/*>v;

A MANUAL OF VETERINARY PHYSIOLOGY.

ERRATUM.

Page 241, fourth line,/™- 1093 Fahr., read 1123 Fabr.

A MANUAL

VETERINARY PHYSIOLOGY.

VETERINARY-CAPTAIN F. SMITH, M.R.C.V.S.,

ARMY VETERINARY DEPARTMENT,

PROFESSOR IN THE ARMY VETERINARY SCHOOL, ALDERSHOT, FELLOW OF THE INSTITUTE

OF CHEMISTRY,

AUTHOR OF 'A MANUAL OF VETERINARY HYGIENE,' ETC.

LONDON :

B A I L L I E R E , TINDALL AND COX

20 & 21, King William Street, Strand.

NEW YORK: W. R. JENKINS.

1892.

[All rights reserved.]

A^

MICHAEL FOSTER, M.A., M.D., LL.D., F.R.S.,

PROFKSSOR OF PHYSIOLOGY IN THE UNIVERSITY OF CAMBRIDGE,

THIS ATTEMPT TO DEAL WITH A BRANCH OF PHYSIOLOGY

IS DEDICATED,

IN ACKNOWLEDGMENT OF

ENCOURAGEMENT AND ASSISTANCE RENDERED TO

THE AUTHOR

IN PROSECUTING THE STUDY OF EQUINE PHYSIOLOGY.

259575

PREFACE.

My object throughout this manual has been to condense the
information as much as possible, for which purpose I have
omitted all special reference to the physiology of the dog,
and have not touched upon the histology of the tissues, or
methods of physiological inquiry.

The reasons for these omissions are obvious : special
canine physiology is of subordinate interest to the pro-
fession, and our information about this animal is so com-
plete, that no difficulty is experienced in obtaining it, when
required, from human text-books. The histology of the
tissues is already before the profession, and methods of
physiological inquiry are only needed for laboratory work,
for which purpose this book is not intended.

In the description of the physiology of the various organs
and tissues, the horse is necessarily taken as the type ; but
the ox, sheep, and pig are dealt with wherever their special
physiology requires it.

It was my original intention to publish nothing until I
had gone over the field of equine physiology, but I found,
after several years of work, that the information I had
collected was a mere drop in the ocean, for inquiries of this

viii Preface

kind are necessarily slow, and as there appeared no reason-
able prospect of covering within the space of one life the
ground I had mapped out, I was advised that only good
could result from placing on record what we do know of
veterinary physiology.

I have, therefore, ventured, I know well how imperfectly,
to state the broad facts of the science, so as to render them
of use to the student and practitioner. The work does cot
pretend to be anything more than a stepping-stone to the
study of physiology ; for those requiring more detailed
information, reference must be made to the various text-
books of human and comparative physiology which are
available.

Incomplete as the work is, it would have been still more
so but for the assistance I have received from my friend
Dr. Sheridan Lea, F.E.S., of Cains College, Cambridge,
who, at great personal inconvenience, has kindly read and
revised nearly all the sheets as they passed through the
press. In saying this, and expressing to him my very
great indebtedness, I in no way wish to shift the respon-
sibility for error or inaccuracy which may exist, but I feel
that whatever merit the book possesses is entirely due
to him.

I have to thank Professor Michael Foster, F.E.S., for
the loan of many of the woodcuts which illustrate this
manual, and elsewhere I have acknowledged bow much I
owe to his encouragement.

To my friend and colleague, Assistant- Professor Butler,
A.V.I )., my best thanks are due for assistance in revising

Preface. ix

the proofs, and in the preparation of the index ; to Mr. W.
Hunting, F.R.C.V.S., for suggestions on the chapter dealing
with Locomotion ; and to Professor M'Fadyean for the loan
of two woodcuts illustrating the chapter on the Foot.

To facilitate the study of locomotion, I have had the
plates so arranged as to face as nearly as possible the
letterpress describing the movements.

I have laid under contribution Colin' s invaluable ' Traite
de Physiologie comparee des Animaux'; Ellenberger's
' Physiologie der Haussiiugethiere ' ; Foster's, M'Kendrick's,
and Landois and Stirling's Text-books of Physiology;
Gamgee's translation of 'Hermann's Physiology'; the
same author's 'Physiological Chemistry of the Animal
Body ' ; Halliburton's ' Text-book of Chemical Physiology
and Pathology ' ; Bunge's ' Physiological and Pathological
Chemistry'; Meade Smith's 'Physiology of the Domestic
Animals,' and others mentioned in the text. With reference
to Dr. Meade Smith's work, I regret to find that on page 105
I have inadvertently given the title as 'A Text-book of
Comparative Physiology.'

I have endeavoured to acknowledge all sources of in-
formation, though it is possible that, in drawing from such
a wide area, I may have omitted in places to do so.

Army Veterinary School, Aldershot,
August, 1892.

TABLE OF CONTENTS.

CHAPTER I.

THE CHEMICAL CONSTITUENTS OF THE ORGANISM.

PAGE

The Elements of the Body— The Organic Compounds, Nitro-
genous and Non-nitrogenous — The Inorganic Constituents 1-23

CHAPTER II.

THE BLOOD.

Physical Characters— Composition— Plasma and Serum— Blood
Proteids— Red Corpuscles— Haemoglobin, and its Deriva-
tives—White Corpuscles— Third Corpuscle— Coagulation-
Fibrin— Extractives of the Blood— Difference between
Arterial and Venous Blood— Salts of the Blood— Quantity
of Blood in the Body — Distribution of Blood — Gases of
Blood— Chemical Composition of Blood - - - 24-46

CHAPTER III.

THE HEART.

Arrangement of — Circulation of the Blood — Valves of the
Heart— A Cardiac Cycle— Cardiac Sounds— Capacity of
the Heart — Intra-cardiac Pressure — Blood Pressure —
Nervous Mechanism of the Heart - - - - 47-61

CHAPTER IV.

THE BLOODVESSELS.

Mechanics of the Circulation — Blood Pressure — Arterial
Tension — The Pulse — Velocity of the Blood — Arterial
Circulation— Capillary Circulation— Venous Circulation-
Influence of the Nervous System over the Bloodvessels-
Peculiarities in the Circulation -•_--- 62-75

xii Contents.

CHAPTER V.

THE VASCTTLAE GLANDS.

PAGE

The Spleen — Thymus— Thyroid— Anterior Renal Capsules —

Pineal and Pituitary Bodies - - - 76-77

CHAPTER VI.

RESPIRATION.

Mechanism of Respiration — Inspiration — Movements of the
Diaphragm— Expiration— The Muscles of Respiration—
The Number of Respirations — Movements of the Nostrils
and Glottis — Respiratory Changes in the Air and Blood —
Law of Dalton and Henry— Partial Pressure of Gases—
Apncea — Dyspnoea - Asphyxia — Nervous Mechanism of
Respiration— Quantity of Air Breathed— Gases of Respira-
tion _ - - - - 78-Jo

CHAPTER VIE

DIGESTION.

Prehension of Food— Mastication— Deglutition— The Saliva,
Amount, Composition, Secretion, and Use of — Amylolytic
Action— Mechanism of the Secretion of Saliva— Stomach
Digestion in the Horse, Peculiarities of— Arrangement of
Stomach— Digestion of Hay— Digestion of Oats— Arrange-
ment of Food in the Stomach — Stomach Acids — Secretion
of Gastric Juice— Stomach Glands— Gastric Juice— Pepsin
— Rennin — Mucin— Action of Gastric Juice on Albumins,
Starch, Fat, Milk, Cellulose— Periods of Stomach Diges-
tion— Stomach Digestion in Ruminants — Arrangement of
the Stomachs— Stomach Digestion in the Pig— Absorption
from the Stomach— Self-digestion of the Stomach— Gases
of the Stomach — Vomiting — Rumination — Nervous
Mechanism of the Stomach— Intestinal Digestion in Small
Intestines — Succus Entericus— Reaction of the Bowels —
Chyme— Large Intestines— Ca;cum, Function of— Colon,
Function of— Single Colon— Putrefactive Processes in the
Intestinal Canal— Intestinal Gases — The Faces, Amount
of, Odour — Defalcation- Meconium— Nervous Mechanism
of the Intestinal Canal - - 96 158

Contents. xiii

CHAPTER VIII.

THE LIVER AND PANCREAS.

PAGE

Bile, Characters of — Composition of — Bile Pigments—Bile Salts
—Quantity of Bile — Use of Bile — Glycogen, Formation
of — Source of — Diabetes — Further Uses of the Liver —
Pancreas— Nature of Secretion— Composition of — Use of —
Pancreatic Ferments — Influence on Digestion — Changes in
the Pancreas while Secreting - - 159-174

CHAPTER IX.

ABSORPTION.

Lymph, Formation of — Use of — Characters of —Lymph Cells —
Analysis of Lymph — Quantity of Lymph in the Body —
Movements of the Lymph — Chyle, Nature of — Analysis of
— Source of— Movements of — Absorption in General, from
Respiratory Passages, Cellular Tissue, Conjunctiva, Skin,
Pleural and Peritoneal Cavities, Intestines — Absorption
of Fat, Sugar, Proteids - - - 175-190

CHAPTER X.

THE SKIN.

Function of the Skin, Area of — Growth of Hair— Sweat, Com-
position of — Peculiarities of — Sebaceous Secretion — Respi-
ratory Function of the Skin ... 191-196

CHAPTER XL

THE URINE.

Use of Kidneys — Composition of the Urine — Physical Characters
of the Urine — Organic Solids — Salts of Urine— Composi-
tion of Horse Urine — Composition of Ox Urine — Com-
position of Sheep Urine — Urine of the Pig — Secretion of
Urine — Micturition — Abnormal Constituents and Urine-
testing ...... 197-219

Contents.
CHAPTER XII.

NUTRITION.

Income and Expenditure, Sources of — Metabolism — Nitro-
genous Food — Non- nitrogenous Food — Inorganic Food —
Starvation — Muscular Exertion — Amount of Food re-
quired— Digestibility of Food — Nutritive Relation 220-236

CHAPTER XIII.

ANIMAL HEAT.

Sources of— Loss of Heat — Amount of Heat produced — Regu-
lation of the Body Temperature — Distribution of Tempera-
ture - - ' - - - 237-241

CHAPTER XIV.

THE MUSCULAR SYSTEM.

Structure and Composition of Muscle— Changes resulting from
Contraction — Irritability of Muscle — Muscle Currents —
Muscle Curves — Elasticity— Fatigue— Laws of Muscular
Work— Rigor Mortis ■ - - 242-252

CHAPTER XV.

THE NERVOUS SYSTEM.

The Nerves, Electrical Phenomena of — Electrotonus — Irrita-
bility of Nerves— Ganglia— Nerve Terminations— Spinal
Cord, Arrangement of — Tracts in the Cord — Spinal
Nerves — Reflex Action — Transference and Radiation of
Impressions — Automatism — Augmentation — Inhibition —
Co-ordination— Conducting Paths in the Cord — Centres in
the Cord— Medulla Oblongata— Centres in the Medulla —
Function of the Medulla— Pons Varolii — Crura Cerebri
Basal Ganglia— Cerebellum, Functions of— Cerebrum — Re-
lative Weight of Brains -Motor Areas— Functions of the
Cerebrum — Cerebral Circulation — Cranial Nerves — The
Sympathetic System - - 253 293

Contents. xv

CHAPTER XVI.

THE SENSES.

PAGE

Sight: The Eye as an Optical Instrument— Lenses — Spherical
Aberration — Chromatic Aberration — Astigmatism — Em-
metropia — Myopia — Hypermetropia — Accommodation —
Katoptric Test — Function of Iris — The Retina — The
Ophthalmoscope — Movements of the Eyeball — Monocular
and Binocular Vision— Cartilago Nictitans — Tears — Eye-
lashes. Smell: Smell Centre — Nasal Chambers — Tur-
binated Bones — Organ of Jacobson — Facial Sinuses. Taste :
Nerves of Taste — Taste Goblets— Papillte of the Tongue
and Mouth. Hearing: Arrangement of Ear — Internal
Ear — Nerves of Hearing — Tympanum — Guttural Pouches.
Touch - - 294-31!)

CHAPTER XVII.

THE LOCOMOTOR APPARATUS.

Muscular Levers — Function of Muscles — Joints, Synovia, Hock
Joint, Stifle, Hip, Shoulder, Elbow, Knee, Fetlock — Func-
tion of Suspensory and Check Ligaments — Centre of
Gravity — Distribution of Weight on the Body— Act of
Standing— Locomotion— The Walk, Trot, Amble, Canter,
Gallop, Jumping, Rearing, Kicking, Buck-jumping, Lying
down, Rising — The Daily Work of Horses — Velocity of
Work— The Weight Carried— Draught - - 320-354

CHAPTER XVIII.

THE FOOT.

Nature of Horn — Analysis of Horn — Vascular Mechanism of
the Foot — The Laminae, their Arrangement and Use —
Anti-concussion Mechanism — The Frog — The Wall —
Elastic Movement of the Foot— The Lateral Cartilages —
The Navicular Bursa — Physiological Shoeing - 355-371

CHAPTER XIX.

THE VOICE.

Various Laryngeal Sounds— Production of Sound — Movements
of the Larynx — Nerve Supply of Larynx — Yawning, Sneez-
ing, Coughing -..-. 372-37C'.

xvi Contents.

CHAPTER XX.

GENERATION AND DEVELOPMENT.

PAGE

Seminal Fluid — Erection— Sexual Intercourse— The Ovum—
' Heat ' — Puberty — Development of the Ovum — The
Amnion — Allantois — Chorion — Umbilical Cord — Fcetal
Circulation — Duration of Pregnancy — Nutrition of the
Embryo — Uterine Milk — Parturition — Mammary Secre-
tion, Colostrum and Milk, Composition of - - 377-304

CHAPTER XXI.

GROWTH, DECAY, AND DEATH.

Growth — Rate and Amount of Increase — Dentition — Decay,

Period of — Death, Causes of - - 395-401

A MANUAL OF VETERINARY PHYSIOLOGY.

CHAPTER I.

THE CHEMICAL CONSTITUENTS OF THE ORGANISM.

Chemistry shows that a large number of the so-called
elements enter into the composition of the body. Oxygen,
hydrogen, carbon, nitrogen, sulphur, phosphorus, chlorine,
fluorine, silicon, potassium, sodium, calcium, magnesium,
and iron are found, not in a free state, or only to a very
slight extent, but brought together in such a way as to
form compounds, and these may be divided into two classes
— Organic and Inorganic.

Before reviewing the compounds of the body, we may
briefly notice the part played in nature by the various
elements, and the methods by which these enter the bodies
of animals ; this is especially interesting to the veterinary
physiologist, as, with few exceptions, the animals with which
he has to deal, and of which this book mainly treats, obtain
their store of the needful elements direct from the vege-
table kingdom, instead of through the intermediate stage of
the animal kingdom.*

Carbon exists in nature principally in the form of carbonic
acid, viz., united to oxygen ; it is only in this compound
that it can be taken up by plants, which in their special
laboratory split off the oxygen molecule and store up the

* Bunge, ' Physiological and Pathological Chemistry,' has been fol-
lowed in this account of the elements of the body.

1

2, A M>t i, f<<l q/ Veterinary Physiology.

carbon, returning the oxygen to the air, and thus supplying
to the atmosphere what animals are momentarily depriving
it of. Even the solid carbon in the form of coal must at
one time have been carbonic acid, for the reason just men-
tioned that this is the only form in which carbon can be
taken up by plants. Carbon enters the animal system with
the carbon of the food, and leaves it either as carbonic acid
or in compounds, such as urea, which readily yield it ; us
carbonic acid, therefore, it is again taken up by the plant.

Hydrogen does not occur in the free state in nature, but
principally as water, and a very small quantity as ammonia ;
in these forms the hydrogen is taken up into the plant, by
which it is introduced into the animal, which gives it off'
again as water and ammonia, or a substance which readily
yields these.

Oxygen is the most widely distributed of the elements,
forming one quarter by weight of the atmosphere, and eight-
ninths the weight of water ; it also forms, by means of its
compounds, one-half the weight of the earth's crust. It is
the only element which enters the animal or vegetable body
in a free state, and then only to a limited extent. We have
mentioned the combination of carbon with oxygen, and it is
this which principally supplies the plant with the oxygen
required ; at the same time the plant returning the oxygen
to the air, maintains the needful balance which should exist
between the carbonic acid and oxygen.

Nitrogen exists largely in a free state, no less than four-
fifths of it being in this form in the atmosphere ; it has but
little affinity for other elements. In the form of ammonia,
nitrous and nitric acids, it enters the plant, free nitrogen
the plant cannot assimilate. In the form of vegetable
proteid it enters the animal, leaving it as urea, etc., which
by rapid decomposition yields ammonia. The animal cannot
utilize free nitrogen any more than the plant, though the
gas is found dissolved to a slight extent in some of the
fluids of the body.

Sulphur exists largely in nature in combination as
sulphates of alkalies and alkaline earths ; in this form it

The Chemical Constituent 's of the Organism. 3

is taken up by the vegetable, and forming a part of the
proteid molecule is taken into the body of the animal,
where, by splitting up and oxidation, it yields sulphuric
acid, in which form it is excreted by the urine.

Phosphorus enters plants as phosphoric acid united with
alkalies ; in soils it exists in only small quantities, hence the
necessity of phosphates as manure. In the plant phosphoric
acid forms a part of the complicated compounds known as
lecithin and nuclein, in which condition it enters the animal
body, forming a part of both the solid and fluid tissues.

Chlorine does not exist in a free state in nature but com-
bined with potassium and sodium, in which form it enters
plants and from these passes in the same compounds into
animals.

Neither sodium, potassium, nor magnesium enter or leave
the body or plant in any organic form, but simply as in-
organic salts. Bunge considers that calcium may enter the
body as an organic compound, his reasons for this view are
mentioned later in this chapter.

Iron occurs free and in a ferrous and ferric state in nature ;
in the soil it permits the retention of carbon, and also
enables it to return to the atmosphere. 1 n the animal it is
an oxygen-carrier, combined with a highly complex body
known as haemoglobin. It furnishes the vegetable with its
colouring matter, for chlorophyll cannot be formed without
it. It is not known in what form iron leaves the body.

Silicon, in the form of silicic acid, is taken up by plants,
through the aid of which the stems, which largely consist of
it, are capable of standing erect. Through the plant it is
taken into the body and passes into the tissues. It is largely
•of use in the development of hair, and much of it passes out
of the bodies of herbivora through the urine ; in sheep, ac-
cording to Bunge, it sometimes causes stone in the bladder.

Bunge, in his remarkably clear style, having thus traced
the cycle of the elments from nature into the plant, from
the plant into the animal, and from the animal back to
nature again, then draws a contrast in the following terms
between the changes occurring in the animal and vegetable :

1—2

4 A Manual of Veterinary Physiology.

1. The plant forms organic substances ; the animal destroys
organic substances. The vital process in the plant is syn-
thetic, in the animal analytic.

2. The life of the plant is a process of reduction ; the life
of the animal a process of oxidation.

3. The plant uses up kinetic energy and produces poten-
tial energy : the animal uses up potential energy and pro-
duces kinetic energy.

Passing now to the organic and inorganic compounds
found in the body, we find that the organic can be divided
into nitrogenous and non-nitrogenous.

M'Kendrick* presents a table of the organic compounds
prepared on a physiological classification, which is here
reproduced.

I.- Nitrogenous Bodies.
I. — Pkoteids.

A. Tkue Albumins.

1. Albumins — Serum albumin (blood), and egg albumin.
•_'. Globulins— Vitellin (yolk of egg), myosin (muscle), para-
globulin (blood), and fibrinogen (blood).
:'. Fibrin (blood-clot).

4. Proteins — Casein (milk), alkali albumin, syntonin or acid

albumin (muscle).

5. Peptones — Albumin peptones, gelatin peptones (both diges-

tive products).

6. Crystallizable albuminoids. Haemoglobin (blood).

7. Soluble ferments — Ptyalin (saliva), pepsin (gastric juice),

pancreatin (pancreatic juice), tripsin (pancreatic juice),
inversive ferment (intestine), rennet (stomach of calf),
lactic ferment (iutestiuesi, fat splitting ferment (pancreas),
blood ferment.

B. Albuminates.
1. Collagen (yielding gelatin;, chondrigen (yielding chondrin),
elastin (from elastic tissue), keratin (from horn and
epidermis), mucin (from mucus), and nuclein (nuclei of
-•ells .

II. Fatty Nttkouenous Matters.

1. Phosphoglyceric acid, nervous matter.

2. Cholin or neurin, bile, etc.

■ \. Lecithin, nervous tissue, blond corpuscles, yolk of egg, etc.
'.'>. Cerebrin, nervous tissues.

• Texl book ot Physiol* in .'

The Chemical Constituents of the Organism. 5

Nitrogenous Bodies — Continued.
III.— Amides.

1. Urea, urine, etc.

2. Oxaluric acid, urine.

3. Allantoin, embryonic fluids.

IV.— Amido Acids.

1. Glycocolle, glycocin or glycin, bile, etc.

2. Leucin, pancreas, spleen, intestinal canal.

3. Tyrosin, pancreas, intestinal canal.

4. Creatin, muscles.

5. Creatinin, urine.

6. Taurin, muscles, lungs, feces.

7. Cystin, urine.

8. Sarcosin, muscle.

V.— Nitrogenous Acids.

1. Sulpbocyanic acid, saliva.

2. Uric acid, urine.

3. Hippuric acid, urine.

4. Inosinic acid, muscle.

b. Bile acids — glycocbolic, taurocholic, and cbolalic acids.

VI.— Salts formed by Organic Acids and Inorganic Basks.

1. Hippurate of soda, urine.

2. Hippurate of lime, urine.

3. Urate of soda, urine.

4. Urate of lime, urine.

5. Oxalate of lime, urine.

6. Glycocbolate of soda, bile.

7. Taurocholate of soda, bile.

8. Sulphocyanide of potassium, saliva.

0. Phenolsulphate of potassium, urine.

VII.— Nitrogenous Bodies containing no Oxygen.

1. Trimethylamine, urine.

2. Indol, fseces.

3. Skatol, faeces.

VIII.— Pigments.

1. Blood pigments— haemoglobin, hsematin, hiematoidin.

2. Bile pigments— bilirubin, biliverdin, choletelin, bilifuscin,

biliprasin, hydrobilirubin.

3. Urine pigments — urobilin and indican.

4. Other pigments— lutein (yolk of egg), melanin (eye), stereo

bilin (faeces).

♦> A Manual of Veterinary Physiology.

II — Non-nitrogenous Bodies.
I.— Alcohols.

1. Ethylic alcohol (muscle), cbolesterine (bile and nervous
tissues), glycerine (intestines;, phenol (feces and urine).

II. Fats.

1. Tristearin, tripalmitin, triolein : soaps of these acids formed
with potash and soda.

III. — Carbo-hydrates.

1. Glucoses — Dextrose, levulose, mannitose, galactose, inosite.

2. Sucroses — Sucrose (cane-sugar), lactose (milk-sugar), maltose.

3. Amyloses — Starch, glycogen, dextrin, inulin, gums, and

cellulose.

IV.— Non-nitrogenous Acids.

1. Acetic Acid Series — Formic, acetic, propionic, butyric,

caproic, palmitic, margaric, and stearic acids.
•J. Glycollic Acid Series — Carbonic, glycollic, and lactic acids.

3. Oxalic Acid Series— Oxalic, succinic, and sebacic acids.

4. Aromatic Acid Series Benzoic acid and phenol.

Proteids.* — This term has been applied to several sub-
stances more or less closely allied, which in one form or
other go to make up by far the largest portion of the animal
body. The proteids possess no definite chemical formula ;
they are highly complex substances, and have never, with
some exceptions, been obtained in a crystalline condition ;
they are colloids — that is, they do not diffuse through an
animal membrane — and they are substances which are not
only indispensable to the body, but nothing else can even
temporarily replace them.

The true type of proteid is the albumin found in blood,
milk, eggs, etc., and these are true proteids, albuminous
bodies, or albumins. Substances termed albuminoid,
albuminate, albumose, albumid, proteose, etc , are not true
albumins or proteids but only derivative bodies, in many
respects closely allied to albumins, but possessing certain re-
actions which clearly distinguish them from true proteids.

* I am indebted to Halliburton's ' Physiological Chemistry, '
M'Kendrick's and Landois and Stirling's "Text-books of Physiology,'
for this account of the chemistry of the body.

The Chemical Constituerds of the Organism. 7

All proteids contain carbon, hydrogen, oxygen, nitrogen,
and sulphur.

Carbon - - 50 to i>i> per cent.

Hydrogen - - GG to l-'\ „
Oxygen 1'.' to 24 ,,

Nitrogen - -15 to l'J „

Sulphur - - '3 to 2-4 .,

In the animal body proteids undergo a breaking up, the
complex body is resolved into simpler bodies, resulting in
the production of such substances as leucin and tyrosin, and
from these the proteids are eliminated as carbonic acid,
urea, and water. The substances resulting from this breaking
up are known as decomposition products.

Some albumins are soluble in water, others in saline solu-
tion strong or weak, and in this way it has been possible to
classify the true proteids.

Albumins are soluble in water, in weak salt solution, and
coagulated by heat ; belonging to this class are serum, egg,
muscle, and vegetable albumin.

Globulins (which are also true albumins or proteids) are
insoluble in water, but soluble in dilute solution of common
salt and precipitated by heat. In this class are found the
globulin and fibrinogen of the blood plasma, also that found
in the crystalline lens, the vitellin of eggs, etc.

Fibrin is a solid albuminous substance produced by a fer-
ment in blood, chyle, and lymph ; it is insoluble in water,
but soluble in weak saline solution.

The Derived Albumins are obtained by the action of acids
or alkalies on true albumins. These bodies are insoluble in
water, but are soluble in dilute acid and alkalies, and in
weak salt solution. They are not coagulated by boiling as
the true proteids are. To this class belong acid albumin
or syntonin, alkali albumin, and the albumin of milk,
caseinogen.

If any of the above proteid bodies be acted upon by the
gastric or pancreatic secretions, they undergo a change into
a substance known as peptone ; but before reaching the
peptone stage they pass through an intermediate one known

3S A Manual of Veterinary Physiology.

as albuniose, or, to follow Halliburton — whose authority on
the nature of proteids is universally recognised — into a class
he terms proteoses. This proteose class consists of albumoses.
globuloses, vitelloses, caseoses, etc., depending upon the
origin of the proteose, viz., whether from albumin, globulin,
vitellin, casein, etc. ; and after the proteids have passed
through this stage they reach the final one of peptones.
But the proteid group is still further complicated by the
fact that there are different sub-varieties of proteose ;
albumose, for example, consists of three different kinds,
known as proto, hetero, and deutero albumose, each giving a
distinctive reaction: and the same remark applies to the
others.

Peptones are not simple bodies, but consist of two forms
hemi- and anti-peptone, the difference between them being
that hemi-peptone under the action of the pancreatic fluid
yields two substances leucin and tyrosin, whilst anti-peptone
does not.

We have previously mentioned that the complicated
proteid molecule is split up in the body into simpler com-
pounds, and we have now seen how this occurs. The
albumin taken in with the food is acted upon in the stomach
by an acid and a ferment, converting it into proteose and
then into peptone. The latter substance in the intestinal
canal, under the influence of an alkali and a ferment, has a
portion of it still further split up into leucine and tyrosin,
and these two eventually assist to form urea, in which con-
dition the bulk of the waste proteid of the body is excreted.

The vegetable proteids may be divided into the same
groups as the animal proteids. The form in which the bulk
of the proteid of plants occurs is as globulin, not albumin,
which is the reverse of what obtains in the animal ; the
ultimate decomposition products of vegetable albumin in
the system are the same as those of animal albumin.

The following table will probably help to render the
classification of albumins clearer :

The Chemical Constituent* of the Organism.

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S bo £

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A

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suixnqoif)

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10 .1 Manual of Veterinary Phy&iology.

Albuminoids are substances closely allied to albumins, but
differing- from them in some important particulars ; they
consist of such substances as gelatin, chondrin, mucin,
elastin, keratin, and many others. These pass through the
proteose and peptone stage in the same way as true albumins,
but with certain differences.

The ordinary Tests for Proteids are based upon their pre-
cipitation by certain reagents, and in the same way it is
possible to distinguish between one proteid and another.
The most common test is the so-called xanthoproteic, ob-
tained by the addition of a drop or two of nitric acid which
produces a precipitate increased by boiling and turned
yellow ; albumoses are rendered clear by boiling with nitric
acid and are thrown down again on cooling. If to the
yellow fluid obtained by the action of nitric acid on an
albuminous body a little ammonia be added, an orange
colour is produced. Professor Halliburton regards this re-
action as one of the most delicate we possess for proteids,
we need hardly, therefore, go further than this for a test,
although there are many other acids, organic and inorganic,
salts of metals, neutral salts, etc., which act as precipitants.
and to which reference will be found in text-books devoted
to physiological chemistry; attention need here only be
drawn to the fact that we are able to distinguish between
serum albumin and globulin, and are also capable of separat-
ing peptones from other proteids, by the action of mag-
nesium sulphate and ammonium sulphate.

A very remarkable fact about proteid substances is that
though they constitute the mainspring of organic life, yet
they number amongst them, or amongst their decomposi-
tion products, some of the most powerful poisons known.
Snake poison is a proteid, and even the albumose formed
during the peptic digestion of albumin is highly poisonous
if injected into the circulation.

The Ferments come under the proteid classification : they
are bodies possessing the most remarkable activity, and
capable of inducing in other bodies with which they may
be brought into contact, changes which result in the pro-

The Chemical Constituents of the Organism. 11

duction of entirely new substances. A common illustration
of ferment activity is the yeast-plant, which is capable of
producing out of sugar, alcohol and carbonic acid ; its func-
tion is due to a living cell, and such a ferment is described
as organized : micro-organisms, such as are found in the
intestinal canal and other places, which are capable of pro-
ducing great changes in the constitution of organic fluids,
are also classed as organized, for example, the lactic acid
ferment or bacillus, and the bacillus splitting up urea into
carbonate of ammonia, etc. In the body another class of
ferment exists, which, as it does not depend upon a living
cell, is described as unorganized or soluble ; such is the
•ferment which converts starch into sugar, the so-called
amylolytic ; the proteolytic or ferment converting proteids
into peptones; the fat-splitting ferment, which breaks up
fat into glycerin and fatty acids ; the milk- curdling ferment
of the fourth stomach of the calf ; the fibrin- forming fer-
ment of the blood, etc. : all these can by appropriate means
be isolated from the various tissues which produce them.

Almost all dead tissues and organic fluids may act as
starch-converting ferments.

Both the unorganized and organized ferments agree in so
far as their general action is concerned. All of them are
destroyed by raising the fluids containing them to a certain
temperature ; none of them appear to suffer, that is to be
worn out or exhausted, by the amount of work they per-
form, and in consequence in each case a small quantity of
them will produce as great an effect as a larger quantity.

The Pigments of the body are classed as proteids ; com-
paratively little is known about them, though they are
widely distributed and perform important functions. The
best known animal pigment is hemoglobin, the red colouring-
matter of the blood ; it is of a proteid nature, yet crystalliz-
able, and it also contains iron ; it acts as an oxygen carrier,
and is often spoken of as a respiratory pigment ; it has
several derivatives (see Blood), which supply the colouring
matter of the bile, urine, and feces. The next pigment
widely distributed is the black pigment of the body, or

12 A Manual of Veterinary Physiology.

melanin : it occurs in the skin, hair, eye, and is the chief
constituent of the melanotic tumours so common in the
horse. There are several other pigments, but nore so im-
portant as the above ; from the lipochromes, or fatty pig-
ments, is derived the visual purple of the retina.

Fatty Nitrogenous Matters. — Though true fatty matters
contain no nitrogen, yet in the body there is found,
especially in the nervous system and blood, a fat -like
substance containing nitrogen known as lecithin, and other
fatty nitrogenous matters known as phospho-glyceric acid,
cholin or neurin, and cerebrin. Lecithin appears to furnish
the majority of these substances, which are found not only
in the animal but also in the vegetable body.

In the Amide Group we have the important substance
urea, the chief end product of proteid decomposition in the
system.

The Amido Acids are an important group, formed by the
breaking up of proteids in the body, and are intermediate
between these and their end products which are excreted
with the urine. Glycocin is connected with one of the bile
acids, and also with hippuric acid : leucin and tyrosin are
formed by the pancreatic ferment from proteids ; creatin
and creatinin are probably connected with the formation of
urea ; and taurin is found in the bile in conjunction with
oholic acid.

Of the Nitrogenous Acids, some are found in the urine,
others in the bile. Sulpho-cyanic acid is said to occur in
the saliva, though I have never detected it in the horse.
Uric acid only occurs in herbivora when they are out of
health ; it is then one of the end products of proteid decom-
position.

Hippuric Acid in the urine of herbivora takes the place of
uric acid ; it is not free but combined with potash or soda
as hippurates of these bases. It is readily formed after par-
taking of benzoic acid. In animals it is said to be derived
from cellulose ; if this were its sole origin it is clear that it
could not be looked upon as a proteid end product; it is
possible, however, that proteid does furnish glycocole and

The Chemical Constituents of the Organism. 13

benzoic acid, the union of which in the body produces
hippuric acid. For further remarks on this acid see the
chapter on the Urine.

Bile Acids. — These probably originate from proteid de-
composition in the body, being furnished by glycocin and
taurin ; see Liver.

Another group of nitrogenous bodies also connected with
proteid decomposition is characterized by the absence of
oxygen. Trimethylamine has been found in the blood of
the calf, and in urine. Indol and Skatol found in the faeces
are due to the decomposition of proteids produced by pan-
creatic digestion. These bodies are closely connected with
the indigo group, which, however, contains oxygen.

Indigo occurs in the urine of herbivora ; it is derived
from indol, which by oxidation becomes indigo blue. In
the urine indican is found united with potassium sulphate,
and should skatol and indol pass by this channel they are
united with the same salt.

The next great chemical group is the Non-nitrogenous.
Fat is composed of a mixture of glycerin and fatty acids .
the latter are known as olein, stearin, and palmitin, the
two latter form the solid fats ; olein and palmitin the more
liquid fats. In the sheep and ox the fat is very firm, and
stearin enters into its composition, whereas in the horse
the fat is more fluid, and olein and palmitin are the chief
components.

The amount of fat in the body must depend upon the
feeding of the animal, and will obviously vary within
extreme limits ; in individual tissues marrow has the largest
amount — nerve, brain, milk, muscle, liver, bone, bile, and
blood, have proportions which decrease in the order
given.

Special fatty acids are found in butter and milk.
The change which the fats undergo in the alimentary-
canal is discussed in the chapter on Digestion, whilst the
origin of fat in the body and its function is dealt with
under Nutrition.

The Carbo-hydrates consist of several substances, which

14 A Manual of Veterlna.ru Physiology.

appear to throw themselves into three distinct groups, viz.,
the glucoses, or grape-sugar class ; the saccharoses, or cane-
sugar class ; and the amyloses, or starchy class.

Glucoses. Saccharoses. Amyloses.

+ Glucose. -+- Saccharose. -(- Starch.

- Levulose. + Lactose. 4- Glycogen.

+ Galactose. 4- Maltose. + Dextrin.

Inosite. Cellulose.

Gums.

The whole of these bodies contain carbon, hydrogen,
and oxygen, the two latter being in the proportion to form
water.

Glucose, also known as Dextrose, is found in fruit, and
occurs in small quantities in blood, in certain tissues of
the body, in the fluid surrounding the fetus of herbivora,
and the urine of the fetal calf and sheep. Under the
influence of yeast it yields alcohol and carbonic acid, and it
may also undergo the lactic fermentation.

The test for glucose is Trommer's, also the fermentation
test with yeast (see chapter on the Urine). There are
several other tests for sugar which will be found described
in any text-book on physiology.

The influence of sugar and other solutions in turning the
ray of polarized light to the right or left is well known ; in
the classification given above the plus sign indicates that
the ray is turned to the right, or dextro-rotatory ; the minus
sign to the left, or Uevo-rotatory.

Levulose is obtained by heating cane sugar with mineral
acids ; it may also be produced in the body through the
inversive ferment in the intestine ; in either case the cane
sugar becomes converted into equal parts of glucose and
levulose, the one differing from the other by its behaviour
to polarized light.

Inosite, or muscle sugar, is found in nearly all the organs
of the body besides the muscles; it may also be obtained
from plants, peas, beans, potatoes, etc.

The cane-sugar group may be converted into the glucose
group in the manner just indicated, cane sugar forming

The Chemical Constituents of tin- Organism. 15

glucose and levulose, lactose or milk sugar forming galac-
tose, and maltose forming glucose.

Maltose is an important substance, as it is the chief sugar
formed in the body by the action of the diastatic ferment on
starch. The inverting ferment of the intestine, as with
lactose and saccharose, can convert it into glucose.

The Amylose or starchy group represents a large class
of substances furnished by the vegetable kingdom, and the
function of which as food is to afford the animal the fuel by
which muscular energy is alone rendered possible. Starch
does not exist in the animal body as a natural constituent ;
animal starch, or glycogen, is derived from vegetable starch,
but glycogen is not a constituent of the body, only a some-
thing stored up in it.

Starch is insoluble in cold water, but under ihe influence
of moisture the starch granules swell considerably ; by boil-
ing these burst and form a solution. If starch be heated it
undergoes change, first into a substance termed dextrin, or
British gum, and secondly into glucose : it may also be
converted into glucose by heating with mineral acids ; by
the diastatic ferments of the saliva and pancreas starch is
converted into maltose : in each case, viz., whether by
mineral acids or ferments, dextrin is an intermediate
product.

Starch gives the well-known blue reaction with iodine,
but if it be acted upon so as to become converted into
dextrin, a red colour, and not a blue, is obtained on the
addition of iodine ; if the process of conversion is carried
still further to the stage of maltose or glucose, no colour
is developed with iodine, but the presence of sugar is abun-
dantly shown.

Dextrin was first discovered in the muscles of the horse ;
it is found in most plants, and its preparation from starch
is alluded to above. In muscles it occurs as an intermediate
stage in the conversion of glycogen into sugar.

Glycogen, or animal starch, is a carbo-hydrate found in
the liver, muscles, blood-cells, etc., it is derived from starch,
and stored up in the tissues for future use in a manner

Hi A Manual of Veterinary Physiology.

fully explained in the chapter dealing with the Liver. It
gives a port-wine red, and not a blue, reaction with iodine.
In the form of starch it cannot be utilized by the system, it
has, therefore, to become converted into sugar ; in its trans-
formation it behaves exactly as vegetable starch, first be-
coming changed into dextrin and then into glucose, not
into maltose as starch is in the intestinal canal. The
ferment of the salivary glands and pancreas can rapidly
induce this change.

Cellulose is an important consideration for the veterinary
physiologist, owing to the considerable proportion in which
it exists in the food of the herbivora. Cellulose forms the
cell-wall and woody fibre of plants ; if subjected to the
action of boiling dilute sulphuric acid it becomes converted
into dextrin. It is generally believed that cellulose can-
not be digested, but there can be no doubt that it is
utilized by herbivora, though in what way it becomes con-
verted we are not prepared to say. The cellulose ferment
has yet to be discovered, but doubtless the large stomachs
of the ox and the capacious intestines of the horse are in-
tended for its dissolution and assimilation. Bunge states that
experiments have proved that 60 per cent, to 70 per cent, of
the cellulose disappears in the intestinal canal, and that
sheep were capable of digesting 80 per cent, to 40 per cent,
of the cellulose of sawdust and paper when mixed with hay.
This authority also lays stress upon the important advant-
ages derived from the use of cellulose, in mechanically stimu-
lating the coats of the intestines and promoting natural
peristalsis; all animals with a long intestinal canal need it.
and if it lie withheld from rabbits they die.

Gums. A substance termed animal gum is found in
mucus, and gives to it its peculiar ropiness. It yields a
sugar which reduces salts of copper, but does not ferment.

The Alcohol Series in organic, chemistry includes an in-
teresting substance, termed cholesterine, which is found
in very many of the tissues of the body, more especially
bile and brain. In the latter, small masses of choles-
terine, exhibiting peculiar glistening fish-scale-like appear-

The Chemical Constituents of the Organism. 17

ance are regularly found about the cerebellum and in the
ventricles ; they form the substance of perhaps the majority
of tumours seen in the brain of the horse. Cholesterine is
also found in the wool of sheep united to a potash soap termed
lanolin. The origin of cholesterine is unknown. Ethyl
alcohol has been found in the muscles of the ox and horse.

Glycerin is found in fats, and, as previously mentioned,
is liberated from them in the intestinal canal by the fat-
splitting ferment of the pancreas ; it has been supposed that
the glycerin formed in the body contributes to the forma-
tion of glycogen.

Phenol, or carbolic acid, is largely formed in the intestinal
canal of herbivora, due to the decomposition of proteid
food the result of pancreatic digestion. It passes out of
the body by the urine, united with sulphate of potash or
combined in some way with sulphuric acid. This is the
type of a number of bodies termed conjugate sulphuric
acids, which are excreted by the urine, and to an extent
form a measure of the amount of proteid decomposition
occurring in the digestive canal.

Of the Fatty or non-nitrogenous organic acids there are
several found in the animal body, such as formic, acetic,
propionic, butyric, caproic, palmitic, and stearic. Acetic
may be present in the digestive canal ; propionic and butyric
have been found in sweat, and as the latter acid is connected
with lactic fermentation, it may be found wherever this is
occurring. The palmitic and stearic acids have been noticed
under the fats.

Several acids relating to the Glycollic Series are found in
the body, the most important being lactic acid which is
found in two or three different forms. It may occur in the
stomach and muscles, and also results from fermentative
changes in milk. The origin of muscle lactic acid is from
glycogen or glucose.

The Oxalic Acid Series furnishes oxalic and succinic acids
as occurring in the body. The oxalate of lime is common
in herbivora, and results from the ingestion of vegetable
food containing oxalates, also, perhaps, it is formed in the

9

18 A Manual of Veterinary Physiology.

body from proteids, sugar, etc. Succinic acid has been
found in the urine after the ingestion of certain fruits con-
taining malic acid and asparagin ; it has also been found
in some of the internal organs.

Inorganic Constituents.

The inorganic substances found in the body are water,
gases, and salts. Water forms nearly 60 per cent, of the
whole body ; it is taken in with the food and drink, and a
small quantity may be formed within the system.

The Gases of the body are oxygen, nitrogen, and hydro-
gen. The two former are taken in with the inspired air,
while hydrogen is formed in the intestinal canal as the
result of cellulose decomposition.

The largest portion of the inorganic matter consists of
the various Salts of sodium, potassium, calcium, magne-
sium, and iron, in the form of chlorides, sulphates, phos-
phates, and carbonates. We find that the distribution of
these salts throughout the tissues is very variable, some,
like bone, are excessively rich, whilst others are remarkably
poor in them. Certain tissues and fluids have a preponder-
ance of some salts to the exclusion of others.

The amount of the salts existing in the body depends
upon the age of the animal, and their nature is modified
by the character of the food partaken of; the daily quantity
ingested and stored up is largely affected by the rate of
growth, young growing animals storing up mineral matter
which the adult rejects.

In the composition of the milk we may obtain an insight
into the nature and quantity of the salts required by growing
animals. Bunge gives the following ash analysis of mare's
and cow's milk :

Cot

r'.s .!/;//.•.

Ma

re's Milk

Potassium

-

1-76

in 1

Sodium

ill

014

Calcium

-

l.V.I

l 23

Magnesium -

-

•21

12

Iron

•on:;

•01.",

Phosphoric acid

1-97

1-31

Chlorine

1 -69

•31

Total ash per 1,000-

-

7 ■*. »7

■117

The Chemical Constituents of the Organism. 19

The large amount of phosphoric acid and the preponder-
ance of lime, afford us some explanation of the rapid growth
of bone in the young of these animals ; the large proportion
of potassium and sodium in the cow, and the excess of
potassium over sodium in the mare, are points more difficult
of explanation, but bear out what I have yet to show, viz.,
the preponderance of potassium over sodium salts in the
excretions of the horse.

Bunge compared the ash of a puppy with the milk of the
mother, and the milk with the blood. It is remarkable
how closely the composition of the puppy's system agreed
with the salts it was receiving with the milk, though when
the ash of the milk was compared with the ash of the blood
of the mother, the greatest diversity in composition was
apparent. This observer showed that the ash of the milk
contained more potassium and less sodium than the ash
found in the body of the young animal. We may also see
that in cow's and mare's milk the potassium exceeds the
sodium, and Bunge explains it by saying that as the animal
grows it becomes richer in potassium and poorer in sodium
salts, depending upon the relative increase in the muscular
structure which is rich in potassium, and the relative
decrease of the cartilaginous material which is rich in
sodium.

In referring to Bunge's analysis of the cow's and mare's
milk, one is struck by the small proportion of chlorine in
the latter ; I cannot offer any explanation why the calf
requires so much more chlorine and sodium than the foal.
The chlorides in the body are required not only for building
up tissues, but in the production of secretions, and some
considerable difference must exist in the constitution of the
calf and foal to admit of such a difference in the amount of
chlorine required.

Turning to the adult, we find that vegetable food furnishes
considerably more potassium than sodium salts to the
system, and Bunge's views about the muscle growth apply
here also.

Sodium and Potassium. — Owing to the poorness of vege-

2—2

20 .1 Manual of Veterinary Physiology.

table food in sodium salts, Bunge believes that the admini-
stration of common salt with the food of herbivora is a
necessity. As I hold different views on this important
practical point, it is necessary that I should put forward his
arguments in the matter, which I have here summarized.

In spite of the many inorganic salts found in the food,
one only, viz., sodium chloride, is taken separately by the
human subject, and in addition to that already existing in
the food. But carnivora avoid salted food, as sufficient
sodium chloride exists in the blood and tissues in the raw-
state in which these are consumed by them. Eerbivora, od
the other hand, have been known to travel considerable dis-
tances to obtain salt. Bunge explains this by saying that
though the difference in the amount of common salt con-
sumed by carnivora and herbivora is not very great, yel
that herbivora consume three or four times as much potas-
sium as carnivora, and he considers this latter fact accounts
for the anxiety shown by them to obtain salt, for a reason
to be presently explained.

In 1,000 parts of dried material, the following are the
proportions of potassium and sodium found in certain
articles of diet :

Potassium.

Sodium.

Rice -

1

•03

Bullock's blood

2

l'.HI

Oats "\

Wheat 1
Rye ' "

- .'» to G -

•1 to -1

Barley;

Dog's milk -

- 5 to 6 -

2 to 3

1'cas -

12

■2

Milk of herbivora -

- '.I to 17 -

- 10 to LOO

Hay -

- 6 to 18 -

•;; to L-5

Beef -

19

30

Beans

21

•l

Clover

■_':'»

I

For one equivalent of sodium the equivalents of potas-
sium are :

The Chemical Constituents of the Organism,. 21

Equivalent K,0.

Mangel-

wurzel

2 0

Milk of

herbivora -

•8 to 6'0

Beef-

.

4-0

Wheat

.

12-0 to 23-0

Barley

-

14 to 21

Oats -

.

15 to 21

Rice -

- „

•24

Rye -

-

9 to 57

Hay -

-

3 to 57

Peas -

.

- 44 to 50

Clover

.

90

Beans

.

110

The preponderance of potassium over sodium salts is
here most marked, and Bunge considers that when a rela-
tion of from 4 to 6 equivalents of potassium to one equivalent
of sodium is obtained in a diet no addition of sodium
chloride is necessary ; but where the proportion of potas-
sium is higher than this the animal instinctively seeks for
sodium, for the reason that the effect of potassium salts in
the blood is to withdraw sodium salts from the system.

I should be sorry to deny the stimulant to the palate which
common salt may afford the herbivora, but so far as horses
are concerned, and I think the same argument must apply
to cattle, I am perfectly clear on the point that no addition
of common salt to the ordinary diet is absolutely necessary,
and that the food furnishes ample sodium, for the secretions,
as shown by my inquiry into the amount excreted by the
urine during rest and work, and the quantity excreted by
the sweat.

From the little we know of the character of the saline
secretions in the horse, we are prepared to find that the
preponderance of potassium over sodium, in both the urine
and the sweat, can only be accounted for by the excess of
potassium salts supplied by the food.

Calcium forms the largest mineral deposit in the body ;
it is taken in by means of the food. Bunge states that it
is probable that the lime salts required for the growth of
bone in young animals are contained in some organic com-

22 A Manual of Veterinary Physiology.

pound, and that the administration of inorganic compounds,
of lime in rickets is irrational and useless.

Lime exists largely in clover and hay, but only in
small quantities in the cereal grains ; it is principally by
the hay that the amount excreted by horses through the
kidneys is supplied; it passes from the body in such
quantities that it cannot be held in solution by the alkaline
urine. In the body the calcium is in the form of phos-
phate, sulphate, and carbonate ; in the urine as carbonate
and oxalate.

Magnesium salts occur in the body principally as phos-
phates, and in this form they enter largely into certain
foods, such as oats. The amount of magnesium passing
away from horses through the kidneys is small, but con-
siderable quantities derived from the food, and which
cannot be utilized in the body, pass out with the fasces ; by
collecting in the bowels this salt produces the ammonio-
magnesium phosphate calculi so common in horses.

