
brain of the highest mammals, so increase in size upward and backward
as to cover more or less completely the remainder of the primary cere-
bral vesicle, the mid-, and hind- brain, so that the mid-brain, composed
of the optic thalamus, corpora quadrigemina, and corpora striata
(mesencephalon), lies beneath the hemispheres. From the hind-brain
originate the cerebellum, pons varolii, and the medulla oblongata
(myelencephalon). At first all these parts consist of thin-walled vesicles
communicating with each other and with the interior of the central
canal of the spinal cord (Figs. 344, 345 and 346).

In higher stages of development the walls of these cerebral vesicles
become not only thicker and their cavities smaller and smaller, but

804

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

elevations (gyri) and depressions (sulci), convolutions and fissures, form

so as to give to the brain its characteristic
appearance, the degree of external com-
plexity differing in different classes of
animals.

In fact, the strongest point in favor
of the high importance of the cerebrum,
and especially its connection with the
mental functions, is seen in the progressive
complexity of its surface in passing from
the lower to the higher animals.

In fishes, amphibia, and reptiles the
cerebral cortex is smooth, and but a faint
trace of the formation of fissures is to
be seen in birds. In the lowest mammals
also the hemispheres are smooth, as in the
marsupials, the lowest rodents, if not also
in the lowest so-called quadrumana, as in
the lemurs. But, ascending to the higher
orders of mammals, the hemispheres be-
come more and more sulcated on the
surface, until the ridges or convolutions
become more and more numerous and
complex as we reach the highest mammals
or the highest genera in the several orders.
The cerebral convolutions may be
said to be characteristic of the brains of
mammals, and may be considered, firstly, in regard to their general
plan, and, secondly, their relative complexity within that plan.

The highest degree of complexity of the cerebral convolutions is seen in the
brain of man, of which the most important are represented in the following
diagrams (Figs. 347, 348, 349). Each cerebral hemisphere is subdivided on its
external surface into five lobes — the frontal, parietal, occipital, ternporo-sphenoidal,
and island of Reil.

In the (1) frontal lobe are found three convolutions — the superior, central,
and inferior frontal convolutions. Behind these comes the ascending frontal, sepa-
rated from them by the precentral fissure and bounded posteriorly by the fissure of
Rolando, which forms the anterior boundary of (2) the parietal }ol>e, the latter being
limited below by the fissure of Sylvius and behind by the parieto-occipital fissure.
In this lobe are found the ascending parietal convolutions immediately behind the
fissure of Rolando, supramarginal convolution arching around the posterior
extremity of the fissure of Sylvius, and the angular gyrus arching around the end
of the first temporo-sphenoidal fissure.

(3) The temporo-splienoidal lobe, bounded in front by the fissure of Sylvius,
contains three horizontal convolutions, superior, middle, and inferior temporo-
sphenoidal convolutions, the first two being separated by the parallel sulcus.

(4) The occipital lobe is separated from the parietal lobe by the parieto-
occipital fissure, and likewise contains three convolutions on its outer surface, — the
superior, middle, and inferior occipital convolutions.

FIG. 346.— DIAGRAM OF A HOR-
IZONTAL SECTION OF A
VERTEBRATE BRAIN, AFTER
HUXLEY. (Yeo.)

Olf, Olfactory lobes ; L.t, lamina termi-
nalis; C.S, corpus striatum ; T h, optic thal-
amus ; Pn, pineal gland; Mb, mid-brain;
Cb, cerebellum; M.O, medulla oblongata;
1, olfactory ventricle; 2, lateral ventricle;
3, third ventricle ; 4, fourth ventricle : -f-
itar e tertio ad quartum ventriculum ; F.M,
foramen of Monro ; 11, optic nerves.

FUNCTIONS OF THE BRAIN.

805

(5) The central lobe, or island of Reil, consists of five or six short, straight
convolutions (gyri operti) radiating out and back from the anterior perforated spot,
and can only be seen when the margins of the fissure of Sylvius are separated.

On the inner surface of each hemisphere is the gyrus fornicatus, or convo-
lution of the corpus callosum, which terminates posteriorly in the gyrus uncinatus
or gyrus hippocampi. Above is the marginal convolution, which is simply the
inner surface of the frontal and parietal convolutions, while the inner surface of
the ascending parietal convolution is termed the quadrate lobe, or prseeuneus.
The parieto-occipital fissure terminates in the calcarine fissure and, running back-
ward in the occipital lobe, incloses the wedge-shaped lobule, — the cuneus.

The importance of an acquaintance with the principal cerebral convolutions
as here sketched will be seen when the functions of the cerebral cortex are
considered.

FIG. 347.— LEFT SIDE OF THE HUMAN BRAIN (DIAGRAMMATIC). (Landois.)

Y frontal, P parietal, O occipital, T temporo-sphenoidal lobes ; S fissure of Sylvius ; S' horizon-
tal, S" ascending ramus of S; c, sulcus centralis, or fissure of Rolando; A ascending frontal and B
ascending parietal convolutions: f\ superior, Fo middle, and F3 inferior frontal convolutions; f\
superior and /2 inferior frontal fissures; /s, sulcus fraecentralis : P, superior parietal lobule; Pg,
inferior parietal lobule, consisting of Po, supramarginal gyrus, and Pg', angular gyrus ; ip, sulcus inter-
parietal is ; cm, termination 01" calloso-marginal fissure; Oi first, Oo. second, O? third occipital convolu-
tions; po. parieto-occipital fissure; o, transverse occipital fissure; o2, inferior longitudinal occipital
fissure; TI first, T2 second, T3 third temporo-sphenoidal convolutions; <j first, f2 second temporo-
sphenoidal fissures.

In most ruminants the convolutions are arranged in the form of
parallel folds, extending from the front to the back of each hemisphere,
but are much more complicated than in the carnivora, where the surface
of the hemispheres is divided into four pairs of antero-posterior convo-
lutions, distributed around the upper end of the S3^1vian fissure and
passing from the frontal to the parieto-temporal lobe (Fig. 350),

806

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In the ruminants traces of the fissure of Rolando may be detected,
but in none of the ruminants, rodents, marsupials, or even carnivora,
with the exception of the seal, is there to be found a backward prolonga-
tion of the lateral ventricle forming a posterior cornu.

In the quadrumana the plan of the arrangement of the cerebral con-
volutions to a certain extent resembles that seen in the cerebrum of man.

The characteristics of this organization are found — first, in the
existence of the occipital lobe, with the prolongation into it of the lateral
ventricle; second, the fissures occupy the position of the fissures of the
human brain, of which the most important are the fissure of Rolando,
dividing the frontal from the parietal lobe, the parieto-occipital fissure

lens
al

.id

FIG. 348.— MEDIAN ASPECT OF THE RIGHT HEMISPHERE. (Landois.)

CC, corpus callosum divided longitudinally; Gf, gyrus fornicatus; H, gyrus hippocampi; 7;, sulc
hippocampi; U, unoinate gyrus ; cm, calloso-marginal fissure ; Fj, first frontal convolution; c, termir
portion of fissure of Rolando ; A, ascending frontal convolution ; B, ascending parietal convolution a:
paracentral lobule; Pi', praecuneus, or quadrate lobule ; Oz, cuneus ; Po, parieto-occipital fissure ; o, trans-
verse occipital fissure; oc, calcarine fissure; oct, superior, oclt, inferior ramus of the same; D, gyrus
descendens ; T4, gyrus occipito-temporalis lateralis (lobulua fusiformis) ; T5, gyms occipito-temporalis
medialis (lobus lingualis).

distinguishing the occipital from the parietal lobe ; and, third, the fissure
of the hippocampi, formed by the folding inward of the cerebral substance
along the posterior cornua. In the higher monkeys numerous other
fissures complicate the cerebral surfaces and to a certain extent corre-
spond with the arrangement of the convolutions in the human brain.-
In all these may be recognized certain primary frontal, parietal, occipital,
and temporal convolutions, which have a general longitudinal direction.
As a rule, the cerebral hemispheres are more convoluted in the larger
species of any group of mammals than in the smaller species of the
same group. For example, in the pachydermata the highest degree of
complexity of the convolutions is found in the elephant.

FUNCTIONS OF THE BKAIN.

807

The basal ganglia likewise depend for their degree of development
upon the position of the animal in the zoological series. Thus, the
corpora quadrigemina are, as their name implies, divided into four emi-
nences in all mammals, the anterior pair being larger in herbivora and
the posterior in carnivora.

In birds, reptiles, and fishes they consist only of a single pair of
ganglionic masses, and are termed the corpora bigemina, or optic lobes.

FIG. 349.— ORBITAL SURFACE OF THE
LEFT FRONTAL LOBE AND THE
ISLAND OF REIL, THE TIP OF
THE TEMPORO - SPHENOIDAL
LOBE REMOVED TO SHOW THE
LATTER. (Landois.)

17, convolution of the margin of the longitu-
dinal fissure ; O, olfactory fissure, with the olfac-
tory lobe removed ; TR, triradiate fissure ; HI and
lift, convolutions of the orbital surface ; 1, 1, 1, 1,
under surface of the infero-frontal convolution; 4,
under surface of the ascending frontal, and, 5, of
the ascending parietal convolutions; C, central
lobe, or island.

FIG. 350.— BRAIN OF DOG, SUPERIOR SURFACE.

(Colin.)

1, 2, 3, 4, the four primary convolutions; a, centre for superior
cervical muscles ; b, for adductors and extensors of anterior ex-
tremity ; c, for flexors and rotators of anterior extremity ; d,
motor centre for posterior extremity ; /, centre for facial muscles.

So, also, the corpora striata in all vertebrates are covered by the cere-
bral hemispheres, but in descending the animal series the reduction in
the size of the cerebral lobes gives a relatively greater importance to the
corpora striata. The size of the optic and olfactory lobes varies in dif-
ferent groups of animals, being largest in those in which the special
senses associated with these parts of the brain are most highly developed.

808 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Further, in descending the vertebrate series, the lateral ventricles
become smaller in extent and of simpler form, the posterior cornna
being absent in all animals below the quadrumana, with the exception
of the seal. The gray matter of the hemispheres likewise diminishes,
until in fishes the gray cortex is so thin as to be almost indistinguish-
able to the naked eye. The corpus callosum has its highest develop-
ment in man, and in the lower mammals becomes both shorter from
before backward and thinner, and gradually becomes inclined upward
and backward. In the marsupials it is rudimentary, and in no vertebrate
lower than mammals is there any trace of the corpus callosum, it being
represented in birds, reptiles, amphibia, and fishes merely by transverse
commissural fibres crossing at the base of the cerebrum. As the hemi-
spheres become reduced in importance there is a corresponding simplifi-
cation in the medulla-oblongata and a diminution of the cerebellum and
pons, the pons being absent in reptiles, amphibia, and fishes.

No olivary bodies or corpora dentata are to be distinguished in
animals lower than mammals, the anterior and posterior prominences and
restiform bodies often constituting the entire mass of the medulla
oblongata.

The fourth ventricle, on the other hand, is more clearly marked in
the lower animals and is more directly continuous with the central canal
and spinal cord.

Like the cerebrum, the cerebellum likewise diminishes in passing
from the highest to the lowest vertebrates. In birds the bulk of the
cerebellum is composed of the vermiform process, while in reptiles,
amphibia, and fishes this median portion is alone present. Like the
cerebrum, the cerebellum, also, becomes progressively simplified, the
laminae or convolutions diminish until they are comparatively few in the
bird, while they are absent in reptiles, amphibia, and fishes, in which the
surface is quite smooth.

In the frog the cerebellum forms a simple, smooth band, and in the
lowest fishes is so reduced in size as to no longer cover the medulla
oblongata.

In many carnivora and ruminants the cerebellum, instead of being
composed of broad, smooth, lateral hemispheres joined by the vermiform
processes, is very uneven on its surface, and apparently consists of a
cluster of a number of lobules.

The internal structure of the cerebellum likewise becomes simplified
and the internal laminae of gray matter disappear. In general, it would
appear that the more complex the character of the movements of which
the animal is capable the higher will be the plane of development of the
cerebellum.

Only in the large cetaceans and pachyderms is the brain absolutely

FUNCTIONS OF THE BRAIN. 809

heavier than in man ; thus, in the whale its weight is about five pounds,
while in the elephant it varies from eight to ten pounds.

Compared with the weight of the body, the brain diminishes in
weight in the following order : —

In mammals, 1 to 186; in birds, 1 to 212; in reptiles, 1 to 1321; and
in fishes, 1 to 5668.

In mammals the relative proportion of the brain to the bod.y is
smaller in the larger species. Thus, in the ox it is as 1 to 860 ; the
elephant, 1 to 500 ; the horse, 1 to 400 ; sheep, 1 to 350 ; dog, 1 to 305 ;
the cat, 1 to 156; the rabbit, 1 to 140; the rat, 1 to 76; field-mouse, 1 to
31 ; man, 1 to 36. It is thus seen that in few animals is the brain
heavier compared to the body than it is in man, though in a few singing-
birds it may amount to as much as 1 to 12.

It must not be forgotten that the estimates of the weight of the
brain include the sensory and motor ganglia at the base of the cerebrum,
the optic thalami, the corpora striati, and the cerebellum, and in the lower
mammals these portions of the brain constitute by far the greater part ;
hence the size of the cerebral lobes as an index of the power of
intelligence is not disturbed by these figures.

To recapitulate, the principal difference noticed in the brain in
passing from the highest to the lowest vertebrata is not only in its
relative decrease in size but also in its gradual simplification in form and
structure, more especially in the cerebral hemispheres and cerebellum.
These organs, indeed, gradually become smaller in proportion to the
sensory and motor ganglia at the base of the cerebrum ; or, in other
words, the ganglia exhibit a greater proportionate size as compared with
the cerebral hemispheres and cerebellum.

In the highest mammals the cerebral hemispheres completely cover
the olfactory lobes in front and the corpora quadrigemina behind, and
in man even overlap the cerebellum ; but in the carnivora, ruminants,
and lower mammals the cerebral hemispheres no longer overlap, but
even fail to cover any part of the cerebellum, while in the ruminants
the anterior part of the hemispheres is so diminished as to permit
the projection of the olfactory lobes beyond them.

In rodents the cerebral lobes have become still more retracted
and now a portion of the corpora quadrigemina becomes visible.
In birds, while the olfactory lobes are covered, the optic lobes are
exposed, and in reptiles, amphibia, and fishes the cerebral hemispheres
become so much further reduced in size as to merely cover the corpora
striata with a thin layer of cerebral substance.

In the lowest vertebrata the parts of the encephalon thus appear to
be arranged in a double symmetrical row, one behind the other. The
most anterior in this row are the ganglionic masses which form the

810

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

olfactory lobes; behind them come the cerebral lobes covering the
corpora striata, and the third and usually the largest mass, correspond-
ing to the optic thalami and corpora quadrigemina ; behind them is seen
the cerebellum as a small central mass, while the medulla oblongata is
the connecting link between the spinal cord below and the basal ganglia
of the brain above. These different parts of the brain will be taken up
in turn, commencing with the medulla oblongata as the cranial
prolongation of the spinal cord.

1. MEDULLA OBLONGATA. — The medulla oblongata, like the spinal
cord, is composed of two symmetrical halves, each capable of separation

FIG. 351.— SECTION OF THK DECUSSATION OF THE PYRAMIDS. (Landois.)

/.La., anterior median fissure, displaced laterally by the fibres decussating at d ; V, anterior column;
C.a., anterior cornu, with its nerve-cells, a, b ; c.c, central canal ; S, lateral column ; />., formatio retic-
ularis ; ce, neck, and, g, head of the posterior cornu ; r.p.C.I., posterior root of the first cervical nerve ;
M.C., first indication of the nucleus of the funiculus cuneatus; n.q., nucleus (clava) of the funiculus gra-
cilis ; HI, funiculus gracilis ; //2, funiculus cuneatua ; s.l.p., posterior median fissure ; x, groups of gangli-
onic cells in the base of the posterior cornu.

by the naked eye into three different divisions, the anterior pyramids,
the olivary and restiform bodies, and the posterior pyramid, or funiculus
gracilis. The lower end of the medulla oblongata, at the point of exit
of the roots of the first cervical nerves, is characterized by a deviation
of the lateral columns (crossed pyramidal tract) of the cord, which, up
to this point running parallel with the axis of the cord, here turn in
through the gray substance of the anterior horn and cross to the oppo-
site side of the cord in the anterior white commissure to join the direct
pyramidal tract. The lateral columns of the cord consequently form a
decussation at the bottom of the anterior longitudinal fissure in the

FUNCTIONS OF THE BKAIN. 811

medulla, this point of crossing being termed the decussation of the
pyramids (Fig. 351).

The anterior pyramids are thus made up of the crossed pyramidal
tract from the lateral column of the opposite side of the cord, and the
direct p3Tramidal tract from the anterior column of the same side of the
cord.

Of the P3~ramidal fibres some pass through the pons directly to the
cerebral cortex in a manner to be described directly, some pass to the
cerebellum, and some join fibres coming from the Olivary body to form
the olivary fasciculus.

The remainder of the anterior column, the antero-external fibres, lie
under the anterior pyramids and form part of the formatio reticularis.

In the neighborhood of the first cervical nerve and the point of
origin of the first root of the hypoglossal nerve, laterally from the
anterior pyramids, lie the remainder of the lateral columns of the cord
which have not undergone decussation, the direct cerebellar tract passing
backward to rejoin the restiform body and go to the cerebellum ; the
remaining fibres, passing underneath the olivary bodies and appearing
in the floor of the medulla, form the fasciculus teres and pass to the
cerebrum.

Farther outward from the anterior pyramids are found the gray
masses of the olivary bodies, the pj'ramidal nucleus, and the accessory
olivary nucleus, through which passes toward the middle line and backward
the remainder of the anterior column. The gray substance of the olivary
bodies on section possesses the form of a horseshoe, whose arch is thrown
up into numerous folds and whose opening is directed toward the centre
of the medulla. It contains numerous small, yellow, pigmented multi-
polar ganglion cells, and embraces like a capsule a tract of medullated
nerve-fibres which enter through the hylus of the olivary bodies and
spread out over the entire inner surface of the gray substance. In all
probability some of these fibres terminate in the ganglion cells of the
olivary bod}^. The remainder pass through the gray substance of the
olivary bodjr and partly unite with the fibrous columns of the restiform
bodies and partly surround the exterior surface of the oliva^ bodies.
The gra}^ substance of the pyramidal nucleus and the accessory olivary
nucleus resembles in all respects that of the olivary bodies. The former
lies in the hylus of the olivary bodies toward the posterior central line
of the pyramidal and olivary columns ; the latter, in the form of a thin,
concave plate of gray matter, lies between the olivaty hylus and the
corpora restiformes, which, by a collection of gray matter (Clarke's
column), form an unbroken continuation of the posterior columns of the
cord to the cerebellum.

The restiform bodies form the posterior division of the medulla

812 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

oblongata and appear to the naked eye as the immediate continuation of
the posterior white columns (postero-external fibres) of the spinal cord.
At the level of the foramen magnum they divide and expose the interior
gray substance of the spinal cord, which, previously covered by the pos-
terior columns, here becomes exposed on the posterior surface. The gray
matter at this point also becomes flattened out through the opening of the
central canal of the spinal cord, its borders being flattened out laterally.
The posterior pyramids form the upward continuation of the postero-
median fibres of the posterior columns of the cord.

While the gray substance of the spinal cord forms a compact mass
traversed only by the narrow central canal and is everywhere surrounded
by a sheath of white substance, in the medulla it becomes exposed and
forms a flattened layer, and is divided into two symmetrical halves lying
on each side of the median line and bounded only by a slight rim, the
last trace of the central spinal canal. This exposed surface of gray
matter in the medulla oblongata has the form of an elongated rhomb,
whose longest diagonal coincides with the median line, and it forms the
floor of the fourth ventricle, communicating above with the aqueduct of
Sylvius and below with the central canal of the spinal cord, the lower
pointed end of this surface bearing the name of the calamus scriptorius.
The gray substance of the floor of the fourth ventricle is entirely similar
to that of the spinal cord ; it contains a large mass of multipolar gan-
glion cells, of which a few form distinct roots and appear to be in direct
communication with the cranial motor nerves.

The ganglionic origin of the sensory cranial nerves is less distinctly
made out. It is, however, clear that all the cranial nerves, from the
oculo-motor to the hypoglossal, originate in the medulla oblongata and
its annexes. Only the optic and olfactory nerves originate within the
cerebrum. The gray matter of the floor of the fourth ventricle forms a
direct continuation of the gray matter of the spinal cord, and is to this
extent analogous to the anterior columns, the p3^ramids, and cerebellar
fibres, which pass without interruption from the spinal cord into the
medulla oblongata.

The anterior divisions of the lateral columns of the spinal cord
likewise pass without interruption into the medulla oblongata and force
themselves between the olivary body and restiform bod}'', without, how-
ever, passing farther toward the median line (Fig. 352).

From the raphe originate numerous nervous fibres, or so-called
internal transverse fibres, which cross the longitudinal fibres of the
medulla at a right angle and split up into a large number of smaller
bundles, the net-work so formed being described as the reticular forma-
tion of the medulla oblongata. This net-work incloses in its spaces
numerous multipolar ganglion cells, in which terminate, in all probabilit}-,

FUNCTIONS OF THE BKAIN.

813

Sip

certain of the fibres of the lateral columns of the cord, and so enable the
medulla, by bringing it into communication with impressions coining
from below, to act as a reflex centre. The transverse fibres of the
medulla are to be regarded as commissural fibres connecting the two
halves of the medulla, especially the olivary bodies.

Closely allied to the anterior surface of the olivary columns are to
be found the gray nuclei, or the column of Goll (Keil string), from which
originate the arciform fibres, or the external transverse fibres which
surround the entire external surface of the medulla to unite with the
internal transverse fibres, from there
to pass into the restiform bodies, and
from there to the cerebellum.

The internal interweaving of
the centrifugal and centripetal
fibres, the presence of numerous
ganglionic cells, and, to a certain
extent, the evident union of different
classes of nerve-elements, the sym-
metrical connection b.y transverse
fibres of both halves of the medulla,
nil speak in the clearest way as to
the high ph}'siological importance of
this portion of the central nervous
system, both as the seat of reflex
centres, as the origin of numerous
cranial nerves, and as the paths of
communication from the spinal cord FlG*
to the brain.

As is evident from the anatom-
ical description of the medulla, in
many respects it forms the most
important part of the central ner-
vous System. It forms the ganglionic n.e.i, external micleus~orth7fun^uius''cun7atu8TTo'
,. ,, i , nucleus of the funiculus gracilis (or clava) • 771 funiculus

termination OI a large number Of gracilis: #2. funiculus cuneatus; c.c., central canal; fa

/o,i /a,2 external arciform fibres.

nbres; most ot the cranial nerves

find in it their origin, and in it the most diverse systems of the animal
body are brought into nervous connection. For the ascending motor
and sensory nerves of the spinal cord it forms not only the means of
conduction, but is the seat of important centres of co-ordination. These
paths, and the most important centres, are represented in diagrammatic
form in Figs. 353 and 354.

It has been seen that when the spinal cord is divided below the level
of the medulla oblongata in the frog it remains perfectly motionless and

DECUSSATION
(Landois.)

OF THE PYRAMIDS.

f.l.a., anterior, s.l.p., posterior median fissures;
n.XI, nucleus of the accessorius vagus; n.XII, nucleus
of the hypoglossal ; d.a., the so-called superior or anterior
decussation of the pyramids; py, anterior pyramid;
n.ar., nucleus arciformis; ol, median parolivary body •
o, beginning of the nucleus of the olivary body n I

814

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in an apparent condition of almost total paralysis, yet after the shock of
the operation has passed off a number of highly complex reflex motions
may be evoked. If, however, the section of the cord be made at the
anterior border of the medulla the position of the frog after the shock of
the operation has passed off is more nearly normal, and allusion has been

01.

ff

FIG. 353.— DIAGRAM OF THE CHIEF TRACTS
IN THE MEDULLA, AFTER ERB.
(Ranney.)

The formatio reticularis is represented by shading.
01., olivary body ; V anterior, S lateral, and H pos-
terior spinal funiculi ; «, pyramido-anterior tract ; d,
pyramido-lateral tract; Py., pyramidal tract; b, re-
mainder of anterior column ; c, remainder of the lateral
column ; e, e, cerebello-lateral tract ; /, funiculus gra-
cilis, and,/', nucleus of the same; g, funiculus cunea-
tus, and, gt, nucleus of the same; P.c.i., internal
fasciculus of the pedunc. cerebelli ; P.c.e., external
fasciculus of the same ; Cq.F., tract from corp. quadr.
to format, retic.; Cq.O., the same to the olivary body;
Thai., tract from the thalamus opticus.

FIG. 354.— TRANSPARENT LATERAL VIEW
OF THE MEDULLA, SHOWING THE
RELATIVE POSITIONS OF THE MOST
IMPORTANT NUCLEI; RIGHT HALF
OF THE MEDULLA, SEEN FROM THE
SURFACE OF SECTION; THE PARTS
THAT LIE CLOSER TO THIS SURFACE
ARE DEEPER SHADED, AFTER ERB.
(Ranney.)

Py, pyramidal tract; Py. Kr, decussation of pyramids;
O, olivary body ; O..s, superior olivary body ; V, motor,
Vt, middle sensory, vn, inferior sensory nucleus of
trigeminus ; VI, nucleus of abdncens ; G. f, genu facialis :
VII, nucleus facialis : VIII, posterior median acoustic
nucleus ; IX, glosso-pharyngeal nucleus X, nucleus of
vagus ; XI, accessorius nucleus ; XII, hvpoglossal nu-
cleus; Kz, nucleus of the funiculus gracilis; RV. tri-
geminus roots ; those of the R VI, abdueens, and R VII,

made to the fact that in the mid-brain is seated a centre which inhibits
reflex action.

When the cerebral lobes only have been removed in the frog, volition
is apparently the only function of the animal which is wanting, and in
the absence of stimuli of all characters the animal remains absolutely
inert. If such a frog is thrown into water it swims ; by stimulating its

FUNCTIONS OF THE BEAIN.

815

body it may be made to leap ; when placed on its back it regains its
normal attitude. When placed on an inclined plane it crawls up until it
gains a new position, and if such an experiment be made by placing a
frog on a small piece of board, by gradually inclining the board more
and more the frog may be made to climb up the board, pass over to the
other side, and the piece of wood may be turned over a number of times,
the frog always moving with it as long as its equilibrium is dis-
turbed. Such a frog will likewise be apparently sensible to light, and if
made to jump will avoid objects casting a strong shadow. Such move-
ments as above described are evidently carried out by co-ordinating
mechanisms and governed by definite afferent impulses (Figs. 355 and
356).

It is evident, from the existence of these motions in the frog
deprived of its cerebral hemispheres, that the mechanism governing
them must lie in parts of the central nervous system below the line of
section. No such operations can be effected in a frog in which the
medulla has been removed. It follows, therefore, that in the medulla,
or perhaps in the corpora quadrigemina and optic lobes, are found the
co-ordinating centres of the most complex muscular movement.

FIG. 3.55.— FROG WITHOUT ITS CEREBRUM
AVOIDING AN OBJECT PLACED IN
ITS PATH. (Landois.)

FIG. 356.— FROG WITHOUT ITS CEREBRUM
MOVING ON AN INCLINED BOARD,
AFTER GOLTZ. (Landois.)

In the mammal or bird a similar state of affairs is present, although,
as might be expected, complicated to a greater degree by the more
severe shock of the operation.

In a bird or a mammal in which the medulla remains after removal
of the cerebral lobes the attitude may become perfectly normal. If
placed on its side it will regain its feet. If a bird be thrown into the
air it will fl}- for a considerable distance, perhaps avoiding obstacles, but
its movements more resemble those of a stupid, sleep3T animal than one
in full possession of its faculties. A mammal, also, so operated on can
stand, run, and leap, and if placed on its back can regain its normal
position, but if left alone it remains absolutely motionless. If food is
placed in the mouth of the animal in whom ablation of the cerebrum
has been successfully performed the animal will eat, and the complicated
motions of mastication and deglutition will be accomplished with perfect
regularity.

816 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In the case of mammals it ought, perhaps with more correctness,
to be stated that these highly co-ordinate movements owe their perform-
ance to parts above the medulla, since the removal of the optic thalami,
crura cerebri, corpora quadrigemina, cerebrum, and pons varolii is
usually followed by various forced movements, or the animal lies partly
on its side, and, although various complex movements may be produced,,
they are much more limited than when the higher parts of the brain are
left intact.

The medulla oblongata is the seat of a large number of centres
governing complex co-ordinate movements, of which the following are-
the most important : —

(a) The Respiratory Centre. — This is located in the medulla behind
the point of origin of the pneumogastric nerves on both sides of the
apex of the calamus scriptorius, between the nuclei of the vagus and
spinal accessory nerves. This centre is symmetrically situated, and
may be separated by a longitudinal incision without interfering with
the respiratory movements. Conditions governing the actions of this
centre have been already given under the subject of respiration.

(b) The Cardio-Inliibitory Centre. — As has been previously stated r
when the pneumogastric nerve is stimulated it may slow or arrest the
heart in diastole, according to the degree of stimulation. The inhibitory
fibres of the pneumogastric reach the latter nerve through the spinal
accessory and have their origin in the medulla oblongata. The conditions
for its action have been likewise given.

(c) The Vaso-Motor Centre. — The collection of nerve-cells which
govern the vaso-motor nerves, and through them tlie calibre of the blood-
vessels, is located in the floor of the medulla oblongata, extending from
the upper part of the floor to within four or five millimeters of the col-
umns of the cerebellum. This centre is also a double one, situated sym-
metrically on each half of the medulla and each part corresponding to the
upward continuation of the lateral columns of the spinal cord. Stimula-
tion of this centre causes contraction of all the arteries with a consequent
increase in the blood pressure; paralysis causes relaxation and dilatation
of the blood-vessels and fall of blood pressure. Its action has also been
described.

(d) Centre for Closure of the Eyelids. — The centre for the closure
of the eyelids lies close to the calamus scriptorius. The afferent impulses
reach it through the sensory branches of the fifth cranial nerve from
stimuli applied to the cornea, conjunctiva, and skin in the neighborhood
of the eye ; reaching the centre of impulse, are transferred to the special
nerve, through which the afferent impulses reach the orbicularis palpe-
brarum.

(e) Centre for Sneezing. — The location of this centre has not been

FUNCTIONS OF THE BRAIN. 817

accurately determined. Stimuli pass through the internal nasal branches
of the trigeminus or olfactory nerves and efferent fibres are found in the
nerves coming to the muscles of expiration.

(f) The Centre for Coughing. — This centre is placed a little above
the respiratory centre. The afferent fibres pass to the centre through
branches of the pneumogastric, the efferent in the nerves of expiration
and in those that supply the muscles that close the glottis.

(g) Centre for the Movements of Suckling and Mastication. — This
centre also has escaped close localization. Afferent paths reach the
medulla through the trigeminal and glosso-pharyngeal nerves. The
efferent fibres in the case of suction reach the lips through the facial, the
tongue through the hypoglossal, and the muscles which depress and
elevate the lower jaw through the inferior maxillary division of the fifth
nerves. The same nerves are concerned in the movements of mastication,
with the exception that when the food passes within the dental arch the
hypoglossal is concerned in the movements of the tongue, and the facial
with the buccinator.

(h) The Centre for the Secretion of Saliva. — This centre lies in the
floor of the fourth ventricle. When the medulla is stimulated, if the
chorda t3rmpani and glosso-pha^ngeal nerves are intact, a profuse secre-
tion of saliva is the result, indicating the efferent course of this impulse.
Afferent impulses reach the centre through the ne.rves of taste.

(i) The Centre for Deglutition. — This, likewise, is located in the
floor of the fourth ventricle. The afferent paths reach the centre through
the second and third branches of the fifth pair, the glosso-pharyngeal and
the pneumogastric. The efferent channels are found in the motor
branches of the phaiyngeal plexus.

(&) The Centre for the Dilatation of the Pupil— This centre, like-
wise, lies in the medulla oblongata, the efferent fibres passing partly
through the trigeminal nerve and partly in the lateral columns of the
spinal cord, as far down as the cilio-spinal region, and from there passing
out by the lowest two cervical and the two upper dorsal nerves into the
cervical sympathetic. The centre is normally excited in a reflex manner
by diminishing the amount of light entering the eye. Its action, together
with that of the centre for contracting the pupil, will be referred to
subsequently.

(/) The centre for vomiting is likewise found in the medulla. Its
functions have been already described.

(in) The medulla oblongata, as discovered by Bernard, exerts a
certain influence on the glycogenic function of the liver. When, as
already described, a puncture is made in the floor of the fourth ventricle
in the neighborhood of the origin of the pneumogastric nerve temporary
glycosuria appears within an hour or an hour and a half after the

52

818 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

operation. The method by which this influence on the liberation of
sugar by the liver is accomplished has been described under the heading
of Gtycogenesis.

2. THE COURSE OF THE FIBRES OF THE MEDULLA OBLONGATA. — We
have now to attempt to trace the paths of communication of the different
divisions of the medulla oblongata with the cerebrum, pons varolii, cor-
pora quadrigemina, and, still more important than all, the formation of
the hemispheres of the cerebrum and their means of communication by
the cerebral peduncles with the mid-brain and its ganglia and with the
cerebellum.

In tracing up the fibres from the medulla, those most readily followed
are the continuations of the restiform bodies, which may be readily
detected to pass directly into the cerebellum. Their termination after
reaching the cerebellum is only partially cleared up, and before attempt-
ing its explanation we must first consider the mode of construction of
the cerebellum itself.

The cerebellum consists, in the domestic animals and man, of two
flattened hemispheres connected across the middle line by the middle
lobe or vermiform appendix, which is the fundamental portion of the
organ. The white substance of the cerebellum exceeds to a considerable
degree the gray matter. The latter is deposited over the entire surface
of the two hemispheres of the cerebellum, forming the gray cortex of the
cerebellum ; within the inner white medullary substance of the hemisphere
is a collection of gra}r matter known as the dentate or ciliary body,
which in its general appearance somewhat resembles that of the olivary
bodies found in the medulla oblongata, and which here, also, has the
shape of a horseshoe, thrown up into numerous folds, and near which are
also found associate nuclei. Although it is clearly established that the
main function of the gray matte;* is to bring the nerve-fibres and nerve-
cells into connection with each other, still, as yet, no direct termination
of nerve-tubes in the ganglion cells of the cerebellum has been detected.
Of course, this does not imply that the terminations of the gray cells in
the cortex of the cerebellum with nerve-cylinders may not be readily
determined. All attempts, however, to follow up these nerve-fibres has
as yet resulted in almost total failure. If, however, we follow the resti-
form bodies (which form the inferior peduncles of the cerebellum) it may
be seen that a certain amount of their fibres decussates and then enters into
the dentate body, forming the so-called hitra-ciliary fibres, while another
passes externally and forms the extra-ciliary column.

In addition to its communication with the medulla, the cerebellum is
likewise in communication with the corpora quadrigemina and the pons
varolii. The fibres passing from the cerebellum to the corpora quadri-
gemina and crura cerebri (superior cerebellar peduncles) originate not

FUNCTIONS OF THE BRAIN. 819

only from the extra-ciliary fibres around the corpora dentata, decussating
in the pons, but also from the associate nuclei, while the fibres from the
extra-ciliary columns alone have been traced into connection with the
pons. It, therefore, is evident that the cerebellum is to be regarded as
a complicated collection of gray ganglionic masses in unbroken connec-
tion with the medulla oblongata and pons on the one side and with the
cerebrum on the other.

The pons varolii is formed by a collection of the continuations of
the reticular formation of the medulla, the pyramids and anterior columns
of the medulla, together with the fibres, coming directly by the middle
peduncle from the cerebellum.

Above the pons the two collections of fibres known as the cerebral
peduncles- (crura cerebri) approach each other, the point at which the
union is accomplished above the medulla being the locality in which the
upper end of the fourth ventricle terminates in the aqueduct of Sylvius.

In the interior of each cerebral peduncle is found a mass of gray
matter, the substantia niger, which separates the fibres of each cms into
two layers, the upper laj-er forming the so-called teymentum cruris
and the lower the basis cruris. The upper division of the tegmentum
contains also a gray nucleus (nucleus tegmentis).

Although these two divisions of the crura are in close anatomical
connection, it has been determined with a considerable degree of posi-
tiveness that the pyramidal fibres are in direct communication through
the basis of the cerebral peduncles with the central convolutions of the
cerebral hemisphere on the same side, although whether a direct commu-
nication, as in the case of the cerebellum, of these fibres with the gangli-
onic cells in the upper surface of the hemispheres exists or not has not
yet been determined. Nevertheless, it appears that they form no direct
communication with the other gray masses of the hemispheres, the
lenticular nucleus, optic thalamus or striated body. And since they
undergo degeneration only after injury of the central convolutions, it
is probable that they are in direct communication with the cortex of
the brain.

Flechsig claims to have followed them in an unbroken course from
the pyramidal columns through the white mass between the lenticular
nucleus and optic thalamus, the so-called internal capsule, direct to the
gray cortex of the cerebral convolutions. The course of these fibres,
together with the other important cerebro-spinal tracts are shown in
Fig. 357.

The cerebrum is divided by a longitudinal fissure into two hemi-
spheres in man, mammals, and birds, and its external surface is divided
by a number of lesser fissures into lobes and convolutions. The cere-
brum contains the ganglia of the brain, the optic thalamus or corpus

820

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

R

Spinal Cord

FIG. 357.— A DIAGRAM DESIGNED TO ILLUSTRATE THE COURSE OF CERTAIN
NERVE-TRACTS WITHIN THE CEREBRUM, CRUS, PONS, MEDULLA, AND
SPINAL CORD. MODIFIED FROM FLECHSIG. (Ranney.)

C.N., caudate nucleus ; L.N., lenticular nucleus ; O.T., optic thalamus : G.P., gray matter of the pons ;
F.R., formatio reticularis; C.D., corpus dentatum; O, olivary body ; N.C., clavate nucleus; T.N., trian-
gular nucleus: C.Q., corpora quadrigemina ; I.C., upper limit of the capsular fibres: m, m, m, motor
centres around the fissure of Rolando; c.r., fibres of the " corona radiata." 1, the "pyramidal tract,"
arising from the motor centres of the cerebrum and terminating in the cells of the anterior horns of the
spinal gray substance (13 and 14) ; 2, 3, and 4, fibres connecting the cerebral cortex, the caudate nucleus,
and the lenticular nucleus with the gray matter of the pons after decussation, and then prolonged as 0
and 7 to the cerebellum ; o, fibres of the superior cerebellar peduncle ; 6, 7, 8, 9, and 10 show by their
colors the tracts with which they are associated, as well as their origin and termination; 11 and 17, the
"direct cerebellar tract" of the spinal cord (whose probable termination is not correctly shown in the
cut, as it probably ends in the vermiform process) ; 12, the lemniscus or "fillet " tract, connecting the
olivary body with the optic thalamus and the corpora quadrigemina: 13, the cells of the cord connected
with the direct pyramidal tract ; 14, the cells of the cord connected with the crowed pi/ramidnl tract; 15,
fibres of the column of Burdach, terminating superiorly in the triangular nucleus ; 16, fibres of the
column of Goll, terminating superiorly in the clavate nucleus ; 19, fibres of the cord which terminate in
the so-called " reticular formation " directly ; 18, fibres of the ret. form, going to the cerebellum.

FUNCTIONS OF THE BKAIN. 821

striati, the caudate and lenticular nuclei, and the corpora quadrigemina,
being connected with the medulla by means of the cerebral peduncles,
above which are situated the corpora quadrigemina.

In the domestic animals the anterior pair of the corpora quadri-
gemina are composed of gray matter, while the posterior are white, in
direct opposition to what is the case in man. In herbivora and in the
hog the anterior pair are the larger, while in carnivora they are of equal
size, or the posterior may be somewhat more developed. Between the
corpora quadrigemina and the optic thalamus lies the third ventricle,
while under the corpora quadrigemina is situated the aqueduct of
Sylvius, connecting the third and fourth ventricle.

We have now to attempt an explanation of the functions of these
different parts of the brain.

3. THE PONS YAROLII. — We have seen that the pons, the superior
continuation of the spinal cord, is composed of two sets of fibres. The
one, the transverse fibres, constituting the median cerebellar peduncles,
serves to connect the two lateral hemispheres of the cerebellum and exists
only in animals in which the cerebellum consists of two lobes. The other
part of the pons is composed of a mass of gray substance in continuity
with that of the medulla and traversed in an antero-posterior direction
by the fibres of the medulla, passing up to form the cerebral peduncles.

As in the study of other portions of the nervous system, we attempt
here to determine the functions of the different parts of the brain by the
method of excitation and excision.

When the pons is stimulated, either mechanically or by an electric
current, pain and muscular spasms are produced, evidently by the mere
implication of adjacent motor and sensor}^ paths. Where section of the
pons is performed there may be sensory, motor, or vaso-motor paralysis,
together with forced movements when the middle cerebellar peduncles
are involved. Thus, if there be an injury to the lower half of one side
of the pons there will be both sensory and motor paralysis of the face
on the same side and more or less general paralysis of the opposite side
of the body ; if the injury be to the upper half of the pons the facial
paralysis will be on the same side as the paralysis of the body.

The pons, like the spinal cord and medulla, also acts as a reflex
centre ; although this fact is not capable of direct demonstration, its
truth is rendered probable by the higher degree of muscular co-ordination
preserved by an animal in which the pons has been retained over animals
in whom the section has been carried through the brain below this point.

4. THE CEREBRAL PEDUNCLES. — The cerebral peduncles form the
upward prolongation of the pons, and are constituted by those portions
of the spinal cord which, after having traversed the pons and medulla,
pass upward through the optic thalamus and corpora striata to enter the

822 , PHYSIOLOGY OF THE DOMESTIC ANIMALS.

cerebral hemispheres. When one of the cerebral peduncles is completely
divided it produces paralysis of voluntary movement on the opposite
side of the body, with a diminution of the sensibility and vaso-motor
paralysis.

Section of the basis of both cerebral peduncles totally abolishes all
voluntary movements, although reflexes apparently of cerebral origin
still persist.

Section of the tegmentum, on the other hand, on both sides entails
the loss of these cerebral reflexes, but allows voluntary motion to remain.

Injury to one cerebral peduncle causes pain and convulsions on the
opposite side of the body, while the blood-vessels contract. As the
irritative effects pass off these symptoms give place to paralysis.

5. THE CORPORA QUADRIGEMINA. — Destruction of the corpora quad-
rigemina on one side causes blindness, which may be either on the side
of the injury or on the opposite side, according to the location of the
mutilation. Total destruction causes absolute blindness in both eyes,
with the absence of the reflex contraction of the pupil when exposed to
the light. In addition to blindness, disturbance of equilibrium and
inco-ordination of movement result. When stimulated the pupils have
been noticed to dilate either on the same side or the opposite side of the
body ; this result is probably produced by conduction of the stimulus to
the origin of the S}Tmpathetic nerve, for after section of the sympathetic
dilatation of the pupil no longer takes place. Stimulation of the right
anterior tubercle causes the eyes to deviate to the left, while if a vertical
incision is made, so as to separate the right and left corpora quadri-
gemina, stimulation of one side only causes this movement to take place
on one side.

The most striking result of injuries to the corpora quadrigemina
are the so-called forced movements, evidentty due to peculiar unilateral
disturbances of equilibrium causing variations from the symmetrical
movements of the two sides of the body. These movements may be of
various kinds. In the so-called circus movement, instead of moving in
a straight line, the animal runs around in a circle ; rolling movement,
where the animal rolls on its long axis, and the index movement, when
the anterior part of the body is moved around the posterior part, which
remains at rest. These different forms of movement frequently pass into
each other, and they may be produced by injury either of the corpus
striatum, optic thalamus, cerebral peduncle, pons, middle cerebellar
peduncle, and certain parts of the medulla.

6. THE FUNCTIONS OF THE BASAL GANGLIA. — (a) Th,e Corpus
Striatum. — We have seen that the corpus striatum consists of two parts,
the intra-ventricular portion projecting into the lateral ventricle to form
the caudate nucleus, and the external portions the lenticular nucleus.

FUNCTIONS OF THE BRAIN. 823

Lying between these are found the fibres of the anterior division of the
internal capsule, which seem to have no connection with these ganglia.

Electrical stimulation of these ganglia causes general muscular con-
traction on the opposite side of the body. Lesions of either of these
ganglia, provided the internal capsule be not injured, do not appear to
cause any permanent symptoms, but destruction of the internal capsule
causes paralysis of motion or sensibility or both on the opposite side of
the body.

External to the lenticular nucleus is the external capsule, whose
function is unknown, as is also the case as regards the claustrum, which
is located externally to the external capsule.

(6) The Optic Thalamus. — Scarcely anything definite is known as
to the functions of this organ, since we have been compelled to abandon
the theory supported by Carpenter as to its purely sensory nature.
Injury to the thalamus of one side sometimes produces partial paralysis
on the opposite side of the body, and, again, sometimes after such an
injury hemiansesthesia of the opposite side of the body, with or without
disturbance of motion, has been observed. Frequently the thalamus may
be irritated without producing any evidence of sensation or motipn.
Since the posterior portion is connected with the origin of the optic
nerve it is in all probabilit}7 concerned in the sense of vision. Together
with the corpus striatum,the optic thalamus is perhaps mainly concerned
in co-ordinate and complex muscular movements, since the cerebrum
may be removed and motion still be normal, provided these basal ganglia
are left intact; when, however, they are disturbed normal progression
and co-ordinated movements are then rendered impossible.

The principal diflicult}r in determining facts in regard to the func-
tions of this part of the brain is that they do not admit of experimental
investigation without the most extensive injury to the other parts of the
brain.

7. THE FUNCTIONS OF THE CEREBRAL LOBES. — In man and the higher
mammals the cerebral lobes represent the greatest part of the brain-sub-
stance, and usually will constitute twelve-thirteenths of the entire weight
of the brain. The cerebral hemispheres are composed of an internal
white substance, representing the continuations of the fibres coming
from below which terminate in an external layer of gray matter. The
external matter, the cerebral cortex, is folded into convolutions sepa-
rated from each other by fissures, some of which being so marked as to
permit of the division of the cerebrum into adjacent lobes. From the
cells of the cortex, in all probability, proceed all the motor fibres which
are concerned in the production of voluntary movement, and to them
come all the fibres from the organs of special and general sense which
enable the brain to appreciate external impressions. Some of the fibres

824 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

terminating in the cortex traverse the basal ganglia ; others, constituting
the so-called pyramidal tracts, proceed from the motor regions of the
cerebrum and pass through the white matter and converge in the internal
capsule, and from there enter the crura cerebri, thence to the pons, and
thence to the opposite side of the medulla oblongata.

The white matter of the cerebral lobes may, therefore, be considered
merely as the continuation of the paths of conduction of the cord and
medulla which terminate in the cells of the gray matter of the convolutions.

The consideration of the cerebral lobes resolves itself, therefore, into
the study of the functions of the gray matter of the cortex. While the
cerebrum has been from time immemorial looked upon as the seat of the
will and intelligence, and, in fact, of all the phj'sical functions, it is only
since 1870 that attempts to localize the different functions of the cortex
have been attended by any measurable success.

In the lower animals, when the cerebral hemispheres are removed
slice by slice, the animals simply become more and more dull and stupid,
until finally they lose all intelligence. When in pigeons both cerebral
hemispheres are removed the animals apparently appreciate no pain
during the operation, nor are any movements produced by operations on
the cerebral substance. After extirpation of the cerebral lobes they
pass into a semi-comatose or stupid condition, and, if not disturbed,
remain absolutely motionless, apparently experiencing no sensation of
hunger, and will die of starvation in the midst of food without making
any effort to feed. If mechanically disturbed, provided the basal ganglia
are intact, they are capable of moving in a perfectly normal manner,
will, to a certain extent, avoid obstacles, the pupils of their eyes react
to light, and they are capable of reacting to violent sudden noises. If
food is placed in their mouths they are capable of swallowing it, and,
in fact, they preserve the powrer of completing numerous co-ordinated
movements which depend upon reflex stimuli, indicating that the
mechanisms concerned in the maintenance of equilibrium are located in
the mid-brain, probably in the corpora quadrigemina.

If a single cerebral lobe is removed in the lower animals no effect
other than the apparent dulling of intelligence is evident. In the higher
animals after such a mutilation there is evident a certain dulling of
sensibility and difficulty in movement on the opposite side of the body,
which, however, finally in the majority of cases gradually disappear. It
is concluded from these experiments that the cortex is the chief if not
the exclusive seat of intelligence.

From the experiments of Fritsch and Hitzig in 1870 dates a new
era in our knowledge of the functions of the cerebral cortex. They
found that stimulation by means of electricity of certain circumscribed
regions on the surface of the cerebral convolutions was followed by

FUNCTIONS OF THE BRAIN. 825

co-ordinated movements in distinct groups of muscles of the opposite
side of the bod}^. They indicated certain areas of the cerebral cortex as
the actual centres for the production of various movements, and their
experiments have been confirmed and extended by a large number of
subsequent observers. These points are termed the motor centres of
the cortex, and have been located in the dog, the monkey, the cat, sheep,
and the rabbit, but are absent in lower animals, such as the frog and fish.
They are all found in the anterior part of the parietal lobe, the most
important being shown in Fig. 358. When any centre which has been
determined to govern any special group of muscles is destroyed or
removed the corresponding part of the body is not permanently para-
lyzed in the dog, but movements which are produced in that part of the
body become irregular and variable, and after a time the disturbance of
movement may almost completely disappear.

In the monkey and man, on the other hand, destructive lesions of
definite motor areas of the cortex cause permanent paralysis, this
difference being, perhaps, explainable as due to the higher importance of
the cortex in higher species, where it assumes more and more the
functions subserved by the basal ganglia in lower animals.

A similar series of experiments has led to the localization in the
cortex of certain parts which are in close relationship with the organs
of sense, for we know that sensory impulses from the opposite side of
the body pass upward through the posterior third of the posterior limb
of the internal capsule to pass, in all probability, to the cortex of the
occipital and temporo-sphenoidal lobes. Excision of these localities
leads to disturbances in the appreciation of sensations coming through
the sensory organs. Thus, for example, in the dog a locality has been
found in the posterior cerebral lobe (outer convex part of the occipital
lobe) the destruction of which produces blindness in the opposite eye ; or,
if both corresponding parts are removed, total blindness results. After
extirpation of this part the channels which connect it with the optic
nerves undergo degeneration. Centres for hearing and for smelling have
also been located. The centre for hearing in the dog lies in the second
prima^ convolution, while in man and the monkey it has been located in
the first temporo-sphenoidal convolution. Such disturbances produced
by removal of parts of the cortex are, like the motor disturbances, not
permanent, but gradually disappear, and dogs rendered deaf or blind by
excision of these parts of the cortex again learn to see and to hear, — a fact
which is explained Toy the substitution of function in some corresponding
part of the .brain-cortex.