Phosphates are united with soda, potash, lime, and mag-
nesium. They are principally taken in with the food,
but may also be formed in the body from the metabolism
of phosphorus-containing compounds. The foods richest
in phosphoric acid are oil-cake and bran, whilst hay and
straw are poorest in this constituent. The combination of
phosphates with magnesium has just been alluded to.
Phosphoric acid is principally execreted by herbivora with
the faeces, only small quantities passing away with the
urine.

Carbonates are found in several of the secretions of the
body, notably in the urine where they cause the most
intense evolution of gas on the addition of an acid. The
carbonates in the system of the herbivora result from the
combustion of the organic acids, malic, citric, tartaric, etc.,
which enter the body as potassium salts, the potassium
being set free and uniting with carbonic acid to form
carbonate of potash ; the potassium also unites with sul-
phuric acid, for which see sulphur.

The Sulphur in the body is derived from the albumin of

The Chemical Constituents of the Organism. 23

the food ; in the system it is converted into sulphuric acid,
and in this form 80 per cent, of the ingested sulphur
appears in the urine. The sulphuric acid is united with
the bases of the alkaline salts of vegetable acids, which, as
just mentioned, are in the body converted by combustion
into carbonates. These bases saturate the sulphuric acid,
and it has been found experimentally that where the basic
salts have been removed from the food, the sulphuric acid
produced from the proteid attacks the bases forming part of
the living body, and animals so fed die more rapidly than
if starved (Bunge).

The importance of the sulphates in the urine is consider-
able ; they afford a passage out of the body for the pro-
ducts of proteid change. Phenol and allied compounds are
in this way got rid of in the form of phenol sulphate of
potassium. Sulphur exists in horn, hair, and epidermis.

Iron is an important constituent of the complicated
proteid haemoglobin. It is also found in the hair, skin,
bile, lymph, most body fluids and tissues, and a small quan-
tity in the fasces. Bunge considers that the iron which
enters the system can only be absorbed when in the form
of an organic compound. Inorganic iron, though largely
used in the treatment of certain diseases, is not absorbed
from the intestinal canal ; food contains only organic and
not inorganic iron, and the hemoglobin of the blood is
formed from the complex organic compounds of iron which
are produced by the vital process of the plant.

CHAPTER II.

THE BLOOD.

The special function of the blood is to nourish the tissues
and to assist in removing from them the products of their
activity. To enable this to be carried out, the blood is
exposed in the lungs to the oxidizing action of the atmo-
sphere, whereby the fluid which has recently been going
the round of the body, and is highly charged with dele-
terious products, is once more revivified.

By means of a peculiar channel the circulation is placed
in direct communication with the nourishing fluid absorbed
into the body from the intestinal canal, by which process
the blood is being constantly renewed.

Blood consists of a fluid portion known as the liquor
sanguinis, floating in which are an immense number of
solid particles known as corpuscles ; it is the object of this
chapter to point out how the liquor sanguinis and corpus-
cles are composed, and their various duties in the system.

Physical Characters of the Blood. — The colour of blood
varies cither as it is drawn from an artery or a vein : in
the former it is of a, bright scarlet colour, whilst in the latter
it is of a bluish or purplish red. The colour of blood is
due to a peculiar crystalline proteid known as haemoglobin,
and depending upon the condition of oxidation in which
this is found is the scarlet or purplish colour obtained.
Blood is opaque, owing to the manner in which the mr
puscles found in it reflect, the light, when these are destroyed
the fluid becomes transparent; the liquor sanguinis is of a
yellow colour.

The Blood. 25

The reaction of the Mood is alkaline; this alkalinity
diminishes in blood drawn from the body until the process
of coagulation occurs. The alkaline reaction is due to the
phosphate and bicarbonate of soda found in the fluid
(Maly) ; the decreasing alkalinity observed on standing is
probably due to the formation of an acid. The alkalinity
of the blood is reduced by muscular work.

The odour of blood depends upon the animal it is
obtained from. The blood of the cat and dog has a most
disagreeable smell. This is not observed in the horse and
ox, though, according to some observers, the odour ol
butyric acid can always be obtained by heating the blood
with sulphuric acid. The taste of blood is saltish. The
specific gravity varies in different animals ; in the ox and
pig, 1060; sheep, 1050-1058; dog, 1050 (Colin); horse,
1060 ; according to Hoppe-Seyler the specific gravity
of the liquor sanguinis of the horse is 1027 to 1028, and
the specific gravity of the cells 1105. The remarkable
difference between the specific gravity of the cells and
the liquor sanguinis in the horse accounts for the rapid
manner in which the latter sink in blood drawn from the
body, producing the so-called ' buffy coat.'

The chemical composition of the blood of animals will, as
might be expected, possess almost absolute uniformity so
far as the presence of various substances is concerned : the
amount of these substances, however, both organic and
inorganic, varies not only in animals of different classes,
but in those of the same class ; the composition of blood
from an artery does not represent exactly that found in a
vein. We will here content ourselves by enumerating the
principal substances found in the blood, leaving the
quantities of these to form a separate table at the end of
the chapter.

Blood rout liny :
Liquor sanguinis or Plasma.
Red Corpuscles.
White Corpuscles.
Extractives.
Mineral matter.

26 A Manual of Veterinary Physiology.

It will be most convenient to deal with these in the
order in which they are given.

The Liquor Sanguinis, or Plasma, forms about GO per
cent, of the total blood ; it is a yellow albuminous fluid,
containing at least three proteids, one of which may by
certain processes be shown to be composed of two or three
others. The proteids are :

Serum albumin, consisting of «, /8, and y albumins.

Serum globulin.

Fibrinogen.

During the life of the blood the liquor sanguinis is
termed the plasma, but after it has been shed from the
body, and coagulation has occurred, it is no longer described
as plasma, but as serum ; Serum is, therefore, plasma which
is modified as the result of coagulation, and as this latter
process is attended by the production of fibrin, we may
say that serum is plasma minus the fibrin-forming
elements.

The Proteids of Serum are serums albumin and globu-
lin, and in addition there is the ferment produced as the
result of coagulation ; fibrinogen, having been used up in
the process of coagulation, does not occur. The following
table from Halliburton exhibits these points very clearly :

Proteids of the Plasma. Proteids of the Serum.

Fibrinogen. Serum globulin.

Serum globulin. Serum albumin.

Serum albumin. Fibrin ferment.

It has been shown that the proportion in which serum
globulin and serum albumin exists in the blood varies in
different animals ; in the horse and ox the globulins are
in excess of the albumins ; in man and the rabbit this
is reversed. The following table from Gamgee,* after
Hammarsten, will render this clear :

* ' Physiological Chemistry.'

The Blood.

27

Variety of Serum.

_c« o

O S

11

as

00

d

1!

as

0Q

IS

3 ~

Serum Globulin.

to
Serum Albumin.

From blood of horse -

8 597

7-257

4-565

2-677

1-340

1

0-591

ox

8-965

7-499

4-169

3-32'J

1-466

1
0-842

„ „ man

9-207

7-619

3-103

4-561

1-587

1
1-511

,, ,, rabbit *

7-525

6-225

1-788

4-436

1-299

1
2-5

The table shows that the amount of total proteids is
more regular than the different albumins of which they
are composed.

The specific gravity of the blood plasma is from 1027-1030,
of the total weight of the blood it constitutes two-thirds,
though, according to Bunge's analysis, the proportion of
serum to total blood is not so large ; he puts it down at
46-5 per cent, serum, and 535 per cent, corpuscles. Plasma
possesses the power of clotting, yielding fibrin and serum.
Sheep's blood yields more serum than any other (Halli-
burton).

Perhaps the nearest approach to pure plasma is the fluid
found in the heart sac and abdominal cavity of the
horse ; even the pathological fluid of the chest, produced
as the result of inflammation, is remarkably pure and free
from white blood cells, and hence uncoagulable unless on
the addition of a little fibrin ferment, when jellying shortly
occurs.

Halliburton has shown by fractional coagulation that
serum albumin may be composed of three other albumins,
which he designates a, /3, y serum albumins. Strange to
say that in the horse, ox, and sheep, no serum albumin a
exists, but (3 and <y are present. Serum globulin (also
known as paraglobulin and fibrino - plastic substance)
exists in different proportions in the blood of domestic

2H A Manual of Veterinary Physiology.

animals ; its greatest interest lies perhaps in the parr it was
supposed to play in the process of coagulation — a part
which we have now good reason to believe does not exist.
Fibrinogen is the precursor of fibrin in the blood — a sub-
stance we shall have more to say about in dealing with
coagulation — it is found in blood plasma, but not in the
serum; it also exists in the fluids thrown out in t < > the
cavity of the chest, pericardium, etc.

Corpuscles of the Blood. — Ittood examined under the
microscope is found to consist of an enormous number of
bodies termed corpuscles floating in the liquor sanguinis.
These corpuscles are found to be both red and white ; the
former are by far the more numerous, the latter are the
larger.

The Red Corpuscles, viewed under the microscope, are bi-
concave discs, circular in shape, and possessing no nucleus,
though, owing to their shape certain focussing may produce
a dark centre Avhich might be mistaken for a nucleus, but
which is really due to the shape of the body, and is, there-
fore, an optical effect. The red cells have a tendency to lie
on top of each other in the form of piles of pence, this con-
dition is spoken of as forming rouleaux, and its cause is
unknown. The circular shape of the red cell is affected by
the amount <>f fluid in the blood : where the latter is small.
as occurs in many diseases, the corpuscles become covered
with spines or projections ; when the fluid is in excess the
corpuscles swell. The opacity of blood is due to the con-
cave character of the corpuscles, reflecting light as from
concave mirrors (M'Kendrick). When the corpuscles are
destroyed the blood becomes transparent.

A red blood coll is composed of a stroma, holding in its
meshes the red colouring matter. The stroma or frame-
work of the corpuscle consists of an albuminous material
allied to the globulins, ami a fatty matter termed lecithin.
The red colouring matter consists of an albuminous crystal-
line substance hremoglobin. The whole of these are con
tained in the corpuscle, not by means of an envelope, but.
retained in the pores of the stroma.

The Blood. 29

The number of corpuscles in the blood is approximately
determined either by the method of Gowers, or Malassex.
The principle on which these are based is the same— a
known quantity of blood is diluted with a known bulk of
artificial serum and accurately mixed ; of this a small drop
is placed in a counting-chamber, which is ruled into squares,
and examined under the microscope. The blood cells
occupying the squares are counted, which can readily be
done, and the mean of them taken.

In the horse the mean number of red blood corpuscles
per cubic millimetre* is 7,212,500, and in the ox 5,073,000.
Taking the amount of blood in the horse at 66 lbs., this
gives 204,113,750,000,000 as the approximate number of
red cells in the body (Ellenberger).t They are increased
by sweating, the excretion of water by the bowels and
kidneys, and by starvation ; they are diminished by
pregnancy and copious draughts of water (Landois and
Stirling).

Each red cell offers a certain absorbing surface for oxygen,
which, if calculated on the total number of corpuscles, is
something enormous, being equal for the horse to a square
having a side of 140 yards.

By freezing and thawing the blood alternately, also by
the addition of certain reagents to it such as chloroform,
ether, bile salts, etc., the red blood cells can be so broken up
as to liberate the colouring matter or haemoglobin, which
then deeply stains the serum, which is naturally yellow or
colourless. The broken-up red cells do not now reflect
light, and when this occurs the serum is seen of a red or
laky colour and quite transparent ; this is termed laky
blood. Blood in its natural state, as previously mentioned,
is opaque, but when treated by the above methods, or by
electrical shocks, it becomes transparent.

The greater part of the red cell is haemoglobin, a sub-
stance possessing a remarkable affinity for oxygen, which

* A cube having its edges about one-twenty-fifth of au inch.
•f ' Physiologie der Haussiiugethiere.'

30 A Manual of Veterinary Physiology.

it obtains at the lungs, and leaves behind it in the tissues.
The hemoglobin of the red cells, therefore, exists in two
states, one in which it is charged with oxygen, called oxy-
hemoglobin, and the other in which it has lost its dxygen,
known as reduced hemoglobin. The process of oxidation
and partial reduction is constantly occurring at every revo-
lution of the circulation, with the ultimate result that the
red blood disc gets worn out and dies. In this condition it
is cast off from the system, being got rid of through the
medium of the liver as bilirubin, and also, probably, being
destroyed in the spleen and elsewhere. When the red cells
die their hemoglobin is set free, and is decomposed into
hseinatin, from which, probably, all the pigments of the
body, but especially those of the bile, are formed.

The probable origin of the red cells is in the red marrow
of bones ; all other seats of formation appear doubtful. It
is certain that their production is a matter of extreme
rapidity, as may be witnessed, for example, after haemor-
rhage. The red cells are not derived from the white. In
the embryo the red cells are nucleated during the early
period of development, but are gradually replaced by non-
nucleated corpuscles before birth.

In speaking of the plasma, we mentioned the con-
tradictory results obtained by various observers as to the
proportion the plasma bore to the cells. According to
some authorities, the blood cells are 35 to 40 per cent, of the
weight of the blood. M'Kendrick gives the proportion of
red cells as 33 per cent., or -*- ; whilst Bunge, from an
analysis of horse's blood, puts the red cells at 53 per cent.,
and the plasma at 47 per cent. It is probable that all these
results were true for the specimen of blood examined, for
there can be no doubt of the variation in the composition
of this fluid.

We have mentioned that retained in the pores of the
stroma of the red cells is the red colouring substance
haemoglobin, and with this we must now deal.

Haemoglobin, also known as hsemato-globulin, and
hemato-crystalline, is a most remarkable body ; it is a

The Blood. 31

proteid, yet crystallizes ; whilst its behaviour in the
dialyser is not that of a colloid but a crystalloid. It is one
of the most complex substances in organic chemistry, and
its molecule is a very large one. According to the analysis
of Kosel,* hemoglobin in the horse consists of:

C 54-87 O 19-73

H 097 S -65

N 1731 Fe -47

The empirical formula for this body, on the assumption
that the molecule contains one atom of iron, is given by
Zinoffsky as follows :

C7],Hm(1X,I4FeSA4,.

Analyses have proved that oxy-ha?moglobin presents a
perfectly constant composition, and is remarkable in being
the only proximate constituent of the body containing
iron.

The total amount of haemoglobin in a horse's body is
about 8*8 lbs. ; and the amount of iron contained in this is
about 257 grains. This calculation is based on the assump-
tion that the amount of blood in the body is 66 lbs.

In the red blood cells hemoglobin exists in the propor-
tion of 86 per cent, to 94- per cent., whilst in the total
blood of the horse it forms 1315 per cent., in the ox 9-96
per cent., sheep 1034 per cent., and pig 127 per cent.
(Ellenberger).

The younger the animal the less hemoglobin ; males
have more than females, and castrated animals more than
entires (G. Miiller).t

Hemoglobin has a remarkable affinity for oxygen. The
laws relating to the absorption of gases by fluids and solids
do not apply to hemoglobin. It has been calculated that
15^ grains of this substance will absorb 0*95 cubic inches
of oxygen gas. We have mentioned that when hemoglobin
is charged with oxygen it is spoken of as oxy-hemoglobin ;
when it has discharged its oxygen, which it is capable of

* Ellenberger's 'Physiologie der Haussiiugethiere.' f Ibid.

32 A Manual of Veterinary Physiology.

doing- with considerable facility, it is spoken of as reduced
haemoglobin. These, therefore, are its two conditions of
oxidation: as oxy-haemoglobin it is charged in the capil-
laries of the lungs, brought back to the heart and dis-
tributed all over the body ; as partly reduced haemoglobin
it is produced in the tissues, and brought back by the veins
to the heart for distribution to the lungs, where it renews
its oxidized condition. Haemoglobin is never completely
reduced in the body, excepting in the last stage of
asphyxia.

Oxy-hainoglobin crystallizes in some animals, hare and
guinea-pig, with facility ; with others, ox, sheep, and pig,
with difficulty. The crystals are generally rhombic plates
and prisms ; but the form differs according to the animal.
Reduced haemoglobin does not crystallize.

The two haemoglobins produce quite distinctive spectra
when examined by the spectroscope, by which they may be
readily recognised. To put the matter roughly, oxy-
hsemoglobin gives a well-marked double band in the green
portion of the spectrum, one band being wide the other
narrow; whilst reduced haemoglobin gives one wide single
band in the same position.

Oxygen and haemoglobin are so lightly bound together
that they are readily separated. The oxygen is given off if
the blood be placed in a vacuum or boiled, or if it be brought
in contact with indifferent gases— such as nitrogen and
hydrogen. It is the facility with which haemoglobin parts
with its oxygen which enables the tissues to obtain it.

Haemoglobin forms, according to some observers, three,
according to others four, compounds with gases :

With oxygen it forms oxy-haemoglobin and methsemoglobin.
„ carbonic oxide it forms CO haemoglobin.
„ nitric oxide „ KO „

Oxy-fuemoglobin we have dealt with : the others, in a
work of this kind, can only receive a short notice at our
hands, though the subject is one which is full of interest.

Methsomoglobin is produced by allowing blood to be ex-

The Blood. 83

posed to the air until it becomes brown in colour and acid
in reaction ; this substance gives a three-banded spectrum,
and parts from its oxygen with difficult}'. In Carbonic oxide
haemoglobin the haemoglobin is already saturated with CO,
and so cannot carry oxygen to the tissues, thereby rapidly
producing death. The blood of people who have died from
CO poisoning is of a cherry-red colour, and yields the
spectrum of CO haemoglobin — viz., two bands very much
like those of oxy- haemoglobin, but situated nearer to the
violet end of the spectrum. Nitric oxide haemoglobin in
many respects resembles CO haemoglobin.

Haemoglobin may be decomposed either by boiling or the
addition of alkalies, acids, or acid salts ; in either case it
splits up into a substance containing all the iron of the
haemoglobin, and known as h3ematin, and a proteid sub-
stance or substances termed globin.

Haematin has a metallic lustre, blue-black colour, is free
from crystalline formation, and yields a dark-brown powder
when pulverized ; it contains 8*82 per cent, of iron.
Haematin presents a distinctive spectrum, both in an acid
and alkaline solution.

When haematin is boiled with glacial-acetic acid it yields
haemin, which, microscopically, is found to consist of prismatic
crystals, dark, or nearly black in colour. Hoppe-Seyler
considers this substance to be hydrochloride of haematin.
The ready production of hcemin crystals by warming the
blood with a drop of acetic acid on a slide is used as a
microscopical test.

There are other derivatives of haematin, such as
Haemochromogen, which is a reduction product ; Haemato-
porphyrin, which is haematin from which the iron has been
removed ; Haematoidin, found in old blood-clots and in the
ovary, it is an iron free product of haematin, and gives the
same reaction with nitric acid as bile pigment, viz., a play
of colours. Haematoidin is, in fact, identical chemically
with bilirubin.

The White Corpuscles, also termed leucocytes, are found
in blood, lymph, pus, connective tissue, etc. They exist in

3

84 A Manual of Veterinary Physiology.

blood in the proportion of 1 to 335 of red (Landois and
Stirling), but vary in their proportion according to the vessel
from which the blood is examined. In the splenic artery
there are very few, in the splenic vein they are exceedingly
numerous. Blood which has been removed from the vessels
contains but few, for the reason that they are probably
broken down during the formation of fibrin. The white
corpuscle is much larger than the red, and consists of what
is known as protoplasm, which is granular in appearance ;
it possesses a nucleus or nuclei, and is endowed with move-
ment ; there is no cell- wall or envelope, but the body is
made up of delicate fibrils, and the nucleus the same.

The movements, known as amoeboid, exhibited by these
corpuscles are remarkable, they are shown by changes of
form, projections shooting out from the surface and being
again retracted. The corpuscle has also the power of taking
up small particles of colouring matter, bacteria, etc., into
its interior. The amoeboid movement is destroyed by heat,
and by shocks from an induction coil.

The white corpuscles contain about 10 per cent, of
solids, which consist of serum globulin, serum albumin,
and myosin, or its precursor, myosinogen, as myosin pro-
bably only occurs after death. Another nitrogenous prin-
ciple is nuclein, which is largely found in the corpuscle ; it
is remarkable for containing phosphorus. Besides these
we have the complex fatty body lecithin, cholesterin,
glycogen (especially in the horse), and salts, the latter
principally phosphates probably derived from the phos-
phorus containing compounds.

The origin of the white corpuscles is from the lymphatic
system, by which they enter the blood stream through the
large lymphatic channels opening into the vena cava at the
junction of the two jugular veins. The white corpuscles, as
well as the red, are constantly being used up and as con-
stantly replaced. This using up consists in the power they
possess of passing through the walls of the vessels into the
surrounding tissues, from which they are removed by the
lymph channels, and so find their way back to the blood.

The Blood. 35

Pas consists largely of white cells collected in the tissues
and forming an abscess.

No doubt many corpuscles leave the blood the destruc-
tion of which we are unable to account for, but it is pro-
bable, as suggested by Michael Foster, that by their death
they influence the composition of the blood plasma, as in
this fluid their component parts must become dissolved
after their death.

During the life of the white corpuscle great activity pre-
vails, it is constantly giving up and taking in material
which must affect the composition of the plasma. We
know that the white cell possesses the power of digesting
certain substances, both solid and liquid. The researches
of Metschnikoff have paved the way towards a better
understanding of the probable way in which protection
against certain diseases is obtained. The white cells
digest the bacteria, taking them up into their own sub-
stance ; it is a fight between bacteria and leucocytes ; the
protection afforded to the system by the white blood-cells
is therefore not the least important of the functions per-
formed by them.

On the death of the blood the white cells yield the so-called
fibrin ferment, which produces the clotting of the blood.

A Third Corpuscle is described as found in the blood,
termed by Hayem Haematoblast, and by Bizzozero Blood-
plate. Their function and nature is unknown, though
according to some they take an active part in that obscure
process the clotting of the blood. Blood-plates are found
in large numbers in the white thrombi found in vessels,
and they may be readily obtained by passing a thread
through a blood-vessel, or suspending threads in freshly-
drawn blood (Bizzozero, Stirling). Semmer calls these
plates red granular corpuscles ; he states that they exhibit
amoeboid movement, and has examined them in the blood of
the horse and other animals (Gamgee).

Coagulation. — We are now brought to a consideration of
the subject of blood clotting, a process by which the
naturally fluid blood becomes converted into a solid.

3—2

36 A Manual of Veterinary Physiology.

If blood be drawn from the body and left at rest, it will
be found within a few minutes to have undergone the pro-
cess of clotting, the fluid first becomes a jelly, and then
a firm clot or crassamentum, taking a complete cast of the
vessel in which it is placed, and so firm in consistence that
the vessel may be inverted without any blood being lost.
In a short time on the surface of the clot fluid may be seen
which has been produced by the process of contraction, and
in the course of a few hours the clot commences to sink in
the now abundant blood-coloured serum which has collected
as the result of this process. The blood of the horse is
remarkable for the slow rate at which coagulation occurs,
and the red cells being specifically heavier than the plasma
have time to fall in the fluid before the process is com-
pleted, the result being that the upper solid la}7er is con-
siderably decolourized, forming the so-called Bufiy coat,
which though natural to the horse, is indicative in other
animals of the presence of an inflammatory process in the
system.

I have here closely followed the account given by human
physiologists of the coagulation of the blood in the horse,
but the appearance described is by no means invariable ;
coagulation of the blood in this animal is often complete in
less than five minutes, when, of course, no buft'y coat forms,
and I am inclined to believe that when life is instantaneously
destroyed, and blood at once drawn, that rapid coagulation
and non-bufty coat is the rule rather than the exception.
The fluid drawn during life in many cases also clots with
extreme rapidity.

The time occupied in coagulation varies in man from two
to six minutes; in the horse Colin puts it at from fifteen to
twenty-five or even thirty minutes, the same observer putting
the sheep and dog at four to five minutes, and the <>x at
eight minutes. In my experience the time mentioned for
the horse is exceptionally long.

If we examine the clot microscopically, it is found to
consist of fine fibrils entangled in which are the blood
corpuscles ; if the fibrin produced be washed completely

T/te Blood.

37

free from blood, its appearance is well described by its
name.

If instead of allowing the blood to clot spontaneously it
be whipped with a rod or bunch of twigs, the fibrin
separates rapidly and coats the rod, whilst coagulation in
the remaining fluid is absolutely prevented. The power
of spontaneous clotting lies then in the production of
fibrin.

These changes may be graphically represented thus :

Blood.

Blood.

Plasma.

Clotting.
I Serum.

\ Fibrin. \

(Red.
.Corpuscles. -J White.

( Mood platelets./

Clot.

(Halliburton.)

Plasma.

pit

.Corpuscles.

When Whipped.
l Fibrin.
\ Serum.
rRed.
\ White.
(Blood tablets.

j Defibrinated blood.

Fibrin is a yellowish-white, stringy-looking bulky mass ;
it may be dissolved by hydrochloric acid forming acid
albumin or syntonin ; also by dilute alkalies with the
production of alkali albumin. Its general appearance
would lead to the belief that it exists in blood in large
quantities, it is found, however, to be by weight relati
small ; in human blood its proportion is 2 per cei
sheep, -2 to S per cent. ; ox, o to -4 per cent. ; hon
•4 per cent. ; pig, -4 to '5 per cent. (Colin).

Fibrin is produced by the action of the fibrin ferment
on fibrinogen, the whole of the latter being used up in the
process. The ferment does not exist in living blood, but
is produced by the disintegration of the white corpuscles
immediately the blood is shed. Schmidt's view that
fibrin can only be produced by the action of the fibrin

88 A Manual of Veterinary Physiology .

ferment on fibrinogen and serum globulin is held to be
against the weight of evidence, which points to the
presence of serum globulin as being unnecessary to coagu-
lation.

The presence of neutral salts is necessary for the con-
version by means of the ferment of fibrinogen into fibrin ;
no fibrin can be produced in their absence. Calcium
sulphate appears to be the essential salt.

The Theories of Coagulation are very diverse, whilst
Schmidt, as mentioned above, considered that the presence
of fibrinogen, serum globulin, and the fibrin ferment, were
all necessary to the process of clotting, Hammarsten
considered that the globulin was unnecessary. Wool-
dridge believed that a substance found in the white
corpuscles, lecithin, diffused into the plasma and produced
clotting. In all cases, however, it was recognised that the
salts of the blood were absolutely essential to the process.

The term ' ferment ' in connection with] fibrin ferment, is
used more as a convenient expression than as an actual
statement of its action ; it is considered doubtful whether
it ' splits up ' fibrinogen into fibrin, and this it would pro-
bably do if a ferment.

It appears to be quite clear that fibrinogen and the
fibrin ferment are the important factors in coagulation,
for if a solution of fibrinogen be prepared in a pure con-
dition, it will clot on the addition of the ferment, even
though serum globulin be absent, the fibrinogen by itself
being non-coagulable ; conversely, if fibrinogen be removed
from a fluid the latter will not coagulate even on the
addition of the ferment. Certain pathological fluids, serum
from the chest, etc., may be made to coagulate on the
addition of a little washed blood clot, which contains the
ferment in considerable quantities. Experiments made by
injecting into the vessels of animals the active fibrin
ferment, do not lead to coagulation of the blood in the
vessels as we might suppose ; the ferment is either
destroyed, or else fibrinogen is not present; the former is
the most likely.

The Blood, 39

It is a matter of common observation, that after death
the coagulation of blood in the vessels is a slow process,
though by exposure to the air clotting is almost at once
produced ; it was supposed that the air in some way
influenced this, but it has been shown that the action
is rather due to the influence on the blood exerted by
the wall of the vessel. The jugular vein of a horse has
been included between ligatures and excised, nevertheless
the blood has remained fluid in it for one or two days,
though suspended in such a way as to be left freely exposed
to the air, yet on removal from the vein clotting will at once
occur; while suspended the corpuscles sink, and it is found
that the serum in the upper layer has considerably lost its
power of coagulation, though the blood drawn from the
lower stratum clots readily ; evidently the corpuscles take
an active part in the production of clotting. This was the
view held by Schmidt, who maintained that the white cor-
puscles were rapidly dissolved in the plasma, in the horse
to the extent of 71 7 per cent., and that the result of this
dissolution was serum globulin and the fibrin ferment.

When blood-vessels are injured during life, or when
pathological changes occur in the blood, coagulation in the
vessels will occur.

Clotting in dead blood may be retarded or hastened
by certain conditions. Blood of a horse received into a
vessel so constructed as to expose it to a freezing tempera-
ture may be kept fluid for an indefinite period, though
coagulation will at once occur when the temperature is
allowed to rise.

The addition to the blood in certain proportions of the
neutral salts of the alkalies and earths, ammonia, and
sulphate of magnesia delay clotting ; the addition of acetic
acid and a current of C02 by precipitating the fibrinogen
entirely prevent it, (venous blood which is rich in CO., is
slow in clotting). By rapidly heating blood to 133° F.
clotting is prevented, owing to the precipitation of the
fibrin-forming substances ; the addition of oil also retards
clotting. The shape of the vessel in which the coagulating

40 A Manual of Veterinary Physiology.

blood is contained has an effect on the rapidity of the
process ; a deep vessel retards coagulation, whilst a rough
and shallow one promotes it.

The Extractives of the Blood are fats, cholesterin, lecithin,
creatin, urea, hippuric and uric acids, grape sugar in small
and varying quantities. Fats occur as neutral fats, olein,
stearin, and palmatin. The amount of fat in the blood
during digestion is '4 to -6 per cent. ; in fasting animals, 2
per cent. ; in dogs fed on a fatty diet it may reach 1'25 per
cent. (Landois and Stirling). Schmidt states that there is
twice as much fat in the serum of recently fed horses as
in the serum of those kept starving. Soaps to the extent
of -05 per cent, to *1 per cent, are found; urea, -02 to -04
per cent.; sugar, -1 to -15 per cent. Bilirubin has been
found in the serum of the blood of calves (M'Kendrick).

The Difference between Arterial and Venous Blood is that
the former contains more oxygen and less CO., ; arterial
blood also contains more water, fibrin, extractives, salts, and
sugar, fewer blood corpuscles, and less urea; its tempera-
ture is, on an average, 1° C. lower (Hermann).

The dark colour of venous blood is not due to the greater
amount of C02 it contains, but to the diminution of oxygen
in the red blood-cells. The alteration in colour effected by
the addition of reagents and gases to blood, is probably due
partly to alterations in the shape of the corpuscles them-
selves, which become more concave on the addition of
oxygen and less concave on its removal: and to the fact
that oxy-lneinoglobin is brighter than reduced.

The Salts of the blood are divided between the plasma
and the corpuscles; the distribution of the salts in these
is not the same in all animals; in the horse and pig, for
example, sodium only exists in the plasma and none in the
Corpuscles, whereas in the ox and dog belli corpuscles and
plasma contain sodium; the salts of the red cells in man
and the pig consist, principally of potash, chlorides, and
phosphates; in the ox potash and phosphates are small,
lime is absent, whilst, soda is huge. In this connection the
following table from Gamgee is interesting :

The Blood.

41

Table showing the Amount of Potassium, Sodium, and Chu »ri» b
Present in 100 Parts of the Inorganic Matters or Blood
Cells and Plasma.

Blood Cells.

Liquor Sanguinis.

K.

Na.

01.

K.

Na.

CI.

Man -

40-89

9-71

21-00

5-19

37-74

40-68

Dog -

6-07

36-17

24*88

3-25

39-6S

37-31

Cat- -

7-85

35-02

27-59

5-17

3764

41-70

Sheep -

14-57

38-07

27-21

6-56

38-56

40-89

Goat -

37-41

14-98

31-73

355

37-89

40-41

To this we may add, from Bunge's observations, for the
horse, ox, and pig :

1,000 grammes of Corpuscles
contain

1,000 grammes, of Serum
contain

Horse -
Ox - -
Pig- -

K.
4-92

•747
5-543

Na.

0

2-093

0

CI.
193
1-635

1-504

K.

•27

•251

•273

Na.
4-43
4-351
4-272

CI.
3-75
3-717
3-611

According to C. Schmidt the blood contains chlorides,
sulphates, phosphates, potassium, sodium, calcium phos-
phate, magnesium phosphate, and iron, which latter is
contained in the haemoglobin. There is no iron in the
serum of the blood of any animal. The blood analyses
quoted at the end of this chapter will give some idea of
how these salts are distributed, and the proportion in
which they exist.

The use of the salts is to assist in secretion, repair, and
disintegration. The growth of the solid tissues of the
body absolutely depends on the inorganic material sup-
plied by the blood.

Water free from salts is destructive to protoplasm, no
doubt, therefore, one important function of the salts in
the blood is to maintain the vitality of the tissues. Sodium
chloride is here especially valuable, and its extensive

42 A Manual of Veterinary Physiology.

presence in blood (60 per cent, to 90 per cent, of the total
amount of ash) corresponds to its importance. As the
blood is simply the carrier of the salts, and the only means
by which the tissues can obtain them, it by no means
follows that all the mineral matter found in it is essential
to its own repair and constitution.

The Quantity of Blood in the Body can only be estimated
approximately ; direct bleeding alone does not furnish us
with a true result ; after all the blood is drained on\ the
vessels require to be washed out, and the quantity of blood
in the water estimated by the colour present ; the body
has then to be minced and macerated, and the quantity
of blood in this estimated by the colour test, comparison
being made with a standard solution of blood.

According to Colin the weight of blood in the body of
oxen is 39 lbs. ; horses, 47 lbs. (35 '2 pints) ; sheep, 41 lbs. :
pigs, 3 lbs. Sussdorf,* quoting recent experiments, puts the
proportion which the weight of the blood bears to the body
weight as being, for the horse, TV7; sheep, r\; pig, .\, : <>x. ','...

The same observer quotes the amount of blood in the
body of the horse at 66 lbs., or nearly .50 pints.

The Distribution of Blood in the Body, according to
Ranke, is as follows :

About one-fourth in the heart, lungs, large vessels, and veins.
„ „ liver.

,, ,, skeletal muscles.

,, ,, other organs.

It is probable that in the horse the liver would contain less
than one-fourth the bulk of blood, whilst the skeletal
muscles would contain more.

The abdominal veins are capable of containing the
whole of the blood in the body. When an organ is active,
it receives from 30 per cent, to 50 per cent, more blood
than when at rest (M'Kendrick).

The Gases of Blood.— The blood gases are obtained by
introducing the fluid into a Toriccllian vacuum, the in-
strument used to obtain it, being a mercury pump. In a
* Ellenbergef's ' Physiologic der Haussaugethiere.'

terial.

Venom

20

12

40

45

2

2

Z%e £Jood. 43

vacuum the blood froths up and gives off its gases, which
are then collected and analysed.

The gases found are oxygen, carbon dioxide, and nitrogen.
The proportion of these found depends upon whether the
blood be taken from an artery or a vein ; in the former the
oxygen is much larger than in the latter, and the car-
bonic acid less. The nitrogen in both cases practically
remaining the same.

At a pressure of 30 inches of the barometer and a tem-
perature of 32° F., the following gases are found in 100
volumes of blood :

Oxygen
Carbonic acid
Nitrogen

The exact amount of gas varies. The above are mean
quantities.

Oxygen exists in arterial blood in the proportion of about
20 per cent. ; whilst in venous blood the proportion is found
to vary within wide limits, depending upon the vessel from
which it is taken.

Carotid artery, O 21 percent. Renal vein (kidney active), O 17 per cent.
Renal „ „ 19 „ Renal „ (kidney passive), „ 6 „

(Landois and Stirling.)

In the blood of asphyxia oxygen is nearly absent.

It will be remembered that by far the greater part of the
oxygen is in combination with the haemoglobin of the red
blood corpuscles. It has been determined that 15 J grains
of haemoglobin is capable of absorbing '95 cubic inches of
oxygen. The serum of blood contains the oxygen simply
absorbed, the amount held in solution is therefore small.
The oxygen chemically united with the haemoglobin is quite
independent of the laws which regulate the absorption of
(see Respiration).

Besides the vacuum of the air-pump, various chemical
substances have the power of deoxidizing the blood-cells,
such reducing substances are ammonium sulphide, sul-

44 A Manual of Veterinary Physiology.

phuretted hydrogen, iron salts, etc. The proportion of
oxygen in the blood bears a relation to the amount of iron
contained by the hemoglobin.

Blood exposed to the air loses oxygen, due to decomposi-
tion leading to the production of reducing substances.

It has been supposed, owing to the readiness with which
haemoglobin parts with its oxygen, that the latter must be
in the form of ozone (Hermann) ; but this view is, however,
incorrect.

The Carbonic Acid in arterial blood is about 39 per
cent. ; in venous blood it varies, depending on the vessel.
The C02 is principally united to the sodium carbonate in
the plasma of the blood.

The Nitrogen in the blood is small in amount, about
2 vols, per cent. ; it does not vary in arterial or venous blood,
as in both cases it is simply absorbed by the plasma ;
though Fernet and Setschenow* consider that a small
portion of it is chemically combined in the blood-cells.

Chemical Composition of the Blood. — The following are the
analytical tables of the blood of animals furnished by
various authors. I have omitted a very large series given
in Simon's ' Chemistry,' from analyses made by Nasse, and
also Lehmann's analyses, published in his ' Physiological
Chemistry,' as the results do not compare with those
obtained in more recent periods, by probably more accurate
methods of inquiry :

Hoksk.

100 parts by weight of blood contain :
Blood corpuscles, 34*418, containing 12-8 per cent, of Bolids.
Plasma, G5'582, „ 10'0

(C. Schmidt, Landois, and Stirling.)

Kill /hi rts of venous blood contain :

Corpuscles

- 32*6 per cent.

Plasma -

- 67-4

The corpuscles contain :

Water -

56"5 per cent.

Solid matter

- 43-5 „

* Hermann's ' Human l'li\ siolog} ' ((iamgee).

The Blood.

4r>

The plasma contains .
Water
Solids -

The solids consist of:
Fibrin -
Albumin -
Fat

Extractives
Soluble salts
Insoluble salts

Horse (continued).

90-8 per cent.
9-2

■4 per cent.
-6

(Hoppe-Seyler and Hermann.)

Percentage Composition op Blood.

Horse.

Ox.

Dog.

(Hoppe-Seyler.) (Bunge.) (Hoppe-Seyler.)

Blood corpuscles - 33'45

31-87 35-70

Solids -

13-03

12-75 1538

Water -

20-42

19-12 20-32

Plasma

66-55

68-13 64-30

Solids -

6-50

' 5-91 5-60

Water -

60-05

62-22 58-70

(M'Kexdrick.)

1,000 Parts by Weight of Defibrinated Blood Contain

PIG.

11 OMSK.

ox.

OB

00

oj

co"S

■m 5

o"3

0 S

t-"S

cp g

O s

-- =1

OO s

t- §

CO 0

s-4

517-9

a

323-6

?D §3

420-1

CO *

a

Water

276-1

191-2

622-2

Fixed substances

160-7

45-3

207-9

48-4

127-5

59-1

Albumin and

haemoglobin -

151-6

38-1

—

—

123-6

49-9

Other organic

substances

5-2

2-8

—

—

2-4

3-8

Inorganic sub-

stances -

3-9

4-3

—

1-5

5-4

K„0 -

2-421

■154

2-62

•13

•238

•173

NaoO -

0

2-400

0

2-08

•667

2-964

CaO -

0

•072

—

—

—

•070

MgO -

■069

•021

—

-

•005

■031

Fe„03-

—

•006

—

—

•111 17

cr -

•657

2-034

1-02

1-76

•521

2-532

p2o5 - - ■■

•903

■106

•224
1

•181

(Bunge.)

46

A Manual of Veterinary Physiology.

1,000 Parts by

1,000 Parts by

Weight of Corpuscles

Weight of S

KRUM

Contain

Contain

6

x

;:

H

g i

£

O

o
599-9

=

Water

632-1

608-9

919-6

896-6

913-3

Fixed substances

367-9

391-1

400-1

80-4

103-4

86-7

Albumin and

haemoglobin -

347-1

—

387-8

67-7

—

73-2

Other organic

substances

12-0

—

7-5

5-0

—

5-6

Inorganic sub-

stances -

8-9 I -

4-8

7-7

—

7-9

K,0 -

5-543 4-92

•747

■273

•27

•254

Na„0 -

0

0

2-093

4-272

4-4:'.

4-3;, 1

Cab -

0

—

0

•136

—

•126

MgO -

-158

—

•017

•038

—

■045

Fe203-

—

—

—

—

—

Oil

01 -

1-504 1-93

1-635

3-611

3-75

.-.•717

P,05 - - -

2-067 —

-703

•188

!!

(BlJNGE.)

These tables do not compare very well, but as the analyses
were made by men whose results are of undoubted accuracy,
they are interesting as showing how the blood may vary in
composition.

Reviewing these analyses, we may say that dividing the
blood into corpuscles and plasma, that the latter consists
of—

Water

-

- 90 parts per cent

Proteids -

-

- 8 or 9 parts.

Fats

-

- 'I

Fibrin

- -2 or 4 „

Extractive-

- -4

Salts

The ( 'orpu8cles

- -8

Water -

56

parts.

Soli, Is

43

„ consisting

L)f 90 per cent, h;rmo

globin, E

per cent, proteids

Salts

1

CHAPTER III.

THE HEART.

The blood in the body has to be kept in constant motion
in order that the tissues which are depending upon it for
their vitality may be continuously supplied, and also in order
that the impure fluid resulting from these changes, may be
rapidly and effectually conveyed to those organs where its
purification is carried, out.

The heart is the organ which pumps the blood over the
body, not only distributing it to the tissues, but forcing
it on from these back to the heart again to be prepared for
redistribution. It may be described as a hollow muscle
divided into two compartments, right and left, each com-
partment being capable of division into an upper one or
auricle, and a lower or ventricle. Opening into the auricles
are large veins which convey the blood back from the body
for redistribution by the ventricles ; the two cavities are
separated by a valvular arrangement. From the ventricles
other vessels, arteries, take their origin for the conveyance
of blood from the heart.

So far the general arrangement of both right and left
sides of the heart are much the same, each having to
receive and then to get rid of a certain quantity of blood
pumped into it ; but the blood pumped into the right heart
is very different from that pumped into the left, and it is
with these differences that we must for a moment deal.

Into the right heart the whole of the impure or
venous blood in the body is brought, for the purpose of
being purified in the lungs : into the left heart the

48 A Manual of Veterinary Physiology.

arterial or purified blood is brought back from the lungs
for distribution over the body. The former is often called
the Pulmonic, the latter the Systemic circulation.

Mention has been made of valves in the cavities of the
heart ; we find them on both right and left sides separating
auricle from ventricle, known as the right auriculo-ventri-
cular or tricuspid valve, and the left auriculo-ventricular
or mitral valve. Besides these, valves are found in the
vessels arising from the ventricles, viz., in the pulmonary
artery and the aorta. These valves called pulmonary and
aortic are often spoken of as the semi-lunar valves. No
valves are found guarding the entrance of the vessels into
the auricles.

In order that we may understand the function of these
valves, which play such an important part in the physiology
of the heart, it is necessary that we should briefly detail the
course which the blood takes from the time it enters the
right auricle until it completes the round of the circulation
and rinds itself at the auricle again.

The venous blood flowing into the right auricle by means
of the anterior and posterior vena cava, passes from this
through the tricuspid valve into the right ventricle ; from
here it passes to the lungs by means of the pulmonary
artery, where having been exposed to the action of the air
and becoming greatly changed in its composition, it returns
to the heart by means of the pulmonary veins, emptying
itself into the left auricle, passing from here through the
auriculo-ventricular opening into the left ventricle, and
from thence into the aorta to be pumped all over the body
to which it is distributed by means of the arteries and
capillaries ; it is then collected by the veins, and eventually
brought back to the heart to undergo afresh its distribu-
tion to lungs and body. The use of the valves is to allow
of the transference of blood from auricle to ventricle,
and from the ventricles to the aorta and pulmonary artery
without any chance of regurgitation.

The heart occupies a position in the middle line of the
chest, being suspended from the spine by its aortic vessels.

The Heart. 49

Its base is uppermost, its apex nearly touches the sternum,
and it occupies a position corresponding to the third, fourth,
fifth, and sixth ribs ; it is between the fifth and sixth ribs,
just at their sternal insertion, where the impulse of the
heart may be felt in the horse. Its other relations are with
the diaphragm which is some five or six inches behind it,
but with which it has no connection. On its right side is
the right lung, and on its left part of the left lung. There
is a triangular notch in the left lung of the horse which
exposes the left ventricle, and allows it to make its impulse
felt against the chest wall. The anterior face of the heart is
formed by the right auricle and ventricle, the posterior by
the left auricle and ventricle.

The heart, though an involuntary muscle, does not con-
form histologically with the involuntary muscular fibre
met with in other parts of the body. It is red in appearance,
its fibres are short, striated, possess no sarcolemma, freely
anastomose, and contain a nucleus. The network formed
by the fibres of the heart is a most distinctive feature. In
some animals, sheep and ox in particular, cells of a peculiar
kind are found beneath the endocardium, they are poly-
hedral in shape, containing protoplasm and a nucleus, and
are surrounded by striated fibres. They are called the cells
of Purkinje.

The arrangement of the fibres of the heart is peculiar ;
those of the auricle are quite distinct from the ventricle,
and both are arranged in layers. Two layers have been
described in the auricle, transverse and longitudinal, with
circular fibres around the entrance of the veins, whilst in
the ventricle no less than seven layers have been de-
scribed. Owing to the peculiar direction in which these
run a somewhat spiral arrangement results, but this is not
fully accepted.

The heart is lined by the endocardium which is reflected
over the valves. The lining membrane of the left auricle of
the horse is naturally of a peculiar gray colour.

Certain fibrous rings are found in the heart where the
valves are situated, and to which these obtain a firm attach-

4

50 A Manual of Veterinary Physiology.

ment. The ring surrounding the aortic opening in the
ox has constantly in its substance one or more pieces of
bony tissue ; this is also common in the horse.

The auriculo-ventricular valves are made up of fibrous
and elastic membrane, in which a small proportion of
muscular fibre is found close to the attached border. The
mitral or bicuspid valve in the horse consists of one large
distinct segment, and several smaller ones united to form
a second. The tricuspid consists of three segments, one
much larger than the others being placed opposite to that
portion of the ventricle leading up to the pulmonary
artery.

All the valves are held in position by large and small
tendinous cords composed of fibrous tissue, which cords are
inserted into large muscular eminences found on the in-
ternal surface of the ventricle ; the cords from one eminence
do not all pass to one segment of the valve, but to two or
three. Their function is to restrain the valves from passing
into the auricle during the contraction of the ventricle.
Other bands pass from one side of the ventricle to
the opposite wall ; they are called moderator bands, and
their function is to restrain the ventricular wall from undue
dilatation.

Both the mitral and tricuspid valves meet in the most
perfect apposition when the ventricle contracts, and
nothing can escape upwards into the auricle. This may
be readily demonstrated in the dead heart by tying the
aorta and pulmonary veins, and introducing into the left
auricle a tube which admits of a powerful jet of water ; the
left side of the heart distends and hardens, and at last
water forces its way out of the side of the vessel or hole
in the auricle in which the tube is inserted. If we now
open the auricle, we find the ventricle cut off from view
by a tense membranous dome, convex towards the auricle,
which is the mitral valve in position ; not a drop of water
will escape from the ventricle, though the heart be turned
upside down, and it requires some little force to depress
the valves. The appearance is a very pretty and singular

The Heart. 51

one, and is exactly represented in Fig. 261 of Chauveau's
' Anatomy,' first edition.

The semi-lunar or sigmoid valves, which guard the
entrance into the aorta and pulmonary artery, are composed
of fibrous and elastic material, and possess at the centre of
each segment a small hard bod}7, corpus Arantii, which is
particularly marked in the aorta.

Owing to the arrangement of the muscular fibres of the
heart, we find that the auricles and ventricles are capable
of acting quite independently of each other : the two
auricles contract, and then the two ventricles. The con-
traction of either auricle or ventricle is spoken of as its
systole, whilst the dilatation is described as its diastole.
We observe that when the two auricles are in a condition
of diastole the two ventricles are in one of systole. Where
death is caused from bleeding, we find that the two ven-
tricles cease beating before the auricles, and the auricular
portion of the right auricle acts longer than the left
auricle.

A Cardiac Revolution or Cardiac Cycle, is the term used to
describe the changes which occur in the heart during the
time which elapses between one contraction or dilatation
of the auricle and the one which immediately succeeds it.
We observe that the auricles are filling with blood, which
pours into them by the vena: cavae and pulmonary veins,
owing to the fact that the pressure within the auricles is
lower than that in the bloodvessels, and also because the
efforts of inspiration favour an aspiratory effect, due to the
dilatation of the walls of the heart producing a sucking
action in the auricles, and so helping to fill them. The
auricles being full of blood the cavities contract, the
mouths of the vessels opening into them also contract
owing to the circular muscular fibres in their coats, and
so produce a slight stagnation of blood in these veins and
a distinct regurgitation in the anterior cava, which can
be readily seen at the root of the neck of most horses.
Systole of the auricle follows, the blood being driven into
the ventricles which have been partly filling during the

4^—2

52 A Manual of Veterinary Physiology.

time the blood was being collected in the auricles ; as the
ventricles fill their valves float up into position, the chordre
tending are rendered tense, and the ventricle contracts
by a peculiar wringing movement produced by the arrange-
ment of its fibres. The blood now presses against the
auriculo-ventricular valves, closing them more firmly, and
as the walls contract the imprisoned blood is forced up
into the aorta and pulmonary artery, pressing open the
valves situated here owing to the difference in pressure
between the blood in the ventricles and that already in
these vessels. During this process of ventricular contraction
a sound is produced, occasioned by the muscular contrac-
tion of the walls, and probably by the vibration of the
tricuspid and mitral valves. Neither ventricle completely
empties itself during contraction (Colin).

The blood now rushes into the aorta and pulmonary
artery, but soon the pressure in the ventricle becomes nega-
tive, viz., lower than that in these vessels, and at the same
time the elastic resistance of these arteries being brought
into play, the blood has a tendency to regurgitate towards
the ventricles and by so doing closes firmly the semi-lunar
valves, a sharp sound being produced at this moment by
their closure. While the ventricle is contracting the auricle
is dilating, and so soon as the semi-lunar valves are closed
there is a pause in the movement of the heart, during
which period the auricles and ventricles are relaxed and
blood is flowing into them ; at the end of the pause the
auricles contract and the whole process is repeated.

We have thus the contraction of the auricles, the con-
traction of the ventricles, and the pause. The periods
these occupy have been determined for the horse, by
Chauveau and Marey, by means of a cardiac sound. The
value of the periods is as follows: auricular systole, two-
tenths of a second, ventricular systole, four-tenths, and
pause, four-tenths of a second. The duration of the ventri-
cular systole always remains the same, viz . tour-tenths of a
second, no matter how fast, the heart, is beating, so that the
frequency depends not, on the time occupied in the con-

The Heart. 53

traction of the heart, but the length of the pause (B.
Sanderson).

While these changes are occurring in the cavities of the
heart, the organ itself undergoes some distinct changes in
shape and movement as the result of them. During
systole the heart becomes narrower from side to side, but
increased in width from front to rear ; it is reduced in all
its diameters excepting its vertical one, and the reduction
of its horizontal diameter assists materially in closing the
auricular ventricular valves. It also alters in shape ; during
the period of diastole it is an oblique cone with an elliptical
base ; during systole it is an upright cone with a rounded
base. This change in shape is accompanied by a rotation
of the heart to the right, and a tilting of the apex to the
left (Hermann).

This tilting outwards of the heart, due to the spiral
arrangement of its fibres, may assist in producing the impulse
against the chest wall, which in the horse occurs between
the fifth and sixth ribs. Colin insists that in the horse the
impulse is not given by the apex alone, but by the lower
half of the wall of the left ventricle. Experiments made on
some animals prove that the apex does not leave the chest
wall, but that the impulse is due to the hardening of the
ventricular wall in contact with the chest wall. This
impulse against the chest agrees with the closure of the
auriculo-ventricular valves, and the bursting open of the
sigmoid valves (Sanderson). In the horse the apex does not
rest on the ribs, but is free and directed towards the sternum.

The action of the valves of the heart during a cardiac
cycle is peculiar and interesting. We have described
how the auriculo-ventricular curtains are floated up as
the ventricle fills, and how with increased pressure they
come together, being prevented by the chordae tendinse
from being carried too far ; we have also noticed how the
reduction in the horizontal diameter of the heart assists
the action of these valves ; further, experimental inquiry
has determined that when the ventricular systole is at its
height these valves bulge upwards into the auricles,

54 A Manual of Veterinary Physiology.

assuming a concave surface towards the ventricle. This
appears to be only the case in the horse, and the informa-
tion is obtained by the researches of Chauveau and Colin.
The pulmonary valves, and probably the aortic, meet not
only at their free border but actually overlap. Chauveau
states that he has tried experimentally to hold back one
of the pulmonary valves, but the others have applied them-
selves so closely around the finger that it was impossible
to produce a patent opening. In the aorta it is probable
that overlapping does not occur to the same extent, and
here the the corpora Arantii are of value. When these
valves are not acting they lie towards the Avail of the
vessel, but do not in the aorta, as was at one time con-
sidered, cover the openings of the coronary arteries.

The elastic recoil of the aorta does not exercise its entire
pressure upon the valves, for we observe that the diameter
of the aorta at its origin is greater than the aortic opening
from the ventricle, and so the muscular substance of the
heart bears largely the shock of recoil.

The Cardiac Sounds are really four in number, but as they
are in pairs we recognise only two. The first sound is a
long one, due to the vibration of the auriculo-ventricular
valves and the muscle sound of the contracting ventricle.
The second sound is due to the closing of the semi-lunar
valves of the aorta and pulmonary artery; it is a short
sound. The two sounds are reproduced by the words ' lubb,
dn pp.'

Various instruments have been designed for the purpose
of displaying in a graphic manner the movements of the
heart, both internal and external. The internal move-
ments are ascertained by means of an instrument termed
a cardiac sound, first used by Chauveau and Marty. It is
a tube containing two hollow balls : the air in these is com-
pressed when the cavities contract, and the compression
moves a lever placed in connection with the tube. The
instrument is passed into the right heart through the
jugular vein, and into the left ventricle through the caret id.
ljurdon Sanderson states that it causes no inconvenience to

The Heart.

55

the animal, due to the fact that no sentient nerves are
supplied to the lining membrane of the bloodvessels or
even to the heart. It is doubtful to my mind whether
tracings produced by this means are completely trust-
worthy, for the presence of these two air-bags in the heart
must interfere to an extent with its normal function ; for
example, the experiment on p. 52 gives a pulse of sixty to
the minute for the horse, which is distinctly abnormal.

A tracing obtained from the heart of the horse is shown
in Fio-. 1 ; each vertical line represents one-tenth of a

Fig. 1. — Simultaneous Tracings from the Right Auricle and
Ventricle of the Horse, after Chauveau and Marey
(Foster).
The auricular curve is a, b, e, the ventricular curve a', &', c', d', e'.

b, the contracting auricle which at once relaxes, and is followed by the
sudden upstroke in the lower curve terminating at r', indicating
the sharp contraction of the ventricle, which is maintained with
certain oscillations for about three-tenths of a second, and then
suddenly relaxes ; the pause follows, a part of which may be seen
at a and a'.

second ; the curves do not indicate the' force of the stroke,
but only the intra-cardiac pressure. It is seen from the
diagram that the auricles contract first, followed by the
ventricles ; the former is slower and shorter than the ven-
tricular systole, which is sudden, maintained for some time,
and then rapidly falls. During the ventricular systole the
heart makes its impulse against the chest wall.

The impulse of the heart against the chest wall is
obtained by means of the cardiograph, of which there are

56 A Manual of Veterinary Physiology.

many forms. Their essential construction consists of a
button which is pressed upon by each impulse of the heart,
and conveys the movement to an elastic air-chamber, which
transmits it to a recording lever. By this means we get a
graphic representation of the heart's impulse.

The cardiograph demonstrates that the aortic valves close
slightly before the pulmonary.

Capacity of Heart. — The quantity of blood in the heart
can only be ascertained approximately ; measuring the
capacity of the chambers is no guide. Munk states that
the capacity of the ventricle in a horse weighing 880 lbs. is
about 1-70 pints, equivalent to 2 35 lbs. of blood : each ven-
tricle contains one-thirtieth of the total blood, so that when
both contract one- fifteenth of the total blood is ejected
(M'Kendrick). My own observations on the capacity of the
heart have not as yet enabled me to make any general
statement.

Colin gives the capacity of the left ventricle of the horse
at 1-76 pints, and states that at each systole two-thirds or
three-fourths of this quantity is injected into the aorta, viz.,
1'172 pints to 1364 pints; the left ventricle at each con-
traction, according to this observer, forces into the aorta
about one-twenty-fifth of the total blood of the body.

Colin gives the following table of capacities of right and
left ventricle :

Right Ventricle. Left Ventricle.

Pints. Pints.

Small horse - 1-42 1 -29

Medium size horse - 1*76 1*23

Big horse - 3-34 2-36

This is only a part of the table, the figures of which arc
found to vary widely. Measuring the capacity of the
heart is therefore fallacious, for in the above table each
side of the organ should have held the same quantity of
blood.

Infra-cardiac Pressure. — Though both ventricles deliver
the same amount of blood, the pressure in each ca\ it \ is
different. Chauveau puts the systolic pressure in the left

The Heart. 57

ventricle of the horse as equal to a column of blood 5'35
feet in height : in the right ventricle as equal to one 1*04
feet in height. According to Colin's experiments, made
with a manometer in the form of a long tube, the left ven-
tricle is capable of sustaining a column of blood 656 feet
high, whilst the force in the right ventricle will support in
the pulmonary artery a column of blood 164 feet high.
This, calculated on the surface of the ventricle, is equal to
a force of 72'6 lbs. for the right ventricle, and 290-4 lbs. for
the left (Colin). The right ventricle does about one-fourth
less work than the left. Munk gives the daily work of the
heart of the horse as equal to one-thirty-sixth of a horse-
power, or nearly 15-3 lbs. lifted one foot high per second.

The term Blood Pressure is frequently used in the physio-
logy of the circulatory system. It is one we shall have to
consider in detail when we come to speak of the blood-
vessels ; but we should clearly understand that the condi-
tion is due to the amount of blood pumped into the vessels
by the heart, and this amount will depend principally on
the rate at which that which is in front of it in the vessels
escapes into the veins. If the arterioles are contracted so
that the amount passing into the veins is reduced in
quantity, then a larger bulk of blood will be between the
pump and its outlets, and the blood pressure rises ; if, on
the other hand, the blood is passing rapidly through its
extensive arterioles into the veins the blood pressure falls.
When the amount poured into the venous system in any given
time, is equivalent to that pumped into the arterial system
during the same time (which is the perfectly normal con-
dition), we speak of the pressure as being a constant one.

The above facts may be tabulated as follows :

When the heart is more active the blood pressure rises.

„ „ , less „ „ „ falls.

When the arterioles contract the blood pressure rises.

,, „ dilate „ „ falls.

Nervous Mechanism. — The heart possesses no sensory
nerves ; it may be handled, pinched, pricked, or otherwise

58 A Manual of Veterinary Physiology.

injured without provoking the least sign of pain on the part
of the animal. Colin's experiments in this direction on
horses are most conclusive. Not only is the external
surface insensible to pain, but the internal surface also.
The experimental introduction of foreign bodies into the
cavities of the heart produces no pain. This fact has
been previously mentioned when speaking of the cardiac
sound.

These results are confirmed by what we know of patho-
logical processes ; those foreign bodies found so commonly
in the heart of the cow are remarkable for the fact that they
produce no suffering, though great disturbance of the circu-
lation occurs.

The nerves supplying the heart are the pneumogastric
and sympathetic. The latter has very extensive connections
with various ganglia before it reaches the heart. The
function of these two nerves is diametrically opposite.
Whilst one, the pneumogastric, has a controlling, or, as it is
termed, an inhibitory effect over the movement of the
heart, the sympathetic has an accelerating or augment-
ing effect. Histologically the two nerves differ greatly in
structure, the pneumogastric being a medullated, whilst the
sympathetic is a non-medullated nerve.

If the vagus nerve in the neck be gently excited, the
heart's beats are reduced in force and freq a< ncy ; if strongly
stimulated, the heart stops in diastole. If the nerve be
divided the heart beats more rapidly, for now the in-
hibitory power over the sympathetic is lost, and the latter
has it all its own way. When the cut end of the pneumo-
gastric is stimulated we restore to an extent the inhibitory
power, and the heart's beats become fewer and more feeble.
If the spinal cord and both sympathetics be divided, the
inhibitory power over the heart produced by the vagus is
intensified, owing to the loss of its antagonistic nerve, and
the result is that even feeble stimulation of its fibres arrests
the action of the heart.

The sympathetic is the augmenting or accelerating nerve
of the heart; and as such is the antagonist of the vagus.

The Heart. 59

SectioD of the sympathetic reduces the number of beats
of the heart, and, as we might expect, stimulation of
the cut end causes the heart to beat with increased rapidity.
Both the pneumogastric and sympathetic have a central
origin in the medulla, but in addition the sympathetic has
extensive connection with the spinal cord. We have, there-
fore, in the medulla an inhibitory and augmenting centre ;
these are both differently affected by the gases brought to
them by the blood. CO, in large quantities excites the in-
hibitory centre, whilst oxygen stimulates the augmenting
centre. The inhibitory or controlling centre is in the con-
stant exercise of its function throughout the whole life of
the animal ; this is not the case with the augmenting or
accelerating centre.

The inhibitory action of the vagus may be excited by
reflex impressions conveyed to the medulla — for instance,
fainting through shock or through blows on the abdomen,
are instances of impressions conveyed to the medulla
exciting the cardio-inhibitory centre.

The fibres conveying inhibition to the heart from the
centre in the medulla are in company with the spinal
accessory, for if these be divided, stimulation of the vagi
has no action on the heart.

If the vagus of an animal be stimulated during the ex-
periment of graphically recording the blood pressure, it is
found that almost immediately after the stimulation the
blood pressure falls, the curve being a sudden one ; when
the current is shut off, the beats of the heart return, and
the pressure rises rapidly until the normal condition is
obtained.

Contrary to what might be imagined, repeated excitation
of the vagus, when reaction sets in after withdrawing the
current, rather increases than decreases the force of the
contraction ; and, on the other hand, repeated stimulation
of the sympathetic is followed in the reactionary period by
a weakening of the heart's beats.

Gaskell does not regard either the cardiac ganglia or the
nerves supplying the heart as the cause of the beat of the

60 A Ma u mi I of Vetervna/ry Physiology.

heart, but rather that this is due to changes taking place
in the muscle itself ; and he calls especial attention to the
cellular and protoplasmic features of the heart's muscle in
support of this statement, likening the contraction of
cardiac muscle to the spontaneous movements of undif-
ferentiated primordial protoplasm.

When life is suddenly destroyed in horses by shooting
through the head, it is not uncommon for the heart to
continue beating for one or two minutes. Colin divided
the spinal cord in a horse and established artificial respira-
tion, fifteen minutes after the operation the heart was
beating 42 to the minute, and it did not cease contracting
for 50 minutes after the section. In another case the cord
and both pneumogastrics and sympathetics were divided ;
artificial respiration being established the heart beat for
24 minutes. In a third experiment the animal was
decapitated and both carotids tied ; artificial respiration
being established the ventricles contracted for 17 minutes,
and the auricles for 34 minutes.

Ganglia are found in the heart — in the frog two are well
defined, known as Remak's and Bidder's ganglia. In
mammals ganglia are found in the venae cavse and pul-
monary veins, also in the walls of the auricles, auriculo-
ventricular groove, and in the base of the ventricles. The
auricular septum in its central parts is free from ganglia
(Foster). The cardiac nerves, viz., the vagus and fibres
from the sympathetic, form plexuses around the aorta. ( hie
of the theories of the cause of left laryngeal paralysis in
horses, is that based on the anatomical position of the left
recurrent nerve relative to the aortic trunk and bronchia]
glands. Aortic compression and bronchial glandular en-
largement are the assigned causes of the muscular atrophy
of the larynx.

The right vagus nerve is said to have more influence
over the heart, than the left.

It would be outside the scopo of this work to enter more
fully into the nervous mechanism of the heart, particularly
that dealing with the nature and causes of contraction, hut

The Heart. 61

in conclusion we must briefly notice the results of Gaskell's
profoundly philosophic work in this direction. According
to this authority the vagus is the trophic nerve of the heart ;
it excites processes of repair (anabolism), builds up the
muscular tissue, and is, in fact, the nutrient nerve to this
organ ; the sympathetic, on the other hand, excites pro-
cesses of decomposition or destruction (katabolism), in just
the same way as a motor nerve passing to muscle excites
katabolic processes in the muscle elements as the result of
work. If we carefully consider this theory in conjunction
with what we have previously stated respecting the opposite
action of the vagus and sympathetic, we can see that it
receives every support.

CHAPTER IV.

THE BLOODVESSELS.

Mechanics of the Circulation.* — The laws which regulate the
flow of fluids through elastic tubes apply with equal force
to the bloodvessels.

An elastic tube converts an intermittent flow into a con-
stant one ; this it is enabled to do by the recoil of its coats
following on previous distension. The effect, however, of
the elastic reaction of the walls of the vessel is to diminish
the rate of flow, though at the same time it increases the
amount of fluid discharged.

Applying these principles to the circulation, we can
readily see their important bearing in the body, and appre-
ciate the considerable economy effected in the work of the
heart through the blood being pumped into elastic rather
than rigid tubes.

In a rigid tube as much fluid as is pumped in at one end
issues at the other, and the same will hold true for elastic
tubes unless they offer resistance to the flow. The effect of
peripheral resistance is to convert an intermittent into a
continuous flow.

In the bloodvessels, the capillaries and smallest arteries.
from their small size and considerable area, offer great
resistance to the flow of blood through the arteries; this
causes the arteries to be distended, and the clastic recoil of
the stretched walls leads to the continuous flow through
them in spite of the intermittent action of the heart .

The pressure exerted on the wall of a tube diminishes the

* ' Physiological I'Iinmc-, by M'Gregor-Robertson, lias helped me
considerably with 1 1 1 * - mechanics of the circulation.

The Bloodvessels. 63

further the tube is removed from the central pump ; this
mechanical law applies to elastic as well as rigid tubes ;
but as applied to the bloodvessels, we find that instead of
there being a gradual reduction in pressure, the latter
decreases irregularly owing to the force being used up in
overcoming the peripheral resistance. In arteries, for
example, the pressure diminishes slowly; in capillaries,
owing to the increased resistance, the reduction is very
rapid, whilst in the veins it decreases slowly.

The velocity of flow is inversely as the sectional area of
the tubes ; the total sectional area of the capillaries is
greater (about 500 times) than that of the aorta, therefore
the velocity is reduced ; from the capillaries to the heart
the area becomes smaller and the velocity increases. The
narrower the vascular bed the more rapid the flow, the
wider the bed the slower the flow.

If fluid be forced into an elastic tube, and the flow main-
tained under constant pressure, the fluid will behave as if
being forced through a rigid tube ; but if the pressure be
rendered an inconstant one, the elastic walls distend at the
increase of pressure and recoil when the pressure is re-
duced ; this distension and recoil occurs throughout the
whole length of the tube, and produces a wave which
we term in living tubes the pulse. We must be careful to
avoid the error of considering that this wave represents the
flow of blood in the vessel, it does not ; it is simply the
outcome of an impression at one end of the tube, which is
travelling very much faster along the walls of the tube
than the blood which is within.

The rate at which the wave travels depends on the elas-
ticity of the walls : the more elastic the tube the slower the
wave and the greater its height ; the more rigid the tube
the faster the wave and the less its height.

By an application of these physical principles to the living
body, we are able to account for many of the physiological
problems of the circulation in bloodvessels ; the intermittent
action of the heart, the elastic walls of the arteries, the
peripheral resistance, the increase in the width of the

64

A Manual of Veterinary Physiology.

bed of the vessels from the heart to the capillaries, and
the decrease in width from the capillaries to the heart,
account for the high blood 'pressure in the aorta, rapid
flow of blood and throbbing in the arteries, the slower flow
and lower pressure in the capillaries, and the pulseless flow
and low pressure in the veins.

We have noted that the pressure of the blood is highest
in the arteries and least in the veins ; it is this difference in
blood pressure which is the cause of the circulation ; if the
pressure were the same throughout the whole circulatory
system there would be no movement of blood, for the latter
naturally moves from the higher to the lower pressure.

By Blood Pressure we understand the actual pressure

Fig. 2. — Diagram of Blood Pressure.

a Arteries. i', Peripheral Region (minute arteries, capillaries,
and veins), v, Veins (Foster).

exerted by the blood on the walls of the vessel due to the
action of the heart ; this pressure can be measured by
suitable instruments, and is found to be in the carotid of
the horse from 8'88 feet to 13-53 feet of blood — that is, the
pressure in the vessel is capable of supporting a column of
blood from !) to 13 feet in height. The pressure is con-
stantly varying, it increases with the contraction <>!' the
ventricle and falls with its relaxation, it increases with
expiration and falls at inspiration.

As we pass from the aorta to the capillaries the Mood
pressure becomes gradually reduced : in the capillaries the

The Bloodvessels. 66

reduction is sudden, and in the veins the pressure is very
low (see Fig. 2).

In the carotid of the rabbit the pressure is equivalent to
3 feet of blood ; in the capillaries it has fallen to 1 0 or 1 5
inches, and in the veins to 1| to 2 inches only. It is pos-
sible for the blood pressure to be negative; such is observed
in the great veins opening into the heart and also in the
auricles, the negative pressure being produced by the act of
inspiration ; by its presence the flow of blood into the heart
is facilitated.

The blood pressure in the veins is from one-twentieth to
one-tenth of that in the corresponding arteries ; these
results have been obtained on vessels near the heart. The
greater distance the veins are from the heart the greater
the pressure. M'Kendrick states that experiment has
shown the blood pressure in the external facial vein of
the sheep to be 15 inches, in the brachial 2 inches, and in
the crural vein 5*8 inches of blood.

Capillary pressure is very difficult to ascertain. Du Bois
Reymoni calculates it as being one-half that in the large
arteries ; it is probable that in many places it is much less
than this.

The larger undulations obtained in blood-pressure ex-
periments are not all variations in pressure due to the
heart-beat, but largely in part to the respiratory move-
ments, the expiratory effort having on the whole the effect
of reducing the pressure in the vessels, whilst, conversely,
inspiration raises the pressure within them.

The conditions affecting the rise and fall of blood pressure
have been dealt with on p. 57 ; we have here only to notice
the effect of blood-letting upon it. Blood pressure, contrary
to what we might anticipate, is not affected until two- fifths
of the blood in the body have been removed.

We have described the recoil of the bloodvessel following
on distension. This elastic recoil produces what is known
as Tension, between which and blood pressure a clear dis-
tinction must be drawn. Blood pressure is the pressure of
the blood on the coats of a vessel, whereas tension is the

66 A Manual of Veterinary Physiology.

pressure of the coats of the vessel on the blood. The term
' tension ' is one in constant use in pathology ; pulses of high
and low tension are frequent accompaniments of disease,
and methods of measuring them have been known for some
time past. The simplest description of the apparatus for
registering the movements of a vessel is that it is a delicate
lever placed on the artery, the excursions of which are
registered on a piece of paper which travels past the end
of the lever. Such a tracing is represented in Fig. 3, from
the human carotid artery.

AAAA)W/j:VAW;.a

,4!

/VU

Fig. 3.

The up-stroke x A, in the second tracing, is due to the contraction of
the ventricle ; from A to x, in the first tracing, the blood is flowing
from the peripheral arteries to the capillaries ; the descent of
the lever is here broken by several irregularities. The first one,
p, in the second tracing, is termed the first tidal or predicrotic
notch ; the second notch in front of C is the aortic notch ; the
elevation, C, is the dicrotic or recoil wave, and is due to the
closure of the aortic valves, and the elevation, Z>, is the post-
dicrotic wave. The curve above is that of a tuning fork with ten
double vibrations in a second (Foster, after Moens).

With the exception of the aortic notch, physiologists are
not agreed as to the cause of the other irregularities in the
down-stroke. The dicrotic wave is often of considerable
practical importance, giving a dcuble beat to the pulse on
each single contraction of the heart.

The instrument which records these movements, and is
known as the sphygmograph,does not register blood pressure,
it simply registers the expansion and collapse of the tube at
the moment the wave is passing along the vessels ; it is not
a representation of the wave itself. In examining a pulse-

The Bloodvessels. 67

tracing we judge of the tension of an artery by the height
of the up- stroke. In a pulse of high tension the vessel is so
full that it can hold but little more ; the upstroke is there-
fore a short one, whilst the down-stroke is very oblique.
In a pulse of low tension the up-stroke is nearly vertical
and high, the down-stroke oblique; the vessel not being
very full is capable of holding much more fluid, and its
movements are correspondingly affected.

The Pulse is due to the wave movement set up in the
vessels, as the result of the aorta being suddenly distended
by the contraction of the left ventricle ; this wave move-
ment is very much more rapid than the progress of the blood
itself. The pulse-wave is about IS feet in length, and tra-
vels at the rate of from 15 to 30 feet a second, whilst the
velocity of the blood, even in the large arteries, is not
greater than l\ feet per second. Owing to the length of
the pulse- wave, the beginning of it is lost in the small
arteries and capillaries before the end of it has left the
aorta (Foster).

The pulse will vary in character depending upon age,
condition, height of body, and state of the system ; it also
differs according to the animal. Colin gives the following
table of pulse-rate in different animals :

Elephant

- 2;"> to 28 beats per minu

Camel -

- 28 „ 32

Horse -

- 36 „ 40

Ox

- 45 „ 50

Sheep -

- 70 „ 80

Pig -

- 70 „ 80

Dog -

- 90 „ 100 „

The pulse is much quicker in the young animal than in
the adult, that of a foal at birth beating 100 to 120 per
minute, and of a calf 92 to 132 per minute ;* in old age the
pulsations become reduced, and the artery much weaker.
As a rule, the higher or bi^er the animal the lower the

* Colin.

f>8 A Manual of Veterinary Physiology.

pulse rate. The more rapid the pulse, the greater the quan-
tity of blood in circulation.

The Velocity of the Blood varies in the arteries, capillaries,
and veins, being greatest in the former, least in the capil-
laries, and rising again in the veins. The velocity of blood-
How is due to the width of the bed formed by the vessels ;
as the arterial system expands, the velocity diminishes. In
passing through the capillaries, with their immense network,
the velocity is at a minimum ; in passing towards the heart
the vessels are reduced in number, hence the bed is less, and
the velocity accordingly increases. The cause of the flow
throughout the entire system is the contraction of the left
ventricle, aided by certain accessory movements, which will
shortly be alluded to. The velocit}' does not depend upon
the blood pressure, but upon the force of the heart and the
peripheral resistance.

The vascular system has been compared to two cones
placed base to base, the apex of one being the left ventricle,
of the other the right auricle : where the bases of the two
cones meet is the capillary network ; the sectional area of
this has been estimated as 500 times greater than that of
the aorta, whilst the passage of blood through it, owing
to the resistance experienced, is 500 times slower than in
the aorta (Volkmann).

According to the same authorit}', the velocity of blood
in the carotid of the horse is from lis inches to 15*75
inches per second ; in the metatarsal artery of the horse
2*2 inches per second ; and in the jugular vein 8*85 inches
per second. Chauvcau found in the great arteries near the
heart a velocity of 20-47 inches per second during systole ;
at the beginning of diastole 866 inches per second, and
during the pause 59 inches per second (M'Kendrick).

The velocity of the blood is increased l>\ each systole of
the ventricle, and in arteries by each expiration ; inspira-
tion, on the other hand, does not retard the flow of blood
in the thick- walled., highly-distended arteries, but assists
it in the veins. The velocity of the blood is greater in
the pulmonary than in the systemic capillaries, while the

The Bloodvessels. fi!>

velocity in the venai cavse is half that in the aorta (Landois
and Stirling).

The Duration of the Circulation depends upon the length
of time which it takes a red corpuscle to travel from a
given point and back to it again. In the horse the com-
plete circuit is performed in 31:5 seconds (Tierordt), and
is equivalent, according to the latter observer, to about
27 beats of the heart : this would give a pulse of 51 for
the horse, which is decidedly abnormal. According to
Munk, an amount of blood equal to that in the body passes
through the heart of a horse in fifty seconds, and of an
ox in forty seconds (M'Kendrick). The blood-cell spends
most of its time in the capillaries of the tissues and lungs.

The volume of an organ depends upon the amount of
blood in it. This is well exemplified in certain patho-
logical conditions, such as engorgements of the spleen,
where the organ may be as much as ten times its normal
size. Physiologically we see the same fact demonstrated
in erection of the penis.

We must now glance at the circulation through the
various systems of the body, and the methods by which it
is assisted.

Arterial Circulation. — The walls of the arteries are both
elastic and muscular ; the former condition is predominant
in the large arteries of the bod}', where an elastic resistance
is necessary to provide for the extra bulk of fluid sent out
at each contraction of the left ventricle, and where, in
addition, the elastic recoil of the vessel converts an inter-
mittent into a continuous flow : the smaller vessels, on the
contrary, are principally muscular, for they act as a tap,
and regulate the blood supply to the part through thq aid
of certain nerves known as vaso-motor.

We have previously drawn particular attention to the
fact that the pulsations in an artery represent a wave
resulting from the expansion and contraction of the larger
arterial walls, which movement travels very much faster
than the blood itself, but does not represent the progress
of the fluid in the tube.

70 A Maimed of Vetcriiinr;/ Physiology.

The Capillary circulation is readily observed microsco-
pically in the web of the frog's foot. The velocity of
blood through the capillaries depends upon their size ; in
some vessels the red cells may be seen rushing along the
centre of the tube, whilst the white ones course leisurely
along the side, exhibiting a tendency to adhere together, a
phenomenon which is not observed in the red cells of the
circulating blood : where the capillary vessels are very small
the cells only pass through one abreast, and the rate of the
current is reduced.

The walls of the capillaries are elastic, and by this means
they readily distend or recoil, and by so doing accommodate
themselves to the increase or decrease in the blood supply
to the part.

The Venous Circulation. — The contraction of the left ven-
tricle is sufficient to drive the blood all over the body, but
in the veins this force is assisted by the muscles compress-
ing the vessels, by the presence of valves which prevent
regurgitation, (especially in the veins of the limbs where
the fluid has to ascend against gravity), and, lastly, the
circulation is assisted in the larger veins by the process of
inspiration and the dilatation of the right auricle, both of
which have an aspirating effect on the blood in the larger
veins. The sucking action of the left auricle assists also
in drawing the blood in the pulmonary veins towards the
heart.

Areins are normally pulseless, but an exception must be
made to this statement in the case of the lower extremity
of the jugulars, just where they enter the chest. It is quite
common in the horse to observe pulsations in these vessels
for an inch or so up them, due no doubt to the action of
the tricuspid valve, it is, however, distinctly abnormal
for these venous pulsations to extend any distance up the
neck, for then it indicates insufficient closure of the tri-
cuspid, due to a debilitated state of the system or actual
disease of the valve itself, which latter in the horse is a
very rare condition.

There are certain veins where no valves exist — for

The Bloodvessels. 71

instance, in the sinuses of the brain and in the veins of
the foot ; in the latter case the movements occurring in the
wall, the result of expansion and contraction, are amply
sufficient to assist in the immense venous circulation of
the part.

Influence of the Nervous System. — When a part requires
more blood— for example, an actively secreting gland — the
vessels leading to it dilate ; when the necessity for the
increase has passed, the vessels contract. This dilatation
and contraction of the bloodvessels is under the control
of the nervous system, through the minute nerves known
as vaso-motor distributed to the muscular walls of the
small arteries, and it is possible that the branches of nerve
which dilate the vessels are not those which constrict them.

The nerves which contract the vessels are called vaso-
constrictor, whilst those which dilate the vessels are called
vaso-dilator : it is believed that in most cases dilatation of
the vessels is due to diminished constricting influences,
rather than to special dilator fibres.

If the sympathetic nerve in the neck of a horse be
divided, the temperature of the face and neck on the same
side rises, the skin becomes congested and sweating occurs.
In other words, the system of nerves which constrict the
bloodvessels is paralysed by division, and dilatation results.
If now the cut end of the nerve be irritated, the temperature
of the part falls, the skin congestion is removed, and
sweating ceases ; the constrictor fibres are now active, and
the amount of blood sent to the part is considerably re-
duced.

The above experiment is best made on the rabbit, where
the vessels may be seen dilating and the skin reddening.

The vaso-motor fibres may run in a sympathetic or a
spinal nerve. The sciatic nerve, for example, contains the
vaso-motor fibres for the posterior extremity, whilst the
sympathetic system contains similar fibres for the abdominal
viscera. It is said that the vaso-dilator nerves are principally
derived from the cerebro-spinal system, whilst the con-
strictors belong to the sympathetic.

72 A Manual of Veterinary Physiology.

Experiment has shown that the vaso-motor nerves over
the whole body are under the control of a vaso-motor
centre in the medulla ; certain centres exist in the spinal
•cord, but these are subordinate to the centre in the
medulla. By means of impulses passing out from this
centre, the whole of the vessels of the body are kept
under control, dilated or contracted as needful, and in
this way vascular tone is maintained.

If the vessels of a part be cut off from the vaso-motor
centre in the medulla, relaxation occurs through paralysis
of their muscular coat, and dilatation follows.

The vaso-motor centre in the medulla is situated in the
floor of the fourth ventricle ; it is readily affected by the
quality and character of the blood circulating through it
— for example, an increased venous condition of the blood
leads to contraction of the smaller arterioles ; this con-
striction means a considerable opposition to the flow
through the arteries, as the result of which the blood
pressure is raised. The rise and fall in blood pressure is
largely under the control of this centre, through the
resistance or otherwise offered to the flow of blood through
the periphery. Stimulation of the vaso-motor centre
means a constriction of the smaller vessels, but it is pos-
sible for the opposite condition to be brought about, viz.,
inhibition of the centre, in which case vascular dilatation
occurs. This is more brought home to us clinically than
physiologically. The engorgement of the spleen, portal
system, etc., seen in certain diseases, must largely be due
to inhibition of the vaso-motor centre, and a foil in blood
pressure due to the dilatation of the vessels.

In the rabbit this can be experimentally produced
through a nerve termed the depressor, which is in con-
nection with the pneumogastric, and runs from the heart ;
if the central end of this nerve be stimulated, though the
heart-beats remain unchanged, the blood pressure slowly
falls, owing to the dilatation of the abdominal vessels due
to the inhibition of the vaso-motor centre in the medulla.

Besides the vaso-motor centre in the brain, and the subsi-

The Bloodvessels. 73

diary ones in the spinal cord, there is reason to believe that
local centres exist which, so long as they are in connection
with the medulla, are subordinate to it, but may, when
separated from it, act as centres on their own account ;
this latter condition being abnormal, it is probable that the
local centres are for the purpose of keeping up a closer
touch with those in the cord and medulla, and so main-
taining the normal vascular tone.

Peculiarities in the circulation through various parts
occur as the result of their special function ; they are
observed in the brain, erectile tissues, etc. The great
vascularity of the brain necessitates that the blood should
pass to it with a degree of uniformity which will ensure
the carrying out of its functions. We see this provided
for in the frequent arterial anastomoses — for example,
the Circle of Willis and the Rete Mirabile of ruminants,
which ensures that not only does the blood enter with
diminished velocity, but that if a temporary obstruction
occurs in one vessel its work is readily performed by the
others. The rete mirabile alluded to, which forms the beauti-
ful arterial plexus on the base of the brain of ruminants, is
considered by some to regulate the flow of blood to the brain
while the head is depressed during grazing, and that it
accounts for the absence of cerebral hemorrhage in these
animals. It is probable that this may be one of its
functions ; but the horse possesses no rete, and his head is
depressed during grazing for more hours out of the twenty-
four than is the case with ruminants. It has probably,
therefore, some other function to perform.

The manner in which the vessels break up in the pia
mater before entering the brain substance, is also another
arrangement for equalizing the distribution of the blood.
The venous arrangement of the brain is very remarkable ;
the walls of the veins are composed of layers of the dura
mater, and even portions of the cranial bones may enter
into their formation. The veins or sinuses of the brain
are large cavities which, from their arrangement, are most
unlikely to suffer from compression, and from the rigidity

74 A Manual of Veterinary Physiology.

of their walls are not capable of bulging as most veins do
when obstructed ; in this way the return of the venous
blood is provided for.

The pulsations observed in the exposed brain are not
due to the pulse in the arteries of the brain, but arise from
the respiratory movements : expiration causes the brain to
rise by hindering the return of blood, whilst inspiration
causes it to fall by facilitating the return of blood.

The cerebral circulation is considerably assisted by the
presence of fluid within the ventricle of the brain. This
fluid readily passes from ventricle to ventricle, and from
ventricle to spinal cord : in this way, as the external pressure
becomes greater the internal becomes less, and so com-
pression of the brain substance is avoided.

The value of these provisions in the case of draught
horses with tightly-fitting collars is very evident ; as a
practical fact a tight collar pressing on the root of the
neck rarely produces any cerebral symptoms ; but this is
probably due to the natural provision existing to prevent
enlargement of the veins or considerable blood pressure on
the brain.

The singular arrangement of the venous plexuses of the
corpus cavernosum penis, admits of this organ attaining a
condition which in the brain every measure is adopted to
prevent — viz., avast increase in size. The enormous size of
these venous plexuses, their frequent intercommunication,
the muscular pressure to which the veins leading from the
sinuses are exposed, produce a considerable increase in the
volume of the organ under the direction of the vaso-motor
nervous system.

In some organs the vascular arrangement is peculiar,
and probably depends on the function of the part. It is
not clear, however, why the spermatic artery and plexus of
veins should possess such a remarkably tortuous course.
Doubtless, in some way or other, it is concerned with the
secretion of the glands with which the vessels are connected,
but its use is far from clear. On the other hand, tortuous
vessels in the walls of the hollow viscera, such as the

The Bloodvessels. 75

stomach and intestines, perform a very evident function.
We have only to think of the size of a collapsed and full
stomach in the horse, to recognise the necessity for some
arrangement existing to prevent stretching of the vessels or
interference with the blood supply.

The vast venous and arterial plexuses of the foot of the
horse is a peculiarity of the circulation which is dealt with
in the chapter devoted to the Foot.

CHAPTER V.

THE VASCULAR GLANDS.

Under this heading are comprised certain so-called
ductless glands or blood glands, of which the spleen is the
representative. Their function is obscure : they secrete
nothing, but they exercise a certain control over the con-
stitution of the blood and other tissues, though in some
cases even this little is unknown respecting them.

The Spleen does not appear absolutely essential to life : it
has constantly been removed without causing death. The
chief facts in connection with its function which have been
ascertained, are those relating to the formation and de-
struction of blood corpuscles. The blood of the splenic
vein contains more white cells than that of the splenic
artery, hence it has been inferred that they have been
formed in the spleen. The worn-out red cells of the blood
appear to undergo disintegration in the spleen ; more iron
is obtainable from the spleen than corresponds to the
amount of blood it contains, and this is supposed to result
from the disintegration of the red cells.

From the intimate connection the spleen has with the
stomach, and the fact that it becomes larger after a meal,
it has been supposed by some to be concerned in elaboral ing
or storing up the proteid principles of the food. Clinical
experience, especially in the tropics, constantly forces on
one the value of the spleen as a reservoir in those cases
where the blood is driven from the surface of the skin
and thrown on the viscera. After an attack of continued
fever 1 have known the spleen contain the greater part of

The Vascular Glands. 77

the blood in a horse's body, and to require two men to
lift it out of the abdomen after death.

Roy has shown that the spleen is possessed of rhythmical
movements, expanding and contracting at regular intervals
through the medium of the muscular fibres of the capsule,
and not by means of the blood pressure, of which the
circulation in the spleen is found to be independent. The
muscular movement is under the control of automatic
ganglia situated in the organ itself. Tizzoni asserts that
new splenic structures are formed in the omentum of the
horse and dog after destruction of the spleen (Landois). It
is certain that when the spleen is destroyed that the
lymphatic glands and red marrow of bones become, as a com-
pensatory effect, more active in forming red blood cells.

The Thymus is especially active during intra-uterine
existence, and for a short time after birth. It forms blood
corpuscles, in this way assisting the other tissues engaged
in this operation, at a time when the greatest activity is
required from them — viz., during early life. The thymus
disappears towards puberty ; in the horse and ox at two years
old. In hybernating animals it acts as a storehouse for fat.
The Thyroid is connected with the production of mucin in
the body, for removal of this gland gives rise to myxoudema,
or mucinoid degeneration of the tissues ; the composition
of the blood is also affected by its removal, for there is a
reduction in the number of red cells and an increase in the
white. Removal of the thyroid leads to a fatal cachexia.
Professor Horsley, whose name is intimately connected with
what is known of the functions of this body, has shown
that both ruminants and horses suffer from fatal cachexia
after removal of the thyroid. The function of this gland
is quite obscure; it is considerably more active in intra-
than in extra- uterine life.

The Anterior Renal Capsules have been supposed to be
connected with the removal of the worn-out pigment from
the body. Their function is involved in mystery.

The function of the Pineal and Pituitary bodies, though
classed as blood glands, is absolutely unknown. The pineal
is considered to be the remnant of an ancestral eye.

CHA I'TER VI.

RESPIRATION.

The means by which the blood becomes purified by passing
through the lungs must now engage our attention, but
we must first glance at the mechanism of respiration.

The lungs occupy the whole cavity of the thorax : during
life no space exists between the pulmonary and costal
pleura, so that the case is an air-tight one. So long as this
air-tight condition is maintained, any movement which tends
to increase the size of the case, such as the retreat of the
diaphragm and the advance of the ribs, causes a distension
of the sacs and the air rushes in ; by a reversed process it
is pressed out, viz., by a collapse of the chest wall. If,
however, the cavity of the chest be opened to the external
atmosphere the lungs collapse, as the pressure within and
without is the same ; such a condition would lead in the
horse to asphyxia, as the pleural cavities communicate : but
in those animals where the right and left pleural sacs are
distinct, the lung on the wounded side only would
collapse.

The process by which the chest is rilled with air,
known as Inspiration, is a purely muscular act. The
diaphragm, as the chief muscle of inspiration, recedes ; the
ribs are drawn forwards and outwards, their posterior edges
everted, the intercostal space widened ; by this means the
capacity of the chest is increased, and air rushes into the
lungs, distending them to the now increased capacity of the
chest.

Respiration. 79

The increase in the size of the chest which occurs during
quiet inspiration in the horse is stated by Colin to be as
follows: the antero-posterior or longitudinal diameter of
the chest is lengthened by 4 to 5 inches, and the transverse
diameter between the eleventh and twelfth ribs increased
by H inches.

Only the last ten pair of ribs take, under ordinary cir-
cumstances, any share in respiration ; this is due to eight
true ribs being covered by the scapula ; when, however, a
difficulty occurs in the breathing, the elbows are turned
out which brings other muscles into play as auxiliaries
in respiration, and a certain number of the true ribs now
assist in increasing the capacity of the chest.

The Movements of the Diaphragm during respiration are,
as might be imagined from the attachments of the muscle,
of a peculiar kind. The diaphragm works to and fro, not
equally over its whole surface, for the central portion
moves but very little owing to its connection with the pos-
terior vena cava, and the part of the diaphragm below this
vessel is so short that its movement is very limited.

The chief motion in the diaphragm lies in its upper part.
At each inspiration this recedes, carrying back with it the
liver, stomach, and spleen. At each expiration it advances,
carrying with it the viscera which were previously dis-
placed.

In Fig. 4 (after Sussdorf) the body is supposed to be
divided horizontally. The position of the diaphragm and
the displacement of the viscera during respiration are
clearly seen.

Expiration. — The chest having been filled with air, the
next process is its expulsion, and the mechanism here con-
cerned is not fully agreed upon by physiologists. Whilst some
hold that it is a purely non-muscular act, others contend
that certain muscles do share in the process. All are
agreed that the elastic reaction of the lung induces it to
retract, the effect being to draw the diaphragm forward,
moreover, that the elastic recoil of the cartilages of the
false ribs decreases the diameter of the chest and assists

80

A Manual of Veterinary Physiology.

the lungs in expelling the air. The compression which
the abdominal contents undergo in inspiration, causes the
abdominal muscles to descend ; this is now relieved, and
the process of expiration is further assisted by the con-
traction of these muscles, which forces the viscera forward
against the diaphragm.

The action of the muscles of the chest during respiration

Fig. 4.— Horizontal Section oe the House's Chest, looked at
kkom above, illustrating the movements of the dlaphragji.

</, right lung ; />, left lung. 1. Position of the diaphragm during deep
expiration : c, liver during deep expiration ; d, stomach during
deep expiration ; e, spleen during deep expiration. 2. Position of
diaphragm during deep inspiration : <:', position of liver; </', of
stomach ; e', of spleen during deep inspiration ; /, posterior vena
cava as ix, passes through the diaphragm (Sussdorfj.

has been much disputed. The external intercostals doubt-
less, from the direction taken by their fibres, draw the
ribs forward, and by so doing increase the transverse
diameter of the chest ; in this respect they are regarded as
inspiratory muscles. The internal intercostals, the Hbres of
which run in an opposite direction to the external, draw the
ribs backwards and act as muscles of expiration ; and speak-

Respiration. 81

ing broadly, we may say that those muscles inserted into
the anterior surface of the ribs are inspiratory, whilst those
inserted into the posterior edge are expiratory, from which
we make the following table :

Inspiratory Muscles of the Ribs. Expiratory Muscles of the Rib*.
External intercostals. Internal intercostal?.

Serratus anticus. Transversalis costarum.

Serratus magnus (during dim- Serratus posticus.

cult respiration).
Levatores costarum.

After the expiratory act there is a pause before the next
inspiration. During repose the process of expiration is
longer than that of inspiration, though the proportion
between the two is not invariable. During work, the value
of the inspiratory and expiratory acts are about equal.

During inspiration a negative pressure exists in the
trachea, and during expiration a positive pressure. In the
pleural cavity a negative pressure exists during expiration
and inspiration, due to the attempt of the elastic lung to
collapse ; the value of this intra-thoracic pressure has been
ascertained for the sheep to be about one-eighth of an
inch of mercury, and during dyspnoea a negative pressure
of three-eighths of an inch (Landois and Stirling).

We can recognise this negative pressure post-mortem by
the inrush of air produced by the collapse of the lungs
when the chest is opened.

The number of respirations will vary with the class of
animal ; as a rule, the larger the animal the slower the
respiration :

Horse

8 to 10 per minute.

Ox

- 12 „ 15 „ „

Sheep and Goat -

- 12 „ -20 „

Rumination increases the respirations, and muscular exer-
tion in all animals at once causes them to rise. In my own
experiments on respiration this has been most marked ; even
walking a horse will nearly treble the number of respira-
tions, and unless the fastest pace has been employed the

6

82 ^4 Manual of Veterinary Physiology.

respirations fall immediately the horse stops, though they do
not reach their normal for a few minutes.

The ratio of heart-beats to respiration has been placed at
1 : 4 or 1 : 5.

We have previously alluded to the influence of respiration
on the circulation, and the assistance which this renders in
aspirating the blood into both sides of the heart. The air
drawn into the veins at the root of the neck in surgical
operations is caused by this aspirating process.

Movements of Nostrils and Glottis. — Before the air reaches
the lungs it is warmed by passing through the nasal cavities,
so that it enters the chest at nearly the body temperature.
In the majority of animals air may pass either through the
nose or mouth to enter the trachea, but in the horse nasal
respiration alone is possible; we therefore lind in this animal
the nasal chambers with their inlets and outlets well
developed.

The opening into the nostrils of the horse is large
and funnel-shaped, and capable of considerable dilatation;
it is partly cartilaginous, and partly muscular. Imme-
diately inside the nostril is a large sac, which does not com-
municate with the nasal chamber; it is termed the false
nostril, and its use appears to be to simply increase the
capacity of the nasal opening by allowing considerable and
rapid dilatation. During forced inspiration the nostril ex-
pands, especially the outer segment, viz., that part in com-
munication with the false nostril, and the air is rapidly
drawn up through the nasal chambers. During expiration
the outer segment of the nostril collapses, but the inner
segment, composed principally of the cartilaginous ala,
dilates. Thus one part of the nostril is principally inspiratory
and one expiratory, producing a peculiar double movement
of the part well seen after a gallop or in acute pneumonia.

The nasal chambers of the horse are remarkable tor their
great depth and extreme narrowness ; the cavities are tilled
up by the turbinated bones, which nearly touch the septum
on each side, so that a deep but extremely narrow column
of air passes through the chambers, tho object of which

Respiration. 83

appears to be to ensure the volume of air being raised to
the proper temperature.

The air having been warmed by passing over the septum
and turbinated bones enters the glottis, the arytenoid car-
tilages of which are separated to a greater or less extent to
enlarge the opening ; in quiet respiration this enlargement
of the glottis is not very remarkable, but during work the
cartilages are powerfully drawn upwards and backwards,
and the Y-shaped glottis fully opened. It is a remarkable
fact that the glottal opening should be so comparatively
small, considering the diameter of the trachea and the size
of the nasal openings.

During inspiration the lar}rnx and trachea slightly descend
to ascend during expiration. This is particularly well seen
in horses during the hurried respirations of disease, pro-
ducing a well-marked rhythmical movement of the laryngeal
region and base of the tongue.

Kespiratory Changes in the Air and Blood. — We must now
consider the changes which the air undergoes on passing
into the lungs.

Atmospheric Am contains in 100 Parts :

By Volume. By Weight.

Oxygen - - 20-96 23016

Nitrogen - - 7901 76-985

Carbonic acid - -03

The proportion of carbonic acid is small, it is a natural
impurity in the air. The atmosphere also contains moisture
the amount of which depends upon the temperature ; the
higher the temperature the greater the amount of water
which the air can contain as vapour, and the lower the
temperature the less the amount.