8. THE FUNCTIONS OP THE CEREBELLUM. — Experiments as to the
function of the cerebellum have led to the conclusion that it is the great
organ for the co-ordination of muscular movements, — a fact which would

826

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

alone be rendered probable when it is recognized that the cerebellum is
in direct connection not only with all the columns of the spinal cord,

i,

F '

FIG. 358.— UPPER SURFACE VIEW OF THE CEREBRUM OF VARIOUS ANIMALS.

(Landois. )

I, cerebrum of the dog; I, u, HI, iv, the four primary convolutions; s, snlcus cruciatus; F, Sylvian,
fossa; o, olfactory lobe; 1, motor area for the muscles of the neck ; 2, extensors and abductors of the fore
limb; 3, flexors and rotators of the fore limb; 4, the muscles of the hind limb: 5, the facial muscles;
6, lateral switching motion of the tail ; 7, retraction and abduction of the fore limb ; 8, elevation of the
shoulder and extension of the fore limb, as in walking; 9, 9, orbicularis palpebrarum. II, aa, retraction
and elevation of the angle of the mouth ; b, opening of the mouth and movements of the oral centre ;
cc, platysma ; d, opening of the eye ; p, optic nerve ; I, t, thermic centre. Ill, cerebrum of rabbit, from
above ; IV, cerebrum of the pigeon, from above : V, cerebrum of the frog, from above ; VI, cerebrum of
the carp, from above. In all these o is the olfactory lobe; 1, cerebrum; 2, optic lobe; 3, cerebellum;
4, medulla oblongata.

especially with the posterior columns, whose division has been found to
lead to inco-ordination, but with the basal ganglia of the cerebrum, which
we have found to be especially concerned in this function. It is

FUNCTIONS OF THE BKAIN. 827

supposed that the direct cerebellar paths of the cord conduct sensoiy
impressions to the cerebellum, and thus indicate the posture of the
trunk and the position of the limbs, while the motor impulses passing
through the cord may be influenced by fibres passing from the
cerebellum through the restiform body to the lateral columns. Injuries
of the cerebellum produce no disturbance of the psychical function, nor
do they give rise to pain. When, however, the cerebellum is gradually
removed, as in a pigeon, at first symptoms of weakness and slight
disturbance of movement are evident ; as more and more of the
cerebellum is removed great excitement appears, and the animal now
makes violent irregular movements, which, while not similar to convul-
sions, are yet free from all apparent purpose; while co-ordinated
movements are impossible vision and hearing, nevertheless, remain
intact.

Again, section of the middle cerebellar peduncle on one side almost
always gives rise to forced movements, the animal revolving rapidly on
its own longitudinal axis, and this disturbance is accompanied by
nystagmus, or oscillation of the eyeballs.

Injury or removal of the lateral lobe produces the same forced
movement as section of the middle peduncle.

In mammals the dangers are so great in operations on the
cerebellum that but few successes are on record. In operations of
extirpation performed on mammals which have proved successful, at
first the symptoms are those of irritation of the divided peduncles, and
consist in clonic contractions of the muscles of the fore limb, neck, and
back, while no sensory disturbances are perceptible. When recovery
from the operation is complete the symptoms dependent upon the
loss of the cerebellum then appear and consist mainly in disturbances
of equilibrium, and, while many muscular groups apparently maintain
their muscular tone intact, the power of associating various groups of
muscles to produce complex actions is lost. When the injurj^ to or
extirpation of the cerebellum has been but superficial the disturbances of
co-ordination soon pass off, while if the injury affects the lowest third
of the cerebellum the effects are permanent.

We may now return to the subject of the conduction of motor and
sensory impulses through the central nervous 53' stem, summarizing the
statements which have been made during the consideration of the func-
tions of the spinal cord, medulla oblongata, and brain (Fig, 359).

Sensory impulses originating in stimulation of the peripheral termi-
nations of afferent or sensory nerves pass into the cord through the
posterior roots of the spinal nerves, and the impulse passes either to the
cerebrum or cerebellum or both. After entering the cord the fibres of
the posterior roots diverge and carry the afferent impulses in different

828

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

directions : part of the fibres communicate with the direct cerebellar
tract and others with the posterior columns, thus furnishing through
the restiform body a direct path to the cerebellum. Other fibres of
these roots cross the middle line of the cord a little above where they

FIG. 359.— SCHEME OF THE BRAIN. (Landois.)

C C, cortex cerebri : C s, corpus striatum ; N 1, nucleus lenticularis ; T o, optic thalamus ; V, corpora
quadrigemina: P, pedunculus cerebri; H, tegmentum, and p, crusta; 1 1, corona radiata of the corpus
striatum : 22, of the lenticular nucleus ; 3 3, of the optic thalamus ; 4 4, of the corpora quadrigemina ; 5,
direct fibres to the cortex cerebri (Flechsig) ; 6 6, fibres from the corpora quadrigemina to the tegmentum ;
m, further course of these fibres : 8 8, fibres from the corpus striatum and lenticular nucleus to the crusta
of the pedunculus cerebri ; M, further course of these : 8 S, course of the sensory fibres ; R, transverse
section of the spinal cord ; v.W, anterior, and h.W, posterior roots ; a a, association system of fibres ; c c,
commissural fibres ; II, transverse section through the posterior pair of the corpora quadrigemina and the
pedunculi cerebri of man ; p, crusta of the peduncle; s, substantia niger; v, corpora quadrigemina with a
section of the aqueduct ; III, the same of the dog ; IV, of an ape ; V, of the guinea-pig.

enter, and some pass up in the lateral column in front of the pyramidal
tract, others into the posterior column, and still others ascend in the
gray matter on the opposite side of the cord. In the medulla the

FUNCTIONS OF THE BKAIN. 829

sensory impulses travel through the reticular formation, through the
posterior half of the pons, and enter the tegmentum of the crura cerebri,
pass under the corpora quadrigemina to enter the posterior third of the
posterior limb of the internal capsule, and thence radiate to the cortex
of the occipital and temporo-sphenoidal lobe. The path of the sensory
fibres, therefore, in some part of its course undergoes decussation, either
in the cord, the medulla, or the pons, so that the cortex of each cerebral
hemisphere receives sensory impulses which originate in impressions
made on the opposite side of the body : hence, a destructive lesion of the
cerebral cortex, internal capsule (posterior third), or of one-half of the
cord causes anaesthesia of the opposite side of the bod}- . The major part
of the crossing, however, occurs in the posterior commissure of the cord.
Voluntary motor impulses originate in the cells of the cortex in the
motor areas of the cerebrum, pass through the radiating fibres of the white
matter of the cerebral hemispheres, to converge into the internal capsule,
which is a collection of white nerve-fibres tying between the caudate
nucleus and optic thalamus internally and the lenticular nucleus external^.
They then enter the basis of the crura cerebri, occup}Ting its middle third,
the fibres for the face being next the middle line and those for the leg most
external, the fibres for the arm lying between the two ; they then pass to
the pons, the facial fibres here undergoing decussation (becoming con-
nected with the nuclei of the facial and hypoglossal nerves), the others
continuing on the same side to the anterior p3Tramids of the medulla
oblongata, where the major part crosses to the opposite side of the cord,
where they descend in the lateral column (the crossed pj-ramidal tract) ;
while the uncrossed fibres descend in the anterior columns of the same
side, ultimately, in all probabilit3r, crossing through the white commissure.
All the fibres of both pj^ramidal tracts terminate at different levels in the
m ult i polar cells of the anterior cornua of the gray matter of the cord,
and from each of these cells originates a single unbranched process which,
joining with similar fibres, passes out of the cord in the anterior roots of
the spinal nerves. The course of these motor and sensory fibres is like-
wise shown in Figs. 360 and 361. The cerebellum receives through its
inferior peduncle the afferent fibres derived from the lateral (direct cere-
bellar tract) and posterior columns of the cord, as well as from the gray
matter. The muscular sense is supposed to be conducted by means of
Clarke's column, together with the direct cerebellar columns, while tactile
sensations pass through Burdach's column. While, therefore, the sensa-
tions of pain are conducted directly to the cerebrum, tactile and muscular
sensations first reach the cerebellum and may from thence be conducted
to the cerebrum through the superior peduncle of the cerebellum, passing
into the posterior part of the corpora quadrigemina and then, perhaps,
forming connection with the caudate nucleus.

830

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

I.

FIG. 360.

FIGS. 360 AND 361.— DIAGRAMS OF THE COURSE OF THE NERVE-FIBRES IN THE
SUBSTANCE OF THE BRAIN AND SPINAL, CORD, AFTER AEBY. (Ranney.)

I, view of a transverse section; II, profile view; III, the nuclei of the medulla (partly after Erb).
The crosses of color corresponding to the lines upon which they are placed designate the point of section of
each tract as it passes through different levels (the crus and pons). C i, internal capsule, with radiating
fibres (in yellow), pyramidal fibres (red), and fibres going to the pons (in purple) ; P C, the crnra cerebri,
with the pyramidal fibres and th<
substantia niger, the fillet tract (i
blue) ; PC, the peduncles of

and the fibres going to the ganglia of the pons anteriorly, and posteriorly the
tract (in dotted lines), the fibres of the superior peduncle'of the cerebellum (in
of the cerebellum, showing the fibres going to the cerebrum, the pons, and the

FUNCTIONS OF THE BKAIN.
II.

831

FIG. 361.

medulla : P,pons varolii, with its ganglia on either side (in purple). In III, the nuclei of the cranial
nerve-roots are numbered to correspond with the nerves. Red is used for the motor nuclei, and blue for
the sensory nuclei. The trncfx in the cord are designated by the area similarly colored in the cross-section
of the cord beneath, c'. column of Tiirck; c, crossed pyramidal column; a, anterior horn; a', anterior
root-zone : e, direct cerebellar column ; b, posterior horn ; b'? column of Burdach ; d, column of Goll.
Higher up are seen b", the inferior peduncle of the cerebellum: df. the fillet or lemniscus tract; f, the
fibres connecting the ganglia of the pons with the cerebrum and cerebellum ; b'", the fibres of the superior
cerebellar peduncle; h. the caudo-lenticular and thalamo-cortical fibres ; i, the commissural fibres : Th,
optic thalamus: nc, nucleus caudatus: nl, nucleus lenticularis: gc. central convolutions.
In this diagram the course of b" seems to be in error in not undergoing a decussation.

832 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

VII. THE CKANIAL NERVES.

The cranial nerves, twelve in number on each side, arise from differ-
ent parts of the brain and pass through foramina in the base of the skull,
their number being given to them from the order in which they pass out
from the base of the brain ; other names are, also, given them from the
parts to which they are distributed or from their functions.

The cranial nerves are either pure sensory nerves, pure motor nerves,
or mixed nerves. The pure sensory nerv*es are the olfactory (1), optic
(2), and acoustic (8); the pure motor nerves are the oculo-motor (3), the
pathetic (4), and the abducens (6); the trifucial (5), or trigeminus, is a
mixed nerve, arising from a distinct motor and a distinct sensory root
comparable to the spinal nerves. Regarding the functions of the other
cranial nerves as determined by the functions of their roots, the pneu-
mogastric and glosso-pharyngeal are sensory nerves and the facial,
spinal-accessory, and hypoglossal nerves are motor. The trunks of these
last five nerves, however, contain both afferent and efferent fibres, the
pneumogastric receiving efferent fibres from the spinal-accessory and the
glosso-pharyngeal from the facial and motor branch of the trigeminus ;
while the facial receives afferent fibres from the trigeminus, pneumogas-
tric, and glosso-pharyngeal, and the hypoglossal sensory fibres from the
trigeminus, vagus, and three upper cervical nerves.

The functions of these nerves, although already considered under
different subjects, will be here recapitulated.

1. THE OLFACTORY NERVE. (See Sense of Smell.)

2. THE OPTIC NERVE. (See Sense of Vision.)

3. THE OCULO-MOTOR NERVE. — This nerve arises from the oculo-
motor nucleus under the aqueduct of Sylvius, the fibres of origin being
traced into the corpora quadrigemina and through the cerebral peduncle
into the lenticular nucleus. It contains three sets of fibres which are
distributed (1) to all the muscles of eyeball, with the exception of the
superior oblique and external rectus muscles and the levator palpebrse
muscles, (2) to the circular muscles of the pupil, and (3) to the ciliary
muscle. Hence, it is the path for voluntary motor impulses to all the
muscles of the eyeball, with the exception of the muscles above mentioned,
it is the efferent nerve for the reflex contraction of the pupil from
the action of light on the retina, and it contains the voluntary motor fibres
to the muscle of accommodation (ciliary muscle).

4. THE PATHETIC NERVE ( Trochlearis). — The fibres of the fourth
cranial nerve may be traced back from their apparent origin on the outer
side of the crus cerebri in front of the pons varolii, beneath the corpora
quadrigemina, to the valve of Yieussens (behind the fourth ventricle), on
the upper surface of which it is connected \>y commissural fibres with its

CBANIAL NERVES. 833

fellow from the opposite side. The gray nucleus from which it arises is
the posterior part of the oculo-motor nucleus in the floor of the aqueduct
of Sylvius ; it also is connected with a gray nucleus in the part of
the floor of the fourth ventricle near to the origin of the fifth nerve. It
is a purely motor nerve and is distributed to the superior oblique muscle
of the eyeball.

5. THE TEIFACIAL NERVE ( Trigeminus). — This is a mixed nerve,
arising, like the spinal nerves, .from a motor and sensory root, the latter
being supplied with a ganglion (ganglion of Gasser). The anterior,
smaller, motor root arises in the motor trigeminal nucleus in the floor of
the fourth ventricle, which is connected with the cortical motor centre on
the opposite side of the cerebrum ; there is also a descending motor
root from the corpora quadrigemina. The larger posterior sensory root
is connected with the sensory trigeminal nucleus at the level of the pons
with the gray matter of the posterior horns of the spinal cord as far as
the cervical vertebra, constituting the ascending root, and with the cere-
bellum through the crura cerebelli. This extensive origin of the sensory
fibres explains the great number of reflex relations of this nerve.

After passing through the cranium the trifacial nerve divides into
three divisions — the ophthalmic, superior maxillary, and inferior maxillary
branches.

The ophthalmic division, which receives fibres from the sympathetic
nerve, supplies sensory branches to the conjunctiva, lachrymal gland,
upper eyelid, brow, and root of nose, trophic fibres to the eyeball, and
vaso-motor fibres to the dura mater and lachn^mal gland. It is also the
afferent nerve for the reflex stimulation of the lachrymal secretion.

The superior maxillary division supplies sensory nerves to the dura
mater, to the angle of the eye, skin of temple and cheek, to the teeth in
the upper jaw, gums, periosteum, the lower eyelid, bridge and sides of
the nose and upper lip as far as the angle of the mouth, nasal chambers,
hard and soft palate. B}^ receiving motor fibres from the facial (super-
ficial petrosal branch to Meckel's ganglion) it gives motor nerves to the
soft palate and uvula, and, receiving vaso-motor fibres from the cervical
plexus, it is the vaso-motor nerve for this entire region.

The inferior maxillary division contains all the motor fibres of the
fifth nerve and supplies motor nerves to the muscles of mastication, the
tensor palati, and tensor tympani muscles. It also contains sensory fibres
which are distributed to the mucous membrane of the cheek, lower lip,
teeth, external auditory canal, and tip of tongue, the lingual branch being,
further, the special nerve of taste. This division also contains trophic
and vaso-motor fibres.

6. THE ABDUCENS NERVE. — The sixth cranial nerve arises from the
emenentia teres in the fourth ventricle in front of and partly from the

53

834 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

nucleus of the facial nerve, its nucleus being connected with the nucleus
of the third nerve on the opposite side. It is the motor nerve of the
external rectus muscle of the eye. In co-ordinate movements of the eyes
its action is involuntary. It receives fibres from the sympathetic nerve
in the neck.

7. THE FACIAL NERVE. — The facial nerve consists solely of efferent
fibres, and arises by two roots from the floor of the fourth ventricle, of
which the smaller, through the nerve of Wrisberg, forms a connection
with the auditory nerve. The origin of the facial, the facial nucleus, lies
behind the origin of the sixth nerve and is connected with the cerebrum
of the opposite side. The facial nerve is the motor nerve of the muscles
of the face, and hence is called the nerve of expression. It also supplies
motor branches to the stylo-hyoid, posterior belly of the digastric,
buccinator, stapedius, muscles of the external ear, platysma, and levator
palati. It is the secretory nerve of the parotid, and through the
chorda tympani of the submaxillary gland. It also contains vaso-
motor fibres for the tongue and side of the face and vaso-dilator fibres for
the submaxillary gland. Through its anastomoses with the trigeminu^
and vagus it perhaps contains afferent fibres.

8. THE AUDITORY NERVE. — (See Sense of Hearing.)

9. THE GLOSSO-PHARYNGEAL NERVE. — This nerve arises from the
glosso-pharyngeal nucleus deep in the medulla oblongata near the olivary
body, and is connected with the nucleus of the vagus. An ascending
root from the spinal cord unites with it and serves for the production of
spinal reflexes. It is supplied to the palatine and pharyngeal muscles,
but its motor function to these muscles is not absolutely established ;
possibly its motor fibres are derived from the facial. It is the nerve of
taste for the back of the tongue and pharynx, as well as being the nerve
of general sensation for these parts, the Eustachian tube and tympanum.

10. THE PNEUMOGASTRIC NERVE. — The vagus nerve has a common
nucleus with the ninth and eleventh nerves in the ala cinerea in the
lower half of the calamus scriptorius. It contains both afferent and
efferent fibres, the latter, probably, being derived from the spinal-acces-
sory. The efferent fibres are distributed to the muscles of the pharynx,
larynx, trachea, bronchi, oesophagus, stomach, and intestines. It is also
the inhibitory nerve of the heart, and contains vaso-motor fibres for the
lungs and trophic fibres for the lungs and heart. It is the sensory nerve
for the external ear, pharynx, oesophagus, stomach, and respiratory
passages. It contains afferent fibres, which may augment or inhibit
(laryngeal nerve) the respiratory centre, augment the cardio-inhibitory
centre, inhibit the medullary vaso-motor centre (depressor nerve) ;
through it afferent impressions may pass which produce the salivary or
inhibit the pancreatic secretions.

SYMPATHETIC NEKVOUS SYSTEM. 835

11. THE SPINAL-ACCESSORY NERVE. — This nerve arises by two
separate roots, one from the accessory nucleus of the medulla, which is
connected with the nucleus of the vagus, the other between the anterior
and posterior roots of the spinal nerves, as far down as the fifth cervical
nerve, its fibres in the cord having been traced to a nucleus on the outer
side of the anterior cornua. The anterior branch passes entirely into
the vagus and gives to it most of its motor fibres and all the cardio-
inhibitory fibres. The spinal-accessory is the motor nerve to the sterno-
mastoid and trapezius muscles ; it receives sensory branches from the
cervical nerves.

12. THE HYPOGLOSSAL NERVE. — The hypoglossal nerve arises from
two large-celled nuclei in the calamus scriptorius and one adjoining
small-celled nucleus, being connected both with the olivary body and
the brain. It is the motor nerve for the muscles of the tongue and most
of the hyoid muscles. It receives afferent fibres from the fifth and tenth
nerves and vaso-motor fibres from the sympathetic.

VIII. THE SYMPATHETIC NERVOUS SYSTEM.

The great sympathetic nerve, constituted by a ganglionic chain,
composed of a series of ganglia connected by nerve-fibres, is located on
each side of the vertebral column. Three different forms of structure
may be recognized in this portion of the nervous system — the ganglia,
the peripheral branches, and the connecting filaments. The two chains
situated on each side of the median line are connected by transverse
fibres, giving off numerous branches, which anastomose among themselves
and form plexuses (Fig. 362).

The sympathetic nerve may be divided into three divisions. In the
cephalic portion are found the ophthalmic, the spheno-palatine, the otic,
the submaxillary, and the sublingual, with the three cervical ganglia. In
the thorax and abdomen are found the other two divisions, which like-
wise consist of a number of ganglia united together by anastomosing
filaments.

The ganglia consist of gray substance united with nerve-tubules.

The fibres are non-medullated and connect the ganglia. Each spinal
nerve forms connections with adjacent sympathetic ganglia by means of
the rami communicantes, which are formed by nerve-fibres coming from
both the anterior and the posterior roots of the spinal nerves. In addi-
tion to the non-medullated fibres entering into the constitution of the great
sympathetic nerve are also fine nerve-tubules, which in their structure
are analogous to those of the cerebro-spinal axis. Such filaments are
much less abundant than the gray or non-medullated fibres of Remak.

The functions of the sympathetic nervous system have already been

836 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

given somewhat in detail in previous sections. The most important

function which it fulfills in the animal
economy is in the regulation of the
calibre of the blood-vessels. This has
already been described under the subject
of the Circulation.

The sympathetic likewise possesses a
number of independent functions either
in the way of inhibiting or stimulating
various processes which ordinarily are
controlled by the cerebro-spinal nerves.
As examples of such action may be men-
tioned the automatic ganglia of the heart,
the mesenteric plexuses of the intestine,
and the sympathetic plexuses of the
uterus, Fallopian tubes, and ureters. Of
course, here, also, the share of the sym-
pathetic in regulating the calibre of the
blood-vessels occupies an important
position.

The sympathetic nerve, also, in addi-
tion to such functions in which this nerve
may be regarded as an efferent nerve,
carrying impulses from the central ner-
vous system, likewise acts as an afferent
nerve ; as, for instance, in the conduction
of sensory impressions from the abdominal
viscera through the splanchnic nerves.
It has further been claimed that the
various ganglia of the sympathetic may
themselves act as reflex centres, but no
clear demonstration of this statement has
ever been reached. Its strongest advo-
cate was Claude Bernard, and he pointed
to the submaxillary ganglion as an illus-
tration of such an independent action on
the part of the sympathetic ganglia,
We have already discussed the grounds
for doubting the correctness of this
FIG. 362.— SYMPATHETIC NERVE OP statement.

mmtL^s-.c, Probably the main function of the

0'1 " ganglia of the sympathetic nervous

system is to modify impulses -coming from the central nervous

GENEKAL AND SPECIAL SENSIBILITY. 837

system, through the cerebro-spinal nerves, so as to inhibit or modify
the function of certain organs. As an illustration of this may be men-
tioned the action of the sympathetic upon the pupil. According to
Budge, the fibres which are concerned in producing dilatation of the
pupil arise from the spinal cord and run from the upper two dorsal and
the lowest two cervical nerves into the cervical sympathetic, which
conveys them to the head. The influence of the sympathetic in
governing the movements of the iris will be given more in detail in the
consideration of the e}Te.

Among other branches arising from the cervical part of the sym-
pathetic are found motor branches going partly to the external rectus
muscle of the eye. vaso-motor branches to the ear, the side of the face,
the conjunctiva, the iris, the choroid, and to the vessels of this portion
of the alimentary and respiratory tract. Secretory and vaso-motor fibres
are distributed to the salivary glands and to the sweat-glands of the
integument ; while, according to certain authorities, the lachrymal glands
receive sympathetic secretory fibres from this portion of the sympathetic.

Of the thoracic and abdominal sections of the sympathetic the car-
diac plexus, which receives accelerator fibres for the heart, occupies the
most important position. The influence of the coeliac plexus of the
sympathetic on the heart has already been given. Of the abdominal
sympathetic, the coeliac and mesenteric plexuses and the splanchnic
nerves are the most important. They also have been already described.

It is thus seen that the fibres of the sympathetic nervous system
act as conductors of both afferent and efferent impressions. Impressions
traveling from the periphery to the centre through the sympathetic
nerve do not produce an impression upon the sensorium. In other
words, the brain is not capable of taking cognizance of afferent im-
pulses traveling through the sympathetic. Nor, on the other hand, can
voluntary motor impulses pass through this nerve.

IX. GENERAL AND SPECIAL SENSIBILITY.

Sensation, or general sensibility, is that function of the brain by
which it perceives or becomes conscious of impressions which are made
upon the surface of the body or upon the nerves running from the
peripher}* to the nerve-centres. Ity perception is meant that faculty by
which sensations are referred to certain external causes. It is important
to understand that all sensations take place, not at the point of contact
of the irritant with the periphery, but in the brain itself, and we have
evidence of this in the fact that if the brain be in a state of torpor no
sensation occurs. Again, if a ligature be passed around an afferent nerve
at some point between its origin on the periphery and its termination in
the nerve-centre no sensation occurs, no matter how severe be the

838 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

stimulation of its peripheral ends ; or, if the nerve-trunk be divided, the
most powerful irritants may be applied to the peripheral area in which
that nerve is distributed without calling forth sensation.

When an impression is made upon a sentient surface, that impres-
sion so changes the molecular equilibrium in the terminal filaments as to
give rise to afferent impressions, which travel along the nerve-trunk to
reach the centres of the brain, and it is the final change which occurs
within the nerve-cells which is to be spoken of as sensation, and it is
only this latter change of which the brain is cognizant.

Two kinds of sensibility may be recognized, — general and special
sensibility. Nerves of general and of special sense are concerned in the
perception of these two kinds of sensation. By the term special sensi-
bility is understood that sensation which arises from an impression of a
peculiar kind and special character, which is capable of affecting only
one kind of nerve ; or, rather, which, when applied to one kind of nerve,
will invariably produce a sensation peculiar to that nerve. Thus, for
example, a stimulus applied to the terminal filaments of the nerve of
hearing will invariably be recognized as an auditoiy sensation ; so a stim-
ulus of the optic nerve, whether mechanical, electrical, or chemical, will
be recognized as a visual sensation.

By general sensibility is meant the appreciation of sensations arising
from impressions of a general character applied to the general tegumen-
tary surface of the body. Under this head are to be included the tactile
sense, the sense of heat and cold, and the muscular sense. The special
sensations are the sensations of smell, taste, sight, and audition.

Certain conditions are necessary to sensibility. First, there must
be a certain degree of vascularity. Unless the part be well supplied with
blood it cannot be endowed with either general or special sensibility.
An illustration of this, may be seen on tying any large arterj^ ; the part to
which it is supplied becomes almost instantly numb ; the blood is cut off',
the vascularity diminishes, and the irritability of the receptive filaments
of the nerve becomes depressed. So, also, cold, as is well known,
reduces sensibility by diminishing the blood-supply of the part.

Secondly, mere vascularity is not, however, sufficient ; there must,
likewise, be continuity with the nerve-trunk. Unless the afferent fibres
be in such continuity with the centre no sensibility, either general or
special, may take place. While, finally, the centre itself must be in a
state of integrity to recognize or convert into perceptions the
impressions brought to it through afferent nerves.

When impressions have been frequently repeated upon nerves of
general or special sensibility the sensations to which they ordinarily ad-
minister become blunted. An illustration of this may readily be drawn
from the nerves of special sense. Sights or sounds constantly present

GENERAL AND SPECIAL SENSIBILITY. 839

to the eye or ear after a while fail to impress them. So, also, odors
may cease to be recognized.

This point, however, must not be misunderstood. If continued
attention be directed to sensations, instead of being blunted they are
exalted. Of this we have numerous examples in the capability of the
senses to attain a high degree of acuteness of perception from education.

When an impression has been made upon a nerve of special sensi-
bility, or even upon one of general sensibility, that impression always
remains a certain length of time after the irritating cause has been
removed ; thus, when an ignited stick is rapidly moved before the eye
the impression made upon the retina in each successive position of the
burning point remains sufficiently long to appear continuous with that
made in the next situation, and thus the appearance of a line of light
is obtained. So in the case of the ear; it is well recognized that
musical tones are produced by a regular succession of vibrations. When
these vibrations succeed each other more frequently than sixteen times
in a second they give rise to a continuous tone. When they occur less
frequently than sixteen times in a second there is produced a succession
of impressions, each one terminating before the other begins. No nerve
of special sense can take upon itself the function of any other ; thus the
auditory nerve is incapable of transmitting visual impressions, nor can
the olfactory nerve serve for audition. In the case of the nerves of
general sensibilit}^, the incapability of interchange of function cannot
be so positively denied, since we know that a motor nerve may so unite
with a sensory nerve as to conduct afferent impressions ; or in the case
of the sense of taste, which is one of the lowest of the special senses,
we shall find that there other than the special nerves of taste may,
perhaps, serve for conducting gustatory impressions.

While the nerves of special sense are especially adapted for receiving
certain impressions, they may yet be thrown into a condition of irritability
by various stimuli, but each of these stimuli will produce the impression
characteristic of the nerve over which it passes.

Sensations have been divided into two classes, external and internal,
or objective and subjective. External impressions are those which arise
from impressions made upon the external surface of the body. By
internal impressions are meant those which arise from impressions made
upon the internal recesses of the body. All sensations, however, originate
and depend upon changes taking place in the gray matter of the brain
itself, and, as a consequence, there is no sensation (which in general
terms is produced by an impression made upon the peripheral termi-
nation of the nerve) which may not to a certain degree be produced
by an impression made upon the nerve in its course or at the
point in the sensorium where the nerve terminates. To this latter

840 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

class of sensations the term subjective is given in contra-distinction
to objective sensations, which result from impressions made upon
the termination of the nerve. It is a curious fact with regard to
internal or subjective sensations that those which arise from impressions
made upon a nerve in its course are always referred to the peripheral
termination of the nerve on the surface of the body. Thus, if the ulnar
nerve is compressed at the elbow-joint the impression is not felt at
the point of stimulation, but at the extremity of the fingers. The most
common cause of subjective sensations is to be found in changes of the
blood-supply of the part; thus, for example, when congestion takes
place about the termination of the optic nerve there are flashes of light
about the eye; if about the auditory nerve, ringing sounds in the ear.

By the term sensory organs is meant those parts of the body by
which, through the nerves of sense, the brain becomes cognizant of its
surroundings.

By means of the special senses the preservation of both the indi-
vidual and of the species is rendered possible. By means of the special
senses animals are rendered capable of seeking and recognizing their
food and are enabled to avoid danger, and, in a way to be indicated
directly, are led to the accomplishment of the act of reproduction.

The more restricted the peripheral portion of any nerve of special
sense the more delicate is the structure of that terminal organ. In the
case of the sensations of taste and of smell the nerves distribute them-
selves over a moist mucous membrane which has other functions to fulfill
in addition to acting as the peripheral terminations of nerves of special
sense. On the other hand, in the case of the nerves of sight and hearing,
the terminations are found in structures whose sole function is found in
ministering to these special sensations, and in them we find the highest
degree of complexity of the end apparatuses.

It is, of course, not possible to decide whether or not in the case of
the lower animals impressions made upon the nerves of sense affect the
brain in the same manner as in man, since in these animals the expression
of sensations is greatly restricted : but from the great similarity of struc-
ture of the organs of sense in man and in the higher mammals it may
be concluded that impressions are appreciated by these animals in the
same manner as in man. As a general rule it may be stated that the
senses of the domestic animals are quite as highly developed as in man,
and in certain instances greatly exceed in acuteness the corresponding
sense in man. Usually, in any special class of animals we find one of
the special senses developed out of proportion to the others. Domesti-
cation has the usual result of reducing the acuteness of the special
senses, since the principal cause for their exercise in the protection of
the animal is no longer present.

SENSE OF SMELL. 841

A. THE SENSE OF SMELL.

By the sense of smell animals are to a certain extent facilitated in
their search for food, in the avoidance of danger, and in seeking the
opposite sex.

By the sense of smell is meant the sensation that is created when
certain substances in a gaseous form are inhaled by the nostrils. It will be
shown that the sense of smell is only excited under certain definite condi-
tions and only when the odorous body comes directly in contact with the
organs of sense. Here, as in the case of taste, the sensation is locally
excited, probably through some chemical influence, and the result is an
entirely specific sensation. It is, therefore, unwarrantable to include
the sense of smell among the other senses, since it is quite as different
from the sense of touch or of taste as from sight or hearing. The action
of the organ of smell is, therefore, due to a special nerve, the olfactory
nerve, the first cranial pair, which differs from the others in origin r
position, extension, and mode of distribution.

Under the name of olfactory nerves are usually described the masses
of gray matter which arise from the anterior portion of the frontal lober
and in many animals exist in such bulk as to project beyond the frontal
lobes. From the structure of these masses, as well as from comparative
anatomy and from their developmental history, it is evident that these
parts are not to be regarded as identical with the peripheral branches of
other nerves of sense, or the cranial nerves, but are to be regarded as
distinct parts of the brain. In many animals the olfactory lobes are
hollow, their ventricles communicating with the other ventricles of the
brain. As olfactory nerves only are to be described the fibres which
originate from these olfactory bulbs and pass through the cribriform
plate of the ethmoid bone to be distributed to the olfactory portion of
the nasal cavities.

Fibres from the olfactory lobes have been traced in three bundles
backward into the cerebral hemispheres, and the centre for smell in the
cortex of the brain has been located in the tip of the uncinate gyrus on
the inner surface of the cerebral hemisphere. Of these three roots, the
inner one is small, the middle one is large and curves inward to
the anterior commissure around the head of the caudate nucleus and
decussates through the anterior commissure to the extremity of the
opposite temporo-sphenoidal lobe. The outer root passes transversely
into the pyriform lobe and ends in the anterior extremity of the optic
thalamus.

Microscopic examination of the olfactory fibres, by which are meant
the fibres passing through the cribriform plate, shows that they are thin,
transparent fibres, included in a nucleated connective-tissue sheath.

842

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

Examination of the structure of the membrane lining the nasal cavities
shows marked points of distinction between the region to which the
olfactory fibres have been traced and other portions of the nasal cham-
bers. The area of distribution of the olfactory nerve is termed the
regio olfactoria, and in the main embraces the upper part of the septum
and the upper part of the middle turbinated bone. The remainder of
the nasal cavity is called the regio respiratoria. The olfactory region
has a thicker mucous membrane than the respiratory part. It is covered
by a single layer of cylindrical epithelial cells, which contain yellow
pigment in sufficiently large quantity to serve even by the naked eye to
distinguish this part of the nose from the respiratory passages. The
latter division of the nasal cavit}^ is covered by ciliated epithelium and
contains tubular glands and serous, acinous glands. In the olfactory
region are found between the ordinary BB

cylindrical epithelium cells peculiar

FIG. 363.— DIAGRAM OF THE STRUCTURE
OP THE OLFACTORY REGION, AFTER
EXNER. (Brucke.)

C C, the terminal net-work of the olfactory nerve in
which both the so-called olfactory cells (A) and cylin-
drical cells are imbedded.

FIG. 364.— DIAGRAM ILLUSTRATING THE
MODE OF CONNECTION OF THE OL-
FACTORY AND CYLINDRICAL CELLS
WITH THE TERMINAL NET-WORK OF
THE OLFACTORY NERVE. (Brucke.)

B B, cylindrical epithelial cells ; A, olfactory cell ;
D, protoplasmic mesh-work in which the olfactory nerve
terminates.

spindle-shaped cells with a large nucleus, containing nucleoli, and sending
up between the cylindrical cells a narrow projection which in various
animals terminates in delicate projecting filaments. These peculiar
olfactory cells are said to form a direct communication with the fibres
of the olfactory nerve.

It is probable, according to Exner, that these cells do not
directly unite with the olfactory fibres, but through the mediation of a
net-work of protoplasmic prolongations of these cells lying below their
bases. Examination has further shown that not only these long so-called

SENSE OF SMELL. 843

olfactory cells form communication with this net-work, but, also, processes
may be traced into it from the so-called cylindrical cells, and, this being
the fact, it would seem unwarrantable now to draw a sharp distinction
between the functions of these two classes of cells (Figs. 363 and 364).

In the herbivora the convolutions of the inferior turbinated plate
are, as a rule, simpler than in the carnivora, but yet more complex than
in man. In the ruminants and solipedes the inferior turbinated bone
divides into two plates which are rolled around each other in opposite
directions. In most of the carnivora it is also similarly convoluted, but
the divisions are much more frequent and the spaces between the
different leaves narrow. In the case of the inferior turbinated bone the
higher degree of complication does not point, as in the case of the
superior turbinated bones, to a higher degree of development of the
sense of smell, but in animals where this condition is present it is to be
regarded as a means of mechanical protection against the entrance of
foreign bodies into the nose.

The different cavities in connection with the nasal chambers, such
as the frontal, sphenoidal, and maxillary sinuses, have no connection
with the sense of smell, but are to be regarded simply as extensions of
the respiratory parts of the nasal chambers; for their mucous membrane
is identical with that lining this portion of the nose and contains no
terminal filaments of the olfactory nerve. This also applies to the case
of the ethmoidal cells ; all these cavities, therefore, are simply concerned
in warming the inspired air.

Jacobson's organ, on the other hand, is to be regarded as an acces-
sory organ of olfaction. It is present in all mammals, and consists of
two narrow tubes protected by cartilage and placed in the lower and
anterior part of the nasal septum. Each tube is closed behind, but an-
terior^ opens into the nasal chamber by a furrow, the naso-palatine
canal. The wall next the middle line is connected with the olfactory
epithelium, which is in direct communication with the terminal filaments
of the olfactory nerve. The outer wall is covered with columnar, ciliated
epithelium.

The nose in mammals is generally but slightly detached from the
bones of the face. In solipedes and ruminants the nares, which are pos-
sessed of a considerable degree of mobility, project but slightly, while in
various members of the hog tribe the nose is prolonged anteriorly,
forming the snout or muzzle. In the elephant and in the tapir this pro-
longation acquires its maximum development. In the cetaceans and
other aquatic mammals in which the olfactory nerve is absent, as in
the dolphin, or where it is only faintly developed, the nasal chambers
lose all significance as organs of olfaction and simply fulfill a respiratory
function.

844 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

In birds the sense of olfaction is less strongly developed than in
mammals, its place probably being taken by the higher degree of devel-
opment of the sense of sight. As a consequence their nasal chambers
are simple ; at the most three turbinated plates (anterior, middle, and
posterior) are present, and these are simple in form. The olfactory nerve
is distributed alone to the posterior turbinated bone. The external
nares show great variations in shape, while the posterior nares commu-
nicate b}r a small, slit-like opening with the aural cavity. The olfactory
lobes are most highly developed in birds of prey and in palmipedes who
feed on living fish.

In amphibia the nasal chambers are even less complicated than is
the case in birds. The turbinated plates are rudimentary and usually
reduced to one in number. In reptiles generally the nasal chambers are
limited in extent and are formed of two canals opening externally, and
internally communicating with the mouth by two canals passing through
the palatine arch.

In the fish the olfactory apparatus is not so arranged as to be trav-
ersed by a current of air. In them the olfactory organ consists of two
small cavities terminating in a cul-de-sac and opening externally by two
nostrils. The bottom of these sacs is generally thrown up into folds,
arranged as radii from a central point to which fibres coming from the
olfactory lobe have been traced. Water carrying odors to this olfac-
tory membrane can affect it but slightly, unless we can conclude that
their method of olfaction differs entirely from what holds in air-breathing
animals ; for we find that if in the latter the nasal chambers be filled
with liquid all impression on the sense of smell is impossible.

In the invertebrates no organ of smell can be recognized in the ar-
ticulates or in the mollusks. It is, nevertheless, certain that in some of
the invertebrates, and particularly in insects, the sense of smell is highly
developed. It has been supposed that here the antennae or tentacula are
the seat of the sense of smell.

For any substance to be odorous it must possess two properties. In
the first place, it must be volatile — that is, be capable of passing into the
atmosphere; and, in the second place, it must to a certain extent be
soluble in water, that it may pass by imbibition into the fluid which
invariably moistens the olfactory membrane. Odorous substances in-
haled with the air are brought into contact with the olfactory mucous
membrane and act on the terminal cells of the olfactory nerve and not
directly upon the nerve-fibres; for we may conclude that just as neither
the optic nerve-fibres are affected by waves of light, nor the auditory
nerve-fibres by waves of sound, the fibres of the olfactory nerve are
equally insensitive to odors. Smell consists, therefore, in the production
of some change, probably of a chemical nature, in the terminal apparatus

SENSE OF SMELL. 845

in the mucous membrane of the olfactory portion of the nose. Changes
there excited are conducted through the nerve-filaments to the brain, and
only then become recognized as the sensation of smell.

It would appear that the sensation of smell is only developed on the
first contact of the odorous particles with the olfactory nerve, and, as a
consequence, in order to obtain an exact perception of delicate odors a
number of rapid inspirations are taken, the mouth being kept closed.
In this way the air is rarified in the nasal chambers and odorous parti-
cles stream over the olfactory region. Consequently, if we hold our
breath the sensation of smell ceases, even if we are in an atmosphere
impregnated with odorous substances. It is further stated that odorous
substances taken into the mouth and then expired through the posterior
nares produce no sensation of smell, possibly from the fact that in this
direction of the atmospheric current the particles are not brought into
contact with the olfactory region ; while, when bodies are inhaled with
the air through the nostrils, the current of entering air is broken up by
striking against the inferior turbinated bone, and part of the current
passes directly through the respiratory passages and part upward
through the olfactory region.

The reason why odorous liquids placed in the nostrils are incapable
of affecting the sense of smell is perhaps to be explained by the action
of the fluid upon the olfactory cells, which perhaps possess a high degree
of imbibition and are paralyzed when brought in contact with large
quantities of fluid. Even water alone, as we know, will temporarily
arrest the sense of smell, and if the nostrils be filled with water some
time will elapse after the removal of the liquid before the sense of smell
is regained.

The amount of substance which may be recognized by the sense of
smell is extremely small. Valentin has calculated that ^ro.irov.iHro of a
grain of musk may be recognized by the sense of smell. Even this is,
perhaps, an inside estimate, for a grain of musk will for years give
its characteristic odor to the atmosphere of a room, and the most deli-
cate balance will at the end of this time fail to recognize any reduction
in weight, and yet we are compelled to suppose that the odor has been
given to the atmosphere through the volatilizing of the particles of the
musk.

As regards the sense of smell, all attempts to classify the impres-
sions which may be made upon it entirely fail. The only distinction
which can be made is into what are termed pleasant and disagreeable
odors, and yet, of course, these are simply relative terms. We may say
that a substance has the odor of turpentine or of roses, but this, of
course, gives us no means of classifying the causes of the sensations
produced.

846

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The intensity of the sense of sinell depends, first, upon the size of
the olfactory surface, since we find that in animals in which the sense
of smell is most acute the turbinated bones of the olfactory region are
most complicated ; secondly, on the concentration of the odorous sub-
stance in the air; and, thirdly, on the frequency with which the columns
of air containing the odorous particles are conducted to the olfactory
organs ; hence sniffing tends to increase the intensity of odors.

The development of the sense of smell is always more highly marked
in animals than in man and plays an important part in their organization.
Game-dogs, as is well known, will recognize the odor from game-birds
at several hundred yards, but even this falls below the acuteness of smell
possessed by various animals which are able to scent the presence of
man at a distance of a mile or more.

B. THE SENSE OF SIGHT.

Vision is the perception of the sensation caused by the impression
of a ray of light upon the retina, and in all animals depends upon the
special sensitiveness of the optic nerve-filaments to the vibration of
luminous rays. Animals may, nevertheless, be sensible of light without
special organs of vision, and may even be capable of giving evidence of
the impression of such light ; thus, the hydra, although it has no distinct

organs of vision, will move around
from side to side of the vessel in
which it is placed until it has
reached that on which the sun is
shining and will turn itself toward
the seat of light.

In its simplest form the visual
apparatus is represented by a col-
lection of pigment-cells in the
outer coverings of the body which
are in connection with the ter-
mination of afferent nerves. The

FIG. 365.— HEAD AND COMPOUND EYES OF ^io-mPTit ah<inrh<a tho rnv« nf lio-hf
THE BEE. (Carpenter.) P'B111 rays Hgni,

The ocelli are in situ on the one side (A) and displaced on the and in that function SOme DrOCCSS,
other (B) ; A A A, stemmata ; B B, antennae.

probably of a chemical nature,

is excited and the sensitive nerves are stimulated. In the medusae,
as the jelly-fish, and at the ends of the rays of the star-fish and other
echinoderms similar collections of pigment are found, but as the
lens is wanting no distinct image can be formed, and, consequently,
in such cases the distinction between light and darkness is all that
is possible. In some of the cephalopod mollusks two simple eyes,
consisting of a globular lens with transparent media analogous to the

SENSE OF SIGHT. 847

cornea of higher animals, are found at the tips of the tentacula. Evi-
dences of a choroid and of a nervous net-work representing the retina
are also found. Such organs are termed ocelli. It is, therefore, seen
that two classes of visual apparatus may be recognized, the simple and
the compound ; the former consisting simply of a mass of pigment in
connection with the nerve-fibres, and the latter of a cornea and of other
accessory organs. In many insects and in some crustaceans both
species of eyes are found. The simple eyes may be three or more in
number and are most usually placed on the summit of the head. In the
articulates, such as insects and crustaceans, are found eyes of a special
type of construction — what may be termed composite eyes — consisting of
a collection of a considerable number of diverging radiating tubes or
cones, terminating on the surface in the shape of polygonal opacities and
inclosing in their interior a fluid analogous to the vitreous body, while
their deep extremity is continuous with the nerve-filament and their

FIG. 366.— SECTION OF THE EYE OF THE COCKCHAFER (Melolontha

vulgaris). ( Carpenter. )

A. A, facets of the cornea; B, transparent pyramids surrounded with pigment; C, fibres of the optic nerve;
D, trunk of the optic nerve. The same description applies to B, which is a portion of the eye more highly magnified.

interior is lined with pigment. Each one of these two eyes, which are
frequently but a few millimeters in diameter, often incloses from ten to
twenty thousand of these little tubes ; while the inclosed membrane,
which is analogous to the choroid, is impregnated with pigment over the
greater part of its extent, except at the centre, where a transparent
opening is present through which the light passes (Fig. 865). These e}7es
are capable of forming distinct images, but each of the diverging cones,
disposed like the rays of a segment of a sphere (Fig. 366), is only
capable of transmitting the ray of light which coincides with its long
axis; all the other rays, striking more or less obliquely on the internal
walls lined, with pigment, are absorbed; as a consequence, in such an
eye the image is formed by the co-ordination of the rays coming from
corresponding isolated points of the object. While, nevertheless, objects
may be clearly appreciated by such an eye, a large quantity of light

848 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

must be lost by absorption by the pigment, and, as a consequence,
the clearness of the image must be sacrificed. The field of vision in
such an e3Te will, of course, depend upon the segment of the sphere
represented by the termination of the cones, since, although the eye is
convex, no movement in an orbit is possible. So, again, accommodation
is not required in such an eye, since all the rays of light appreciated by
each cone must be coincident with the axis of each cone. Therefore,
such a compound eye may be regarded simply as a combination of an
immense number of ocelli compressed together and taking an angular
form, in insects six-sided and in crustaceans four-sided. The color of
the pigment in such eyes varies, being white, yellow, red, green, purple,

FIG. 367.— DIAGRAM OP A HORIZONTAL SECTION THROUGH THE HUMAN

EYE. (Yeo.)

1, cornea; 2, sclerotic; 3, choroid ; 4, ciliary processes ; 5, suspensory ligament of lens; 6, so-called
posterior chamber between the iris and the lens : 7, iris ; 8, optic nerve ; 8', entrance of central artery of
retina; 8", central depression of retina, or yellow spot; 9, anterior limit of retina; 10, hyaline mem-
brane; 11, aqueous chamber; 12, crystalline lens; 13, vitreous humor; 14, circular venous sinus which
lies around the cornea ; a a, antero-posterior, and b b, transverse axes of bulb.

or black. Each cornea, or the termination of each ocellus or tube, is
convex on one side and convex or flat on the other, so that, to a certain
extent, it takes the part of a lens.

Among the invertebrates the eyes of the cuttle-fish are the largest
and most perfect, resembling the eyes of higher animals in possessing a
crystalline lens and a chamber behind filled with vitreous humor.

In the vertebrates the eye is formed by a folding in of the external
integument to form a lens and an outgrowth from the optic vesicles of
the brain to form a sentient surface. The eyeball in vertebrates consists
of an external white, spherical case, or sclerotic coat, which serves to

SENSE OF SIGHT. 849

protect the eye from external injury, and, although not transparent, is to
a certain extent translucent. Anteriorly it passes into the cornea, which,
though equally thick, is absolutely transparent. The latter membrane
rises in thickness in front of the eye like a watch-glass. In other words,
the radius of curvature of the cornea is that of a smaller circle than that
of the body of the eye. The shape of the eye is preserved by two fluids,
the aqueous humor filling the cavity behind the cornea, and the denser,
jelly-like vitreous humor occupying the larger posterior cavity (Fig. 367).

Between these two chambers is a diaphragm the size of whose aper-
ture is capable of being modified — the iris. Behind the iris lies the cr}Ts-
talline lens and between the vitreous humor and the sclerotic is found
the choroid membrane, covered with dark pigment-cells, which are
arranged like a mosaic on its inner surface. Between the choroid and
the vitreous humor is found the retina, which is the transparent expan-
sion, in a number of layers, of the terminal filaments of the optic nerve.

The most sensitive part of its surface is that which lies in contact
with the black pigment. Externally, in most vertebrates, the eyes are
protected by eyelids, which are, however, absent in fishes ; in them, the
eyes being continually bathed in fluid, the lachrymal apparatus is like-
wise absent. Their eyes are, as a rule, but slightly mobile, the crystal-
line lens is spherical, the cornea almost flat, and the iris but slightly
contractile. In most fishes the eyes are placed so far back that the fields
of vision are distinct.

In reptiles three eyelids are often found, although in some, as in the
serpents, they are entirely wanting. In the latter case, as in fishes, the
ocular globe is then covered only by the transparent conjunctiva. In
many reptiles there is often a rudiment of the lachrymal apparatus. The
crystalline lens varies greatly in form.

In birds the sense of sight is especially developed. Those which are
in the custom of flying at great heights in the atmosphere appear to be
able to distinguish with the greatest exactness small bodies on the sur-
face of the earth. In birds, at the centre of the ocular globe and pos-
terior to the cr}'stalline lens, is found a peculiar projection of the
choroid, impregnated with the choroid pigment and covered by an exten-
sion of the retina, which is termed the pectin. It is not known in what
way this structure serves to assist vision. Perhaps it contains muscular
fibres which act upon the crystalline lens and aid in accommodation.

In mammals the ocular apparatus takes about the same form as is
seen in the human species, there scarcely being any difference except in
the relative volume of the eyeball and the pupillary opening, and in the
fact that sometimes the shape of the eyeball is elongated rather than
spherical. Animals which pass the greater part of their time under
ground are remarkable for the smallness of their eyeballs. In others

54

850

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

which are aquatic, such as the cetaceans, the crystalline lens is almost as
spherical as in the fish, and in them, also, the difference in the refrangi-
bility of the different media of the eye is much less than in animals living
in the air.

In many mammals, at the base of the eye is found a collection of
brilliant pigment-cells, which reflect the rays of light falling upon the
retina and so give to these eyes when seen in semi-darkness a peculiar,
luminous appearance. This tapetum is yellow in the ox, reddish yellow
in the cat, and blue in the horse.

In mammals the eyes are placed in orbits whose direction is more
or less inclined toward the sides. Only in man, apes, and nocturnal
birds of prey are the orbits so arranged that vision may be directed
forward simultaneously on the two sides.

The Iachr3rmal apparatus of mammals is composed of a single or
double lachiymal gland placed at the external angle of the orbit. Gar-
ni vora, rodents, pachyderms, and
some ruminants have in addition in
the internal angle of the orbital cav-
ity the so-called gland of Harder,

FIG. 368.— FORMATION OF AN IMAGE BY
REFLECTION. ( Ganot. )

The rays from the object A B are reflected by the
mirror N M so as to make their angle of reflection equal
to their angle of incidence; if a perpendicular, A D, is
let fall from the point, A, and one, B C, from the
point, B, and the reflected rays prolonged until they
meet these perpendiculars, the image is apparently
formed behind the mirror at a distance equal to the
actual distance of the object in front of the mirror.

FIG. 369.— DIAGRAM ILLUSTRATING RE-
FRACTION OF LIGHT. (Ganot.)

The incident ray, S O, on striking the surface, n in,
is bent in the direction OH. SAO being the angle of
incidence, HOB the angle of refraction.

which furnishes a thick, whitish secretion, which often accumulates at
the corresponding angle of the eyelids. Rudiments of this gland are
also found in solipedes. The tears are collected by the lachrymal points,
which conduct them through the lachrymal duct and nasal canal to the
nasal cavities.. In certain rodents, the hares in particular, the lachrymal
canals are replaced by fissures which establish communication between
the conjnnctival surface and the nasal fossae.

In the study of the appreciation of the impression of a ray of light
upon the retina and the formation of an image a comprehension of the
laws of light is essential. The eye is furnished with certain mechanisms
by which an image is formed somewhat in the same manner as in a
camera obscura. Such mechanisms are what are termed the dioptric
mechanisms of the eye. Rays of light striking the 'retina give rise to

SENSE OF SIGHT.

851

sensations, and we shall, therefore, have then to consider the mode of
production of the visual sensations.

1. The Dioptric Mechanisms of the Eye. — When rays of light
proceed from a luminous body they always pass in straight lines, form-
ing in their divergence a cone, the apex of which is the luminous body
and the base such a plane as may intercept them. So long as the medium
is of uniform density rays pass in straight lines, and if they come in
contact with an opaque, polished surface they will be reflected, and the
angle of reflection is equal to the angle of incidence and lies in the same
plane (Fig. 368). If the rays fall perpendicularly to this opaque surface
they will be reflected in the same straight line in which they impinged.
If the raj7s fall upon a translucent surface as they emerge from the
opposite side they will be found to be bent from their original course

FIG. 370.— DIAGRAM ILLUSTRATING REFRACTION. (Landois.)

If Sj D represent a ray of light passing through water, when it emerges at D into the atmosphere it will
be bent away from the perpendicular G D and lie in the direction S D.

through the medium, and though they pass out of the medium in a line
parallel with that in which they entered, yet they are not coincident with
it so long as the medium is bounded by parallel surfaces (Fig. 369). If
these rays pass from a rarer to a denser medium they are bent toward
the perpendicular at the point of incidence. If they pass from a denser
to a rarer medium tliey are refracted from the perpendicular (Fig. 370).
Thus, when an oblique luminous ray passes through a piece of plate-
glass its course from the atmosphere is from a rarer to a denser medium,
hence it is, in the glass, bent toward the perpendicular; but in passing
out it passes from a denser to a rarer medium, hence it is refracted from
f the perpendicular, and as the two surfaces are parallel the amount of
refraction toward the perpendicular is equal to the amount of refrac-
tion from the perpendicular ; therefore the course of the emergent ray is
parallel to the course of the entering ray, although not coincident with it.

852

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

By the term " refractive index " is meant the number which shows
how many times the sine of the angle of incidence (a 6, in Fig. 370,
regarding S D as the incident ray) is greater than the sine of the angle
of refraction (c d), it being always assumed that in comparing the
refractive indices of two media the incident ray passes from air into the
medium. On passing from air into water the ray is so refracted that the
sine of the angle of incidence is to the sine of the angle of refraction as
4:3; with glass, the proportion is 3 : 2.

Fro. 371.— DIAGRAM ILLUSTRATING THE COMPOSITION OF A CONVEX LENS OF
A NUMBER OF PLANE SURFACES. (Ganot.)

An illustration, first suggested by Professor Henry Morton, of Hoboken,
serves greatly to simplify the conception of refraction. It has been stated that in
passing from a rarer to a denser medium the luminous ray is bent toward the
perpendicular. If a line of men, as of soldiers, be marching obliquely toward the
edge of a plowed field, the men first reaching tbe uneven ground will experience
difficulty in walking over the rough surface and their end of the line will move
more slowly than the end still remaining on the level ground, and, as a conse-
quence, the entire direction of the line of men will be changed. On the other

FIG. 372.— DIAGRAM SHOWING REFRACTION BY A DOUBLE CONVEX LENS.

(Ganot.)

The incident ray, L B, is refracted at the points of incidence. B, and emergence, D, toward the axis,
M N A, which it cuts at F.

hand, as they reach the opposite side of the plowed surface the end of the line
which first entered will be the first to emerge, and, as a consequence, progress
now being easier, that end of the line will travel faster than the end still remain-
ing on the plowed ground, and, therefore, the line of men will now be bent from
ihe perpendicular; and as the entire line emerges the line of progress will be
parallel with the original line, but will not be coincident with it.

SENSE OF SIGHT. 853

Refraction takes place not only through media with plane surfaces,
but likewise through media bounded by curved surfaces, for the circum-
ference of a circle may be supposed to be made up of a number of infinitely
small, straight lines : this is indicated in the case of a lens in Fig. 371.
Rays of light passing through a double convex lens in passing in are bent
toward the perpendicular (Fig. 372). Now, if the rays thus acted upon
be followed they will be found to meet at a point on the opposite side
of the lens, called the focus, at which light and heat rays will converge.
Rays of light striking the centre of curvature of both surfaces of the lens
will pass through unchanged. Such a line is called the chief axis, and
the centre of this line is the optical centre of the lens. Rays passing
through the optical centre are termed principal or chief rays. Rays
parallel with the principal axis of the lens are refracted so that they are
collected on the opposite side of the lens at a point called the principal
focus ; the distance of this point from the central point of the lens is
called the focal distance. On the other hand, it is evident that rays
diverging from a luminous point at the principal focus will be so refracted

FIG. 373.— DIAGRAM ILLUSTRATING ACTION OF A DOUBLE CONVEX LENS OF
HIGH CURVATURE ON DIVERGENT RAYS. (Ganot.)

The divergent rays from the luminous point, L. are brought to a focus at I behind F, the principal focus
at which parallel rays, S B, converge.

as to be parallel when they pass from the lens. Again, ra}Ts of light in the
principal axis and from a point beyond the principal focus will converge
to a point on the opposite side of the lens (Fig. 373).

Four cases are possible : First, when the distance of the light from the
lens is equal to the focal distance the focus will lie at the same distance
on the opposite side of the lens, i.e., twice the focal distance; second,
if the luminous body approach to the lens, or, what is the same thing, to
the focus, then the focal point is moved farther away ; third, if the light
is still farther from the lens than twice the focal distance, then the focal
point comes correspondingly nearer to the lens ; fourth, if the rays
proceed from a point on the chief axis within the focal distance they
will diverge on the opposite side of the lens and not again come to a
focus ; whilej on the other hand, converging rays passing through a convex
lens will have their focal distances at a nearer point than that at which
parallel rays are collected. These facts are illustrated in the following
diagrams (Fig. 374).

854

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in ordinary lenses the amount of refraction at the centre and at the
circumference is not equal. Rays passing through the optical centre, as
already stated, pass directly without refraction, while those which pass
near the centre are less refracted than those which pass near the circum-

FIG. 374.— ACTION OF A CONVEX LENS ON LIGHT. (Landois.)

I. m m, chief axis : O, optical centre : rays (>i n) passing through this centre are principal rays, and
are not refracted. II. Parallel rays are collected at a focus,/, /O being the focal distance. III. Rays
diverging from a point, b, on the chief axis, within the focal distance, pass out of the other side of the
lens less divergent, but do not come to a focus. IV. Rays from a source of light, 7, beyond the principal
focus,/, again converge on the opposite side of the lens. V. Formation of an inverted image by a convex
lens.

ference ; consequently, the amount of refraction increases as the circum-
ference of the lens is approached. This is known as spherical aberration.
If a screen be placed in the focus of the rays passing near the centre of

FIG. 375.— DIFFERENT KINDS OF LENSES. (Ganot.)

A, double convex ; B, plano-convex ; C, converging concavo-convex ; D, double concave : E, plano-concave ;
F, diverging concavo-convex ; C and F are also called meniscus lenses.

the lens the resulting image will be bright in its central portion, and will
have surrounding it a halo which becomes fainter and fainter as we pass
from the centre to the circumference (Fig 376).

Spherical aberration may be corrected in two ways : by increasing

SENSE OF SIGHT. 855

the density of the lens at its central part, in order that it may act more
strongly on rays of light, by which the refracting power is increased
at that point ; this is accomplished in the ciystalline lens of the eye in
this manner since it is less dense at the circumference than in the centre :
or, spherical aberration may be diminished by placing a diaphragm
between the object of which the image is to be formed and the lens, so as
to cut off those rays which pass through the circumference and allow the
image to be formed only by the central rays. This method, also, is
adopted in the construction of the eye, where the movable diaphragm is
represented by the iris.

Again, another point is to be mentioned : white light, as is well
known, is composed of seven colors, which vary in their different degrees
of refrangibility — violet, indigo, blue, green, yellow, orange, and red. If
a beam of white light is passed through a triangular prism of glass it is

FIG. 376.— DIAGRAM ILLUSTRATING SPHERICAL ABERRATION. (Ganot.)

The rays passing through the edges of the lens have a shorter focal distance than those passing nearer to

the centre.

decomposed into its constituent ra}Ts, the violet ra}^s being refracted
most strongly and the red the least (Fig. 377). A white point on a black
ground does not form a simple image on the retina, but many colored points
appear after each other. If the eye is accommodated so as to focus to a
sharp image the violet rays are refracted most strongly ; the other colors
will form concentric diffusion circles, being most marked in the case of
the red rays. In the centre of all the colors a white point is produced by
their mixture, while around it are placed colored circles. Such an action,
of course, produces dimness of the object, and is known as chromatic
aberration.

This, top, may be corrected in two ways : either by making use of
the diaphragm and cutting off the rays passing through the circumfer-
ence of the lens ; or in optical instruments by the use of two kinds of
glass, one of which has a different dispersing power from the other, but

856 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

equal refracting power. Of the one a double convex lens is made, of the
other a double concave, and the two combined. They must be of dif-
ferent dispersive power, or the degree of concavity which would correct
the chromatic aberration would also destroy the converging power of the
convex lens. In crown glass and flint glass we have such media. The
flint glass has greater dispersive power, hence the degree of concavity
necessary to correct the chromatic aberration will be attained before the
degree of concavity will be reached which would destroy the converging
power of the convex lens of crown glass.

In the different refractive media of the eye such combinations are
to a certain extent represented, and serve, together with the action of
the pupil in shutting off the circumferential rays, to correct chromatic
aberration.

The eye as an optical instrument is analogous to the camera obscura,
and forms, in a manner to be described directly, an inverted image in

FIG. 377.— DIAGRAM ILLUSTRATING THE DECOMPOSITION, IN PASSING THROUGH
A PRISM, OF WHITE LIGHT INTO THE SEVEN COLORS OF THE SPECTRUM.
(Btclard.)

r, red ; o, orange ; j, yellow ; v, green ; b, blue ; i, indigo ; vi, violet.

reduced size of objects before it. Instead of a single lens, as in the
camera, the eye is composed of a number of different refractive media
placed behind each other — the cornea, the aqueous humor, and the lens.
The field of projection, or the point on which the image is focused, is the
retina, and from changes which have recently been discovered to take
place in the retina in which the visual purple becomes bleached the
analogy to the process of photography is very striking.

As is well known, by means of a convex lens an image of any object
may be formed upon a screen ; thus, if a convex lens be held before a
window, and a piece of paper placed behind it as a screen, at a certain

SENSE OF SIGHT. 857

distance behind the lens, a reversed image of the window will be formed
upon it. The manner in which this image is formed may be represented
in the following diagrams (Figs. 378 and 319).

In these figures it is seen that rays from any point of the object, which
may be regarded as diverging rays, are brought to a point behind the
lens. If the figures should be completed, and lines drawn from each indi-
vidual point of the objects in the manner represented in the illustrations, it
must be evident in tracing each- of these lines that a small inverted image

FIG. 378.— DIAGRAM ILLUSTRATING THE FORMATION, BY A DOUBLE CONVEX
LENS, OF A SMALLER INVERTED IMAGE. (Oanot.)

must be formed behind the lens. If a screen be placed at this point,
which corresponds to the focal length of the lens, it is evident that the
image will be distinctl}' defined. On the other hand, if the screen be
either approached or removed farther from the lens an indistinct image
will be formed. If the object be farther removed from the lens the
image will decrease in size, and to have a distinct image the screen must
be approached to the lens ; and, conversely, if the object be approached

FIG. 379.— DIAGRAM ILLUSTRATING THE FORMATION OF AN IMAGE BY A
DOUBLE CONVEX LENS.

to the lens the image will be increased in size, and to have sharp definition
the screen must be moved farther from the lens.

A similar process occurs within the eye, although the refraction of
rays of light is much more complicated than in the simple convex lens,
for in the eye the ray of light passes through several media and is
refracted by each. Nevertheless, in the eye, a small inverted image is
formed on the retina, as may be readily determined by removing the eye
from a recentty killed animal, and if the sclerotic be removed from the

858

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

posterior portion of the eyeball the image of external objects in a
strong light may be seen upon the retina inverted and reduced in size
(Figs. 380 and 381).

The principal surfaces by which rays of light passing through the
eye are refracted are the cornea and the anterior and posterior surfaces
of the lens. Since rays of light passing from the atmosphere to the
cornea pass from a rarer to a denser medium, the rays of light will be
bent toward the perpendicular. The degree of refraction at this point
will be more marked than in passing from the cornea to the aqueous
humor, both of which possess the same refractive power. On the
other hand, the refraction will be still greater in the lens, so that the
rays will be still more strongty deflected inward. It has been seen
that rays of light passing through the central point of the optical
centre of a convex lens do not undergo refraction, and in a double
convex lens of equal curvature the optical centre will coincide with the

FIG. 380.— FORMATION OP AN IMAGE IN THK EYE. (Landois.)

By following the rays from the object, A B, it may be seen that they are brought to a focus on the retina,
where a small inverted image is formed.

geometrical centre. In such a compound system of refracting media
as in the eye the optical centre is less readily determined. It has been
determined that in the eye the optical centre lies, not exactly in the
centre of the crystalline lens, but between that point and the posterior
surface of the lens ; consequently, the rays passing through this point
will practically undergo no refraction. It has been stated that a screen
may be so arranged in relation to a convex lens that a distinct image of
the object will fall upon it. This relation is attained when the screen is
in the exact focus of the lens. If approached to the lens or removed
a greater distance from it the image becomes indistinct. So, also, simi-
lar blurring or indistinctness is produced when the distance between
the object and the lens is altered.

In looking at a distant object the rays of light may be regarded as
parallel, and, as is well known, are focused with the greatest readiness
upon the retina. The difference between the action of the eye in

SENSE OF SIGHT. 859

forming an image and that of a simple lens is evident in the fact that
with the normal eye an object may be seen with equal distinctness
whether at a great distance or closely approached to the eye. This
indicates that there must be some mechanism in the eye by which the
focal length of the refracting media can be altered. If the finger be
held a short distance before the eye, the other being closed, it may
be distinguished with the greatest distinctness. If the finger remain
in the same position, and the eye now be fixed on some more distant
object, the finger is seen indistinctly, so that at will we may focus our
eyes on either the near or the far object and either may be distinctly
seen: yet when the eye is arranged for near objects far objects are seen
indistinctly, and the reverse. Such an adjustment of the refracting
powers of the eye is termed accommodation. It was for a time thought
that the accommodation of the e}'e was accomplished by approaching or
withdrawing the receiving surface, the retina, to or from the lens. It

FIG. 381.— DIAGRAM ILLUSTRATING THE FORMATION OF AN IMAGE ON THE
RETINA. (Yeo.)

The rays from the point, a, passing through the cornea, lens, etc., are collected in the retina at 6. Thosa
from a' meet at b', and thus the lower point becomes the upper.

has, however, been shown that this is not the case, and that accommo-
dation is accomplished by changes in the curvature of the cr3rstalline lens.
Referring again to our illustration of an object, a convex lens, and a
screen, as has been stated, if we determine the focal length of the lens
or the point at which a distinct image will be formed upon the screen and
then approach the object to the lens, the screen not being removed from
its position, the image will be indistinct. If, now, we remove the object,
the screen remaining unmoved, and substitute for the lens originally
used one of a greater degree of curvature, the degree of refraction will
evidently be greater and the focal length shorter, so that the rays from
the object in the near position, being more diverging, may be brought to
a focus at a point corresponding to that of the less diverging rays from
the farther-removed object. So, again, if the point of distinct image be
determined and the object farther removed, the screen would then have
to be approached to the lens in order to obtain a distinct image. In this

860

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

case, also, a distinct image might be formed by substituting a lens of a
less degree of curvature.

In the eye accommodation is accomplished by muscular action through
which the shape of the lens is changed. When the eye after viewing an
object at a distance is adjusted to form a sharp image of a nearer object
the crystalline lens becomes thicker through an increase of the curvature
of its anterior surface. This change may be represented in the following
diagram, after Helmholtz (Fig. 382).

The left portion of the figure represents the eye adjusted for distant
objects, while the right half is accommodated for near objects. It is here
seen that the anterior surface is increased in convexity, moving nearer
the cornea, and has carried the iris with it. It is well known that the
refraction of light rays caused by a convex lens increases with its increase
of curvature, and that the focal length of one lens will be longer than

CS.

asf

FIG. 382.— SCHEME OF ACCOMMODATION FOR NEAR AND DISTANT OBJECTS,

AFTER HELMHOLTZ. (Landois.)

The right side of the figure represents the condition of the lens during accommodation for a near
object, and the left side when the eye is at rest. The letters indicate the same parts on both sides ; those
on the right side are marked with a stroke. A, left, B, right half of lens ; C, cornea ; S, sclerotic ; C.S.,
canal of Schlemm ; V.K., anterior chamber ; J, iris ; P, margin of the pupil ; V, anterior surface, H,
posterior surface of the lens ; R, margin of the lens ; F. ', margin of the ciliary processes ; a b, space be-
tween the two former; the line Z Vindicates the thickness of the lens during accommodation for a near
object ; Z Y, the thickness of the lens when the eye is passive.

that of one of greater curvature — in other words, the latter will produce
a greater convergence of the light-rays.

A similar state of affairs holds in the adjustment of the lens in the
e3Te. When the object of our vision is closely approached to the eye
the lens is more convex than when the distance is greater, and its refract-
ing power is, therefore, increased and the formation of an image on the
retina rendered possible. Of course, with every variation in distance
there must be a corresponding variation in the degree of curvature of
the lens.

The mechanism by which the change in the curvature of the lens is
accomplished is the ciliary muscle. The capsule of the lens is attached
at its edge to the zone of Zinn, which radiates outward and keeps the
lens in a state of constant tension. At the point where the fibres of this

SENSE OF SIGHT. 861

ligament are attached to the outer membrane are also attached the fibres
of the ciliary muscle. When the eye is in a condition of rest, and,
therefore, adjusted for distant objects, the ciliary muscle is relaxed and
the zone of Zinn, by means of its elastic tension, pulls on the edges of
the lens-capsule, thereby extending the lens in a radial direction toward
its edge, diminishing its thickness and flattening its curvature. When
we want to focus for near objects the zone is drawn forward and inward
by the contraction of the ciliary muscle. Its tension, therefore, decreases,
and the lens, by means of its elasticity, bulges forward from the release
of the tension of the capsule of the lens and so increases in thickness,
and its anterior surface becomes more curved. It is, therefore, evident
why a strain on the eyes is experienced when looking at near objects,
since in a condition of rest of the eye the muscle is relaxed and the eye
is adjusted for parallel rays or for viewing distant objects; but when near
objects are closely examined a prolonged muscular effort is required, and
this, like all other muscular exertions, results in fatigue.

FIG. 383.— MYOPIC EYE. (Landois.)

In the normal eye the far point of vision may be placed at an infinite
distance, for in the normal eye the degree of refraction of the dioptric
media is such that parallel rays of light are brought to a focus on the
retina. In myopia, or near-sightedness, parallel rays are not focused on
the retina in a condition of rest of the ciliary muscle, but cross within
the vitreous humor, and after crossing form a diffused image on the
retina. The focal point in the myopic eye for parallel rays falls in front
of the retina (Fig. 383). The eyeball is, therefore, too long as compared
with the focal length of the refracting media. The near point, on the
other hand, or the nearest point at which objects may be distinctly seen,
lies abnormally near, and the range of accommodation is diminished.

On the other hand, it is conceivable that the refracting media of the
eye may be such that, without accommodation, parallel rays of light,
instead of being focused on the retina, as in the emmetropic or normal
eye, or in front of the retina, as in the myopic eye, will come to a focus
behind the retina (Fig. 384). Such a defect is spoken of as hypermetropia,
and is due to the fact that the degree of refraction of the media of the

862 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

eye is not sufficiently great to bring parallel rays of light to a focus on
tile retina. When such an eye is at rest only convergent rays are capable
of forming a distinct image on the retina, so that, therefore, distinct
images can only be formed by rendering all the rays of light which
enter the eye convergent; and, therefore, such an individual will not be
able to see distinctly without a convex lens in front of the eye. In such
an eye the far point is negative, while the near point is abnormally
distant and the range of accommodation great. In the hypermetropic
eye, consequently, the distance between the retina and the lens is
abnormally short.

When the eye is accommodated for near objects the pupil contracts ;
when in accommodation for distant objects it dilates. So, also, when
the eye is exposed to a bright light the pupil becomes reduced in size,
while, on the other hand, it dilates when the light becomes reduced in
intensity.

Changes in the pupil are accomplished by the action of the muscular
fibres of the iris, which by their relaxation and contraction increase or

diminish the size of the pupil.
The iris, therefore, fulfills the
function of a diaphragm and
serves to cut off the circum-
ferential rays of light, which
otherwise would lead to the
production of spherical aberra-
tion. So, also, as it contracts
FIG. 384,-HYPEKMETROPic EYE. (Landois.) in a bright light, it serves to

regulate the amount of rays of

light entering the eye, while, further, it to a certain extent supports
the action of the ciliary muscle, as is seen in the changes which occur in
the size of the pupil during accommodation.

The iris is supplied with two sets of muscular fibres, the circular or
sphincter fibres, which are supplied by the oculo-motor nerve, and the
radiating fibres, or the dilator of the pupil, supplied chiefly by the cervical
sympathetic and the trigeminus. When the oculo-motor nerve is divided
the pupil dilates, owing to the contraction of the dilator fibres, which
still preserve their integrity. On the other hand, when the sympathetic
is divided in the neck the pupil contracts through the antagonistic
action of the sphincter fibres. The contractility of the circular fibres is,
nevertheless, the stronger, for if both nerves be stimulated together
contraction of the pupil will take place. The radial muscular fibres are
especially developed in birds, while they have been claimed to be absent
in many other animals.

Changes in the size of the pupil fall under the head of reflex actions,

SENSE OF SIGHT. 863

since they cannot be produced through the exercise of the will. When
a ray of light falls upon the retina it leads to contraction of the pupil,
In which the optic nerve is the afferent nerve, the oculo-motor nerve the
efferent nerve, while the centre lies in some place in the brain below the
corpora quadrigemina. This is proven by the fact that when the optic
nerve is divided intense light no longer produces contraction of the pupil,
while, also, the division of the third pair renders the pupil insensitive
to light, and stimulation of the peripheral portion of the oculo-motor
leads to contraction of the pupil. So, also, stimulation of the floor of
the aqueduct of Sylvius will, likewise, if the oculo-motor nerve be intact,
lead to contraction of the pupil.

In contradistinction to what will be found in many instances, two
symmetrically disposed centres are not to be found in the brain for gov-
erning the movements of the pupil, since in normal conditions a stimulus
applied to one optic nerve will lead to contraction of both pupils, while,
also, stimulation of the centre will react on both eyes.

In addition to the oculo-motor nerve, the iris receives nerve-fibres
from the short ciliary nerves coming from the ophthalmic ganglion,
which is connected by its root with the third nerve, the cervical sympa-
thetic nerve, and the nasal branch of the ophthalmic division of the fifth
nerve. It has been mentioned that section of the cervical sympathetic
causes contraction of the pupil, and stimulation of the cervical sympa-
thetic dilatation of the pupil. It is evident that these effects on the
pupil are directly opposite to those seen in the blood-vessels on stimu-
lation of the sympathetic nerve.

The centre for the dilatation of the pupil likewise lies in the front
part of the floor of the aqueduct of Sylvius, while a second or inferior
centre, the so-called cilio-spinal centre, lies in the lower cervical portion
of the cord and extends downward to the first or third dorsal vertebra.
This centre may be reflexly stimulated by irritation of various sensory
nerves, when, of course, dilatation of the pupil will take place. It is
likewise stimulated by the blood in dyspnoea, and also a single centre
governs the movements of both pupils, for if one retina be shaded both
pupils will dilate. The cilio-spinal centre is in connection with the upper
centre for the dilator of the pupil through fibres passing through the
lateral columns of the cord, and it, together with the inferior centre,
reacts to the same stimuli.

When the 83-111 pathetic nerve is divided in the neck the pupil con-
tracts. This contraction is accompanied by a great increase in the vascu-
larity of the iris from the consequent paralysis of the walls of its
blood-vessels. This at one time was supposed to be sufficient to explain
the production of contraction of the pupil after section of the sym-
pathetic. Various other conditions which lead to an increased blood

864

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

supply of the iris will influence the size of the pupil. Thus, in forced
expiration, by which the return of the blood from the head is retarded,
the pupil is contracted. So, also, when the intra-ocular pressure is dimin-
ished, as by puncture of the anterior chamber, there is less resistance to
the flow of blood to the blood-vessels of the iris and the pupil is imme-
diately contracted. On the other hand, strong muscular exertion, which
leads to the blood flowing freely into the contracting muscles, will produce
dilatation of the pupil.

The size of the pupil may be modified by various drugs. Substances
which dilate the pupil are called mydriatics ; those which lead to its con-
traction, myotics. Of the former
may be mentioned atropine, hom-
atropine, duboisine, daturine, and
hyoscyamine. They act chiefly
by paralysis of the oculo-motor
nerve, while also acting slightly
upon the dilator fibres, for after
complete paralysis of the oculo-
motor nerve the moderate dila-
tation thereby produced may be
intensified by the administration
of atropine. Atropine appears to
act mainly by a local mechanism,
since it- produces dilatation of
the pupil even after destruction
of the ophthalmic ganglion and
division of all the nerves of the
eye except the optic, and even,
according to some authorities,
will produce dilatation of the
pupil in an excised eye.

Myotics, of which physostig-
mine or eserine is the best known,
may produce contraction of the pupil either by stimulation of the
oculo-motor nerve or paralysis of the sympathetic.

2. Visual Sensations. — Our considerations of the action of the organ
of vision have thus far dealt simply with physical processes. The rays
of light entering the eye have been traced backward through the trans-
parent media of the eye until they resulted in the formation of an image.
When the rays reach the retina, sensory impulses are excited and are
carried through the optic nerve to the sensorium, where they give rise to
a sensation.

The nature of the changes that take place within the retina does not

FIG. 385.— DlAGKAM OF THE FORMATION OP

THE RETINA. (Yeo.)

The fibres of the optic nerve, N, pass along the inner
surface of the retina, R, to meet the ganglion cells, whence
special communications pass outward to the layer of rods and
cones in the pigment layer, p, next the choroid, c.

SENSE OF SIGHT.

865

admit of as close analysis as the physical action of the different refract-
ing media of the eye. It is known that it is only the layer of rods and
cones of the retina that is concerned in the formation of the image, since
rays of light pass through the anterior layers of the retina without giv-
ing rise to any sensations. The retina is a highly complicated nervous
apparatus, which may, by the use of the microscope, be divided into
eight and probably ten distinct layers. The
innermost layer — i.e., the layer in contact
with the vitreous humor — consists of nerve-
fibres in which the optic nerve terminates,
radiating from the entrance of the optic

WfS

FIG. 386.— VERTICAL SECTION OF HUMAN
RETINA. (Landois.)

a, rods and cones ; b, external, j, internal limiting
membranes; c, external, and/, internal nuclear layers;
•e, external, and g, internal granular layers; k, blood-
vessel and nerve-cells ; t, nerve-fibres.

FIG. 387.— LAYERS OF THE RETINA.

(Landois.)

Pi, hexagonal pigment cells; Sf, rods and cones;
Le, external limiting membrane; auK, external nuclear
layer; iiugr, external granular layer; inK, internal
nuclear; ingr, internal granular; Gtjl, ganglionic
nerve-cells; O. fibres of optic nerve ; Li, internal limiting
membrane : Rk, fibres of Miiller ; K, nuclei ; Sg, spaces
for the nervous elements.

nerve (Fig. 385). At this point, therefore, the retina will consist
only of nerve-tubules. At one spot in the centre of the retina no nerve-
fibres are to be distinguished, and on account of its color this point is
termed the macula lutea, or yellow spot, and is the point of most acute
vision.

The layers of the retina have been described as follows : First, and

55

866 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

most internally, exists a fine limiting membrane ; second, externally, a
layer of nerve-fibres ; third, a layer of nerve-cells analogous to the gan-
glionic cells of the brain ; fourth, a granular layer consisting of an indis-
tinct mass of fine gray granules ; fifth, the inner granular la}rer, composed
of little round granules ; sixth, the intermediate granular la}Ter, in which
the granular mass is intermingled with small fibres ; seventh, the outer
granular layer, analogous to the inner granular layer ; eighth, a second
delicate membranous structure ; and ninth, the layer of rods and cones
(Figs. 386 and 387).

It is this most external layer of the retina which is concerned in the
reception of the rays of light and the formation of the image. It con-
sists of small, transparent rods packed closely together at right angles to
the surface of the retina, while at different intervals between them is seen
a small rod expanded at the end so as to form a conical shape. These
cones are especially abundant in the yellow spot, where there is a slight
depression in the retina and where no rods are present. To reach the
layer of rods and cones, the rays of light must evidently pass through
all the superimposed la}*ers, and are finally stopped at the choroid, whichr
with its pigment layer, may be regarded as forming a background for the
retina.

That the nerve-fibres themselves are insensitive to light may be
readity determined by proving that the point of entrance of the optic
nerve is entirely insensitive to light. If one eye is closed and the other
fixed on a black spot on a white sheet of paper and some other small
body be gradually moved laterally toward the outside of the field of
vision, at a certain distance the moving body will entirely disappear from
sight, while, if the motion be continued, it will again come into the field
of vision ; or if we place two wafers upon a board at a distance of four
or five inches apart and stand at about five times this distance, and
closing the right eye, with the left look at the right-hand wafer, the left-
hand wafer will disappear. The explanation of this is that when so placed
the rays of light from the left-hand wafer will be received directly on the
optic nerve, and so indicates that the optic fibres themselves' are insen-
sible to light, and that it is only through the retinal expansion of these
fibres that sensations of vision are possible. On the other hand, the
macula lutea is the locality of most distinct vision. When we fixedly
regard a point with the eye, then the ra3Ts of light from that point pass
through the middle of the pupil and the centre of the lens and fall
almost on the centre of the retina, directly on the yellow spot. The for-
mation of the macula lutea indicates the reason of its especial sensitive-
ness to light, while at the same time pointing out the constituents of the
retina which are concerned in the formation of the image. It has been
mentioned that the optic fibres surround the yellow spot without passing

SENSE OF SIGHT. 867

over it. This would appear to indicate such an adjustment of the con-
stituents of the retina as to avoid the slightest interference with rays
striking on this point, since we have seen that the optic nerve-fibres are
not sensitive.

Again, in the yellow spot the cones of the retina are closely packed
together, and in addition numerous ganglionic cells are found, while the
other layers of the retina are fainter than elsewhere. The yellow color
is due to the deposit of numerous yellow pigment cells.

If it be admitted in the first place that the optic nerve-fibres are not
sensitive to light, and in the second place that the layer of rods and
cones represents the sentient surface for light-waves, a connection must
evidently exist between the receiving surface and the nerve-fibres to
admit of the impression becoming a sensation and being perceived by
the brain. Microscopical examination will succeed in tracing a connec-
tion by means of fine filaments penetrating all the layers of the retina
and connecting the nerve-fibres with the ganglionic cells, the granular
layers, and finally with the rods and cones. It is through this path that
the irritation caused by the rays of light and received in the meshes of
the rods and cones passes to the optic nerve-fibres, and thence to the
brain, there creating the sensation of light.

Like other nerves of special sense, the fibres of the optic nerve,
though insensitive to light, respond to other irritants, and then the brain
perceives the sensation peculiar to that special nerve and recognizes
that an irritant has acted upon the nerve of vision, and a flash of light
is the result. Thus, in cases of section of the optic nerve a flash of
light is experienced, and then total darkness follows; so, also, if the
optic nerve be stimulated by electricity a sensation of light is the
result. All the nerves of special sense to this extent agree in their
nature, and the optic nerve no more conve3^s sound-waves to the brain
than does the auditory nerve waves of light; but both nerves at their
terminations are supplied with special forms of apparatus, the so-called
special sense organs, which only admit of being excited by appropriate
stimuli; thus the terminal fibres of the optic nerve are especially
adapted for receiving impressions of waves of light, the auditon^ nerve
waves of sound, the difference lying in the different impressions made
upon different special centres in the brain.

As to the mode in which rays of light call into action the specific
functions of the layer of rods and cones, but little is definitely known.
Recent investigations appear to point to a chemical decomposition being
concerned in this process. It is well-known that r&3'S of light produce
decomposition in many substances, which are then spoken of as sensitive
to light. That a ray of light shall produce such decomposition, it must
be absorbed. We therefore, perhaps, see the explanation of the invariable

868 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

existence of pigment cells in the organ of vision. It has been mentioned
that the first indication of organs of vision is represented by an accumu-
lation of pigment cells, and we never find the presence of an eye which
is totally free from such pigment matters.

A fact which at first seemed to show exactly how this process was
accomplished was the discovery in the retina of the purplish-red pigment,
the so-called visual purple, or rhodopsin, which is so extremely sensitive
to light that by proper means external objects may actually be photo-
graphed in it on the retina. This substance may be extracted from the
retina by means of a 2.5 per cent, solution of the bile acids, especially if
the eyes have been kept for some time in a 10 per cent, solution of com-
mon salt. Kiihne stated that by illuminating the retina actual pictures
could be produced on the retina, and that they gradually disappeared.
The analogy between this fact and the action on the sensitive plate in the
photographic apparatus is very striking, and the further behavior of the
purple pigment of the retina would perhaps show that it is concerned in the
appreciation of light. Thus, if a rabbit is kept in the dark for some time
and then killed, and its retina examined by a monochromatic light, it will
be found to be of a brilliant purple-red color with the single exception of
the macula lutea; on the other hand, exposure to light will result in
quickty bleaching it, but it will, however, have its color restored if the
eye be again placed in darkness.

Unfortunately, we are as yet entirely unwarranted in forming any
such conclusion or affirming any such close connection between this
peculiar substance and the sensation of vision by the fact that the pigment
is confined to the outer segments of the rods and is absent in the cones,
which we have found to be the most sensitive layer; and is, in fact, absent
in the macula lutea, which we have found to be the most sensitive point
of the retina. Finally, it is absent in pigeons, hens, and bats, although
the retina of the latter only consists of cones, while it is found in both
nocturnal and diurnal animals. Finally, it is entirely wanting in animals
which undoubtedly see very distinctly, and may be entirely removed
from the eyes of certain animals, as the monkey, by prolonged exposure
to strong light, when the retina will become completely bleached, but
will still apparently be perfectly sensitive to light. We cannot, there-
fore, at present explain visual sensations as due to chemical changes
occurring in this pigment. The discovery of the retinal pigment is,
nevertheless, to be regarded as an advance in the elucidation of this sub-
ject, for it is almost impossible to conceive that it is not in some way
concerned in vision.

It has been stated that the two pupils act simultaneously, and
as we know the function of the pupil is concerned in regulating the
entrance of rays of light to the eye and that vision takes place simul-

SENSE OF SIGHT. 869

taneously with the two eyes, the question arises, Why is it that with
two retinae, each capable of receiving a distinct image, the image so
formed by the use of the two eyes is not double ? The explanation of
this lies not so much in the anatomical distribution of the tunics of
the eye as in the fact that when rays of light proceed from a luminous
body and fall upon the retinae they fall upon parts that are accustomed
to act together. Every point of the image on one retina falls upon a
coincident point upon the other. These points are accustomed to act
together and we see a single image. The eyes, indeed, receive a double
impression, and this may be illustrated by placing two small bodies,
as the lingers, at different distances from the e}Tes. Directing the eyes
to the nearer, the more remote will appear double, or, if the eye be
directed to the more remote, the nearer will appear double. This is
due to the fact that the images of the object upon which the eye is not
especialty directed do not fall upon coincident parts of the retina.
The same thing may be accomplished by throwing the two parts of the
retina out of coincidence with each other, when, almost instantaneously,
double vision will occur. If, while looking at a single object, we press
to one side the globe of one eye, we bring two parts of the retina to act
together which did not ordinarily thus coincide, and double vision ensues.
Any other cause, such as various poisons, disease, or fatigue, which will
disturb the co-ordination of the eyes or such an adjustment of the posi-
tion of the eyes that rays of light do not fall upon corresponding or
coincident parts, will result in double vision.

Again, it has been stated that the image formed upon the retina is
an inverted one, and yet it is a matter of common experience that every
body is seen in the field of vision as upright. This second mental rever-
sion of the image is the result of experience acquired in the exercise of
the sense of sight. It is not to be understood that the brain takes cog-
nizance of the picture upon the retina and that vision is an actual trans-
mission of this image to the sensorium. The mind does not look upon
the picture so formed, but vision is a mental act excited by an impres-
sion upon the optic nerve whose neurility is excited. There need be no
more correspondence between the change in the brain and the image in
the eyes than between the signs of the telegraph operator and the words
of the written message. It must be remembered that vision consists in
the change developed in the central organ as a consequence of changes
in the optic nerve. Even supposing that the image on the retina is
inverted, what difference does it make? Everything is inverted and the
relative position of things is unchanged. All objects hold the same rela-
tion to each other whether the image be inverted or erect ; hence the
mind is not conscious of any inversion.

Although each retina receives an image from the object the pictures

870

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

are not precisely the same. If we hold up any object and look at it first
with the right eye, having the left eye closed, and then with the left eye,
having the right eye closed, it will be readily seen that the picture is not
precisely the same. With the right eye we see the right side of the
object, and with the left eye the left side. When these two pictures
come to be fused in the brain there results an image which differs from
either of the other two and which is projected into space, giving the
idea of one solid body (Fig. 388).

It is upon this principle that the stereoscope is constructed. The
stereoscopic picture is composed of two images, one representing the
object as seen by the right eye, and another representing the object

as seen by the left. When these two
pictures are fused the resulting picture
is formed, which is a compound of the
two, and this fusion of the two images
gives the idea of solidity of the object.
When the e}^e has looked at an ob-
ject for a long time, especially if that
object be luminous, the retina becomes
fatigued and no longer capable of re-
ceiving impressions from it. If the
object be small only a small portion of
the retina will be impressed. If we
turn away from the object and fix the
eye upon a white wall we see a dark
spot upon the wall corresponding in
size with the object upon which we
have been looking. Suppose that we
fix the eye upon a bright red wafer
FIG' ^u^RGvfswNLL7Sa™G Bl" strong^ illuminated, and look at it

The lines from the object indicate that the rays Steadily With OU1* eVCS, tllC raVS DrO-
from the back of the book fall on coincident points of

of^rilfon*' while each eye> further> has a special field ceeding from that wafer and falling upon

one point of the retina will fatigue that

point so that it will not be capable of receiving rays from less luminous
objects, and when we turn our eye to the wall we see a spot on the wall
like the wafer in size but of a different color, made up of all the colors
of the spectrum except red. This combination constitutes what are
termed accidental or complementary colors. Again, if we look at
a white object for a long time and then look at the wall we see there an
object of the size of the original one of a black color. The point of the
retina upon which the image fell has become so fatigued that it cannot
receive an impression from the fainter rays reflected from the wall, while
all the other parts of the retina are impressed by these rays. We, there-

SENSE OF SIGHT.

871

fore, see the wall with a dark spot upon it. These accidental colors are
produced Ity fatigue of the retina, and consist of all the other colors of
the spectrum except that of the luminous object at which we have been
looking. The primary colors, so-called, are red, yellow, and blue. The
intermediate points of the spectrum are made up by combinations
of these ; thus, violet is a mixture of red and blue, green of yellow and
blue, and orange of red and yellow. Blue is thus the complement of
orange and yellow of violet.

FIG. 389.— DIAGRAM ILLUSTRATING IRRADIATION. (Stirling.)

If this diagram is held some distance from the eyes, especially if not exactly focused, the white dot will
appear larger than the black, though both are exactly of the same size.

When rays of light from a strongl}r luminous body fall upon the
retina they are not confined exactly to the precise points upon which
they impinge, but extend themselves to a greater or less degree around
them. Thus, if we make a circular white spot upon a black ground, and
a black spot of corresponding dimensions upon a white ground, the
former will appear considerably larger than the latter, apparently, be-
cause the excitation of the retina by the luminous impression tends to
spread itself over the adjacent unexcited space (Figs. 389, 390, and 391).

The same phenomena are seen when
the experiment is performed with

FIG. 390.— DIAGRAM ILLUSTRATING IRRA-
DIATION. (Stirling.)

The two white squares appear the larger, and they
appear to run into each other, and to be joined by a
white strip.

FIG. 391.— DIAGRAM ILLUSTRATING IRRA-
DIATION. (Stirling.)

The white strip, which is of equal width through-
out, appears wider below, between the black squares,
than above.

different colored bodies. If the impressing bod}', though small in size,
illuminate the retina strongly, it may irradiate its impression upon the
surrounding part of the retina and make itself appear larger.

In our perceptions of the nature of external objects we find that
the sense of vision, like the other sensations, is not infallible, but that

872

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

various errors in judgment of visual sensations frequently occur. Some
of these admit of explanation, others do not. The most striking example
of such an error in perception, and one which is the most readily
explained, is as follows : —

If a series of parallel vertical black lines, two millimeters in diameter,
are drawn on white paper, with equal white areas between them, and then
intently regarded in a good light, in a short time the lines will assume
the shape seen in Fig. 392 at A. They appear of this shape because of

a

FIG. 392.— DIAGRAM ILLUSTRATING BERG-
MANN'S EXPERIMENT. (Stirling.)

FIG. 393.— ZOLLNER'S LINES. (Stirling.)

the manner in which the images of the lines fall on the cones in the
yellow spot, as shown in B.

If a series of oblique lines are drawn perfectly parallel to each otherT
and then they are crossed in different directions by a number of short
parallel oblique lines, although the long oblique lines are perfectly
parallel, the short oblique lines cause them to appear to slope inward or
outward, according to the direction of the oblique lines (Fig. 393).

In the figure 8 and the capital letter S the upper half to most per-
sons appears of about the same size as the lower half. If, however, the
page on which they occur be inverted it will be seen that the lower part

ssssssss

88888888

FIG. 394.— DIAGRAM ILLUSTRATING AN IMPERFECTION OF VISUAL JUDGMENT.

(Stirling.)

is considerably the* larger (Fig. 394) ; or if the centre of Fig. 395 be
fixed at about three or four centimeters from the eye, by indirect vision
the broad black and white peripheral areas will appear as small and the
lines bounding them as straight as the smaller central areas.

If a disk similar to that seen in Fig. 396 is rotated the disk appears
to be covered with circles, which, arising in the centre, gradually become
larger and disappear at the peripheiy. If, after looking at such a revolv-
ing disk for some moments, it be attempted to read a printed page, or to
look at a person's face, the letters appear to move toward the centre,
while the person's face appears to become smaller and recede. If the
disk be rotated in the opposite direction the opposite results are obtained.

SENSE OF SIGHT. 873

Movements of the Eye. — The position of the eyeball in the orbit

FIG. 395.— DIAGRAM ILLUSTRATING IMPERFECT PERCEPTION OF SIZE. (Stirling.)

corresponds to a ball-and-socket joint, and each eyeball is capable of
moving around an immovable centre of rotation, which has been found to be

FIG. 396.— DIAGRAM ILLUSTRATING RADIAL MOVEMENT. (Stirling.)

placed a short distance behind the centre of the e}^e. The movements of
the eye are accomplished b}^ six muscles — four straight and two oblique.

874

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The recti, or straight muscles, all take origin about the optic foramen and
radiate outward, being inserted in the globe of the eye on either side,
tibove and below, constituting thus the external and internal straight
muscles and the superior and inferior straight muscles. Of the oblique
muscles, the superior alone arises from the optic foramen and runs
forward over the superior and inner part of the orbit through a pulley
in the depression just within the inner extremity of the superior orbital
margin, then outward and backward beneath the superior straight muscle,

til

FIG. 397.— SCHEME OF THE ACTION OF THE OCULAR MUSCLES. (Landois.)

and is inserted in the eyeball midway between the latter and the external
straight muscle, the cornea, and the optic nerve. The inferior oblique
muscle arises from the anterior portion of the edge of the orbit, and runs
by its tendon to be inserted beneath that of the external rectus muscle.
The function of the superior oblique muscle is to roll the eye downward
and inward, that of the inferior oblique muscle upward and inward,
although this may be accomplished by the different recti muscles acting
simultaneously. The above diagram indicates the action of the ocular
muscles (Pig. 397).

SENSE OF HEAKING. 875

The oculo-motor nerve supplies all of the muscles of the eye with
the exception of the external recttis and the superior oblique. The ex-
ternal rectus muscle is supplied by the abducens, or sixth pair, while the
superior oblique is supplied by the patheticus or fourth pair.

C. THE SENSE OF HEAEING.

The sense of hearing or audition may be defined as that sense by
which the mind takes cognizance of the undulations of the elastic
medium which give rise to the sensation of sound. The mind recog-
nizes not the body producing the soimd, but the impression made by its
vibrations upon the sensorium. Sound, then, does not take place in the
ear, but in the brain. When we speak of a resounding string or a
sonorous bell we make a mistake ; the string and the bell simply
vibrate. These vibrations give rise to undulations in the elastic ether,
which undulations are transmitted in various directions, and finally
through the auditory passages impress the auditory nerve and give rise
to sound. The physiological aspects of the question are here alone
regarded. Regarding sound as the recognition of the impressions
made by vibrating sonorous bodies on the auditory nerve, if every one
were deaf there would, of course, be no sound; but, on the other hand,
we say that no sound may be produced in a vacuum, although we know
that sonorous vibrations still take place ; hence we are also permitted in
a physical sense to give the above explanation of the word sound.

The simplest form of the organ of hearing is a sac filled with fluid,
in which the ends of the auditory nerve terminate. In all groups of
animals the essential part of the organ of hearing consists in a certain
special form of termination of the nerve, which is alone capable of
receiving auditory impressions and of transmitting them to the central
ganglia of the brain. The more highly complicated forms of auditory
apparatus simply depend upon modifications which assist in the trans-
mission of sound to this part.

In all the invertebrates the organ of hearing is restricted to such a
simple sacular form, in some instances containing otoliths,or small, hard
granules, and the vibrations of the sonorous body are communicated to
the nerve of hearing spread over this sac. In such animals it is prob-
able that while a nerve of hearing is present only simple sounds and
noises can be recognized, while no difference in pitch or intensity can be
distinguished. Such a simple form of apparatus, consisting simply of
liquid contained in a sac, is found in mollusks.

In crustaceans there is a rudimentary organ of hearing present,
placed on each side of the base of the anterior antennae. It likewise
consists simply of a membranous sac filled with fluid, and on which
ramify the fibres of the nerve of hearing.

876 PHYSIOLOGY OF THE DOMESTIC ANIMALS. •

Many insects are apparently free from any evidences of anything
resembling an organ of hearing, yet it is clear that these animals are
sensible of external sounds. It is possible that in these animals, as in
certain radiates and many mollusks, the vibrations of sound are not
appreciated as sound, but, perhaps, as some modification of the sense of
touch.

In fishes there is no external ear, no tympanic cavity, and no
cochlea. The ear is reduced to the membranous part of the vestibule
and the semicircular canals, the latter varying from two to three in
number, while the vestibule and semicircular canals represent a closed
cavity, since there is neither oval nor round window, no tympanic
cavity, nor auditory ossicles. Sometimes, as in cartilaginous fishes, the
membranous internal ear is lodged in the cartilaginous substance of the
bones of the head, while in osseous fishes it is sometimes in part within
the bones of the cranium, and part free in the cephalic cavity, resting
against the brain. The internal ear is in all cases supplied with terminal
fibres of the auditory nerve, and is filled with a liquid in which are
found various calcareous concretions of greater or less volume.