Air may be dry or saturated, the latter term implying
that it contains as much vapour as it can hold at the
observed temperature ; it generally contains about 1 per
cent, of moisture, and is spoken of as dry if it contains
{ per cent. The air which passes from the lungs is always
saturated with moisture.

6—2

84 A Manual of Veterinary Physiology.

When air is taken into the lungs it loses a certain pro-
portion of its oxygen and gains a considerable amount of
carbonic acid, and perhaps some other gases. More oxygen
is abstracted from it than is replaced by carbonic acid, so
that if both volumes be reduced to standard barometrical
pressure and temperature, there is actually less air returned
during expiration than entered by inspiration; owing, how-
ever, to the expansion caused by the warming it undergoes,
the expired air is larger in volume than the inspired.

The proportion which the oxygen absorbed bears to the
carbonic acid given off is termed the respiratory quotient,

CO

and is expressed as -• The quotient varies with different

animals, and probably depends upon the nature of the

diet.

In herbivora the respiratory quotient is "9 to 1 0
In carnivora „ ,, ,, "75 „ '8

In omnivora „ „ „ '87

(Mink)*

which reads thus, for every 1 part of oxygen absorbed by
herbivora there is produced -9 to 1 part of carbonic acid,
and for every 1 part of oxygen absorbed by carnivora "75 to
•8 parts of C0.2 are produced. In carnivora it will be
observed that the amount of C0.2 produced is considerably
less than the amount of oxygen absorbed.

We have said that there are other gases returned from
the lungs besides CO., and 0 ; as very little is known about
these, we had better dispose of them at once. According to
Reiset, both hydrogen and marsh gas are given off in the
expired air of ruminants; in fact, he places the latter at
183 cubic inches in 24 hours. Both are supposed to be
derived from the intestinal canal, being absorbed into the
blood by the vessels of the intestinal wall. In my own
experiments on the gases of respiration, 1 found, after
deducting the oxygen, carbonic acid, and nitrogen, that a
balance remained, the nature of which was unfortunately

* Quoted by M'Kenariok.

Respiration. 85

not ascertained ; probably it was a mixture of these gases,
and I have spoken of them as ' undetermined '; they did
not, however, amount to 183 cubic inches in the 24 hours.
Nitrogen in small quantities may probably be given off
from the lungs of horses during rest, and Regnault and
Reiset found this to be the case in dogs, though it is denied
by Pfliiger.

We have previously learned the changes occurring in the
blood during its passage through the lungs, we have now
to study the way in which the interchange of gases
between this fluid and the air are brought about.

The law regulating the absorption of gases by fluids is
very clear; every fluid in which a gas is soluble absorbs the
same volume of gas, no matter what the barometric pres-
sure may be ; but as the number of molecules in a gas
depends upon the pressure, it is evident that the weight
of the absorbed gas rises and falls in proportion to the
pressure. This is known as the law of Dalton and Henry.

The volume of gas absorbed by a fluid depends
upon the gas ; for instance, 1 volume of water will absorb
1180 volumes of ammonia gas, whilst the same volume
of water will only absorb -00193 volumes of hydrogen.
The temperature of the water is also an important factor,
for the higher the temperature the less the gas absorbed.

If now, instead of taking a single gas to be absorbed
by a fluid, Ave take a mixture of gases, it is found
that the volume of each gas forming the mixture is ab-
sorbed as perfectly as if it were the only gas present ;
no more and no less is absorbed whether the gas be
by itself or whether it forms only a proportion of the mixed
gases present ; this is explained by Dalton as resulting
from the tact that one gas does not exercise any pressure
upon the other gases with which it forms a mixture, and
the weight of the gas absorbed depends upon the pressure.
The term used by Bunsen to define the pressure exerted by
one gas in a mixture of gases is termed the ' partial pressure."
For example, 100 volumes of air contain at freezing-point
and standard barometric pressure (30 inches) 21 volumes of

N6 A Manual of Veterinary Physiology.

ox}'gen and 79 volumes of nitrogen : what is the partial
pressure exercised by each gas in this mixture ?

30X21 _ 6*3 inches of mercury, which is the partial
1 1 id pressure of the oxygen,

and

30x79 23*7 inches of mercury, which is the partial
](J() pressure of the nitrogen.

The term ' partial pressure ' occurs so constantly in the
following pages, that the above may make the matter
clearer.

If a mixture of gases, say the atmosphere, be exposed
over a fluid already containing some of these gases dissolved
in it, it is found that if the proportion of gases dissolved in
the fluid is less than the proportion in the atmosphere
above it, the latter pass into the fluid until the amount of
gases in the fluid and that in the air above it are equal :
but, on the other hand, if the fluid contain more dissolved
gas than the atmosphere above it, gas will pass from the
fluid to the atmosphere until the amounts both in the fluid
and in the atmosphere are equal. This is really a process
of diffusion, and it is a most important physical law in
respiration, as it is the means by which the CO., passes from
the blood into the air-cells, and the oxygen from the air-
cells into the blood.

If two different gases be placed on either side of a porous
partition, in a short time a complete mixture has occurred,
as both gases will pass through the porous diaphragm in
opposite directions until a complete and equal mixture has
occurred. This is termed the process of diffusion, and is
the chief means by which the air in the deeper part of the
lungs mixes with the fresh air introduced by breathing.

Such are the physical laws which it is necessary to
understand before the processes involved in respiration can
be fully comprehended.

The blood having been robbed of oxygen in the tissues
the ha'inoglobin makes its way back to the lungs in a partly

Respiration. NT

reduced condition ; here it circulates through the vast
capillary system spread over the alveoli of these organs,
and is brought as closely as possible into contact with the
air in the ultimate air-passages. Between it and the air we
have only the membrane of the air-sac and the wall of the
capillary, both of which are bathed in fluid; through this
wet membrane the oxygen instantaneously passes, being
greedily absorbed by the haemoglobin of the red cells ; the
gas must, of necessity, first pass into the blood plasma, and
from here it is taken up by the red corpuscles.

The oxygen is not simply absorbed by the red cells but
forms with the, haemoglobin a Aveak chemical compound, for
experiment has clearly shown that the union of hemo-
globin with oxygen is largely independent of pressure, and
therefore does not obey the law of Dalton and Henry,
which it certainly would do if simply absorbed.

We have yet to learn why it is that the oxygen in the air
vesicles rushes into the capillaries to form this chemical
union with hemoglobin. Here we have one of the physical
laws brought into play which we have previously described.
When the venous blood arrives in the lungs it has lost
much of its oxygen, the partial pressure of the oxygen is
low, whereas the partial pressure of the oxygen in the
atmosphere of the air-cells is high ; the result of this is
that practically instantaneous diffusion occurs through the
moist membrane separating the gas and the fluid. The
oxygen entering the blood plasma unites at once with
hemoglobin, this latter taking up all or nearly all
the oxygen it is capable of holding, (an amount which
is infinitely greater than if simple absorption of oxygen
by hemoglobin occurred), and distributes it to the tissues
through the medium of the arterial circulation.

The tissues are greedy for oxygen, their oxygen pressure
is practically nil, once more the physical law of diffusion
occurs; the high partial pressure of the oxygen in the
arterial blood becomes, through loss of oxygen in the
tissues, low partial pressure in venous blood, and the
partly reduced hemoglobin rushes to the lungs, when the

88 A Manual of Veterinary Physiology.

process just described is repeated. But the loss of oxygen
in the tissues is not the only change the blood undergoes,
for not only is its haemoglobin reduced, but as the outcome
of tissue activity increased quantities of another gas are
added to it, the gas alluded to is carbonic acid ; this is
largely taken up by the venous blood and conveyed to the
lungs, and the method by which it is got rid of will bo
presently explained.

The changes occurring to the oxygen in the tissues are
quite unknown ; it is supposed to be stored up in some
way or other until required. It has been suggested that
the storing up in the tissues may be closely, allied to the
storing up of oxygen by haemoglobin, though with this
difference, that the tissue ox}^gen-holding substance is
more stable than the blood oxygen-holding substance. All
we do know of the fate of the oxygen is that it eventually
assists in producing certain changes in the tissues, which
lead to the production of carbonic acid and other sub-
stances ; but the changes which the oxygen undergoes
from the time, to use the words of Professor Foster, it slips
from the blood into the muscular substance, to the moment
it issues from the tissues united with carbon as carbonic
acid, constitute the whole mystery of life. We do know,
however, that the oxidations take place in the tissues, and
not in the blood as was formerly supposed.

In the systemic capillaries the partial pressure of the
carbonic acid is lower than the partial pressure of this
gas in the tissues, the result of which is that it is hurried
into the blood by the process of diffusion ; but here, as
with oxygen, simple absorption of the gas by the plasma
would not be sufficient for the purpose of carrying off the
whole of the C02 resulting from tissue activity. Now,
although there is no compound of CO, and hcemoglobin
definitely known, still there is a substance in the blood
capable of fixing CO, until the lungs are reached.

If the serum of blood be exposed to the vacuum of an
air-pump, it is found to yield little oxygen but a quantity
of C02; it yields but little O, because, as we have already

Respiration. 89

learned, this is combined in the red cells, but the fact of
its yielding large quantities of CO., points to the blood
plasma as the chief means by which this substance is
carried.

It has been determined experimentally that blood plasma
will absorb more CO., than the same quantity of water,
and it is evident, therefore, that there is something in the
plastna which assists in carrying the C02; this something
has been variously stated, but it is generally believed that
the sodium carbonate of the blood unites with a portion
of the carbonic acid, though other substances may assist.
Between the amount absorbed in the plasma, and that
held in chemical combination by certain salts of the plasma,
the total amount is carried along in the venous blood
stream, the partial pressure of the C02 in the fluid being
high; on arriving at the lungs it circulates through the
capillary network spread over the walls of the alveoli,
the same wet membrane existing between it and the
external air as was described in speaking of the oxygen.

The partial pressure of the CO._, in the air of the air-
sacs being much lower than that of the blood, diffusion
occurs between the blood and the air, the COo passing out
until equilibrium is established. The air now in the alveoli
of the lungs having lost some of its oxygen, and consider-
ably gained in its carbonic acid — in other words, having
the partial pressure of its gases altered— diffusion between
the air in the ultimate air-cells and bronchial tubes rapidly
occurs until the balance is restored, and the air in the
alveoli rendered fit for further blood-reviving processes.

Before closing this part of the subject it is necessary to
allude to the manner in which the combiued oxygen is
liberated in the tissues, and the combined CO., liberated
in the lungs, so that the law of diffusion may act, this
being, as we have now learned, the chief process by which
the balance of gases in these regions is restored.

Certain gases have a tendency to leave the substances
with which they are united when the pressure upon them
becomes reduced, this process is termed 'dissociation'; it

90 A Manual of Veterinary Physiology.

liberates the oxygen in the tissues, and assists in liberating
the C02 in the lungs from the substances with which these
are chemically combined, viz., hemoglobin and carbonate
of soda.

When an animal is compelled to breathe the same air
over and over again, there is a gradual loss of oxygen and
increase in carbonic acid, and though death will ultimately
ensue unless the air be renewed, it is remarkable that
before this occurs nearly the whole of the oxygen will
have been consumed from the atmosphere, which is further
evidence, if any be needed, that the oxygen is not simply
absorbed by the blood, and that it does not obey the laws
of pressure. Experimental inquiry has proved that animals
may live in an atmosphere containing only 14*8 per cent.
of oxygen, but that rapid asphyxia follows when the oxygen
falls to 3 per cent.

By increasing the amount of oxygen in a mixture over
and above that contained normally in air, the blood cannot
be made to take up much more oxygen than if the normal
amount only were present ; a pressure of ten atmospheres
only causes an increase of 3*4 per cent, absorbed, so that
the blood contains 234 per cent, of oxygen instead of
20 per cent. The practical application of this fact in the
treatment of certain diseases by the inhalation of oxygen
is obvious : if we double the amount of oxygen in the air.
less than 1 per cent, of the extra addition is absorbed.

Apnoea may be produced by distending the lungs several
times with air, and holding the breath ; during this period
the respiratory centre is controlled by certain impulses
occurring through the vagus.

Dyspnoea is increased respiration due to an insufficient
quantity of oxygen in the blood.

If the air supply be entirely cut off, asphyxia and death
rapidly ensue. Asphyxia has been divided into three stages.
hi the. first stage the attempts at breathing arc laboured ami
painful, deep and frequent, and all the respiratory muscles,
including the complemental ones, are brought into play :
convulsions occur, and the blood pressure rises. In the

Respiration. (.|L

second stage the inspiratory muscles are less active, the
expiratory still powerful, and the convulsions cease. In
the third stage the animal lies unconscious, occasionally
gasping, the mouth open (even in the horse), the pupils
dilated, the pulse barely perceptible or absent. During this
stage the blood pressure rapidly falls. Death occurs in
from five to six minutes from the commencement of the
first stage.

The Nervous Mechanism governing respiration may tem-
porarily be under the control of the will, but under ordinary
circumstances is independent of it. The respiratory centre
lies in the medulla, close to the deep origin of the
pneumogastric nerves ; it is supposed to consist of an
inspiratory and expiratory portion, and there are good
reasons for believing that the pneumogastric contains fibres
which lead to expirator}'- efforts on the one hand, and
inspiratory on the other. From experimental inquiry,
it is certain that the vagus contains fibres which may
have the effect of controlling and augmenting respiration.
But the nervous mechanism is by no means so simple as
the above statement might suggest. The number of
muscles brought into play during the respiratory process, and
the exact order in which they must work, necessitate the
most careful co-ordinating nervous arrangement, and that
will be fully brought home to us when we consider that
the respiratory wave from the nostrils to the diaphragm,
and from the abdominal muscles to the nostrils, must be
evenly and regularly performed.

Further, the nervous influences concerned in the process
are complicated by their connection with the spinal cord,
which under some conditions has been known to carry on
the respiratory process independent of the centre in the
medulla, though under ordinary circumstances destruction
of the centre in the medulla means instantaneous death.

If the spinal cord be divided below the origin of the
phrenic nerves there is paralysis of the intercostal and
abdominal muscles, but the action of the diaphragm is
rendered stronger, while expiration is carried out by the

92 A Manual of Veterinary Physiology.

elastic recoil of the chest wall and lungs ; division of one
phrenic nerve leads to paralysis of one half of the dia-
phragm, and of both nerves to complete cessation of its
action, inspiration being carried on by the muscles which
elevate the ribs. Division of both vagi in the neck leads
to a modification of the respiratory process though it still
continues, and division of the cord below the medulla does
not interfere with the facial and laryngeal movements.

Sussdorf states that division of the phrenic nerves in the
horse leads to increased respiration, difficulty in breathing,
the latter being chiefly thoracic ; increased heart's action,
and the fieces collect in the rectum. In about 24 hours
these symptoms pass away, and if the animals be worked
no appreciable difficulty in breathing is observed. The
result of the operation is fatty degeneration of the muscular
portion of the diaphragm.

The respiratory centre is considerably affected, not only
by the nervous influences conveyed to it, but by the quality
of the blood circulating through it. The violent respira-
tory efforts observed in the second stage of asphyxia are
said to be due to the deoxidized condition of the blood
circulating through the medulla. At one time it was
supposed that the excess of carbonic acid in the blood
stimulated the expiratory centre, whilst a deficiency of
oxygen stimulated the inspiratory movement ; this view is
not generally held at the present day, or only partly believed
to be true. The changes in the blood no doubt lead to
stimulation of the respiratory centre, but whether these
changes are due to the difference in the composition of the
blood gas, or to some other substance circulating in the
fluid, is not known. It has been suggested that sarco-
lactic acid, which is produced as the result of muscle
activity, may increase the respiratory movements and
explain the increased respiratory activity which, as we
know, accompanies rapid work.

The Quantity of Air breathed. — The amount of air passing
into a horse's lungs in an hour during perfect repose
amounts to about 80 cubic feet; it is sometimes much

Respiration. 93

higher than this ; the largest amount T ever obtained was
145 cubic feet per hour. Assuming that the animal breathes
ten times per minute, the amount of each inspiration may
be taken at 230 cubic inches. It is to be noted that the
amount of air expired, even under apparently identical con-
ditions, is liable to great variation. We have no means of
knowing the amount of the residual, reserve, or comple-
mental air which may be used.

Respiratory experiments have been made on nearly all
animals. I will principally confine my remarks to the
horse, on Avhich some very extended observations have
been carried out.

100 parts of inspired air contain ;
Oxygen - - 20-96

Carbonic acid - - -03

Nitrogen - - - 79-01

100 parts of air collected from the lungs during repose contain :
Oxygen - - - - 18 96

Carbonic acid - - 1"25

Nitrogen - - - 79*01

Undetermined gases - *78

The expired air has thus lost 2 per cent, of its oxj^gen.
and has gained 1*22 per cent, of C02. In other words, it
leaves the lungs containing about forty times more C02 than
when it entered, in addition to which there is added § cubic
foot of gases of unknown composition — probably a mixture
of nitrogen, hydrogen, and marsh gas.

More oxygen is absorbed than C02 expired, and my obser-
vations show that the respiratory quotient for the horse
at rest is -69, a figure which is much lower than that
generally quoted, viz., -9 (see p. 84).

If we take the C02 of repose at 1£ cubic feet per hour for
a horse, the carbon of this would be equal to 293 grains, or
14f ozs. in 24 hours.

These results, however, do not agree with those obtained
by Zuntz and Lehmann in Germany.* The horses used by

* Ellenberger's ' Physiologie.'

!)4

A Manual of Veterinary Physiology.

these observers absorbed more oxygen and gave out more
carbonic acid than the English cavalry horses with which I
worked, and according to their experiments the amount of
carbon produced by a horse in 24 hours is about 25.'. ozs.
Here is a table of my own, showing the respiratory changes
for one hour in a horse during perfect repose :

Cubic feet of air per hour .... 74-25

Carbonic acid expired per hour in cubic feet- - TG3

Oxygen absorbed per hour in cubic feet - - 1-13

Undetermined gases - -429

Respiratory quotient ----- -69

There are certain conditions which influence the produc-
tion of carbonic acid, of which the most important is mus-
cular work. As the result of increased muscular activity
the production of carbonic acid is considerably increased.
This increase is carried away by the blood-stream, and got
rid of at the lungs as previously explained. It is evident
that the more severe the work, or the greater the strain
thrown on the muscles, the greater the amount of CO. pro-
duced. I have endeavoured to ascertain what this amount
is for each pace of the horse, and the results of a large
number of observations are embodied in the following
table :

1

!

Atr expired

per it o;r
in cubic feet.

C02 expired

per hour
in cubic feet.

1

0 absorbed
per hour

ill ruble feet.

Respiratory
Quotient.

Gases in cubic
feet per hour.

Walk -

133-55

1-08

2-0-1

•5327

•7568

Trot -

:'S7 sT

3-98

6-47

■5917

2-5060

Canter-

3901

4-9

8*35

•5959

3-3087

Gallop-

849-1

14-97

26 07

•5743

6-6955

The above table does not agree with the elaborate re-
searches of Zuntz and Lehmann, but, then, the work per-
formed by their horses was executed on a revolving platform,
whereas work of a normal kind was performed by tho

Respiration. 95

animals experimented upon by me, though of necessity
some slight loss must have occurred in the short time
elapsing between the termination of the work and the com-
munication made between the animal and the respiratory
apparatus.

I was surprised to rind how greatly the respiratory pro-
ducts at the same pace and in the same horses varied, and
I do not believe it to be possible to obtain anything like
exact results with animals performing work in a natural
manner.

M'Kendrick, quoting from Munk, gives the following
table of respiratory changes in animals :

Gases of Rkspikation in 24 Houus.

Body Weight.

Oxygen in
cubic feet.

Carbonic Acid
in cubic feet.

Ox

1,322 lbs.

196

190

Horse

991 „

150

171

Sheep

154 „

20

20

The oxygen requirements of an animal bear no propor-
tion to its size : a small singing-bird will use up, per unit of
body weight, ten times as much oxygen as a hen. In the
human subject it has been shown that the nature of the
diet influences considerably the amount of CO., excreted
and 0 absorbed. The C0.2 is increased by giving food rich
in starch ; fats have not such a marked effect in this
direction, whilst albuminoids increase the absorption of
oxygen.

CHAPTER VII.

DIGESTION.

Prehension of Food. — The horse carries the food into the
mouth by means of his lips, which are highly endowed
with nerves and extremely muscular, the upper being the
stronger of the two. When grazing, the fodder is first
bitten off by means of the incisor teeth, and then carried
into the mouth by the lips. The upper lip of the horse
being solid he cannot bite close to the ground, and it is a
matter of common remark that he starves where sheep
thrive.

The extreme delicacy of touch with which the lips arc
endowed serves a highly beneficial purpose ; the long hairs
growing from the muzzle are all in contact with nerve-
endings in the skin.

In the choice or rejection of food the horse is mainlv
guided by the sense of smell. When grazing, the animal
invariably extends and flexes one fore-leg to enable it
to reach the ground, which, owing either to the shortness
of neck or the length of leg, it is unable to reach other-
wise.

In the ox the tongue is the organ of prehension ; it is
protruded and passed round the blades of grass, which are
nipped oil' between the incisor teeth and the dental pad.

The food having been carried into the mouth, is passed
between the teeth by means of the tongue. A considerable
anatomical difference exists between the tongue of the horse
and that of the ox, the most remarkable, perhaps, being the
smoothness of the one and the extreme roughness of the

Digestion. 97

other. The papiihe of the tongue will be dealt with in
speaking of Taste.

The prehension of liquids is caused by the formation of a
vacuum in the mouth by the pumping action of the tongue,
whilst the lips are kept tightly sealed, excepting an opening-
left in the front which is kept below the level of the water.
At each swallow the ears are drawn forwards, and during
the interval they fall backwards.

During Mastication certain movements of the jaws are
performed, to admit of which the articulation of the upper
and lower jaw is exceedingly large. The disc of cartilage
placed here between the two bones is to save the parts from
injury, and to admit of the extensive lateral or rotatory
motion so marked in the herbivora.

It is singular to observe that the upper jaw in the horse
is so much wider than the lower one ; the upper molar teeth
are also much larger. Owing to this, the tables of the
teeth instead of wearing with a level surface, present a very
oblique and chisel-shaped arrangement, the upper teeth
being sharp on the outside, the lower row of teeth on the
inside. This is an important clinical fact, sharp teeth
giving rise to much trouble and suffering.

Mastication in both horse and ox is lateral and some-
what rotatory ; that is to say, after the teeth have crossed
each other from left to right, or vice versa, the mouth is
opened, and the molars brought back to their original
position. In the horse the lateral movement occurs from
left to right, or from right to left, never from rear to front,
or front to rear. Mastication occurs on one side only, and
when that gets tired the food is passed to the other. One
side takes a long time to tire ; mastication may be per-
formed for a whole hour in one direction.

In the peculiar lateral movement of the jaws of the horse
and ox, the changes which occur in the articulation have
been pointed out by Gamgee* to be as follows : During the
rotatory movement, or lateral displacement, one of the

* 'Our Domestic Animals in Health and Disease.'

7

08 A Manual of Veterinary Physiology.

articulating heads remains as a fixed point, simply turning on
its centre, whilst its fellow describes an arc. This is why the
movement can only occur on one side at a time. The same
observer, noticing the one-sided mastication in the ox: states
that the first stroke of the molars is in an opposite direction
to the regular action which follows. Thus, if masticating
from right to left the first stroke is made from left to
right.

My own observations on the movements of the articulation
of the horse do not agree with Gamgee's. On opening the
mouth preparatory to masticating (say from right to left), the
right articulation at once rises, the left becomes depressed,
and the contents of the orbital fossa on this side bulge :
the teeth now crush from right to left, the right articulation
descending, the left ascending. As the right teeth meet
the right orbital fossa ascends ; by standing in front of the
horse we can observe that the elevation of the fossae is
alternately performed, that one on the side opposite to the
masticating surface bulging the most.

Id the horse mastication is slow, and as a rule well per-
formed ; it takes a horse from five to ten minutes to eat
one pound of corn, and fifteen to twenty minutes to eat one
pound of hay. In the ox the food does not undergo the
same amount of preliminary crushing, as by the process of
rumination it is brought back to the mouth for remastica-
tion.

The muscles which close the mouth are the masseter
internus and externus, temporalis and pterygoideus ; those
which open it are the sterno- and stylo-maxillaris and dia-
gastricus.

The extensive development of the molar teeth in all her-
bivora can be readily understood, when we remember the
wear and tear to which they are exposed in crushing the
fibrous portion of plants.

The molars wear away more rapidly than the incisors,
due to the fact that they perform more work. They become
so much reduced in length that they would not meet were
it not that the incisors become more oblique.

Digestion. 99

It is a remakable fact that in all herbivora the teeth
never leave off growing ; if one molar be removed its fellow
in the lower jaw, through the absence of friction, grows
into the space left. This is a practical fact of clinical im-
portance. In the incisor teeth the changes due to constant
growth assist in determining the age.

Deglutition comprises three stages. In the first stage
the food is passed backwards by means of the tongue
under the soft palate, which is raised to allow it to pass ;
in the second stage, the tongue is drawn upwards and
backwards, the pharynx and larynx are advanced, and the
base of the tongue and bolus close the epiglottis. The soft
palate, which in the horse reaches well into the pharynx, is
still up and cuts off the communication with the nose ;
without this provision both food and water would return by
the nostrils. In the third stage, the bolus is grasped by the
pharyngeal muscles, which contract on it from before back-
wards and gradually pass it along the u'sophagus, either
with or against gravity. In the horse and ox the passage
of the bolus along the channel of the neck can be dis-
tinctly seen.

Part of the act is under the control of the will, but once
the food reaches the fauces the action is entirely reflex ; the
closure of the glottal opening and the presence of food in
the pharynx excites the action of swallowing, which is a
purely reflex condition the centre for which exists in the
medulla. The pharyngeal muscles are remarkably strong
and stoutly grip the bolus.

Though the epiglottis closes the glottal opening, this
closure is not absolutely essential to swallowing. When the
epiglottis has been removed the base of the tongue takes
its place ; but horses can swallow when the glottis is open
— for example, when the arytenoid cartilage has been re-
moved.

Owing to the length of the soft palate in the horse, food
rejected from the stomach or unable to pass along the
(esophagus can only be returned by the nostrils.

Though the passage cf food along the oesophagus is com-

7—2

mo A Mciwdl of Veterinary Physiology.

paratively a slow process, the passage of liquid, on the
other hand, is very rapid. As many as sixty movements
may be made in a minute, the motion being capable of
occurring against gravity — for example, when an animal
drinks from the ground.

The process of swallowing solids is facilitated by the saliva.
Thus, when the salivary secretion lias been experiment-
ally diverted, swallowing only occurs with difficulty and
very slowly.

The upper portion of the oesophagus for two-thirds of its
length is composed of striped muscular fibre, though not
under the control of the will ; the lower or posterior third
consists of unstriped muscle and is exceedingly thick.

The nervous mechanism employed in swallowing is very
complicated. The swallowing centre, which is situated in
the medulla and pons Varolii, has to be stimulated, and the
muscles employed have to act regularly and in their proper
order.

The reflex act of swallowing is as follows : By means of
the sensory glossopharyngeal and superior laryngeal nerves
an impression is conveyed to the brain of the presence of
material in the pharynx : a motor impression is then sent
out, putting in action the motor fibres of the glosso-
pharyngeal supplying the muscles of the pharynx, and
causing them to contract.

The tongue is supplied with sensation by the glosso-
pharyngeal, and portions of the fifth pair ; the pharynx
by the glossopharyngeal, and the opening into the larynx
by the superior laryngeal. The motor nerves of the tongue
are the hypo-glossal, inferior maxillary division of the fifth
and branches of the facial. The palate is supplied by the
pharyngeal plexus formed by the vagus, glosso-pharyngeal,
andsympathetic ; the glosso-pharyngeal supplies the muscles
of the pharynx with motor powers, and the branches of the
fifth supply the muscles of mastication.

In ruminants swallowing is carried on by the same
physiological process. Both the mouth and pharynx are
very large and wide, and the oesophagus of considerable

Digestion. 101

.diameter ; the food can therefore be swallowed not only
with rapidity but with ease, which the physiological condition
of the stomachs of these animals requires. Reversed muscular
action of the oesophagus assists the process of rumination.

The Saliva.

During the process of mastication the food becomes mixed
in the mouth with a fluid known as the saliva ; the secretion
of which occurs in three distinct pairs of glands. The
method by which it is formed is important for us to under-
stand, as much the same process occurs in other secretory
glands which we have not the same opportunity of watch-
ing during activity.

The three glands which secrete saliva are the parotid,
submaxillary, and sublingual; and these are divided into
two systems, anterior and posterior. The former comprises
the submaxillary and sublingual ; the latter the parotid.
The two systems are further divided into mucous and
serous (or albuminous), the submaxillary and sublingual
being types of the first, the parotid the type of the last.

The salivary glands in the herbivora are of considerable
size, the anterior system in the ox being well developed,
whilst in the horse it is rudimentary. According to Colin,
there is no connection between the weight of the glands
and the amount of fluid they secrete. The parotid in all
cases secretes more than the others ; in the horse it is four
times heavier than the submaxillary, but it secretes
twenty-four times as much saliva. In the ox the parotid
is not so large as the submaxillary, but it secretes four or
five times as much saliva. The same observer places the
daily secretion of saliva in the horse at 84 lbs., and in the
ox at 11*2 lbs., though the amount will vary depending on the
nature of the food consumed ; thus, hay absorbs more than
four times its weight of saliva, oats rather more than its own
weight, green fodder half its own weight. The amount of
saliva secreted, therefore, depends on the dryness of the food.

Mixed saliva is an opalescent or slightly - turbid fluid
which readily froths. On standing it throws down a

102 A Manual of Vetcr'vao.ry Physiology.

deposit of carbonate of lime due to the removal of its carbonic
acid ; in reaction it is alkaline, and its specific gravity is
1005 in the horse, and 1010 in the ox. Saliva examined
microscopically is found to consist of granules, epithelial
cells, bacteria, and salivary corpuscles.

About "0 per cent, of the saliva consists of mineral matter,
and "2 per cent., more or less, of organic matter ; the latter
consisting of mucin, which gives saliva its well-known vis-
cidity and ropiness, and proteid bodies of the serum albumin
and globulin class. We make no mention of ptyalin, a sub-
stance of which we shall shortly speak, as it is doubtful if
it exists in the herbivora, and under any circumstances its
amount has not been determined.

Lassaigne gives the following analysis of the mixed saliva
of the horse and ox :

Ease. Ox.

Water - - - 99200 990*74

Mucin and albumin - - 2'00 • 44

Alkaline carbonates - - 1-08 .'> :!S

„ chlorides - - - 4!»_' 2-Sf>

„ phosphates and phosphate

of lime (traces) - — 2*59

Lehmann gives the following analysis of horse saliva
from the parotid :

Water -

- 990-00

Solids -

- 10-00

Mucin and epithelium j

Soluble organic matter )

4-00

Salts -

6-70

The salts of saliva are principally carbonate of lime,
alkaline chlorides, and phosphate of lime and magnesia. A

substance known as sulphocyanide of potassium has been
found in minute quantities in the saliva of the human sub-
ject, but is absent from that of the horse.

The gases of the saliva are principally carbonic acid with
traces of oxygen and nitrogen. There is no fluid in the
body which contains so much C02 as saliva.

Digestion. 103

The three salivas secreted have different physical pro-
perties. Parotid saliva is watery, clear, free from mucin,
but containing a small quantity of proteid. Submaxillary
saliva is clear, viscid, contains formed elements, and in
those animals the saliva of which is amylolytic it possesses
ptyalin. The sublingual is more viscid than the submaxil-
lary, and contains more formed elements and organic salts.

Colin has observed certain peculiarities in the salivary
secretion of herbivora which deserve our careful attention.
He has discovered that the secretion from the parotids is
unilateral ; the gland on that side of the mouth on which the
horse is masticating secretes much more than on the opposite
side ; the parotid on the masticating side gives two or three
times as much as its fellow ; the submaxillary and sub-
lingual glands, on the other hand, secrete equally, no matter
on which side mastication is being performed. Further,
the parotids secrete during rumination, the unilateral
secretion still being maintained, whilst the submaxillary
and sublingual glands are during this process in a state of
rest. In a fasting horse the parotids are quiet, whilst in
the ox they are active ; and observations tend to show that
in both animals during fasting the mouth is kept moist
by secretions from the sublingual, palatine, and molar
glands. These latter glands of the mouth are extensively
developed in the horse, particularly the palatine and some
large glands close to the epiglottis ; their secretion is viscid.

Neither the sight of food nor the introduction into the
mouth of sapid substances produce any effect over the
salivary secretion from the parotid of the horse. Sapid
substances, however, stimulate submaxillary secretion.

The use of the saliva in the herbivora is essentially that
of allowing of perfect mastication and lubrication of the
anterior digestive tract, of stimulating the nerves of taste,
and in ruminants assisting in rumination ; according to
my observations on the horse it has no chemical action on the
starch of food. So intimately, however, is salivary secretion
associated with starch conversion, that it is not possible to
pass over without further notice the action produced on

104 A Manual of Veterinary Physiology.

starch in man and the dog-, and according to some observers
in horses and cattle, by the presence of ptyalin in the saliva.

If boiled starch be mixed with filtered human saliva and
kept at a temperature of <).*> F., in a short time the charac-
teristic reaction of a blue colour with iodine disappears,
and a reddish colour is formed on the addition of this
reagent, indicating the presence of a substance known as
erythrodextrin. At this time the fluid, which before was
sugar-free, now contains distinct evidence of its presence ;
by continuing the action of the saliva it is found that
shortly the red colour on the addition of iodine has dis-
appeared, and the fluid now contains a considerable propor-
tion of sugar. Analysis shows that for the amount of starch
employed the full amount of sugar has not been obtained ;
in other words, there is a second substance present in
addition to sugar as the result of the action of the saliva.
and this is described as achroodextrin. The sugar formed
from starch by the action of saliva is not grape-sugar but
maltose, glucose (dextrose or grape - sugar) only being
found in small quantities if at all.

This action of the saliva on starch is described as the
Amylolytic action ; it is due to the presence of Ptyalin which
acts the part of a ferment. The process is destroyed by a
high or low temperature, retarded by a slightly acid or
alkaline medium, and destroyed by free hydrochloric acid.

If starch be boiled with a dilute acid conversion into
sugar occurs ; but the difference between the action of this
and saliva is, that whereas the latter can only produce
maltose the acid produces dextrose.

The view 1 hold as to the non-amylolytic action of saliva
in herbivora is not supported by other observers. Ellen-
berger* distinctly states that both the parotid and sub-
maxillary saliva of the horse and ox can convert starch
into sugar, but in the case of the horse it is only the saliva
first secreted by the gland after a rest, which possesses this
property to a high degree: as secretion proceeds the power

* ' Physiologic der Hausaaugethiere.'

Digestion. 1<>;~>

is nearly, though not entirely, lost. Ellenberger's observa-
tions are so reliable that we are bound to accept as a fact
that at some period of digestion horse saliva may possess
amylolytic properties.

Meade Smith* states that the saliva of the horse will
convert crushed raw starch into sugar in fifteen minutes,
and that the process will continue in the stomach (where
the early acidity, according to Ellenberger, is due to lactic
and not hydrochloric acid) ; he further states that horse
saliva will convert cane into grape-sugar. In ruminants
he believes the starch conversion takes place both in the
mouth and rumen.

Though I do not accept these views, we shall shortly
show how starch is converted into sugar in the horse's
stomach.

Secretion of Saliva. — The mechanism concerned in the
secretion of saliva deserves our careful attention, for the
reason that it throws considerable light on other secretory
processes. It has been worked out by so many competent
observers that the leading points in its action are beyond
all doubt. The submaxillary gland of the dog has afforded
the desired information, and we have reason to believe that
the same process holds good for the parotid and other
glands, both of this animal and herbivora.

The chief point in the secretion is that it is controlled by
the nervous system, and is independent of the blood pres-
sure in the gland. Afferent nerves, viz, the gustatory
division of the fifth and the glosso-pharyngeal, convey from
the mouth to the medulla a certain sensation, which by
means of an efferent nerve is conveyed to the gland and
secretion results. The efferent nerve of the submaxillary
gland of the dog is supplied by the chorda tympani, a small
branch given off' by the seventh cranial nerve which enters
the gland at its hilus, and supplies the vessels with dilator
and the cells with secretory fibres. How the nerve ter-
minates in the gland is unknown. The second nerve supply -

* ' A Text-book of Comparative Physiology.'

106 A Manual of Veterinary Physiology.

ing the submaxillary gland is a branch of the sympathetic,
which spreads out and invests with constrictor tibres the
walls of the artery supplying the part.

Thus the chorda tympani supplies the gland with secre-
tory fibres, and the walls of the vessels with dilator tibres,
whilst the sympathetic supplies the vessels with constrictor
fibres, and only a few secretory fibres.

If the chorda be stimulated the vessels dilate, the gland
becomes red, the blood flowing from the veins is arterial in
tint, and the veins pulsate. In addition to this, there is an
abundant secretion of watery saliva poor in solids. When
the sympathetic is stimulated the vessels contract, only a
small quantity of extremely viscid saliva flows which is
rich in solids, the blood in the veins becomes very dark
in colour, and the blood-stream slows.

That the increased flow of blood to the gland produced
by irritating the chorda does not produce the secretion, is
proved by the fact that the pressure of the saliva in the
duct of the gland is higher than the blood pressure outside
the gland. Further, if before stimulating the chorda some
atropine be injected, stimulation of the nerve still produces
to the full all the vascular changes, but not a trace of
saliva is secreted. Hence, secretion is not due merely to
increased blood pressure.

This atropine experiment proves the existence in the
chorda of the two sets of nerves, viz., of the secretory and the
vaso-dilator. Through the atropine the secretory are
paralysed, the dilators are not. Atropine does not affect
the action of the sympathetic nerve.

Twenty-four hours after the chorda has been divided ;i
watery secretion occurs, not only on the side operated upon
but on the opposite side also; this has been termed paralytic
secretion, it diminishes about the eighth day.

Though the action of the nerves on the submaxillary
gland is universally accepted, great difference of opinion
exists as to how they act. Heidenhain's view is that a gland
is supplied with a trophic nerve which excites chemical
changes in the protoplasm, and a secretory nerve which

Digestion. 107

separates the manufactured products. Building up, anabo-
lism, and breaking down, katabolism, are occurring constantly
in all the cells of the body. The cranial nerves are chiefly
secretory, whilst the sympathetic are trophic, hence stimula-
tion of the chorda gives a watery saliva poor in solids, whilst
stimulation of the sympathetic gives a scanty saliva rich in
solids.

Langley considers that this view is not tenable, and that
it is more reasonable to believe that there is only one kind
of fibre engaged in secretion, which, being mixed with
nerves having opposite actions on the bloodvessels, pro-
duces the difference in the results observed.

During secretion the temperature of the gland rises 27 F.,
and the blood in the veins is warmer than the blood in the
arteries.

The method by which secretion in the parotid gland is
carried out differs in no essential respect from that of the
submaxillary. The nerves supplying the parotid are the
glosso-pharyngeal (the action of which corresponds to the
chorda of the submaxillary) and the sympathetic ; both of
these contain secretory fibres and dilator and constrictor
nerves for the bloodvessels.

The changes occurring in the cells of the salivary glands
during secretion depend upon the nature of the gland. We
will therefore describe separately, from Langley's observa-
tions, the changes in the cells of a serous gland, such as the
parotid, and the changes in a mucous gland, of which the
submaxillary is a type. In both we distinguish certain
differences depending upon whether the gland is at rest
or whether it is active, viz., whether the cells are charged
or whether they are rapidly getting rid of the material
which has been formed. In connection with this point,
we must remember that differences in the cells may be
observed which are more accidental than real, and depend
upon the methods which have been employed in demon-
strating them. Discordant results are not, however, obtained
when by suitable means the gland-cells in the living animal
are examined during rest and activity.

IDS

,1 Manual of Veterinary Physiology.

During the stage of rest in a living serous gland, the cells
are found to be filled with a quantity of granular material,
and the outline of each individual cell is indistinct ; the
lumen of the gland is also occluded, and no nucleus can be
observed in the cells ; in other words, the gland is char!

J&%

Fig.

Parotid durini

-Changes in the Cells of tiii
Secretion.
A, at rest ; B, in the first stage of secretion ; C, after prolonged
secretion (Foster, after Langley).

with its secretory products (Fig. 5, A). During activity
the cells get rid of their granular material, which gradually
passes towards the centre of the acinus or lumen, leaving
each cell with a clear outer edge, whilst that edge next
the lumen is still granular (Fig. 5, B). In an exhausted

Fig. 6.— Cells from Mucous Gland.

a, from loaded gland ; b, from discharged gland ; a'. b\ treated with
dilute acid ; a', from loaded ; b', from discharged gland.

condition the cells are remarkably clear, only a few granules
being left in them on that edge next the lumen, which
latter is now distinct and large, and the nuclei are clearly
scon occupying a central position (Fig. .">, ( ').

If a mucous gland at rest be examined under like condi-

Digestion. 109

tions, the cells are found filled with granules much larger
than those of a serous gland, and a nucleus is seen occu-
pying one edge of the cell (Fig. (i, a . During activity the
granules are passed into the lumen of the gland, but they
do not leave behind them in the cells the same clear space
seen in the serous cell (Fig. 6, b). If the cells while in
an active condition be acted upon by water or dilute acetic
acid, they swell up and become transparent owing to the
mucin they contain, and a delicate network is seen to
invade the cell (Fig. 6, a'). A similar appearance is pro-
duced in the exhausted cell (Fig. 6, b'), excepting that less
transparent mucin is seen and more granular substance,
whilst the nucleus of the exhausted irrigated gland is seen
passing towards the centre of the cell instead of remaining
towards the outer wall.

In hardened specimens of mucous glands, towards the
outer edge in some of the acini, cells may be found shaped
like half- moons or crescents, but are not loaded with mucin,
since they stain with carmine which stains mucin with
difficulty. These crescents of Gianuzzi are not found in
hardened preparations of serous glands.

The outcome of these changes proves that the organic
elements found in the salivar}r secretion are manufactured
by the cells in the glands, whilst the inorganic constituents
are probably the result of the transudation through the
cells, of the lymph which reaches them through the lymph
passages, though experiments made by Langley and Fletcher*
go to prove that even water and salts are the result of an
act of cell secretion and not of mere transudation.

Stomach Digestion.
The subject of stomach digestion in the horse has been
worked out only by means of feeding experiments, as it has
been found impossible to establish a gastric fistula in this
animal owing to the distance the stomach lies from the
abdominal wall; pure gastric juice has, therefore, probably
never been obtained from the horse.

* Phil. Trans., 1889, vol. clxxx., B., p. 10'.'. Quoted by Halliburton.

lie A MdiKKil of Veterinary Physiology.

It is to Colin, Ellenberger, and Hofmeister that we owe
nearly all we know about the physical and chemical changes
occurring in the stomach, these observers having experi-
mented with different foods on a large number of animals
which were destroyed at certain intervals. Working on the
same lines, I have for many years carried on, as opportunity
occurred, observations of a similar nature. In this way a
large number of facts have been obtained, a summary oi
which can only be embodied in this chapter.

The first peculiarity to be noticed in soliped digestion is
that the stomach is rarely empty ; no matter at what period
of digestion observations are made, food is still to be found
in it. It is only when horses have purposely been deprived
of nutriment for not less than twenty-four hours that an
empty stomach can be obtained. On the other hand, feed-
ing experiments show that very shortly after food arrives
in the stomach it commences to pass out, and the difficulty
thus presented to the observer in reconciling these opposite
facts is at first sight insuperable.

It is perfectly true that food does pass out early, it is
equally true that it is long retained ; these opposite condi-
tions are the result of the periods of digestion. When food
enters an empty stomach it passes towards the pylorus,
where it meets with a fluid of an alkaline or neutral reac-
tion which has come from the mouth. As more food is
consumed some commences to pass out at the pylorus into
the bowel, the amount passing out not equalling at present
the amount passing in; the stomach becomes gradually dis-
tended, and when two-thirds full, which is the condition
in which the most active digestion occurs, the amount pass-
ing out will, if more food be taken, equal the amount being
swallowed, so that we have a stream of partially peptonized
chyme streaming out of the right extremity, while a cor-
responding bulk of ingesta is entering the inert Left sac.
In fact, the stomach may pass out during feeding two or
three times the bulk of food remaining in it when the feed
is finished. Let us suppose now that by this time the
'feed' is finished; at once the passage of chyme into the

Digestion. 1 J 1

duodenum ceases, or becomes so slowed down that only
small quantities of material pass out, and so slowly will
this occur that it will be many hours before the stomach
is really empty, though had the process continued as it
commenced, it would not have contained anything at the
end of an hour.

This condition of stomach digestion in the horse may be
variously modified depending on the nature of the food,
the quantity given, the form in which it is given, the order
in which one food follows another, and whether water be

Fig. 7.— Longitudinal Section of the Stomach of the Hoi:se.

CARD., cardia ; PYL., pylorus ; L.s., left sac ; R.P.. right sac ; cut., cuti-
cular coat ; vil., villous coat ; isou., boundary line between the
cuticular and villous portions ; fund., fundus of the stomach : the
dotted area indicates the position of the secretion of gastric juice.

given before or after feeding. All these are points which
require our attention, but before giving it we must briefly
look at the stomach itself.

The mean capacity of a horse's stomach is, according to
Colin, from 25 to 30 pints, or from -5 to -63 of a cubic foot.
These figures are obtained from a very large number of
observations, and give the extreme size of the organ when
distended. The viscus is under the best conditions for

112

A Manual of Veterinary Physiology.

digestion when it contains about 17^ pints, or is distended
to two-thirds of its capacity.

The mucous membrane of the stomach of the horse is
peculiar; one portion of it, practically half, is a continuation
of the membrane of the oesophagus ; this .ends abruptly,
and then the villous coat commences which runs to the
pylorus. It is in this coat that a true digestive juice is
secreted though not from the entire surface, for on examining
the villous membrane it is found to differ greatly in appear-
ance, the fundus being channelled or furrowed and velvety,
whilst the pyloric portion is smooth. It is in the fundus
only where true gastric juice, viz., pepsin and acid, is

Fig, 8.— Longitddinal Section of the Stoma< h of the Horse,

showing the Syphon Trap or the Duodenum.
u .. oesophagus ; py., pyloius ; d, left sac ; r, fundus ; duo., duodenum.

secreted, in the smooth pyloric mucous membrane only
pepsin is formed, but this will be fully dealt with presently.
The area of the membrane of the fundus-secreting surface
is about one foot square. Fig. 7 shows the relative posi-
tion of the various parts of the mucous membrane of the
stomach of the horse. The drawing accurately indicates
the shape of the stomach, the position of the inlet and
outlet, and the direction and position of the various areas.
A very remarkable amount of mucin is secreted by the

Digestion. 113

villous sac of the stomach, which forms over the surface of the
viscus a thick gelatinous firmly adherent coating like white
of egg, which cannot be washed away even by a powerful
jet of water. We shall later draw attention to its functions.

The pyloric orifice of the stomach is usually large and
open, the cardiac is tightly closed; these two openings
are situated close together. There is a distinct pyloric
ring, behind this the duodenum is dilated, and the gut here
comports itself in such a singular manner (which has a very
important bearing on the pathology of the organ) that men-
tion must be made of it here. From the pylorus the
duodenum curves down at once and then up again, forming
a letter U ; so much does this remind one of a well-known
form of trap used in drainage, that I have described it as
the syphon trap of the duodenum (Fig. 8). The use of this
trap appears to be to regulate the passage of material from
the stomach into the intestines. I have shown that its
presence in all probability influences rupture of the stomach,
for the more distended the large bowels become, the greater
the pressure exercised on the duodenum, and in cases of
severe tympany the passage from the stomach to the
intestines is completely cut off; as fermentation still con-
tinues in the stomach, and the material can neither escape
forwards into the oesophagus, nor backwards into the bowel,
the coats of the viscus are completely lacerated through the
intense strain.

The physiological points of interest in the structure of
the horse's stomach are : 1, its small size ; 2, not being in
contact with the abdominal wall, but resting on the colon ;
3, the outlet and inlet situated close together ; 4, the con-
tracted cardia; 5, only a portion of its surface being capable
of secreting a digestive fluid ; 6, the remarkable differences
in its mucous membrane.

We must now return to the points which we have pre-
viously stated as possessing an important influence on the
process of gastric digestion.

The length of time food remains in the stomach will
depend upon its chemical composition and bulk, also as

8

114 A Manual of Veterinary Physiology.

to whether more than one kind of food is partaken of at the
same time; bulky food, such as hay, passes out more rapidly
than condensed food, such as oats. Oats contain consider-
ably more nitrogenous matter than hay, therefore a longer
period must be devoted to their digestion in the stomach :
we will, therefore, consider first of all the digestion of hay,
then that of oats.