In reptiles there is no external ear, neither a pinna nor an external
auditory canal, the tympanic membrane being flush with the head and
lying directly below the skin, although in some instances a drum mem-
brane is absent. When present, as is the case in the majority of instances,
it communicates generally b}^ a large opening — the Eustachian tube —
with the pharynx. The auditory ossicles are usually reduced to two in
number. When the tympanic membrane is absent, the ossicles, attached
at one side to the oval window, are fastened on the other directly against
the external integument.

In lizards, crocodiles, and serpents the internal ear is composed of
the vestibule, semicircular canals, and cochlea. In them, consequently,
the internal ear communicates with the cavity of the tympanum by the
oval window and by the round window. The cochlea in them is not con-
voluted, but almost straight.

In the batrachians no cochlea is present, and, as a consequence, no-
round window, the internal ear being reduced to the vestibule and the
semicircular canals, the only communication with the tympanum being
by the oval window.

In birds the apparatus of hearing is almost as complete as in mam-
mals, with the single exception of the external auditory pinna, which is
absent. The external auditory canal is formed by a bony canal travers-
ing the temporal bone, and the t3-mpanic cavity, separated from this
canal by the tympanic membrane, is well developed. It communicates
with bony cavities in the interior of almost all the cranial bones, and by
the intermediation of the Eustachian tube with the pharynx. The

SENSE OF HEARING. 877

internal ear is formed of the vestibule, semicircular canals, and cochlea ;
the latter, being but little developed, is not convoluted in a spiral form,
but, resembling that of lizards and serpents, consists of an almost straight
osseous tube canal terminating in a cul-de-sac.

In mammals the ear, for the convenience of study, ma}^ be divided
into three parts — the external, the middle, and the internal ear. Of these
three the internal ear is the essential, and the others are simply for the
purpose of receiving or modifying impressions from the sounding body.

In the external ear we include the auricle, or pinna, and the external
auditory meatus, bounded internally b}- the membrane of the tympanum ;
in the middle ear, the tympanum, or drum of the ear, with its contained
ossicles ; and in the internal ear, that portion situated in the petrous por-
tion of the temporal bone, consisting of the semicircular canals, the
vestibule, and the cochlea (Fig. 398).

FIG. 398.— SCHEME OF THE ORGAN OF HEARING. (Landois.)

AG, external auditory meatus ; T, tympanic membrane ; K, malleus with its head (h), short process
(Kf ), and handle (m) ; a, incus with its short process (x) and long process: the latter is united to the
stapes (s) by means of the Sylvian ossicle (z) ; P, middle ear; o, fenestra ovalis; r, fenestra rotunda; x,
beginning of the lamina spiralis of the cochlea ; pt, itsscala tympani; vt, its scala vestibuli ; V, vestibule;
S, saccule ; U, utricle ; H, semicircular canals ; TE, Eustachian tube. The long arrow indicates the
line of traction of the tensor tympani ; the short, curved one, that of the stapedius.

In different groups of mammals a marked difference is found in the
form and size of the auricle, or pinna. This, in the majority of cases, is
a trumpet-shaped dilatation of the external auditory canal formed for the
purpose of receiving the undulations communicated to the atmosphere,
collecting them, and transmitting them inward to the middle ear. This
portion of the external auditory canal owes its shape to the cartilages
present in it, which in some instances, as in the horse, the ass, the goat,
and the rabbit, are erect and straight ; while in other cases the cartilages
are more delicate and soft, folding on themselves so that the auricles lie

878

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

in contact with the side of the head, although they may by the influence
of various muscles be drawn into a more or less erect position. Such is
the case in the elephant and in the do^. In most mammals the auricle

FIG. 399.— DIAGRAM OP THE EXTERNAL, SURFACE OP THE LEFT TYMPANIC
MEMBRANE. (Hetuen.)

a, head of the malleus ; b, incus ; e, joint between malleus and incus ; between c and d is the flaccid
portion of the membrane; ax, axis of rotation of ossicles. The deeply shaded central portion is called
the "umbo."

is much more mo'bile than in man, and may be directed toward the source
of sound by the contraction of voluntary muscles and thus be enabled to
accomplish more successfully its functions.

FIG. 400.— TYMPANIC MEMBRANE AND AUDITORY OSSICLES SEEN FROM THE
TYMPANIC CAVITY. (Landois.)

M, manubrium, or handle of the malleus ; T, insertion of the tensor tympani ; h head, 1 F long proc-
ess, of the malleus; a, incus with the short (K) and the long (1) processes; S, plate of the stapes; Ax,
Ax is the common axis of rotation of the auditory ossicles ; S, the pinion-wheel arrangement between the
malleus and incus.

The external auditory meatus is a canal, partly cartilaginous and
partly bony, which varies in length according to the species. Thus,
while it is five or six centimeters long in ruminants, it is very short in

SENSE OF HEAKING. 879

carnivora. It is bounded internal!}- by the tympanic membrane and its
function is to conduct to the middle ear the undulations collected bv
the auricle. In the external auditor}' canal are found the ceruminous
glands secreting the wax, which is principally intended for lubricating
purposes, and thus facilitates the transmission of sound, while, also, by
its extremely bitter taste it perhaps prevents the entrance of insects.

The tympanic membrane forms the boundary between the external
auditory canal and the middle ear. This membrane consists of three
distinct layers, the outer, the external integument, the middle or fibrous
Ia3'er, and the inner or mucous la}*er, continuous with mucous membrane
lining the middle ear. This membrane is an elastic, almost unyielding,

Ax

Fro. 401.— LEFT TYMPANUM AND AUDITORY OSSICLES. (Landois.)

A.G., external meatus ; M, membrana tympani, which is attached to the handle of the malleus, n,
and near it the short process, p : h, head of the malleus ; a, incus ; K. its short process, with its ligament;
1, long process : s, Sylvian ossicle : S, stapes : A x, A x, the axis of rotation of the ossicles, shown in per-
spective : t, line of traction of the tensor tympani. The other arrows show the movements of the ossicles
when the tensor contracts.

membrane, elliptical in form, and is placed obliquely in the floor of the
external meatus at an angle of about 40°, being directed from above
downward and inward. This oblique position enables a larger surface
to be presented to the undulations conducted from the external auditory
canal than if it were placed vertically. This membrane is not entirely
flat, but at its centre is drawn slightly inward where the handle of the
malleus is attached to it, while the short process of the malleus causes
a slight bulging of the membrane near its upper margin (Figs. 399 and
400).

The middle ear, or the drum of the ear or the tympanum, is bounded
by the tympanic membrane on the exterior, and on the interior by the

880

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

labyrinth. It connects interiorly with the fauces by the Eustachian tube,
and posteriorly with the mastoid cells of the mastoid portion of the tem-
poral bone. In some animals these mastoid cells are greatly developed
and so form an important augmentation of the tympanic cavity, while the
Eustachian tube, which is short and straight in the case of most rumi-
nants, is very much dilated in the horse where it forms what may be
termed guttural pouches (Fig. 401).

FIG. 402.— I. THE MECHANICS OF THE AUDITORY OSSICLES, AFTER HELM-
HOLTZ. II. SECTION OF THE MIDDLE EAR, AFTER HEUSEN. (Munk.)

I. rt. malleus ; h, incus : am, long process of incus ; s, stapes ; the arrows show the direction of mo-
tion. II. G, external auditory canal ; M.t., membrana tympani ; C, tympanum ; H, malleus ; L.S.,
superior ligamant ; S, stapes.

Stretching across the middle ear from one side to the other is the
chain of bones, each named from its resemblance to some instrument ;
thus, the malleus, so-called from its resemblance to a hammer, is attached
to the membranum of the tympanum by its handle (Fig. 402). The second

bone, from its resemblance to an anvil, is
called the incus, and is attached on the
one side to the malleus and on the other
to the stapes or stirrup-bone, which is
connected by its base to the membrane
of the fenestra ovalis, which opens into
the internal ear. All these ossicles are

/upper, h horizontal, and s posterior semi- rnnvaKIp nn Pnoh nthpr Vint tliPir VIQVA r»r»
circular canals of the left side. The cochlea is niOVaDlC OU CaCll OtDer, Dtlt tliey HaVC UO

lateral connection with any structure.

Sometimes at the end of the incus is found a separate bone known as the
os orbiculare. In the inner boundary of the middle ear is placed, in
addition to the oval window, a second, also communicating with the
vestibule, and called the fenestra rotunda, or round window.

The internal ear, or labyrinth, is composed of bone, and consists of

FIG. 403.— EXTERNAL, APPEARANCE
OF THE LABYRINTH AND FE-
NESTRA OVALIS. (Landois.)

SENSE OF HEARING.

881

the vestibule, and, communicating with this, three semicircular canals and
the cochlea (Figs. 403 and 404). Lining the internal ear and forming a
complete cast of the vestibule and semicircular canals is the so-called
membranous labyrinth, while between the walls of the membranous

\ »

FIG. 404.— SCHEME OF THE AUDITORY APPARATUS. (Beaunis.)

A, external ear; B, middle ear; C, internal ear; 1, auricle: 2, external auditory canal: 3, tympanic
cavity; 4, tympanic membrane: 5, Eustachian tube; 6, mastoid cells; 7, malleus; 8, incus; 9, stapes;
10, round window; 11, oval window; 12, vestibule; 13, cochlea; 14, scala tympani; 15, scala vestibuli;
16, semicircular canal.

labyrinth and the semicircular canals and vestibule is a fluid called the
perilymph, which is also contained in the cochlea. Within the mem-
branous labyrinth is a similar fluid termed the endolymph. In .the
interior of the membranous lab}^rinth are
often found little particles consisting
almost entirely of carbonate of lime,
called otoliths, or ear-stones (Fig. 405).
Sometimes these are attached to the walls
of the membranous labyrinth, and some-
times they are found tying loosely and
are intended to increase the intensity of
the sounds.

The cochlea consists of a spiral
canal making two and one-half revo-
lutions about a central axis. It is divided
by a spiral lamina, partly membranous and partly bony, into two
divisions known as scalae, of which one is above the other. The superior
at its inferior extremity terminates in the vestibule and is known as the

56

FIG. 405.— A, OTOLITHS FROM THE
HORSE ; B, EPITHELIUM WITH
AUDITORY HAIRS FROM THE
CRISTA ACOUSTICA OF THE
BABBIT. ( Munk. )

882

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

scala vestibuli, while the other, or inferior, terminates in the round
window and is called the scala tympani. On these laminae spirales fire
distributed portions of the auditory nerve, which takes origin from the
floor of the fourth ventricle and runs into the petrous portion of the
temporal bone through the meatus auditorius internus and divides into
two divisions, one going to the cochlea and the other to the vestibule
near to the end of the semicircular canals. It loses itself upon the walls
of the vestibule and the walls of the ampullae, or membranous dilatations
at the commencement of the three semicircular canals (Fig. 406).

The cochlear nerve is distributed to the scalae of the cochlea, where
its terminal fibres form connection with Corti's organ, which is placed

FIG. 406.— SCHEME OF THE LABYRINTH AND TERMINATION OF THE AUDITORY
NERVE. (Landois.)

I. Transverse section of a turn of the cochlea. II. A. ampulla of a semicircular canal : a p. auditory
cells, p, provided with a fine hair; T, otoliths. III. Scheme of the human labyrinth. IV. Scheme of
a bird's labyrinth. V. Scheme of a fish's labyrinth.

in the ductus cochlearis, a small, triangular chamber, cut off from the
scala vestibuli by the membrane of Reissner (Fig. 401).

Corti's organ is placed on the membranous portion of the lamina
spiralis, and consists of an apparatus composed of the so-called Corti's
arches, each of which consists of two Corti's rods. Every two rods
unite to form an arch, so that there are always two or three inner rods
and two outer rods. Toward the apex of the cochlea the rods become
longer and the span of the arches increases. The terminal organs of
the cochlear nerve are the <rylindrical hair-cells described by Corti, of
which there are two rows, the row of inner cells resting on a layer of
small, granular cells, and the outer cells distributed in three or four rows
resting on a basement membrane. Between the outer cells there are

SENSE OF HEARING.

883

other cellular structures to be noticed, which are, perhaps, to be regarded
as special cells (Fig. 408).

Waves of sound falling upon the auditory nerve produce no sound,
but only when the terminal organs are stimulated.

The Function of Hearing. — To be enabled to understand the use of
the different portions of this complicated organ it will be necessary to
refer to some of the more important laws governing the propagation of
sound. Sound, as before stated, is the result of the vibrations of elastic
bodies, which result in the production of alternate condensation and
rarefaction of the surrounding medium. As a consequence, sound-waves

FIG. 407.— SCHEME OF THE DTJCTTTS COCHLEARIS AND THE ORGAN OF CORTI.

(Landois.)

N, cochl ear nerve ; K inner and P outer hair-cells ; n, nerve-fibrils terminating in P: a, a, supporting
cells : d, cells in the sulcus spiralis ; z, inner rod of Corti : Mb. Corti, membrane of Corti, or the niem-
brana tectoria ; o, the membrana reticularis ; H, G, cells filling up the space near the outer wall.

are produced, in which the particles vibrate longitudinally, or in the
direction of the propagation of the sound, forming so-called waves of
condensation and rarefaction, occurring in concentric circles around the
sounding body.

Like rays of light, sound-waves may be reflected when they impinge
upon an opaque solid, and the same rules as to the angle of incidence
and reflection prevails. It is this throwing back of sound from a resisting
medium that constitutes the echo.

When transmitted through the atmosphere these waves of sound
are collected by the auricle, and from the auricle they are transmitted
through the external auditory meatus to the membrana tympani, which
is thus thrown into vibration. Thus, they are communicated to the

884

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

chain of bones and reach the membrane of the fenestra ovalis. From
that point they are communicated to the peritymph, thence to the
membranous labyrinth, thence to the endolymph, and finally to the
otoliths, which serve to increase the vibratory impression upon the
nerve of hearing. This transmission of sound from the exterior and its
recognition in the centre plainly involves important considerations with
regard to the propagation of sounds.

Sounds are transmitted in three ways : first, by reciprocation; second,
by sympathetic vibration; and, third, by conduction. As regards vibra-
tions by reciprocation, if two strings of equal tension, length, and

St

FIG. 408.— I. SECTION THROUGH THE UNCOILED COCHLEA. II. SECTION
THROUGH THE TERMINAL NERVE-APPARATUS OF THE COCHLEA, AFTER
HEUSEN. (Munk.)

I. F. r., Fenestra rotunda; H, the helicotrema ; St.., the stapes. II. z, Huschke's process; bt, basilar
membrane; e, Corti's arch; g, supporting cells ; h, cylindrical cells; i, Deiter's hair-cells; c, membrana
teetoria; n, nerve-fibres; nt, non-medullated nerve-fibres.

density be stretched side by side each one is capable of producing the
same musical tone when thrown into vibration. Now, when one of these
strings is thrown into vibration the other will fall into vibration by
reciprocation, although it be not itself touched. The same thing will
occur when the same musical note is sounded on another instrument, as
the tuning-fork, if in sufficient proximity. If one of the strings be
stretched tighter than the other a higher musical note will be produced.
If this string be thrown into vibration near one of lower note the latter
will be divided into equal divisions, which are likewise thrown into vibra-
tions of reciprocation, and increased sound will result. If, however,

SENSE OF HEAEING. 885

a string of less tension be thrown into vibration near one of higher
tension there will be no response, for no membrane or string can recip-
rocate a note lower than its own fundamental note. By the term funda-
mental note we mean the lowest note which any string or membrane can
produce. If a higher note be sounded alongside of a string of low
tension the latter, as before stated, will divide itself, and the divisions
will be separated by points of rest, called nodal points, while the
intermediate parts of the string in vibration are termed loops.

These remarks are true not only of strings, but also of membranes.
If some sand be sprinkled on a membrane stretched across a drum-head,
so as to be capable of a musical tone, and then another note of precisely
the same pitch be struck near it, the sand will begin to dance on the sur-
face of the drum-head, thrown into vibrations of reciprocation, and will
accumulate on the lines of rest — the nodal lines ; but if we sound near
it a note higher than that of the membrane stretched across the drum,
then the membrane, instead of vibrating across its whole surface, will
divide itself, and the sand will collect in dark lines on the nodal points
as before. If we sound near the membrane a note lower than its
fundamental note, it will not respond.

A column of air may be thrown into vibrations of reciprocation by
sounding a note in proximity to it.

Sounds are also propagated by resonance. If an instrument capable
of producing a musical note while vibrating be placed in contact with a
medium whose molecules are capable of being thrown into vibration, the
second substance will vibrate and increase the intensity of the original
sound, even if the medium with which we place the sounding instrument
in contact is not itself capable of producing musical tones. Thus, when
we strike a tuning-fork under ordinary circumstances in the air the sound
is but faintly heard, while if we place the fork in contact with a piece
of wood, the sound is greatly increased in intensity. The woody fibres
are thrown into vibrations which reciprocate the original sound.

Sound is also propagated by conduction, and this occurs when an}'
sonorous body during its vibrations is brought in contact with any
medium capable of being thrown into vibration. A familiar example of
this is found in the fact that while the tuning-fork held in the air is but
indistinctly heard, if placed in contact with the bones of the head it is
heard distinctly. In this case the sound is conducted from the tuning-
fork to the nerve of hearing through the bones of the head. All media
do not conduct sounds with the same degree of rapidity. Solids conduct
better than fluids, fluids better than gases, while in a vacuum no sound
whatever can be conducted.

That a sound may be appreciated, it is evident that it must be con-
ducted to the terminal filaments of the auditory nerve in the labyrinth,

886 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

and the first process, therefore, to be considered in the study of the
function of hearing is the means by which sound-waves reach the laby-
rinth, and then the way in which they excite the nerve of hearing.

It has been seen that every sonorous body is in a state of vibration
and that it transmits these vibrations to the surrounding atmosphere,
resulting in waves of condensation and rarefaction traveling in radii from
the locality in which the sonorous body is located.

It has been further stated that sound-waves may be conducted through
any elastic medium, but in the appreciation of sound by the ear evidently
the greatest importance is to be placed on the conduction of sound-
waves through the air, since the conduction of sounds through solids
can but infrequently be of any importance. It has been stated that
sound-waves can be conducted through the bones of the head, and
although this must be exceptional in the case of man, yet in fishes, where
no external ear, auditory canal, or ear-bones are present, it plays an
important part. So, in this case, the sound-waves of the water are
directly transferred to the labyrinth.

We have now to trace the path of the sound-waves from the sonorous
body, through the external ear and auditory canal, through the tympa-
num to their termination in the labyrinth, with the operation of the
different apparatuses by which this transfer is facilitated.

The external ear evidently fulfills the part of an ear-trumpet, and
the great improvement in hearing produced by artificial addition to the
auricle serves to emphasize this point. The external ear is evidently of
a certain amount of assistance in recognizing the direction of sound,
but, as is well known, we are liable in this respect to make errors of
judgment. The origin of sound-waves is determined simply b}r the fact
that the sound is heard most distinctly when the auditory canal is in the
line of propagation of the sound-waves, and, therefore, in order to
determine the direction of a sound we turn the head from one side to the
other until the sound appears to be the loudest. In the lower animals
this is, to a certain extent, facilitated by the exceptional degree of mobility
possessed by the auricle, where we must assume that the recognition of
the direction of a sound is a matter of greater importance and accom-
plished with a greater degree of facility and perhaps exactness.

Having reached the auricle, sound-waves enter through the external
auditory canal and strike against the tympanic membrane. It has been
stated that if a tightly stretched membrane be set into vibration it will
produce a sound, the lowest note being termed the fundamental tone;
and, further, that if a sound which corresponds with the fundamental
tone of such a membrane be sounded in its proximity the membrane will
be set in vibration by sympath}^. It is evident, if such a fact were ap-
plicable to the tympanic membrane, the greatest confusion would result

SENSE OF HEARING. 887

in the perception of sounds. Sounds which coincide with the funda-
mental tone of the tympanic membrane would so predominate as to
drown or confuse all other sounds. The tympanic membrane, however,
is free from this disadvantage, while it possesses in the highest degree
the power of being set in motion by an immense range of vibrations.
Thus, sounds may be recognized that are dependent upon thirty-two
vibrations a second up to such an extremely high pitch as sounds with
thirty-eight thousand vibrations a second will produce. This property
of the tympanic membrane by which it appreciates such a wide range of
sounds, while being free from any fundamental tone itself, is due to two
factors — in the first place, the funnel-shaped form of the membrane, and,
in the second place, its being damped by the chain of ear-ossicles. If a
sheet of india-rubber be stretched over a wide tube and be pressed by a
rod in the centre perpendicularly inward it will form a funnel-shaped
surface curved from within outward. It is evident that in such a mem-
brane the tension will vary at different parts, increasing toward the cen-
tre. Such a membrane, like the tympanic membrane, will have no funda-
mental tone, since its tension is not equal, while the tympanic membrane
will also have in principle the same form, since it radiates from the cen-
tre, within outward, in a convex form. The tympanic membrane, there-
fore, is not very extensible, but its tension is just sufficient to draw it
slightly inward from the centre without it being able to produce any
audible fundamental tone.

On the other hand, great resistance is offered to the vibrations of the
tympanic membrane by its union with the auditory ossicles, which not
only deprive the membrane of every trace of a fundamental tone, so that
it can accommodate itself equally well to vibrations of every degree of
rapidit}r, but by loading the membrane entirely prevent the occurrence
of after-vibrations ; so that, therefore, in this respect the ear-bones act
like the dampers of the pianoforte, which fall upon the wire after every
note has been struck.

Another point is worthy of attention in this connection. Since the
tympanic membrane possesses the shape of a funnel, the point of greatest
vibration must be situated somewhere between the apex and the edge, but
the force of all vibrations passes from the sides toward the centre and at
this point vibrations of the greatest intensity are produced. Moreover, the
tension of the tympanic membrane may be altered by muscular action in
a way to be directly described. The t3rmpanic membrane is in direct
contact with the chain of ear-bones, and this serves to transfer the vibra-
tions of the tympanic membrane to the perilymph of the Iab3'rinth, and,
likewise, by their points of attachment to different muscles, serve to vary
the tension of the membrana tympani and at the same time the pressure
on the lymph of the labyrinth.

888 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The ear-ossicles form a jointed chain of bones connecting the mem-
brane with the oval window. As is well known, solids are capable of
conducting sound-waves by being thrown into molecular vibration, and
the rapidity of such conduction is greater on account of the greater
elasticity and density than in the atmosphere. From the very fact of
the greater rapidity of the conduction through solids the wave length
will be longer, but the conduction of sound through the ear-ossicles is
entirely distinct from such molecular vibrations. In the transmission
of sound-waves from the tympanic membrane to the labyrinth the chain
of bones vibrates as a whole. The average wave length of medium
tones in the ear varies from one-half to one meter, while in solid bodies
it is still greater. The ear-bones are by no means immovably fixed.
From their small mass they are extremely light, so that an impulse acting
on one end will set the whole chain of bones in motion. Consequently,
when waves of sound strike against the t}rmpanic membrane the vibra-
tions are transmitted directly to the ear-bones, and the}' vibrate in a
transverse direction and carry the vibrations to the oval window by
vibrating in mass and not through molecular vibration.

The mode of movement of the ear-ossicles has been a subject of
considerable study. As is known, the handle of the malleus is attached
to the tympanic membrane through its entire length, while its head pro-
jects above the edge of the membrane into the tympanic cavity. Besides
this, the malleus is fixed by ligaments in such a way that motion is only
possible in a to-and-fro vibration around the so-called axis of rotation,
which lies in a plane almost parallel to the tympanic membrane and passes
through the neck of the malleus. When the handle of the malleus is
drawn inward its head will, of course, move in the opposite direction, and
as the handle of the hammer is set in vibration the anvil will also be set
in motion through its articulation with the head of the hammer. The
incus is only loosely connected by a ligament passing through its short
process to the posterior wall of the tympanic cavity in front of the open-
ings of the mastoid cells, while its mode of articulation with the malleus
has been compared by Helmholtz to the action of cog-wheels ; so that
when the handle of the malleus moves inward to the tympanic cavity the
incus and its long process, which is parallel with the handle of the malleus,
also passes inward, from the fact that the head of the malleus pulls the
articulating surface of the incus outward. Therefore, the handle of the
malleus and the long process of the incus vibrate in the same direction.
As the long process of the incus moves inward it gives an impression to
the stirrup-bone, with which it articulates almost at right angles. If,
however, as by a great condensation of air in the tympanum, the tym-
panic membrane is moved outward it, of course, draws the handle of the
malleus with it, and, as a consequence, the hammer-head is forced inward,

SENSE OF HEAKING.

889

and the tendency would be to drag the stapes from the oval window.
This is, however, prevented by the loose articulation of the malleus and
incus, which separate to a certain extent and thus prevent dragging on
the stapes (Fig. 409).

Hence, the system of ear-ossicles forms an angular lever, which
moves around a common axis in a plane vertical to the plane of the
membrana tympani, one arm of the lever on which the power of the
vibrations act being the hammer-handle, the other, the hammer-head with

FIG. 409.— MOVEMENTS OF THE MALLEUS AND INCUS. (Beaunis.)

M, malleus ; E, incus ; A, short process of the incus ; R, long process of the incus ; P, handle of the
malleus ; A B, axis of movement of the ossicles.

the handle, serving to set the entire fluid of the labyrinth into vibration.
The vibrations of the ear-ossicles are, therefore, transverse, although not
analogous to the transverse vibrations occurring in a stretched cord,
since the ear-ossicles do not vibrate on account of their elasticity, but
resemble a system of movable levers. As the long process of the incus
is only one-third the length of the handle of the malleus, of course the
excursions of the former, and with it the stapes, will be less than that of
the tip of the malleus, while, on the other hand, the force of the vibration
in the former will be increased ; so that the stapes is forced inward by

890 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

a more powerful but less extensive vibration. So much for the mode of
conduction of sound through the ossicles.

By contraction of the muscular fibres in connection with the ear-
ossicles the position and tension of the tympanic membrane, as well as
the pressure on the lymph of the labyrinth, may be altered. Two
muscles are found in connection with the ear-ossicles, the tensor tympani
and the stapedius muscle. The tensor tympani lies in the osseous
groove above the Eustachian tube, and has its tendon inserted into the
malleus immediate!}7 above the axis. When this muscle contracts the
handle of the malleus is pulled inward and the tympanic membrane
tightened. As a consequence, the stapes is likewise pressed inward.
On the other hand, when this muscle relaxes the elasticity of the axial
ligament and of the tympanic membrane itself causes the membrane to
again assume its condition of equilibrium. By the increased tension of
the tympanic membrane a greater resistance is offered to the sympathetic
vibrations when the sound-waves are very intense, since it has been found
that stretched membranes are less susceptible to sympathetic vibrations
than are relaxed membranes ; and increase of the tension of the t}^mpanic
membrane by contraction of this muscle, therefore, serves to protect the
auditory apparatus by preventing intense vibrations reaching the nerve
terminations.

The stapedius muscle arises within the pyramidal eminence, and is
inserted into the head of the stapes. When it contracts it draws upon
the head of the stapes and causes the bone to assume an oblique position,
the posterior end of the plate being pressed deeply inward into the
fenestra ovalis, while the anterior edge of the plate is displaced outward.
The stapes is thus firmly fixed and the annular ligament surrounding
the fenestra ovalis becomes more tense. The function of this muscle is
likewise directed to preventing the communication of too intense an
impulse from the incus to the stapes. The stapedius muscle is supplied
by the facial nerve and the tensor tympani by a branch of the trigeminus
which passes from the otic ganglion.

The chain of bones lies within the tympanic cavity, and it is
evident that the vibration of the tympanic membrane will greatly vary
according as the air in the tympanic cavity is in a greater or less degree
of condensation. If this space were entirely shut off from the atmos-
phere the air in it would evidently soon be absorbed, or, at any rate,
undergo change in its composition, and probably be replaced by fluid
secretions, since we know that the middle ear is lined by a secreting
mucous membrane. By means of the Eustachian tube the ventilation
of the middle ear is rendered possible. Through it secretions are con-
ducted out, and by it the equilibrium of pressure between the air in the
tympanum and the atmosphere is rendered possible. As soon as the

SENSE OF HEARING. 891

pressure of the atmosphere is greater than that within the tympanum
the membrane of the tympanum would be pressed inward. On the
other hand, if the pressure within the tympanum be greater than that of
the atmosphere the membrane would be pressed outward, and in both
cases the movements of the tympanic membrane would be restricted and
sound to such an extent interfered with. The equilibrium is maintained
through the opening of the Eustachian tube in the act of swallowing, —
an act which is performed not only during eating, but also at frequent
intervals to carry away the secreted saliva, At other times the Eusta-
chian tube is closed, and by this means the conduction of sound-waves
downward into the pharynx or the conduction upward of sound-waves
from the voice is rendered impossible.

The sound-waves are thus conducted from the tympanic membrane
to the chain of ossicles, and thence by the vibration of the stapes to the
oval window. The membrane of the fenestra ovalis is, as a consequence,
set into transverse vibration, and these vibrations are directly communi-
cated to the fluid of the labyrinth. The lymph, like other fluids, is incom-
pressible, and if, therefore, the membrane of the oval window be pressed
inward there must be a corresponding exit at some other point of the
apparatus. This counter-opening is found in the round window, and as
soon, therefore, as the stapes vibrates inward the membrane of the circu-
lar window vibrates outward, and the pressure upon the fluid of. the
labyrinth is thus relieved while being set into vibrations corresponding
with those of the stapes.

From the oval window the wave travels into the vestibule and from
there into the cochlea, and we must assume that it there throws the
membranous apparatus with its organ of Corti into vibration. The ves-
tibule is, however, divided by the two membranous sacs which it contains
into two portions, each containing fluid, the one in connection with the
oval window and the other with the round window ; so that, therefore,
we cannot imagine that the fluid in the vestibule is directly driven by
the vibrations of the stirrup-bone to the round window, for the scala
vestibuli of the cochlea, which is in connection with the oval window,
is shut off from the scala tympani by the membrane, and ai^ wave, there-
fore, started by the vibrations of the stapes will pass rapidly up the
scala vestibuli, while it will also transfer its vibrations to the membran-
ous partition and thus throw the fluid of the scala tympani likewise into
vibration.

In the cochlea the vibrations of the peritymph throw into vibration
the fibres of the basilar membrane and the organ of Corti, consisting of
the rods and the inner and outer hair-cells, which may be regarded as a
series of stretched strings, a portion of which may be thrown into sym-
pathetic vibration independently of the whole.

892 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The vibrations communicated to these structures in some way give
rise to nervous impulses passing into the terminal filaments of the
auditory nerve. As to the way in which this is accomplished but little
is known. The temptation is strong to find the receiving apparatus
in the organ of Corti, which is composed of a long series of rods
varying regularly in length and in the span of their arches. The
analogy between these structures and, for example, the strings of the
piano is very striking. As is well known, a musical tone sounded
in front of an open piano will set into vibration the corresponding
string of this instrument. The temptation is almost irresistible to
suppose that a similar mechanism is concerned in the perception of
different sounds. If we could imagine that certain definite parts
of the organ of Corti were thrown into vibration only by appropri-
ate sounds the complex process of the perception of different musical
intervals would be greatly simplified, but the more the subject is
examined into the greater are the difficulties surrounding such an
explanation.

In the first place, the terminal filaments of the auditory nerve have
been traced to the inner and outer hair cells, and it must, therefore, be in
this locality and not in the rods of Corti that the sensory impulses
commence.

. In the second place, the rods of Corti are entirely absent in birds,
who, without doubt, are capable of appreciating musical sounds; while,
again, the variation in length of the rods of Corti would be insufficient to
explain the great scope which the ear possesses in the recognition of the
pitch of sounds.

On the other hand, the basilar membrane is tense in a radial
direction and loose longitudinally, and, therefore, as Helmholtz has
suggested, may be compared to a series of strings of varying tension
and length.

If this basilar membrane be looked upon as the receptive organ we
must then assume that each vibration travels up the scala tympani,
throws into sympathetic vibration a small part of the basilar membrane,
which transfers the vibration to the sensory structures above it.

In support of this view it may be mentioned that the radial dimen-
sions of the basilar membrane offer a wider field of difference than
we find in the length of Corti's rods. The whole subject is, however, in
the highest degree obscure, and all that we can say is that the organ of
Corti, composed of the basilar membrane, the rods, and hair-cells, is in
some way concerned in the reception of sound-waves; the manner is,
however, entirely unknown. After all, it must not be forgotten that the
perception of sound takes place not in the ear but in the brain, and that
sound-waves, received in whatever way by the terminal filaments of the

SENSE OF TASTE. 893

auditory nerve, must be conducted to the brain to be recognized as
sounds, and that the analysis of sounds take place not in the ear,
although, perhaps, we may have there a special organ set aside for the
observation of certain sounds, but in the brain.

D. THE SENSE OF TASTE.

The sense of taste is generally described as the facultj^ by which
the flavors of different sapid substances is distinguished. It will be
shown direct^ that the sense of taste is much more limited than this, as
many substances which are said to be appreciated through the sense of
taste are only effective through exciting the sense of smell. The sense
of taste even in this restricted sense is more highly developed in man
than in other animals, for it is not the sense of taste but the sense of
smell which guides animals in their choice of food, for that choice
precedes the prehension of food.

Even in man and the higher mammals there is a considerable
difference of opinion as to what regions of the mouth are endowed with
the sense of taste, and this difficulty of location becomes even more
marked as we descend the animal series. In animals where a tongue is
present it is probable that that organ partakes, with the upper part of
the digestive tract, in the property of presiding over the sensation of
taste, but in many animals the tongue is absent or is so horny as to pre-
clude this possibility. In invertebrates, where no analogue of a tongue
exists, if the sense of taste is present, as it would seem without doubt
to be, as in insects, its seat must be in the parts about the mouth, such
as the proboscis, suckers, etc. In fishes the tongue is rudimentary and
in many it is covered with horny scales or even rudimentary teeth, and if
the sense of taste is present in this group of animals it is either
confined to the upper part of the digestive passages or perhaps to the
olfactory cavities.

In reptiles a thick, fleshy tongue is often present, but it is more fre-
quently slender, sometimes bifid and protractile, and is to be regarded,
as already indicated, as an organ for the prehension of food.

In birds the sense of taste must be very obtuse, since they swallow
their food without comminution, and the tongue is usually hard or semi-
cartilaginous, especially at the point. This particularly obtains in her-
bivorous birds, while in birds of prey, where the tongue is fleshy, it may
perhaps be supposed that the sense of taste is present.

In mammals the sense of taste may, to a certain extent, be definitely
localized in the tongue, and special sense organs have been detected
which apparently preside over this function. The so-called taste bulbs
are found on the lateral surface of the circumvallate papillae and upon
the external side of the depression which surrounds the central eminence

894

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

(Fig. 410). They are also found to a less extent on the fungiform papillae,
the papillae of the soft palate and uvula, and even on the posterior surface
of the epiglottis and on the inner side of the arytenoid cartilages, and on
the vocal cords. These latter localities would seem to throw doubt upon
the connection between these structures and their connection with the
sense of taste, but the fact that after section of the glosso-pharyngeal
nerve these taste bulbs degenerate, and that direct communication can
be traced between this nerve and these cells, would seem to place their
position as the terminal organs of the special nerve of taste beyond doubt.
These taste bulbs are barrel-shaped and consist of series of nucleated
external, almost cylindrical protecting cells, arranged so as to leave an
opening, — the so-called gustatory pore. Lying in the axis of such a
structure are found from one to ten gustatory cells, some provided with

FIG. 410.— STRUCTURE OF THE GUSTATORY ORGANS. (Landois.)

I. Transverse section of a circumvallate papilla: W, the papilla; v, v, the wall in section; R, R, the
circular slit of fossa; K, K, the taste bulbs in position: N, N, the nerves. II. Isolated taste bulbs: D.
supporting or protective cells ; K, under end ; E, free end, open, with the projecting apices of the taste
cells. III. Isolated protective cell, d, with a taste cell, e.

delicate processes at their free extremities, while their lower, fixed ends
become continuous with the non-medullated terminations of the nerve of
taste (Figs. 411, 412, and 413).

The tongue of mammals in its general characteristics resembles that
of man, and similar papillae are found on it. In the different domestic
animals, especially in the herbivora, the sense of taste must differ from
that in the carnivora, although we have every da}' evidences of its exist-
ence, and we know that in the herbivora likewise decided preference for
different substances are manifest, which evidently must be dependent upon
differing degrees of excitation of the sense of taste, although the expla-
nation of that fact is yet entirely beyond us. Thus, as to why a horse
should prefer oats to hay, or the latter to straw, must evidently be ex-
plained by some difference in impression of the substances on the nerve
of taste and not a mere matter of instinct.

SENSE OF TASTE.

895

Only four different varieties of taste can be distinguished. Sub-
stances may be either bitter, sweet, acid, or saline. Substances to
which we attribute the property of flavor owe that characteristic more
to their implication of the sense of smell than of taste. Thus, we speak
of tasting wines, onions, asafeticla, and so on, while, as is well known,
their flavor is due to the excitement of the sense of smell, and not to a
specific stimulation of the nerve of taste ; this may be readily proven by
the disappearance of their characteristic flavors when smell, by closure
of the nostrils or by catarrh, is rendered impossible.

That substances may be tasted it is necessary, in the first place,

FIG. 411.— STRUCTURE OF THE GUSTATORY ORGANS. (Munk.)

A, perpendicular section through the taste organs of a rabbit's tongue; g, taste furrows. B, isolated
protective (a) and (b c) taste cells.

that they should be dissolved in the fluids of the mouth, while the
intensity of the sensation will depend upon the size of the surface acted
upon and upon the concentration of the solution. It has been found
that the following series of substances cease to be distinguished in the
order here stated, as the}' are gradually diluted : syrup, sugar, common
salt, aloes, quinine, and sulphuric acid. Thus, quinine may be diluted
twenty times more than salt and still be distinguished.

The time elapsing between the contact of the substance with the
tongue and its appreciation by the taste also varies with different
substances. Saline substances are tasted most rapidly, perhaps, from
their more rapid diffusion.

896 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The galvanic current is likewise capable of producing the sensation
of taste, which varies according to the direction of the current. Thus,
a bitter metallic taste is developed when the anode, and an acid taste
when the cathode, is placed on the tongue. In this instance it is
doubtful whether the sensation of taste is due to a direct stimulation of
the taste bulbs or to electrolytic changes occurring through the action
of the galvanic current.

All the localities in which the taste bulbs have been detected are
probably possessed of the sense of taste, although certain regions, as
the entrance to the larynx and the hard palate, do not admit of experi-
mental demonstration as regards this point. Without doubt the root of
the tongue and its tip and margins are gustatory, while it is probable
that the under surface of the tongue possesses no power of taste.

The nerves which preside over the sense of taste are certain fibres
of the lingual and the glosso-pharyngeal. After the lingual nerve is
divided the sense of taste disappears from the tip of the tongue. When
the glosso-pharyngeal is divided the sense of taste is lost in the posterior

FIG. 412.— TASTE FURROW IN MAYER'S FIG. 413.— SECTION or MAYER'S ORGAN IN THE
ORGAN IN THE HOG. (Csokor.) HORSE. (Csokor.)

part of the dorsum of the tongue. Contrary to our experience with the
other nerves of special sense, stimulation of the trunks of these nerves
does not give rise to the sense of taste, probably owing to the fact that
both of these nerves are mixed nerves, and contain other afferent fibres
as well as those of the sense of taste.

Certain substances seem to possess the power of antagonizing the
impressions which others ordinarily make on the terminal filaments of
the nerves of taste ; thus the taste of bitter and sour substances may to
a certain extent be corrected by the admixture of sugar, even without
any chemical change occurring in the mixture. Such a result is only to
be explained as some kind of interference of the sensations; on the other
hand, substances having a sweet taste do not possess the power of modi-
fying saline tastes.

Any explanation as to why certain substances possess one peculiar
taste and others another is in our present state of knowledge impossible,
with the single exception of the characteristic taste of acids and alkalies,
where we find the characteristic taste associated with certain definite
chemical characteristics.

SENSE OF TOUCH. 897

The acuteness of the sense of taste admits of education, but is by no
means as delicate as the sense of smell ; thus, a solution of one part of
sulphuric acid to one thousand of water gives its characteristic taste
when only one drop, which may be said to contain about s^oo Par^ °f a
gramme, is placed upon the tongue.

E. THE SENSE OF TOUCH.

When any portion of the external integument is brought in contact
with a foreign body we appreciate what is termed the sensation of touch,
and we are, therefore, warranted in regarding the skin as a sensory organ,
inclosing our entire body and adapted to render everjT part of the body
sensible to external impressions. These may be of the most manifold
kind, and excite peculiar sensations dependent upon the nature of the
contact. To a limited extent this power of tactile sensibility possessed
by the integument belongs likewise to the internal mucous surfaces of
the body, but only for a short distance from their respective orifices.

Tactile sensations, as we shall find directl}T, vary among themselves,
and give us means of determining the physical characters of the body
producing the contact and the locality at which the contact takes
place. When such a tactile sensation is increased in intensity it may be
converted into a painful sensation. If, for example, as in the illustra-
tion given b}T Weber, the edge of a knife is placed on the skin we feel
the edge by means of the sense of touch, a sensation is perceived which
is referred to the object which has caused it. If, however, the skin is
cut by the knife pain is felt, a feeling which is no longer referred to the
cutting knife, but which we feel within ourselves, and which indicates to
us the fact of a change of condition in our own body. By the sensation
of pain we are neither able to recognize the object which causes it nor its
nature. Thus, if a body is placed within the month we are able to
recognize its general characters and to a certain extent its shape,
whether it be solid or liquid, hot or cold; but if the body be swallowed
tactile sensation disappears as soon as the body reaches the oesophagus,
and then, if any sensation be excited, it can only be a painful sensation.
The sensation caused by a too hot liquid cannot be distinguished from a
corroding acid liquid, or from the passage of an irregular hard body
through the oesophagus.

The sense of touch is the simplest and is the only universal sense,
and exists in all members of the animal kingdom. In the articulata,
whether covered by horny (insects) or by calcareous (crustaceans) cover-
ings, the sensation of touch is possessed by all parts of the body in
common, while it is especially developed in the antennae which project
from the sides of the head.

In mollusks and zoophytes sensibility is much more obtuse, but is

57

898 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

likewise distributed over the entire surface of the body, and here, also, is
perhaps more highly developed in the tentacles or pseudopods which are
so often found.

In fishes projecting organs at the side of the buccal opening receive
terminations of afferent nerves, and these, together with the fins, may be
regarded as especially developed tactile organs, although here, also, the
entire body surface possesses general sensibility.

In reptiles no special tactile organ is present, unless the tongue, in
certain instances, may fulfill this function.

In birds the tactile sensibility of the skin must be to a certain ex-
tent interfered with by the thick coating of feathers and the sensibility
of the feet by the dense scales which usually cover these parts. In birds
in general it is the beak which possesses tactile sensibility in the highest
degree.

In mammals the greatest variation exists in the specialization of
certain parts of the body for the appreciation of tactile sensations. In
monkeys, although four hands may be said to be present, they are not to
be regarded as sensitive organs as are the hands of man; since, in the
first place, their fingers do not possess the power of separate movement
and their thumb is much shorter and incapable of being brought into
apposition with the fingers ; while the palm of the hand, which frequently
serves as a means of progression, is covered with calloused epithelium.
In certain monkeys with prehensile tails this organ is doubtless possessed
of tactile power in the highest degree.

In solipedes, ruminants, and carnivora, in whom the extremities of
the limbs terminate in a single or double hoof, in claws, or calloused
skin, in these localities the sense of touch must be very imperfect. But
these parts of the animal body must be capable, nevertheless, of giving
distinct notions as regards resistance, solidity, and consistence, since
these horny parts rest on a highly developed papilkuy layer of the derm.
In solipedes and ruminants, especially in the former, the lips possess a
considerable degree of mobility, and are, as has been shown, the princi-
pal organs of prehension and are highly endowed with tactile sensibility.
In carnivora the termination of the soft parts about the anterior nares is
extremely sensitive and is employed by them as a tactile organ, while it
is only a step farther to the hog or the elephant, where the prolongation
of this part of the body acquires extreme perfection as an organ of
tactile sensibility. In certain animals the long hairs growing from the
upper lip, as in the cat and the rat and the seal, are to be regarded as
tactile organs, since they conduct tactile impressions to the sensory
nerves. Probably, also, the spines of the porcupine fulfill the same
function.

Like the more specific sensations, the sensations of touch require for

SENSE OF TOUCH. 899

their production terminal organs which are found in the epidermis of the
skin and surrounding the underlying nerve structures. The manner in
which the terminal filaments of the sensory nerves are distributed to
the skin varies.

Five general different modes of distribution have been recognized.
The touch corpuscles of Wagner and Meissner lie in the papillae of the
true skin and are most numerous in the palm of the hand and the sole
of the foot, and especially on the fingers and toes. They are oval
or elliptical bodies covered by layers of connective tissue arranged
transversely and containing within a granular mass with longitudinally
striped nuclei. Each of these corpuscles is surrounded in a special
manner b}^ a medullated nerve-fibre which loses its nryelin and divides
into a number of fibrils within the corpuscle.

Pacini's corpuscles are oval bodies likewise found in the subcu-
taneous tissue of the skin of the fingers and toes and of various other
localities. They consist of numerous layers of nucleated connective
tissue separated from each other by fluid and lying one within the other,
like the coats of an onion. Into the axis of each passes a medullated
nerve-fibre whose sheath of Schwann becomes united with the capsule.
In the interior or central core of the corpuscle each nerve-fibril
terminates in a small, hair-shaped enlargement.

Grouse's corpuscles are elongated or rounded bodies found in the
deeper layers of the conjunctiva, the floor of the mouth, and various
other mucous surfaces. The sheath of Henle communicates with the
nucleated capsule, while the non-medullated fibre is continued into the
internal core.

Merckel's tactile corpuscles occur in the beak and tongue of the
duck and goose, in the tactile hairs or feelers, and also in the epidermis
of man and other mammals. They are composed of a capsule
containing two or three or more granular nucleated cells piled one
on another in a vertical row. Each corpuscle receives at one side
a medullated nerve-fibre which terminates either in the cells themselves
or in the transparent protoplasmic substance between the cells. In
addition to these special terminal organs of the afferent nerves in
many localities their axis cylinder splits up into fibrils to form a
nervous net-work which is to be regarded as an organ of sensation.

Nerve-trunks are supposed to contain fibres which are especially
concerned in conducting painful impressions and tactile impressions.
Sensations of temperature fall under the second head. As already
indicated, the -first of these modes of sensation may be converted into
the second.

Thus, when a body is brought in contact with the skin we may form
a conception of the weight of the bod}" — that is, the amount of pressure

900

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

which it exerts upon the skin — and to a certain extent its temperature.
If the degree of pressure be greatly increased, the sensation of pressure
gives place to one of pain, and so, also, for extremely hot or extremely
cold bodies. On the other hand, impressions which are not localized on
the terminal organs, as, for example, the passage of the electric current
through the skin, are not capable of being regarded as tactile sensations.
In other words, we are unable to distinguish one such mode of stimula-
tion, except within narrow limits, from another. Thus, for example, the
sensation of mechanically pricking the skin is probably identical with
that produced by the passage of the current. Again, the contact of a fluid
with the skin will cause a tactile sensation, since it is in contact with the
nerve terminations, and if that fluid be an acid and pass below the terminal
organs and implicate the nerve-fibres a sensation of pain will be caused ;
so that stimulus which when applied only to the nerve terminations may
cause a tactile impression, when applied to the nerve-trunk results in a
painful sensation.

The intensity of the sensation produced by pressure depends almost
as much upon the rapidity of the application of the pressure as upon the
degree of the pressure. If the increase be gradual, more pressure may
be applied with scarcely a perceptible sensation ; while, on the other
hand, the rapid application of a less pressure may cause a much more
intense sensation. All parts of the skin are not equally susceptible to
pressure for the simple reason that all parts are not equally supplied
with tactile corpuscles. In man the most sensitive localities are on the
palmar surface of the fingers, on the forehead, and on the flexor surfaces
of the limbs as contrasted with the extensor surfaces.

If two points of the skin are subjected to pressure the sensation
becomes fused when the two points are sufficiently close. When an im-
pression is made upon any part of the body, not only the character but
the locality are appreciated. This power, however, of localizing pressure
sensations varies in different localities.

The following table from Weber gives the minimum distances at
which simultaneous stimulation of two points may be recognized as two
distinct sensations : —

Tip of tongue, ....

Palm of last phalanx of finger, .

Palm of second phalanx of finger,

Tip of nose, .

White part of lips,

Back of second phalanx of finger,

Skin over malar bone,

Back of hand,

Forearm,

Sternum,

Back, .

1.1 millimeter.

22

4.4

6.6

8.8

11.1

15.4

29.8

39.6

44.
66.

BOOK III.

THE REPRODUCTIVE FUNCTIONS.

(901)

SECTION I.

THE REPRODUCTIVE PROCESSES.

ALL of the functions of the animal body economy which have as yet
been considered have dealt solely with the preservation of the individual.
Through the exercise of the reproductive function is accomplished the
preservation of the species. The duration of the life of any single
animal is a limited one, and if, therefore, each species did not possess
the power of reproducing itself in a new and similar individual the
species would eventually die out.

The mechanism by which reproduction is accomplished greatty
differs in different groups of the animal kingdom. In all vertebrates it
is accomplished by the union of two individuals of opposite sexes, male
and female. In a large number of the invertebrate animals the two
sexes, or at least the two sexual organs, are found united in the same
individual, and the different acts of generation are thus accomplished in
the body of the same animal; while the mode of reproduction offers
a strong analogy to that of the vegetables, which, likewise, contain
within the same floral envelope the organs of the two sexes. In other
animals still more imperfect a mode of generation may be observed
which is analogous to that of cryptogamous plants. Here no organs of
generation can be detected, and reproduction is accomplished by sep-
aration of parts of the parent body which possess the power of
development and growth. Sometimes the germ detaches itself from
the individual in the form of a vesicle, which passes through all the
phases of development. Such a mode of reproduction is spoken of as
generation by spores. At other times a bud may be noticed to form
from within or without the animal, which, after having acquired a more
or less complete development, separates itself from the parent, and after
the separation continues to grow and develop into a new animal. Such
a mode of reproduction is spoken of as gemmiparous generation.
Finally, the new organism may develop from the parent organism by a
simple process of detachment of a part of the parent, after the separa-
tion the detached portion forming a new animal, while the parent
replaces the part which was lost. Such a mode of reproduction is
spoken of as generation by fission.

In all animals provided with organs of generation, whether borne
by different individuals or united in the same individual, generation is

(903)

904 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

invariably accomplished by the formation of an egg by the female and
of a fecundating liquid by the male, which, coming in contact with the
egg developed by the female organism, gives to the latter its power of
independent growth and development. Sometimes the fluid formed by
the male conies in contact with the egg of the female after it has passed
from the body of the female, as is the case in fishes, while at other
times the male fecundates the egg before its exit and while it is still
within the body of the female, where it undergoes a certain part of its
developmental changes, as in the bird. Finally, the egg fecundated by
the male may be retained within the cavity of the female until it has
undergone the first phases of its development.

Although numerous differences may be met with in different mem-
bers of the animal kingdom, these fundamental facts are always observed :
on the one side the production of an egg, and on the other the production
of a fecundating fluid.

In all the vertebrates, whether mammals, birds, reptiles, or fishes,
generation is accomplished by the union of the two sexes, the sexual
organs being found in different individuals.

In mammals the process of fecundation takes place within the
interior of the sexual organs of the female, and copulation is, therefore,
essential. In most reptiles a similar process takes place, although in
some fecundation is external •" that is to say, the male extrudes the
seminal fluid upon the eggs as they leave the body of the female. This
latter process is also that which holds in fishes. In the fishes the eggs,
covered, as in the case of the batrachians, with a soft membrane, are
usually deposited along the banks or at the bottoms of rivers or ponds,
while the male deposits at variable intervals the fecundating liquid. As
a consequence of the exposure to so many different causes of destruction
a large number of eggs escape fecundation, but the immense number de-
posited b}' the fishes serves, however, to prevent the ultimate extinction
of the species. As many as a million eggs have been said to be extruded
at one time from the body of the female of various fishes.

The ovaries of the female fish are two voluminous glands, which
almost fill the abdominal cavit}^ of the fish at the time of spawning. In
most of the bony fishes the oviducts are continuous with the ovaries and
form the extrusory canal. In many of the cartilaginous fishes the
abdominal extremity of the duct is free, as is the case in mammals,
reptiles, and birds. The oviducts open into the cloaca.

The testicles form in the male two voluminous glands, opening by
means of the spermatic canals either into the cloaca, or by a special
opening in the neighborhood of the anus. In certain of the 'cartilaginous
fishes fecundation occurs within the body of the female, and there is,
therefore, true copulation analogous to that in birds. In these fishes the

REPRODUCTIVE FUNCTIONS. 905

eggs are covered by a horn}- envelope. In others the fecundated eggs
remain in the interior of the oviducts and there develop, and the animal
bears its young.

In reptiles, as in birds, the product of generation comes from the
female organs in the state of an. egg, while in most cases fecundation
precedes, as in the birds, the escape of the egg, and the egg at the time
of its exit is contained within a solid envelope, although, as a rule, less
resistant than that surrounding the egg of the bird.

Various batrachians extrude their eggs before fecundation and the
male fecundates them while clinging to the body of the female at the
moment of their exit. In cases where copulation takes place the exit of
the eggs occurs at a considerable interval after their detachment from the
ovary, and the egg retained in the oviduct develops and is not expelled
until just at the point at which the young is able to carry on a separate
existence; while in some instances, as in some serpents, incubation is
terminated and the eggs are ruptured within the body of the female, and
the living young are expelled from the body of the mother. Reptiles, as
a rule, do not incubate their eggs themselves after extrusion, but the}^ de-
posit them in the sand or in the water, as in the case of the amphibious
reptiles, where the external heat is sufficient to accomplish their
incubation.

Females of the class of reptiles have two ovaries and two oviducts,
which open separately into the cloaca, the oviducts, as in birds and
mammals, not being continuous with the ovary, but being free in the
abdominal cavity, and possessing trumpet-shaped extremities analogous
to the fimbriated extremities of the Fallopian tubes in mammals.

The male organs of generation differ in different species. In the
batrachians there are no organs of copulation. The spermatic canals open
into the cloaca, and fecundation occurs, as in the birds, by the application
of the ani, when fecundation precedes the expulsion of the eggs. In other
groups of reptiles a penis is present, into which the spermatic canals
open.

Of all the reptiles batrachians are the most productive. Turtles
extrude four to five eggs, serpents ten to twenty, and frogs many hun-
dreds. After escaping from the egg batrachians are not, as a rule, fully
developed, but during the first two weeks undergo a true metamorphosis,
first existing in the form of tadpoles, deprived of limbs, but having a
tail and breathing by branchia situated at the side of the neck. Grad-
ually limbs develop and the tail as well as the gills disappear, and the
animal then breathes by lungs.

In birds the product of generation leaves the sexual organs of the
female while still within the egg, and such animals are, therefore, termed
oviparous, although it must not be forgotten that man and other animals

906 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

are also in the strict sense of the word oviparous animals, only in them
the egg does not leave the body of the female until completely developed.

In mammals the fecundated egg passes through the Fallopian tube
and becomes arrested in the uterus and is there fixed, and there under-
goes what may be termed an internal incubation, while at the same time
vascular connections between the egg and the body of the mother are
established. In birds, likewise, the fecundated egg passes through the
oviduct and there becomes coated with an albuminous layer, around
which is finally deposited a la}^er of calcareous matter which hardens
before the egg is extruded. It, therefore, contains within itself the
materials necessary for the development of the embryo, and is, as a con-
sequence, more voluminous than that of the mammal. The eggs of birds
are finally developed by external incubation.

Birds, like reptiles, are, as a rule, possessed of no external male
organs of copulation. The testicles are placed near the kidneys, and the
spermatic canals open at the inferior extremity of the digestive tract at
the cloaca, and it is by the application of the anus of the male to the
cloaca of the female that fecundation is accomplished. In certain birds,
as the ostrich, duck, and goose, a rudimentary penis is, nevertheless,
present.

The fundamental part of the egg, or the yelk, is formed in the ovary
of the female. When the yelk has. attained its full development the
ovarian capsule breaks and the yelk, inclosed by the vitelline membrane,
passes into the oviduct. There it meets with the seminal fluid and becomes
enveloped by a layer of albuminous matter, while the yelk undergoes a
rotatory movement and the chalazae, or albuminous ligaments, found
in the white of the egg are formed. About six hours after the exit from
the ovary, and when the egg has reached the lower third of the oviduct,
the albuminous layer, or the white of the egg, becomes enveloped by a
membrane, at first transparent, and which finally doubles itself into two
folds. The fold adhering to the albumen remains in the state of a mem-
brane, while calcareous matters are deposited in the more external
membrane so as to form the egg-shell. The formation of the shell is
much slower than that of the albumen, and it is only after about twent}7-
four hours that the complete egg is expelled from the inferior part of the
oviduct into the cloaca and thence to the exterior, the small point of the
egg being first extruded.

If examined while still within the oviduct, or immediately after its
extrusion, it may be readily determined that characteristic changes have
occurred within the germinal vesicle, and these progress until the embryo
is completely developed, its life being sustained during the period of
incubation by the albuminous matters stored up in the egg, while respi-
ration takes place through the pores of the shell membrane. In the case

BEPKODUCTIVE FUNCTIONS. 907

of birds, in contradistinction to what holds in mammals, segmentation
is partial, while the remainder of the yelk contained within the umbilical
vesicle, and consequently communicating with the intestine of the bird,
serves for its nutrition ; as a consequence the umbilical vesicle persists
during the entire period of incubation and even up to the time when the
bird issues from the shell.

The heat necessary for the development of the embiyo within the
egg is, as a rule, supplied by the body of the mother, but, as is well
known, eggs may be artificially incubated, it only being necessary
to place them at a constant temperature of from 35° to 40° C., turning
them each day.

In mammals the female nourishes its young for a variable period
after birth through the secretion formed by the mammary glands.

In mammals the different acts of generation closely correspond with
similar processes in man, the principal differences lying in the number
of the young, the duration of gestation, the frequency of the acts of
reproduction, and certain anatomical peculiarities relative to the mode
of adherence of the foetus or foetuses to the uterine cavity. Among
mammals some bear but one young at a time. These are the cow, mare,
ass, stag, elephant, and monkey ; the bear, the roebuck, the castor, the
marmot, and the guinea-pig three to four; the lion, the tiger, and the
leopard four to five ; the dog, the fox, the wolf, and the cat five to six ;
the rabbit and the water-rat six to eight ; the pig and the rat as many
as fifteen.

The duration of gestation is three weeks in the guinea-pig, four
weeks in the rabbit and hare, five weeks in the rat and marmot, six
weeks in the ferret, eight weeks in the cat, nine weeks in the dog and fox,
ten weeks in the sloth, fourteen weeks in the lion, seventeen weeks in the
castor and sow, twenty-one weeks in the sheep, twenty-two weeks in the
goat, twenty-four weeks in the roebuck, thirty weeks in the bear, thirty-
six weeks in the stag, forty-one weeks in the cow, forty-three weeks in
the mare, the ass, and the zebra, forty-five weeks in the camel, and one
hundred weeks in the elephant.

The number of young borne by mammals is capable of being modi-
fied under different conditions. Animals which in a state of nature,
copulate but once in a year, when reduced to a state of domestication
enter anew into heat and may copulate a short time after the previous
birth ; this is, without doubt, due to the more abundant nourishment sup-
plied to such animals in a state of domestication. The mare may pass
into heat ten or twelve days after the birth, the cow after twenty days.

The number of young borne by mammals is principally subordinate
to the duration of gestation. Small mammals, which carry their young
but a short time, as a rule bear more frequently than those in which

908 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

gestation is of longer duration. Thus, the water-rat or guinea-pig may
bear five or six times a year.

In most mammals the uterus is not constituted by a single cavity,
as in the human female, but is prolonged more or less on each side, con-
stituting what are termed the horns of the uterus. Sometimes, as in car-
nivora, the division of the uterus is prolonged up to the vaginal orifice
of the uterus. This division of the uterus into two horns, or two pouches,
more or less distinct, does not occasion any difference in the mode of
connection of the eggs with the uterine mucous membrane. In the
carnivora and in rodents the mucous membrane, as in the human species,
adheres to the body of the organ and separation is extremely difficult.
In solipedes and the pachyderms the uterine mucous membrane is but
slightly adherent to the subjacent tissue and may even be thrown into
folds.

In horned ruminants, as the cow, the mode of union of the egg
with the uterine mucous membrane presents a remarkable peculiarity.
The foetal placenta occurs in isolated cotyledons, the cotyledons being
formed, as in the human species, of vascular loops implanted in the
mucous membrane of the uterus, being designated under the name of the
uterine cot}7ledons. These uterine cotjdedons exist in the female even
before pregnancy and persist after the separation of the foetus and its
multiple placenta.

When the young of a mammal is born the membranes of the egg and
the umbilical cord frequently rupture spontaneously. In other cases the
female breaks the membranes and the cord with her teeth. Most car-
nivorous animals devour the after-birth. In the horned ruminants the
adhesion of the cotyledons of the foetal placenta with the uterine coty-
ledons is so close that frequently several days elapse after the birth of
the foetus before the placenta becomes detached. In such animals the
expulsion of the placenta cannot be facilitated by drawing on the umbili-
cal cord without great risk of hemorrhage from rupture of the uterine
vessels.

When the animal is multiparous the membranes and placenta of each
are expelled with the young to which they belong. In certain species of
mammals the young are but slightly developed and are incapable of
making use of their limbs. Many such animals, as the marsupials,
remain permanently attached to the breasts of the mother while carried
in pouches formed by a fold of the integument of the abdomen.

1. THE REPRODUCTIVE TISSUES OF THE FEMALE. — As already stated,
reproduction is dependent upon the union of the ovum contributed by
the female with the spermatozoa formed by the sexual organs of the
male. These reproductive tissues in mammals now deserve somewhat
further attention. Nothing need be added to the morphological descrip-

KEPEODUCTIVE FUNCTIONS. 909

tion of the ovum, which has already been fully considered. Some points
in the development of the ovum and its attendant phenomena neverthe-
less deserve consideration.

The ova are developed in the matrix of the ovar}*. The latter con-
sists of a connective-tissue frame-work supplied with blood-vessels,
nerves, and lymphatics, whose surface is covered with a layer of columnar
epithelium — the remains of the germinal epithelium. The most super-
ficial layer of the ovary is called the tunica albuginea and contains no
ova; but if section be made of the ovar}^, throughout its entire sub-
stance will be found small follicles varying from one-hundredth to one-
thirtieth of an inch in size. In each of these Graafian follicles will be
found an ovum in different stages of development. Immediately after

FIG. 414.— SECTION OF ATS OVARY. (Landois.)

e, germ epithelium; 1, large-sized follic'es : 2 2, smaller sized follicles; o, ovum within a Graafian follicle;
v v, blood-vessels of the stroma ; y, cells of the membrana granulosa.

birth the ovary contains immense numbers of ova — in the human female
infant from fort}T thousand to sevent3r thousand. The ova develop from
the layer of germinal epithelium which originally completely surrounded
the ovary. At different intervals on the surface depressions form, which
serve to carry in a la}^er of germinal epithelium to form the so called
ovarian tubes. These tubules gradually become deeper and deeper, and
contain within their interior large, single, spherical cells, with a nucleus
and a nucleolus, in addition to the small, columnar cells lining the tube.
As the tubules extend into the ovary the growth of the stroma of the
ovary serves to constrict the orifices of the tubules, and finally their
openings become completely obliterated, and the tubule, which originally
began as a pocket-shaped depression on the surface of the ovary, now

910 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

exists as a closed, more or less circular follicle, completely separated by
the ovarian stroma from the surface (Fig. 414).

Each compartment, or Graafian follicle, so formed usually contains
one, or at the most two, ova, which develop from the large cells
(primordial cells) already referred to.

The lining of the tubule, which it must not be forgotten was derived
from the exterior covering membrane of the ovary, is spoken of as the
membrana granulosa, and at one point its cells become elevated to form
a projection, the proligerous disk, by which the ovum is connected with
the membrana granulosa. The follicles are at first only .03 millimeter
in diameter, but they gradually become larger, especially at the time of
puberty. The entire cavity of the Graafian follicle is occupied by a fluid,
the so-called liquor folliculari, which gradually accumulates during the
growth of the Graafian follicle. Each Graafian follicle is, therefore, com-
posed of an external tunic which is highly vascular in character. Within
this is the granular layer rising at one point to form the proligerous
disk, in contact with which is the ovum, while the remainder of the fol-
licle is occupied with fluid. As the follicles increase in size they
become depressed toward the centre of the ovary, but when about to
burst again rise to the surface, until, finally, the walls of the Graafian
follicle will lie directly below the germinal epithelium on the surface of
the ovary. Its diameter is now from one millimeter to 1.5 millimeters.
The rupture of the first Graafian follicle corresponds with the occurrence
of puberty or of fertilit3r and indicates the period at which the female
organism first becomes capable of the functions of generation. The
smaller the mammal the earlier does this capability for procreation
appear. In the smaller mammals, such as the rabbit, the guinea-pig, and
the rat, as well as in birds, it appears within the first year ; in larger
animals, as the cat and the dog, in the second year, while in the largest
mammals, as the horse, cattle, and the lion, in three years ; in the llama,
in four years ; in the camel, in five years ; in the human female, about
the fourteenth year, and in the elephant, between the twentieth and the
thirtieth year.

Puberty in the human female is recognized by the first occurrence
of menstruation, which consists in the escape of blood from the external
genitals. In warm climates menstruation first sets in between the ages
of eleven and twelve }Tears ; in cold climates between the ages of four-
teen and sixteen years. The duration of each single menstrual period
varies, as a rule, from three to five days, although it may last as long as
eight, or only one or two days. Toward the age of forty or fifty
years in the human female the procreative faculty disappears and with
it the menses cease. Such a period is spoken of as the climacteric or
menopause.

KEPKODUCTIYE FUNCTIONS. 911

At the occurrence of puberty various changes take place which mark
the appearance of reproductiveness. As such may be mentioned in-
creased vascularity and development of the external and internal gener-
ative organs, the characteristic changes which now commence in the
pelvis, the development of the mamma?, and the growth of hair on the
pubes and in the axilla. Menstruation recurs, usually, at intervals of
twent3T-eight days, and each menstrual period corresponds with the ripen-
ing and rupture of a Graafian follicle. During menstruation from one
hundred to two hundred grammes of blood escape. This blood has lost
its power of coagulation, probably through mixture with the alkaline
secretions of the uterus and vagina. The source of the hemorrhage is
the mucous membrane lining the uterus. The ciliated epithelium of the
uterus becomes swollen, congested, and soft, and almost entirely shed.
A similar congestion likewise occurs in the ovaries and Fallopian tubes,
the congestion of the ovary leading to a greater transudation of fluid
into the Graafian follicle and consequent rupture, while the great conges-
tion and engorgement of the blood-vessels of the uterus lead to the
rupture of the finer capillaries and the consequent escape of blood.

In addition to the congestion of the internal genital organs, the
external genital organs also become more strongly congested and
swollen.

Phenomena analogous to the process of menstruation in the human
female occur in all females of the class of mammals, in the domestic animals
the condition being spoken of as heat, and its first occurrence marks not
only the first appearance of the power of procreation but also the times
at which copulation with the male will be permitted. In all of the
domestic animals the occurrence of heat coincides with the rupture of
one or more Graafian follicles and the escape of one or more ova from
the ovar}~, together with the increased vascularity of the genitals. The
external signs of heat are the following : Slight swelling and reddening
of the vagina and vulva, more or less flow of mucous, reddish discharge
from the genitals, characterized by a peculiar odor, which especially seems
to possess the power of attracting the male, frequent urination, often
slight swelling of the mammary gland with alteration in the characters
of the milk ; the disposition of the animal becomes restless, it seeks the
male of the same species, frequently gives vent to various cries, and
sometimes refuses to eat. The characteristics of heat vary somewhat
in different animals. In the mare urination is frequent, the vulva is the
seat of spasmodic discharge, and the clitoris becomes erect. The mare
whinnies and seeks the male. Occasionally a small amount of blood
escapes from the external genitals. The cow becomes very restless, con-
tinually bellows, and attempts to mount other animals even of the same
sex. In sheep the appearances of heat are less characteristic, and are

912 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

evidenced simply by greater uneasiness, leaving the flock and seeking the
ram, and will only then permit the act of copulation. The same remarks
also appty to the goat. The sow at this time appears to grunt more than
usual, is more irritable and more vivacious, is restless, may bite, and
shows loss of appetite. Heat reaches its maximum in twelve to sixteen
hours. In the bitch there occurs a great hypersemia of the genital parts
and an abundant exudation of bloody mucus. The vulva is congested
and swollen, and the animal is much more lively and vivacious than usual
and playful, especially with dogs which are attracted from a great dis-
tance by the peculiar odor of the discharge.

In all the domestic animals the phenomena of heat have a longer or
shorter duration. In the mare they last from two to three days ; in the
cow, from fifteen to thirty hours ; in the sow, from one to three days ; in
the sheep, from two to three da}-s ; in the goat, from two to three days,
and in the bitch, from nine to fourteen days.

If conception occurs the phenomena of heat only make their reap-
pearance after delivery. In the cow this occurs in three to four weeks
after delivery, and recurs every three weeks if impregnation does not
occur. In the mare heat may appear from five to nine weeks after
delivery, and, if impregnation does not occur, every nine days afterward.
So long as the sow is suckling phenomena of heat do not appear, but
after the removal of the young heat comes on about the third day, and,
if impregnation does not occur, recurs every nine or twelve days. In
the sheep, after delivery, heat occurs in from three to four weeks ; when
suckling only two to four months later, and recurs at intervals of from
seventeen to twenty-five days. The mare is in heat usually in the spring
and again in the autumn; the goat in the autumn; the sheep in the
autumn and spring, while the other animals are in heat at intervals
throughout the entire year at the intervals already mentioned (Strebel).

The occurrence of menstruation and heat coincides with the ripening
of an ovum. In the human female, as in the mare and cow, one ovum or,
at the most, two ripen at one time ; in the goat, from one to four, while
in the dog and cat as man}^ as ten ova may mature together.

Through an increase of the blood pressure in the vessels of the
ovary blood transudes into the interior of the Graafian follicle, and thus,
by increasing the pressure, causes a rupture of the wall at its thinnest
point, and the ovule, together with the proligerous disk and the follicular
fluid, escape into the abdominal cavity. The ovary lies free in the
abdominal cavity in a fold of the peritoneum. As the ovule escapes from
the ovary the Fallopian tube, and its fimbriated extremity, is found, from
its state of congestion, in a condition of erection, and in all probability
the fimbriated extremity becomes closely applied to the ovary. As a con-
sequence, the ova escaping from the ovary fall within the mouth of the

REPRODUCTIVE FUNCTIONS. 913

ovarian tube and are carried toward the uterus by means of the cilia
lining the Fallopian tube. Frequently such a close contact does not
occur, since numerous cases of failure of the ova to enter the Fallopian
tube are recorded, and, as a consequence, abdominal pregnancy may
take place. Still, there is no doubt that the congestion of the Fallo-
pian tubes must result in their erection, as may be accomplished arti-
iicially by injection of their blood-vessels. It is probable that the cur-
rents set up by the continued motion of the cilia in the Fallopian tubes
are the main cause in leading to the entrance of the ova into the Fallo-
pian tubes.

After the ovum has entered the Fallopian tube from one to three
days is required for its passage to the uterus. Here, if not already
impregnated, it may meet with spermatozoa, or ma}^ undergo fatty degener-
ation, although certain changes, as already detailed, may occur in the ovum
even when unimpregnated.

As the Graafian follicle bursts it discharges its contents and col-
lapses, while in its interior remains the residue of the granular membrane
and a small quantity of blood, which rapidly coagulates. The vascular
walls of the follicle swell up, and connective-tissue proliferation gradually
leads to the filling up of the follicle, whose contents finally undergo fatty
degeneration, and from the yellow appearance thus produced the name
corpus luteum has been applied to this spot. If pregnancy has not
occurred the fatty matter is rapidly absorbed, the blood breaks up into
hsematin and other derivatives, while the entire mass gradually shrivels,
and by the end of four weeks has almost disappeared. Such a corpus
luteum is spoken of as a false corpus luteum. If impregnation has taken
place this corpus luteum instead of disappearing increases in size, so that
at the end of three or four months its walls are thicker and its color
deeper, and at the termination of gestation it may be as large as six or
ten millimeters in diameter, and may remain for a long time afterward.
Such a form is spoken of as a true corpus luteum. It is, however, prob-
able that too much importance has been laid upon the distinction between
these two forms.

2. THE REPRODUCTIVE TISSUES OF THE MALE. — The secretion of the male
genital organs is known as the seminal fluid, or sperm, and it is formed
by the secreting tubules of the testicles. It consists of a whitish-yellow,
sticky fluid of high specific gravity and of neutral or alkaline reaction.
In the seminal fluid of the horse are found 18 per cent, of solids, in that
of the bull 17.6 per cent., while in that of man there is only 10 per cent,
of solids, of which 4 per cent, consists of inorganic salts, especially of
calcium and magnesium phosphate. When exposed to the air it becomes
more fluid, and when water is added to it, it becomes gelatinous. The
seminal fluid as discharged from the urethra is mixed with the secretions

58

914

PHYSIOLOGY OF THE DOMESTIC ANIMALS.

of the glands of the vas deferens, of Cowper's glands, of the prostate
gland, and of the vesiculae seminales. It contains water, varying from
80 per cent, to 90 per cent, in different animals, serum-albumen, alkali albu-
men, nuclein, lecithin, cholesterin, fats, salts, especially the phosphates
of the alkaline earths, with sulphates, carbonates, and chlorides, and
a peculiar odorous principle the nature of .which is unknown.

When examined with the microscope it is found that the seminal
fluid may be divided into a plasma and formed elements. The constit-
uents already mentioned constitute the plasma of the semen and the
formed elements are the so-called spermatozoa, and it is the latter which
are the active elements of the secretion in the function of reproduction.

k

m

mm

FIG. 415.— SPERMATOZOA. (Landois.)

1, human (X 600), the head seen from the side ; 2, on edge ; 7c, head ; m, middle piece ; /, tail ; e, ter-
minal filament. 3, mouse. 4, bothriroephalus latus. 5, deer. 6, mole. 7, green woodpecker. 8, black
•wan. 9, from a cross between a goldfinch (m) and canary (/). 10, cobitis.

Each spermatozoon consists of a flattened or pear-shaped head, fol-
lowed by a rod-shaped middle piece with a long, tail-like prolongation, or
cilium. When examined shortly after extrusion from the testicle, the
cilium is found to be in rapid vibration, and by this motion the entire
spermatozoon is propelled forward at the rate of about half a millimeter
in a second. The movement of the spermatozoon is identical with that
of other forms of ciliated movement and is affected in the same way by
the same reagents. At first the movements are active, and, under favor-
able circumstances, they come to rest only after two or three days. The
spermatozoa of different animals differ in shape and size, as is shown in

REPKODUCTIYE FUNCTIONS.

915

the accompanying diagram (Fig. 415). In man the spermatozoa are about
.05 millimeter in length, the head being oval with a thickened posterior
border, and their shape is, therefore, somewhat analogous to that of a pear.
The spermatozoa are developed from the nucleated protoplasmic
cells which line the seminal tubules of the testicle. These tubules are
lined by several layers of more or less cubical cells. The outer cells,
next the basement membrane, often show a large nucleus in process of
subdivision. Internal to these are several layers of inner cells with
nuclei, often dividing so that they form a progeny of cells internal to
those toward the lumen of the tube. From these cells so formed by sub-
division and which are termed spermatoblasts the spermatozoa are
formed. These spermatic cells are spindle-shaped and form nucleated
protoplasmic prolongations which project into the lumen of the tube and
break up at their free ends into flat, round, or oval lobules. During the

a

FIG. 416 —SEMI-DIAGRAMMATIC SPERMATOGENESIS. (Landois.)

I. Transverse section of a seminal tubule; a, membrane; b, protoplasmic inner lining; c, Spermato-
blast ; x, seminal ceils. //. Unripe Spermatoblast ; /, rounded cleavage lobules ; p, seminal cells. ///.
Spermatoblast, with a fre* spermatozoon, t. IV. Spermatoblast, with ripe spermatozoa, k, not yet
detached ; r, tail ; n, wall of the seminal tubule ; h, its protoplasmic layer.

process of development of these spermatoblasts each lobule lengthens
into a tail or cilium-like prolongation, while the deeper part still in
connection with the walls of the tube will ultimately form the head and
middle portion of the spermatozoon : so that in this stage of its develop-
ment the sperm is composed of an enlarged cylindrical cell terminating
in cilium-like prolongations. When the development is complete the
head becomes detached and the remainder of the Spermatoblast under-
goes fatty degeneration, although a, small amount of the protoplasm may
remain temporarily attached to the head of the spermatozoon (Fig. 416).
Between the spermatoblasts lining the lumen of the seminal tubules
are found numerous round cells possessed of amosboid movement, the so-
called seminal cells, which are probably concerned in the formation of
the fluid parts of the semen.

916 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

As in the maturity of the ova, so the formation and maturity of the
spermatozoa indicate the occurrence of puberty. In the human male this
takes place about the age of fifteen or sixteen years, and in other mammals
it occurs a short time later than the occurrence of fertility in the female of
the same species. The appearance of puberty in the male is also attended
with certain characteristic signs. The larynx undergoes a rapid increase
in size, and, as a consequence, the voice becomes deeper, while hair
makes its appearance on the pubes, in the axillae, and on the face. The
sebaceous glands become larger and more active. In the male of the
domestic animals the appearance of procreativeness is recognized by the
occurrence of the capability of erection of the penis and the birth of
sexual desires. In the domestic animals in a state of nature sexual ex-
citement occurs in the male only at definite periods of the year, but in
domestication this makes its appearance whenever a mature male is in
the neighborhood of a female of the same species when in heat.

IMPREGNATION. — Only those mammalian ova become developed into
embryos which are fecundated through contact with the male spermatic
element, and that this may be accomplished the introduction of the
seminal fluid within the internal genital organs of the female is essential.
That this process, which is termed coition, may be accomplished the
erection of the male genital organ, the penis, is essential in order to
permit its penetration within the vagina of the female.

The penis is composed of the two cylindrical corpora cavernosa with
the corpus spongiosum, perforated by the urethra, lying between and
below them, these three bodies being held together by fibrous and mus-
cular sheaths. The corpora cavernosa, and to a less extent the corpus
spongiosum, are composed of erectile tissue, which consists of a tendinous
connective-tissue sheath containing thickly woven elastic tissue and
smooth muscular fibres, forming thus a fibrous envelope ; while the in-
terior is composed of numerous fibrous interlacing trabeculae, the spaces
being in communication with the veins, and 'are thus to be regarded as
venous sinuses. At the outer part of the corpus spongiosum some of
the small arteries terminate directly in the outer venous sinuses, while
some, however, terminate in capillaries which ultimately reach the venous
sinuses, to be collected again in the venous radicals which converge to
form the dorsal vein of the penis.

Erection is accomplished by the overfilling of these venous sinuses,
while the engorgement so produced by compressing the outgoing venous
trunk serves to prevent the escape of blood from these parts. The
overfilling of the blood-vessels of the penis results in a three- or four-
fold increase in its volume, while, at the same time, a higher tempera-
ture, pulsatile movement, an increased consistence, and erection of the
organ results. The first phenomenon in the production, of erection is to

KEPRODUCTIVE FUNCTIONS. 917

be found in the dilatation of the minute arteries through the action of
the nervi erigentes. These nerves are to be regarded as containing vaso-
dilator fibres which are in connection with a centre in the spinal cord,
controlled to a certain extent by the medulla oblongata, and also capa-
ble of being reflexly excited by impressions made upon the terminal
filaments of the sensory nerves of the penis. The centre in the lumbar
portion of the cord is also capable of being controlled by various other
afferent impulses, especially by the psychical activity of the cerebrum.
When, through any impression on the centre for erection, the blood-ves-
sels dilate through the action of the nervi erigentes, the completion of
the act of erection is accomplished by the action of several transversely
striated muscles. The ischio-cavernosus muscle arises from the coccyx,
and by its tendinous union with its fellow from the opposite side sur-
rounds the root of the penis, and by its contraction compresses the penis
so as, to a certain extent, to prevent the flow of blood from the organ.
This muscular action was at one time supposed to be the main factor in
the accomplishment of erection, but that this is not the case is proven
by the fact that the dorsal vein, lying in the groove between the two
corpora cavernosa, is protected from compression, and the congestion of
the organ is by no means due to the complete arrest of the venous circu-
lation. Otherwise, in certain pathological conditions where erection is
continuous, gangrene would result. The deep transverse muscle of the
perineum also serves to facilitate erection by compressing the deep veins
of the penis as they come from the corpora eavernosa between its con-
tracted horizontal fibres; while, finally, the bulbo-eavernosus muscle com-
presses the bulb of the urethra and so assists in the erection of the
urethral corpus spongiosum. That erection is dependent upon the nerv-
ous system is proven by the fact that section of the nerves of the penis
will prevent erection, as has been experimentally proven in the case of
the stallion.

In the bull, in the process of erection, the S-shaped curve disappears
and the erected organ, protruding from the sheath, may acquire a length
of a meter or more, while the increase in diameter, owing to the great
development of the fibrous sheath of the organ, is less than in other
mammals.

The erection of the penis has simply for its object the giving such
an increase to the rigidity of the organ as to permit of its introduction
within the genital organs of the female.

The contact of the sensitive glans with the rugae of the vagina
inaugurates, a reflex process which terminates in the discharge of the
seminal fluid through the urethra.

In this process, which is termed ejaculation, two different factors
are concerned. In the first place, the passage of the seminal fluid to the

918 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

vesiculse seminales is caused by the newly secreted fluid forcing on,
through the influence of the ciliated epithelium and the peristaltic action
of the vas deferens, the fluid already formed in front of it ; so that, there-
fore, the seminal fluid, being continuously formed by the secreting surface
of the testicle, is gradually pushed onward, even in the intervals of sexual
excitement, to the vesiculse seminales, where it collects. Ejaculation is,
however, due to strong peristaltic contraction of the vasa deferentia and
the vesiculse seminales, due to the reflex stimulation of the centre in the
spinal cord, which co-ordinates the muscular phenomena of ejaculation.
The mechanical stimulation of the sensitive integument of the glans,
through action on this centre, leads to rhythmical contraction of the
bulbo-cavernosus muscles and to strong peristalsis of the vasa deferentia
and the vesiculse seminales, which discharge their contents into the
urethra. At the same time the ischio-cavernosus and the deep transverse
muscle of the perineum contract, although the former has no effect on
the act of ejaculation, and through their rhythmical contraction the
seminal fluid is projected from the extremity of the urethra. The degree
of stimulation of the glans which is required to start this mechanism
varies very considerably in different animals. In all, the role fulfilled by
the male is an active process, the female being passive, although a condi-
tion somewhat similar to that of ejaculation also exists in the female. It
has been found that at the moment of ejaculation a reflex movement sets
in in the Fallopian tubes and uterus resulting in the discharge of a cer-
tain amount of uterine mucus into the vagina. This is followed by a
rhythmical contraction of the sphincter cunni, which is the analogue of
the bulbo-cavernosus and of the ischio-cavernosus and of the deep trans-
verse muscle of the perineum, while, at the same time, the uterus is
erected by the contraction of its muscular fibres and round ligaments,
at the same time descending toward the vagina. In the case of the bull,
ejaculation occurs almost immediately after the introduction of the male
organ within the vagina of the female, and the to-and-fro movement
characteristic of the process in other animals is here absent. This is
probably to be explained by the peculiar shape of the penis of the bull.
In the first place, as has been stated, the organ increases but slightly in
its diameter, and, as a consequence, any friction of the body with the
capacious vagina of the female would be at best at a minimum. In the
second place, the glans penis of the bull is extremely pointed, and it has
been supposed that the glans directly enters the open mouth of the uterus,
and that the irritation thus produced is sufficient to start the process of
ejaculation. This view is to a certain extent supported by the fact that
examination of the female ruminant immediately after the act of copula-
tion will disclose the presence of spermatozoa within the uterine cavity.
This has frequently been determined to be the case in sheep, where the

EEPEODUCTIVE FUNCTIONS. 919

process is similar. In the case of the horse the process is more pro-
longed. Here the glans, instead of being pointed, as in the case of the
bull, possesses a considerably larger diameter than other portions of the
organ, and it is found that complete erection of this portion of the penis
does not take place until after the introduction of the organ within the
vagina of the female. The penis completely fills the vagina of the mare,
and more or less prolonged friction between its surface and that of the
penis is necessary before the act of ejaculation is accomplished.

In the dog, on the other hand, the process differs from what has
been described in either of the other groups of mammals. After the
introduction of the penis within the vagina of the female spasmodic con-
traction of the sphincter cunni muscle sets in, and, as a consequence, the
withdrawal of the male organ from the body of the female is, on account
of its peculiar shape, rendered impossible until almost complete relaxa-
tion has taken place. In the dog the process -of relaxation is slower than
in other animals, and may not be completed until within half an hour or
even so long as two hours after the act of ejaculation. In these animals,
therefore, after the act of coition is accomplished, the penis becomes in-
verted on itself, until, instead of projecting anteriorly, it is drawn back-
ward between the hind legs of the animals through the attempts of the
male to leave the body of the female, and the two posterior surfaces are
kept in contact by the imprisonment of the male organ.

Ejaculation is accompanied by the contraction of various other
muscles. The cremaster muscle elevates the testicle within the scrotum,
and the walls of the urethra contract in its various portions, serving to
compress the prostate and Cowper's glands and so cause the extrusion
of their contents. In the stallion the act of ejaculation is accompanied
by a rhythmical contraction of the muscles inserted into the tail. By
every contraction of the ejaculator urinse muscles the muscles passing
from around the anus to the tail are compressed, and, as a consequence,
the rhythmical motion of the ejaculator seminae is communicated to the
tail, and, therefore, by its movement affords an index to the completion
of the act of ejaculation. After the act of copulation is completed the
male organ is withdrawn and erection gradually disappears, while there
may be an escape of seminal fluid from the genital organs of the female.
This is especially observable in the case of the mare, where it has become
the custom immediately after the completion of the act of copulation to
either load the back of the mare or to make her move rapidly, so as to
prevent to a certain extent this loss.

A single spermatozoon is, in all probability, sufficient to fertilize an
ovum, and this is accomplished by the entrance of the spermatozoon into
the ovum by a boring movement through the vitelline membrane, either
through the porous canals or the micropyle.

920 PHYSIOLOGY OF THE DOMESTIC ANIMALS.

The locality in which fertilization takes place may be either the
ovary, as is shown by the occurrence of abdomidal pregnancy, the Fal-
lopian tube, or the cavity of the uterus itself. The manner in which the
spermatozoa obtain access to the ovum is not capable of clear demon-
stration. In the case of the ruminants, as has been seen, there are reasons
for believing that the spermatozoa are deposited directly within the
cavity of the uterus. In other animals, where in all probability this does
not take place, the entrance of the spermatozoa into the uterus may be
accomplished by the suction which results from the relaxation of the
uterus as this condition of erection and engorgement passes off, and it is
a matter of common experience that the introduction of semen even
within the vestibule of the vagina is frequently sufficient to produce fer-
tilization. It is probable that the vibration of the cilia is concerned in
causing their movement to meet the ova. It must not be forgotten, how-
ever, that within the uterus, and especially within the Fallopian tubes, the
motion of the ciliated epithelium is normally in the opposite direction
to that in which the spermatozoa must move to reach the ovary, so that
while this ciliary motion would facilitate the descent of the ovum, it must
offer an obstacle to the ascent of the spermatozoa.

Nothing absolutely definite is known as to the manner in which
the bringing together of the male and female spermatic elements is
accomplished. It is only clearly known that the spermatozoa in some
way possess the power of rapidly ascending through the internal sexual
organs of the female. Spermatozoa have been found within the uterine
cavity of the dog a quarter of an hour after the act of copulation, and in
the Fallopian tube, even at its abdominal end, within one or two hours.

The spermatozoa retain their power of fertilizing the ovum, as indi-
cated by the persistence of their power of movement, for as long as eight
days while within the body of the female, — a period which is abundant to
permit the ripening and discharge of an ovum and its contact with the
spermatozoa. Even if copulation takes place in the intervals between
the maturing of the ova, fertilization may, nevertheless, take place.

As a rule, fertilization of ova is only possible from the contact with
spermatozoa from the same species ; }ret in certain instances fertilization
may take place between different species of the same genus of animals,
as, for example, between the horse and the ass, between the dog and the
wolf, between the dog and the fox, between the lion and the tiger, and
between the rabbit and the hare. The results of such impregnation are
spoken of as hybrids, and possess characteristics midway between the
two species. The products of such impregnation are, as a rule, barren
from arrested development of their genital organs (testicle and ovary).

The impregnated ovum, whatever be the locality in which impreg-
nation takes place, is borne to the interior of the uterus, there to

KEPEODUCTIVE FUNCTIONS. 921

undergo the changes which, starting in the clevage of the blastodermic
membrane, as already described, terminate in the development of the
embryo. When such a fecundated ovum reaches the uterus it inaugu-
rates certain changes in the mucous membrane of that organ. It has
been noticed that the maturity and escape of the OArum is accompanied
by congestion and swelling of the uterine mucous membrane with the
ultimate solution and discharge of the mucous surface. When the im-
pregnated ovum reaches the uterus it becomes covered by a membrane
which was first described by William Hunter as the membrana decidua,
because it was removed at birth. Three different divisions of this mem-
brane may be recognized. The decidua vera is the thickened, highly
vascular, and softened mucous membrane of the uterus. As the ovum
reaches the uterine cavity it becomes fixed (conception) in a fold of the
uterine decidua or decidua vera, which grows up in the form of folds,
entirely surrounding the ovum. These folds finally meet over the back
of the ovum and so form the decidua reflexa. The part of the decidua vera
behind the ovum, i.e., between the ovum and the uterine wall, is spoken
of as the decidua serotina, in which locality the placenta is ultimately
formed. The ovum, covered with villous processes, is thus entirety sur-
rounded by the decidua, and, gradually increasing in size, remains within
the cavity of the uterus until mature.

For the consideration of the development of the different tissues and
organs of the embryo, the reader is referred to text-books on Anatomy or
Embryology.

to

0

INDEX.

Abdominal muscles, action of, in expira-
tion, 579

Abducens nerve, 833, 875
Aberration^ chromatic, 855

spherical, 854

Abomasum, structure of, 320
Absorption, 453

by the lymphatics, 456

by the skin, 656

coefficient of, 59

of fat, 456

of gases, 58

of tissues for colors, 68
Accelerator nerves of the heart, 551
Accessory foods, 160

muscles of inspiration, 578
Accommodation, mechanism of, 859
Acid albumen, 98

of gastric juice, 349
Adamkiewicz's test for proteids, 92
Adhesion, 40

Adipose tissue, formation of, 120, 664
Age, signs of, in domestic animals, 262

the determination of, by the teeth, 255
Air-vesicles, 571
Ajutage, influence of, 518
Albumen, alkali, 101

destruction of, in starvation, 676

factor of, 673

of milk, estimation of, 634
Albumens, 92
Albuminates, derived, 98
Albuminoids, 104

collagenous, 105
Albuminous bodies, 85
classes of, 92
decomposition of, 109
general characteristics of, 88

food-constituents, fate of, 660
Alcoholic fermentation, 147
Alimentary rations, 195
Alkali albumen, 101

albuminate, 101
Alkaline phosphates, 130
Amandin, 94
Amble, the, 746
Ammonium carbonate, 136
Amoeba, 13

digestive processes in, 204
Amoeboid contractility, 14

movements, 14, 75
Amphiarthroses, 729
Amphibia, brain of, 804

olfaction in, 844

Amyloid substance, 102, 115

Amylolytic ferment, 112

Amy loses, 112

Amylum, 113

Analysis of milk, 631

Anelectrotonus, 780

Animal cells, chemical processes in, 142

foods, 188

composition of, 184

heat, 693

influence of nervous system on, 697
of different animals, 696

locomotion, 731
Animals and plants, distinctions between, 5

diet of, 193
Anode, 777

Anterior pyramids, structure of, 811
Antipeptone, 409
Aortic valves, action of, 514
Arabin, 120
Arabinose, 120
Area opaca, 21

pellucida, 21

Arterial blood, characteristics of, 597
gases of, 592

tension, 526

tonus, 557
Arteries, blood pressure in, 528

circulation in, 523

elastic tissue of, 525

influence of the nervous system on, 552

muscular coat of, 525

physical structure of, 524
Arterioles, circulation in, 538
Articulata, nervous system of, 767
Articulations, classification of, 729
Arthrodia, 730
Asphyxia, 604
Ass, larynx of, 760
Aster, 17

Atropine, action of, on heart, 543
Audition, 875

Auditory apparatus of birds, 876
of fishes, 876
of reptiles, 876

canals, 880

nerve, 834
Augmentation, 785
Auricle, 877
Auricles, contraction of, 503

muscular fibres of, 501
Auriculo-ventricular valves, action of, 510
Automatism, 765, 784

of protoplasm, 14

(923)

924

INDEX.

Ball-and-socket joint, 730
Barley -bran, 171

composition of, 170

straw, 171
Basal ganglia of the brain, development of,

807

functions of, 822
Basis cruris, 819
Beef-tea, composition of, 190
Beet residue, 182
Beets, 174
Bile, 382

acid, preparation of, 385

acids, 384

chemical characteristics of, 383

coloring matters of, 387
test for, 388

composition of, 383

crystallized preparation of, 385

inorganic constituents of, 390

physiological action of, 393

salts, test for, 385

secretion of, 391
Biliary fistulae. 394
Bilirubin, 388
Biliverdin, 389
Birds, auditory apparatus of, 876

brain of, 804

digestive apparatus of, 211

gastric digestion in, 379

nervous system of, 770

olfaction in, 844

organs of circulation in, 497

production of sound in, 759

reproduction in, 905

respiratory apparatus of, 568

vision in, 849

Biuret reaction of proteids, 91
Blastema, 16
Blastoderm, 20

changes in form in impregnation, 22

section of, 21

segmentation of, 22
Blastodermic vesicle, 25
Blastopore, 25
Blood, 469

absorption of carbon dioxide, 595
of gases, 592

circulation of, 491

coagulation, 483

composition of, 471

corpuscles, 27
red, 471, 474
white, 479

crystals, 475

current, velocity of, 530

gases of, 490, 592

plasma, 483

plates, 483

pressure, 525

experiment, 526

in arteries, 528

in different mammals, 530

Blood pressure in the capillaries, 538

quantity of, 470

respiratory changes in, 591

serum, 489, 595

tension of gases in, 596
Bone-corpuscles, 29
Bone, development of, 35
Bones of the ear, 880

heart, 509
Bran, barley, 171

Branching tubes, flow of liquids in, 521
Brain, development of, 803

functions of, 803

of mammals, 809

size of, in different animals, 808

weight of, in different animals, 809
Bread, composition of, 165
Brewers' grains, 179
British gum, 116
Bronchi, structure of, 570
Brunner's glands, 416
Buckwheat, 171
Buckwheat-meal, 172
Buckwheat-straw, 172
Budding, 16
Bulbs and roots, 174
Burdach, column of, 787, 797
Butter, 617

estimation of, 633
Buttermilk, 188
Butyric acid, 122
Butyrin, 122

Csecal fistulae, 428
Cfficum, 221

functions of, 423

secretion of, 428

structure f, 426
Calcium carbonate, 130

fluoride, 136

phosphate, 133

sulphate, 136
Cane-sugar, 119

gastric digestion of, 354
Canter, 751
Capillaries, blood pressure in, 538

circulation in, 536

development of, 34

of the lung, 571

structure of, 536
Capillarity, 40

Capillary phenomena, explanation of, 40
Carbohydrate food-constituents, fate of, 666
Carbohydrates, 112

action of pancreatic juice on, 406

as sources of fat, 666

construction of, 85

gastric digestion of, 354

influence of, on nutrition, 683
Carbonate of ammonium, 136

of calcium, 130

of magnesium, 130

of potassium, 129

INDEX.

925

Carbonate of sodium, 129

Carbon dioxide, absorption of, by blood, 595

Cardiac contraction, phases of, 508

ganglia, 541
Cardiograph, 506
Cardio-inhibitory centre, 551, 816
Carnivora, characteristics of, 196
urine of, 637

dentition of, 254

digestive power of, 436

faeces of, 446

foods of,. 160

gastric digestion in, 360

mastication in, 239

prehension of food in, 235

stomach of, 215
Cartilage, fibrillar, 35

fibro-, 35

forms of, 29

hyaline, 35

structure of, 35
Casein, 102, 614

estimation of, 634

gluten, 94, 95

mode of formation of, 627
Caserns, vegetable, 94
Cat-fat, 123
Cathode, 777

Cattle, normal foods for, 690
Cell-constituents, inorganic, 123

nitrogenous organic, 88

non-nitrogenous, 112
Gel], contents of, 12

variation in, 29

definition of, 13

doctrine, 15

formation, endogenous, 17
free, 16

membrane, 13

nucleolus of, 13

nucleus, 13

pigment, motions in, 75, 76

polar, 18

typical, 12
Cells, 11

chemical constituents of, 85

chemical processes in, 136

ciliated epithelial, 77

development of force in, 147

difference in size of, 27

endogenous formation of, 16

epiblastic, 25

form of, 27

general properties of, 12

hypoblastic, 25

inorganic constituents of, 86

mechanical movement in, 70

modification in the form of, 26

of spinal cord, 27

origin of, 14

physical process in, 37

protoplasmic, movements in contents of,
73

Cells, reproduction of, 16

water of, 86
Cellular chemistry, 85

physics, 37
Cellulose, 114

digestion of, 429
Cement, structure of, 246
Centre, cardio-inhibitory, 551, 816

cilio-spinal, 795

for closure of the eyelids, 816

for coughing, 817

for deglutition, 817

for dilatation of the pupil, 817

for glycogenesis, 817

for inhibition of reflex action, 793

for micturition, 649

for respiration, 816

for secretion of saliva, 817

for sneezing, 816

for suckling and mastication, 817

for vomiting, 817

of gravity of animals 731
Cereals, 163

Cerebellar peduncle, results of section o£
827

tract, 797
Cerebellum, functions of, 825

structure of, 818
Cerebral convolutions, 804

cortex, functions of, 824

hemispheres, 809

lobes, 804

functions of, 823

peduncles, functions of, 821
Cerebrin, 775
Cerebrum, structure of, 823

functions of, 824

Chameleon, movements of pigment-cells, 75
Cheeks, action of, in mastication, 264
Cheese, 188
Chemical constituents of cells, 85

phenomena in respiration, 587

processes in animal cells, 142
in cells, 136
in vegetable cells, 137
Chloride of magnesium, 136

of potassium, 128, 129

of sodium, 128

Chlorophyll, functions of, 136, 137
Cholesterm, 389
Cholic acid, 387
Chondrin, 107
Chondrogen, 107

Chorda tympani, influence on salivary se-
cretion, 298

Choroid membrane, 849
Chromatic aberration, 855
Chyle, 459

composition of, 461

movement of, 462
Chyle-vessels, 457
Chyme, characteristics of, 419
Cicatricula, 20

926

INDEX.