Digestion of Hay. — Hay, as we have shown, mixes in the
mouth with four times its bulk of saliva, and after a very
perfect grinding passes into the stomach ; assuming the
stomach to be empty, it passes at once to the right side ;
the gastric juice begins to act, and, as before described,
chyme commences to pass into the intestines probably in a
very imperfectly elaborated form. Assuming the animal to
have finished the hay, we now find the output into the
intestine becomes small and slow ; the gastric juice has an
opportunity of acting upon the ingesta, which turns yellow
on that surface in contact with the stomach-wall ; the
compression of the latter on the contents causes them to
become distinctly moulded into a mass, the shape of the
stomach, being more fluid towards the pylorus than else-
where. The greater curvature in all probability is fuller
than the lesser. The material is perfectly comminuted,
and resembles firm, dry, green and yellow fajces, and the
smell is peculiar, like sour tobacco.

The yellowness is due to the gastric juice, and is conse-
quently more marked towards the pylorus ; the portion
coloured green is the part as yet unacted upon by the juice.
The total surface of the stomach and its contents are now
acid, though Colin says otherwise. The acidity is greater at
the fundus than at the cardia. This acidity shows that a
diffusion of the gastric juice must have been going on.
There is no evidence of any churning motion, the cake-
like condition into which the hay is compressed in spite of
its four equivalents of saliva is due to the compression of
the material by the stomach walls.

The duration of stomach digestion of hay is variable, but
I quote one or two of Colin's experiments. A horse

Digestion. 115

received oh lbs. of hay, which he took two hours to eat ;
at the end of that time he was destroyed, and the stomach
contained 22 lbs.; thus in two hours he had digested
3-3 lbs. Another horse received oh lbs. hay, and was de-
stroyed three hours from the time of commencing to feed ;
in the stomach was found ]-54 lbs. ; in three hours he had
digested 396 lbs. ; in the third hour (during which time he
was not feeding), judging from the first experiment he had
digested only '66 lb., whereas the previous rate of digestion
for the first two hours was at the rate of V65 lbs. per hour.
To return to our previous statement, when the animal is no
longer feeding the rate of digestion at once becomes re-
duced, and it is probable that several hours must elapse,
assuming no further food be given, before the stomach
completely empties itself. This period may be fifteen,
eighteen, twenty-four to thirty-six hours.

I starved a horse for twenty-four hours, and at 6 a.m.
gave him G lbs. of dried grass ; he was destroyed at 3 p.m.,
and the stomach still contained 2h lbs. ; in nine hours,
therefore, only Sh lbs. had been digested. In another
observation carried out under similar conditions, only 1 lb.
had been digested in four hours and three-quarters. Of
4 lbs. hay given only 1 lb. 11 ozs. was digested in six hours ;
of 3h lbs. hay, 2^ lbs. were digested in five and a half hours,
and of 4< lbs. hay, 2 lbs. 12 ozs. were digested in five hours.

Colin's elaborate researches furnish us with very complete

data on the question of hay digestion in the horse. He fed

fourteen horses on hay, and destroyed two of them at regular

intervals ; each animal received 5 "5 lbs. of hay, and digestion

was counted from the time they were fed. Here are the

results :

Amount of Hay given, 5*5 Lbs.

lbs.

lbs.

After 2

hours, the first horse had digested 3-37 ;

the second, 3-08

„ 3

,i it »

3-83

4-24

„ 4

11 >! ))

4-04

3-56

n 5

•1 -1

4-32

5-03

„ 6

„

440

4-55

» 7

H

4-01

4-35

» 8

•) »

4-87

4-44

8—2

116 A Manual of Veterinary Physiology.

We observe that the rate of digestion during the first two
hours is rapid, and it then falls off, so that even at the end
of eight hours there is still something left in the stomach.
The second horse in the five hours' observation had very
nearly digested the whole of the ration, but this is an ex-
ception.

There is no doubt that it is extremely difficult to get the
stomach to empty itself. I fed a horse on dried grass and
destroyed it eighteen hours later ; there was still a small
quantity of food in the stomach. In another case the
stomach, after fifteen hours, was found empty. In a third
case a horse was given grass twice at intervals of twenty-
four hours. He Avas destroyed eighteen hours after eating
his last feed, and a handful of grass was still found in his
stomach.

Digestion of Oats. — We must now consider the digestion
of oats, and here we observe the same remarkable fact noted
under hay, viz., that the stomach commences to pass its
contents into the intestine during feeding, and that this
considerably slackens when no more food is entering the
viscus. Colin fed six horses on 5*5 lbs. of oats each, and
destroyed them at certain intervals.

lbs. lbs.

After 2 hours one horse had digested 2'728 : a second, 2*5564
„ 4 „ „ „ 3-095 „ 3-4562

„ 6 „ „ „ :$-553 „ 3-0250

I have observed in a horse which had received 2 lbs. of
oats, and was destroyed twenty hours later, that the stomach
had not completely emptied itself; in another experiment
four hours after feeding on 1 lb. of oats, I recovered 6 ozs.
from the stomach.

A horse received

And was destroyed in

Amount digested,

/I/.-:, oatx.

hours.

lb8. o:s.

4

4

2 3

3

.

4.1,

1 111

4

•1

2 4

3

.

;ii

2 24

3

.

4

—

4

.

4

1 l ••>.'.

3

.

r..'.

2 Gi

4

.

4"

3 0

4

-

4

0 12

Digestion.

117

I include the last horse to illustrate a point of some little
importance in the feeding of animals. For eighteen months
d d

Yig. 9. —Longitudinal Section op the Horse's Stomach,
showing the arrangement op the food according to the
order in which it was received.

In each case ce. is the oesophagus,^?/., pylorus ; d, the left sac ; v, the
fundus. /. Hay first, followed by oats : b, the hay ; a, the oats ;
the latter are passing along the lesser curvature and escaping with
the hay at the pylorus. II. Oats first, followed by hay : a, the
oats ; b, the hay. Ill The order of three successive feeds : c, the
the first feed ; b, the second ; a, the first (Ellenberger).

this horse had never tasted corn, having been fed on a
patent food ; a sudden change in diet is the explanation

118 A Manual of Veterinary Physiology.

why it only digested 12 ozs. of oats in four hours. It will
be observed that the fifth horse in this series digested
nothing, even at the end of four hours ; I can only account
for this by the animal being in a strange place where the
feeding experiment was carried out, and being of a very
nervous disposition.

Arrangement of Food in the Stomach. — An interesting
practical and physiological study is the effect of feeding
horses on different foods in succession. When hay is given
first and oats afterwards, the hay is found close to the
greater curvature and pylorus, and the oats in the lesser
curvature and cardia. No mixing has occurred ; both
aliments are perfectly distinct, and a sharp line of demarca-
tion exists between them (Fig. 9, I.). The presence of the
oats, however, has caused the hay to pass out more rapidly
than it would have done had it been given alone. Colin
observed that half the hay, but only one- fourth or one-
sixth of the oats, would, under these conditions, pass into
the intestine in two hours. During digestion a mixing
of these foods occurs at the pylorus, but nowhere else.
Ellenberger has shown that when hay and oats are given
in this order, a portion of the oats may pass out into the
bowel by the lesser curvature without entering either cardia
or fundus of the stomach (see Fig. 9, I.). No matter what
compression the contents have undergone as the result of
gastric contractions, the foods always remain distinct.

When oats are given first, and followed up by hay, the
oats commence to pass out before the hay ; but the presence
of the hay causes the oats to pass more quickly into the
intestines (Fig. 9, II.).

We may summarise these facts by saying that in a BUC
cession of foods the first taken passes out first; that does not
mean to say that the whole of it passes out before any por-
tion of the succeeding food enters the bowel, for we have
shown that after a time at the pylorus they mis and pass out
together; but the actual influence of giving a food first is
to cause it to pass out first. The practical deduction is that,
when foods are tnven in succession, the least albuminous

Digestion. 119

should be given first. This appears to distinctly reverse the
English practice of giving oats first and hay afterwards,
but perhaps only apparently so, for experiment shows that
the longer digestion is prolonged, the more oats and the less
hay pass out, so that some hay (under ordinary circum-
stances a considerable quantity) is always left in the
stomach until the commencement of the next meal. Now,
the presence of this hay from the previous feed may pre-
vent the corn of the succeeding feed from passing out too
early. Ellenberger says that in order that horses may
obtain the fullest possible nutriment from their oats, hay
should be given first and then water, which carries some of
the hay into the bowel ; after some time the oats are to be
given. The hay now passes into the bowel, and the oats
remain in the stomach. This will hardly fit in with our
English views of feeding and watering.

If a horse be fed on three or four foods in succession,
they arrange themselves in the stomach in the order in
which they arrived, viz., they do not mix ; the first enters
the greater curvature, the last the lesser curvature, and it
is only at the pylorus that any mixing occurs under ordinary
conditions (Fig. 9, III.).

This regular arrangement of the food in layers, when
taken in succession, is only disturbed when a horse is
watered after feeding ; under these circumstances the con-
tents are mixed together and digestion thereby impeded.
Apart from this, the ingestion of a considerable quantity of
fluid into a stomach already containing as much as it
should hold, means that material is washed out of the
stomach into the small intestines, and this sets up irritation
and colic. In this way more than half the food may be
washed at once out of the stomach. The water which a
horse drinks does not remain in the stomach, but passes
immediately into the small intestines, and in the course of
a few minutes finds its way into the caicum ; hence we have
the golden rule of experience that horses should be watered
first and fed afterwards.

The appearance of the food in the stomach depends upon

120 A Manual of Veterinary Physiology.

the period of digestion ; we have previously drawn attention
to the fact that an hour or two after hay has been taken,
the material is found in a finely chopped condition, firm,
one may almost say dry in places, though towards the
pylorus it is liquid. This ha}' contains between four and
five parts of saliva ; is yellow in colour where the gastric
juice has attacked it, but rather of a greenish tint else-
where. It has a peculiar odour. Some hours after a feed
the stomach is found to contain a variable quantity of
watery fluid discoloured by the hay which is left behind,
part of which may be found floating on the fluid. At
other times, when the stomach is empty, the fluid is viscid,
contains numerous air bubbles, and is of an amber or
yellow tint. This particular fluid is no doubt saliva and
mucin, with possibly a little bile.

When oats alone have been given the contents of the
stomach are found liquid, the fluid being creamy in con-
sistency and colour ; the oats are swollen, soft, and their
interior exposed. Towards the end of digestion the creamy
fluid is repfaced by the frothy yellow one. With both hay
and oats, and also other foods, there is a peculiar sour-
milk-like smell from the contents of the stomach, more
marked with bran and oats than with hay, which, as
previously mentioned, smells like sour tobacco.

The reaction of the contents of the stomach is strongly acid ;
this acid reaction may be obtained on the cuticular as well
as the villous portion of the viscus, and is very persistent :
the cuticular membrane even after prolonged washing-
gives an acid reaction. The acidity is derived entirely from
the juice secreted by the villous membrane of the fundus.

My observations on this subject do not agree with those
of Ellenberger, who says that during the first hour of
digestion the stomach maybe alkaline; acidity then com-
mences in the fundus and extends to the eanlia, though
for some time the proportion of fundus acidity is three or
four times greater than that of the cardia; in the course
"f live or six hours the proportion of acid throughout the
stomach is equal.

Digestion. 121

When the stomach is empty, as after a few days' starva-
tion, its reaction is neutral or alkaline. I have observed
extreme alkalinity towards the pylorus under these con-
ditions, due no doubt to the regurgitation of bile and
pancreatic fluid.

The Stomach Acids. — It is not necessary here to enter into
a long discussion on the nature of the gastric acids. Both
in the horse and man a considerable amount has been
written to prove that the acidity depended upon lactic or
hydrochloric acids. It is possible that both these views
may be reconciled. Ellenberger and Hofmeister are of
opinion that immediately after a meal lactic acid predomi-
nates in the horse's stomach, to be replaced by hydrochloric
at about four or five hours from the commencement of
feeding. These observers found that the nature of the acid
depends upon the region of the stomach, the period of
digestion, and the nature of the food, oats inducing an
outpouring of hydrochloric acid, whilst hay favoured the
organic acids, as seen in the following table :

Total

Hydrochloric

Lactic

Acid.

' Acid.

Acid.

•045%

•0163%

•0287%

•110%

•049%

■061%

•182%

•002%

•no;;

On a diet of chopped straw and oats
On a diet of oats
On a diet of hay

In the contents of the stomach, hydrochloric, lactic,
butyric and acetic acids may be found, the two latter in
insignificant quantities only. In flesh feeders HC1 pre-
dominates 25 per 1,000, and lactic, in small quantities,
•07 per 1,000. In grain feeders lactic acid at first pre-
dominates, and later HC1 in small quantities. Lactic acid
exists throughout the whole stomach, but predominates in
the right and left sacs, whilst hydrochloric acid principally
exists in the fundus region. Lactic is the first digestive
acid employed, but towards the end of digestion hydro-
chloric exists throughout the whole stomach. The amount
of lactic acid found in the stomach of the horse during the
first hours of digestion is considerable, amounting to If ozs.
or even as much as 31 ozs. (Ellenberger;.

122 A Manual of Veterinary Physiology.

Having gone very carefully into the question of the
presence of hydrochloric and organic acids in the stomach
contents, I can only say that, no matter at what period of
digestion I have made the observation, I have never yet
succeeded in finding hydrochloric acid in the stomach of
the horse, and I am convinced that lactic is the chief,
if not the sole, digestive acid in this animal.

The Secretion of Gastric Juice is accomplished in certain
glands, known as the gastric glands. In man these are
divided into cardiac and pyloric glands, each having not
only a different structure, but a distinct function. In the
horse cardiac glands are impossible, owing to the presence
of the cuticular coat ; but it has been shown that the
villous coat contains glands corresponding to cardiac,
which are principally situated in the greater curvature, not
far from the margin of the cuticular coat, and extending
over a comparatively small area, described on p. 112 as not
larger than 1 foot square, this portion of the stomach being
known as the fundus (Fig. 7). Mucus is secreted in large
quantities by the villous coat of the horse's stomach, and
is formed principally in the fundus. This mucus is
secreted by the epithelial cells lining the villous coat and
the upper portion or outlets of the gastric glands.

The two kinds of gland employed in the production of
gastric juice are both found in the villous coat, the one
in the fundus, the other in the pyloric portion. They are
simple or divided tubes lying side by side, and opening
generally in groups on the surface of the mucous membrane
by means of a shallow depression in the coat, which can
readily be seen studded over the tunic of the fundus, giving
it a rough appearance owing to the elevation of the mucous
membrane between the openings of the glands, whilst in
the pyloric region the membrane is as smooth as that found
in the intestine. Each gland consists of a body, neck, and
mouth, and is lined with cells. It is in respect of the
cellular contents that the so-called pyloric and fundus
glands differ.

The cells of the fundus glands aro small, polyhedral,

Digestion. 123

granular, and nucleated ; those which line the lumen of
the gland are called the principal cells. Scattered amongst
the principal cells, but existing in larger numbers at the neck
of the gland than at its base, are found certain large cells
(oval, granular, and nucleated), which from their position
relative to the lumen of the gland are called parietal,
marginal, or border cells. These cells are distinctive of
the fundus glands, and they stain readily with aniline blue.

The pyloric gland has below its neck but one variety of
cell — viz., the cylindrical — containing a nucleus at its
attached edge. The duct is lined above the neck by the
ordinary epithelium of the stomach, and the same remark
applies to the cardiac glands ; it is from this epithelium
that the mucus is secreted. Lying deep in the mucous
membrane of the stomach between the gastric glands may
be found large mucus secreting glands, which, doubtless,
contribute to the formation of the remarkable amount of
mucin found in the stomach of the horse.

The difference in the structure of the follicular glands of
the stomach depends upon their function. The important
distinction between the fundus gland with its principal and
parietal cells, and the pyloric gland with its principal cells
only, is that the former secretes both the pepsin and acid
of the gastric juice, the acid being separated from the
blood, or secreted, by the parietal cells, whilst the pepsin
only is formed by the principal cells ; the pyloric glands,
on the contrary, only secrete pepsin and no acid.

Ellenberger states that he has found fundus glands in
the pyloric region.

We have previously mentioned that the cells of the
salivary glands undergo certain changes in appearance, the
result of rest and activity ; the same remark applies to the
gastric follicles. These changes have been worked out by
Heidenhain and Langley. The former found that the large
marginal cells of the fundus glands during activity — viz.,
digestion — bulged from the side of the gland and en-
croached on the lumen, and also became much larger than
ordinary ; the principal cells of the gland were found as

124

Manual of Veterinary Physiology.

the result of digestive activity to become very granular.
The active pyloric cells also became more granular, and the
nuclei left the base of the cell and worked towards the
centre of it. During hunger the chief cells of the fundus
glands are clear and large, the parietal cells small.

Xo doubt the appearance presented by the secretory cells
depends upon the method by which they are prepared for
examination. Langley has therefore, by another method of
inquiry, given an opposite description of the active and
passive cells of the gastric glands. He found that in the
active state the granules decreased in number, the cells
becoming clear, and being capable of differentiation into a
clear outer and a granular inner zone, just as we have seen
in the parotid gland. During rest the entire cell became
granular. The parietal cells were found to increase in size,
but did not become granular.

Gastric Juice of the horse has not been obtained pure.
The experiments made by Tiedemann and Gmelin of intro-
ducing foreign bodies into the stomachs of horses did not
lead to a pure secretion, owing to the amount of saliva
swallowed. The following table, constructed by C. Schmidt,
represents the composition of this juice in man, the dog,
and sheep :

Man.
994-40

Dog.

973-06

Sheep.
986-14

Water -

Organic matter -

3-19

17-13

1-05

Sodium chlor.

1-46

2-50

I'.'m

Calcium „

•06

•26

•11

Hydrochloric acid

3-19

17-13

1-05

Potassium chlor.

•55

L-12

1-52

Ammonium ,,

•17

■47

Calcium phosph. ")

( -08

IMS

Magnesium ,, >

■125

•57

Ferric , 1

•33

The following table from Ellenberger* gives an analysis
of the so-called gastric juice of the horse, and also of the
* Op. cit.

Digestion. 125

stomach-fluid after feeding on different foods ; in connection
with the latter, it is to be remembered that the fluid con-
sists of the soluble, organic, and inorganic portions of the
food, mixed with saliva, and gastric juice :

Stomach-fluid after feeding on

Gastric Juice.

Oat Straw.

Oats.

Ha;,.

Water

982-8

843-4

925-0

972-6

Organic matter -

9-8

69-9

40 0

20-2

Inorganic matter

7-4

86-7

35-0

7-2

Hydrochloric acid

1-3

—

—

—

Gastric juice is acid in reaction, clear when filtered,
slightly yellow in the horse, brownish in sheep, with a
specific gravity of 1010. A remarkable peculiarity of the
gastric juice of flesh feeders is the power it possesses of
resisting putrefaction. This is not the case with the horse.
Examined by the polariscope, gastric juice turns the ray of
polarized light to the left. The effect of reagents on the
secretion shows that acids produce no precipitate, whilst
alkalies do, and that alcohol produces a heavy precipitate,
which is in part due to the ferments found in the fluid.
The amount of salts present is about '7 per cent, or -S per
cent.

The acidity of the gastric juice we have before spoken of,
it only remains to speak of the ferments — viz., pepsin and
rennin — and of the substance known as mucin.

Pepsin is a body allied to proteids, which by appropriate
methods can be obtained in the form of a yellowish powder,
soluble in water, insoluble in alcohol ; it does not give all
the tests characteristic of the proteid group of bodies. The
ferment is secreted in the principal cells of the fundus and
pyloric glands, but exists in them, not in the form of pepsin,
but as its immediate precursor, pepsinogen. There is no
pepsin secreted by the cuticular or left sac of the stomach
of the horse, and Ellenberger considers that even the
pyloric region contains no ferment during the first hour
of digestion.

It is found that if pepsin be obtained in a pure con-

126 A Manual of Veterinary Physiology.

dition it produces no action on food. It is essential to its
function that it should be associated with an acid, which the
majority of observers regard as hydrochloric. In this con-
dition it readily acts on proteids, converting them into
peptones. This function is spoken of as peptonizing.

Pepsin may be destroyed by heat. It loses its activity
at 134° to 136° F., though in the dried state it may be
raised to 212° F. without being destroj^ed. It best mani-
fests its activity at a temperature of 104° F.

Pepsin is described as a ferment, inasmuch as, besides
splitting up the proteid substances of food, one of its lead-
ing characteristics is that a very small amount of it is
capable of performing a considerable amount of work. It
is probable that so long as it is acting in an acid medium it
is not appreciably used up.

The Rennin, or milk-curdling ferment, is also formed in
the same cells as the pepsin ; it is destroyed at a lower
temperature than pepsin. By means of magnesium car-
bonate the two ferments may be separated.

The action of rennin is to clot the casein of milk. This
process is used in the manufacture of cheese, an infusion of
the mucous membrane of the stomach being sufficient to
set up this action in the milk. The ferment acts without
the presence of an acid, but it is essential in order that
the rennin may clot casein that calcium phosphate should
be present.

In the fourth stomach of the calf and sheep this ferment
may be readily found, and it has been said to exist in the
stomach of the horse.

A third or lactic acid ferment has been described as
existing in the gastric juice, which has the power of con-
verting milk-sugar into lactic acid. Dilute caustic soda,
which will destroy both pepsin and rennin, has no effect on
this ferment.

Mucin. — The remarkable amount of mucin in the stomach
of the horse is secreted by epithelial cells and mucous
glands, as previously mentioned. How much mucin is
formed, independent of the gastric juice, Ave have no means

Digestion. 127

of knowing ; all we know is that it is less during hunger than
during digestion, and is less in ruminants than in horses.

We have no knowledge of the nerves governing the
secretion of gastric juice.

The action of the gastric juice is directed solely against
the proteid principles of the food. There are other changes,
no doubt, besides peptonizing occurring in the stomach,
but these are independent of the gastric juice, and are
perhaps, in some cases, inhibited by it.

Gastric juice converts albumins into Peptones. This
change occurs whether an animal or vegetable proteid be
given. The conversion is not a direct one, as between
albumins and peptones occur the intermediate products
albumoses.

It is well known that albumins cannot pass through an
animal membrane, whereas the distinctive character of
peptones is their power of dialysing, which enables them,
no doubt, to pass readily into the absorbent vessels of the
intestines.

The amount of peptone at first produced is small;
especially is this the case early in digestion, for, as we shall
presently show, according to Ellenberger, peptic digestion is
the second stage of stomach digestion in the horse.

The amount of peptone in the stomach is stated by the
same observer to be smaller in the left half of the stomach
than in the right ; according to my experience peptone
disappears as soon as it is formed, for I have never suc-
ceeded in finding any in the stomach of the horse.

But the gastric changes are not quite so simple as would
at first sight appear. Experimental inquiry shows that
peptones are obtained in two forms, one remaining stable
and undergoing no further change, whilst the other may,
under the influence of one of the ferments of the pancreatic
juice (trypsin), be split up into leucin and tyrosin, two
amido acids which will engage our attention later on.

All peptones which yield as further products leucin and
tyrosin are termed hemi-peptones, whilst those which do not
are called anti-peptones.

128 A Manual of Veterinary Physiology.

This remarkable difference indicates that the proteid
molecule may consist of two parts, an anti and hemi
portion yielding respectively anti-albumose and anti-
peptone, and hemi-albumose and hemi-peptone.

Much confusion has occurred through the difference in
the nomenclature adopted by various observers in describ-
ing these different products. The one most generally em-
ployed is that of Kuhne's, given above, and here tabulated :*

Albumin.

I

I I

Hemi-albumin. Anti-albumin.

I I

Hemi-albuminose. Anti-albuminose.

I I

Hemi-peptone. Anti-peptone.

Amylolytic Changes. — We have referred to other changes
occurring in the stomach independently of peptonizing
There can be no doubt that starch is converted into sugar ;
all the sugar I have found in the stomach could not have
been converted in the mouth, considering the feeble action
of horse's saliva. Assuming, however, that the saliva assists,
we know from the researches of Ellenberger and Hofmeister
that it can convert starch into sugar even in the presence
of 2 per cent, lactic acid ; whilst it ceases in the presence
of -5 per cent, hydrochloric acid. The whole of the starch,
however, is not converted in the stomach, for some may be
distinctly found in the early part of the small intestines.

Ellenberger and Hofmeister are of opinion that starch
conversion in the stomach of the horse occurs not only
through the saliva swallowed, but by the development of
ferments from the food ; they found that oats could yield
a starch-converting ferment active at the body temperature,
but destroyed by boiling ; they have further stated that
starch-converting ferments may in the horse be derived
from the air swallowed with the food.

The view I hold as to the means by which the
starch is converted into sugar by the horse is as follows :
* Copied from Halliburton.

Digestion. 129

Starch is not converted in the mouth, but it is in the
stomach by means of a starch- converting ferment contained
in the oats, which is capable of acting in the presence of
lactic acid. My observations on this subject are incomplete,
and therefore unpublished.

After this, and with what we have to say on the cellulose
ferment, we need seek for no other explanation of the reason
why oats are so universally adopted as food for horses.

According to Ellenberger, starch is the first substance
digested in the stomach of the horse, a diastatic ferment
existing in the left inert sac, and also in the fundus.

Starch when attacked by a diastatic ferment is first
converted into soluble starch, then into dextrin, and lastly
into sugar ; part of the starch may be converted into lactic
acid by lactic fermentation.

Fats are not acted upon in the stomach, though the
envelope surrounding the fat globule is digested, and the
fat set free.

Milk is curdled in the stomach by means of the rennin ;
the casein thus produced is converted into peptones in the
ordinary manner.

Cellulose fermentation is considered by Tappeiner to
occur in the left sac of the stomach, and when marsh-gas
has been found in this organ, it results from cellulose
decomposition. Ellenberger lays no stress on these results,
but recently Brown * has shown that the destruction of the
cell-wall of oats and barley occurs in the stomach, where it
is dissolved by a cyto-hydrolytic ferment pre-existent in
the grain. The changes occur with extraordinary rapidity
in the stomach of the horse. The researches of this
observer on a cellulose-dissolving ferment are of the
greatest interest to the veterinary physiologist, and of con-
siderable practical importance.

The Various Periods of Stomach Digestion. — From what
has been previously said, it will be seen that digestion in
the stomach of the horse may be divided into certain

* ' On the Search for a Cellulose-dissolving Enzyme,' H. J. Brown,
F.R.S., Journal of the Chemical Society, 1892, p. 352.

9

130 A Manual of Veterinary Physiology.

periods, the existence of which has been determined by
Ellenberger and Hofmeister, whose views are here given :

First period : lasts but a short time, during which starch is
converted into sugar, accompanied by lactic fermentation.

Second period : during this starch is principally converted
into sugar in the left sac, and a small quantity of proteid is
converted into peptone in the fundus ; the acids present
are lactic in the left, and a little hydrochloric in the right
sac.

Third period : one of mixed digestion ; both starch and
proteid conversion occurs — the former in the pylorus, the
latter in both fundus and pylorus. The acid present is
principally hydrochloric.

Fourth period consists of pure proteid digestion ; no starch
conversion can occur owing to the universal presence of
hydrochloric acid. It is impossible to state definitely the
length of these various periods, for so much depends upon
the presence of fresh food in the stomach. Where the
interval between the meals is considerable, the periods
extend over several hours ; and in all cases they run into
one another. Had it not been for the Aveight of Ellen-
berger's authority, I should not have considered it necessary
to have mentioned the various periods given above.

After a moderate feed digestion is at its height in 3 or 4 hour*.
„ full „ „ ,, „ 6 to 8 „

„ an immoderate „ ,, delayed still longer.

Gastric Digestion of Ruminants. — Ruminants are described
as having four stomachs — viz., the rumen, reticulum,
omasum, and abomasum. Physiologically considered, there
is but one stomach — viz., the abomasum ; the others may
be regarded as (esophageal dilatations.

The Rumen is of enormous size, capable of holding
GO gallons ; it is divided into certain sacs, has a well-
developed mucous membrane, which in part is covered by
leaf-like papilla1, the glands are small and unimportant,
and contribute no digestive fluid. The muscular fibres of
the wall are distinctly striated, which is a remarkable

Digestion. 131

circumstance, and probably connected with the function of
rumination. The contents of the stomach are alkaline, except-
ing in calves fed on milk, and consist of food only roughly
comminuted, containing an amount of fluid which plays an
important part in rumination, and which is derived from
the fluid consumed, mixed with enormous quantities of
saliva. This stomach communicates with the oesophagus
and the reticulum.

The Reticulum is arranged like a honey-comb ; it is a
very small stomach, and its contents are normally fluid
and alkaline. In the pouches formed by the reticulated
arrangement foreign bodies are commonly found, and when
they penetrate the heart it is from here that they pass into
the chest.

The use of the reticulum is to contain fluid; so that
the openings leading from this stomach into the cavities
of the first and third are considerably above the base of the
viscus. This fluid is used during rumination, and is [forced
into the oesophagus by muscular contractions. In reaction
the second stomach is alkaline, and it possesses no secretion
from its walls.

The muscular coats of the stomachs vary in thickness.
The rumen is comparatively thin, the reticulum thick. By
means of the muscular tissue the food is submitted to a
constant churning motion, which continually revolves the
contents. This process in the rumen is one of considerable
importance, as it brings the food towards the opening of
the oesophagus for the purpose of rumination, The process
is slow and deliberate, the material at the posterior portion
of the rumen being gradually forced ■ forward and upward,
and made to revolve within the cavity.

Solid material, no doubt, enters the rumen and reticulum
tirst, but liquids may enter all four stomachs at one and
the same time ; this has been proved by the investigations
of Flourens. It is probable that the greater part of the
fluid drunk passes direct to the rumen and reticulum, for it
is certain that the presence of fluid in these stomachs is
absolutely essential to rumination.

9—2

132 A Manual of Veterinary Physiology.

The food which newly arrives in the stomach mixes at
once with that already there, and undergoes, in the pre-
sence of saliva and the water consumed, a peculiar macera-
tion which suits it for remastication. Cellulose is also
digested in the rumen through the presence of ferments,
and the amount of conversion which can thus occur has
been estimated at between CO per cent, and 70 per cent.

Ellenberger's views on the function of the rumen and
reticulum are as follows :

In the rumen the food is mechanically divided through
the motion of the walls of the organ, and a thorough
incorporation occurs ; owing to the quantity of fluid found
in this stomach, softening and maceration of the food
substance takes place ; carbo-hydrates are digested through
ferments contained in the food itself ; in this way starch is
converted into sugar, cane-sugar into maltose, and cellulose,
especially in the sheep, undergoes decomposition ; further,
proteids are slowly converted into peptones through food
ferments, not through a true peptic ferment ; the rumen is
the seat of fermentation and gas production.

The reticulum has the same function as the rumen, and
it regulates the passage of food from the first to the third
stomach, and from the first stomach into the mouth.

In young ruminants digestion principally occurs in the
fourth stomach, as the others are almost rudimentary. It
is remarkable, however, how soon they develop, and how
easily the process of remastication is acquired in young
animals placed on solid food.

The Omasum, or third stomach, is peculiar. Its physiology
has been elaborately worked out by Ellenberger. This
authority says that it possesses no secreting power, that its
function is to compress and triturate the food, which it
crushes between its powerful muscular loaves, and rasps the
ingesta down by means of its papillae. The contents of this
stomacli arc always dry, due to the fluid portion being
squeezed off and flowing into the fourth stomach by the
action of gravity and the pressure exercised bj the viscus.
Normally it possesses no reaction ; if found arid, it is due to

Digestion. 133

regurgitation from the fourth stomach. The third stomach
has a separate source of nerve supply. Irritation of the
pneumogastric produces contraction of all the other stomachs
but this one.

In the Abomasum, or fourth stomach, true digestive
changes occur. The acid secretion, formed in the manner
before described, converts the proteids into peptones, this
change being more active at the cardia than at the pylorus.
Ellenberger states that in the abomasum the digestion of
starch is the first to take place, and then proteid digestion.

In the fourth stomach of the calf a milk-curdling ferment
exists.

Stomach digestion in the Pig has also been worked out
by Ellenberger and Hofmeister. The stomach of the pig is
peculiar ; it is a type between the carnivorous and ruminant,
and is divided by the above observers into live distinct
regions, which do not all possess the same digestive activity.

The gastric juice of the pig contains for the first hour or
two of digestion lactic, and afterwards hydrochloric, acid ;
pepsin is present, and a ferment which converts starch into
sugar.

The remaining points in gastric digestion in the pig, viz.,
the various periods of digestion, the changes in the acid,
and the slowness with which the viscus empties itself when
no fresh food is given, are identical, strange to say, with
those of the horse.

Absorption from the Stomach.— The needful changes having
occurred in the stomach, and I now refer principally to the
stomach of the horse, our next step is to inquire into the
proportion of food so altered as to be fit for absorption.

Experiment shows that in the stomach 40 to 50 per cent,
of the carbo-hydrates of the food have been converted into
sugar ; whilst 40 to 70 per cent, of the proteids are con-
verted into peptones. Where food has been long in the
stomach, not more than 2 to 10 per cent, of the proteids
pass out unacted upon ; but under ordinary circumstances
we cannot count upon a larger digestion of proteids than
40 per cent.

134 A Manual of Veterinary Physiology.

In ruminants probably the greater part of the food
substance is acted upon in the stomachs, leaving com-
paratively little for the intestines to perform.

In spite of the changes which occur in the stomach, it has
been proved by the experiments of Colin that no absorption
occurs from /// is organ in the horse. It would be useless to
recapitulate all his experiments. They were generally per-
formed with strychnine, and he found that so long as the
pylorus was securely tied, no symptoms of poisoning would
occur when the alkaloid was introduced into the stomach
no matter how long it was left there, but that when the
ligature was untied, and the contents of the stomach
passed into the intestines, poisoning rapidly followed.
These remarkable results were obtained by him so often,
and under such varying conditions, as to leave no doubt as
to the accuracy of the observations. We can only surmise,
therefore, that no absorption of sugar or peptones occurs
in the stomach. It is certainly very remarkable what
becomes of the peptones. I have never found any in the
stomach contents, no matter what the period of digestion
may be; and if they are not absorbed in the stomach,
they must pass very rapidly into the intestines and enter
the vessels at once, as no peptone can be found in the
small intestines.

I am not at all prepared to explain this non-absorption
from the stomach of the horse, and will touch on it later.
Colin attributes it to the small area of the mucous mem-
brane, which, he says, cannot be secreting gastric juice and
absorbing at the same time ; and in the empty stomach he
attributes the non-absorption of poisons to the thick layer
of tenacious mucus, which we have previously mentioned
covers the villous stomach of the horse.

Self-digestion of the Stomach. — A question which has for a
long time given rise to an energetic discussion, is the reason
why the stomach during life does not digest itself, seeing
that the action of its secretion is so potent that portions <»f
living material, legs of frogs, ears of rabbits, etc., it' intro-
duced into it are readily digested, also that post-mortem

Digestion. 135

digestion of the stomach in some animals is far from rare.
No perfectly satisfactory solution of the problem has yet
been afforded ; the alkalinity of the circulatory blood is not
considered to meet the difficulty. In an extensive post-
mortem experience amongst horses, I have never yet met
with post-mortem digestion of the stomach. Whether this
is due to the horse's acid being mainly or wholly lactic, I
cannot say.

The Gases of the Stomach. — The nature of these largely
depends upon the food; traces of oxygen, a quantity of
carbonic acid, and variable amounts of marsh-gas, sul-
phuretted hydrogen, hydrogen, and nitrogen are found.
The oxygen and nitrogen are derived from the swallowed
air ; the carbonic acid is derived from the fermentation of
the food, and the action of acids on the saliva ; and the
marsh-gas is obtained by the decomposition of cellulose.

Tappeiner found the following gases in the stomach of
the horse :

Carbonic acid - - - 75*20 07"73

Oxygen - - - -23 "00

Hydrogen - - - 14-56 12-66

Nitrogen - - - 9'99 19\54

I have found in the stomach of a horse in perfect health,
which had been fed on oats, the following gases in every
100 volumes :

Carbonic acid - - - - - 2 1 "2

Oxygen - - - 11*8

Hydrogen ... - o-6

Nitrogen - - - 61 "4

but I take it that the proportion of these gases must vary
considerably, and depend largely on the diet.

In cattle, by feeding on hay, the following gases were
found by Tappeiner in the rumen :

Carbonic acid and sulphuretted hydrogen

- 65-27

Hydrogen

•19

Marsh-gas

- 30-55

Nitrogen - -

3-99

136 A Manual of Veterinary Physiology.

Vomiting.

Vomiting amongst solipeds and ruminants is rare, and
I doubt whether in the former animal it should not be
considered rather as a pathological than a physiological
phenomenon.

The reasons given why the horse cannot vomit are
various : (1) The thickened and contracted cardiac extremity
of the oesophagus ; (2) the oblique manner in which this
latter enters the gastric walls ; (3) the dilated pylorus lies
close to the contracted cardia, so that compression of the
stomach contents forces them into the duodenum ; (4) the
cuticular coat is thrown into folds over the opening of
the cardia; (5) encircling the cardia are muscular loops
the contraction of which keeps the opening tightly closed :
(6) the stomach is not in contact with the abdominal wall.
All these and other reasons have been assigned as the
cause of non- vomiting in the horse ; yet on turning to
ruminants, which normally do not vomit, we find these
conditions reversed. The stomach or stomachs and oeso-
phagus freely communicate, the largest stomach lies in
contact with the abdominal wall, the cardia is freely open,
the oesophagus of great size, and, still stranger, the animal
has the ability under the control of the will to bring up
food from the stomach as a normal condition, and yet no
vomiting occurs.

It is evident, therefore, that all these theories are not
sufficiently satisfactory to account for the absence of vomit-
ing, and we are bound to suppose that the vomiting centres
in the medulla of both horse and ox, are either only rudi-
mentary or very insensitive to ordinary impressions.

Vomition in the horse is no doubt seriously Interfered
with by the thickened cardia and the arrangemenl of the
muscular fibres; the folds of mucous membrane filling up
the orifice I do not think could offer a serious obstruction
to a distended stomach, for wo know that even when this
membrane is dissected away post-mortem, a Stomach will
burst, rather than allow iluid or air to be forced from the

Digestion. 137

pylorus through the cardia, until the muscular fibres sur-
rounding it are partially divided.

Vomition in the horse is generally indicative of ruptured
stomach, and much has been written as to whether vomit-
ing occurs before or after the rupture. From no inconsider-
able experience in these cases, I have arrived at the
conclusion that it may occur at either time. I am convinced
that a horse may vomit though a rent seven or eight inches
long exists in the stomach walls.

Dilatation of the cardia is the great inducement for
vomiting to occur in the horse, and in every case examined
post-mortem where vomiting occurred during life, I have
found the cardia so dilated that two or three fingers might
be readily introduced into it.

It is perfectly possible for a horse to vomit and recover
(showing that it had not a ruptured stomach), and it is not
unusual to have attempts at or actual vomition when the
small intestines are twisted.

The only case of vomiting I have seen in the horse
which resembled the distressing appearance presented by
the human subject was in a case of volvulus of the small
bowels ; the ingesta gushed in a stream from both nostrils,
the horse lying on his chest with the nose extended ; more-
over, it was the only case I have observed where any sound
accompanied the expiratory effort.

Vomiting in the horse is not as a rule attended by any
distressing symptoms ; the ingesta dribbles away from one
or both nostrils ; occasionally an effort may be made on the
part of the patient, the head being depressed to facilitate
expulsion. More than this is very rarely seen.

Why a horse should vomit more often with a ruptured
stomach than a sound one is a fact I cannot explain.

It is important to notice in connection with the subject
of vomiting, that agents such as tartar emetic which
excite vomiting by their action on the cerebral centre, have
no effect on the horse, nor do horses vomit as the result of
sea-sickness, though they suffer extremely from it. The
same remarks apply to ruminants.

13S

.4 Manual of Veterinary Physiology.

In those animals where vomiting is a natural process, the
three important operations are the dilatation of the cardia
by active contraction of the longitudinal fibres of the
oesophagus, pressure on the walls of the stomach by the
abdominal muscles, and closure of the pylorus.

Rumination.
The physiology of rumination has been principally
worked out in France by Flourens and Colin, and our
knowledge of this singular process is based entirely on
their observations.

Fig. LO.— Diagram op the (Esophageal G-roove.

03, oesophagus entering the stomach ; c, its cardiac opening ; RP, right
pillar of oesophageal groove ; LP, left pillar of the same ; 0, open-
ing into the omasum ; GBG, oesophageal groove extending from
c to o. To the right of the figure is the rumen, to the h-i't the
reticulum. (After Carpenter.)

The oesophagus in ruminants enters the rumen and forms
a singular groove or channel known as the oesophageal,
which on the left communicates with the first and second
stomachs, and on the right, by a very small opening, with
the third stomach (Fig. 10). In this way food coming
down the oesophagus may enter either of the three first

Digestion. 139

stomachs, the choice of stomach being determined, as we
shall presently point out, by the condition in which the
food is swallowed.

The oesophageal groove possesses two so-called lips or
pillars, the anterior being formed by the reticulum, the
posterior by the rumen. These pillars are composed of
involuntary muscular fibres arranged longitudinally and
transversely, by which means the groove can be shortened
and constricted. By a contraction of the pillars the third
stomach may be shut off from the first and second, and
the opening into it brought nearly into apposition with the
• esophagus ; when the pillars are relaxed the oesophagus
communicates more directly with the first and second
stomachs. Another function of the groove is to cut off a
pellet of food pressed into it by the contraction of the
rumen and reticulum, the pellet or bolus being then passed
into the oesophagus for remastication.

The food which has been lightly crushed in the mouth
enters the rumen, meeting there with material from the
last meal, as the rumen never empties itself. Here the
maceration previously spoken of occurs, the food the whole
time being slowly and deliberately churned. In the second
stomach the same changes are occurring as in the rumen.

In rumination the oesophageal groove has been con-
sidered to play an important part ; but Colin has shown
that even if the lips be stitched together rumination may
occur, so that the theory that the bolus is formed between
the lips of the canal, and forced up the oesophagus by the
powerful contraction of the rumen, is not correct according
to this observer. What he says occurs is, that during the
churning movement the food is gently pressed against the
lips of the groove, when, by a spasmodic contraction of
the diaphragm and abdominal muscles, some of the liquid
from the reticulum and some of the solid from the rumen
is carried up the oesophagus, which latter by the contrac-
tion of its funnel-shaped extremity cuts off the bolus, and
by its reversed peristaltic action conveys it to the mouth.
In passing under the velum palati the liquid portion is

140 A Manual of Veterinary Physiology.

squeezed out and is at once res wallowed, and passes to the
third stomach, whilst the solid mass undergoes grinding.
After the bolus is reswallowed, it may either pass again to
the rumen, or, if in a rinely comminuted condition, it passes
at once from the oesophagus into the third stomach.

Flourens excised the reticulum, but this did not interfere
with the process of rumination.

Rumination can only be performed by means of the
united action of the walls of the stomach, abdominal walls,
and diaphragm ; it is impossible when the abdominal
muscles or the Avails of the stomach are paralysed ; it can
occur if the diaphragm be paralysed, but only through an
extra effort of the abdominal muscles. The pillars of the
diaphragm of the ox are specially arranged, so as to prevent
compression of the oesophagus when the diaphragm con-
tracts (Steel).* Further, rumination is only possible when
the stomach contains a fair amount of food and a con-
siderable quantity of liquid.

The ascent of the food in the oesophagus can be dis-
tinctly seen in the neck, and a sound may be heard on
auscultation over the region of the oesophagus, due to the
passage of the bolus with its fluid admixture. The amount
of each bolus has been estimated by Colin at 3 h ozs. to
4 ozs. Its formation in the stomach and ascent will occupy
about three seconds, and its descent after remastication
one and a half seconds ; its remastication occupies about
fifty seconds. Altogether, Colin has calculated that a
period of at least seven hours is required for the process
of rumination.

During rumination the parotids secrete, but not the
submaxillar}'- or sublingual glands.

Rumination is a reflex nervous act, the centre of which
is probably in the medulla. The nerves in the rumen
convey the sensation to the brain by means of the pneumo-
gastrics, which if divided cause rumination to be sus-
pended.

The Nervous Mechanism of the Stomach.— ( >f this we know
• Diseases of the Ox' J, II. Steel.

Digestion. 141

very little ; as previously mentioned, we have no knowledge
of the nerves which govern the secretion of gastric juice >
there is no nerve the artificial stimulation of which has led
to a secretion of the fluid.

The movements of the wall of the stomach are excited
by the presence of food or irritation applied to the mucous
membrane, and these movements may be increased by
stimulation of the vagus nerve. It is found, however, that
when the nerves leading to the stomach are divided so as
to completely cut the organ off from any nervous influence,
it still possesses the power of contraction, this being prob-
ably induced by the ganglia found in its walls.

The stomach is supplied by the pneumogastrics, which
are here both non-medullated nerves, and also by the
splanchnics through the semilunar ganglion. Irritation of
the vagus leads to powerful contraction of the stomach
walls, whilst irritation of the splanchnics causes the move-
ment to cease ; the vagus is therefore an augmentor nerve
to the muscle of the stomach, whilst the splanchnics are
inhibitory. On the contrary, the vagus supplies the blood-
vessels of the stomach with inhibitory fibres, whilst the
splanchnics supply them with constrictor fibres.

It is probable that the different muscular layers forming
the wall of the stomach have a separate source of nerve
supply, so that the circular can act independently of the
longitudinal fibres.

Of the fibres opening and closing the cardia and pylorus
we have no knowledge.

It has been previously mentioned that the nerve supply
to the third stomach of the ox is quite distinct from that
of the other stomachs ; irritation of the pneumogastric
produces contraction of all the stomachs but the omasum.

Intestinal Digestion.
Small Intestines. — The chyme which is poured from the
stomach into the small intestines meets here with three
other digestive fluids, viz., the succus entericus, the bile,
and the pancreatic juice.

142 A Manual of Veterinary Physiology.

The Succus Entericus is prepared by the glands of the
small intestines. In the duodenum we meet with the
glands of Brunner and the follicles of Lieberkuhn, the
latter supplying a considerable quantity of intestinal juice,
whilst the secretion from the former is scanty. Brunner's
glands, which are very large in the horse, are arranged on
the same principle as the gastric glands, whilst those of
Lieberkuhn are tubular glands, amongst the lining cylin-
drical epithelial cells of which numerous mucus-forming
goblet cells may be found.

Colin endeavoured to obtain succus entericus by clamp-
ing a loop of bowel in the horse ; by this means he
obtained from 6i feet of small intestine 2-8 ozs. to 4 ozs. of
fluid in half an hour.

We have no satisfactory analysis of intestinal fluid in the
horse ; it is probable that the methods adopted to obtain it
are not completely satisfactory, nor is it likely that, in spite
of the precautions taken, it can be obtained free from
bile, pancreatic fluid, or gastric juice. Colin states that the
juice he obtained was mixed with a little mucus, which he
got rid of by nitration ; the fluid was then clear, of slightly
yellow colour, saltish taste, alkaline reaction, specific gravity
1010, and its analysis showed it to be composed as follows :

Water - - - 98'15

Albumin - - - "45

Chloride of sodium \

Chloride of potassium r 1*45

Phosphate and carbonate of soda J

Colin endeavoured to obtain the secretion of Brunner's
glands in the horse by ligaturing the common duct and
pylorus, and emptying the bowel. In an hour he obtained
28 ozs. of viscous thick liquid of saline taste, slightly
alkaline reaction, specific gravity 1008, and it was found to
give the following analysis :

Water - 98'47

Mucus - - - "95

Chloride of sodium

< iarbonate <>f Boda

Bypophosphate of lime - '10

Digestion. 143

This fluid did not coagulate on heating, nor did it form
an emulsion with fatty matter.

According to Ellenberger and Hofmeister, the succus
entericus contains three ferments. Starch can be converted
into sugar, cane-sugar into grape-sugar (being the only body
secretion, so far as we are aware, which possesses this
power), and proteids are converted into peptones. These
results were also previously obtained by Colin. They do
not harmonize with the views of human physiologists, who
attribute but a slight action to the intestinal fluid, and con-
sider its chief function is to change maltose into dextrose.
Buno-e considers that in the human subject the chief use of
the intestinal fluid is to neutralize the acid of the intestinal
contents, which it is capable of doing owing to the con-
siderable quantity of carbonate of soda it contains ; its
further function is to emulsify fats with the surplus soda.

This view will not hold good for the horse, as the contents
of the stomach are no doubt neutralized by the pancreatic
and biliary secretions immediately or shortly after they
leave the stomach, so much so that on the duodenal side
of the pylorus the reaction of previously acid chyme is
neutral, and a few inches further back alkaline ; this alka-
line reaction, faint at first, becomes more marked as we
reach the ileum.

Reaction of the Contents. — It is strange that on questions
of fact any difference of opinion should exist. Ellenberger
describes the small intestines as two-thirds acid, then
neutral as far as the ileum, where it becomes alkaline. I
have only once found it otherwise than alkaline throughout.
He further states that in the fasting horse the contents are
alkaline, but that in the digesting animal, whether horse,
ox, or sheep, they are acid, the acidity decreasing after
passing the common duct, and becoming decidedly alkaline
at the lower, or what we would call the posterior, portion of
the small intestine. This, as I have said, does not agree
with my experience in the horse. It is usual to find the
duodenum neutral. As we approach the middle of the
small intestines the reaction becomes faintly alkaline, whilst

144 A Manual of Veterinary Physiology.

in the ileum the contents are always markedly alkaline.
I have only once found them acid in the horse, no matter
what diet has been given, or the period of digestion : neutral
or faintly alkaline in the anterior part of its course, markedly
alkaline in the posterior portion, is doubtless the rule rather
than the exception.