Ciliary movement, 77

influence of acids on, 80
alkalies on, 81
anaesthetics on, 81
imbibition on, 80
mechanical force of, 78
protoplasmic nature of, 81
temperature on, 80

nerves, 863

Ciliated epithelial cells, 77
Cilio-spinal centre, 795
Circulation, hydraulic principles of, 516

estimation of duration of, 531

in arteries, 523

in fishes, 494

influence of nervous system on, 540
of the respiration on, 605

in mammals, 497

in the capillaries, 536

in the veins, 539

of lymph, 467

of the blood, 491

organs of, 491

rapidity of, 531
Clarke's column, 799
Cleavage of ovum, 15, 19
Clover, composition of, 187
Coagulated proteids, 102
Coagulation of blood, 483

of milk, 614
Cochlea, 877
Cochlear nerve, 882
Co-efficient of absorption of gases, 59

of elasticity, 66
Cohesion, 38

of tissues, 62

Cold, action of on heart, 548
Collagen, 106

Collagenous albuminoids, 105
Colloids, osmosis of, 52
Colon, functions of, 429
Colostrum, 609

changes in, 620

corpuscles, 610

Comparative physiology, definition of, 1
Complemental volume of air, 573
Conduction in the spinal cord, 795
Conglutin, 94
Connective-tissue constituents, 104

tissues, 34

Constituents of food, fate of, 664
Contents of cells, 12
Contractile tissues, 701
Contractility of protoplasm, 14, 70
Convolutions of the brain, 804
Co-ordination, 785
Copper, 136
Cornea, 849
Corpora bigemina, 807

quadrigemina, 807
functions of, 822

striata, 807
Corpuscles of bone, 29

Corpus luteum, 913

Corpus striatum, functions of, 822

Cortex of the brain, functions of, 524

Corti's organ, 882

Cotton-seed cake, 183

Coughing, 605

centre for, 817
Cranial nerves, 832

origin of, 812
Cream, 617

composition of, 618
Crop, functions of, 380
Crura cerebri, 818

functions of, 821
Crying, "605
Crystallin, 97
Crystalline lens, 849
Cutaneous absorption, 656

functions, 651

respiration, 656
Cyclosis, 73
Cytoblasts, 16

Decomposition of the albuminous bodies,

109

Decussation of pyramids, 810
Defecation, 451
Deglutition, 307

centre for, 817
Dental formula, 252
Dentine, structure of, 246
Dentition in domestic animals, 263

in herbivora, 258
Depressor nerve, 556
Derived albuminates, 98
Development of bone, 35

of tissue, explanation of, 15

of tissues and organs, 31
Dextrin, 116

test for, 116
Dextrose, 117

Diabetes, production of, 672
Diabetic centre, 671, 817
Dialysis, 53
Diapedesis, 539
Diarthroses, 729
Diarthrosis rotatoria, 730
Diastatic ferment of the liver, 671
Diaster, 17

Dicrotic wave, explanation of, 536
Diet of animals, 193

Diffusion, application of to respiration, 596
Diffusion of gases, 56

in the animal organism, 60

in the lungs, 592

through porous partitions, 58

of liquids, 49

Digastric muscle, functions of in mastica-
tion, 242

Digestibility of food-stuffs, 432
Digestion, 203

gastric, 337

m the mouth, 268

INDEX.

927

Digestion in the small intestine, 382
Digestive apparatus, characteristics of, 203

co-efficient, 435

Dionaea muscipula, movements of, 72
Dioptric mechanisms of the eye, 851
Distillery mash, 180
* Diuretics, mode of action of, 647
Division of nucleus, 17
Dog, dentition in, 260

fat, 123

larynx of, 761

urine of, 640
Dogs, diet of, 362
Double refraction, 6'8
Drinking, mechanism of, 236
Dry fodder, 162

composition of, 184
Duodenal follicles, 416
Dyspnoea, 603

Ear-ossicles, 880

movements of, 888
Ear, structure of, 877
Egg-albumen, 93
Egg of hen, formation of, 20, 21
Egg-osmometer, 55
Eggs, composition of, 190
Egg-yelk, structure of, 20
Elasticity, co-efficient of, 66

of tissues, 65
Elastic tissues, 35

tubes, flow of liquids through, 522
Elastin, 108

Electrical phenomena of tissues, 70
in muscle, 721
in nerves, 779

Electricity, influence of, on nerves, 777
Electrotonus, 780
Elementary organisms, 11
Enamel, structure of, 245
Enarthrosis, 730
Encephalin, 775
Endogenous cell-formation, 16
Endolymph, 881
Endothelia, 33
Ensilage, 177
Enzymes, 111
Epiblast, 23
Epiblastic cells, 25

spheres, 24
Epithelial cells, 28
Epitheliums, structure of, 33
Erection, mechanism of, 916
Esparcet, 176
Eustachian tube, 880, 890
Expiration, mechanism of, 578
Expired air, constituents of, 588
temperature of, 588
watery vapor of, 588
Extensibility of tissues, 66
External intercostal muscles, action of, in

inspiration, 577
Eyeball, muscles of, 874

Eye, development of, 848

formation of image in, 857

refraction in, 858
Eyes, composite, 847

structure of, 848

Facial nerve, 834

Faeces, composition of, 445

Fat, absorption of, 456

feeding with, 682
Fat-ferment, 112
Fat of milk, production of, 626

influence of, on nitrogenous waste, 677
on nutrition, 680

metabolism of, 673

sources of, 665
Fats, 120

action of pancreatic juice on, 406

composition of, 123

detection of, 121

factor of, 673

of milk, 617

Fattening animals, foods of, 687
Fatty acids, construction of, 85

constituents of food, fate of, 664

tissue, formation of, 664
Feeding, nutritive processes in, 680

proper intervals between, 689

witn carbohydrates, nutritive pro-
cesses in, 683

with meat, nutritive processes in, 680
Fenestra ovalis, 880

rotunda, 880
Ferment, amylolytic, 112

diastatic, 112

fat, 112

fibrin, 487

inversive, 112

milk-curdling, 112

of the liver, 112, 671

proteolytic, 112
Fermentation, alcoholic, 147

of -lactic acid, 147

in small intestine, 418

putrefactive, 147
Fermentations, 145
Ferments, 110

of the pancreatic juice, 403, 404

soluble, 110

Fertilization of ovum, result of, 15
Fibrillar cartilage, 35
Fibrin, 98, 488

ferment, 487

formation of, 485

gluten, 95

vegetable, 95
Fibrinogen, 97, 487
Fibrinoplastin, 487
Fibro-cartilage, 35
Fibrous tissue, 35
Filtration, 48

in the kidneys, 644
Fishes, auditory apparatus of, 876

928

INDEX.

Fishes, brain of, 804

circulation in, 494

digestive apparatus of, 210

eyes of, 849

nervous system of, 770

olfactory apparatus in, 844

reproduction in, 904

respiratory apparatus of, 566
Fistula, gastric, 342

pancreatic, 398

parotid, 275

submaxillary, 279
Flexibility of tissues, 67
Flustra, digestive apparatus of, 205
Fodders, amounts of salts in, 679

changes in, 176

composition of, 184

dry, 162

green, 162'

influence of chopping on, 688

nutritive proportions in, 685
Food, action of gastric juice on, 351

carbohydrate, fate of, 666

constituents, albuminous, fate of, 660

for cattle, horses, sheep, and swine,
690

prehension of, 226

products, composition of, 184

required by the herbivora under dif-
ferent conditions, 684

stuffs, digestibility of, 432
Foods, 157

animal, 188

inorganic, 191

nutritive values of, 685

of animals, 158

of carnivora, 160

of herbivora, 160

vegetable, 161
Force, consumption of, in cells, 147

development of, in cells, 147
Formatio reticularis, 811
Form of cells, modification in, 26
Frog, heart of, 502
Frohde's test for proteids, 92
Fructivora, characteristics of, 197
Functions, animal, 8

definition of, 8

nutritive, 155

of relation, definition of, 8

reproductive, 8, 901

specialization of, 15, 32

vegetative, definition of, 8
Funiculus cuneatus, 797

gracilis, 810

Gaits of the horse, 739
Gall-bladder, 382
Gallop, 749
Ganglia of the heart, 541

sporadic, 782
Ganglion-cell, 27
Ganglionic cells, structure of, 772

Gaseous diffusion, 56

in the animal organism, 60
through porous partitions, 58
Gases, absorption of, 58

of blood, 490
Gastric digestion, 337
in birds, 379
in carnivora, 360
in omnivora, 363
in the horse, 368
in ruminants, 374
fistula, 342

glands, changes of, in digestion, 357
juice, acid of, 349

action of, on food, 351

artificial, 341

chemistry of, 342

influence of nervous system on,

360

mechanism of secretion of, 360
secretion of, 356
movements, 340
Gelatin, 106

vegetable, 96
Gelatinous tissue, 35
Gemmation, 16
Gemmiparous generation, 903
General physiology, definition of, 1
Generation by fission, 903

by spores, 903

Germinal disk of hen's egg, 23
spot, 15
vesicle, 15
Gestation, duration of in different animals,

907

Ginglymous joint, 730
Gizzard, functions of, 381
Glands, mammary, structure of, 624
of stomach, tubular, 356
structure of, 36
Glandular tissue, 34
Gliadin, 96
Globulins, 96

vegetable, 97

Glomerulus, functions of, 642
Glosso-pharyngeal nerve, 834
Glottis, movements of, 762

in respiration, 579
Glucoses, 117

tests for, 118
Glucosides, 117
Gluten, 95
casein, 95
fibrin, 95
Glycerin, 122
Glyceryl, 121
Glycin, 387
Glycochol, 387, 664
Glycocholate of sodium, 384
Glycocholic acid, 386
Glycogen, 116

characteristics of, 668

influence of the nervous system on, 671

INDEX.

929

Glycogen, origin of, 669

preparation of, 668

relation of, to diet, 669
Glycogenic centre, 817
Glycogenesis, 667
Goat and sheep, urine of, 640

prehension of food in, 235
Goll, column of, 787, 797
Graafian follicles, 909
Graham's law of the diffusion of gases, 58
Grains and fruits, composition of, 184
Granivora, characteristics of, 197
Granulose, 114
Grape-sugar, 117
Grasses, 175
Green fodder, 162

composition of, 184
Growth of protoplasm, 14
Gustatory cells, 894

nerves, 896

Haemoglobin, 475, 593

reduced, 594

spectrum of, 594
Harder's gland, 850
Hauling, mechanism of, 755
Hay, composition of, 187
Hearing, function of, 883

sense of, 875
Heart, accelerator nerves of, 551

action of, 499
heat on, 547

changes of shape in contraction, 505

inhibitory nerves of, 549

intrinsic nervous system of, 540

movements of, 502

in mammals, 503, 504

of frog, 502

of mammals, 498

of ox, 509

sounds of, 514

structure of, 500

tetanus, 547

work of, 532
Heat, action of, on heart, 547

animal, 693

centres, 698

modes of loss of, 696

sources of, 694, 696

symptoms of, in animals, 911
Hemipeptone, 409
Hen's egg, structure of, 20
Herbivora, characteristics of, 197
urine of, 637

digestive power of, 436

faeces of, 446

food required by, 684

foods of, 160
Hiccough, 604
Hippunc acid, 663
Hog, composition of bile of, 384

larynx of, 761

structure of stomach of, 363

Hogs, food required in fattening, 688

normal foods for, 690
Holoblastic ovum, 19
Homocerebrin, 775
Horse, dentition of, 253

fat, 123

gaits of, 739

gastric digestion in, 368
juice of, 370

glottis of, 760

mechanics of the limbs of, 739

normal foods for, 690

power, 755

prehension of food in, 234

respiratory movements of, 582

tongue of, 233

urine of, 638

Human physiology, definition of, 1
Hunger, 692
Hyaline cartilage, 35
Hydra, digestive processes in, 205
Hydrates, formation of, from anhydrates,

146

Hydraulic principles of the circulation, 516
Hydrocarbons, 120

construction of, 85
Hydrochloric acid, 135
Hypermetropia, 861
Hypoblast, 24

division of, 25
Hypoblastic cells, 25

spheres, 24
Hypoglossal nerve, 835

Imbibition, 44

influence on ciliary movements, 80

on protoplasmic motion, 82
Impregnation, 916
Incus, 880
Indican, 412
Indol, 411
Infusoria, ciliated movement in, 77

digestive processes in, 204
Inhibition, 785

Inhibitory nerves of the heart, 549
Inorganic cell-constituents, 123

constituents of cells, 86

foods, 191
Inosite, 118
Insects, digestive apparatus of, 207

eyes of, 847

Inspiration, mechanism of, 574
Intensity of sound, 758
Intercellular tissues, 34
Intercostal muscles, action of, in inspira-
tion, 577

nerves, influence of on respiration, 599
Intestinal digestion, 382

in different animals, 419

fistula, 416

juice, 416

action of on food -stuffs, 418
characteristics of, 417

930

INDEX.

Intestinal reaction, 421
Intestines, characteristics of, 217

fermentation in, 418

large, digestion in, 423

movements of, 448

muscular structure of, 448
Inulin, 116

Inversive ferment, 112, 418
Invert-sugar, 119, 418
Iris, 849

muscular fibres of, 862
Iron, 136
Irradiation, 871
Irritability, muscular, 709

of muscle, influence of temperature on,
719

of nerves, 776

Jacobson's organ, 843
Jaws, movements of, 241
Joints, formation of, 729

gliding, 730
inged, 730
rotatory, 730
Jumping, mechanism of, in man, 738

Karyokinesis, 17

Kathelectrotonus, 780

Keratin, 109

Kicking, 753

Kidney, structure of, 640

Kidneys and skin, correlation of, 645

Kreatin, formation of, 66J

Labyrinth of the ear, 880

Lachrymal apparatus of mammals, 850

duct, 850

secretion, 658
Lacteals, 457

Lactic acid fermentation, 147
Lactose, 120
Laevulose, 118
Lardacein, 102
Large intestine, digestion in, 423

structure of, 430

Larvae, digestive apparatus of, 206
Laryngeal muscles, action of, 762
Larynx, nerves of, 764

of birds, 760

Latent period in muscular contraction, 713
Laughing, 605
Lecithin, 481
Legumin, 94
Leguminous plants, 173
Lens, action of, 853
Lenses, formation of images by, 857
Leucin, 410

Levatores costarum, action of in inspira-
tion, 577

Lever motion of muscles, 725
Levers, 724

Lieberkuhn's glands, 416
Light, reflection of, 851

Lignin, 115

Lips, action of, in mastication, 264

Liquids, cohesion of, 39

diffusion of, 49

flow of, through elastic tubes, 522
rigid tubes, 518

surface tension of, 39
Liver ferment, 112, 671

glycogenic function of, 667
Lobes of the brain, 804
Localization of the functions in the cortex

825

Locomotion, animal, 731
Lungs, diffusion of gases in, 592
Lying down and rising up, mechanism of,

754
Lymph, 463

circulation of, 467
Lymphatics, absorption of, 456

Macula lutea, 865
Magnesium-ammonium phosphate, 136

carbonate, 130

chloride, 136

phosphate, 134
Malleus, 880
Maltose, 120
Mammalian heart, 498

ovum, changes in, from impregnation,

segmentation of, 19
Mammals, brain of, 809

circulation in, 497

digestive apparatus of, 213

movements of the heart in, 503

ocular apparatus in, 849

process of fecundation in, 904

reproduction in, 906
Mammary glands, histological changes in,

628

innervation of, 629
structure of, 624

secretion, 609
Manganese, 136
Manometer, 526
Manyplies, functions of, 377

structure of, 319
Marey's tambour, 581
Margaric acid, 122
Margarin, 122

Masseter muscle, action of, 243
Mastication, 338

centre for, 817

duration of, 266

influence of saliva on, 267
Meal, buckwheat, 172
Meat, 188

composition of, 189

nutritive processes of feeding with,

680

Mechanical movement in cells, 70
Meconium, composition of, 445
Medulla oblongata, 810, 816

INDEX.

931

Medulla oblongata, course of fibres of, 818

functions of, 814
Membrane of cells, 13

vitelline, 15
Mesencephalon, 803
Mesoblast, 23, 25
Meta-albumen, 103
Micturition, centre for, 649

mechanism of, 648
Milk, 188

cistern, 624
coagulation, 614
curdling ferment, 112r 347
action of, 615
of pancreatic juice, 411
gases of, 619
gastric digestion of, 354
globules, 610

influence of albuminoids on, 622
diet on quantity of, 622
fat on, 623
water on, 622

inorganic constituents of, 619
inspection and analysis, 631
of different animals, composition of,

613
physical and chemical properties of,

610

quantity of, 620
reaction of, 611
secretion of, 609, 624

influence of nervous system on,

629

skimmed, 619
solids, estimation of, 633
sugar, 120, 616

estimation of, 634
origin of, 627
uterine, 610

variation in the quantity and compo-
sition of, 619

Millon's reaction for proteids, 91
Mimosa pudica, 71
Mitral valves, 509
Mollusks, digestive apparatus of, 209

nervous system of, 767
Motion from imbibition in cells, 70
Motor centres of the cortex, 825

impulses in spinal cord, path of, 801
Motory impulses, paths of, 829
Mouth, digestion in, 268
Movement, ciliary, 77
physiology of, 701

protoplasmic, general conditions of, 82
Movements, amoeboid, 75

from imbibition in cells, 70

of cell contents, 70
in cells, 70

in protoplasmic contents of cells, 73
of intestines, 448
of stomach, 340
of the heart, 502
Mucedin, 96

Mucoid tissue, 35
Mulberry mass, 15, 19
Muscarine, 546
Muscin, 104

characteristics of, 105
preparation of, 105
Muscle, accessory, 578
analysis of, 709
chemical composition of, 704

processes in, 708
coagulation of, 705
current, 722
curve, 713

electrical phenomena in, 721
ferment, 706
gases of, 708

microscopic changes of, in contrac-
tion, 719
plasma, 705
serum, 707
stapedius, 890
tensor tympani, 890
Muscles, classification of, 722
intercostal, action of, 577
of the eye, 874
structure of, 36, 701
Muscular contraction, 81, 710, 714
chemical changes in, 719
heat production in, 720
phenomena of, 710
wave of, 718
work of, 721

contractility, applications of, 722
corpuscles, 703
fibres, isolated, 28
of heart, 500
striped, 701
structure of, 701
unstriped, 703
irritability, 709
preparation, 711
sound, 716
stimuli, 710
tissue, 34

Myelencephalon, 803
Myo-albumose, 707
Myoglobulin, 707
Myograph, 712
Myopic eye, 861
Myosin, 97, 99, 704

ferment, 706
Myosinogen, 706, 707
Myriapods, digestive apparatus of, 206

Negative impulse, 508

variation of nerve-current, 780
Nerve, abducens, 833

auditory, 834

centres, general physiology of, 78}
of spinal cord, 789

corpuscles, structure of, 772

current, 779

depressor,. 556

£32

INDEX.

Nerve, facial, 834

fibres, physical properties of, 775

structure of, 30
Lypoglossal, 835
oculo-motor, 832
olfactory, 832'
optic, 832
pathetic, 832
pneumogastric, 834
gpinal accessory, 835
stimuli, 776

tissue, development of, 34
trifacial, 833
trigeminal, 833
trunk, structure of, 772
Nerves, acceleratory, 551
afferent, 772
centrifugal, 772
centripetal, 772
degeneration of, 778
efferent, 772

electrical phenomena in, 779
functional, distinctions between, 772
influence of constant current on, 777,

780

inhibitory, 549
intercostal, 599
laryngeal, influence of, in respiration,

601

of taste, 896
phrenic, 599

pneumogastric, influence of in respira-
tion, 600

vaso-constrictor, 558
vaso-dilator, 558
vaso-motor, 554
Nervous influence on protoplasmic motion,

76

irritability, 776

system, conduction of motor and sen-
sory impulses through, 827
influence of, on arteries, 552
on bodily temperature, 697
on circulation, 540
on micturition, 649
on renal secretion, 645
on respiration, 598
secretion of milk, 629
of articnlata, 767
of birds, 770 .
of fishes, 770
of mollusks, 767
of reptiles, 770
of star-fish, 766
of the heart, 540
^of vertebrates, 769
'organs of, 36
physiology of, '765
scheme of, 766
• structure of, 770'
sympathetic, 835

tissues, chemical and physical charac-
teristics of, 774

Neurokeratin, 775
Nicotine, action of, on heart, 546
Nitrogen, excretion of, 672
Nitrogenous matter, metabolism of, 673

organic cell-constituents, 88

tissue, constituents of, 85
Nceud vital, 600

Non-nitrogenous organic cell -constituents,
112

tissue, constituents of, 85
Nostrils, movements of, in respiration, 579
Nuclein, 482
Nucleolus of cells, 13
Nucleus, deviation in form of, 27

division of, 17

of cells, 13

of Pander, 21
Nutrition, 659

of nerves, influence of spinal cord on,
778 :

of protoplasm, 14

statistics of, 672
Nutritive functions, 155

processes in feeding, 680

proportion in foods, 684

proportions, 195

salts, 192

substances, 159

Oats, composition of, 167;
CSsophageal canal, 320

functions of, 376
Ocelli, 847
Ocular apparatus in mammals, 849

muscles, 875
Oculo-motor nerve, 832, 875

action of, on pupil, 862
Odorous substances, properties of, 844
'Oleic acid, 122
Olein, 122
Olfactory cells, 842

lobes, 807, 841

nerve, 832, 841

distribution of, 842
Olivary bodies, 811
Omasum, structure of, 319
Omnivora*, characteristics of, 198

digestive power of, 436

gastric digestion in, 363
Optical characteristics of tissues, 68
Optic lobes, 807

nerve, 832

nerve-fibres, 867

thalamus, functions of, 823
Organic acids, construction of, 85

nitrogenous cell-constituents, 88
Organisms, elementary, 11
Organized and unorganized bodies, distinc-
tions between, 2

bodies, structure of, 11

body, definition of, 2
Organs and tissues, development of, 31 ,

classification of, 36 ;

INDEX.

933

Organs, composition of, 36

of circulation, 491

of respiration, 562
Origin of cells, 14
Osmosis, 51

causes of, 55

explanation of, 54

illustrations of, 56

rapidity of, 52
Osmotic equivalent, 52
Osteoblaste, 36 ;
Otoliths, 881
Ova, 909
Ovary, 909
Ovum, 15

changes of fertilization in, 18

cleavage of, 15, 19

fertilization of, 15

holoblastic, 19

meroblastic, 19

of animals, classes of, 19

of mammals, 18

of rahrbit, size of, 25

size of, 15
Ox, dentition in, 258

fat, 123

heart of, 509

prehension' of food in, 234

tongue of, 233

urine of, 639

Oxen, food required in fattening, 687
Oxygen, absorption of, by haemoglobin, 594
by the blood, 592

influence of protoplasmic movements,

83
Oxy haemoglobin, 476

spectrum of, 594

Pacing, 747
Palmitic acid, 122
Palmitin, 122
Pancreas, anatomy of, 639

histological changes of, in digestion,

413

of the bird, 398
of the cat, 398
of the dog, 397
Pancreatic ferments, 403
isolation of, 404
fistulaa, 398

juice, action of, on carbohydrates, 406
on fats, 406
on food-stuffs, 405
on proteids, 408
artificial, 405

chemical composition of, 402
milk-curdling ferment of, 411
secretion of, 412
secretion, 396

influence of nervous system on,

415

Pander, nucleus of, 21
Papillary muscles, 510

Para-albumen, 103
Paraglobulin, 97, 487
Paramyosinogen, 706
Parapeptone, 99
Parotid fistula, 275

gland, nervous supply of, 303

saliva, composition of, 278

secretion, 274
Pathetic nerve, 832, 875
Pathology, definition of, 1
Peas, composition of, 173
Penis, structure of, 916
Pepsin, 112

preparation and characteristics of, 346
Pepsinogen, 358
Peptone, absorption of, 454

characters of, 353
Peptones, 103
Perichondrium, 36
Peristalsis of the intestines, 448
Perspiration, 652
Phosphate of alkalies, 130

of calcium, 133

of magnesium, 134

of magnesium and ammonium, 136

of potassium, 130

of sodium, 130
Phrenic nerves, influence of, in respiration,

599
Physical process in cells, 37

properties of proteids, 89

of tissues, 61
Physiology, definition of, 1

of inpvement, 701
Pig, dentition in, 261

fat, 123

prehension of food in, 235

urine of, 640

Pigment-cells, motions in chameleon, 75
Pinna, 877
Pitch of sounds, 758
Placenta of ruminants, 908
Plants and animals, distinction between, 5

reproduction in, 903

respiration in, 562
Plasma of blood, 483
Plasmine, 486
Pneumogastric, direct stimulation of, 550

influence of section of, 551

reflex action of, 550

nerve, 834

action of, on heart, 549
of frog, 545

nerves, influence of, in respiration, 600
Polar cell, 18
Pons varolii, functions of, 821

structure of, 819
Potassium carbonate, 129

chlorides, 128

phosphates, 130

sulphate, 135
Prehension of food, 226

of liquids, 236

934

INDEX.

Prehension of solids, 226

Processes, reproductive, 903

Pronucleus, female, 18

Prosencephalon, 803

Protagon, 775

Protamceba primitiva, 13

Proteids, action of pancreatic juice on, 408

Adamkiewicz's test for, 92

biuret reaction of, 91

chemical properties of, 90

coagulated, 102

coagulation of, 90

composition of, 88

Frohde's test for, 92

general characteristics of, 88

Millon's reaction for, 91

origin of, 88

physical properties of, 89

fechultz's test for, 92

tests for, 90

xantho-proteic reaction of, 91
Proteolytic ferment, 112
Protoplasm, 11

automatism of, 14

characteristics of, 73

contractility of, 14

nutrition of, 14

properties of, 14, 73

reproduction of, 14

respiration of, 14

Protoplasmic contents of cells, movements
in, 73

growth, 14

movement, 70

general conditions of, 82
influence of degree of imbibition

on, 82
chemical and physical agents

on, 84

nervous system on, 76
oxygen on, 83
temperature on, 82

nature of ciliary movements, 81
Psalter, functions of,. 377

structure of, 319
Pseudo-fibrin, 101
Pseudopodia, 14
Ptyalin, 112, 273
Pulmonary capillaries, 571

infundibula, 570

valves, action of, 514
Pulse, 533

and blood pressure, causes of modifica-
tions in, 560

of different animals, 548

wave, production of, 534

rate of movement of, 533
Pupil, centre for the dilatation of, 817,
863

changes of in accommodation, 862

influence of drugs on, 864

nerve supply of, 862
Putrefactive fermentation, 147

Pyloric glands, 356

Pyramidal tract of spinal cord, 797

Quality of sounds, 758

Rabbit ovum, size of, 25
Rack, the, 747
Rations, alimentary, 195
Rearing, 751

Red blood-corpuscles, 474
Reduced haemoglobin, 594
Reflection of light, 851
Reflex action, 782

laws of, 791

inhibitory centre, 793

nutritive action, 794

secretory action, 793

vaso-motor action, 793
Refraction, double, 68

of light, 851

of tissues, 68
Refractive index, 852
Regio olfactoria of the nose, 842

respiratoria, 842
Relation, functions of, 8
Remak's division, 17
Renal secretion, 635

mechanism of, 640
Rennet, 112

action of, on milk, 615
Reproduction, 903

of cells, 16

of protoplasm, 14
Reproductive functions, 8, 901

processes, 903

tissues of the female, 908

of the male, 913
Reptiles, auditory apparatus of, 876

brain of, 804

digestive apparatus of, 210

nervous system of, 770

organs of circulation in, 496

reproduction in, 904

respiratory apparatus of, 568

vision in, 849

Residual volume of air, 574
Resistance to traction, 63
Resonance, 885
Respiration, 561

changes of the air in, 588

chemical phenomena in, 587

cutaneous, 656

influence of, on circulation, 605

mechanical processes of, 574

nervous mechanism of, 598

of protoplasm, 14

organs of, 562

rhythm, 579

Respirations, numbers of, in different ani-
mals, 581
Respiratory centre, 816

action of blood on, 602
location of, 600

INDEX.

935

Respiratory changes in the blood, 591

curve, 581

movements, modified, 604

organs of birds, 568
of fishes, 566
of reptiles, 568
types of, 563

volumes of air, 585
Restiform bodies, 811
Reticulum, functions of, 376

structure of, 318
Retina, functions of, 867

structure of, 865
Retinal purple, 868
Rheoscopic frog, 722
Rhodopsm, 868
Rhythm of respiration, 579.
Ribs, movements of, in respiration, 575
Rigid tubes, flow of liquids through, 518
Rigor mortis, 704
Rising up and lying down, mechanism of,

754

Roots and bulbs, composition of, 184
Rotatory joint, 730
Rumen, functions of, 374
Ruminants, convolutions of the brain of,
805

dentition of, 258

gastric digestion in, 374

larynx of, 761

respiratory movements of, 582
Rumination, 316 w

changes of food in, 323

influence of nervous system on, 330

structure of, 317
Ru :m-ing in quadrupeds, 749

mechanism of, m men, 738
Rtr.OLl
K/e residue, 181

SacHiarates, 119

Saccharose, 119

Saliva, centre for secretion of, 817

chemical composition of, 271

course of, 270

physiological uses of, 287

quantity of, 286

Salivary glands, experiments on, 295
histological changes in, 305

secretion, 268

characteristics of, 284
mechanism of, 293
Salts, absorption of, 454

amount of, in fodders, 679

influence of, on nutrition, 678

nutritive, 192
Saponification, 121
Sarkin, 663
Scalene muscles, ' action of, in inspiration,

577

Schleiden's cell doctrine, 15
Schultze's test for reaction of proteids, 92
Schwann's cell doctrine, 15

Sclerotic, 849

Sebaceous secretion of the skin, 655

Secretion of bile, 391

of gastric juice, 356

of milk, 609

of sweat, 652

of tears, 658

of the skin, sebaceous, 655

parotid, 274

salivary, 268

sublingual, 283

submaxillary, 279
Secretory phenomena, 793
Section of spinal cord, results of, 800
Segmentation of mammalian ovum, 19
Semicircular canals, 877
Semilunar valves, action of, 513
Seminal fluid, 913
Sensation, 837
Sensations, tactile, 897

visual, 864
Sense of hearing, 875

of sight, 846

of smell, 841

of taste, 893

of touch, 897
Sensibility, conditions of, 838

general and special, 837
Sensitive plant, 71

motions of, 71

Sensory impulses, paths of, 801, 827
Serum-albumen, 92

of blood, 489

Setchenow's inhibitory centre, 793
Sheep and goat, urine of, 640
Sheep, dentition of, 259

fat, 123

food required in fattening, 687

normal foods for, 690

prehension of food in, 235
Shell-membrane of egg, formation of, 22
Sighing, 604
Sight, sense of, 846
Silicon, 136
Sinus venosus, 503
Sitting, mechanism of, in man, 733
Skin as a heat regulator, 651

as an excretory organ, 651

functions of, 651

sebaceous, secretion of, 655
Smell, intensity of, 846

sense of, 841
Sneezing, 605

centre for, 816
Soaps, 121
Sobbing, 605
Socket-and-ball joint, 730
Sodium carbonate, 129

chloride, 128

phosphate of, 130

sulphate, 135
Solids, prehension of, 226
Solipedes, gastric digestion in, 368

:93B

INDEX.

Soluble ferments, 110
Solution, 43

Sound, reflection of, 883
Sounds, conduction of, 884
of the heart, 514
pitch of, 884
reciprocation of, 884
sympathetic vibration of, 884
transmission of, 884
variations in, 758
Special physiology, definition of, 1
Specialization of function, 15, 32
Specific gravity of tissues, 62
Spectra of haemoglobin, 477
Spermaceti, 122
Spermatic cells, 915
Spermatoblasts, 915
Spermatozoa, 28, 914
development of, 915
motion of, 77 •
Spherical aberration, 854
Sphygmograph, 536 <
Spinal accessory nerve, 835

cord as a collection of nerve-centres,

789

course of fibres in, 789, 797
functions 'of, 786
histology of, 789
influence of on renal secretion,

645

reflex action of, 790
section of antero-lateral columns

of, 801

experiments on, 800
longitudinal section of, 80.1
section of, 800
structure of, 786
'tracts of, 796
roots, course of fibres in, 798 -

influence of, on nervous nutrition,
| 778... . ,v.;
Splanchnic nerves, influence of, on renal

seerefcmn, 645

Spleen, influence of on pancreas, 409
Stability of animal bodies, 731
Stable equilibrium, 731
Standing in quadrupeds, 733

mechanism of, in man, 732
Stapedius muscle, 890
Stapes, 880

Starch, changes of, through saliva, 289
Starches, 112

gastric digestion of, 354
test for, 114

Star- fish, nervous system of, 766
Starvation, loss of weight in different tis-
sues, 676

tissue changes in, 674
Stearic acid, 122
Stearin, 122
Stereoscope, 870
Stimuli of nerves, 776
Stomach, accumulation of food in, 338

Stomach, changes of food in, 341

characteristics of, 215

of hog, 216

structure of, 363

of horse, 215

of ruminant, capacity of, 339

structure of, 356
Straw, barley, 171

buckwheat, 172

composition of, 178
Stroma of blood-corpuscles, 474
Structure of organized bodies, 11
Sublingual secretion, 283
Submaxillary saliva, composition of, 280

fistula, 279

secretion, 279
Succus entericus, 416
Suckling and mastication, centre for, 817
Sugar, -absorption of, 454

fate of, 670
,':.: -milk, 120,

of milk, 616
Sulphate of calcium, 136

of potassium, 135

of sodium., 135

Supplemental volume of air, 573
Sweat, composition of, 652

influence of nervous system on, 654

quantity of, 653

secretion, 652

of, 654

Swimming in the horse, 755
Swine, normal foods for, 690
Sympathetic nerve, 835

action of, on pupil, 862

influence of, on temperature, 697
Synarthroses, 729
Syntonin, 99
Syrinx of birds, 760

Tactile sensations, 897
Taste bulbs, 893

nerves of, 896

sense of, 893
Taurin, 387

Taurocholate of sodium, 384
Taurocholic acid, 386
Tears, composition of, 658
Teeth, ;action of, in mastication, 245

compound, structure of, 246

structure of, 245
Tegmentum cruris, 819
Temperature influence on ciliary motion, 80
on nerve irritability, 776
on protoplasmic movement, 82

of different domestic animals, 696
Temporal muscle, action of, 243
Tensor tympani muscle, 890
Tetanus, 715
Thirst, 92

Thoracic duct, chyle of, 460
Thorax, 571
Tidal volume of air, 573

INDEX.

937

Timbre of sounds, 758
Timothy, composition of, 187
Tissue changes in starvation, 674:

elastic, 35

fibrous, 35

gelatinous, 35

glandular, 34

mucoid, 35

muscular, 34

nerve, development of, 34

nitrogenous constituents of, 85

non-nitrogenous constituents of, 85
Tissues, absorption of, for colors, 68

and organs, development of, 31

classification of, 33

cohesion of, 62

connective, 34

contractile, 701

development of, 15

elasticity of, 65

electrical phenomena of, 70

extensibility of, 66, 67

flexibility of, 67

intercellular, 34

optical characteristics of, 68

physical properties, 61

refraction of, 68

reproductive, of the female, 908

resistance of, to flexion, 64
to pressure, 63
to torsion, 64
to traction, 63

specific gravity of, 62
Vongue, action of, in mastication, 264

of horse, 233

of ox, 233

,Torricelli's theorem, 517
Touch corpuscles, 899

sense of, 897

Trachea, structure of, 569
Tradescantia virginica, 73
Transudation, 48
Tread, 20

Trifacial nerve, 833
Tricuspid valve, 509
Trigeminal nerve, 833
Trochlearis, 832
Trot, 748
Trypsin, 409

Tubular glands of stomach, 356
Tympanic membrane, 879
Tympanum, 877, 879
Tyrosin, 410

Unformed ferments, 111
Unorganized and organized bodies, distinc-
tions between, 22
Unstable equilibrium, 731
Urea, excretion of, in starvation, 676

formation of, 661, 662
Uric acid, 663

source of, 662
Urinary secretion, mechanism of, 640

Urinary tubules, functions of, 643, '646
Urination, mechanism of, 648
Urine, composition of, 636

of carnivora, 637

of dog, 640

of herbivora, 637

of horse, 638

of ox, 639

of pig, 640

of sheep and goat, 640

physical and chemical properties of,

635 '
Uterus, 908

Vagus nerve of frog, 545

wave, 549

Vallisneria, movements in, 74
Valves of the heart, action of, 508
Vaso-constrictor nerves, 558

dilator nerves, 558

motor centre, 555
centres, 794
nerves, 554
Vegetable albumens, 93

caseins, 94

cells, chemical processes in, 137

fibrin, 95

foods, 161

gelatin, 96

globulins, 97

physiology, definition of, 10
Vegetative functions, definition of, 8
Veins, blood pressure in, 539

circulation in, 539

velocity of circulation in, 540
Velocity of the blood, 530
Vena contracta, 518
Venous absorption, 453

blood, gases of, 592

sinus, 503

Ventricle, fourth, of the brain, 812
Ventricles, capacity of, 532

movements of, 503

muscular fibres of, 502
Ventriculus, functions of, 3'80
Venus' fly-trap, motions of, 72
Vernix caseosa, 655
Vertebrates, digestive apparatus of, 209

nervous system of, 769
Vesicle, blastodermic, 25

germinal, 15

modifications of free fertilization

in, 18

Vestibule of the ear, 877
Villi, structure and functions of, 456
Vision, sense of, 846
Visual apparatus, structure of, 846

imperfection, 872

purple, 868

sensations, 864

Vital capacity, volume of, 586
Vitellin, 97
Vitelline membrane, 15

938

INDEX.

Vitreous humor, 849

Vocal cords, 757

muscles of, 762

Voice, 757

production of, 758

Vomiting, centre for, 817
mechanism of, 330
nervous mechanism of, 334

Walking backward in the horse, 754
mechanism of, in the horse, 744
in man, 737

Water, 124, 191
in cells, 86

White blood-corpuscles, 479

Wool-producing animals, food required by,

688
Worms, digestive apparatus of, 205

Xanthin, 663

Xantho-proteic reaction of proteids, 91

Yawning, 604

Yelk of egg, structure of, 20

Yellow spot of the retina, 865

Zona pellucida, 15

radiata, 15
Zymogen, 409

MARCH, 1890.

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JUST PUBLISHED— A NEW AND VALUABLE WORK ON

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MEDICINE AND SURGERY.

G. A. LIEBIG, Jr., Ph.D.,

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-AND-

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Professor Rohe, who writes on Electro-Therapeutics, discusses at length the recent
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The applications of Electricity in dermatology, as well as in the diseases oi the
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THE SECOND VOLUME IN THE PHYSICIANS' AND STUDENTS'
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OF

Materia Mediea, ptiarmaeij, and Therapeutics

By CUTHBERT BOWEN, M.D., B.A.,

Editor of " Notes on Practice."

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This excellent manual comprises in its 366 small
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In going through it, we have been favorably im-
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tem, and the other things which must be known in
order to write good and accurate prescriptions. —
Medical and Surgical Reporter.

Many works claim more in their title-pages than
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criticism we can make on this volume is that it does
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The book is one of the very best of its class. —
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This is a very condensed and valuable resume
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Dr. Bo wen's work is a very valuable one indeed,
and will be found "to fill a want" beyond a doubt.
— Cincinnati Medical News.

It is short and concise in its treatment of the
subjects, yet it gives sufficient to gain a very correct
knowledge of everything that comes under this head-
ing. . This is a ready work for the country physician,
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One 12mo volume of 37O pages. Handsomely Bound in Dark-Blue Cloth.

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-4HBOO

The Physician Himself

AND THINGS THAT CONCERN

HIS REPUTATION AND SUCCESS.

BY

D. W. CATHELL, M.D.,

BALTIMORE, MD.

Being the NINTH EDITION (Enlarged and Thoroughly Revised) of the "PHYSICIAN

HIMSELF, AND WHAT HE SHOULD ADD TO HIS SCIENTIFIC ACQUIREMENTS

IN ORDER TO SECURE SUCCESS."

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This remarkable book has passed through eight (8) editions in less
than live years, has met with the unanimous and hearty approval of the
Profession, and is practically indispensable to every young graduate
who aims at success in his chosen profession. It has just undergone a
thorough revision by the author, who has added much new matter cover-
ing many points and elucidating many excellent ideas not included in
former editions. This unique book, the only complete one of the kind
ever written, will prove of inestimable pleasure and value to the practi-
tioner of many years' standing, as well as to the young physician who
needs just such a work to point the way to success.

We give below a few of the many unsolicited letters received by
the author, and extracts from reviews in the Medical Journals of the
former editions :

'• 'The Physician Himself is an opportune and
most useful book, which cannot fail to exert a good
influence on the morale and the business success of
the Medical profession." — Front Prof. Roberts
rarf.holo-M, Philadelphia, Pa.

"I have read 'The Physician Himself with
pleasure — delight. It is brimful of medical and
social philosophy ; every doctor in the land can
study it with pleasure and profit. 1 wish I could
have read such a work thirty years ago." — From
Prof. John S. Lynch, Baltimore, Md.

"'The Physician Himself interested me so
much that I actually read it through at one sitting.
It is brimful of the very best advice possible for
medical men. I, for one, shall try to profit by it." —
From Prof. William Goodell, Philadelphia.

" I would be glad if, in the true interest of the
profession in 'Old England,' some able practitioner
here would prepare a work for us on the same line as
'The Physician Himself.'"— From Dr. Jukes de
Styrap, Shrewsbury, England.

" I am most favorably impressed with the
wisdom and force of the points made in 'The Phy-
sician Himself,' and believe the work in the hands

Prof. D. Hayes

of a young graduate will greatly enhance his chances
for professional success." — From }
Agnew, Philadelphia, Pa

"This book is evidently the production of an
unspoiled mind and the fruit of a ripe career. I
admire its pure tone and feel the value of its practi-
cal points. How I wish I could have read such a
guide at the outset of my career!" — Front Prof.
James Nevins Hyde, Chicago, III.

" It contains a great deal of good sense, well
expressed." — From Prof . Oliver Wendell Holmes,
Harvard University.

" 'The Physician Himself is usefu! alike to the
tyro and the sage — the neophyte and the veteran. It
is a headlight in the splendor of whose beams a
multitude of our profession shall find their way to
success."— From Prof. J. M. Bodine, Dean Uni-
versity of Louisville.

" It is replete with good sense and sound phi-
losophy. No man can read it without realizing that
its author is a Christian, a gentleman, and a shrewd
observer." — From Prof. Edward Warren (Bey),
Chevalier of the Legion of Honor, etc., Paris,
France.

"I have read 'The Physician Himself,' care-
fully. I find it an admirable work, and shall advise
our Janitor to keep a stock on hand in the book de-
partment of Bellevue." — From Prof. William T.
Lusk, New York.

" It must impress all its readers with the belief
that it was written by an able and honest member of
the profession and for the good of the profession." —
From Prof. W. H. Byford, Chicago, III.

" It is marked with good common sense, and
replete with excellent maxims and suggestions for
the guidance of medical men." — From The British
Medical Journal, London.

" We strongly advise every actual and intend-
ing practitioner of medicine or surgery to have
' The Physician Himself,' and the more it influences
his future conduct the better he will be." — From
The Canada Medical and Surgical Journal,
Montreal.

" We would advise every doctor to well wotgh
the advise given in this book, and govern his con-
duct accordingly." — From The Virginia Medical
Monthly.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

AN IMPORTANT PUBLICATION OF GREAT VALUE TO THE MEDICAL
AND LEGAL PROFESSIONS.

SPINAL CONCUSSION:

Surgically Considered as a Cause of Spinal Injury, and Neurologi-

oally Restricted to a Certain Symptom Group, for

•which is Suggested the Designation

ERICHSEN'S DISEASE, AS OHE FORM OF THE TRAUMATIC NEUROSES,

S. V. CLEVENGER, M.D.,

CONSULTING PHYSICIAN REESE AND ALEXIAN HOSPITALS; LATE PATHOLOGIST COUNTY INSANE ASYLUM,
CHICAGO; MEMBER OF NUMEROUS AMERICAN SCIENTIFIC AND MEDICAL SOCIETIES; COLLABORATOR
AMERICAN NATURALIST, ALIENIST AND NEUROLOGIST, JOURNAL OF NEUROLOGY AND
PSYCHIATRY, JOURNAL OF NERVOUS AND MENTAL DISEASES; AUTHOR OF "COM-
PARATIVE PHYSIOLOGY AND PSYCHOLOGY," "ARTISTIC ANATOMY," ETC.

For more than twenty years this subject has occasioned bitter con-
tention in law courts, between physicians as well as attorneys, and in
that time no work has appeared that reviewed the entire field judicially
until Dr. Clevenger's book was written. It is the outcome of five years'
special study and experience in legal circles, clinics, hospital and private
practice, in addition to twenty years' labor as a scientific student, writer,
and teacher.

The literature of Spinal Concussion has been increasing of late years
to an unwieldy shape for the general student, and Dr. Clevenger lias in this
work arranged and reviewed all that has been done by observers since
the days of Eriehsen and those who preceded him. The -different and
sometimes antagonistic views of many authors are fully given from the
writings of Eriehsen, Page, Oppenheim, Erb, Westphal, Abercrombie,
Sir Astley Cooper, Boyer, Charcot, Leyden, Rigler, Spitzka, Putnam,
Knapp, Dana, and many other European and American students of the
subject. The small, but important, work of Oppenheim, of the Berlin
Universit3T, is fully translated, and constitutes a chapter of Dr. Cleven-
ger's book, and reference is made wherever discussions occurred in
American medico-legal societies.

There are abundant illustrations, particularly for Electro-diagnosis,
and to enable a clear comprehension of the anatomical and pathological
relations.

The Chapters are : I. Historical Introduction ; II. Eriehsen on
Spinal Concussion ; III. Page on Injuries of the Spine and Spinal Cord:
IV. Recent Discussions of Spinal Concussion; V. Oppenheim on Trau-
matic Neuroses; VI. Illustrative Cases from Original and all other
Sources; VII. Traumatic Insanity; VIII. The Spinal Column; IX.
Symptoms; X. Diagnosis; XI. Pathology; XII. Treatment; XIII.
Medico^legal Considerations.

Other special features consist in a description of modern methods
of diagnosis by Electricity, a discussion of the controversy concerning
hysteria, and the author's original pathological view that the lesion is
one involving the spinal sympathetic nervous system. In this latter
respect entirely new ground is taken, and the diversity of opinion con-
cerning the functional and organic nature of the disease is afforded a
basis for reconciliation.

Every Physician and Lawyer should own this work.

In one handsome Royal Octavo Volume of nearly 400 pages, with
Thirty Wood-Engravings. Net price, in United States and Canada,
$2.50, post-paid ; in Great Britain, Us. 3d. ; in France, 15 fr.

CF. A. DAVIS, Medical Publisher, Philadelphia, Pa.. U.S.A.)

JUST READY-A NEW AND IMPORTANT WORK.

ESSAY

MEDICAL PNEDMATOLOGY I AEROTHERAPY:

A PRACTICAL INVESTIGATION OF THE CLINICAL AND THERAPEUTIC VALUE

OF THE GASES IN MEDICAL AND SURGICAL PRACTICE, WITH ESPECIAL

REFERENCE TO THE VALUE AND AVAILABILITY OF

OXYGEN, NITROGEN, HYDROGEN, AND NITROGEN MONOXIDE.

BY d. N. DEMARQUAY,

Surgeon to the Municipal Hospital, Paris, and of the Council of State ; Member of the Imperial Society

of Surgery ; Correspondent of the Academies of Belgium, Turin, Munich, etc. ; Officer

of the Legion of Honor ; Chevalier of the Orders of Isabella-the-

Catholic and of the Conception, of Portugal, etc.

TRANSLATED, WITH NOTES, ADDITIONS, AND OMISSIONS,

BY SAMUEL S. WALLIAN, A.M., M.D.,

Member of the American Medical Association ; Ex-President of the Medical Association of Northern New
York ; Member of the New York County Medical Society, etc.

In one Handsome Octavo Volume of 316 Pages, Printed on Fine Paper, in the Best
Style of the Printer's Art, and Illustrated with 21 "Wood-Cuts.

United States. Canada (duty paid). Great Britain. France.

NET PRICE, CIX>TH, Post-paid, S2.OO S2.2O SB. 6d. 12 fr. 4O

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For some years past there has been a growing demand for something more satisfac-
tory and more practical in the way of literature on the subject of what has, by commom
consent, come to be termed " Oxygen Therapeutics." On all sides professional men of
standing and ability are turning their attention to the use of the gaseous elements about
us as remedies in disease, as well as sustainers in health. In prosecuting their inquiries,
the first hindrance has been the want of any reliable, or in' any degree satisfactory,
literature on the subject.

Purged of the much quackery heretofore associated with it, Aerotherapy is now
recognized as a legitimate department of medical practice. Although little noise is made
about it, the use of Oxygen Gas as a remedy has increased in this country within a few
years to such an extent mat in New York City alone the consumption for medical pur-
poses now amounts to more than 300.000 gallons per annum.

This work, translated in the main from the French of Professor Demarquay, contains
also a very full account of recent English, German, and American experiences, prepared
by Dr. Samuel S. Wallian, of New York, whose experience in this field antedates that of
any other American writer on the subject.

Plain Talks on Avoided Subjects.

HENRY N. GUERNSEY, M.D.,

Formerly Professor of Materia Medica and Institutes in the Hahnemann Medical College of Philadelphia;

Author of Guernsey's " Obstetrics," including the Disorders Peculiar to Women and

Young Children ; Lectures on Materia Medica, etc.

IN ONE NEAT 16mo VOLUME. BOUND IN EXTRA CLOTH. Price, Post-paid, in
United States and Canada, 81. OO; Great Britain, 4s. 6d. ; France, 6 fr. 2O.

This is a little volume designed to convey information upon one of the most important subjects con-
nected with our physical and spiritual well-being, and is adapted to both sexes and all ages and conditions
of society ; in fact, so broad is its scope that no human being can well afford to be without it, and so com-
prehensive in its teachings that, no matter how well informed one may be, something can yet be learned from
this, and yet it is so plain that any one who can read at all can fully understand its meaning.

The Author, Dr. H. N. Guernsey, has had an unusually long and extensive practice, and his teachings in
this volume are the results of his observation and actual experience with all conditions of human life.

His work is warmly indorsed by many leading men in all branches of professional life, as well as by
many whose business connections have caused them to be close observers.

The following Table of Contents shows the scope of the book: —

CONTENTS. CHAPTER I.— INTRODUCTORY. II.— THE INFANT. III.— CHILDHOOD. IV.— ADOLES-
CENCE OF THE MALE. V. — ADOLESCENCE OF THE FEMALE. VI. — MARRIAGE: THE HUSBAND. VII. —
^'HE WIFE. VIII. — HUSBAND AND WIFE. IX. — To THE UNFORTUNATE. X. — ORIGIN OF THE SEX.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.) 7

Lessons in Gynecology.

By WILLIAM GrOODELL, A.M., M.D., Etc.,

PKOFKSSOR OF CLINICAL GYNECOLOGY IN THE UNIVERSITY OF PENNSYLVANIA.

With 112 Illustrations. Third Edition, Thoroughly Revised and Greatly Enlarged.
XONE VOLUME, LARGE OCTAVO, 578 PAGES.

This exceedingly valuable work, from one of the most eminent specialists and teachers in gynecology
in the United States, is now offered to the profession in a much more complete condition than either of the
previous editions. It embraces all the more important diseases and the principal operations in the field of
gynecology, and brings to bear upon them all the extensive practical experience and wide reading of the
author. It is an indispensable guide to every practitioner who has to do with the diseases peculiar to
women.