Physical Characters of the Chyme.— The chyme having
passed into the bowel, its appearance at once changes, for
the acid albumin is precipitated by the alkaline secretion
found there. It is now observed that the material consists
of clots floating or suspended in a yellowish fluid, extremely
slimy in nature, and resembling in appearance, through its
precipitated albumin, nasal mucus suspended in fluid. The
proportion of mucin must be considerable, judging from
the manner in which it pours, and this mucus is probably
derived from the stomach. Throughout the small intestines
this condition obtains, viz., a yellow, frothy, precipitated,
slimy, intestinal fluid ; but we observe in that fluid taken
from the latter part of the small intestines that it has a
distinctly focal odour, while that from the early intestines
has a peculiar mawkish smell. In the ileum the proportion
of fluid material is reduced considerably in amount, and
we are capable of recognising the nature of the ingesta,
which previously was almost impossible.

As the flow of material into the small intestines is con-
trolled by a sphincter, so is the flow out of it. The ileum is
a remarkably thick and powerful bowel ; it is always found
contracted and containing ingesta, which is dry compared
with that found in the anterior portion of the bowel. One
of the functions of the ileum is to control the passage of
material into the caecum.

Colin describes the food as circulating between the
pylorus and ileum, viz., that it is poured backwards and
forwards in order to expose it sufficiently to the absorbent
surface. This would necessitate a reversed peristaltic
action. He says that were it not tor this the material
could not be acted upon and absorbed, as the passage of
fluid through the small intestines is so very rapid. It

Digestion. 14.5

would never have occurred to me that the fluid material
of the small intestines passed to and fro between the
stomach and the ileum, exposed twenty times over, as
Colin expresses it, to the absorbent surface of the bowels.
He must have observed this as the result of his vivisections.
Experiment shows that water will pass from the stomach
to the ca?cum in from five to fifteen minutes. By applying
the ear over the duodenum as it passes under the last rib on
the right side, I have heard the water which a horse at that
moment was drinking rushing through the intestines on its
way to the ca?cum.

One is always struck by the fact that the small intestines
are never seen full, in fact, are often practically empty.
From this I judge that material passes very rapidly through
them. This material is always in a liquid condition
excepting at the ileum ; the fluid is derived from the
secretions poured into and originating in the bowel, and
that active absorption goes on in the intestines is proved by
the difference in the physical characters of the contents, say
in the middle of the small intestines and at their termination.
The rate at which the chyme passes through the small
intestines will vary with the nature of the food, and the
frequency with which the horse is fed. Ellenberger says
it reaches the csecum six hours after feeding, but has not
entirely passed into this bowel for twelve or even twenty
hours. I have known it reach the crecum in four hours.

The remaining digestive fluids which the chyme meets
with in the small intestines are the bile and pancreatic
juice ; the action of these on food is described in the
chapter dealing with the liver and pancreas. The little we
know about the absorption of lymph and chyle, and their
elaboration before reaching the blood, are points which
must be reserved for the chapter on ' Absorption.'

Large Intestines. — There can be no doubt that in solipeds
digestion in the large intestines is a very important process;
at least, we judge so from the fact of their enormous
development. In many respects they present a consider-
able contrast to the small intestines ; for instance, they are

10

146 A Manual of Veterinary Physiology.

always found filled with ingesta, the contents are more
solid, the material lies a considerable time in them, and
there are no juices other than the succus entericus poured
into the bowel. These are points exactl}r opposed to what
we have found in the small intestines.

The bowels which we speak of as the large intestines are
the caecum, double and single colon, and the rectum.

The Caecum has been described by Ellenberger as a second
stomach ; its enormous capacity, fantastic shape, etc., have
always rendered it an intestine of considerable interest. To
my mind its most remarkable feature is that it is a bag, the
opening into and out of which are both found at the upper
part, close together, the exit, strange to say, being above
the entrance, so that the contents have to work against
gravity in order to obtain an entry into the next intestine,
the double colon. The contents of the caecum are always
fluid, sometimes quite watery, occasionally of the colour
and consistence of pea-soup, in which condition they are
full of gas bubbles. When watery the fluid is generally
brown in colour, with particles of ingesta floating about in
it. The reaction of the contents is always alkaline ; Colin,
Ellenberger, and I all agree on this point.*

My own view of the function of the caecum is that it is
certainly not a second stomach so far as food is concerned ;
it is, however, most admirably arranged as a receptacle for
fluids, and though undoubtedly absorption occurs from it,
and digestion of cellulose occurs in it, yet I believe its chief
function is the storing up of water for the wants of the body
and the digestive requirements, for it is absolutely certain
that digestion in the horse can only be properly carried
out when the contents are kept in a fairly fluid condition.
I do not say that the caecum produces no digestive changes
in the food, especially in the face of Ellenberger's and
Hofmeister's experiments, who hold that the digestion in
the caecum is an important one, but I consider its digestive
functions subordinate to its water-holding one.

Ellenberger views the caecum as a bowel for the digestion

* I ouce foun 1 the ca c im acid.

Digestion. 147

of cellulose, where by churning, maceration, and decom-
position, this substance is dissolved and rendered fit for
absorption, and he likens it to the stomach of ruminants
and the crop of birds ; he further considers the caecum
exists owing to the small size of the stomach and the
rapidity with which the contents are sent along the small
intestines. It has also a large secreting surface, the glands
being like those of Lieberkiihn, and he considers that
absorption takes place from the caecum.

This observer's experiments demonstrated that the entire
'feed' reached this bowel between 12 and 24 hours after
entering the stomach, that it remained 24 hours in the
caecum, and that during this time 10 to 30 per cent, of the
cellulose disappeared. The digestion of cellulose is no
doubt a very important matter, especially as we know that
the poorer the food the more cellulose is digested ; but I
am not prepared to admit that food remains in the caecum
24 hours, and I believe that cellulose digestion principally,
though not entirely, occurs in the colon. The gas found
in the caecum chiefly arises from the decomposition of
cellulose.

My experiments on digestion have shown that ingesta
may be in the caecum 3 to 4 hours after entering the
mouth, and I am quite clear on the point that oats may
reach even some distance along the colon in 4 hours from
the time of feeding, though I regard this as exceptionally
rapid.

I fed a horse, which had never had maize in its life, and had
not tasted oats for two or three years, with, first, 2^ lbs. of
maize, and 17 hours later with 4 lbs. of oats. He was
destroyed 4 hours from the time of commencing to eat the
oats. Much maize and a few oats were found in the pelvic
flexure of the colon, and a certain proportion of maize and
a quantity of oats in the stomach. This bears out what we
have said about gastric digestion slowing oft' (p. 115), and
proves how great is the distance food may travel through
the bowels in a short time, though I consider in this case
its progress was much more rapid than usual.

10—2

148 A Manual of Veterinary Physiology.

Colin believes that in the caecum starch can be converted
into sugar, fats emulsified, and that active absorption of
assimilable matters occurs.

It is remarkable how the material finds its way against
gravity out of the caecum. The capacious folds in the
intestine are likened by Colin to the buckets of the Persian
water-wheel, by which means the fluid is handed up and
passed on into the colon.

In the absence of experimental evidence, I would hardly
like to suggest that food may pass directly from the
opening of the ileum into the colon, but I certainly have
reason for thinking that this may occur.

The Colon. — The direction taken by the colon of the hors ■
is remarkable. It commences high 'under the spine on the
right side, its origin being very narrow, but it immediately
becomes of immense size. It descends towards the
sternum, and, curving to the left side, rests on the ensiform
cartilage and inferior abdominal wall. The colon now
ascends towards the pelvis, and here makes a curve, the
bowel becoming very narrow in calibre. The pelvic flexure
having been formed, the bowel retraces its steps towards
where it started from ; running on top of the previously
described portion it descends towards the diaphragm,
gradually getting larger in calibre, and then ascends
towards the loin, being here of immense volume — in fact,
at its largest diameter ; it then suddenly contracts, and
forms the single colon. The object of the difference in
the volume of the double colon appears to be for the con-
venience of its accommodation in the abdominal cavity.
The double colon may be divided into four portions for con-
venience of description : the ingesta in the first and third
descend, in the second and fourth they ascend. We find
that the physical characters of the contents are not the
same throughout. In the first colon the food is fairly
firm, and the particles of corn, etc., can be readily recog
nised. In the second colon I lie material is becoming more
fluid, whilst at the pelvi<- flexure the contents are invariably
in a liquid pea-soup condition, and the particles composing

Digestion. 149

them are not readily recognised. In the third colon the
material becomes firmer, but only slightly so, and bubbles
of gas are being constantly given off from its surface. In
the fourth colon the entire ingesta are like thick soup, the
surface covered with gas bubbles, and the material com-
posing them is in a finely comminuted condition ; for the first
foot or so of the single colon this condition is maintained,
when quite suddenly the contents are found solid and formed
into balls. The remarkable suddenness of this change is
invariable in a state of health, and indicates the most
active absorption, perhaps the most active absorption of
fluid in the intestinal canal.

The entire contents of the colon are yellow in colour or
yellowish green, rapidly becoming brown or olive-green on
exposure to light, or, what is more probable, to the oxygen
of the air. The contents of the colon are normally alkaline
throughout. I once, however, found them acid.

The muscular movements of the large intestine are much
slower than those of the small bowels, for the food has to
remain a longer time in contact with the absorbing surface ;
at least forty-eight hours.

In the colon the food undergoes a further elaboration.
Thanhoffer has claimed that starch may be converted into
sugar, and proteids into peptones, and I see no reason why
the latter, at any rate, should not take place, for it is posi-
tively certain that in the colon much material may be
found which requires further acting upon ; this we may see
in almost any feeding experiment, particularly with grain.
Cellulose, no doubt, is here also acted upon ; perhaps the
chief action of the colon is directed against the cellulose.

In my opinion it is impossible that this enormous intes-
tine can exist simply as a reservoir for ingesta, as has been
suggested. Such a view is incompatible with its structure
or the appearance of its contents.

The marked fermentative changes occurring in the fourth
portion of the colon are probably especially associated with
cellulose digestion, as we know that the intestinal gases
consist amongst others of CH4.

150 A Manual of Veterinary Physiology.

Unless cellulose performs some more important function
than that of yielding sugar, it is difficult to conceive that
such enormous and elaborate bowels should exist for its
digestion. We are even ignorant of the means whereby
it undergoes digestion. A cellulose ferment, such as that
found by BroAvn in oats and barley (p. 12!)), is probably the
explanation, but such has not yet been found in hay, or
the digestion may occur under the influence of intestinal
organisms. Bunge imagines that the epithelial cells of the
intestine dissolve cellulose as well as convert dextrin into
sugar.

We have previously (p. 16) mentioned Bunge's views on
the value of cellulose in a diet. He considers that it is
absolutely essential to animals with a long intestine, as it
acts as a natural stimulus to the bowel, and promotes
peristalsis.

In the single colon we have noted the remarkable and
sudden change of highly fluid, thick, soup-like ingesta,
into comparatively dry feces. As the material moves
towards the anus it becomes drier and drier, and more
thoroughly formed into balls by the action of the bowel-
sacs, which squeeze the mass into a round or oval shape.
The contents of this portion are still alkaline, or slightly so,
though as we approach the rectum a distinctly acid reaction
is obtained on the surface of the fauces, though at this time
the interior of the ball may be, and often is, alkaline ; the
converse of this may also be obtained. In the rectum the
single balls collect in masses, to be forced out of the body
at the next evacuation. The reaction of this mass is acid,
the colour depending on the food, but having rather a
reddish-yellow or brownish tint on ordinary diet.

Absorption from the single colon and rectum is very
rapid. Animals may be killed by the rectal injection of
strychnine, or life may bo supported by nutritive enemata.
Narcosis can also be produced by the rectal administration
of ether.

Putrefactive Processes in the Intestinal Canal. — We may
here consider the nature of the putrefactive processes

Digestion. 151

occurring in the digestive canal, the presence of which we
recognise by the production of ill-smelling gases.

In the anterior part of the small intestine no putrefactive
odour is obtained, but after the admixture and action of
the pancreatic juice a distinctly faecal odour is given to the
contents. There can be no doubt of the large number of
organisms found in the small intestine, which, to a certain
extent, may be useful in assisting digestion, especially that
of proteids, and perhaps of fats. By means of organisms
also leucin and tyrosin, indol and skatol, lactic and butyric
acids, may be formed (Halliburton), and the function of
these organisms may further— according to the same ob-
server— be protective in destroying poisonous products,
such as cholin (the alkaloid derived from lecithin).

The decomposition of proteids in the large intestine
leads to the formation of carbonic acid, sulphuretted
hydrogen, ammonia, phenol, kresol, skatol, and certain
organic sulphur compounds ; the latter, with phenol and
indican, are excreted by the kidneys, and in carnivora and
omnivora are regarded as a measure of the putrefactive
processes occurring in the bowel. This, however, will not
hold good for the herbivora, as the phenol with them is
largely derived from the food.

Phenol, or carbolic acid, is largely formed in the horse,
and is excreted by the kidneys. Indol and skatol give to
faeces their characteristic odour.

The longer the food remains in the bowel, the more indol
and phenol is formed ; they are decomposition processes,
and have nothing to do with nutrition, and are got rid of
in flesh-feeders by disinfecting the intestinal canal with
calomel.

According to Tappeiner, phenol is found in the stomachs
and intestines of cattle, skatol in the paunch, and indol in
the large and small intestines. In the horse, indol is
present up to the caecum ; in the colon, its place is taken
by skatol. Phenol and ortho-kresol are found throughout
the large intestines.

The fermentation in the intestines of the horse may be

152 A Manual of Veterincvry Physiology.

either acid or alkaline, both leading to the production of
marsh gas ; but the acid fermentation occurs iu the
presence of skatol, whilst the alkaline occurs in the
presence of indol (Ellenberger). Intestinal fermentation in
the horse is allied to that occurring in the rumen of
cattle. In all cases the fermentation can occur without the
presence of oxygen.

By the decomposition of starchy matters lactic, formic,
acetic, butyric, and propionic acids are formed. It is to
some of these that the acid reaction of normal fieces is due.

In the large intestines of horses Colin describes no less
than eight or ten species of Infusoria. The most charac-
teristic of these are the Colopodes, recognisable by their
ovoid form, with lateral indentation, at the base of which
the mouth is found. Others have an ovoid form but lack
the lateral indentation of the previous species ; some have
an elongated rectangular form, and others are unsym-
metrical in shape. All these infusoria are found in the
caecum and anterior parts of the double colon ; they die in
the last part of the intestines, and leave nothing more than
their debris in the excreta. In ruminants similar organisms
are found in the rumen. As to the action of these organ-
isms we know nothing.

The largest amount of gas found in the intestinal canal
is in the caecum and colon. The small intestines do not
naturally contain much, whatever is formed there being
probably rapidly passed into the large bowels. In these
intestines we know that marsh-gas commonly exists, form-
ing, with CO., the bulk of the gases present in these parts.
We are all practically aware of the conditions arising in
horses in the large bowels, and in cattle in the rumen, as
the result of the fermentation of food — particularly green
grass — and the enormous size to which the animal may be
distended. In both the gas may generally be ignited a
short distance away from the cannula, which has been
passed into the parts to give relief, the CH4, or marsh-gas.
igniting readily on meeting with the proper proportion of
oxygen.

Digest k

153

The gases of the large intestine in the horse contain,
according to Planer, 50 per cent, of carburetted hydrogen,
42 per cent, of nitrogen, and 8 per cent, of carbonic acid.

Tappeiner, quoted by Ellenberger, gives the following
analysis of intestinal gases in the horse :

Small Intestines (Hay Diet).

Anterior

Posterior

portion.

portion.

Carbonic acid

.

72

15

Sulphuretted 1

lydrogen and hydrogen

19

24

Nitrogen -

-

37

59

]

Large Intestines (Hay Diet).

Cwcum.

Colon.

Rectum.

Carbonic acid

and sulphuretted |

55 "5

29-0

hydrogen

Hydrogen

2-0

1-7

1-0

Marsh-gas

11-0

33-0

56-0

Nitrogen -

•9

On Cokn and Hay Diet
Small

10-0

13-0

Intestines.

Colon.

Rent inn.

Carbonic acid

11-0

75-00

45-0

Hydrogen

4-0

•38

3-0

Nitrogen -

84-0

6-00

120

Oxygen -
Marsh-gas

1700

40-0

The Faeces.

The freces consist of that portion of the food which is
indigestible, together with that part which though diges-
tible has escaped absorption. Mixed with these we have
water, colouring substances, mucin, and other organic
matters, inorganic salts, bile pigment, volatile fatty acids,
remains of digestive fluids, organisms, etc.

The composition of the fasces depends largely on the
diet. The following table from Gamgee * can only give a
general idea of their nature :

* ' Our Domestic Animals in Health and Disease,' p. 253.

154 ^i Manual of Veterinary Physiology.

Approximate C

ioMPOsrric

in OF THE

F BCES OF THE

Horse,

Cow.

Sht ep. Pig.

Water -

76-0

84-0

58'0 80-0

Organic matter -

21-0

L3-6

:;»;•( i 17-0

Mineral „

30

2"4

6-0 3-0

lLiii-0 100-0 LOO'O [100-0

Considerable differences exist amongst animals in the
consistence of the faeces ; they are moderately firm in the
horse, pultaceous in the ox, and very hard in the sheep.
These differences depend upon the amount of fluid they
contain. It is necessary to remember that the proportion
of fluid in the fasces does not depend upon the water con-
sumed, but rather on the character of the food, the activity
of intestinal peristalsis, and the energy with which absorp-
tion is carried out in the digestive canal. Succulent food in
horses produces a liquid or pultaceous motion ; other foods,
such as hay and chaff, have a constipating effect, the fasces
being small and hard ; excess of nitrogenous matter in the
food produces extreme foetor of the dejecta, and frequently
diarrhoea ; nervous excitement rapidly induces a free action
of the bowels, accompanied by very liquid fasces ; this latter
is explained by the increased production of peristaltic action.
The colour of the faeces in the horse is yellowish or
brownish-red ; they rapidly become darker on exposure to
the air. When the animal is grass-fed the faeces are green,
and when fed wholly on corn they become very yellow and
more like wet bran in appearance.

The fasces of the horse are moulded into balls in the
single colon, an intestine where, as wo have previously
indicated, the most active absorption of fluid must occur,
for the contents becomes almost suddenly converted from a
liquid into a solid condition.

The fasces of the horse are always acid, the acidity pro-
bably depending upon the development of some acid from
the carbo-hydrates of the food.

Faeces contain, amongst the indigestible portion of the
ingesta, lignin, a proportion of cellulose, husks of grains,

Digestion. 153

the downy hair found on the kernel of oats, vegetable tubes
and spirals, starch and fat granules, gums, resins, chloro-
phyl, etc. ; unabsorbed proteid, carbo-hydrate and fatty
material ; products of digestive fermentation, such as
lactic, malic, butyric, succinic, acetic, and formic acids ;
leucin, tyrosin, indol, skatol, and phenol ; biliary matters
and altered bile pigment, which latter gives the colour to
the dejecta, and is known as stercobilin ; and, lastly,
mineral matter in varying proportions. The faeces always
float in water.

Amongst the inorganic matter silica exists in largest
amounts, then potassium and phosphoric acid, sodium, lime,
magnesium, and sulphuric acid, forming a smaller but still
important proportion.

The horse excretes but little phosphoric acid by the
kidneys, but considerable quantities pass with the feces in
the form of ammonio-magnesium phosphate. This salt is
derived principally from the oats and bran of the food, and
through collecting in the colon and becoming mixed with
organic substances, frequently forms itself into calculi.
Other intestinal calculi are formed from lime deposits in
the bowel, and collections of the fine hairs from the kernels
of oats form the so-called oat-hair calculus.

The following table by Roger gives the mineral com-
position of the faxes in every 100 parts of the ash :*

Horse. Or.

Sheep.

Sodium chloride

•03 "23

•14

Potassium

-

11 -HO 2-91

8-32

Sodium

.

1-98 -98

3-28

Lime

-

4-63 5-71

18-15

Magnesium

-

3-8+ 11-47

5-45

Oxide of iron -

-

1 -44 5-22

2-10

Phosphoric acid

-

10-2-2 s-47

9-10

Sulphuric acid -

-

1-83 1-77

2-69

Silica -

62-40 62-54

50-11

Oxide of magnesium

2-13 —

—

Roger observed that the ash of herbivorous

feces con-

;ained scarcely any alkaline carbonates.

* Que

.ted

by Ellenberger.

156 A Manual of Veterinary Physiology.

The amount of faeces produced in 24 hours varies with the
quantity and nature of the food given. I have observed
that on a diet consisting of 12 lbs. of hay, 6 lbs. of oats, and
3 lbs. of bran, that the average amount of faeces passed by
fifteen horses during an experiment lasting seven days,
amounted to 29 lbs. 13 ozs. in 24 hours, the frcces being
weighed in their natural condition, viz., containing 70 per
cent, water ; the dry material of this bulk of faces is about
7| lbs. More faeces are passed during the night than
during the da}7. In the above experiment, during the
12 hours (6 p.m. to 6 a.m.), the average amount of f;eces
per horse was 18 lbs. 3 ozs., whilst from 0 a.m. to G p.m.
the amount was 11 lbs. 10 ozs. The largest amount of
faeces I have known a horse produce was an average of
73-3 lbs. (weighed in their natural state) for the 24 hours ;
the diet consisted of 12 lbs. of oats, 3 lbs. of bran, and
2cS lbs. of hay.

In an experiment carried out for several months with
different horses all receiving 12 lbs. hay and varying pro-
portions of bran and oats, the average daily amount of
faeces, weighed in their natural state, amounted to 24 lbs.

A horse will evacuate the contents of the bowels about
ten or twelve times in the 24 hours, and the food he con-
sumes will take at least four days to pass through the body.

In the ox the amount of fleces in 24 hours is about
66 lbs. per diem, containing about 10 lbs. of dry material.

The odour of faeces is distinctly unpleasant, due to the
presence of indol and skatol. In disease the faeces are
often extremely fostid ; the odour probably depends upon
the indol and skatol and the decomposing unabsorbed pro-
teid.

The act of defaecation is performed by a contraction of
the rectum, assisted by the abdominal muscles, the glottis
being closed. In the horse the contraction of the rectum
alone is sufficient to expel its contents ; this is well shown
by the fact that this animal can defeecate while trotting.
The anal sphincter dilates under the pressure of the faeces,
the tonic contraction of the muscle — the centre for which

Digestion. 157

exists in the lumbar cord — having been liberated by a
voluntary act. If this centre be destroyed the anus be-
comes flaccid and the rectum remains full, showing that
the mechanism which contracts the anus also contracts the
rectum.

After the contents of the bowels have been evacuated
the sphincter closes, and in doing so imprisons a portion of
the mucus membrane of the bowel, which temporarily
remains everted and is then gradually withdrawn.

Meconium is the dark-green material found in the intes-
tines of the foetus. It consists of biliary matters, both
acids and pigments, fatty acids, and cholesterin ; whilst the
salts of magnesium and calcium, phosphoric and sulphuric
acids, sodium chloride, soda, and potash are also found
in it. The meconium is the product of liver excretion.

Nervous Mechanism of the Intestinal Canal. — What we
have previously said about the stomach nervous mechanism
applies equally to the bowels. Secretion can be excited by
chemical, thermal, and other stimuli, the normal irritation
being naturally the food passing along the canal. Irrita-
tion of the vagus produces no influence on the secretion ;
extirpation of the coeliac and mesenteric plexuses causes a
profuse secretion ; and in the same way division of the
nerves leading to a loop of bowel produces an outpouring
of intestinal fluid. The injection of pilocarpine causes a
considerable secretion, and powerful contraction of the
intestinal walls ; the action of this drug on the horse, and
its elective affinity for the salivary, pancreatic, and intestinal
glands is very remarkable.

The intestines contain local ganglia, and these are
capable of sustaining the movements of the bowel when
all other sources of nerve-supply are cut off"; this is well
seen in the movements of the intestines of a recently-
destroyed horse. The augmentor fibres from the vagus,
and the inhibitory fibres from the sympathetic system,
such as are described on p. 141, apply with equal force to
the muscular wall of the intestinal canal; it is possible
that the two intestinal muscles have a distinct source of

158 A Manual of Veterinary Physiology.

supply : in the same way the opposite action of the vagus
and sympathetic on the bloodvessels of the stomach are
observed to apply to the intestinal walls.

Practically we know that bulk is necessary for intestinal
digestion, a horse cannot be kept in condition on con-
centrated food ; bulk promotes intestinal peristalsis, and
probably the presence of gases in the intestine within
certain limits also has an influence in this direction.

When the blood-supply to the bowel is cut off, increased
peristaltic action occurs ; this is the probable explanation
of the movements seen in bowels removed from an animal
recently destroyed, and is possibly the cause of the expul-
sion of the contents of the rectum when life is suddenly
and violently taken away.

The nervous mechanisms employed in defsecation are
described on p. 156.

CHAPTER VIII.
THE LIVER AND PANCREAS.

Bile.

The bile is a fluid of an alkaline reaction, and of a
yellowish-green or dark -green colour in herbivora, though
in man and carnivora it is of a golden red tint. This
difference in colour depends upon the character of the
pigment present, to which we will shortly allude.

Bile has a bitter taste, a specific gravity in the ox of
1022 to 1025, in the sheep from 1025 to 1031, in the horse
1005. By standing in the gall-bladder the solids are con-
siderably increased, owing to an absorption of part of the
water of the bile. Bile taken direct from the liver is watery
in consistence, that taken from the gall-bladder is viscid,
due to admixture with mucin during its stay in the latter
receptacle. The secretion contains no proteid, which is
somewhat remarkable. It contains mucin (which is derived
from the gall-bladder), biliary pigments, bile acids, fats,
soaps, lecithin, cholesterin, a small quantity of diastatic
ferment, and inorganic salts. The secretion in the horse
contains no mucin, and, according to Ellenberger, there is
very little mucin in the bile of sheep.

The dried alcoholic extract of bile contains in the ox
3'58 per cent, of sulphur, sheep 5-71 per cent., and pig
•33 per cent * The gases found in bile are CCX,, and traces
of O and N.

The chief inorganic salts are sodium chloride and sodium
phosphate, besides which are found lime, magnesium,

* Quoted by Halliburton.

160 A Manual of Veterinary Physiology.

potassium, iron, phosphoric and sulphuric acids ; the
sodium salts are always the largest. The iron, which exists
as phosphate, is probably derived from the haemoglobin of
the blood during the formation of the bile pigments.

The following analysis of ox-bile is given by Ber-
zelius :*

Water

- 90-4

Solids

- i)-G

Bile salts -

Lecithin, cholesterin, fats, soaps

[• 8*0, cholesterin 2*5 per cent.

Mucus and pigment

•3

Inorganic salts

1-3, including iron -003 to -OOG.f

The following table is compiled from Ellenbergei

Ox Bile, Sheep Bile. Horse Bile.

Water - - 92'91

86-90 Water 95 per <

3ent.

Bile acids - .r>-f>l

16-69 Solids 5 „

Bile pigments - '32

•2'J

Fat - - -03

(?)

Mucus - - -51

•94

Salts - - 1-30

11-83

Percentage Composition of the Ash of Ox Bile.

Sodium chloride - 27'7

Manganese peroxide -

•12

Potassium - - 4'K

Phosphoric acid

10-45

Sodium - - 377

Sulphuric „

6-39

Lime - -1*4

Carhonic ,,

1 1 -20

Magnesia - - "53

Silica -

•36

Iron oxide - - -23

It is to be regretted that no complete analysis has been
made of bile in the horse, but the difficulties attending its
collection in a pure state are obvious.

The fat present is in the form of lecithin, a complex
nitrogenous substance united with phosphoric acid, and
found in several of the tissues and secretions of the body.

Cholesterin, another singular substance, is an alcohol and
not a fat, though from its appearance it has been termed
bile-fat. It is found in very regular quantities, and forms

Quoted by M'Kendrick.
f Young, quoted by Halliburton.

The Liver and Pancreas. 161

the principal constituent of certain gall-stones. It is kept
in solution in the bile by means of the bile salts.

The Bile Pigments are two in number, bilirubin and bili-
verdin ; the latter is produced by oxidation from the former.
Bilirubin is the colouring matter of human bile and that of
carnivora, whilst biliverdin gives the colour to that of
herbivorous animals.

Both pigments are insoluble in water, but soluble in
alkalies ; in the bile they are held in solution by the bile
acids and alkalies. Bilirubin may be obtained from gall-
stones of the ox in the form of an orange-coloured powder,
which can be made to crystallize in rhombic tablets and
prisms. If an alkaline solution of bilirubin be exposed to
the air it becomes biliverdin by oxidation, and this latter
pigment by appropriate treatment may be obtained as a
green powder.

Both colouring matters of the bile behave like acids, form-
ing soluble compounds with metals of the potassium group,
insoluble ones with those of the calcium group (Bunge).

On the addition of nitric acid (containing nitrous acid) to
the bile pigments, a play of colours is observed, known as
Gmelin's test. In the case of bilirubin the colours pass from
yellowish red to green, then to blue, violet, red, and yellow.
Each of these colours is indicative of a different degree of
oxidation of the original bilirubin. Biliverdin gives the
same play of colours excepting the initial yellowish red,
which is, of course, absent.

Although bilirubin has not been obtained from haemo-
globin, there appears to be no reasonable doubt that this is
the source of the pigment, for haemoglobin may be readily
decomposed, yielding a proteid and htematin, and if this
hrematin be deprived of iron, the residue thus obtained is
not very dissimilar in composition to bilirubin. Old blood-
clots contain an iron free substance known as hamiatoidin,
which is identical in composition with bilirubin. The iron
which is found in the bile probably results partly from
the hcomoglobin after it has become converted into the iron
free substance bilirubin.

n

162 A Manual of Veterinary Physiology.

The actual production of bile pigments takes place in the
liver, but the means by which the latter organ is furnished
with free hemoglobin for the purpose is still obscure.

The Bile Salts are two in number, glycocholate and tauro-
cholate of soda. They are formed by the union of cholalic
acid with glycin or taurin, and exist in combination with
soda. These salts are found to exist in varying proportions
in different animals — thus, while glycocholate of soda is
largely found in herbivora, taurocholate is the principal
constituent of dog's bile, and in pig's bile hyoglycocholic
and hyotaurocholic acids are found. Both salts are soluble
in water, have a decided alkaline reaction, rotate the plane
of polarized light to the right, and may be obtained in the
crystalline form of acicular needles highly deliquescent.

Glycocholic acid is the chief bile acid in herbivora ; it is
produced by the union of glycin with cholalic acid. Glyco-
cholic acid is diminished b}~ an animal diet, and increased
by a vegetable one.

Taurocholic acid is produced from taurin and cholalic
acid, and exists principally in carnivora, though small
quantities may be found in the ox. This acid differs from
the first characteristically by containing sulphur, by which
it shows its proteid origin.

In the intestine the constituents of the bile are absorbed :
both acids are decomposed or split up by ferments into
cholalic acid and glycin or taurin, the two latter being re-
absorbed.

Glycin or glycocoll originates from proteids, and if ad-
ministered it reappears externally as urea. It cannot be
traced in the free state in the body, but occurs with
benzoic acid, from which combination is formed hippuric
acid ( Bunge).

In rettenkofer's test for bile acids the reaction obtained
is due to cholalic acid. The test is performed as follows :
A drop of the fluid is placed on a white earthenware sur-
face, and to it is added a drop of a strong solution of cane-
sugar, and a similar quantity of strong sulphuric acid; a
beautiful purple-red colour forms, which ina\ be assisted

The Liver and Pane in is. 103

by warming. This test is not solely indicative of bile acids ;
other substances also give it.

The origin of the bile acids is wrapped in obscurity;
taurin is formed in the body, probably also glycin, and
cholalic acid is formed in the liver. Beyond this we know
but little, not even why glycin should predominate in some
animals and taurin in others.

Bile is secreted under a very low pressure, which is the
reverse of what occurs in the saliva ; but low as the pres-
sure is (-58 inch of mercury), it is higher than that of the
blood in the portal vein — in fact double. The secretion of
bile is a continuous one ; whether the horse be in full diges-
tion or fasting the flow does not intermit like the saliva.
During digestion the amount of bile increases.

Quantity of Bile. — The amount secreted varies, but is
greater in herbivora than carnivora. Colin's experiments
gave him the following amounts as hourly secretions :

Ox - " 3tt ozs. to 4|- ozs. per hour.

Sheep - j oz. to bh ozs. „ ,,

Horse - 8=^ ozs. to HH ozs. ,, .,

In those animals possessing a gall-bladder this receptacle
is filled during abstinence, or, if it be empty, it is filled
even during digestion. It empties itself through its own
contractions.

The nervous influence controlling the secretion of bile is
unknown.

The Use of the Bile from a digestive point of view is very
disappointing, inasmuch as it does not digest in the sense
that pepsin and trypsin do. That it is intimately connected
with that of the pancreas would appear to be the case, from
the fact that the secretions are poured out either close
together in the bowel, or, as in the horse, by a duct common
to the two glands. As the horse possesses no gall-bladder,
the secretion as fast as it is prepared is poured into the
intestine ; not so with the ox, where it is stored up in a
capacious gall-bladder until required. From what has
been previously said, we can see the reason of this remark-

11—2

164 A Manual of Vet&Hmary Physiology.

able difference in two purely vegetable-feeding animals.
In the horse food in greater or less quantity is always passing
along the small bowels ; as the stomach under ordinary cir-
cumstances practically never empties itself, it is, therefore,
necessary that bile should always be poured into the intes-
tine In the ox, where the food makes a prolonged stay in
the stomachs, bile is only required at the moment when the
chyme finds its way into the duodenum : in the interval it
is stored up ready for use.

The bile being alkaline, its first action on the chyme is to
precipitate the acid albumin which has escaped the process
of peptonizing in the stomach. One effect of this is pro-
bably to protect the pancreatic ferments from the pepsin
of the gastric juice, and further, to delay the progress of
the chyme along the bowel, and so give the pancreatic
juice time to act. On proteids the bile has no digestive
action; on fats, however, it has a solvent and emulsifying
effect, being more active in the presence than in the
absence of pancreatic juice. Bile cannot split up fats into
fatty acids and glycerine as the pancreas does, but if free
fatty acids are present the bile salts are decomposed, their
soda set free, and soluble soaps formed ; the soaps so
formed assist in rendering the emulsifying effect of the
bile permanent and the absorption of fat much easier.
Fat will not readily pass through a membrane, but if the
latter be first moistened with bile the passage is readily
effected. On the starch of the food bile in the herbivora
is said to exert some action, but it would appear that, in
this respect it mainly assists the pancreas, the juice of the
latter being more active on starch in the presence of than
in the absence of bile.

The further action of bile on the intestinal contents is to
keep them from putrefaction and promote peristalsis, for it,
is found that when the bile is prevented from entering the
intestines, constipation and extreme foetor of the intestinal
contents results.

Bunge states that, the clay-coloured feeces obtained in
jaundice is due to the presence of una. 'ted-on fat; the fat

The Liver and Pancreas. 165

encloses the proteids, which putrefy, hence the odour. The
bile, he states, is not an antiseptic, but acts as a natural
purgative and keeps up intestinal peristalsis, and by so
doing hurries the food out of the system before it undergoes
putrid decomposition.

Some of the constituents of the bile are broken up in
the bowel : for instance, the bile acids yield cholalic acid,
setting free glycin and taurin. The latter, being absorbed
again are carried to the liver, and may probably there
excite the further secretion of bile acids ; cholalic acid is
excreted with the faeces. In the bowels the pigments also
undergo change, yielding stercobilin (the colouring matter
of the fgeces) and urobilin (the colouring substance of the
urine).

Glycogen.

It is quite certain that the largest gland in the body
must have some other function than that of the secretion
of a fluid of comparatively unimportant digestive power,
and such is the case. The liver manufactures and stores
up in its cells a peculiar substance known as Glycogen, or
animal starch.

The literature of glycogen is extensive ; perhaps no sub-
stance has given rise to greater controversy. All we can
attempt here is to give a general and brief outline of a
complicated subject on which much diversity of opinion
has existed.

The sugar in the food, or that derived from starch -con-
version, finds its way by means of the intestinal blood-
vessels into the portal vein ; from here it passes into the
liver. Under ordinary circumstances it is stored up in the
liver as glycogen, being, in fact, reconverted into a kind
of animal starch, and it is gradually doled out to the
system as sugar as the body is in need of it.

The liver regulates the amount of sugar which should
pass into the blood ; so much and no more is admitted to
the circulating fluid, the amount varying between "05 and
'15 per cent. The sugar in the blood of the ox was esti-
mated by C. Bernard at -17 per cent. ; in the calf, 1 per

166 A Manual of Veterinary Physiology.

cent. : and in the horse, 09 per cent. (M'Kendrick). One
use of the liver is to regulate this amount and avoid a
surplus. During starvation the amount of glycogen in the
liver falls, and eventually disappears ; the liver has now
liberated to the blood the entire amount of sugar it is
capable of yielding. If food, particularly carbo-hydrates,
be now taken, the store of glycogen is replenished, and the
sugar-liberating function once more occurs.

The method by which the glycogen becomes converted
in the liver into glucose (not maltose, as in the bowel),
before being issued to the blood, is generally considered to
be by means of a ferment (see p. 167), and this glucose, of
course, reaches the general circulation through the hepatic
veins.

It is curious to observe that the starch must first be
converted into sugar before the bloodvessels of the bowel
can take it up, then in the liver once more converted into
a kind of starch, and, lastly, again into sugar before enter-
ing the blood.

Glycogen differs in some respects from starch, one of its
principal differences being that it dissolves in cold water,
and is stained reddish brown by iodine.

The total amount of glycogen obtained from a given
quantity of food is not wholly stored in the liver, as the
latter organ cannot contain more than about 10 per cent, of
this substance, which would represent only a small amount
of the soluble carbo-hydrates passing into the blood. Wo
know as a fact that the liver, having taken up all the sugar
it can from the portal vessels and converted it into stored-
up glycogen, allows the balance to pass through the hepatic
veins into the general circulation as sugar, and that it
is deposited in other organs (principally the muscles) as
glycogen for future use. The muscles of the borse contain
in this way a considerable quantity of glycogen. Even
after nine days' starvation, from I per cent, to 2'4 per cent.
of glycogen was found by Aldchoft'.* Blood contains no
glycogen.

* Quoted by Bunge.

The Liver and Pancreas. 107

The use of glycogen is to supply muscular energy and
animal heat. During work it diminishes in the muscles,
and during rest it is stored up.

Foster warns us against regarding the glycogen of muscle
as of any value in the production of muscular energy until
it has actually become muscle. As he expresses it, ' It
cannot be fired off as raw glycogen, or even as dextrose, in
the interstices of the muscular fibre ' ; it must first become
muscle.

The source of glycogen is a disputed point: carbo-hydrates,
no doubt, contribute largely to its production ; but there is
reason to believe that proteids also assist in its formation.
The majority of observers agree that fat takes no part in
the production of glycogen.

The hepatic blood contains, roughly, twice as much sugar
as the portal (Seegen, quoted by Halliburton). Lehmann
states that in starving horses he found no sugar in the
portal vein, although it was always to be detected in the
hepatic vein.

When the liver is removed from the body the glycogen
diminishes and the sugar increases. No ferment theory,
according to Halliburton, is required to explain this con-
version, as a diastatic ferment can be obtained from all
living proteids. By the administration of glycerin the
post-mortem conversion of glycogen into sugar may be
prevented (Ransom).* The same observer discovered that
the administration of glycerin also prevented the diabetes
of rabbits which follows an injury of the medulla, and he
concludes that glycerin inhibits the formation of sugar in
the liver-cells.

If glycocin be injected into the blood, according to
some observers the formation of glycogen in the liver
as well as of urea is increased.

Bernard discovered that by puncturing the floor of the
fourth ventricle sugar appeared in the urine. The explana-
tion of this may be that it is due to paralysis of the blood-
vessels of the liver, the nerves of which originate in the

* Quoted by Halliburton.

168 ^1 Minimi of Veterinary Physiology.

medulla; through paralysis the liver becomes gorged with
blood, which is followed by sugar in the urine. This view
appears to be the correct one, since stimulation of the upper
end of the divided pneumogastric is followed by sugar in the
urine, and this sugar is also produced by vaso- motor
paralysis, the pneumogastric being a controlling nerve of
the vaso-motor centre.

Further Uses of the Liver.

We have studied two uses of the liver, viz., the forma-
tion of bile and the storing up of glycogen ; but we have
yet other uses of this gland to detail.

The material carried by the portal vein to the liver con-
tains, besides peptones, some other ultimate products of
proteid digestion, viz., leucin and tyrosin ; these are con-
veyed to the liver, and the leucin contributes to the forma-
tion of urea.

Carbonate of ammonia is converted in the body into urea
and uric acid, and this change occurs in the liver. Pos-
sibly many of the antecedents of urea in the body are in the
liver converted into this substance. This is a point to be
dealt with more fully in the chapter on the urine — all we
wish to impress here is the function the liver possesses of
converting into urea and uric acid certain nitrogenous
products of digestion.

As the result of proteid decomposition in the intestinal
canal, certain aromatic compounds are formed : these are
united with sulphuric acid, and got rid of by the kidneys
as conjugated sulphuric acids. In this combination the
previously poisonous proteid products are converted into
non-poisonous ones, and this change is effected in the
liver (Jiunge.)

Here we have a very important function of the liver
demonstrated, viz., as a neutralizer of poisons introduced
into the blood by the intestines. Many metallic poisons arc
also arrested in the liver, notably mercury and arsenic.

The numerous and complicated changes produced l>\ the
liver may thus be summarized : It forms bile, regulates the

The Liver and Pancreas. 109

supply of sugar to the system, storing up as glycogen
what is not required ; it guards the systemic circulation
against the introduction of certain nitrogenous poisons, such
as ammonia, by converting them into urea and uric acid,
and against other poisons of proteid origin by converting
them into harmless products, by conjugation with alkaline
sulphates (Bunge).

Pancreas.

The fluid secreted by the pancreas performs certain im-
portant functions in digestion. It is remarked by Bunge
that there is scarcely any animal which does not possess a
secretion allied to the pancreas ; even those invertebrates
without a peptic or biliary apparatus are in possession of
one.

From the resemblance of the pancreas to the salivary
glands, it has been termed the abdominal salivary gland. The
pancreatic fluid from the herbivora can only be obtained
with extreme difficulty ; to establish a pancreatic fistula
in the horse is a formidable operation, necessitating an
incision from the sternum to the pubis and the turning back
of the bowels. Colin has established these fistulse both in
the horse and ox ; but the profound impression on the
nervous system produced by such extensive interference,
must considerably affect the character of the secretion and
the amount manufactured.

Pancreatic fluid is alkaline, clear, colourless like water,
and though viscid in some animals is not so in the horse.
It has a saltish unpleasant taste, and a specific gravity of,
about 1010; the viscid secretion of the dog has a specific
gravity of 1030.

The following analysis of the fluid in the horse is given
by Hoppe-Seyler :*

Water-* - 082-53

Solids - - 17-47

Organic matter 8-88 containing 8-6 of ferments.

Salts - - 8-59 „ much sodium phosphate.

* Quoted by Halliburton.

170 A Manual of Veterinary Physiology.

The salts present are sodium chloride in abundance,
potassium chloride in traces, sodium carbonate and
phosphate, calcium and magnesium phosphates in small
quantities. The total solids appear to be subject to great
variation, but the salts are constant. The organic solids
are remarkable for the amount of proteid present in them.

Uses of the Secretion.— The pancreatic juice is poured
into the bowel in the horse by a duct common to the
pancreas and liver ; in the ox the two ducts are separate,
and open within an inch or two of each other. I have
seen a similar arrangement in the horse. Pancreatic juice
is essentially a digestive fluid, acting as it does on all the
elements of food, viz., proteids, fats, and carbo-hydrates :
all of these undergo certain changes — the proteids into
peptones, the fats into fatty acids and glycerin, and the
carbo-hydrates into sugar. These changes are so definite
that it has been assumed, with very good reason, that each
is brought about by a distinctive ferment, though every
attempt to isolate them has failed. It is convenient, how-
ever, to speak of them as separate ferments, the total
amount of which in the horse has been estimated by Hoppe-
Seyler to be 80 per 1000— forming, in fact, nearly the total
organic matter existing in the secretion.

The ferments found in the pancreatic fluid arc :

Trypsin — which converts proteids into peptones.

Amylopsin — which converts starch into sugar.

Steapsin— which splits up tats into fatty acids ami glycerin.

A milk-curdling ferment has been described ; but in
adult digestion there can be but little need for one.

The action of this ferment on proteids is much the same
as we have previously studied in the gastric juice, proteids
being converted into peptones, especially those difficult of
this conversion in the stomach, and the bemi peptones of
the stomach are split up into Leucin and tyrosin ; but there
are certain important differences which serve to distinguish
between proteid digestion in the stomach and that in the
intestines, thus :

The Liver and Pancreas. 171

1. Peptic digestion is an acid one; pancreatic is essen-
tially an alkaline one.

2. If fibrin be digested by trypsin, during the action of
the ferment the fibrin does not swell up as in peptic diges-
tion. Further, the fibrin is eroded by the action of
trypsin, rather than dissolved as in peptic digestion.

3. The outcome of pancreatic digestion is an alkali-
albumin, and not an acid one, as in the stomach ; and the
proteids in the case of pancreatic digestion ,undergo a
change not only into peptones, but a portion of them is
further converted into leucin, tyrosin, and other sub-
stances. The production of indol, phenol, and skatol in
pancreatic proteid digestion cannot be regarded as due to
the pancreas, but to the presence of micro-organisms and
consequent putrefaction.

By these reactions it is easy to distinguish between a
peptic and pancreatic digestion ; it is very remarkable that
peptone products can be obtained through the action of
two such apparently opposite secretions as gastric and
pancreatic juice.

The action on starchy food is to convert it into sugar,
and this it is capable of doing with extreme rapidity;
15£ grains of pancreatic juice can convert in half an hour
71 grains of starch into sugar ; the form of sugar produced
is maltose, with a little glucose ; the fluid has no action on
cane-sugar, but on starch it acts on the unboiled as well as
on the boiled variety.

On fats the action is very marked : the fats are first con-
verted into an emulsion, by which means the particles of
oil are finely divided; in the next stage the fat itself is
split up into its constituents, viz., fatty acids and glycerin,
and th3 former in the presence of an alkali forms soaps.
The alkaline salts of the pancreatic juice assist in this
action.

The pancreatic juice of the horse emulsifies less com-
pletely than that of other animals.

The presence of alkaline salts, especially carbonate of
soda, assists in the emulsifying of fat.

172 A Manual of Veterinary Physiology.

Fats are chemically neutral, but if rancid they are acid ;
if carbonate of soda be added to a fat containing even a
small proportion of free fatty acid, the fatty acid unites
with the alkali and forms a soap ; this soap envelops the
fat globules and a true emulsion results.

If the fat acted upon be a neutral fat, nothing less than a
free alkali, such as caustic potash, can liberate the fatty
acids.

Pancreatic juice, however, can attack perfectly neutral
fats, splitting them up into free fatty acids and glycerin,
and this it is enabled to do by means of the fat-splitting
ferment it contains.

The most important action on the fat is probably the
formation of the minute oil globules or emulsionizing, by
which means rapid absorption through the intestinal villi
occurs.

Colin's experiments on horses and other animals, showed
that fats were as perfectly absorbed from the intestine in
the entire absence of pancreatic juice as in its presence.
This is probably due to the alkaline intestinal fluid.

The ferments of the pancreas which bring about all the
changes we have described do not exist ready formed in the
gland, but they are formed from a mother-substance termed
Trypsinogen, which is manufactured in the cells of the
gland. This zymogen by decomposition yields the ferments.

The changes occurring in the cells of the gland cor-
respond very closely with those we have described in the
salivary secretion. There is a period of rest during which
the gland is rapidly forming the mother-substance of the
ferments, which can be seen as minute granules tilling the
cells, and there is a period of activity during which the
gland is discharging its manufactured products. In the
herbivora the gland is practically constantly secreting, but
the periods of rest, and activity still occur tor the reason
that all the lobes are not active at the same time.

When a pancreas or lobe of a pancreas has been some time
at rest the cells forming it- are rendered very indistinct, the
lumen of the alveolus is nearly obliterated by the swollen

The Liver and Pancreas.

173

condition of the cells, and the latter are seen crowded with
granules which are so arranged as to form on the margin
next the basement membrane a clear or fairly clear zone,
and within this an intensely granular zone. When activity
commences the granules appear to pass centrally towards
the alveolus, leaving the cell comparatively clear, excepting
that portion immediately abutting on the alveolus, which,
even in the exhausted condition, is still granular. These
changes have resulted in the cells becoming distinct and
clearly defined from each other, and moreover, as they have
emptied their granular contents into the alveolus as pan-
creatic secretion they have consequently become much

Fk;. 11.— A Portion of the Pancreas of the Rabbit (Kuhne
and Sheridan Lea). A, at rest ; B, in a state of activity.

a, The inner granular zone, which in A is larger, and more closely
studded with fine granules, than in B, in which the granules are
fewer and coarser, b, The outer transparent zone, small in A,
larger in B, and in the latter marked with faint stria?, c, The
lumen, very obvious in B, but indistinct in A. d, Indentation of
the junctions of the cells seen in the active but not in the resting
gland (Foster).

smaller; the narrow clear zone seen in the resting gland
now becomes a broad, clear one, the choked alveolus
becomes readily defined, whilst the nucleus of the cell
hidden in the charged condition, is now clearly seen. These
changes have been worked out on the pancreas of the living
rabbit by Kiihne and Sheridan Lea (see Fig. 11).

Amount of Secretion. — From the investigations of Colin
and others we know that in the herbivora the secretion of
pancreatic juice is continuous, though not uniform, reach-

174 A Manual of Veterinary Physiology.

ing its maximum in ruminants towards the end of rumina-
tion, when the secretion may attain the rate of 7 ozs. to
!).', ozs. per hour: in the horse the hourly secretion was
found to be about the same : and in the sheep about \ oz.
per hour.

There is no ratio between the size of the animal, the
weight of the gland, and the amount of pancreatic fluid
secreted : for example, carnivora secrete more than her-
bivora.

The pressure under which the pancreatic juice is secreted
is low ; it is said to be equal to "67 inch of mercury,
which is very little greater than that of the bile.

Nervous Mechanism.— Of this nothing is known : the
gland is supplied by the vagus and sympathetic. It is
probable that a mechanism exists, allied to that found in
the salivary glands, but of this nothing is definitely known.
The head centre for the pancreas lies in the medulla. The
action of pilocarpine and atropine on the secretion is the
same as in the salivary glands ; the former increases the
flow, the latter stops it entirely.

CHAPTER IX.

ABSORPTION.

Lymph.
The methods b}< which the lymph in the body passes out
of the bloodvessels into the tissues, are generally considered
in conjunction with the physical process of the diffusion
and filtration of fluids. It is more than probable that
these may assist in the passage of fluid from the blood into
the tissues, yet neither of such purely physical processes
is capable of wholly explaining the many facts in connec-
tion with lymph formation, and it is therefore more in
agreement with advanced physiological thought to attribute
its formation to changes in the walls of the capillary blood-
vessels, the epithelium of which is probably as intimately
concerned in the production of lymph from the blood, as
the other cells of the body are concerned in the manufac-
ture of secretions.

The tissues are bathed in lymph, which is contained in
the lymphatic spaces which exist between the capillary
bloodvessels and capillary lymph- vessels. There is a con-
stant passage of material from the blood into the tissues,
and from here through the capillary lymphatics into the
main lymphatics, and thence through the thoracic duct
into the venous system.

The largest lymph-spaces in the body are the pleural
and peritoneal cavities ; both these communicate with
lymphatic vessels, many of which are in the diaphragm.

Lymph may be regarded as the material by which the
tissues are directly nourished ; but besides this it may be
looked upon as a means by which effete material is col

176 A Manual of Veterinary Physiology.

lected from the tissues and taken back into the blood.
There are certain non-vascular tissues, such as the cornea,
where the lymph circulation is the only means by which
the part is supplied with nourishment. Speaking gener-
ally, however, the lymphatic system may be described as
the drainage system of the body, in contradistinction to
the blood or irrigating system.

Lymph is a slightly yellow-coloured fluid, alkaline in
reaction, with a specific gravity of 1012 to 1022, and
possessing the power of spontaneous clotting. The clot
it yields is not so firm as that of blood, and takes longer
to form; moreover, the bulk of fibrin is much smaller.
Lymph may be regarded as blood minus the red corpuscles :
it contains, therefore, the proteids of that fluid, cells resem-
bling the white cells of the blood, extractives, salts, and
gases. The fluid in which these are contained may be
spoken of as lymph-serum. The gases consist principally
of CO., (which is greater than in arterial, but less than in
venous, blood), a small quantity of nitrogen, but no oxygen.

The Lymph Cells possess amoeboid movements, and are
identical with white blood cells. They are more numerous
in those vessels which have passed through lymphatic
glands, as it is these latter which principally add the cor-
puscles to the lymph. The cells consist of proteids, lecithin,
cholesterin, and fat, and their nuclei contain nuclein. Owing
to their power of movement, they are able to pass through
the bloodvessels into the tissues and vice versa. The pro-
portion of lymph corpuscles to fluid is about the same as
the proportion of white corpuscles to blood.

In the lymph plasma is found the fibrin factors, hence
the power the fluid possesses of spontaneous cloning.

Amongst the extractives some observers have found
urea, which is said to be always present in the cow;
more urea exists in lymph than in blood (Halliburton).
The salts arc distributed much as those in blood, viz.,
potash and phosphoric acid in the corpuscles, and soda
in the serum.

The lymph corpuscles originate in the lymphatic -lands.

Absorption.

3 77

the mucous membrane of the intestines, the red marrow of
bone, and in the spleen. In the body they undergo decay
and death, and are then broken up and help to form the
fibrin factors (Landois and Stirling).

Analysis of the Lymph obtained from the Lymphatics ok
a Horse* (0. Schmidt).

Constituents in 1,000 parts.

I.

ii.

Water .....

963-93

955-36

Solid matters

36-07

44-64

Fibrin -

[ 28-84

Albumin -

Fats and fatty acids

34-99

Other organic matters

Inorganic matters -

7-22

7-47

Sodium chloride

5-43

5-67

Sodium - -

1-50

1-27

Potassium -

0-03

0-16

Sulphuric acid ....

0-03

0-09

Phosphoric acid combined with alkalies

0-02

0-02

Calcium and magnesium phosphate

0-22

0-26

In the serum from 1,000 parts of lymph

Schmidt found :

Albumin ....

| 23-32

30-59

Fats and fatty acids

1-17

Other organic matters -

4-48

1-69

Analysis of the Lymph of a Cow (C. Schmidt) :
Serum ...... 95*52

Clot ..... 4-42

In 100 parts serum. In 100 parts

dot.

Water -

-

95-76

90-73

Fibrin -

-

—

4-86

Other albumins

-

3-20

—

Fats -

0-12

3-43

Organic matter

017

—

Salts -

0-74

0-96

Sodium chloride

0-56

0-60

Soda -

-

0-13

0-06

Potash -

.

0-01

0-10

Sulphuric and phosphoric

acids

and earthy phosphates

-

0-04

023

* I am indebted for these analyses of lymph and chyle to Gamgec
Physiological Chemistry ' and Colin's 'Physiologic Compan'e.'

12

178

A Manual of Veterinary Physiology.

Here is an analysis comparing lymph with blood

Lymph (Wurtz).

Blood

(Ncutse).

Ox.

Cow.

Ox.

Calf.

Water

- 938-97

955-38

799-590

826-440

Fibrin

2-05

2-2H

3-620

5-737

Albumin and extractives ■

50-90

34-76

66-901

56-414

Fats

0-42

0-24

2-045

1-610

Salts

7-46

7-41

7-041

8241

Blood corpuscles

121-865

102-803

It can be easily understood that the chemical composition
of the lymph will depend upon the nature of the food sup-
plied, and also the sources from which the lymph is
obtained. The following table illustrates the differences in
the lymph of the horse, depending on its source :

1 l~

mph collected
from the
deal Vessels.

ret and Las-

saigne.)

lift

4' E§

*l

g s

Water

964-30

925-00

983-70

965-36

Solids

35-70

75-00

16-30

34-64

Fibrin

l-9o

3 30

0-40

1-20

Albumin and Extrac-

tives

2317

57-36

8-90

27-59

Fats -

traces

traces

traces

Inorganic matters -

10-63

14-34

7-00

5-85

The Quantity of Lymph in the body is very difficult to
arrive at, and varies considerably; 13] lbs. of lymph have
been collected in two hours from a lymphatic vessel in the
neck of a horse (M. Smith). Landois mentions that 2.1 ozs.
to 3£ ozs. have been collected from the same place in l\ to
2 hours. Colin obtained from a lymphatic in the neck of
horses a quantity which varied between 1 to 4 lbs. in
24 hours; the mean amount was 2 lbs. G ozs. for the same
period, but he notes that the variations are wry wide, and
that herbivora secrete more than carnivora, and young
animals more than adults. The amount of material col-

Absorption. 179

lected from the thoracic duct of a cow in 24 hours has been
found to be 209 lbs. ! but this is no guide to the quantity
of lymph in the body, as the material in the thoracic duct
is mixed with the chyle from the intestines. It is usual,
however, in this vessel to consider two-thirds of the contents
to represent chyle and one-third lymph. The quantity of
mixed chyle and lymph obtained by Colin some hours after
the animals had been fed is as follows :

Horse, 30 lbs. to 90 lbs. in 24 hours.
Oxen, 46 lbs. to 209 lbs. in 24 hours.
Sheep, (\h lbs. to 10 lbs. in 24 hours.

The amount of lymph in the tissues is increased by the
activity of the parts, by increase in the blood pressure, and
by obstruction or otherwise to the free passage of lymph
back to the general circulation. As a rule, no more lymph
bathes the tissues than can be carried off by the capillary
lymphatics. If the irrigation exceeds the drainage capacity
oedema results.

It should be noted that excessive transudation is a more
potent factor in the production of oedema than defective
drainage. This excessive transudation may be brought
about by obstructed venous flow (more lymph passing into
the spaces than the latter can get rid of), or by changes in
the character of the blood permitting it to pass through the
walls of the capillaries ; this is well exemplified in anthrax
and inflammatory oedema of the horse.

The method by which the lymph passes from the blood-
capillary into the lymph-space is termed transudation. We
have before mentioned that certain physical processes, such
as osmosis and nitration, may assist in the production of
lymph, but it is to the blood pressure and the wall of the
vessel that the chief results are to be attributed. When
the lymph has passed into the lymph-space, its next move-
ment is towards the capillary lymph- vessel, and the methods
by which this is accomplished are probably by passages
which exist between the space and capillary, and not by
transudation, or, in other words, not by any purely physical

12—2

180 A Manual of Veterinary Physiology.

process such as is assumed by some observers, who have
not been able to trace any communicating channels, paths,
nicks, or crannies between the lymph-space and the capil-
lary.

The lymph having now reached the capillaries from the
spaces, we have next to consider how it is pressed onwards
so as to reach the thoracic duct.

The Movements of the Lymph are due partly to the blood
pressure in the arteries at the seat of the formation of
lymph, which, with certain factors now to be mentioned,
forces the fluid from the lymph-spaces to the thoracic
duct. The pressure in the lymphatic of a horse has been
ascertained by Weiss to be -4 to 78 inch of mercury.
There is a gradual fall of pressure from the tissues to the
duct. Muscular contractions also mechanically favour the
passage of the lymph, the vessels for which are provided
with valves, which prevent the fluid from flowing backwards:
the obstruction caused by the lymphatics passing through
the various glands must be considerable, yet these latter,
by means of the contraction of their covering of involuntary
muscular fibre, more than compensate for the obstruction
caused by the gland itself. Once the lymph has found its
way into the thoracic duct, its passage into the general
circulation is not only favoured by gravity, but also by the
negative pressure produced in the jugular vein by the
process of inspiration, the result being that the lymph is
aspirated out of the duct into the vessel. This aspirating
influence has been proved by experimental inquiry, a
negative pressure having been observed during inspiration,
though a positive pressure of *5 inch of mercury exists in
the thoracic duct of the horse during expiration. That
this is not due to the positive pressure in the jugular vein
is certain, for the latter is prevented from forcing blood into
the thoracic duct by the presence of a valve, which only
allows fluid to pass from the duct into the vein.

The lymph moves slowly in its vessels. WYiss has ob-
served !» inches to 11 inches per minute in a largo lyui
phatic in the neck of a horse.

Absorption. 181

The movements of the diaphragm, tendons, and fasciae
produce an aspirating effect on the lymph circulating
through them. In the case of the diaphragm the lym-
phatic vessels drain the two large lymphatic sacs— the
pleura and peritoneum. Owing to the direction taken by
the fibrous tissue of the diaphragm, compression is exerted
on the lymph-spaces during its contraction, forcing the
fluid onwards, whilst a sucking action is produced when
the part relaxes by which the vessels are filled. This pump-
ing arrangement exists in tendons, fascia of muscles, etc.,
and is a valuable aid in lymph circulation. The swollen
condition of the legs of horses standing idle is due to lymph
stasis ; hence the value of hand-rubbing and bandaging the
limbs, exercise, etc., as methods of treatment.

The whole of the lymph in the body, excepting that from
the right side of the head, neck, and off fore-leg, is collected
and poured into the thoracic duct, which empties itself into
the left jugular vein ; the other parts above mentioned
are drained by vessels emptying themselves into the right
jugular vein. In both cases the part of the vein penetrated
is close to its bifurcation.

There is no special system of nerves known as governing
the lymphatic vessels and spaces.

Chyle.

In the thoracic duct the lymph from the body meets
with the lymph coming from the intestines, termed here
chyle. Chyle is closely allied to lymph in its chemical
composition, but it differs from it in containing a quantity
of neutral fat, which gives it its milky appearance. The
fat is in the condition of fine particles, owing to the emul-
sifying process it has undergone in the intestines before
passing into the villi. The particles of fat are remarkable
for their small size ; these give to chyle what is known as
the molecular basis. It is this molecular basis which dis-
tinguishes chyle from lymph.

The following analyses of chyle will give an idea of its
composition :

182

A Manual of Veterinary Physiology.

Analyses of Chyle ok the Horse (Hoppe-Seyleb).

Constituent* hi 1,000 parts.

I.

Chyle of

Horse.

II.
Chyle of

Horse.

III.

Blood-

serum of

Horse.

Water -

960-97

956-19

930-75

Solids ....

39-03

43*81

69-25

Fibrin

257

1-27

—

Albumin

•22-60

29-85

56-59

Fat, cholesterin and lecithin -

009

0-53

—

Fatty acids in the form of soaps

0-76

0-28

1-57

Other organic matters

5-37

2-24

3-85

Haematin

0-05

0-06

—

Mineral salts - - -

7-59

7-49

7-14

Sodium chloride

5-76

5-84

5-74

Sodium

J 1-31

1-17

0-87

Potassium

0-13

0-14

Sulphuric acid

007

0-05

0-11

Phosphoric acid

n-iil

0-05

o-oi

Calcium and magnesium phos-

phates

0-44

0-25

0-26

Carbonic acid -

1 -02

0-82

056

Chyle from

the Thorack Duct

(WUETZ).

Ox.

Cow.

C0%Y.

lit tare

After

Fed with

Fed with

Rumina-

Rumina-

Hail ami

SI ran- ami

tion.

tion.

Straw.

('/or, r.

Water

950-89

929-7]

951 -24

96251

Fibrin

t-76

t-96

282

0-93

Albuminoids

39-74

.V.I -ci

38-84

26-48

Fats -

0-81

2-55

0-72

0-49

Salts (soluble in

alcohol)

2 47

2-50

2-77

192

Salts (soluble in

water)

1-:;:;

3-61

:; 59

7-97

Chyle contains more solid material than lymph, and, as
mentioned above, very much more fat. Though the pro-
toidfl arc absorbed as peptones, yet no peptones are found
in chyle, owing to the fact that these pass away by the

Absorption. 183

bloodvessels, after undergoing a change in the intestinal
wall which we shall presently indicate. It is said that no
sugar, or but very little, is taken up by the lacteals from the
bowels, the bulk of the carbo-hydrates being carried off by
the portal vein to the liver ; but Colin states that sugar is
found in the chyle of the horse, -12 to -14 per cent, and
that this amount is increased by the introduction of glucose
into the bowels.

The gases in chyle are much the same as in lymph, viz.,
a considerable quantity of carbonic acid, a little nitrogen,
and a mere trace of oxygen.

The composition of chyle varies with the nature of the
food; on a hay diet the fat is small, but when fed with
oats the amount of fat increases considerably. I have
not been able to obtain chyle from the horse that is not
slightly reddish in tint ; its reaction is alkaline, and the
specific gravity varies from 1007 to 1022. In starving
animals, the chyle is more transparent than when collected
after a meal. Colin observes that the chyle of herbivora is
yellowish or yellowish-green, very slightly opalescent, and
in appearance like turbid milk. He also says that the chyle
of starving animals, besides being limpid and transparent,
has almost lost its coagulability.

The chyle while passing upwards through the mesenteric
glands has added to it certain formed elements — lymph
corpuscles — and now possesses the power of spontaneous
clotting.

The movement of chyle is due to the muscular contraction
of the villi forcing the chyle onwards, the valves in the
lacteals preventing its return. Intestinal peristalsis may
also assist, and the negative pressure in the thoracic duct
during inspiration must largely help in aspirating the
contents of the chyle vessels upwards.

Absorption in General.
The activity of absorption in the horse has been made
known to us by the experiments of Colin.

Absorption from the Respiratory Passages is remarkably

184 A Manual of Veterinary Physiology.

rapid. Stimulated by Colin's researches, I have for years
administered certain alkaloids by the trachea rather than
by the skin.* Colin showed that potassium ferrocyanide
could be detected in the blood 2 minutes after being
injected into the trachea, and that it appeared in the blood
before it was found in the chyle. The same salt was also
found in the urine 8 minutes after being introduced
into the trachea. A solution of mix vomica injected into
the trachea produced tetanic symptoms in 3 minutes ;
turpentine, alcohol, and ether were also rapidly absorbed,
but oil could not be taken up, and it was rejected by the
nostrils.

Such drugs as morphia, pilocarpine, physostigmin, etc.,
are all rapidly absorbed ; according to my observations they
produce their therapeutical effect in a shorter time than
when simply injected under the skin. The absorption of
water from the trachea is also remarkably rapid. Colin
introduced 6 quarts of water per hour into the trachea of
a horse; the animal was destroyed at the end of 3?, hours,
and no fluid was found in the bronchi ; he also poured into
the air-passages one pint of water at a time, repeating this
without intermission : in this way he poured in 74 pints of
water before he caused death. A horse may be placed
under chloroform almost instantaneously by an intra-
tracheal injection of the drug.f

The rapidity of absorption from the respiratory passages
is therefore remarkable; and, further, the lungs have the
power of absorbing certain poisons like curare, which are
not absorbed when introduced into the digestive canal.

Absorption from the Cellular Tissue is very active ; ferro-
cyanide of potassium injected into the face was detected in
a carotid lymphatic in 7 minutes, though in order to

* It is interesting to observe that the injection of Liquids into the
trachea (either high up or as low as its bifurcation) excites the reflex
act of swallowing, probably due to stimulation of the recurrent or
other laryngeal nerve.

■\ It is not intended here to recommend the intra-tracheal adminis-
tration of chloroform.

Absolution. 185

reach this place the salt had to pass through the sublingual,
parotid, pharyngeal, and tracheal lymphatic glands. The
rapidity of cellular tissue absorption is hastened by muscular
movement.

Absorption from the Conjunctiva is very pronounced for
some drugs and certain organic poisons, but there are other
drugs and poisons which are not absorbed in this manner.
Cut-are is not absorbed through the conjunctiva, and Colin
could not infect horses with anthrax by placing anthracoid
blood and fluids in the conjunctival sac.

Absorption by the Skin is slow, even for those drugs
which will pass through it, and there are many organic and
inorganic substances which refuse to pass through the un-
broken epidermis. Colin kept the lumbar region of a horse
wet for 5 hours with a solution of ferrocyanide of potas-
sium. The salt was detected in the urine in 4^ hours,
although the skin was quite unbroken. From a wound or
abraded surface absorption will occur rapidly with some
agents, slowly with others. The above observer placed a
horse's foot, with a wound on the coronet, in a solution of
ferrocyanide of potassium ; in 20 minutes he detected the
salt in a lymphatic of the thigh. In connection with
absorption from a wounded surface, he found that the
poison was taken up quite as readily by the lymphatics as
by the bloodvessels. The mucous membrane of the vagina
only absorbs very slowly.

Experiments made on Absorption from the Pleural and
Peritoneal Cavities showed that such drugs as strychnine
rapidly produced fatal symptoms when injected into these
sacs ; even in such a short time as from 3 to 7 minutes
tetanic symptoms supervened. Potassium iodide injected
into the peritoneal cavity of a sheep was detected in the
thoracic duct 5 to 8 minutes after the operation. When
we consider the numerous connections these large lymphatic
spaces have with the lymphatic system, the rapidity of
absorption cannot be wondered at.

Some colouring matters are readily absorbed by serous
membranes.

186 A Manual of Veterinary Physiology.

Intestinal Absorption.

The remarkable fact that no absorption occurs from
the stomach of horses (see p. 134) points to intestinal
absorption as being of considerable importance. That this
absorption is very rapid is proved by Colin's experiments.
Hydrocyanic acid injected into the small intestine of a
horse caused death in 1 to 1 1 minutes, and potassium ferro-
cyanide injected into the bowel, after tying the lymphatics,
may be detected in the blood 6 minutes later.

The Paths of Absorption. — The paths by which intestinal
absorption occurs are (1) through the villi into the lacteals,
and (2) through the bloodvessels into the venous system.

The villi are found only in the small intestines ; they are
•04 to -07 inch long, and possess a diameter of from '02 to
•04 inch. They are comparatively small in herbivora, and
their number in the horse and ox, according to Colin, is
from 45,000,000 to 55,000,000, and these are distributed
over a surface of from 48 to 58 square feet. The lacteals
pass up the mesentery, and each of the 1,200 vessels
counted by Colin passes through a lymphatic gland before
gaining the receptaculum chyli ; here the chyle mixes with
the lymph coming from the posterior extremities, and the
whole is passed into the left jugular vein.

The material absorbed by the bloodvessels passes into
the portal vein and reaches the liver before entering the
general circulation. This arrangement would point to the
fact that there are certain substances which need only pass
through a lymphatic gland before being suitable for the
blood, whilst others must pass through or undergo changes
in the liver previous to being rendered suitable for the
system. Physiologists have therefore devoted considerable
consideration to this subject, but it is far from being in a
satisfactory condition. In the large intestines there are
practically no villi. It must not, therefore, be supposed
that absorption is here exclusively carried on by the blood-
vessels; for, remembering the large chain of glands along
the colon in particular, it, is probable that the material
absorbed passes through these glands to a greater or less

Absorption. 187

extent, as in the mesentery, before entering the circulation.
There is, at any rate, a well-developed lymphatic system in
the walls of the large intestines ; it is possible, therefore,
that material is taken up in the large intestines both
through the bloodvessels and lymphatics, and that this
absorption is something considerable may be readily under-
stood when we remember the size of these bowels and the
nature of their contents ; in the caecum, for instance, the
contents are fluid, derived largely from the water consumed,
and we know that this is readily taken up into the system,
the path in this instance being probably exclusively by the
bloodvessels.

Absorption from the large intestines is active ; we have
given reasons for believing that it may be lymphatic as well
as capillary. That substances can be taken up with ex-
treme rapidity from the large bowels is a well-known fact ;
anaesthetics, such as ether, may be administered to the
horse per rectum. Colin observed that 18 minutes after
injecting a solution of nux vomica into the caecum con-
vulsions began, and 8 minutes later the animal was dead.

The absorbent surface of the large intestines is equal to
75 square feet, and, according to Colin, each square yard
collects 16 i lbs. of solid and liquid matter in 24 hours in
both horse and ox. This observer gives a table showing
the solid and liquid material poured into the intestinal
canal in 24 hours, from which we may judge that the
enormous absorbent surface to which it is exposed is none

too large :

Diet - - - 26 lbs.

Water consumed - 66

Saliva - - - 92 £

Gastric juice - - 11

Bile - - - 11

Pancreatic juice - - 11

Intestinal juice - - 22

Returning, however, to the small intestines, it has been
observed by Colin that in the horse, almost immediately
after food has been given, waves of chyme are passed into
the duodenum, and at once the lacteals in the mesentery in

188 A Manual of Veterinary Physiology.

connection with this portion of intestine become opaque,
though previously they were tilled with a colourless fluid.
As the chyme passes along the bowel the other lacteals in
their turn become opaque, until at last the whole of them
are tilled with this milky fluid. Colin draws especial
attention to this regular invasion of the lacteals from the
duodenum to the ileum.

The various principles of the food having been rendered
fit to be taken up into the system, by what channels is this
accomplished ?

Absorption of Fat. — Experimental inquiry, limited almost
entirely to dogs, points to the lacteals as the means by which
the fatty part of the food is taken up. It has been observed
that these vessels after a diet rich in fat are filled with a
milky fluid rich in the same substance, whilst the blood in
the portal vein does not contain more fat than that of any
other vein in the body. Clearly, therefore, in dogs at least,
the lacteals take up the fat. But what about herbivora,
the diet of which contains but little fat, that of the horse in
particular? Exactly the same appearance of milky lacteals
is obtained in the horse after feeding on a diet notoriously
deficient in fat ; it is possible, therefore, that in the horse
the lacteals may take up other substances than fat, and that
the milky appearance is not due to fat alone. The absorp-
tion of fats is not perfect, for even in dogs only about
60 per cent, of the fat eaten can be recovered from the
thoracic duct, and none, as we have mentioned before, enters
the blood.

Colin expressly states that proteids and sugar are also
absorbed by the lacteals in the horse, and on this point 1 am
certainly inclined to agree with him, in spite of experiments
to the contrary on dogs. This observer injected glucose
into the intestine, and the chyle contained in a short time
a decided increase in sugar.

Returning to the question of fat absorption, we obsorve
that by the action of the epithelium covering the villi the
minute fat globules forming the emulsion arc drawn in and
passed on to the lacteals . from here they ascend the

Absorption. 189

mesentery, passing through the mesenteric glands, where
certain additions are made to the stream in the shape of
cells, and the whole is poured into the general circulation.
It is a well-known fact in human surgery that fat embolism
is not an infrequent accompaniment of certain injuries,
fractures, etc. The fat of the body is taken into the blood-
vessels and blocks the capillaries, especially those of the
lungs. Fat embolism in lacteal absorption is prevented by
the fine emulsion produced in the intestines, for no emul-
sion can occur in any other part of the body, in spite of
the alkaline nature of the blood, owing to the fact that the
body fat is neutral, and neutral fats can only be emulsified
by free alkalies, and not by their carbonates (Bunge).

Absorption of Sugar. — The sugar formed in the bowel is
said to reach the general circulation via the portal vein
and liver. We have reason, however, to believe that some
portion of it may find its way into the lacteals ; but the
bulk of it must of necessity be absorbed by the blood-
vessels, and pass by the portal vein into the liver. We
have seen, in speaking of the liver, how important is the
function of this gland in regulating the supply of sugar
to the system, and the method it possesses of storing
it up.

The Absorption of Proteids is said to be exclusively by
the bloodvessels, from whence they are conveyed to the liver
by the portal vein ; but here a curious point arises : little or
no peptone can be found in the portal vein or even in the
general mass of blood. If peptone be experimentally in-
jected into the blood it is rapidly excreted by the kidneys,
so that it is evident the pe ptone taken up from the intestinal
canal must undergo some important and rapid change before
entering the portal system. Hofmeister's work in this
direction has shown that the peptone is converted once
more into proteid, and that this change occurs in the
intestinal mucous membrane, so that peptones enter the
system in the form of proteid. The process is analogous
to that we have previously dealt with in speaking of
glycogen, where the starch enters the blood as sugar, but is

190 A Manual of Veterinary Physiology.

again converted into a kind of starch in the liver; from here
it is converted into sugar for the use of the blood. Similarly
the proteids are converted into peptones in the intestine in
order that they may be more readily absorbed into the
intestinal walls, but they are no sooner in the capillaries
than they are found to be proteid once more.

The blood of the portal vein does, however, contain a
small portion of peptone, which appears to have escaped
this conversion ; but instead of passing out of the blood by
means of the kidneys, as injected peptones do, it is enabled
to circulate in the stream by being lodged in the white
cells of the blood, and Hofmeister and his pupils have
shown that the number of white blood cells depends upon
the proteid matter in the food, and is not affected b}-
carbo-hydrates, fats, salts, or water.*

* Bunge.

CHAPTER X.

THE SKIN.

It is obvious that one important function the skin performs
is that of affording cover to the delicate parts beneath, and
wherever the chance of injury is the greatest we generally
find the skin is the thickest, whilst in those parts where
sensibility is most required the skin is thinnest. The skin
of the back, quarters, and limbs are good examples of the
first type; on the back especially we have a protective
covering which, in some horses, is as much as a quarter of
an inch in thickness. The face and muzzle is a good example
of the latter variety, the skin in some parts being as thin as
paper. In those parts not exposed to violence we also find
the skin thin, as on the inside of the arms and thighs.

According to Colin, the surface of the horse's skin is equal
to from 50 to 60 square feet.

The skin as an organ of touch is of great importance.
All animals appear most sensitive to slight skin irritation ;
Hies will cause horses to go nearly mad with irritation, and
the elephant, with his thick hide, is quite as sensitive to
these tormentors as a highly-bred horse.

The skin is highly endowed with sensory nerves, par-T
ticularly in those parts connected with the organs of pre-
hension, where also the long hairs growing from the part
are brought into contact with distinct nerve-endings.

The skin is a bad conductor of heat, and this is con-
siderably assisted by the layers of fat found beneath it or
at no great distance from it, as in the abdominal region,
where the subperitoneal fat protects the viscera of animals
living in the open and lying in wet places.

192 A Manual of Veterinary Physiology.

The epidermal covering of the skin relieves the part from
excessive sensitiveness, such as would occur to an exposed
sensory surface, and through the sebaceous secretion it
assists in preventing loss of heat, whilst the greasy covering
throws off the rain, prevents the penetration of water, and
thus saves the epidermis from disintegration.

By means of the hair growing from the skin the heat of
the body is maintained and prevented from passing off too
rapidly. The thickness of the hairy covering varies con-
siderably with the class of horse : the better bred the animal
the finer the coat. I have obtained from draught horses
between 7 lbs. and S lbs. of hair by clipping : in a well-bred
horse this would be reduced to 10 ozs., or even less.

It is a well-known fact that, excepting the hair of the
mane and tail, that of every other part of the body has
only a temporary existence, and is changed twice a year —
once for a thick, and once for a fine coat. It is found that
the heavy coat grown by horses is the cause of considerable
sweating at work, and the general practice of clipping has
been introduced. Of its value there can be no doubt : it
considerably reduces the risk of cold and chest disease,
for animals, instead of coming in from work with a wet
skin — which in some cases will not dry for hours — are
readily dried and easily protected against inclement weather.

Animals Avhich sweat freely at work lose condition. 1
have shown that this is due to the proteid lost by the skin,
for, as we shall presently see, proteids are regularly found in
the sweat of the horse ; clipping largely prevents this loss.
As to the influence of clipping on temperature, see 'Animal
Heat.'

The loss of epidermis by the skin from grooming and
other causes is something considerable, and is an explana-
tion of the nitrogen deficit met with in experiments on the
body-waste. The amount of epidermis lost during an
ordinary grooming will vary considerably, depending on the
cleanliness of the animal and the state of the coat ; in fairly
clean horses it, has nraounted to between '2~> to 60 grains,
and in very dirty animals from 170 grains to '220 grains.

The Skin. 193

As epidermis largely contains sulphur, this is one channel
of removing it from the body.

By means of the glands in the skin we find secreted an
albuminous fluid termed ' sweat,' and a fatty material
known as 'sebum.'

Sweat, or perspiration, is not found to occur over the
general surface of the body in any other hairy animal than
the horse. It is said that sheep perspire (?), the ox to a less
extent and principally on the muzzle, and the dog and cat
on the foot-pads.

The sweat exists in two forms : viz., the invisible vapour
which is always rising from the surface of the skin, and
distinguished as the 'insensible perspiration '; and the visible
material, which is termed ' sweat.'

Colin gives various figures representing the insensible
perspiration, from which we gather that 11 lbs. of water
probably represents this loss in the horse for 21 hours.
Much depends upon the humidity of the atmosphere : the
drier it is the greater the insensible perspiration.

Sweat obtained from the horse by scraping is always
alkaline — strongly so ; after filtration it is the colour of
sherry, and possesses a peculiar horse-like odour, with a
specific gravity of 1020. One specimen examined by me
gave the following analysis :*
Water - - 94-3776

r Serum albumin

- -1049

Organic matters -

•5288 1 „ globulin

- •327:'.

(.Fat

- -0020

Chlorine

- -3300

Lime -

- -0940

Magnesia

- -2195

Ash

5-0936-

Phosphoric acid

- traces

Sulphuric ,,

„

Soda -

- -8265

.Potash

- 1-2135

The proteids are thus seen to be serums albumin and
globulin, and their constant presence has been determined
by a number of observations. The mineral matter is very

* Journal of Physk>logy,vo\. xi., No. 6.

13

194 A Manual of Veterinary Physiology.

high and consists of soda and potash, especially the latter.
It will be observed that the mineral matter exceeds the
organic matter, and in horses which have sweated ireely
the matted hair (which is due to the albumin) is often seen
covered with saline matter, looking like tine sand. In the
paper referred to I have shown that there appears to be
some complemental action between the skin and the
kidneys in the elimination of soda and potash ; during rest
the kidneys eliminate these salts, whilst during work they
are assisted by the skin.

It is difficult to see why horses should excrete albumin
by the skin.

The secretion of sweat in the horse is governed by some
different nervous apparatus to that which exists in man
and other animals. I am not prepared to state what this
difference is ; it may only be a slight one, but it manifests
itself in the action of pilocarpine, which has absolutely no
effect on the sweat glands of the horse, though it produces
the most profuse salivary flow.

The peculiar breaking out into sweats which occurs in
horses after work has no parallel in man ; nothing is more
common after a horse has been perfectly dried than to find
him break out two or three times into a sweat, which leaves
him as wet as he was originally.*

We have no drug which can excite the sudoriferous secre-
tion in the horse ; this is an explanation of the common use
of nitre in veterinary practice : we make the kidneys do
what the skin is unable to. All this points to some
difference in the nervous arrangement, but until these
differences are ascertained we may provisionally adopt, as
the probable changes in the glands during sweating, the
results obtained on the sweat glands of carnivora.

Sweating is produced by the action of the nerves supply-
ing the vessels of the sweat gland, and by special secreting
fibres supplying the gland itself: under ordinary circum-
stances these work together, the bloodvessels dilate and

the Secreting fibres are active; but it is not. essential to
* I have ;ils<> observed sweating to occur immediately after death

caused by Bhooting through the head.

The Skin. 195

the secretion that the vaso- dilator fibres should be in
operation, for we know that sweating will occur in a nearly
bloodless skin, as in the cold sweats following on ruptures
of such viscera as the stomach : and against this we have
the fact that in many cases of arterial thrombosis of the
hind limbs the sweat is pouring off the general surface of
the body (probably from pain), whilst the quarters and
hind extremities remain dry.

The special secreting fibres supplying the cells of the
sweat glands have centres in the cord for the body and
limbs, and in the cervical sympathetic for the head. There
is also, probably, a sweat centre in the medulla. Dupuy
divided the cervical sympathetic of the horse, and obtained
sweating of the head and neck on the operated side.*

The changes occurring in the secreting cells of the sudo-
riferous glands of the horse are described by Renaut.f
When charged the cells are clear and swollen, the nucleus
being situated near their attached ends ; when discharged
they are smaller, granular, and their nucleus more central.

The amount of sweat secreted daily can only be roughly
guessed at : there are many conditions which affect it, such as
the length of coat, nature of the work, and pace. I should
think a minimum secretion would be about 1 pint, and this
I arrived at by brushing a horse lightly over with water.

Doubtless the compensating action existing between the
kidneys and skin observed in men exists also in the horse,
viz., when the skin is acting freely less water passes by the
kidneys, and vice versa.

Sebaceous secretion or sebum is very extensive in the
horse ; its action is protective to the skin. The glossy coat,
which is due to the natural skin fat, throws off a con-
siderable amount of water before penetration occurs.^ In
certain places, as in the prepuce, considerable quantities of
this secretion are found. The sebaceous secretion of the
prepuce of the horse consists of 50 per cent, fat, and also
contains calcium oxalate (Lehmann).§ The secretion of

* Landois and Stirling. f Quoted by Halliburton.

I I have found that the dandruff removed from horses by grooming
contains a large quantity of fat. § Quoted by Halliburton.

18 — 2

I or, A Manual of Veterinary Physiology.

smegma is very considerable in the horse. The ear-wax
and eyelid secretion is also of a sebaceous nature.

In the sheep a considerable quantity of fatty substance
is found in the wool : it exists in two forms, (1) as a fatty
acid united to potash to form a soap, and (2) a fatty acid
combined with cholesterin instead of glycerin : the latter
is known as lanolin, and is largely used as a basis for
ointments. It is also found in hair, horn, feathers, etc.

The fatty substance in the fleece is known to shepherds
and others as ' suint ' : in merino sheep it may amount to
more than one-half the weight of the unwashed fleece, but
in ordinary weather-exposed sheep it may be 15 per cent,
or less. The large amount of potash in unwashed wool is
very remarkable ; a fleece must sometimes contain more
potash than the whole body of the shorn sheep (War-
rington).*

The respiratory function of the skin, so marked in the
frog, is not very active in the higher animals : CO,, passes
out and 0 passes in through the skin. The amount of the
latter for the horse, so far as I am aware, has not been
determined ; it is probably very little.

Gerlachf is said to have collected \ oz. of carbonic acid
in 24 hours from the skin of horses at rest, and 3 ozs. at
work ; it is difficult to know how these figures were arrived
at unless the horse were enclosed in a rubber bag.

Varnishing the skin will rapidly cause death in rabbits,
and more slowly in horses. Death is due to loss of body
heat, and not to suffocation as was at one time supposed.
Horses shiver when varnished, and the surface of the body
and expired air become cold, the visible membranes ar<
violet, and the animals die after several days (( ierlacli, ;
Bouley§) ; but according to Ellenberger, if only partly
varnished they do not die, but exhibit temporary loss of
temperature, and show signs of weakness.

For absorption from the skin, sec article ' Absorption.'
p. is."..

* ' The Chemistry of the Farm.' f Quoted by fil'Kendrick.

! Landoia and Stirling. ^ Colin.

CHAPTER XI.

THE URINE.

It is usual to speak of the urine as a secretion, but this is
not strictly correct ; speaking broadly, we may say a secre-
tion is something which is formed in a part for the purpose
of being eventually utilized by the system. This does not
apply to the urine, the chief ingredients of which are not
even formed in the kidneys, but only separated by them :
moreover, the urine having once been formed is of no further
use to the body, and is excreted. An excretion, therefore,
is a something removed from the system as being no longer
required, and the retention of which would be harmful.

The kidneys may be regarded as the niters of the body,
and one of the channels by which waste and poisonous pro-
ducts are removed or filtered off from the blood, by which
means the latter fluid is maintained in a healthy condition.
We have seen how both nourishment and waste materials
are poured into the circulation, and we have studied several
of the channels by which the latter are removed, viz.,
by the lungs, skin, and intestinal canal : we have now to
examine the last excretory path, viz., the kidneys.

We regard the kidneys as the means by which the waste
products of the body are removed, or by which even
normal constituents of the blood are got rid of if in excess ;
and, according to Bunge, by the selective power which the
epithelial cells of the tubules possess, the alkalinity of the
blood is maintained, alkali being got rid of or sent back
to this fluid as it needs it.

The structure of the kidney is peculiar, inasmuch as that

198 A Manual of Veterinary Physiology.

portion of it which excretes the water does not excrete all
the solids : the water is removed from the blood by the Mal-
pighian bodies, the solids are removed from the blood in the
tubules : in both cases the epithelial cells which line these
parts are the active factors in the matter. The Malpighian
body is arranged so that the blood is always at high
pressure within it : this is accomplished by the efferent
vessels being smaller than the afferent. At this high
pressure the watery part of the blood transudes through
the epithelium into the capsule surrounding the tuft
(known as Bowman's capsule), and thence into the
tubules. It has been stated that a certain proportion of
proteid also passes through the epithelial wall of the tuft,
to be reabsorbed later on in the tubules : but as proteids
do not occur in normal urine, we may safely believe that
the epithelium of the tuft does not in an undamaged con-
dition allow any to pass. During the passage of the water
through the tubule, the secretory cells of the latter pass
into it the organic and inorganic material which they have
separated from the capillary vessels which surround them,
and at the same time it is stated that a portion of the water,
of which an excess is excreted in the Malpighian tufts, is
reabsorbed.

There are no known secretory nerves of the kidneys ; the
vessels are under the control of the vaso-motor system, and
depending upon Avhether they be dilated or constricted, so
we have an excess or diminished secretion, but no secretory
nerves proper are known.

The Composition of the Urine depends upon the class of
animal. In all herbivora, with certain minor differences,
the urinary excretion is much the same, bul not so with
omnivora or carnivora, which possess, especially the latter.
a distinctive urine. When herbivorous animals live on
their own tissues, as during starvation, they become car-
nivora, and their urine alters completely in character,
corresponding to the urine of flesh feeders. The young oi
herbivora, if still sucking, also have a urine possessing
much the same properties as that of carnivora.

The Urine. 199

Urine consists of :

Water.

r Nitrogenous end products : urea, uric acid, hippuric

acid, creatin, creatinin.

Organic matter- Aromatic compounds : benzoic acid, ethereal sulphates

I of phenol, cresol, etc.

'Colouring matter and mucus.

I Sodium, potassium, calcium, magnesium, combined

\ with chlorine, sulphuric and phosphoric acids.

The Reaction of the urine of herbivora is alkaline, the
alkalinity being due to carbonate of potash. The urine of
all vegetable feeders is alkaline, owing to the combustion
in the system of the acid potash salts, the potash appearing
in the urine as carbonate, and producing considerable
effervescence on the addition of an acid. The nature of
the food influences the reaction, for it is stated that the
urine of the horse may be rendered acid by feeding entirely
on oats. A considerable quantity of the alkalinity present
in stale horses' urine is due to the exceedingly rapid change
which occurs in it on standing, leading to the breaking up
of part of the urea and the formation of ammonia carbonate.
The fixed alkalinity of the urine for the twenty-four hours, in
the horse is equivalent to the excretion of between 45 grains
to 60 grains of potassium oxide.

The following remarks apply solely to the urine of the
horse ; what is known of this excretion in other animals
will be spoken of subsequently.

The Specific Gravity of urine varies considerably : the
mean of a large number of observations was 1036 ; the
highest registered was 1050, and the lowest 1014.

The Quantity of urine for the 24 hours is about 8| pints ;
working horses excrete less, owing to the loss by the skin,
etc.

In estimating the urinary constituents for the 24 hours,
they should always be calculated on the total amount
passed, and the sample examined should be a portion of
the 24 hours" fluid. Without the total urine it is impos-
sible to estimate the changes in the system. For clinical
purposes, where the presence or absence of a substance is

200 A Manual of Veterinary Physiology.

all we wish to know, the examination of a single portion of
urine may suffice.

The Odour of urine is said to be due to certain aromatic
substances of the phenol group. Perfectly fresh urine has
a most distinct though faint smell of ammonia.

The normal fluid is always turbid, some specimens more
so than others : very rarely is it clear, and then only for a
short time. The turbidity is due to the amount of sus-
pended carbonate of lime and magnesia which exists in it ;
as the urine cools, particularly if it undergoes ammoniacal
fermentation, the amount of turbidity becomes intense.

The consistence of the fluid depends upon sex, and per-
haps on the season. It is certain that some mares excrete
quite a glairy tenacious fluid, which can be drawn out in
strings, due to the amount of mucin it contains : it is very
common to find it as thick as linseed-oil, and very rare to
find it fluid and watery.

Of the total water consumed, about one-fifth passes away
in the urine, though Munk* considers that one-third passes
away by the kidneys and two-thirds by the lungs. An
interesting point is the ultimate disposal of the water con-
sumed by various animals ; it has been found that carni-
vora excrete by the kidneys the greater part of the water
they drink, whilst herbivora excrete the greatest part by the
lungs.

Here is Munk's table :

Man : 60 per cent, of water escapes by the kidneys, and 40 per cent.

by the lungs and skin.
Carnivora : 70 per cent, of water escapes by the kidneys, and 30 per

cent, by the lungs and skin.
Herbivora : 30 per cent, of water escapes by the kidneys, ami 70 per

cent, by tin; lungs and skin.

The Colour of the urine is yellowish-red, rapidly turning
to brown, the dark tint commencing en the surface of the
fluid and gradually travelling into its depth. The cause of
the colour will be dealt with shortly.

* Quoted by M'Kendrick.

The Urine. 201

The Total Solids of the urine consist of organic and in-
organic matter, of which 5 ozs. are organic and 3 ozs. in-
organic ; they are liable to great variation, sometimes being
found to be considerably in excess of that mentioned.

The total solids are considerably affected by the diet.
E. Wolff* found that Avhen he reduced the hay and increased
the corn ration, the solids in the urine decreased ; thus, on
a diet of 17"6 lbs. hay and 4'4 lbs. oats the urinary solids for
24 hours amounted to 20 ozs., whilst on a diet of 8\S lbs.
hay, 13-2 lbs. oats, the total solids fell to lGj ozs.

Urea is the chief end product of proteid change ; it re-
presents the wear and tear of proteid tissues, but is not, as
we shall see in another chapter, a measure of the work pro-
duced. The amount of urea excreted daily is about 3f ozs.
Half the weight of urea consists of nitrogen. The sources
of urea have given rise to considerable discussion ; it was
supposed to originate in the muscles, but muscular substance
only contains a trace of urea, if any. It is considered that
it may be formed in two or three ways : 1. From the nitrogen
of the food split off during pancreatic digestion in the
form of leucin and aspartic acid, bodies known as the amido
acids. 2. But these amido acids do not account for all the
urea, and it is supposed that the ammonia and carbonic acid
split off from the proteid molecule subsequently combine to
form urea. 3. It is possible that creatin, a substance which
exists largely in muscle, may undergo conversion into urea.

In whatever way urea is formed the seat of the change is
principally in the liver, while probably the spleen and lym-
phatic glands may participate (Halliburton).

The origin of urea from ammonium carbonate is an inter-
esting practical point, and one worth bearing in mind in
the case of a patient receiving this drug medicinally, in
examining the urine in disease for excess of urea.

Uric Acid does not, in my experience, occur in the urine
of the horse excepting as the result of disease, and prac-
tically we may regard uric acid in herbivora as replaced by
hippuric acid, though the latter is at once replaced by uric
* Ellenberger's % Physiologie.'

202 A Manual of Veterinary Physiology.

acid in starvation (when the animal becomes carnivorous)
or, as mentioned before, in the young animal still sucking
its mother.

Hippuric Acid.— Our knowledge of the seat of formation
of this acid in the animal body is due to the experiments of
Bunge and Schmiedeberg, and I shall attempt here to
embody the authors' views on the subject.*

The carbon of the food which is not rejected by means of
the lungs, unites with nitrogen and forms a series of bodies
which escape by the kidneys ; these bodies are urea, uric
acid, hippuric acid, creatin, and creatinin. Hippuric acid
is formed in the animal body by the combination of benzoic
acid and glycocoll, the latter arising possibly from the de-
composition of albuminous tissues, the former being derived
from the food through various aromatic combinations con-
tained in plants.

Great doubts having arisen as to where the synthesis of
glycocoll and benzoic acid occurred, the authors, by means
of experimental inquiry, ascertained that the combination
occurred in the kidneys, that it was brought about by the
living cells of the kidney, and that the red blood corpuscles
took an active part in the process through the oxygen they
contain.

They cautiously observe that in dogs only has the exclu-
sive formation in the kidney of hippuric acid been observed,
for rabbits can form this acid even when the kidneys arc
extirpated.

Hippuric acid exists in the urine either as hippurate of
lime or potash, probably the former. There are no free
acids in the urine, even in carnivora : and in omnivora the
same holds good, the acidity of the fluid with them being-
due to acid salts.

The amount of hippuric acid excreted varies with the
diet; it is increased by using meadow -hay and oat -straw,
and decreased by using clover, peas, wheat, oats, etc.; as
the urea rises the hippuric acid falls.

According to Munk, a horse fed on meadow-hay excreted
* 'Physiological ami Pathological Chemistry,1 Bunge.

The Urine. 203

176 ozs. of hippuric acid per diem ; fed on oats and a
moderate amount of hay l oz. to | oz. per diem is yielded.
This was the mean amount I found in horses fed on the
same diet.

Lie big, many years ago, started a theory that benzoic
acid was found in the urine of working horses, and hippuric
acid in the urine of those at rest ; I have endeavoured to
find out what truth there was in the statement. My
observations showed that hippuric acid is generally found
in the urine of working horses, and seldom found in the
urine of horses at rest — in fact, the reverse of Liebig's
theory. Hippuric acid is rarely to be found in urine 24
hours old ; in fifty-four specimens I only found it eight
times ; this is due to its fermentative decomposition.

Benzoic Acid is the antecedent of hippuric. As just
mentioned, it is derived from the benzoic-acid-forming
substances in vegetable food. The amount found in the
urine of horses at rest is about £ oz. per diem.