FIG. 44.

NATURAL POSITION OP THE WOMB WHEN THE BLADDER is FULL.
AFTER BRIESKY.

These lessons are so well known that it is en-
tirely unnecessary to do more than to call attention
to the fact of the appearance of the third edition. :
It is too good a book to have been allowed to remain !
out of print, and it has unquestionably been missed.
The author has revised the work with special care,
adding to each lesson such fresh matter as the prog-
ress in the art rendered necessary, and he has en-
larged it by the insertion of six new lessons. This
edition will, without question, be as eagerly sought
for as were its predecessors. — American Journal
of Obstetrics.

The former editions of this treatise were well
received by the profession, and there is no doubt
that the new matter added to the present issue makes *
it more useful than its predecessors. — New York
Medical Record.

His literary style is peculiarly charming. There

is a directness and simplicity about it which is easier
to admire than to copy. His chain of plain words
and almost blunt expressions, his familiar compari-
son and homely illustrations, make his writings, like
his lectures, unusually entertaining. The substance
of "his teachings we regard as equally excellent.—
Phila. Medical and Surgical Reporter

Extended mention of the contents of the book is
unnecessary; suffice it to say that every important
disease found in the female sex is taken up and dis-
cussed in a common-sense kind of a way We wish
every physician in America could read and carry
out the suggestions of the chapter on "the sexual re-
lations as causes of uterine disorders — conjugal
onanism and kindred sins." The department treat- \
ing of nervous counterfeits of uterine diseases is
a most valuable one. — Kansas City Medical
Index.

Price, in United States and Canada, Cloth, $5,00; Full Sheep, $6.00. Discount, 20 per

cent., making it, net, Cloth, $100; Sheep, $4.80. Postage, 27 Cents extra. Great

Britain, Cloth, 18s. ; Sheep, £1.2s., post-paid, net. France, 30 fr. 80.

8 (F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

AMERICAN RESORTS,

WITH NOTES UPON THEIR CLIMATE.

Member of the American Association for the Advancement of Science, the American Public Health Association, the

Pennsylvania Historical Society, the Franklin Institute, and the Academy of Natural Sciences. Philadelphia;

the Society of Alaskan Natural History and Ethnology, Sitka, Alaska, etc.

WITH A TRANSLATION FROM THE GERMAN, BY MR. S. KAUFFMANN,

Of those chapters of '•' Die Klimate der Erde" written by Dr. A. Woeikof, of St. Petersburg, Russia, that
relate to North and South America and the islands and oceans contiguous thereto.

In One Octavo Volume. Handsomely Bound in Cloth. Nearly 30O Pages. Price,
Post-paid, in U. S. and Canada, SS2.OO, net. Great Britain, 8s. 6d. France, 12 fr. 4O.

This is a unique and valuable work, and useful to physicians in all parts of the country. It is just such
a volume as the MedicaLProfession have stood in need of for many years. We mention a few of the merits
it possesses: First. List of all the Health Resorts of the country, arranged according to their climate.
Second. Contains just the information needed by tourists, invalids, and those who visit summer or winter
resorts. Third. The latest and best large railroad map for reference. Fourth. It indicates the climate
each one should select for health. Fifth. The author has traveled extensively, and most of his suggestions
are practical in reference to localities.

Taken altogether, this is by far the most complete ex-
position of the subject of resorts that has yet been put
forth, and it is one that every physician must needs possess
intelligent information upon. We predict a large demand
for this useful and attractive book.— Buffalo Med. and
Surg. Jmtr.

The special chapter on the therapeutics of climate . .
is excellent for its precautionary suggestions in the selec-
tion of climates and local conditions, with reference to
known pathological indications and constitutional predis-
positions.— The Sanitarian.

It is arranged in such a manner that it will be of great
service to medical men whose duty it often becomes to rec-
ommend a health resort.— N. W. Med. Jour.

A well-arranged map of the United States serves as the
frontispiece of the book ; and an almost perfect index is
appended, while between the two is an amount of informa-
tion as to places for the health-seeker that cannot be gotten
elsewhere. We most cordially recommend the book to
travelers and to the doctor.— Virginia Med. Monthly.

This is a work that has long been needed, as there is
has not had occasion to look up
«, elevation, drvness, humidity,

eic . etc.. of the various health resorts, and has had great
•difficulty in finding reliable information. It certainly

scarcely a physician who hj
the authorities on climate,

Clh,

ought, as it deserves, to receive a hearty welcome from the
profession. — Medical Advance.

The book before us is a very comprehensive volume,
giving all necessary information concerning climate, tem-
perature, humidity, sunshine, and indeed everything neces-
sary to be stated for the benefit of the physician or invalid
seeking a health resort in the United States.— Southern

This work is extremely valuable, owing to the liberal
and accurate manner in which it gives information regard-
ing the various resorts on the American continent, without
being prejudice_d in the least in favor of any particular one,
but giving all in a fair manner. . . . All physicians
need just such a work, for the doctor is always asked to
give information on the subject to his patients. Therefore,
it should find a place in every physician's library.— The
Med. Brief.

The author of this admirable work has long made a
study of American climate, from the stand-point of a phy-
sician, with a view to ascertaining the most suitable locali-
ties for the residence of invalids, believing proper climate
to be an almost indispensable factor in the treatment, pre-
vention, and cure of many forms of disease. . . . The
book evidences careful research and furnishes much useful
information not to be found elsewhere. — Pacific Med. Jjiir.

JUST PUBLISHED'

RECORD-BOOK OF MEDICAL EXAMINATIONS

For Life Insurance.

Toy

In examining for Life Insurance, questions are easily overlooked and the answers to
them omitted ; and, as these questions are indispensable, they must be answered before the
case can be acted upon, and the examiner is often put to much inconvenience to obtain
this information.

The need has long been felt among examiners for a reference-book in which could be
noted the principal points of an examination, and thereby obviate the necessity of a
second visit to the applicant when further information is required.

After a careful study of all the forms of examination blanks now used by Insurance
Companies, Dr. J. M. Keating has compiled such a record-book which we are sure will fill
this long-felt want.

This record-book is small, neat, and complete, and embraces all the principal points
that are required by the different companies. It is made in two sizes, viz. : No. 1, cover-
ing one hundred (100) examinations, and No. 2, covering two hundred (200) examina-
tions. The size of the book is 7 x3| inches, and can be conveniently carried in the
pocket.

PRICES, I»OST-I»AID.

U. S. and Canada. Great Britain. France

No. 1, For 100 Examinations, in Cloth, - & .50 »s. 6d. 3 fr. 6O
No. 2, For 2OO Examinations, in Full

Leather, witk Side Flap, .... i.oo 4s. 6d. 6 fr. 2O

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S A.) 9

OF THE

Heart and Circulation

IN INFANCY AND ADOLESCENCE.

Witli an Appendix entitled " Clinical Studies on the
Pulse in Childhood."

JOHN M. KEATING, M.D.,

©bstetrician to the Philadelphia Hospital, and Lecturer on Diseases of Women and Children; Surgeon to

the Maternity Hospital ; Physician to St. Joseph's Hospital; Fellow of the

College of Physicians of Philadelphia, etc.,

— AND —

WILLIAM A. EDWARDS, M.D.,

Instructor in Clinical Medicine and Physician to the Medical Dispensary in the University of Pennsylvania ^

Physician to St. Joseph's Hospital ; Fellow of the College of Physicians ; formerly

Assistant Pathologist to the Philadelphia Hospital, etc.

ILLUSTRATED BY PHOTOGRAPHS AND WOOD-ENGRAVINGS.

About 225 Pages. 8vo. Bound in Cloth. Price, post-paid, in U. S.
and Canada, $1.5O, net; Great Britain, 6s. 6d. ; France, 9 fr. 35.

There are many excellent text-books on children's diseases, but they have failed to give a satisfactory
account of the diseases of the heart ; and, indeed, as far as known, this work of Keating and Edwards' n nv
presented to the profession is the only systematic attempt that has been made to collect in book form the
abundant material which is scattered throughout medical literature in the form of journal articles, clinical
lectures, theses, and reports of societies,

The authors have endeavored, in their difficult task, to collect these valuable materials and place them
within easy reach of those who are interested in this important subject. That they have succeeded will, we
believe, be conceded by all who obtain and make use of their very valuable contribution to this hitherto-
neglected field of medical literature.

An appendix, entitled " Clinical Studies on the Pulse in Childhood," follows the index in the book, and
will, we are sure, be found of much real value to every practitioner of medicine. The work is made available
for ready reference by a well-arranged index. We append the table of contents showing the scope of the
book :—

CHAPTER VII. — General Diagnosis, Prognosis, and
Treatment of Valvular Disease.

CHAPTER VI11.— Endocarditis— Atheroma— Aneu-
rism.

CHAPTER IX. — Cardiac Neuroses — Angina Pectoris-
— Exophthalmic Goitre.

CHAPTER X. — Diseases of the Blood : Plethora,
Anaemia, Chlorosis, Pernicious Anaemia. Leu-
kaemia—Hodgkin's Disease — Hssmophilia,Throm-
bosis, and Embolism.

INDEX.

APPENDIX.— CLINICAL STUDIES ON THE PULSE
IN CHILDHOOD.

CHAPTER I. — The Methods of Study — Instruments —
Foetal Circulation — Congenital Diseases of the
Heart — Malformations — Cyanosis.

CHAPTER II. — Acute and Chronic Endocarditis —
Ulcerative endocarditis.

CHAPTER III. — Acute and Chronic Pericarditis.

CHAPTER IV.— The treatment of Endo- and Peri-
carditis— Paracentesis Pericardii — Hydropericar-
dium — Haemopericardium — Pneumopericardium.

CHAPTER V. — Myocarditis — Tumors, New Growths,
and Parasites

CHAPTER VI.— Valvular Disease: Mitral, Aortic,
Pulmonary, and Tricuspid.

Drs. Keating and Edwards have produced a work that
•will give material aid to every doctor in his practice among
children. The style of the book is graphic and pleasing,
the diagnostic points are explicit and exact, and the thera-
peutical resources include the novelties of medicine as well
as the old and tried agents.— Pittshnruli M<->J. BfoSetD.

A very attractive and valuable work has been given to
the medical profession by Drs. Keating and Edwards, in
their treatise on the diseases of the heart and circulation
in infancy and adolescence, and they deserve the greatest
credit for the admirable manner in which they have col-
lected, reviewed, and made use of the immense amount of
material on this important subject.— A rchives of Pedintrirx.

The plan of the work is the correct one, viz., the sup-
plementing of the observations of the better class of prac-
titioners by the experience of those who have given the
subject systematic attention. — Medical -Age.

It is not a mere compilation, but a systematic treatise,
and bears evidence of considerable labor and observation on-
the part of the authors. Two fine photographs of dissect
tions exhibit mitral stenosis and mitral regurgitation ;
there are also a number of wood-cuts. — Cleveland Medical
Gazette.

As the works upon diseases of children give little or no
attention to diseases of tbe heart, this work of Drs. Keat-
ing and Edwards will supply a want. We think that
there will be no physician, who takes an interest in the
affections of young folks, who will not wish to consult it.
— Ciiirhinfifi M':<1. K'nra.

The work takes up, in an able and scientific manner,
diseases of the heart in children. This is a part of the
field of medical science which has not been cultivated to
the extent that the importance of the subject deserves.—
Canada Lancet.

10

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

PERPETUAL CLINICAL INDEX

MATERIA MEDICA, CHEMISTRY, AND PHARMACY CHARTS.
By A. H. KELLER, Ph.G., M.D.

Consisting of (1) the "Perpetual Clinical Index," an oblong volume, 9x6 inches,
neatly bound in extra Cloth ; (3) a Chart of "Materia Medica," 32x44 inches,
mounted on muslin, with rollers ; (3) a Chart of » Chemistry and Phar-
macy," 32 x44 inches, mounted on muslin, with rollers.

United States. Canada (duty paid). Great Britain. France.

Net Price for the Complete Work, $5,00 $5,50 £l.ls. 30 fr. 30

Bead the Following Description and Explanation of the

In presenting the objects and advantages of these Charts and " Perpetual Clinical Index" it becomes
necessary to state that the Author's many years' experience as a physician and Pharmacist enables him
to produce, in terse language, a volume of facts that must be of inestimable value to the busy physician and
pharmacist, or to any student of either profession. He has endeavored to describe all that have borne inves-
tigation up to date.

The system will prove to be of great value in this, that so little labor will be required to add new
investigation as fast as may be gathered from new books, journals, etc. The classification is alphabetical
and numerical in arrangement, and serves so to unite the various essentials of Botany, Chemistry, and
Materia Medica, that the very thought of the one will readily associate the principal properties and uses, as
well as its origin.

The "MATERIA MEDICA" CHART, in the first place, aids at a glance: ist, Botanical or
U. S. P. Name; 2d, The Common Name ; ^d, Natural Order ; 4th, Where Indigenous ; sth, Principal Con-
stituent; 6th, Part Used — herbs, leaves, flowers, roots, barks, etc. ; yth, Medicinal Properties — mainly con-
sidered ; 8th, The Dose — medium and large.

On this Chart there are 475 first names ; Section A. is numbered from i to 59, each section commencing
with the capital letter, and having its own numbers on both left-hand and right-hand columns, to prevent
mistakes in lining out, all in quite large type. In the centre of the Chart, occupying about 6 inches in
width, is a term index of common names. In the second column of Chart, like this :

ACONITE LEAVES, . . • 4 A.

Then by reference to 4 A in first column, you there find the Botanical or U. S. P. N«.me. On this Chart is
also found a brief definition of the terms used, under the heading " Medicinal Properties."

The "CHEMISTRY" CHART takes in regular order the U.S. Pharmacopoeia Chemicals, with
the addition of many new ones, and following the name, the Chemical Formula, the Molecular Weight, and
next the Origin. This is a brief but accurate description of the essential points in the manufacture : The
Uose, medium and large; next, Specific Gravity; then, whether Salt or Alkaloid; next, Solubilities, by
abbreviation, in Water, Alcohol, and Glycerine, and blank columns for solubilities, as desired.

Alkaloids and Concentrations are tabulated with reference numbers for the Perpetual Clinical Index, giving
Medicinal Properties, Minute Dose^and Large Dose For example, ALKALOIDS AND CONCENTRATIONS :

A. MEDICINAL PROPERTIES. MINUTE DOSE, i LARGE DOSE.

(a) Aconitine. Narcotic and Apyretic. 1-500 gr. 1-16 gr.

Following this, Preparations of the Pharmacopoeia, each tabulated. For example :

TINCTURAL.

TlNCTURA.

DRUG.

AMOUNT.

ALCOHOL.

DOSE.

* Aconiti.

$ Aconite.
I Tartaric Acid, 60 f P. j

S1A oz. to 24 gr.

100

i to 3 drops.

* 60 Fineness of Powder as per U. S. P.

t P. Macerate 24 hours. Percolate, adding Menstruum to complete (1) pint tincture.

They are all thus abbreviated, with a ready reference head-note.

Next, Thermometers, Metric Table of Weights, Helps to the Study of Chemistry, Examples in Work-
ing Atomic Molecular Formulae Next, Explanation of Terms Used in Columns of Solubilities, List of
Most Important Elements Now in Use, and Definitions or Terms Frequently Used in Chemistry and
Pharmacy.

The "PERPETUAL, CLINICAL INDEX" is a book 6 by 9 inches, and one-half inch thick.
It contains 135 pages, divided as follows (opposite pages blank) :

The Index to Chemistry Chart occupies two pages; Explanations, Abbreviations, etc., forty pages, with
diseases, and with an average of ten references to- each disease, leaving room for about forty more remedies
for each disease. The numbers refer to the remedies used in the diseases by the most celebrated physicians
and surgeons, and the abbreviations to the manner in which they are used. Eight pages, numbered and
bracketed, for other diseases not enumerated. The Materia Medica, Explanations, Abbreviations, and
Remedies suggested for, occupy twenty-six pages. For Abbreviated Prescriptions, seventeen blank pages.
Then the Index to Alkaloids and Concentrations. These, already enumerated, with their reference, number
six blank tabulated pages, for noting any new Alkaloids and Concentrations. Then the Chemistry Index,
giving the same number as on Chart, with Name, Doses, Specific Gravity, Salt or Alkaloid in the same
line, as for example :

NAME. DOSES. j SPECIFIC GRAVITY. j SALT OR ALKALOID. MEMORANDA.

~: ! !' i

This Alemorarlda place is for Physicians' or Pharmacists' reference notes ; and with the addition of
several tabulated blank pages, in which to add any new chemical, with doses, etc. The remaining sixteen
pages for Materia Medica Index, leaving blanks following each other for new names and reference numbers.

To show the ready and permanent use of the "Perpetual Clinical Index" of the "Chemistry" and
"Pharmacy" Charts or Index in the book, suppose the Physician reads in a book or journal that Caffeine
Citras is useful in the disease Chorea, and he wishes to keep a permanent record of that, he refers to the
Chart, and if it does not already appear there, it can be placed opposite and numbered, and thereafter used
for reference. But we find its permanent number is No. 99, so he will write down in the line left blank for
future use in his book, in line already used, running parallel with other reference numbers in Chorea, the
No. 99, and immediately under he can use the abbreviation in the manner in which it is given. Though
years may have passed, he can in a moment, by referring there, see that No. 99 is good for Chorea. If fail-
ing to remember what No. 99 is, he glances at the Chart or Index. He sees that No. 99 is Caffeine Citras,
and he there learns its origin and dose and solubility, and in a moment an intelligent prescription can be
constructed.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.AJ 11

New Edition of an Important and Timely Work Just Published.

Electricity in the Diseases of ^fomen

"With Special Reference to the Application of Strong Currents.

G. BETTON MASSEY, M.D.,

Hospi
Neurological Ass'n, of the Philadelphia Neurological Society, of the Franklin Institute, etc.

By

Physician to the Gynecological Department of Howard Hospital ; Late Electro-Therapeutist to the Phila-
delphia Orthopaedic Hospital and Infirmary for Nervous Diseases ; Member of the American

ZEoLitioia.-

ZES-e-srised. smd.

WITH NEW AND ORIGINAL WOOD-ENGRAVINGS. HANDSOMELY BOUND IN CLOTH. OVER 200 PAGES.

12mo. Price, in United States and Canada, $1.50, net, post-paid.

In Great Britain, 6s. 6d. In France, 9 fr. 35.

This work is presented to the profession as the most complete treatise yet issued om
the electrical treatment of diseases of women, and is destined to fill the increasing demand
for clear and practical instruction in the handling and use of strong currents after the
recent methods first advocated by Apostoli. The whole subject is treated from the present
stand-point of electric science with new and original illustrations, the thorough studies of
the author and his wide clinical experience rendering him an authority upon electricity
itself and its therapeutic applications. The author has enhanced the practical value of
the work by including the exact details of treatment and results in a number of cases
taken from his private and hospital practice.

FIG. 15.— AUTHOR'S FIBROID SPEAR.

FIG. 18.— BALL ELECTRODE FOR ADMINISTERING FRANKLINIC SPARKS.

CHAPTER I, Introductory ; II, Apparatus required in gynecological applications of the galvanic current ;
HI, Experiments illustrating the physical qualities of galvanic currents ; IV, Action of concentrated gal-
vanic currents on organized tissues ; V, Intra-uterine galvano-chemical cauterization; VI, Operative details
of pelvic electro-puncture; VII, The faradic current in gynecology ; VIII, The franklinic current in gyne-
cology'; IX, Non-caustic vaginal, urethral, and rectal applications ; X, General percutaneous applications in
the treatment of nervous women ; XI, The electrical treatment of fibroid tumors of the uterus ; XII, The
electrical treatment of uterine hemorrhage; XIII, The electrical treatment of subinvolution ; XIV, The
electrical treatment of chronic endometritis and chronic metritis ; XV, The electrical treatment of chronic
diseases of the uterus and appendages; XVI, Electrical treatment of pelvic pain; XVII, The electrical
treatment of uterine displacements; XVIII, The electrical treatment of extra-uterine pregnancy; XIX,
The electrical treatment of certain miscellaneous conditions ; XX, The centra-indications and limitations to
the use of strong currents.

An Appendix and a Copious Index, including the definitions of terms used in the work, concludes
the book.

The author gives us what he has seen, and of which

he is assured by scientific study is correct We

are certain that this little work will prove helpful to all
physicians who desire to use electricity in the management
of the diseases of women. — The American Lancet.

To say that the author is rather conservative in his
ideas of the curative powers of electricity is only another
way of saying that he understands his subject thoroughly.
The mild enthusiasm of our author is unassailable, because
it is founded on science and reared with experience.— The
Medical Analectic.

The work is well written, exceedingly practical, and
can be trusted. We commend it to the profession." — Mary-
land Medical Journal.

The book is one which should be possessed by every
physician who treats diseases of women by electricity.—
The Brooklyn Medical Journal.

The departments of electro-physics, pathology, and
electro-therapeutics are thoroughly and admirably con-

sidered, and by means of good wood-cuts the beginner has
before his eye the exact method of work required.— The
Medical Register.

" The author of this little volume of 210 pages ought
to have added to its title, " and a mo'st happy dissertation
upon the methods of using this medicinal agent; " for in
the first 100 pages he has contrived to describe the techni
of electrization in as clear and happy a manner as no
author has ever succeeded in doing, and for this part of the
book alone it is almost priceless to the beginner in the

treatment with this agent The little book ia

worthy the perusal of every one at all interested in the
subject of electricity in medicine. — Tfie Omaha Clinic.

The treatment of fibroid tumor of the uterus will,
perhaps, interest the profession more generally than any
other question. This subject has been accorded ample
space. The method of treatment in many cases has been
recited in detail, the results in every instance reported be-
ing beneficial, and in many curative.— Pacific Med. Jour.

r>

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.}

PRACTICAL SURGERY.

By J. EWING MEARS, M.D.,

Lecturer on Practical Surgery and Demonstrator of Surgery in Jefferson Medical College; Professor of
Anatomy and Clinical Surgery in the Pennsylvania College of Dental Surgery, etc.

With 490 Illustrations, Second edition, revised and enlarged, 794 pp. 12mo,

PRICE, IN UNITED STATES AND CANADA : CLOTH, $3.00. DISCOUNT, 20 PER CENT., MAKING IT, NET,
$2.40; POSTAGE, 20 CENTS EXTRA. GREAT BRITAIN, 13s. FRANCE, 18 fr. 75.

MEARS' PRACTICAL SURGERY includes chapters on Surgical Dress-
ings, Bandaging, Fractures, Dislocations, Ligature of Arteries, Amputa-
tions, Excisions of Bones and Joints. This
work gives- a complete account of the
methods of antiseptic surgery. The dif-
ferent agents used in antiseptic dressing,
their methods of preparation, and their
application in the treatment of wounds are
fully described. With this work as a guide
it is possible for every surgeon to practice
antiseptic surgery. The great advances
made in the science and art of surgery are
largely due to the introduction of anti-
septic methods of wound treatment, and it
is incumbent upon every progressive sur-
geon to employ them.

An examination of this work will
show that it is thoroughly systematic in

its plan, so that it is not only useful to the practitioner, who may be
called upon to perform operations, but of great value to the student in
his work in the surgical room, where he is required to apply bandages
and fracture dressings, and to perform operations upon the cadaver. The
experience of the author, derived from many years' service as a teacher
(private and public) and practitioner, has enabled him to present the
topics discussed in such a manner as to fully meet the needs of both prac-
titioners and students.

is full of common sense, and may be safely

taken as a guide in the matters of which it treats
It would be hard to point out all the excellences of

tioner who follows it intelligently cannot easily go

astray. — Journal American Medical Asso'

We cannot speak too highly of the volume under

this book. We can heartily recommend it to students H review.— Canada. Med. and Surg . Jour.
and to practitioners of surgery.— American Jour- ji The space devoted to fractures and dislocations

nal of the Medical Sciences.

We do not know of any other work which would
be of greater value to the student in connection with
his lectures in this department. — Buffalo Medical

— by far the most difficult and responsible part of
surgery — is ample, and we notice many new illustra-
tions explanatory of the text. — North Carolina
Medical Journal.

*nd Surgical journal. It is one of the most valuable of the works of its

The work is excellent. The student or practi- kind.— New Orleans Med. and Surg. Jour.

(F. A, DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.) 13

AN ENTIRELY NEW PHYSICIAN'S VISITING LIST.

MEDICAL BULLETIN VISITING LIST

- OR -

- PHYSICIAN'S QALL RECORD.

ARRANGED UPON AN ORIGINAL AND CONVENIENT MONTHLY AND WEEKLY PLAN
FOR THE DAILY RECORDING OF PROFESSIONAL VISITS.

Frequent Rewriting of Names Unnecessary.

THIS YISITING LIST is arranged upon a plan best adapted to the most
convenient use of all physicians, and embraces a new feature in recording
daily visits not found in any other list, consisting of STUB OR HALF LEAVES
IN THE FORM OF INSERTS, a glance at which will suffice to show that as the
first week's record of visits is completed the next week's record may be
made by simply turning over the stub-leaf, without the necessity of re-
writing the patients' names. This is done until the month is completed,
and the physician has kept his record just as complete in every detail of
VISIT, CHARGE, CREDIT, etc., as he could have done had he used any of the
old-style visiting lists, and has also SAVED himself three-fourths of the
time and labor formerly required in transferring names EVERY week.
There are no intricate rulings ; everything is easity and quickly under-
stood ; not the least amount of time can be lost in comprehending the
plan, for it is acquired at a glance.

The Three Different Styles Made.

The UTo. 1 Style of this List provides ample space for the DAILY
record of seventy (70) different names each month for an entire year
(two full pages, thirty-five [35] names to a page, being allowed to each
month), so that its size is sufficient for an ordinary practice ; but for
physicians who prefer a List' that will accommodate a larger practice we
have made a UTo. 2 Style, which provides ample space for the daily
record of ONE HUNDRED AND FIVE DIFFERENT NAMES (105) each month for
an entire year (three full pages being allowed to each month), and for
physicians who may prefer a Pocket Record Book of less thickness than
either of these styles we have made a Wo. 3 Style, in which " The
Blanks for the Recording of Visits In " have been made into removable
sections. These sections are very thin, and are made up so as to answer
in full the demand of the largest practice, each section providing ample
space for the DAILY RECORD OF 'TWO HUNDRED AND TEN (210) DIFFERENT
NAMES for one month; or one hundred and five (105) different names
daily each month for two months ; or seventy (TO) different names daily
each month for three months ; or thirty-five (35) different names daily
each month for six months. Four sets of these sections go with each
copy of No. 3. Style.

Special Features Not Found in Any Other List.

In this No. 3 STYLE the PRINTED MATTER, and such matter as the
BLANK FORMS FOR ADDRESSES OF PATIENTS, Obstetric Record, Vaccination
Record, Cash Account, Births "and Deaths Records, etc., are fastened
permanently in the back of the book, thus reducing its thickness. The
addition of one of these removable sections does not increase the size
quite an eighth of an inch. This brings the book into such a small com-
pass that no one can object to it on account of its thickness, as its bulk

14

is V'ERY MUCH LESS than that of any visiting list ever published. Every
physician will at once understand that as soon as a section is full it can
be taken out, filed away, and another inserted without the least incon-
venience or trouble.

This Visiting List contains a Calendar for the last six months
of last year, all of this, and next year; Table of Signs to be used
in Keeping Accounts; Dr. Ely's Obstetrical Table; Table of Cal-
culating the Number of Doses in a given R, etc., etc.; for converting
Apothecaries' Weights and Measures into Grammes ; Metrical Avoirdu-
pois and Apothecaries' Weights ; Number of Drops in a Fluidrachm ;
-Graduated Doses for Children ; Graduated Table for Administering
Laudanum ; Periods of Eruption of the Teeth ; The Average Frequency
of the Pulse at Different Ages in Health; Formula and Doses of Hypo-
dermic Medication; Use of the Hypodermic Syringe; Formulae and
Doses of Medicine for Inhalation; Formulae for Suppositories for the
Rectum ; The Use of the Thermometer in Disease ; Poisons and their
Antidotes ; Treatment of Asphyxia ; Anti-Emetic Remedies ; Nasal
Douches ; Eye-Washes.

Most Convenient Time- and Labor- Saving List Issued.

It is evident to eve^ one that this is, beyond question, the best and
most convenient time- and labor-saving Physicians' Record Book ever
published. Ph3rsicians of many years' standing and with large practices
pronounce this the Best List they have ever seen. It is handsomely
bound in fine, strong leather, with flap, including a pocket for loose
memoranda, etc., and is furnished with a Dixon lead-pencil of excellent
quality and finish. It is compact and convenient for carrying in the
pocket. Size, 4 x 6| inches.

IN THREE STYI^ES-KET PRICES, POST-PAID.

U. S. and Canada. Great Britain. France.

No. i. Regular Size, for 70 patients daily each month for one year, SI. 25 5s. 3. 7 fr. 75

"No. 2. Large Size, for 105 patients daily each month for one year, 1.5O 6s. 6. 9 fr. 35

No. 3. In which "The Blanks for Recording Visits in" are in re-
movable sections, as described above, ... - 1.75 7s. 3. 12 fr. 2O

EXTRACTS FROM REVIEWS.-

" While each page records only a week's visits,
"yet by an ingenious device of half leaves the names
-of the patients require to be written but once a
month, and a glance at an opening of the book
shows the entire visits paid to any individual in a
month. It will be found a great convenience." —
Jioston Medical and Surgical Journal.

"Everything about it is easily and quickly
understood." — Canadian Practitioner.

"Of the many visiting lists before the profes-
sion, each has some special feature to recommend
it. This list is very ingeniously arranged, as by a
series of narrow leaves following a wider one, the
name of the patient is written but once during the
month, while the account can run for thirty-one
days, space being arranged for a weekly debit
and credit summary and for special memoranda.
The usual pages for cash account, obstetrical
record, addresses, etc., are included. A large
amount of miscellaneous information is presented
in a condensed form." — Occidental Medical
Times.

"It is a monthly instead of a weekly record,
thus obviating the transferring of names oftener
than once a month. There is a Dr. and Cr. column
following each week's record, enabling the doctor
to carry a patient's account for an indefinite time,
•or until he is discharged, with little trouble." —
Indiana Medical Journal. "

"Accounts can begin and end at any date.
Each name can be entered for each day of every
month on the same line. To accomplish this, four
leaves, little more than one-third as wide as the
usual leaf of the book, follow each page. Oppo-
site is a full page for the recording of special
memoranda. The usual accompaniments of this
class of books are made out with care and fitness."
— The American Lancet.

"This is a novel list, and an unusually con-
venient one." — Journal of the Amer.Med.Assoc.

"This new candidate for the favor of physi-
cians possesses some unique and useful points.
The necessity of rewriting names every week is
obviated by a simple contrivance in the make-up
of its pages, thus saving much valuable time,
besides reducing the bulk of the book." — Buffalo
Medical and Surgicai Journal.

"This list is an entirely new departure, and
on a plan that renders posting rapid and easy. It
is just what we have often wished for, and really
fills a long-felt want."— The Medical Waif.

"It certainly contains the largest amount of
practical knowledge for the medical practitioner
in the smallest possible volume, besides enabling
the poorest accountant to keep a correct record,
and render a correct bill at a moment's notice." —
Medical Chips.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

HAND-BOOK OF ECLAMPSIA;

OK,

Notes and Cases of Puerperal Convulsions.

E. MICHENER, M.D., J. H. STUBBS, M.D., R. B. EWING, M.D.

B.THOMPSON, M.D., S. STEBBINS, M.D.

Price, in United States and Canada, Bound in Cloth, I6mo, Net, 75 Cents; in Great
Britain, 3 Shillings ; in Prance, 4 fr. 20.

In our medical colleges the teachers of Obstetrics dwell upon the use of blood-letting (phlebotomy) ia
cases of puerperal convulsions, and to this method Dr. Michener and his fellows give their unqualified
support — not to take a prescribed number of ounces, but to bleed for effect, and/Vow a large orifice. This
is plainly and admirably set forth in his book. To bleed requires a cutting instrument, — not necessarily a
lancet, — for Dr. M. states how in one case a pocket-knife was used and the desired effect produced.

Let the young physician gather courage from this little book, and let the more experienced give testi-
mony to confirm its teaching.

have always thought that this treatment was
1 ' ' s generally;
ig we would

3rsed, approved, "and practiced by physicians generally ;
and to such as doubt the efficacy of blood-lettins

)mmend this little volume. — Southern Clinic.

The authors are seriously striving to restore the

'• lost art" of blood-letting, and we must commend the
modesty of their endeavor. — North Carolina Med. Jour.

The cases were ably analyzed, and this plea for vene-
section should receive the most attentive consideration from
obstetricians. — Medical and Surgical Reporter.

JTJST

A MANUAL OF INSTRUCTION

FOR GIVING

PROK.

NISSKN,

Director of the Swedish Health Institute, Washington, D.C. ; Late Instructor in Physical Culture and.

Gymnastics at the Johns Hopkins University, Baltimore, Md. ; Author of

" Health by Exercise without Apparatus."

ILLUSTRATED WITH 29 ORIGINAL WOOD-ENGRAVINGS.

In One 12mo Volume of 128 Pages. Neatly Bound in Cloth. Price,,

post-paid, in United States and Canada, Net, $1.OO; in

Great Britain, 4s. 3d. ; in France, 6 fr. 2O.

This is the only publication in the English language treating this very important,
subject in a practical manner. Full instructions are given regarding the mode of
applying

The Swedish Movement and Massage Treatment

in various diseases and conditions of the human system with the greatest degree of
effectiveness. Professor Nissen is the best authority in the United States upon this prac-
tical phase of this subject, and his book is indispensable to every physician who wishes to-
know how to use these valuable handmaids of medicine.

This manual is valuable to the practitioner, as it
contains a terse description of a subject but too little under-
stood in this country The book is got up very

creditably.— N. Y. Med. Jour.

The present volume is a modest account of the appli-
cation of the Swedish Movement and Massage Treatment,
in which the technique of the various procedures are clearly
stated as well _ as illustrated in a very excellent manner.
— North American Practitioner.

This little manual seems to be written by an expert,
and to those who desire to know the details connected with

the Swedish Movement and Massage we commend the-
"book . — Practice. '

This attractive little book presents the subject in a very
practical shape, and makes it possible for every physician to
understand at least how it is applied, if it does not give him
dexterity in the art of its application. He can certainty
acquire dexterity by following the directions so plainly ad-
viied in this book. — Chicago Mf.d. Times.

It is so practical and clear in its demonstrations that
if you wish a work of this nature you cannot do better than-
peruse this one.— Medical Brief.

H)

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

JUST READY— THE LATEST AND BEST PHYSICIAN'S ACCOUNT
BOOK EVER PUBLISHED.

PHYSICIAN'S-

ALL-REQC1I5ITE TIME*

A- LABOR- SAVINS

Account-

BEING A LEDGER AND ACCOUNT-BOOK FOR PHYSICIANS' USE, MEETING ALL
THE REQUIREMENTS OF THE LAW AND COURTS.

DESIGNED BY

Of

PROBABLY no class of people lose more money through carelessly kept
accounts and overlooked or neglected bills than physicians. Often
detained at the bedside of the sick until late at night, or deprived of
even a modicum of rest, it is with great difficulty that he spares the
time or puts himself in condition to give the same care to his own
financial interests that a merchant, a lawyer, or even a farmer devotes.
It is then plainl}7 apparent that a system of bookkeeping and accounts
that, without sacrificing accuracy, but, on the other hand, ensuring it, at
the same time relieves the keeping of a physician's book of half their
complexity and two-thirds the labor, is a convenience which will be
eagerly welcomed by thousands of overworked physicians. Such a sys-
tem lias at last been devised, and we take pleasure in offering it to the
profession in the form of THE PHYSICIAN'S ALL-REQUISITE TIME- AND
LABOR- SAVING ACCOUNT-BOOK.

There is no exaggeration in stating that this Account-Book and
Ledger reduces the labor of keeping your accounts more than one-halfr
and at the same time secures the greatest degree of accuracy. We may
mention a few of the superior advantages of THE PHYSICIAN'S ALL-
REQUISITE TIME- AND LABOR- SAVING ACCOUNT-BOOK, as follow: —

First — "Will meet all the requirements of
the law and courts.

Second — Self-explanatory ; no cipher code.

Third— Its completeness without sacrificing
anything.

Fourth — No posting; one entry only.

'Fifth — Universal ; can be commenced at any
time of year, and can be continued in-
definitely until every account is filled.

Sixth — Absolutely no waste of space.

Seventh — One person must needs be sick
every day of the year to fill his account,
or might be ten years about it and re-
quire no more than the space for one
account in this ledger.

Eighth — Double the number and irfany times
more than the number of accounts in

any similar book; the 300-page book
contains space for 900 accounts, and the
600-page book contains space for 1800
accounts.

Ninth — There are no smaller spaces.

Tenth — Compact without sacrificing com-
pleteness; every account complete on
same page — a decided advantage and
recommendation.

Eleventh — Uniform size of leaves.

Twelfth — The statement of the most com-
plicated account is at once before you
at any time of month or year — in other
words, the account itself as it stands is
its simplest statement.

Thirteenth — No transferring of accounts,
balances, etc.

To all physicians desiring a quick, accurate, and comprehensive
method of keeping their accounts, we can safely sa}r that no /book as
suitable as this one has ever been devised.

Great
Britain.

NET PRICES, SHIPPING EXPENSES PREPAID.

No. 1. 3OO Pages, for 90O Accounts per Year, Canada

Size 10x12, Bound in ?i Russia, Raised In U- S- (duty paid).

Back-Bands, Cloth Sides, . . . 85.0O 85.5O SO. 18s.
No. 2. GOO Pages, for 18OO Accounts per Year,

Size 10x12, Bound in % Russia, Raised

Back-Bands, Cloth Sides, . . . 8.0O 8.8O 1.13s.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

France.
3O fr. 3O

49 fr. 4O

17

PHYSICIANS' INTERPRETER

IN FOUR LANGUAGBS.

(ENGLISH, FRENCH, GERMAN, AND ITALIAN.)

Specially Arranged for Diagnosis by m. von \.

The object of this little work is to meet a need often keenly felt by
the busy physician, namely, the need of some quick and reliable method
of communicating intelligibly with patients of those nationalities and
languages unfamiliar to the practitioner. The plan of the book is a sys-
tematic arrangement of questions upon the various branches of Practical
Medicine, and each question is so worded that the only answer required
of the patient is merely YES or No. The questions are all numbered,
and a complete Index renders them always available for quick reference.
The book is written by one who is well versed in English, French, Ger-
man, and Italian, being an excellent teacher in all those languages, and
who has also had considerable hospital experience.

Bound in Full Russia Leather, for Carrying in the Pocket. (Size, 5x2£

Inches.) 2O6 Pages. Price, post-paid, in United States and

Canada, $1.OO, net; Great Britain, 4s. 6d. ; France, 6 fr. &O.

To convey some idea of the scope of the questions contained in the
Physicians' Interpreter, we append the Index : —

NOS.

General health 1-50

Special diet 31- 47

Age of patient 52- 62

Necessity of patients undergoing an opera-
tion 63- 70

Office hours 7i- 77

Days of the week 78- 84

Patient's history: hereditary affections in his
family; his occupation; diseases from

his childhood up 85-130

Months of the year. 106-117

Seasons of the year 118-121

Symptoms of typhoid fever. . . . . 131-158

Symptoms of Bright's disease 159-168

Symptoms of lung diseases 169-194 and 311-312

Vertigo • 195-201

The eyes 201-232

Paralysis and rheumatism 236-260

Stomach complaints and chills.

?6 1-269

Falls and fainting spells 271—277

How patient's illness began, and when pa-
tient was first taken sick 278-279

Names for various parts of the body 283-299

The liver 300-301

The memory 304-305

Bites, stings, pricks 314-316

Eruptions 317-318

Previous treatment 3 19

Symptoms of lead-poisoning 320-3*4

Hemorrhages 325-3*8

Burns and sprains 33°~33*

The throat 332-335

The ears 336-339

General directions concerning medicines,
baths, bandaging, gargling, painting

swelling, etc 34°-373

Numbers .pages 202-204

The work is well done, and calculated to be of great
service to those who wish to acquire familiarity with the
phrases used in questioning patients. More than this, we
believe it would be a great help in acquiring a vocabulary
to be used in reading medical books, and that it would fur-
nish an excellent basis for beginning a study of any one of
the languages which it includes. — Medical and Surgical
Reporter.

Many other books of the same sort, with more ex-
tensive vocabularies, have been published, but, from their
size, and from their being usually devoted to equivalents
in English and one other language only, they have not had
the advantage which is pre-eminent in this — convenience.
It is handsomely printed, and bound in flexible red leather
in the form of a diary. It would scarcely make itself felt
in one's hip-pocket, and would insure its bearer against any
ordinary conversational difficulty in dealing with foreign-
speaking people, who are constantly coming into our city
hospitals.— New York Medical Journal.

In our larger cities, and in the whole Northwest, the
physician is constantly meeting with immigrant patients,
to whom it is difficult for him to make himself understood,
«r to know what they say in return. This difficulty will

little work.— The Phy-

be greatly obviated by use of tin
sician and Surgeon.

The phrases are well selected, and one might practice
long without requiring more of these languages than this
little book furnishes.— Phi/a. Medical Tiiutf.

How ofttn the physician is called to attend those with
whom the English language is unfamiliar, and many phy-
sicians are thus deprived of the means, save through an
interpreter, of arriving at a correct knowledge on which to
base a diagnosis. An interpreter is not always at hand,
but with this pocket interpreter in your hand you are able
to ask all the questions necessary, and receive the answer
in such manner that you will be able to fully comprehend.
— The Medical Brief.

This little volume is one of the most ingenious aids
to the physician which we have seen. We heartily com-
mend the'book to any one who, being without a knowledge
of the foreign languages, is obliged to treat those who d»
not know our own language.—^. Louis Courier of JMH>

It will rapidly supersede, for the practical use of the
doctor who cannot take the time to learn another language
all other suggestive works.— Chicago Medical Times.

18

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

An Important Aid to Students in the Study of Anatomy.

THREE CHARTS or

The Nervo- Vascular System.

PART I.— THE NERVES.

PART II.— THE ARTERIES.

PART III.— THE VEINS.

ARRANGED BY W. HENRY PRICE, A.M., M.D., AND S. POTTS EAGLETON.
ENDORSED BY LEADING ANATOMISTS.

PRICE, IN THE UNITED STATES AND CANADA, 50 CENTS, NET, COMPLETE;
GREAT BRITAIN, 2s. 6d. FRANCE, 3 fr. 60.

"THE NERVO-VASCULAB SYSTEM OF CHARTS" far Excels Every Other System
in their Completeness, Compactness, and Accuracy.

I. The Nerves. — Gives in a clear form not only the Cranial
and Spinal Nerves, showing the formation of the different Plexuses
and their branches, but also the complete distribution of the
k OIPATHETIC NERVES, thereby making it the most complete and
concise chart of the Nervous System yet published.
Part II. The Arteries. — Gives a unique grouping of the Arterial
System, showing the divisions and subdivisions of all the vessels,
beginning from the heart and tracing their CONTINUOUS distribution
to the periphery, and showing at a glance the terminal branches
of each artery.

Part III. The Veins. — Shows how the blood from the periphery
of the body is gradually collected by the larger veins, and these
coalescing forming still larger vessels, until they finally trace
themselves into the Right Auricle of the heart.

It is therefore readily seen that " The Nervo- Vascular System of
Charts" offers the following superior advantages: —

1. It is the only arrangement which combines the Three Systems,
and yet each is perfect and distinct in itself.

2. It is the only instance of the Cranial, Spinal, and Sympathetic
Nervous Systems being represented on one chart.

3. From its neat size and clear type, and being printed only upon
one side, it may be tacked up in any convenient place, and is always
read}r for freshening up the memory and reviewing for examination.

4. The nominal price for which these charts are sold places them
within the reach of all.

For the student of anatomy there can possibly be no '
more concise way of acquiring a knowledge of the nerves, ;
veins, and arteries of the human system. It presents at a
glance their trunks and branches in the great divisions of
the body. It will save a world of tedious reading, and will '•
impress itself on the mind as no ordinary vade mecum, j
«veu. could. Its price is nominal and its value inestima-
ble. No student should be without it.— Pacific Record of
Mrili-inn and Surgery.

We take pleasure in calling attention to these charts,
as they are so arranged that a study of them will serve to ;
impress them more indellibly on your mind than can be
gained in any other way. They are also valuable for
reference.— Medical Brief.

These are three admirably arranged charts for the
•se of students, to assist in memorizing their anatomical
studies.— Bu/nlo Jftd. and Surg. Jour.

This is a series of charts of the nerves, arteries, and i

veins of the human body, giving names, origins, distribu-
tions, and functions, very convenient as memorizers and
reminders. A similar series, prepared by the late J. H.
Armsby, of Albany, N.Y., and framed, long found a place
in the study of the writer, and on more than one occasion
was the means of saving precious moments that must
otherwise have been devoted to tumbling the pages of ana-
tomical works. — Med. Age.

These three charts will be of great assistance to
medical students. They can be hung on the wall and read
across any ordinary room. The price is only fifty cents for
the set. — Practice.

These charts have been carefully arranged, and will
prove to be very convenient for ready reference. They

are three in number, each constituting a part

It is a high recommendation that these charts have beem
examined and approved by John B. Beaver, M.D., Demon-
strator of Anatomy in the University of Pennsylvania.—
Pacific Med. and Surg. Jour, and Western Lancet.

(F. A. DAVIS, Medical Publisher Philadelphia, Pa., U.S.A.)

19

EVERY SANITARIAN SHOUJLD HAVE ROME'S "TEXT-BOOK OF HYGIENE"
AS A WORK OF REFERENCE.

SEOOIsTID

TEXT-BOOK OF HYGIENE:

A COMPREHENSIVE TREATISE ON THE PRINCIPLES AND PRACTICE OF PREVENTIVE MEDICINE
FROM AN AMERICAN STAND-POINT.

By GEORGB H. ROHK, M.D.,

Pwfessor of Obstetrics and Hygiene in the College of Physicians and Surgeons, Baltimore ; Director of the Maryland

Maternite ; Member of the American Public Health Association ; Foreign Associate of the Societe Franchise

d'Hygiene, of the Societe des Chevaliers-Sauveteurs des Alpes Maritimes, etc.

Net Price, in the United States, $2.5O; in Canada (duty paid), 82.75; in
Great Britain, lls. 3d. ; France, 16 fr. 8O.

SECOND EDITION — THOROUGHLY REVISED AND LARGELY REWRITTEN, WITH MANY ILLUSTRATIONS
AND VALUABLE TABLES. Robe's Hygiene is the Standard Text-Book in many Medical Colleges in the
United States and Canada. It is a sound guide to the most modern and approved practice in Applied
Hygiene. This New Edition will be issued early in the Spring of 1890, in one handsome
Octavo volume of about 400 pages, bound in Extra Cloth. Read what competent critics have said of the
first edition of Robe's "Text-Book of Hygiene":—

A storehouse of facts. — British Medical Journal.

Of invaluable assistance to the student.— Sanitary News.

This interesting and valuable book.— Pacific Medical
mnd Surgical Journal.

Based upon sound principles and good practice. — Phila-
delphia Medical Times.

Full of important matter, told in a very interesting
•tanner. — Science.

In harmony with the most recent advances in pathology.
—Medical Times and Gazette, London.

Nothing better for the teacher, practitioner, or student,
—Mississippi Valley Medical Monthly.

Contains a mass of information of the utmost impor-
tance.— Independent Practitioner.

Just the work needed by the medical student and tht
busy, active, sanitary officer. — Southern Practitioner.

This very useful work. — American Jour. Med. Sciences.

Comprehensive in scope, well condensed, clear in style,
and abundantly supplied with references. — Journal Amer-
ican Medical Association.

JUST ISSUED

PHYSICIANS' AND STUDENTS' READY-REFERENCE SERIES

The Neuroses of the Genito-Urinary System

I3NC
WITH STERILITY AND IMPOTENCE.

BY

DR. R. UI/TZNIANN,

PROFESSOR OF GENITO-URINARY DISEASES IN THE UNIVERSITY OF VIENNA.
TRANSLATED, WITH THE AUTHOR'S PERMISSION, BY

GARDNER W. ALLEN, M.D.,

SURGEON IN THE GENITO-URINARY DEPARTMENT BOSTON DISPENSARY.

Illustrated. 12mo. Handsomely Bound in Dark-Blue Cloth. Net Price, in the United
States and Canada, 81.0O, Post-paid ; Great Britain, 4s. 6d. : France, 6 fr. 2O.

This great work upon a subject which, notwithstanding the great strides that hav»
been made in its investigation and the deep interest it possesses for all, is nevertheless
still but imperfectly understood, has been translated in a most perfect manner, and pre-
serves most fully the inherent excellence and fascinating style of its renowned and
lamented author. Full and complete, yet terse and concise, it handles the subject with
such a vigor of touch, such a clearness of detail and description, and such a directness to
the result, that no medical man who once takes it up will be content to lay it down until
its perusal is complete, — nor will one reading be enough.

Professor Ultzmann was recognized as one of the greatest authorities in his chosen
specialty, and it is a little singular that so few of his writings have been translated into
English. Those wfyo have been so fortunate as to benefit by his instruction at the Vienna
Polyclmic can testify to the soundness of his pathological teachings and the success of his
methods of treatment. He approached the subject from a somewhat different point of
view from most surgeons, and this gives a peculiar value to the work. It is believed,
moreover, that there is no convenient hand-book in English treating in a broad manner
the Genito-urinary Neuroses.

SYNOPSIS OF CONTENTS. FIRST PART.— I. Chemical Changes in the Urine in
Oases of Neuroses. II. The Neuroses of the Urinary and of the Sexual Organs, classi-
fiVd as : 1, Sensory Neuroses ; 2, Motor Neuroses ; 3, Secretory Neuroses. SECOND PART. —
Sterility and Impotence.

THE TREATMENT IN ALL CASES is DESCRIBED CLEARLY AND MINUTELY.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

HAY FEVER

ITS SUCCESSFUL TREATMENT BY SUPERFICIAL ORGANIC
ALTERATION OF THE NASAL MUCOUS MEMBRANE.

CHARLES K. SAJOUS, M.O.,

Lecturer on Rhinology and Laryngology in Jefferson Medical College : Vice-President of the American Laryngological

Association : Officer of the Academy of France and of Public Instruction of Venezuela ; Corresponding

Member of the Royal Society of Belgium, of the Medical Society of Warsaw (Poland),

and of the Society of Hygiene of France ; Member of" the American

Philosophical Society, etc., etc.

WITH 13 ENGRAVINGS ON WOOD. 13nao. BOUND IN CL.OTH. BEVELE»

EDGES. PKICE, IN UNITED STATES AND CANADA, NET, Sl.OO;

GREAT BRITAIN, 4s. 3d.; FRANCE, 6 fr. 2O.

The object of this little work is to place in the hands of the general
practitioner the means to treat successfully a disease which, until lately,
was considered as incurable ; its history, causes, pathology, and treat-
ment are carefully described, and the latter is so arranged as to be
practicable by any physician.

Dr. Sajous' volume must command the attention of
those called upon to treat this heretofore intractable com-
plaint.— Medical and Surgical Reporter.

Few have had the success in this disease which has
so much baffled the average practitioner as Dr. Sajous, con- j
•equently his statements are almost authoritative. The
book must be read to be appreciated.— American Medical \
Digest.

Dr. Sajous has admirably presented the subject, and, •
AS this method of treatment is now generally recognized '
*c efficient, we can recommend this book to all physicians I

who are called upon to treat this troublesome disorder.—
The Buffalo Medical and Surgical Journal.

The symptoms, etiology, pathology, and treatment of
Hay Fever are fully and ably discussed. The reader will
not regret the expenditure of the small purchase price of
this work if he has cases of the kind to treat.— California
Medical Journal.

We are pleased with the author's views, and heartily
commend his book to the consideration of the profession
— The Southern Clinic.

PHYSICIANS' AND STUDENTS' READY REFERENCE SERIES.

ILTo.

OBSTETRIC SYNOPSIS

By JOHN S. STEWART, M.D.,

Demonstrator of Obstetrics and Chief Assistant in the Gynaecological Clinic of the Medico-Chirurgical

College of Philadelphia.

WITH AN INTRODUCTORY NOTE BY

WILLIAM S. STEWART, A.M., M.D.,

Professor of Obstetrics and Gynaecology in the Medico-Chirurgical College of Philadelphia.

42 ILLUSTRATIONS. 202 PAGES. 12 mo. HANDSOMELY BOUND IN DARK-BLUE CLOTH.

Price, Post-paid, in the United States and Canada, Net, $1.OO;
Great Britain, 4s. 3d. ; France, 6 fr. 2O.

By students this work will be found particularly useful. It is based
upon the teachings of such well-known authors as Playfair, Parvin,
Lush, Galabin, and Cazeaux and Tarnier, and, besides containing much
new and important matter of great value to both student and practi-
tioner, embraces in an Appendix the Obstetrical Nomenclature sug-
gested by Professor Simpson, of Edinburgh, and adopted by the
Obstetric Section of the Ninth International Medical Congress held in
Washington, D.C., September, 1887.

It is well written, excellently illustrated, and fully up [
to date in every respect. Here we find all the essentials of j
Obstetrics in a nutshell, Anatomy, Embryology, Physi- I
•logy. Pregnancy, Labor, Puerperal State, and Obstetric
Operations all being carefully and accurately described.—
Buffalo Medical and Surgical Journal.

It ie clear and concise. The chapter on the develop-
ment of the «vum is especially satisfactory. The judicious

use of bold-faced type for headings, and italics for impor-
tant statements, gives the book a pleasing typographical
appearance. — Medical Record.

This volume is done with a masterly hand. The
scheme is an excellent one. . . . The whole is freely
and most admirably illustrated with well-drawn, new
engravings, and the book is of a very couvenieat size.—
St. Louis Medical and Surgical Journal.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

DIPHTHERIA:

CROUP, TRACHEOTOMY, **> INTUBATION

FROM THE FRENCH OF A. SANNE.

TRANSLATED AND ENLARGED BY

Z. GILL, Nl.D., UL.D.

United States. Canada (duty paid). Great Britain. France.

Net Price, Post-paid, Cloth, - -$100. $140. £ 0.18s. 24fr.6Q

Leather, - 5.00. 5.50. 1. Is. 30 fr. 30

The above work, recently issued, is a translation from the French of SANNE'S great
work on " Diphtheria," by H. Z. GILL, late Professor of Surgery in Cleveland, Ohio.

SANNE'S work is quoted, directly or indirectly, by every writer since its publication,
as the highest authority, statistically, theoretically, and practically. The translator,
having given special study to the subject for many years, has added over fifty pages, in-
cluding the Surgical Anatomy, Intubation, and the recent progress in the branches
treated down to the present date; making it, beyond question, the most complete work
extant on the subject of Diphtheria in the English language.

Facing the title-page is found a very fine Colored Lithograph Plate of the parts con-
cerned in Tracheotomy. Next follows an illustration of a cast of the entire Trachea, and
bronchi to the third or fourth division, in one piece, taken from a photograph of a case
in which the cast was expelled during life from a patient sixteen years old. This is the
most complete cast of any one recorded.

Over fifty other illustrations of the surgical anatomy of instruments, etc., add to the
practical value of the work.

Diphtheria having become such a prevalent, wide-spread, and fatal disease, no
general practitioner can afford to be without this work. It will aid in preventive meas-
ures, stimulate promptness in the application of, and efficiency in, treatment, and
moderate the extravagant views which have been entertained regarding certain specifics
in the disease Diphtheria.

A full Index accompanies the enlarged volume, also a List of Authors, making
altogether a very handsome illustrated volume of over 680 pages.

In this book we have a complete review and j
compendium of all worth preserving that has hitherto
been said or written concerning diphtheria and the
kindred subjects treated of by our author, collated,
arranged, and commented on by both author and
translator. The subject of intubation, so recently
revived in this country, receives a very careful and
impartial discussion at the hands of the translator,
and a most valuable chapter on the prophylaxis of
diphtheria and croup closes the volume.

Sanne's work is quoted, directly or indirectly,,
by many writers since its publication, as the highest
authority, statistically, theoretically, and practi-
cally. The translator, having given special study
to the subject for many years, has added over fifty
pages, including the surgical anatomy, intubation,
and the recent progress in the branches treated,
down to the present date ; making it, beyond ques-
tion, the most complete work extant on the subject
of diphtheria in the English language. Diphtheria
having become such a prevalent, wide-spread, and
fatal disease, no general practitioner can afford to

His notes are frequent and full, displaying deep
knowledge of the subject-matter. Altogether the

book is one that is valuable and timely, and one i be without this work. It will aid in preventive

that should be in the hands of every general practi- j measures, stimulate promptness in application of, and

tioner. — St. Louis Med. and Surgical Journal. | efficiency in, treatment. — Southern Practitioner.

PRACTICAL AND SCIENTIFIC PHYSIOGNOMY i

TO E2.EJQLID

By MARY OLMSTED STANTON.

Copiously Illustrated. Two Large Octavo Volumes.

United States. Canada (duty paid). Great Britain. France.

Price, per Volume, Cloth, 885.OO $5.5O JEl.ls. 3O fr. 3»

« " Sheen, 6.OO 6. GO 1.6s. 36 fr. 4O

Half-Russia, 7.0O 7.7O 1.9s. 43 fr. 3O

$1.00 DISCOUNT FOB CASH. Sold only by Subscription, or sent direct on receipt of price, shipping expenses prepaid.

The author, Mrs. Mary O. Stanton, has given over twenty years to the preparation of this work. Her
style is easy, and, by her happy method of illustration of every point, the book reads like a novel, and
memorizes itself. To physicians the diagnostic information conveyed is invaluable. To the general
reader each page opens a new train of ideas. (This book has no reference whatever to Phrenology.)

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

ANNOUNCEMENT.

A TREATISE

Materia Medica, Pharmacology, $ Therapeutics.

*

BY

dOHN U. SHOEMAKER, A.M., M.D.,

Professor of Materia Medica, Pharmacology, and Therapeutics in the Medico-Chirurgical College of Phila-
delphia, and Member American Medical Association,

AND

dOHN AULDE, M.D.,

Demonstrator of Clinical Medicine and of Physical Diagnosis in the Medico-Chirurgical College of Phila-
delphia, and Member American Medical Association.

IN TWO HANDSOME ROYAL OCTAVO VOLUMES.

NET PRICES, per Volume, in United States: Cloth, S2.5O; Sheep, $3.25. In Canada

(duty paid) : Cloth, 82.75 ; Sheep, S3. 55. In Great Britain: Cloth, 11s. 3d. ;

Sheep, 14s. 6d* In France: Cloth, 16 fr. 20 ; Sheep, 2O fr. 20.

THE Publisher takes pleasure in announcing that VOLUME I of this eagerly -looked-for
work is Now READY, and that the utmost diligence will be exercised in filling with
she greatest rapidity, and in regular order of receipt, the numerous orders now awaiting
its publication.

The general plan of the work embraces three parts, each of which is practically inde-
pendent of the other, as will be understood from the accompanying analysis, and of which
Parts I and II are contained in the volume now announced ; this, however, is not the only
advantage accruing from the preparation of the work in two volumes. Each volume will
thus be much smaller and more convenient to handle, while some may wish to secure a
particular portion of the work, and to them the cost is lessened.

Several blank sheets of closely -ruled letter-paper are inserted at convenient places in
the work, thus rendering it available for the student and physician to add valuable notes-
concerning new remedies and other important matters.

PART I embraces three subdivisions, as follow : —

first. A brief synopsis upon the subject of pharmacy, in which is given a clear and
concise description of the operations and preparations taken into account by the physician
when prescribing medicines, together with some practical suggestions regarding the most
desirable methods for securing efficiency and palatability.

Second. A. Classification of Medicines is presented under the head of " General Phar-
macology and Therapeutics," with a view to indicate more especially the methods by
which the economy is affected. Thus, there are Internal and External Remedies, and,
besides, a class termed Chemical Agents, including Antidotes, Disinfectants, and Anti-
septics, and an explanatory note is appended to each group, as in the case of Alterative-.
Antipyretics, Antispasmodics, Purgatives, etc.

Third. A Summary has been prepared upon Therapeutics, covering methods of
Administration, Absorption and Elimination, Incompatibility, Prescription-writing, and
Dietary for the Sick, this section of the work embracing nearly one hundred and fifty
pages.

PART II is devoted to "Remedies and Remedial Agents Not Properly Classed with
Drugs," and includes elaborate articles upon the following topics : Electro-Therapy,
Hydro-Therapy, Masso-Therapy, Heat and Cold, Oxygen, Mineral-Waters, and, in addi-
tion thereto, other subjects, perhaps of less significance to the practitioner, such as Clima-
tology, Hypnotism- and Suggestion, Metallo-Therapy, Transfusion, and Baunscheidtisnms.
have received a due share of attention. This section of the work embraces over two hun-
dred pages, and will be found especially valuable to the student and recent graduate, a*
these articles are fully abreast of the times.

VOLUME II, which is Part III of the work, is wholly taken up with the consideration
of drugs, each remedy being studied from three points of view, viz., the Preparations, or
Materia Medica; the Physiology and Toxicology, or Pharmacology, and, lastly, its
Therapy. IT WILL BE READY ABOUT MAY 1, 1890.

The typography of the work will be found clean, sharp, and easily read without
injury to the visual organs, and the bold-face type interspersed throughout the text makes
the different subjects discussed quick of reference. The paper and binding will also be up
to the standard, and nothing will be left undone to make the work first-class in every
particular,

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S A.) 23

:JUST PUBLISHED.:

THE PHYSIOLOGY

OF THE

DOMESTIC ANIMALS.

A TEXT-BOOK FOR VETERINARY AND MEDICAL
STUDENTS AND PRACTITIONERS.

—BY—

ROBERT MEADE SMITH, A.M., M.D.,

Professor of Comparative Physiology in University of Pennsylvania ; Fellow of the College of Physicia»8

and Academy of the Natural Sciences, Philadelphia ; of the American Physiological

Society ; of the American Society of Naturalists ; Associe Etraager

de la Societe Francaise U' Hygiene, etc.

FIG. 117. —PAROTID AND SITBMAXILLARY FISTULA IN THE HORSE, AFTER COLIN.

(Thankoffer and Tormay.)
K, K', rubber bulbs for collecting saliva; cs, cannula in the parotid duct.

In One Handsome Royal Octavo Volume of over 95O Pages, Pro-
fusely Illustrated with more than 4OO Fine "Wood-
Engravings and many Colored Plates.

United States. Canada (duty paid). Great Britain. France.

NET PRICES, CLOTH, $5.00 $5.50 £1. 30 fr. 30.

SHEEP, 6.00 6.60 1.6. 36 fr. 20.

nPHIS new and important work, the most thoroughly complete in the English language
on this subject, has just been issued. In it the physiology of the domestic animals
is treated in a most comprehensive manner, especial prominence being given to the sub-
ject of foods and fodders, and the character of the diet for the herbivora under different
conditions, with a full consideration of their digestive peculiarities. Without being over-
burdened with details, it forms a complete text-book of physiology, adapted to the use of
students and practitioners of both veterinary and human medicine. This work has already
been adopted as the Text-Book on Physiology in the Veterinary Colleges of the United
States, Great Britain, and Canada.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

ABSTRACTS FROA

PHYSIOLOQY.

The work throughout is well balanced.
Broad, though not encyclopaedic, concise
without sacrificing clearness, it combines
the essentials of a successful text-book. It
is eminently modern, and, although first in
the field, is of such grade of excellence that
successors must reach a high standard be-
fore they become competitors. — Annals of
Surgery.

Dr. Smith has conferred a great benefit
upon the veterinary profession by his con-
tribution to their use of a work of immense
value, and has provided the American vet-
erinary student with the only means by
which he can become properly familiar with
the physiology of our domestic animals.
Veterinary practitioners and graduates will
read it with pleasure. Veterinary students
will readily acquire needed knowledge from
its pages, and veterinary schools which
would oe well equipped for the work they
aim to perform cannot ignore it as their
text-book in physiology. — American Veteri-
nary Review.

Dr. Smith's presentment of his subject
is as brief as the status of the science per-
mits, and to this much-desired conciseness
he has added an equally welcome clearness
of statement. The illustrations in the work
are exceedingly good, and must prove a
valuable aid to me full understanding of
the text. — Journal of Comparative Medicine
and Surgery.

We have examined the work in a great
many particulars, and find the views so
correct, where we have had the means of
comparison of statements with those of some
recognized authority, that we will be com-
pelled hereafter to look to this work as the
text-book on physiology of animals. The
book will prove of incalculable benefit to
veterinarians wherever they may be found ;
and to the country physician, who is often
called upon - to attend to sick animals as
well as human beings, we would say, lose
no time in getting this work and let him
familiarize himself with the facts it con-
tains.— Virginia Medical Monthly.

Altogether, Professor Smith's " Physi-
ology of the Domestic Animals" is a happy
production, and will be hailed with delight
in both the human medical and veterinary
medical worlds. It should find its place
besides in all agricultural libraries. — PAUL
PAQUIN, M.D., VA, in the Weekly Medical
Review.

It, may be said that it supplies to the
veterinary student the place in physiology
that Chauveau's incomparable work — " The
Comparative Anatomy of the Domesticated
Animals" — occupies in anatomy. Higher
praise than this it is not possible to bestow.
And since it is true that the same laws of
physiology which are applicable to the vital
process of the domestic animals are also ap-
plicable to man, a perusal of this carefully
written book will repay the medical student
or practitioner.— Canadian Practitioner.

The work before us fills the hiatus of
which complaint has so often been made,
and gives in the compass of less than a
thousand pages a very full and complete
account of the functions of the body in both
carnivora and herbivora. The author has
judiciously made the nutritive functions thn
strong point of the work, and has devoted
special attention to the subject of foods and
digestion. In looking through the other
sections of the work, it appears to us thai a
just proportion of space is assigned to ea.rh.
in view of their relative importance to tin-
practitioner. Thus, while the subject of re-
production is dismissed in a few pages, a
chapter of considerable length is devoted
to locomotion, and especially to the gaits of
the horse. — London Lancet.

This is almost the only work of the kind
in the English language, and it so fully
covers every detail of general and special
physiology that there is no room for any
rival. The excellence of typographical
work, and the wealth, beauty, and clear-
ness of the illustrations, correspond with
the thoroughness and clearness of the
treatise. — Albany Medical Annals.

It is not often that the medical profes-
sion has the opportunity of reading a new
book upon a new subject, and doubtless
English-speaking physicians will feel grai< •-
ful to Professor Smith for his admirable
ainl pioneer work in a branch of medical
science upon which a great amount of ignor-
ance prevails. . . . The last portion of
the work is devoted to the reproductive
functions, and contains much valuable in-
formation upon a portion of animal physi-
ology concerning which many are ignorant.
The book is a valuable one in every way,
and will be consulted largely by veterinary
and medical students and practitioners. —
Buffalo Medical and Surgical Journal.
The appearance of this work is mo
portune. It will be much appreciated, a-
tending to secure the thorough comprehen-
sion of function in the domesticated ani-
mals, and, in consequence, their general
well-being — a matter of world- wide impor-
tance. With a thorough sense of gratifica-
tion we have perused its pages : throughout
we find clear expression, clear reasoning,
and that patient accumulation of facts so

li valuable in a text-book for students. —

| British Medical Journal.

For notice this time, I take up the vol-
J! ume on the " Physiology of the Domestic
:| Animals." by Dr. R. Meade Smith, a volume
of 938 pages, closely printed, and dealing
with its subject in a manner sufficiently ex-
haustive to insure its place as a text-book
for fifteen years at the very least. Its
learning is only equaled by 'its industry,
; and its industry by the consistency and
; skill with which its varied parts are brought
: together into harmonious, lucid, an«l in-
' tellectual unity. — DR. BENJAMIN WARD
RICHARDSON, in the London

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

International poeket Medical

ARRANGED THERAPEUTICALLY.

BY G. SUMMER WlTMERSTlNE, M.S., M.D.,

Associate Editor of the "Annual of the Universal Medical Sciences ;" Visiting Physician of the Home for
the Aged, Germantown, Philadelphia; Late House-Surgeon Charity Hospital, New York.

More than 1800 Formulae from Several Hundred Well-Known Authorities.

With an APPENDIX containing a Posological Table, the newer remedies included ; Important Incompati-
bles ; Tables on Dentition and the Pulse ; Table of Drops in a Fluidrachm and Doses of Laudanum graduated
for age ; Formulae and Doses of Hypodermic Medication, including the newer remedies; Uses of the Hypo-
dermic Syringe; Formulae and Doses for Inhalations, Nasal Douches, Gargles, and Eye-washes ; Formulae
for Suppositories; Use of the Thermometer in Disease; Poisons, Antidotes, and Treatment; Directions for
Post-Mortein and Medico-Legal Examinations; Treatment of Asphyxia, -Sun-stroke, etc.; Anti-emetic
Remedies and Disinfectants; Obstetrical Table; Directions for Ligation of Arteries ; Urinary Analysis;
Table of Eruptive Fevers : Motor Points for Electrical Treatment, etc., etc.

This work, the best and most complete of its kind, contains about 275 printed pages, besides
extra blank leaves. Elegantly printed, with red lines, edges, and borders ; with illustrations. Round
in leather, with side flap. It contains more than 180O Formulae, exclusive of the large amount of
other very valuable matter.

Price, Post-paid, in the United States and Canada, $2.OO, net ;
Great Britain, 8s. 6d. ; France, 12 fr. 4O.

WHY EVERY MEDICAL MAN SHOULD POSSESS A COPY OF
THE INTERNATIONAL POCKET MEDICAL FORMULARY.

1. Because it is a handy book of reference, replete with the choicest formulae (over 1800 in number) of
more than six hundred of the most prominent classical writers and modern practitioners.

2. Because the remedies given are not only those whose efficiency has stood the test of time, but also the

newest and latest discoveries in pharmacy and medical science, as prescribed and used by the best-
known American and foreign modern authorities.

3. Because it contains the latest, largest (66 formulae) and most complete collection of hypodermic formulas

(including the latest new remedies) ever published, with doses and directions for their use in over
fifty different diseases and diseased conditions.

4. Because its appendix is brimful of information, invaluable in office work, emergency cases, and the

daily routine of practice.

5. Because it is a reliable friend to consult when, in a perplexing or obstinate case, the usual line of treat-

ment is of no avail. (A hint or a help from the best authorities, as to choice of remedies, correct
dosage, and the eligible, elegant, and most palatable mode of exhibition of the same.)

6. Because it is compact, elegantly printed and bound, well illustrated, and of convenient size and shape

for the pocket.

7. Because the alphabetical arrangement of the diseases and a thumb-letter index render reference rapid

and easy.

8* Because blank leaves, judiciously distributed throughout the book, afford
favorite formula;.

place to record and index

9. Because, as a student, he needs it for study, collateral reading, and for recording the favorite prescriptions

of his professors, in lecture and clinic ; as a recent graduate, he needs it as a reference hand-book for
daily use in prescribing (gargles, nasal douches, inhalations, eye-washes, suppositories, incompatibles,
poisons, etc.) ; as an old practitioner, he needs it to refresh his memory on old remedies and combi-
nations, and for information concerning newer remedies and more modern approved plans of treatment.

10. Because no live, progressive medical man can afford to be without it.

It is sometimes important that such prescriptions as
have been well established in their usefulness be preserved
for reference, and this little volume serves such a purpose
better than any other we have seen.— Columbus Medical
Journal.

Without doubt this book is the best one of its class
that we have ever seen. .,. . . The printing, binding.
and general appearance of the volume are beyond praise.—-
University Medical Magazine.

It may be possible 'to get more crystallized knowledge
in an equally small space, but it does not seem probable.—
Medical Classi.cn.

A very handy and valuable book of formulae for the
physician's pocket. — St. Louis Medical and Surg. Journal.

This little pocket-book contains an immense number
of prescriptions taken from high authorities in this and
other countries. — Northwestern Lancet.

This one is the most complete as well as the most
conveniently arranged of any that have come under our
attention. The diseases are enumerated in alphabetical
order, and for each the latest and most approved remedies
from the ablest authorities are prescribed. The book is in-
dexed entirely through after the' order of the first pages of
a ledger, the index letter being printed on morocco leather
and thereby made very durable.— Pacific Medical Journal.

It is a 'book desirable for the old practitioner and for
his younger brothers as well.— St. Joseph Medical Herald.

As long as "combinations" are sought sm-h :i book
will be of value, especially to those who cannot spare the
time required to learn enough of incompatibilities before
commencing practice to avoid writing incompatible and
dangerous prescriptions. The constant use of such a book
by such prescribers would save the pharmacist much
anxiety.— T he. Drugg-islx1 Circular.

In judicious selection, in accurate nomenclature, in
arrangement, and in style it leaves nothing to be desired.
The editor and the publisher are to be congratulated on tin-
production of the very best book of its clsuBS.—Ptttthttrg/i
Mi'dicii! I{i'ri''ir.

One must see it to realize how much information can
be got into a work of so little bulk.— Canadn Medical
Record.

To the young physician just starting out in practice
this little book will prove an acceptable companion

The want of to-day is crystallized knowledge. This
neat little volume contains in it the most accessible form.
It is bound in morocco in pocket form, with alphabetical
divisions of diseases, so that it is possible to turn instantly
to the remedy, whatever may be the disorder or wherever

the patient mav be situated To the physi.-ian

it is invaluable*, and others should not be without it. We
heartily commend the work to our readers.— Jfi»««*»M
Medical Journal.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S. A

JUST ISSUED

PHYSICIANS' AND STUDENTS' READY-REFERENCE SERIES.

— INTO. a. —

Synopsis of Human Anatomy

Being a Complete Compend of Anatomy, including1 the
Anatomy of the Viscera, and Numerous Tables.

JAMES K. YOUNG, M.D.,

Instructor in Orthopaedic Surgery and Assistant Demonstrator of Surgery, University of Pennsylvania;
Attending Orthopaedic Surgeon, Out-Patient Department, University Hospital, etc.

ILLUSTRATED WITH 76 WOOD-ENGRAVINGS. 390 PAGES.

12 mo. HANDSOMELY BOUND IN DARK-BLUE CLOTH.

Price, Post-paid, in the United States and Canp,da, $1.4O, net;
Great Britain, 6s. 6d. ; France, 9 fr. 25.

While the author has prepared this work especially for students, sufficient de-
scriptive matter has been added to render it extremely valuable to the busy practitioner,
particularly the sections on the Viscera, Special Senses,
and Surgical Anatomy.

The work includes a complete account of Osteology,
Articulations and Ligaments. Muscles. Fascias, Vascular
and Nervous Systems, Alimentary, Vocal, and Respiratory
and Genito-Urinary Apparatuses, the Organs of Special
Sense, and Surgical Anatomy.

In addition to a most carefully and accurately prepared
wherever possible, the value of the work has been
enhanced by tables to facilitate and minimize the labor of
students in acquiring a thorough knowledge of this impor-
tant subject. The section on the teeth has also been
especially prepared to meet the requirements of students
of Dentistry.

In its preparation. Gray's Anatomy [last edition],
edited by Keen, being the anatomical work most used, has
been taken as the standard.

Anatomy is a theme that allows such concen-
tration better than most medical subjects, and, as
the accuracy of this little book is beyond question,
its value is assured. As a companion to the dis-
secting-table, and a convenient reference for the
practitioner, it has a definite field of usefulness. —
Pittsburgh Medical Review.

This is a very carefully prepared compend of
anatomy, and will" be useful to students for college
or hospital examination. There are some excellent
tables in the work, particularly the one showing the
origin, course, distribution, and functions of the
cranial nerves. — Medical Record.

Dr. Young has compiled a very useful book.
We are not inclined to approve of compends as a
general rule, but it certainly serves a good purpose
to have the subject of anatomy presented in a com-
pact, reliable way, and in a book easily carried to
the dissecting-room. This the author has done.
The book is well printed, and the illustrations well
selected. If a student can indulge in more than one
work on anatomy, — for, of course, he must have a
general treatise on the subject, — he can hardly do
better than to purchase this compend It will save
the larger work, and can always be with him during
the hours of dissection. — Buffalo Medical and
Sn rgica, I Jo urnal.

Excellent tables have been arranged, which
tersely and clearly present important anatomical
facts, and the book will be found very convenient
for ready reference. — Columbus Medical Journal.

The book is much more satisfactory than the
"remembrances" in vogue, and yet is not too cum-
bersome to be carried around and read at odd
moments — a property which the student will readily
appreciate.— Weekly Medical Review.

If a synopsis of human anatomy may serve a
purpose, and we believe it does, it is very important
that the synopsis should be a good one. In this
respect the above work may be recommended as :i
reliable guide. Dr. Young has shown excellent
judgment in his selection of illustrations, in the
numerous tables, and in the classification of the
various subjects. — Therapeutic Gazette.

Every unnecessary word has been excluded, out
of regard to the very limited time at the medical
student's disposal. It is also good as a reference
book, as it presents the facts about which he wisihes
to refresh his memory in the briefest manner
consistent with clearness. — Neiv York Medical
yournal

It is certainly concise and accurate, and should
be in the hands of every student and practitioner. —
The Medical Brief.

(F. A. DAVIS. Medical Publisher, Philadelphia, Pa., U.S.A.)

•27

ANNUAL-

<.'!' THP;

Universal Medical

A YEARLY REPORT OF THE PROGRESS OF THE GENERAL SANITARY
SCIENCES THROUGHOUT THE WORLD.

Edited by CHARLES E. SAJOUS, M. D.,

LECTURER ON LARYNGOLOGY AND RHINOLOGY IN JEFFERSON MEDICAL COLLEGE, PHILADELPHIA, KTC.

AND

SEVENTY ASSOCIATE EDITORS,

Assisted by over TWO HUNDRED Corresponding Editors and Collaborators.

In Five Royal Octavo Volumes of about 500 pages each, bound in Cloth and Holf-Rn**
Magnificently Illustrated with Chromo -Lithographs, Engravings,
Maps, Charts, and Diagram*.

1st. To assist the busy practitioner in his efforts to keep abreast of the rapid strides
of all the branches of his profession.

3d. To avoid for him the loss of time involved in searching for that which is n.-\v in
the profuse and constantly increasing medical literature of our day.

3d. To enable him to obtain the greatest possible benefit of the limited titim lie is
able to devote to reading, by furnishing him with new matter ONLY.

4th. To keep him informed of the work done by ALL nations, including many other-
wise seldom if ever heard from.

5th. To furnish him with a review of all the new matter contained in the periodicals
to which he cannot (through their immense number) subscribe.

6th. To cull for the specialist all that is of a progressive nature in the general and
special publications of all nations, and obtain for him special reports from countries in
which such publications do not exist, and

Lastly, to enable any physician to posses^. ;u a moderate oost, ;i eomplof-

CONTEMPORARY HISTORY OF UNIVERSAL MEDICINE, -

edited by many of America's ablest teachers, and superior in every detail, of print, paper,
binding, etc., etc., a befitting continuation of such great works as " Pepper's System of
Medicine/' "Ashhurst's International Encyclopaedia of Surgery," " Buck's Reference
Hand-Book of the Medical Sciences," etc., etc.

EDITORIAL STAFF of the ANNUAL of the UNIVERSAL MEDICAL SCIENCES. '

ISSUE OF 1888.
- Chief Editor, DR. CHARL.ES E. SAJOUS, Philadelphia --

-A-SSOOI-A-TZE

Volume I. — Obstetrics, Gynaecology, Pediatrics, Anatomy, Physiology, Pathoi-o;/?/.
Histology, and Embryology.

Prof. Wm. L. Richardson, Boston. Prof. William Goodell and Dr. W. C. Prof. H. Newell Martin and Dr. W. H.
Prof. Thwphilus Parvin, Philada. Goodell. Philadelphia. Howell. Baltimore.

Prof. Louis Starr, Philadelphia. Prof. E. C. Dudley, Chicago. Dr. Chas. S. Minot. Boston.

Prof. J. Lewis Smith, New York Citv. Prof. W. H. Parish, Philadelphia. Dr. E. O. Shakespeare, Philadelphia.

Prof. Paul F. Munde and Dr. E. H. * Prof. William S. Forbes, Philadelphia. > Dr. W. X. Sudduth. Philadelphia.
Grandin, New York City.

Volume H. — Diseases of the Respiratory, Circulatory, Digestive, and JWrro?/.s ,S'yx//'///.s:
Fevers, Exanthemata, etc., etc.

Prof. A. L. Loomis, New York City.
Prof. Jas. T. Whittaker, Cincinnati.
Prof. W. H. Thomson, New York City.
Prof. W. W. Johnston, Washington.
Prof Jos. Leidy, Philadelphia.

Prof. E. C. Seguin, New York City. ; Prof. Jas. Tvson, Philadelphia.

Prof. E. C. Spitzka, New York City. \ Prof. N. S. Davis, Chicago.

ProfChas.K. Mills and Dr. J.H.Lloyd, ; Prof. John Guit^ras, Charleston, S. C.

Philadelphia. I Dr. Jas. C. Wilson, Philadelphia.
Prof. Francis Delafteld, N. Y. City.

Volume III. — General Surgery, Vemereol Diseases, Anaesthetics, Surf/iff//

Dietetics, etc., etc.
Prof. D. Hayes Agnew, Philadelphia.

Prof. Hunter McGuire, Richmond
Prof. Lewis A. Stimson, New York.
Prof. P. 8. Conner, Cincinnati.
Prof. J. EwingMears, Philadelphia.

Prof. F. R. Sturgis, New York City. Prof. T. G. Morton and Dr. Win. Hunt,

Prof. N. Senn, Milwaukee. Philadelphia.

Prof. J. E. Garretson, Philadelphia. Dr. MorrisJLongstreth, Philadelphia

Prof. Christopher Johnston, Baltimore.

Dr. Cha3. B. Kelsey, New York City.

Dr. Chas. Wirgman, Philadelphia.
Dr. C. C. Davidson, Philadelphia.
Prof. E. L. Keyee, New York City.

Volume IV. — Ophthalmology, Otology, Laryngology, Jthinology, Dermatology, Dentisfa
Hygiene, Disposal of the Dead, etc., etc.

Prof. William Thomson, Philadelphia. I Prof. C. N. Peirce, Philadelphia. Dr. Chas. S. Turubull, Philadelphia.

Prof. J. Solis Cohen, Philadelphia. Prof. John B. Hamilton, Washington. Dr. Edw. C. Kirk, Philadelphia.

Prof. D. Bryson Delavan, New York. Prof. H. M. Lyman, Chicago. Dr. John G. Lee, Philadelphia.

Prof. A. Van Harlingen, Philadelphia. ! Prof. S. H. Guilford, Philadelphia. Dr. Cha*. E. Sajous, Philadelphia,
ffi

List of Collaborators to Dental Department.

Prof. James Truinan. Philadelphia. Prof. E. H. Angle, Minneapolis, Minn. Dr. J. D. Patterson, Kansas City. Mo.

Prof. J. A. Marshall, Chicago, 111. Prof. J. E. Cravens, Indianapolis, Ind. Dr. J. B. Hodgkin, Washington, D. C.

Prof. A. W. Harlan, Chicago, 111. Prof. R. Stubbleneld, Nashville, Tenn. Dr. R. R. Andrews, Cambridge, Mass.

1'rof. G. V. Black, Chicago. 111. Prof. W. C. Barrett, Buffalo, N. Y. Dr. Albion M. Dudley, Salem. Mass.

Prof. C. 11. Stowell. Ann Arbor. Mich. ' Prof. A. H. Thompson, Topeka, Kan. Dr. Geo. S. Allen, New York City.

Prof. L. C. Ingersoll. Ke.ikuk. Iowa. Dr. James W. White, Philadelphia. Dr. G. S. Dean, San Francisco, Cal.

Prof. F. J. S. Gorgas. Baltimore, Md. Dr. L. Ashley Faught, Philadelphia. i Dr. M. H. Fletcher, Cincinnati, Ohio.

Prof. H. A. Smith, Cincinnati. Ohio. Dr. Robert S. Ivy, Philadelphia. \ Dr. A. Morsman, Omaha, Neb.

Prof. C. P. Pengra, Boston. Mass. Dr. W. Storer How, Philadelphia. Dr. G. W. Melotte, Ithaca, N. Y.

Volume V. — General and Experimental Therapeutics, Medical Chemistry, Medical
Jurisprudence, Demography, Climatology, etc., etc.

Prof. William Pepper, Philadelphia.' , Prof. George H. Rohe, Baltimore. Dr. W. P. Mantou, Detroit. Miofe.

Prof. F. W. Draper, Boston. Dr. Albert L. Gihon, U. S. N. Dr. Hobart A. Hare, Philadelphia.

Prof. J. W. Holland, Philadelphia. Dr. R. J. Dunglison,. Philadelphia. ' Dr. C. S. Witherstine, Philadelphia.

Prof. A. L. Ranney. New York City.

(Including the "SATELLITE" for one year).

United State-. Canada (duty paid). Great Britain. France.

Cloth, 5 Vols., Royal Octavo, - - $15.00 $16.50 £3.6s. 93 fr. 95

Half-Rusaia, 5 Vols., Royal Octavo, - 20.00 22.00 16s. 124 fr. 35

EXTRACTS FROM REVIEWS.

We venture to say that all who saw the ANNUAL as it appeared in 1888 were on the

>ut for its reappearance this (1889) year ; but there are many whose knowledge of this
magnificent undertaking will date with this present issue, and to those a mere examina-
tion of the work will suffice to sho"w that it fills a legitimate place in the evolution of
knowledge, for it does what no single individual is capable of doing.

These volumes make readily available to the busy practitioner the best fruits of
iiR-dical progress for the year, selected by able editors from the current literature of the
world:, such a work cannot be overlooked by anyone who would keep abreast of the
i :mes. With so much that is worthy of notice incorporated in one work, and each depart-
ment written up with a minuteness and thoroughness appreciated particularly by the
-!>"<-ialist, it would avail nothing to cite particular instances of progress. Let it be suffi-
cient to say. however, that while formerly there was a possible excuse for not having the
latwst information on matters pertaining to the medical sciences, there can no longer be
>uch an excuse while the ANNUAL is published. — Journal of the American Medictol
Association.

We have before us the second issue of this ANNUAL, and it is not speaking too
strongly when we say that the series of five volumes of which it consists forms a most
important and valuable addition to medical literature.

Great discretion and knowledge of the subjects treated of are required at the hands
of those who have taken charge of the various sections, and the manner in which the
gentlemen who were chosen to fill the important posts of sub-editors have acquitted
themselves fully justifies the choice made. We know of no branch of the profession to
which this ANNUAL could fail to be useful. Dr. Sajous deserves the thanks of the whole
profession for his successful attempt to facilitate the advance of medical literature and
practice. — London Lancet.

This very valuable yearly report of the progress of medicine and its collateral
sciences throughout the world is a work of very great magnitude and high importance.
IT is edited by Dr. C. E. Sajous, assisted, it is stated, by seventy associate editors, whose
names are given, making up a learned and most weighty list. Their joint labors have
combined to produce a series of volumes in which toe current progress throughout the
world, in respect to all the branches of medical science, is very adequately represented.
The general arrangements of the book are ingenious and complete, having regard to
thoroughness and to facility of bibliographical reference. — British Medical Journal.

ANNUAL, 1890.

The editor and publishers of the ANNUAL OF THE UNIVERSAL
MEDICAL SCIENCES take this opportunity to thank its numerous friends
juid patrons for the liberal support accorded it in the past, and to
announce its publication, as usual, in 1890. Recording, as it does, the
progress of the world in medicine and surgery, its motto continues to
be, as in the past, •' Improvement," and its friends may rest assured that
no effort will be* spared, not only to maintain, but to surpass, the high
standard of excellence already attained.

The Subscription Price will be the same as last year's issue and
the issue of 1888.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.) 29

ISSUE OK 1889

The Annual of the Universal Medical Sciences.

In Five Royal Octavo Volumes of over 5OO pages each, bound in Clotli and

Half-Russia, Magnificently Illustrated with Chromo-Lithographs,

Kngravings, Maps, Charts, and Diagrams.

THE SUBSCRIPTION PRICE (including the "Satellite" for one year).

United States. Canada (duty paid). Great Britain. France.

Cloth, 5 Vols., Royal Octavo, - - $15.00 $16.50 £3.6s. 93 fr. 95

Half-Russia, 5 Vols., Royal Octavo, - 20.00 22.00 16s. 124 fr. 35

This work is bound in above styles only, and sold by Subscription.

PUBLISHED IN CONNECTION WITH THE ANNUAL AND FOR SUBSCRIBERS ONLY.

THE SATELLITE

OF* THK UBJIVKK-SAr, MEDICAL

A Monthly Review of the most important articles upon the practical branches of medicine appearing in
the medical press at large, edited by the Chief Editor of the ANNUAL and an able staff.

Editorial Staff of the Annual of the Universal Medical Sciences, issue of 1889.

Chief Editor, Dr. CHAS. E. SAJOUS, Philadelphia.

jft.S5SOCljRi.TE;

Volume I. — Diseases of the Lungs, Diseases of the Heart, Diseases of the Gastro-
Hepatic System, Diseases of the Intestines, Intestinal Entozoa, Diseases of
the Kidneys and Bladder, Fevers, Fevers in Children, Diphtheria, Rheu-
matism and Gout, Diabetes, Volume Index.

Prof. Jas. T. Whittaker, Cincinnati.
Prof. A. L. Loomis, New York City.
Prof. E. T. Bruen, Philadelphia.

Prof. W. W. Johnston, Washington.
Dr. L. Emmett Holt, New York.
Prof. Jos. Leidy, Philadelphia.

Dr. Jas. C. Wilson, Philadelphia.
Prof. Louis Starr, Philadelphia.
Prof. J. Lewis Smith, New York.
Prof. N. S. Davis, Chicago.
Prof. Jas. Tyson, Philadelphia.

Volume II. — Diseases of the Brain and Cord, Peripheral Nervous System, Mental
Diseases, Inebriety, Diseases of the Uterus, Diseases of the Ovaries, Diseases
of the External Genitals in Women, Diseases of Pregnancy, Obstetrics, Dis-
eases of the Newborn, Dietetics of Infancy, Growth, Volume Index.
Prof. E. C. Seguin, New York City. Prof. W. H. Parish, Philadelphia.

Prof. Henry Hun, Albany. ?ro:[- Theophilus Parvin, Philadelphia,

elphia.

Dr. E. N. Brush, Philadel

Dr. W. R. Birdsall, New Vork.

Prof. Paul F. Munde, New York City.

Prof. Wm. Goodell, Philadelphia.

Dr. W. C. Goodell, Philadelphia.

Prof. Wm. L. Richardson, Boston.
Dr. A. F. Currier, New York.
Prof. Louis Starr, Philadelphia.
Dr. Chas. S. Minot, Boston.

Volume III. — Surgery of Brain, Surgery of Abdomen, Genito-Urinary Surgery, Dis-
eases of Rectum and Anus, Amputation and Resection and Plastic Surgery,
Surgical Diseases of Circulation, Fracture and Dislocation, Military Surgery,
Tumors, Orthopaedic Surgery, Oral Surgery, Surgical Tuberculosis, etc., Sur-
gical Diseases, Results of Railway Injuries, Anaesthetics, Surgical Dressings,
Volume Index.

Prof. N. Senn, Milwaukee.
Prof. E. L. Keyes, New York City.
Prof. J. Ewing Mears, Philadelphia.
Dr. Chas. B. Kelsey, New York City.

Prof. D. Hayes Agnew, Philadelphia.
Dr. Morris Longstreth, Philadelphia.
Dr. Thos. G. Morton, Philadelphia.
Prof. J. E. Garretson, Philadelphia.
Prof. J. W. White, Philadelphia.
Prof. C. Johnston, Baltimore.
Prof. E. C. Seguin, New York City.

Prof. P. S. Conner, Cincinnati.

Dr. John H. Packard, Philadelphia.

Prof. Lewis A. Stimson, New York City.

Dr. J. M. Barton, Philadelphia. |

Volume IV. — Skin Diseases, Ophthalmology, Otology. Rhinology, Diseases of Pharynx,
etc., Intubation, Diseases of Larynx and (Esophagus" Diseases of Thyroid
Gland, Legal Medicine, Examination for Insurance, Diseases of the Blood,
Urinalysis, Volume Index.

Prof. A. Van Harlingen, Philadelphia.
Dr. Chas. A. Oliver and Dr. Geo. M.

Gould, Philadelphia.
Dr. Charles S. Turnbull, Philadelphia.
Prof. J. Solis Cohen, Philadelphia.
Prof. John Guiteras, Charleston, S. C.

Dr. Chas. E. Sajous, Philadelphia.
Prof. D. Bryson Delavan, New York.
Prof. R. Fletcher Ingals, Chicago.
Prof. F. W. Draper, Boston.
Prof. Jas. Tyson, Philadelphia.

Volume V. — General Therapeutics, Experimental Therapeutics, Poisons, Electric
Therapeutics, Climatology, Dermography, Technology,, Bacteriology, Embry-
ology, Physiology, Anatomy, General Index.

Dr. J. P. Crozer Griffith, Philadelphia.
Dr. Hobart A. Hare, Philadelphia.
Prof Geo. H. Rohe, Baltimore.
Prof. John B. Hamilton, Washington.
Dr. Harold C. Ernst, Boston.
Prof. H. Newell Martin, Baltimore.
Dr. R. J. Dunglison, Philadelphia.

Dr. C. Sumner \Vither*tine, Philadelphia.

Prof. J. W. Holland, Philadelphia.

Prof. A. L. Ranney. New York.

Dr. Albert H. Gihon, U. S. N.

Dr. W. P. Manion, Detroit.

Dr W X Sudduth, Philadelphia.

Prof. Wm. T. Forbes, Philadelphia.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

THE LATEST BOOH OF REFERENCE ON NERVOUS DISEASES.

Lectures on Nervous Diseases,

FROM THE STAND-POINT OF CEREBRAL AND SPINAL LOCALIZATION, AND

THE LATER METHODS EMPLOYED IN THE DIAGNOSIS AND

TREATMENT OF THESE AFFECTIONS.

BY AMBROSE L. RANNEY, A.M., M.D.,

Pri "cssor of the Anatomy and Physiology of the Nervous System in the New York Post-Graduate Medicai

School and Hospital ; Professor of Nervous and Mental Diseases in the Medical Department of the

University of Vermont, etc. ; Author of "The Applied Anatomy of the Nervous System,"

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With Original Diagrams and Sketches in Color by the Author, carefully selected Wood-
Engravings, and Reproduced Photographs of Typical Cases.

ONE HANDSOME ROYAL OCTAVO VOLUME OF 780 PAGES.

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SOLID OiETIjY BY STJBSCIRIIPTIOICT.

It is now generally conceded that the nervous system controls all of the physical
functions to a greater or less extent, and also that most of the symptoms encountered at
the bedside can be explained and interpreted from the stand-point 01 nervous physiology.

The unprecedented sale of this work during the short period which has elapsed since
its publication has already compelled the publishers to print a second edition, which is
already nearly exhausted.

appeared in medical literature, is presented in com-
pact form, and thus made easily accessible. In ou

We are glad to note that Dr. Ranney has pub-
lished in c^ok form his admirable lectures on nervous
diseases. His book contains over seven hundred
large pages, and is profusely illustrated with origi-
nal diagrams and sketches in colors, and with many
carefully selected wood-cuts and reproduced photo-
graphs of typical cases. A large amount of valua

opinion, Dr. Ranney's book ought to meet with a
cordial reception at the hands of the medical pro-
fession, for, even though the author's views may be
sometimes open to question, it cannot be disputed
that his work bears evidence of scientific method and

ble in for mat ion, not a little of which has but recently .] honest opinion. — American Journal of Insanity

LECTURES

ON THE

Diseases of the Nose and Throat.

DELIVERED AT THE JEFFERSON MEDICAL COLLEGE, PHILADELPHIA,
BY CHARLES E. SAdOUS, M.D.,

Lecturer on Rhinology and Laryngology in Jefferson Medical College; Vice-President of the American Laryngological

Assqpiation : Officer of the Academy of France and of Public Instruction of Venezuela : Corresponding Member

of the Royal Society of Belgium, of the Medical Society of Warsaw (Poland), and of the Society of

Hygiene of France ; Member of the American Philosophical Society, etc., etc.

ILLUSTRATED WITH 1OO CHBOMO-LITHOGBAPHS, FROM OIL PAINTINGS BY
THE AUTHOR, AND 93 ENGRAVINGS ON WOOD.

ONE HANDSOME ROYAL OCTAVO VOLUME. SOLD ONLY BY SUBSCRIPTION.

United States. Canada (duty paid). Great Britain. France.

Cloth, Royal Octavo, ... $4.OO #4.4O *O.18s. 24 fr. 6O

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ince the publisher brought this valuable work before the profession, it has become :
1st, the text-book of a large number of colleges ; %d, the reference-book of the U. S. Army,
Navy, and the Marine Service ; and, 3d, an important and valued addition to the libraries,
of over 7000 physician?.

This book has not only the inherent merit of presenting a clear expose of the subject,
but it is written with a view to enable the general practitioner to treat his cases himself.
To facilitate diagnosis, colored plates are introduced, showing the appearance of the differ-
ent parts in the diseased state as they appear in nature by artificial light. No error can
thus be made, as each affection of the nose and throat has its representative in the 100
rhromo-lithographs presented. In the matter of treatment, the indications are so complete
that even the slightest procedures, folding of cotton for the forceps, the use of the jirobe,
etc., are clearly explained.

It is intended to furnish the general practitioner
lot only with ? guide for the treatment of diseases of
the nose and throat, but also to place before him a

they would appear to him were they seen in the
living subject. As a guide to the treatment of the
nose and throat, we can cordially recommend this

representation of the normal and diseased parts as work. — Boston Medical and Surgical Journal.

(F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.) 31

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IN PRESS SECOND EDITION.

Ointments and Oleates in Diseases of the Skin.

dOHN U. SHOEMAKER, A.M., M.D.,

ica, Pharmacology, Therapeutics, and Clinical Medicine, and Clini
of the Skin in the Medico-Chirurgical College of Philadelphia, etc.

Professor of Materia Medica, Pharmacology, Therapeutics, and Clinical Medicine, and Clinical Professor of Diseases
in the

16mo. NEATLY BOUND IN CLOTH. PRICE, IN UNITED STATES AND CANADA,
NET, $1.OO, POST-PAID ; GREAT BRITAIN, 4s. 3d. ; FRANCE, 6 fr. 2O.

The accompanying Table of Contents will give a general idea of the work :

fTC-siNT1 1 ' t-»rT<rrrrc={ PART I. — HISTORY AND ORIGIN. PART II. — PROCESS OF MANUFACTURE. PART
111. — PHYSIOLOGICAL ACTION OF THE OLEATES. PART IV. — THERAPEUTIC EFFECT OF THE OLEATES.
PART V. — OINTMENTS : Local Medication of Skin Diseases. — Antiquity of Ointments. — Different Indi-
cations for Ointments, Powders, Lotions, etc. — Information about Ointments: Scanty, Scattered, and
Insufficient — Fats and Oils: Animal and Vegetable. — Their Chemical Composition. — Comparative
Permeability of Oils into Skin ; of Animal, of Vegetable. Incorporation of Medicinal Substances into
Fats: (i) Mode of Preparation, (2) Vegetable Powders and .Extracts, (3) Alkaloids, (4) Mineral Sub-
stances, (5) Petroleum Fats ; Chemical Composition; Uses and Disadvantages. — List of Officinal Oint-
ments.— Indications. — Substances often Prescribed Extemporaneously in Ointment Form. — Indications.
A FULL INDEX RENDERS THE BOOK CONVENIENT FOR QUICK REFERENCE.

CRITICISMS OF FIRST EDITION.

The profession in both countries is deeply in-
debted to Dr. Shoemaker for his excellent work in
this department of medicine. — William Whitla,
M.D. (Q.U.I.).

It is the most complete exposition of their action
which has yet appeared. They are very valuable
accessions to the materia medica, and should be
familiar to every practitioner. — Medical and Sur-
f i \ al Reporter.

To those of our readers who wish to learn the
therapeutic effects of a class of preparations which
are destined to grow in favor as their merits be-
come more generally known, we commend this
book. — Journal of Cutaneous and Venereal
Diseases.

No physician pretending to treat skin diseases
should be without a copy of this very instructive
little book. — Canada Medical Record.

32 (F. A. DAVIS, Medical Publisher, Philadelphia, Pa., U.S.A.)

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