Sulphuric Acid exists in the urine in two forms : first, as
an inorganic compound; second, as ethereal sulphates.
Both are derived from the decomposition of proteids, but
the ethereal sulphates or sulphonates are combined in the
form of a potash salt with phenol, cresol, catechol (or
pyrocatechin), indol, and skatol.

These ethereal sulphates occupy an important position in
the composition of the urine of herbivora, as they are
largely derived from the aromatic substances found in their
food, or from the splitting up of the complex albumin
molecule during pancreatic digestion. In carnivora and
omnivora the ethereal sulphates are a measure of the
amount of decomposition occurring not only in the proteids
of the body, but of active putrefactive changes occurring
either in the intestinal canal or outside it, such as in septic
and suppurative diseases. This will not hold good for the
herbivora, as much of the material excreted does not arise
from putrefaction, but is taken iu with the food.

The union of the ethereal sulphates with the aromatic
compounds takes place in the liver. When the phenol

204 A Manual of Veterinary Physiology.

sulphate is excreted it undergoes change in the presence
of the oxygen of the air, forming, amongst other bodies,
pyrocatechin, which gives the brown colour to stale urine.
The daily amount of ethereal sulphate compounds is
about I oz.

Another sulphur compound of the urine is sulphocvanic
acid, found regularly in the urine of herbivora. The only
other substance of this class to which allusion will be made
is indoxylor indican, which is formed from indol, and yields
on oxidation indigo blue, which is commonly found in the
urine of the horse.

The Colouring Matter of the Urine is urobilin, which is a
decomposition product of haemoglobin ; the change may
possibly take place in the liver, though it is generally
supposed to occur in the small intestine, through the bile
pigment being acted upon by the nascent hydrogen, the
product being absorbed and excreted by the kidneys. It is
generally considered that there is only the one urine pig-
ment ; it is certain, however, that in a diseased condition
other decomposition products of hemoglobin appear.

The inorganic substances found in the urine are chlorine,
salts of calcium, magnesium, sodium, and potassium, phos-
phoric, sulphuric, and silicic acids.

The nature and proportion of the salts vary with the
diet. Of the alkalies, potassium salts predominate in the
urine of the horse ; calcium salts are also largely repre-
sented. Meade Smith gives the following ash composition
of horse's urine :

Potassium

- 36-85 pei

• cent.

Sodium

- :5-7l

it

Calcium

- -_>1 •!»•_'

,,

Magnesium

Ill

Phosphoric acid.

—

Sulphuric ,,

- 17- lti

Chlorine

- 15-36

,,

Silicic acid

-

The quantities in this ash analysis do not agree with
my observations, but they convey the same truths, viz., the

The Urine. 205

heavy proportion of potassium salts, the small proportion
of sodium salts, the excess of lime salts, the small proportion
or absence of phosphoric acid, the large proportion of
sulphuric acid, and the small amount of magnesia.

There is a considerable variability in the ash analysis,
which, no doubt, is largely due to the difference existing in
foods. It has been found that in ruminants the calcium
salts are mostly excreted with the feces, whereas in the
horse the bulk passes through the kidneys ; in the same
way it is said that sheep excrete nearly all the potassium
of the food by the kidneys, whilst the horse only excretes
rather more than half by this channel. It is certain that
phosphoric acid, which forms such a prominent feature in
the urine of carnivora and omnivora, is in the horse almost
wholly excreted by the intestines.

Calcium.— More lime exists in the urine than is soluble
in an alkaline fluid, so that we have both suspended and
dissolved lime, the former increasing with the age of the
urine owing to the development of ammonia, until pre-
sently the whole of the lime is precipitated. The lime
exists in combination with oxalic, carbonic, hippuric, and
sulphuric acids. The whole of these combinations do not
necessarily exist in one specimen of urine ; the salts formed
depend upon the amount of lime and the affinity it possesses
for the unsaturated acids. I cannot find that the amount
of lime in the food influences the production through the
kidneys, but I have found more lime in the urine of horses
at work than of those at rest. Oxidate of lime crystals are
common microscopic deposits in the urine of the horse ; the
oxalic acid is probably in part derived from the food.

Magnesium in the urine is also suspended and dissolved,
the amount which is suspended being increased by that
thrown down by the ammonia generated as the urine gets
older.

Potassium exists largely in the urine, derived from the
potash of the food ; it forms numerous combinations, the
one with carbonic acid being the cause of the fixed alka-
linity of the urine. There is more potash found in the

206 A Manual of Veterinary Physiology.

urine of horses at rest than of those at work, which is
explained by the considerable amount of potassium excreted
with the sweat.

Sodium only exists in the urine in small quantities, which
is due to the fact that very little sodium is found in vege-
table food. In the chapter on 'The Constituents of the
Organism ' the question of sodium in the feeding of
herbivora is discussed (p. 19).

The Sulphuric Acid in its organic combination has been
dealt with previously. The inorganic sulphur is combined
with the alkalies : work does not influence its production ;
about I oz. is excreted daily. The origin of the urinary
sulphates is from the decomposition of the proteids of the
tissues.

Chlorine is supplied by the chlorides of the food. The
proportion of chlorine in the food of herbivora is not very
high ; the amount secreted by horses is between § ozs. to
1 oz. per diem, and this, united to the small amount of
sodium present, equals a daily excretion of 85£ grains of
common salt.

Phosphoric Acid, though existing largely in food, such as
oats, passes off almost wholly by the alimentary canal.
Sometimes only traces are to be found in the urine ; at.
others the amount is marked, but never considerable. Work
does not influence its production.

Ammonia, — I believe that free ammonia exists in the
urine of herbivora. It may be that, owing to the amount
of mucin, the urine has undergone ammoniacal fermenta-
tion in the bladder; but it is certain that perfectly fresh
urine gives marked evidence of the presence of free ammonia.
On standing a short time, especially in summer weather,
the urea decomposes and carbonate of ammonia is largely
formed.

The following table, published in my papei on 'The
Urine of the Horse,' gives the mean composition of this fluid,
which lias been compiled from a considerable number of
analyses :*

* Proceedings Royal Sooiety, No. 283.

The Urine.

207

Table showing the Mean Composition of the Twenty- four
Hours' Urine of Horses at Best and Work.

Rett.

Work

Quantity -

8-689 pints

7-877 pints

Specific gravity

1036

1036

Total solids

8-lUozs.

8-188 ozs.

Organic solids

5-155 „

5-368 „

Inorganic solids

2-94 „

2-820 „

Urea

3-4744 ozs.

Ammonia carbonate as urea

•4626 „

Ammonia - - -

■887 „

•187 „

Benzoic acid

•23 „

Hippuric acid

•549 „

Phosphoric anhydride

•046 „

•067 „

Sulphuric

•375 „

•539

Other sulphur compounds

•258 „

•271 „

Chlorine

1-118 „

•775 „

Calcium oxide

•121 „

•067 „

Magnesium oxide -

•105 „

•093 „

Potassium „

L-290 „

•954 „

Sodium ,,

•088 „

1

•064 „

The following summary of the urines of animals other than
the horse is from Tereg.*

The Urine of the Ox is much the same as the horse, except-
ing that it is secreted in larger amounts, 21 to 28 pints, more
or less, the differences largely depending upon the amount
of nitrogenous matter in the diet, for it has been shown
that the more nitrogen a diet contains the larger the
amount of water consumed.

The fluid is clear, yellowish, and of an aromatic odour ;
it is of a lower specific gravity than the horse, 1020 to 1030
(in milch cows, according to Munk, 1006 to 1015), owing to
the larger amount of water secreted, and being poorer in
solids.

The nitrogenous matter in the urine, mainly represented

by urea and hippuric acid, varies according to the diet.

On a diet of wheat straw, clover hay, beans, starch, and

oil, the amount of urea was found to be 4*00 per cent. ;

* Ellenbergers ' Physiologie,' Art. ' Ham.'

208 A Mm tool of Vetervncvry Physiology.

whilst on one of oat straw and beans the urea fell to '84
per cent. When the urea is high, the hippuric acid is low,
and vice versd. The largest amount of hippuric acid is
produced by feeding on the straw of cereals, the smallest
amounts by feeding on leguminous straw, whilst a medium
amount is produced by feeding on hay.

The urine of ruminants contains less aromatic sulphur
compounds than that of the horse, and more of the in-
organic sulphur, but, like the horse, the phosphates are
either absent, or only occur in small amounts.

Here is a table of Tereg's showing the composition of the
urine of the ox on different diets, the observations extend-
ing over four months :

— o

lbs.

lbs.

lbs.

lbs.

Total i

piantity of mine

26*026

31-174

29-986

18-326

„ dry matter

1-716

1-518

1 -41 IS

1-14 4

„ ash

■880

1-01 -i

1-034

•i;r,n

Calves still sucking excrete an acid urine, rich in
phosphates, uric acid, creatinin, and a peculiar substance
allantoin; it is poor in urea, and, according to Moeller,
contains hardly 1 per cent, of solids.

The Urine of the Sheep has an alkaline reaction, and the
amount excreted is from '85 pint to 1-36 pints. Tereg gives
the following percentage composition of a sample :

Specific
Water

gravity

- 1(17-2

- 86-48

Organic

matter

- 7-96

Inorganic matter

- 5-56

The organic matter contained
Urea

•l->\

The inorganic matter c

Chlorine -

'in tained :
- 105

Hippuric acid

3-24

Potassium c-ln >ri> 1 1-

- is J

Ammonia -

•01'

Potassium

- 2*08

Other organic substances -

2-07

Lime

•07

C.nl ionic acid

■42

Magnesia
Phosphoric acid

-JO
•ill

7-96

Sulphuric ,, -
Silica

•24

•07

The Urine. 209

In sheep urea and hippuric acid stand in the proportion
of 2 to 3, whereas in cattle on the same diet the proportion
is 16 or 20 of urea to 11 or 13 of hippuric acid.

It is strange that the food most productive of hippuric
acid in the horse is the least productive of this substance
in the sheep. Old meadow hay produces a large quantity
of hippuric acid in the horse, whilst new meadow hay has
this effect on sheep.

In sheep there is three times more magnesia than lime
in the urine, whereas the reverse is the case in the faeces of
the same animal.

The urine of the pig resembles that of carnivora, but its
composition, etc., depends on the character of the food.
The specific gravity is 1010 to 1015, it is either acid or
alkaline, and contains uric acid, xanthin, guanin, and much
urea.

Secretion of Urine. — The physiology of the secretion of
urine was touched on at the early part of this chapter
(p. 197) ; it is a comparatively simple process, and consists
in the difference in pressure between the blood in the
Malpighian bodies and the tubules; in this it differs
markedl}7 from the saliva, gastric juice, and bile (Landois
and Stirling). When the pressure in the tubules amounts
to two-thirds of the pressure in the renal arteries, the
secretion of urine ceases.

This theory of urinary secretion has been termed the
filtration theory, but there are certain facts which tend to
show that such a view of the matter is incomplete, and that
it is necessary to take into consideration the vital activity
of the cells lining the tubules. Blood pressure doubtless
plays an important part in the process, but it will not
account for an acid urine, nor the presence of a large
quantity of such substances as urea, hippuric acid, creatine,
etc., which are either absent from the blood or only found
in it in traces, and these are beyond doubt excreted by the
epithelial cells of the tubules.

We have before drawn attention to the parts of the
kidney in which the various constituents are excreted.

14

210 A Manual of Veterma/ry Physiology.

The waste products, viz., the organic and inorganic matters,
are doubtless excreted in the tubules, the water in the
Malpighian tufts, and if Ludwig's idea is correct of a partial
reabsorption of water after leaving Bowman's capsule of the
tuft, then it appears probable that the remarkable con-
strictions in the tubules are for this purpose.

The peculiar elective power so often shown in the
tissues of the body is nowhere better demonstrated than in
the kidney. After the water has been removed from the
blood in the Malpighian tuft, the efferent vessel forms a
plexus around the tubules, and from the same blood which
has had the water removed, we now have the waste products
and inorganic matter separated.

The urine is always being excreted, and falls drop by
drop into the bladder, the ureters penetrating the coats of
the latter obliquely, so that as the. organ becomes dis-
tended pressure is exercised on these openings, and no re-
flux can occur.

Micturition. — In the lumbar portion of the spinal cord is
situated the centre for micturition ; it is by afferent and
efferent nerves in direct communication with the bladder.
Through it the sphincter of the bladder is controlled re-
flexly, tightening its grip consciously and unconsciously
on the neck of the bladder as the fluid within increases
in quantity, and by means of this centre the mind is
made aware of the distension which exists. The desire for
micturition having become pressing, the sphincter through
the same channel is relaxed as a voluntary act, the dia-
phragm is fixed, the abdominal muscles and involuntary
muscle uf the bladder wall contract, the urine is forced
into the urethra, where it is hurried along by the accele-
rator urinse muscle. During the act both the horse and
mare stand with the hind-legs extended and apart, resting
on the toes of both hind-feet, thereby sinking the posterior
part of the body : the penis or vulva is protruded, the tail
raised and quivering. The stream which flows from the
two sexes is very different in size, depending on the relative
diameters of the urethral canal. The urethra, excepting

The Urine. 211

when urine is flowing along it, is a closed channel, the
walls of which are in apposition. The mare after urinating
spasmodically erects the clitoris, the use of which it is
difficult to see ; it may be due to the passage of a hot
alkaline fluid over a remarkably sensitive surface.

The horse can under ordinary circumstances only pass
his urine when standing still, though he can defalcate while
trotting ; but a mare, if considerably excited, can empty the
bladder even at a canter.

In the ox, owing to the curves in the urethral canal, the
urine simply dribbles away, being directed towards the
ground by the tuft of hair found on the extremity of the
sheath. The ox can pass his urine while walking.

The cow sinks her body to urinate, but instead of
extending her hind -limbs as does the mare, she brings
them under the body, at the same time raising her tail.

The centre for the renal nerves is said to be in the floor
of the fourth ventricle, puncture of which part produces
diabetes.

The nerves supplying the neck of the bladder originate
in the sacral region, and injury to the part produces
paralysis of the neck and constant dribbling of urine.
Severe injury to the spinal cord may exist far forward with-
out any immediate sign of bladder trouble being present ;
in such cases the work is carried on by the centre in the
lumbar cord.

Abnormal Constituents and Urine-testing.

Although I have made it a rule throughout this work to
avoid the introduction of methods of inquiry, for the
reasons stated in the preface, yet I feel compelled to depart
from this course in the present instance, as the question of
the composition of the urine in health and disease has a
most important clinical aspect. I shall here mention the
abnormal substances found, and afterwards deal generally
with urine-testing.

Albumin. — At least two forms of albumin may exist in
the urine, viz., serum albumin and serum globulin, and to

14—2

212 A Manual of Veterinary Physiology.

these we may add a third, albumoses. If urine containing
globulin be saturated by prolonged shaking with crystalline
magnesium sulphate, a precipitate is produced which is
serum globulin ; the precipitate is best obtained with a
faintly acid urine. This test, however, applied to the urine
of the horse is liable to fallacy, for the reason that there
are certain other substances of a normal kind precipitable
by saturation with MgS04 ; the process, therefore, can only
be employed where albumin is proved by other tests to be
present, and when we are capable of recognising by sight
the difference in the physical character of a MgSO, albu-
minous precipitate and a non-albuminous one. Assuming
a proteid is thrown down by MgS04 the fluid is filtered,
and is then saturated by crystalline ammonium sulphate ;
this throws down serum albumin and albumoses, the former
in flocculent masses. By these tests we are capable of dis-
tinguishing the nature of the proteid excreted ; by the
following tests the presence of albumin only is indicated :

(1) Take the reaction of the urine : if acid add a drop or
two of nitric acid and boil — a precipitate appears ; if the
urine be alkaline rather more acid will be required, but an
excess must be avoided, or acid albumin will be formed
which is not precipitable in an acid fluid on boiling.
(2) Boil the urine ; phosphatic turbidity may occur, or
proteid. if present, be precipitated. Add a drop of acid,
the phosphates or carbonates are at once cleared up,
whilst the proteid is unaffected. This test is an important
clinical one.

When a urine to which nitric acid has given a turbidity
clears up on boiling and becomes turbid on cooling, albu-
moses— a peculiar variety of proteid — are present. These
appear to bo common in the horse.

The proportion of albumin present in a urine is roughly
judged of by the height of the precipitate in the test-tube
after standing from 12 to 24 hours; thus we speak of '. or |
albumin; for clinical purposes this is often sufficiently
accurate.

There are many other tests for proteid in urine, but

The Urine. 213

those mentioned are generally at hand and readily ap-
plied.

Albuminuria is a rare disease amongst horses as the
result of kidney affection, but common enough in many
febrile states of the system ; for instance, in pneumonia it
is exceedingly common, and its presence or absence a
valuable guide in forming an opinion of the case.

Sugar in the urine is distinctly rare, though other sub-
stances may be present which give a sugar reaction and yet
are not sugar.

Sugar is detected by adding to urine a few drops of a
weak solution of copper sulphate and an excess of caustic
potash; the fluid is boiled, and if sugar be present the
whole is turned yellow or red, and throws down a brick-red
deposit of the suboxide of copper.

The only error which can be made in this test is taking
for suboxide of copper the precipitate which always forms
in urine when boiled with copper and potash ; the pre-
cipitate is brown, and the fluid is not turned yellow or red.

Substances may be present in urine other than sugar
which reduce copper. When this is suspected, the only
reliable clinical test is the fermentation one : yeast is mixed
with the urine in a test-tube inverted over mercury, and if
sugar be present it undergoes fermentation, C02 is given
off' and collects in the tube.

Bile. — In many cases of liver di&ease it is important to
know whether any of the bile pigments or bile acids are
passing out with the urine. For this purpose a drop or
two of the urine is placed on a white plate and touched
with a rod dipped in strong common nitric acid ; a play of
colours occurs — green, blue, violet, red, and orange. This
test, known as Gmelin's, is characteristic of the bile pig-
ments. (See p. 161.)

The bile acids are recognised in urine by what is known
as Pettenkoffer's test. To the urine in a test-tube is added
a strong solution of cane-sugar, followed by a few drops of
strong sulphuric acid ; a purple colour is indicative of the
presence of glycocholate and taurocholate of soda.

L'14 A Manual of Veterinary Physiology.

Mucus in large quantities is a normal constituent of
horse's urine, but under disease the amount may be so
increased as to render the urine more like linseed-oil. This
might be taken for albumin. To distinguish it as mucin,
it presents none of the albumin reactions mentioned, and is
not affected by boiling. Acetic acid gives a precipitate
or cloudiness with mucin, Insoluble in exci 88.

Pus is rarely present in urine, due to the fact that sup-
purative disease of the kidneys or bladder in animals is
certainly uncommon. Pus is distinguished by its micro-
scopical appearance ; the urine likewise gives an albuminous
reaction.

Blood. — The only reliable clinical test is the microscope.
The presence of blood can with certainty be determined
by the spectroscope. The coffee-coloured urine of azoturia
is due to methremoglobin.

Carbolic Acid is found in the urine of horses combined
with sulphuric acid. It can readily be detected by dis-
tilling urine with sulphuric acid ; the distillate smells
strongly of the acid. It is a normal constituent, but is
said to be absent in bowel affections, though this does not
accord with my experience, so far as I have had an oppor-
tunity of observing.

A rough but useful clinical examination of the urine may
be made in the following way :

Take the Reaction of the fluid with test-paper; it is
always markedly alkaline in health, and almost invariably
acid in inflammatory diseases.

The Specific Gravity may be taken by an ordinary urino-
meter, using it at the temperature at which the instrument
is graduated, generally (iO Fahr.

The Colour is judged of by transmitted light, some filtered
urine being placed for this purpose in a test-tube and held
up to the light. Occasionally the urine gives one colour by
reflected, and another by transmitted Light ; the reflected
light is often blue. This is generally, perhaps always,
found in stale urine or urine 24 hours old. 1 have never
seen it in the perfectly fresh fluid ; it, is due to indigo blue.

The Urine.

215

The colour of healthy filtered ■ urine is yellowish-red or
yellow ; but a great deal depends on its age. It always
turns brown on standing a few hours, the brown colour

Fig. 12.— Crystals of Nitrate of Urea (Funke).*

commencing on its surface and extending downwards, due
to the oxidation of pyrocatechin. This substance reduces
salts of copper (see Sugar).

Urea, if in excess, may be precipitated by strong nitric

Fig. 13.— Crystals of Impure
Hippuric Acid.

Fig. 14. — Crystals of Purified
Hippuric Acid (Funke).

acid. If the normal bulk of urine is being excreted, urea is
not precipitated until after gently evaporating the urine to

* ' Atlas of Pathological Chemistry.' Supplement to Lehmann's
Physiological Chemistry ' (Cavendish Society).

21(J

A Manual of Veterinary Physiology.

half its bulk, and then adding the acid. The crystals should
be examined microscopically to prove their nature, as hip-
puric acid may be thrown down (Fig. 12). Should albumin
be present in the urine, it must be removed before carrying
out the urea test.

Hippuric Acid is precipitated by evaporating the urine to
half its bulk with milk of lime, and adding HC1 in excess ;
either at once or in the course of a few hours dark sea- weed-
like masses of impure crystals are obtained (Figs. 13 and 14).

Benzoic Acid is obtained by the same method as hippuric.
The deposit is much more granular and occurs immediately
on the addition of the acid ; but the microscope should be

Fk;. 15.— Ckysta

At in.

used to determine between them, hippuric acid being in
long needles, benzoic in irregular leaf-like plates (Fig. L5).

Uric Acid, if present (abnormal), is precipitated by
evaporating the urine to small bulk and adding 11(1.
The crystals may be identified by the microscope (Fig. L6),
or by evaporating them to dryness by means of gentle heat
with nitric acid on a white surface, and touching them with
dilute ammonia, a beautiful purplish-red colour is developed.
This is known as the nuirexido test.

Indigo is readily precipitated in a while basin by the IK'l
method. On standing a few hours the vessel has well-
marked films of blue on it.

The Urine.

217

Chlorides are detected by acidulating the urine with dilute
nitric acid, and adding a few drops of silver nitrate ; the
white curdy precipitate is completely soluble in strong
ammonia, but insoluble in nitric acid. This test should be

Fig. 16.— Crystals of Uric Acid (Funke).

regularly used in cases of pneumonia, where a decrease in
chlorides occurs which persists until death ; the return of
chlorides generally means recovery. It is obvious that the

Fig. 17. — Crystals of Oxalate
of Lime (Funke).

Pig. 18.— Crystals of Carbonate
of Lime (Funke).

same bulk of urine should always be acted upon, as it is
simply by judging the depth of the precipitate that we
can surmise an increase or decrease in the chlorides, and

218 A Manual <>f Veterinary Physiology.

even this is liable to fallacy from concentration or other-
wise of the urine, or from the administration of chlorides
to the patient.

Lime is precipitated by the addition of ammonium oxalate.
The fluid should stand some hours to allow the white pre-
cipitate to settle. A considerable quantity exists in the
urine of herbivora in combination with oxalic and carbonic
acids (Figs. 17 and 18).

Magnesium. — To the fluid from which the lime has been
removed by filtration add phosphate of soda and ammonia ;
allow to stand some hours ; magnesium settles. Very large
crystals may be produced by this process (Fig. 19).

Sulphuric Acid. — A white precipitate, formed on the addi-
tion of barium chloride, insoluble in nitric acid. Before

Fig. l!». — Crystals <»f Triple Phosphate (Funke).

adding the barium the fluid should be acidulated with
hydrochloric acid ; but the latter must be pure and free
from sulphuric acid.

Phosphoric Acid. — Found only in small quantities in
healthy, but largely in acid urine. Phosphates produce a
turbidity on heating the urine, removed by the addition of
a drop of nitric acid. They produce a precipitate with
silver nitrate, soluble in nitric acid.

Soda and Potash cannot be roughly determined, as they

The Urinel j 219

require a tedious isolation which can only be carried out in
a laboratory.

For all the above observations filtered urine should be
used.

To obtain deposits for microscopical examination, the
unfiltered urine is placed in a glass and allowed to stand
for some hours ; the deposit may be taken up with a
pipette and placed on a slide.

In this way red blood corpuscles, pus, casts, epithelium,
etc., may be readily determined. The inorganic deposits
of healthy urine are carbonate of lime in beautiful large
wheel-shaped, dumb-bell, or rosette crystals (Fig. 18), and
oxalate of lime (Fig. 17), in unmistakable octohedra or
square envelope-shaped crystals, insoluble in acetic acid,
carbonate of lime being soluble. Occasionally considerable
quantities of oxalate crystals are formed ; they are nearly
always very small in size, though sometimes large. If the
urine be very alkaline from standing, quantities of the large
tombstone or coffin lid crystals of ammonio- magnesium
phosphate are found; they can be readily seen by the
naked eye as glistening glass-like masses (Fig. 19).

Such are the common crystals found in normal urine.

I

CHAPTER XII.

NUTRITION.

Income and Expenditure. — A constant and fairly regular
waste is daily occurring in the bodies of animals, due to
the internal work of the system, the production of heat,
and, if labour be performed, to muscular movement. It is,
therefore, best to describe the work of the body as of two
kinds : viz., internal work, such as the movement of the
heart, lungs, bowels, and the production of animal heat ;
and external work, due to muscular movement.

If the food an animal receives is neither greater nor less
than its requirements, the body- weight remains unaltered ;
if, on the other hand, the food is deficient in amount the
body loses weight, whereas if in excess it gains weight. By
physiological equilibrium we understand that the income
is equal to the expenditure, and the body- weight remains
unchanged.

It is necessary, however, that the food an animal receives
should supply the various tissues of which the body is
composed, for it is quite possible to conceive a food which,
though equalling in weight a diet which has produced
physiological equilibrium, is yet one on which a loss of
body-weight is occurring, for the reason that it is deficient
in some of the elements out of which the tissues arc
repaired.

The animal body consists of proteids, fats, salts, water,
and ;i wry small proportion of carbo-hydrates. Every food
must cither contain these principles, or must be capable of
conversion into them after having entered the body. Ac-
cording to Bischoff, the animal body consists of —

Nutrition.

221

Water

Proteids

Fat -

Salts

Carbo-hydrates

G4 per cent.
1G

K »

i !!

The water being in the largest, and, excluding the carbo-
hydrates, the salts being in the smallest, proportion. If the
body of an animal be examined, it is found that the largest
portion of it is muscular tissue — in the horse 45 per cent,
at least.

The following table is from Tereg's article on the
' Exchange of Material.'*

Ox.

Sheep.

Pig. Fat.

Half fattened.

For 500 parts of

For 50 parts of For 75 parts of

body weight.

body weight.

body weight.

Water -

257-5

25-1

31-0

Dry substance

201-5

20-3

41-0

Contents of intestines
Composition of the dry

41-0

4-6

3-0

500-0

50-0

75-0

substance :

Proteids - - -

83-0

7-00

8-2

Fat

95-5

11-75

31-6

Ash

Elementary composition of
the organic substance :

23-0

1-55

1-2

V01 5

20-30

41-1

Carbon
Hydrogen

116-97
17-20

12-71
1-89

28-52

4-28

Oxygen -
Nitrogen -
Sulphur -

3020
13-30

•83

2-96
1-12

•07

5-60
1-32

•08

Composition of the ash :

Phosphoric acid -

9-150

•605

•477

Lime

10-500

■682

-465

Magnesia -

•423

•0262

•0234

Potassium

1-020

•085

•101

Sodium -

•727

•052

•0534

Iron

•199

•0211

•0098

Sulphuric acid

•189

•0177

•0212

Carbonic acid

•434

•0267

•0154

Chlorine -

•294

•0257

•0314

Sili ic acid

•064

•0101

•0022

* Ellenberger's ' Physiologic.'

222 A Manual of Veterinary Physiology.

We can readily understand why it is that the food taken
into the body should contain the same principles as the
organism.

These principles are constantly undergoing change, the
nitrogen being oxidized into urea and other products of
nitrogenous metabolism, and the fats into carbonic acid and
water.

The Income of the body is the food taken into the diges-
tive canal, and the oxygen taken in at the lungs.

The Expenditure consists of the Carbon in the form of
carbonic acid expired at the lungs, the small and unknown
quantities given off by the skin, and the carbon excreted
by the urine ; the Nitrogen excreted in the form of urea,
hippuric acid, and other substances given off by the kidneys ;
the Inorganic Salts excreted by the kidneys, through the
skin, and mixed up with the various digestive secretions ;
the Water given off at the lungs by transpiration, through
the skin, by the kidneys, and an amount got rid of by
ordinary secretions.

Besides these we have the excretion of faeces, containing
those portions of the food which the s}-stem has been
unable to assimilate, and mixed up with them are certain of
the secretions found in the intestine. The f;oces do not con-
stitute an expenditure, though, in ascertaining what the
system has assimilated, it is clear that they must be
deducted from the food ingested.

There are other sources of loss besides those mentioned
above, such as the production of milk, wool, and semen ;
but as these have only special application, the general
statement made above is not affected.

The material supplying the income of the body consists
of so much carbon, hydrogen, oxygen, nitrogen, sulphur.
and phosphorus ; and the matter forming the expenditure
also consists of the same elements. When the body is in a
state of equilibrium, the amount of these elements excreted
is the same as the amount ingested, and this is the principle
on which all observations on the wear and tear of the body

Nutrition. 223

have been made. The composition of everything passing
into the body and the exact composition of everything
passing out of it is a tedious experiment to make, and one
liable to considerable error.

Boussingault many years ago made income and expendi-
ture experiments on all domesticated animals, and recently
a most elaborate balance-sheet has been drawn up for the
horse from the experiments of Zuntz and Lehmann* I
have reproduced this table, converting the weights into
pounds and ounces ; this latter has occasioned a slight
discrepancy, inasmuch as the elements expended do not
agree exactly with those taken in. The error, however, is
trivial, and the table is introduced as an example of how
observations of this kind are made. The first portion of it
illustrates also the method by which digestion experiments
are carried out. As the horse on which this experiment was
carried out neither lost nor gained weight, and was kept at
rest, it is evident that the income balanced the expenditure,
so that the quantities representing the income are the
amounts of the elements required by this horse for 24
hours.

In looking at income and expenditure tables of a
body in perfect equilibrium, it is necessary to remember
that, though the amount of the elements going out corre-
spond to the amount taken in, the elements passing away
are not immediately derived from those which have passed
in ; everything passing out must have been of tissue origin,
and have formed part and parcel of the tissues. To make
the matter clearer, take the nitrogen in the table — viz.,
nearly 3 ozs. per diem — excreted by the kidneys : it does
not follow that this nitrogen was derived from the 18 ozs.
of proteid entering the system, but it was derived from
18 ozs. of living proteid which formed part of the
body.

* ' Landwirthschaftliche Jahrbucher,' Band xviii., 1889, Heft 1.

224

A Man/nil of Veterinary Physiology.

Horse.
Composition of the twenty-fotjb hours' Diet.

Fuud in Natural State.

Oats
Hay

Straw

lbs. lbs. ozs. ozs. ozs. ozs. ozs. ,

10-inr.i '. -J'- -2 17-4T.S '.i-s2'j «is-«:',7 17-7" .V21'.i

6-612 5-271 9417 3*851 37*975 24-812 8422

6-306 2-794 -709 1*174 14-61524-865 3*181

Total - - 23*827117-357

Amount unconsumed - -357

27*584 14-854

•638 -257

15 1-427 07-047 16-822
2-581 1-671 -560

Amount consumed
Faeces

17-000 26-946 14*597 148*846
8-104 8-817 6-087 45-985

65*376116-262
56*32612*471

Amount digested

8-896J18-129 8*510|l02*861 9*050 3-791

The lungs absorbed 10-550 lbs. of oxygen.

The elementary composition of the above diet was

[ncome.

Total amount of food required to support
the body for twenty-four hours.

ozs.
18*100

[OIUU I

8-528 '

; Proteids

i Fat -

Carbo-hydrates - 1 1 1 -951 > i

- 168-844 1

1

i

If

bo

1 1 ■ ■ - • n.

6

o

=

Z

y.

i.

ozs.

ozs.

OZS.

ozs.

ozs.

65*872

9-190

229*286

2*895

•180

Atmospheric oxygen

The urine contained 2890 ozs. of nitrogen, and 6*179 ozs.

of carbon.

Expenditure.

i

drogen.
xygen.

o

W °

y.

T.

ozs.

ozs.

ozs. ozs.

ozs.

>>/.*.

•4521

Sulphuric acid -

•271

■180

13-536

Urinary organic matter

6-179

■655 3-806

2-896

■564

Marsh gas

■423

•1 11

75-551

Water -

8-394

67-156

217-321

( 'arbonic acid

59-269

158-052

Total -

65-871

9-190

229-285

2-896 180

Nutrition.

225

In the preceding table the channels whereby loss occurred
to the system were the lungs, urine, skin, etc. ; but where
animals are yielding milk, wool, etc , these have also to be
taken into consideration, the milk especially causing a
considerable bod}7 drain.

In the following table by Henneberg, quoted by Tereg,*
we have a balance-sheet furnished for an ox fed for beef.
The food supply is here in excess of the requirements, and,
in consequence, material is stored up in the system.

Henneberg fed a full-grown ox, weight 1. 570 35 lbs , for
28 days with 1102 lbs. of clover-hay, 13-224 lbs. of oat-
straw, 8154 lbs. of crushed beans, "132 lb. of salt, and
123'644 lbs. of water. During the experiment the animal
increased daily 2-281) lbs. in weight.

The following table shows the income and expenditure
occurring in the body during the above observation. The
author offers no explanation of the discrepancy occurring
in the income and expenditure of hydrogen and oxygen :

Ox

Income.

Mineral
Water. matter.

c.

n.

N.

0.

lbs.

Respiration, food and water 128-272

lbs.
1-961 1

lbs.
2-838

lbs.
16-530

lbs.
•683

lbs.
10-799

Expenditure.

Water.

Mineral
matter.

c.

H.

N.

0.

lbs.
89-632 Fseces

lbs.
- 77-305

lbs.

1-267

lbs.

5-697

lbs.
•683

lbs.

•231

lbs.

4-408

30-6*5 Urine

- 28-817

•672

•484

•055

•374

•231

21'5S9 Carbonic acid

-

5-884

15-675

•06G Marsh gas

-

■044

•022

20-9 4 3 Water by the
and skin -

lun

"1 1 20-943

Total -

- 127-065

1-939

12-109

■760

•605

20-314

Difference

- 1-207

■030

•72! i

•110(?)

•078 1

'873(1)

The difference represents the amount of material stored
up daily in the body of this animal.

* Ellenberger's ' Physiologie.'

15

226 A Manual of Veterinary Physioloyy.

These latter figures corresponded to a daily increase of :

lbs.
Albumin - - - '-184

Fat - - -U17

Salts - - -022

Water - - 1157

Metabolism. — By this term is understood the changes
occurring in living tissues.

It is evident, from all that has been said, that constant
breaking down and building up is occurring in the
body : every muscular contraction, every respiration, the
beating of the heart, the movements of the bowels, all
mean wear and tear, and as rapidly as a part is destroyed
it must be replaced. The processes of construction and
destruction are known as anabolism and katabolism ; in a
perfect state of health they should be in equilibrium.
Both are dependent upon definite chemical changes oc-
curring in the system, some of which we have a fair know-
ledge of; others are wrapped in obscurity.

We have followed the constructive processes from the
mouth until the elements of the food pass into the tissues;
we have no knowledge of what there endows them with life.
We have traced the products of katabolism from the tissues
to the lungs and kidneys, and in a future chapter will state
what is known of the immediate processes in the muscular
tissue, whereby the living substance becomes destroyed,
and is cast off from the body through the excretory
channels previously dealt with.

Of the total amount of carbon which enters the body
with the food, by far the largest quantity is excreted by the
lungs; a certain though small proportion is given oil* from
the skin, and in animals which sweat, as the horse, the
amount passing off during work may not be inconsiderable ;
the remainder of the carbon is got rid of in the form of urea.
hippuric or benzoic acids, and minor carbon compounds.

The hydrogen of the body is excreted as water, the
oxygen as carbonic acid and water, only a small proportion of
it being returned in the lowest form of oxidation, viz., urea.

Nutrition. 227

The nitrogen is almost wholly excreted by the kidneys ;
a small portion may possibly be got rid of by the lungs, and
in working horses by the skin. It is usual to regard the
urine nitrogen as a measure of the proteid changes in the
system, and this nitrogen is got rid of in the form of urea,
hippuric acid, colouring matter, and probably ammonia.

The sulphur of the body is got rid of through the kidneys,
and by means of the cast-off epithelium, hair, and horn.

It is now necessary to glance at the form in which the
various elements of the body enter it, and we will deal first
with proteids.

Nitrogenous Food. — If an animal be fed exclusively on a
proteid diet, it is found that, practically, the more it gets
the more nitrogen is excreted by the kidneys, until at
length a stage arrives when the amount of proteid excreted
equals the amount taken in; this condition does not list
long, and the term applied to it is 'nitrogenous equilibrium.'
These experiments have been made on dogs, and it has
been observed that in order to produce this nitrogenous
equilibrium, a considerable quantity of flesh has had to be
ingested, the result being that the animal has gained weight.
It is evident, therefore, that if the amount of nitrogen
passing out of the body is equal to the amount passing in,
and yet, in spite of this fact, the animal is gaining weight,
a something in proteid food which is not nitrogen is being
stored up ; this something is the carbon portion of the
proteid substance, and it is found that this is stored up in
the body in the form of fat. From these observations it
has been determined that a proteid breaks up in the body
into two portions : one, the nitrogenous portion, which is
excreted as urea ; the other, the non-nitrogenous portion,
which is stored up in the system as fat.

Under ordinary circumstances the whole of the nitrogen
of the proteid is not excreted as urea ; a portion remains in
the system and is converted into tissue. According to
some observers the nitrogenous portion which gives rise to
urea has been termed ' the circulating albumin,' the other
or smaller portion 'the tissue albumin.'

15—2

228 A Manual of Veterinary Physiology.

Considerable discussion has occurred with reference to
this theory of A'oit's of circulating and tissue albumin, and
it is generally considered that the line drawn by this able
observer between the two does not hold good, and that he
is not warranted in stating that urea is derived from that
portion of the proteid which never becomes a part of the
living body, and which he terms ' circulating albumin.' That
under ordinary circumstances a portion of the nitrogen taken
in does form urea and allied substances, whilst another por-
tion is stored up in the tissues, is undoubted ; but it by no
means follows from this that the urea moiety is not derived
from living tissue — in fact, the total weight of evidence is
against Voit, for, as Burdon Sanderson expresses it, the
production of urea and other nitrogenous metabolites is
exclusively a function of living material.

So long, therefore, as we are careful not to regard the
circulating albumin as so much dead substance, no harm
can arise from the use of the terms ' circulating ' and ' tissue
albumin,' as expressing the idea that part of the proteid is
retained in the body and part cast off from it.

All true proteids are equally capable of becoming part of
the tissues when taken as food ; but when albuminoids,
such, for instance, as gelatin, are consumed, they produce
the same amount of urea as an assimilable proteid, but the
animal loses flesh, viz., none of the material is stored up
in the system.

Non-nitrogenous Food.— When animals are fed on an
exclusively fat or starch diet they soon succumb. It is
impossible to maintain life on a nitrogen-free diet. In
experiments made with fat and starch sonic proteid must,
therefore always be given at the same time.

The most remarkable effect of proteid and fat being given
together, is the sparing destruction of the proteid : much less
is used in the system when fats are given than without
them: this is spoken of as the proteid-sparing action of
fats. The amount of albumin required l>y the system is
also diminished by the presence of carbo-hydrates; this is
an important feature in the feeding of herbivora, in the

Nutrition. 229

food of which very little fat exists. It has been suggested
that the proteid-sparing action of carbo-hydrates and fats
is due to the fact that they are oxidized more readily than
albumin, and that they thus prevent the action of oxygen
on this body.

The formation of fat occurs in three ways : (1) From the
fat which enters the body, which in the herbivora is small ;

(2) from the carbonaceous residue of the proteid substances ;

(3) from the carbo-hydrates of the food. It has been
clearly shown by experiment that animals have stored up
fat on a purely proteid diet, and, no doubt, the vast quanti-
ties of fat found in highty-fed animals, have their origin in
the proteid and carbo-hydrate substances of the food.

Owing to the large amount of carbo-hydrate food used
by herbivora, and to the fact that carbo-hydrates require
less oxygen for their oxidation than fat, more of the oxygen
consumed finds its way back in the C02 of the egesta with
herbivora than is the case with carnivora, where the greater
portion of the oxygen leaves the body combined with
hydrogen in the form of water. Herbivora therefore use
less oxygen than carnivora, and the respiratory quotient, as
seen in the chapter on ' Respiration,' is consequently
greater.

Inorganic Food. — The changes occurring in the inorganic
substances of the body are extremely interesting. It is
evident that the daily quantity of salts required must
depend upon the age of the animal : young growing animals
requiring more than adults.

The remarkable thing about Boussingault's nutrition-
tables is, that his animals gave out more salts than they
took in with the food. This can only be explained by
supposing that the system has the power of storing up
inorganic material for future excretion.

In a special experiment made on a cow to determine the
income and expenditure of salts, he found that the animal
gave up -205 oz. more silica than it received in the food,
but it stored up phosphoric acid and lime. The largest
excretion of salts was in the urine the smallest in the milk,

230 A Manual of Veierina/ry Physiology.

and the amount of salts passing away with the f;eces and
of no use to the system was nearly half that ingested.

The salts in the body perform important functions in
connection with secretion and excretion ; as Foster ex-
presses it, they 'direct the metabolism of the body.' Their
distribution throughout the structure is remarkably regular,
sodium and chlorides being found in the blood-serum, potas-
sium and phosphates in the red cells, sulphur in horn,
potassium in sweat, phosphates and lime in bones, etc.
When a deficiency in salts occurs, the body apparently for
some time draws on its own store, and then certain nutri-
tive changes follow. Both organic and inorganic salts are
required.

I have drawn attention to the remarkable fact that
potassium is largely the salt used by herbivora, and sodium
only slightly so (p. 20) ; and further, that horses can be kept
in perfect condition without receiving sodium chloride with
their food, that which is naturally in it (and the amount is
small) being quite sufficient for the uses of the economy.*

Starvation. — When an animal is starved it lives on its
own tissues ; in the herbivora the urine becomes acid ,
hippuric is replaced by uric acid, and the secretion becomes
clear. The elimination of nitrogen in the starving animal
at first falls rapidly, then gradually, and shortly reaches a
fluctuating daily quantity.

During starvation the C02 excreted falls in amount, and
the oxygen absorbed becomes reduced, though not in pro-
portion to the fall of the C02.

If water be given, life is considerably prolonged. Colin
records a case (to be mentioned presently) where a horse
receiving water lived thirty days without food. The loss in
weight by starvation consists of two-thirds water, one-twelfth
albumin, and one-fourth fat. It is notorious that herbivora.
though they lose less proteid during starvation than car-
nivora, yet do not withstand starvation so well. Nor need
we go so far as a starvation experiment to ascertain this
fact: when men and horses are being worked hard, whether
* Journal of Physiology, vol. xi., No. 6.

Nutrition. 231

the food given be insufficient or sufficient, the loss in
condition amongst the horses sets in early, and is extremely
marked for some time before the men show any appreciable
muscular waste.

One explanation offered as to the reason why herbivora
withstand starvation so badly is that they possess less
circulating albumin and less tissue albumin. A full-grown
ox during starvation has been known to use up only
2f lbs. of proteid per diem, whilst, judging from carnivora,
at least double this amount should have been destroyed
(Meade Smith).

Horses have been known to live without food or water
for as long as three weeks ; but it is said that if they have
suffered 15 days' starvation, the administration of food
after this time will not save them.

Colin records an experiment where a horse weighing
892*6 lbs. was starved for 30 days, only being allowed
2-46 pints of water per diem. He was nourished on his
own tissues, the daily loss in weight being 5-865 lbs., con-
sisting of: ozs>

Carbon - - 27-771 .

Hydrogen - - 4-083

Nitrogen - 2 '647

Salts - - - -745

which may be taken as representing the daily waste during
starvation.

When this animal died, the body weight was 715 lbs.,
and it was found that of all the organs the kidneys had
suffered the greatest loss, 41*6 per cent, of their weight:
next the lungs, 38 per cent. ; the stomach and intestines
(empty), 35 per cent. ; the skeleton, 26 per cent. ; skin and
hoofs, 21 per cent. ; muscles, 196 per cent. ; heart, 17 8 per
cent. ; pancreas, 17 per cent. ; spleen, 16 per cent. ; liver,
12 per cent. ; brain and spinal cord, 2*3 per cent.

It is most remarkable that the muscles should have
suffered so little. It was found that the amount of fat
after 30 days' starvation was actually greater than that
found in a healthy control animal of equal weight destroyed

232 A Manual of Veterinary Physiology.

for the purpose of comparison ; the case must therefore be
regarded as exceptional.

In starvation about 90 to 100 per cent, of the fat dis-
appears, and the muscles lose from 60 to 70 per cent, in weight.

Muscular Exertion. — The chief cause of body-waste is
work. There are other and smaller causes, but this is
obviously the most important. The performance of mus-
cular work increases the action of the heart, lungs, muscles,
skin, etc. Potential energy is converted into heat and
work, and this is produced by the oxidation of food into
its decomposition products.

The changes in the tissue resulting in heat and motion
occur almost entirely, if not exclusively, amongst the non-
nitrogenous elements. This has been settled beyond all
doubt. It is not the nitrogenous substances, as we might
suppose, considering their essential nature, which lead to
heat and motion ; and the urea of the urine does not con-
sequently represent a measure of the work performed.
Heat and motion are exclusively the function of the non-
nitrogenous food. This is a curious fact, ami apparently
plunges us into the difficulty of explaining why an animal
cannot live, let alone work, without receiving proteids, and
that the heavier the work performed the more proteid re-
quired. The explanation is that the absorption of oxygen,
without which no oxidation of the non-nitrogenous elements
can occur, is dependent on the amount of proteid taken in.

Amount of Food required.— Muntz (quoted by Colin), from
his investigations into the food required by the Paris
omnibus-horses, came to the conclusion that, five- twelfths
of the total ration was expended on internal work and
repair, and seven-twelfths on muscular work ; and he showed
that a horse performing 9 to 10 miles per diem required for
1,000 lbs. of body-weight: ,b

Nitrogenous matter - - 2*83

Fatty matter - "75

Non-nitrogenous extractives 17*00

( 'ellulose ami lignin - - t> '-'i>

On this diet they neither lost nor made flesh.

Nutrition.

233

From experiments made in Germany by Wolff, the follow-
ing table of food requirements for every 1,000 lbs. of
body-weight was compiled :

Horses at light work

„ moderate work -

,, full work
Oxen at complete rest in stall
Oxen at moderate work

„ full work -
Milch cows-

Fattening oxen : 1st period

2nd ,. -

„ 3rd „ -

Fattening sheep: 1st period

„ 2nd „ -

Sheep fed for wool :

Stronger breeds

Finer breeds

2 ■■;£

rtO,S

.2 -.■-*-
o o

1

I 3

lbs.
21-0
22-5

25-5
17-5
24-0
26-0
24-0
27-0
26-0
25-0
26-0
25-0

20-0

22-5

lbs.

9-5
11-2
13-4

8-0
11-3
13-2
12-5
1 5-0
148
14-8
15-2
144

lbs.

•40
•60
•80
•15

lbs.
11-40
13-60

17-00
8-85

I -30 | 13 20
50116 10
40 ' 15-40
50 18 00
70 18-50

60 18-10

50 18-70

60 ! 18 50

10-3 i -20 11-70
11-1 -25 113-50

1 :

7-0

1 :

7-0

1 :

5-5

1 :

120

1 :

75

1 :

6-0

1 :

5-4

1 :

6-5

I

5-5

1

(V0

1

5-5

1

5-4

1

9-0

1

8-0

It will be observed that the quantities given in the above
table are of ' assimilable matter.' It is a well-known fact
that animals can only obtain from food a certain proportion
of its nourishment; neither reducing the quantity given
nor adding substances to the food will make them digest
more than a certain proportion of each proximate principle ;
the 17 lbs. of assimilable matter for horses in hard work
would probably only be extracted by the administration of
25 lbs. of food. Each food and each proximate principle
has a digestive co-efficient of its own ; and before we can
form any opinion of the amount of nourishment a food is
capable of supplying, we must apply to it the digestive
co-efficients which have been obtained as the result of
direct experimental inquiry.

2:>4 A Manual of Veterinary Physiology.

Digestibility of Food.

From a physiological point of view we understand by the
digestibility of food, that a portion of each of the proximate
principles it contains is capable of being absorbed. Every
food contains albumin or proteid, fat, carbo-hydrates,
and salts. Of each of these there is a distinct proportion
absorbed, and the remainder rejected and excreted with the
fseces. The number which represents the quantity absorbed
is spoken of as the digestive co-efficient. In each food
there is a distinct co-efficient for each proximate principle.
The methods employed by which these results have been
obtained, have been to feed animals on food of known com-
position and analyse the excreta ; the difference between
the albumin, fat, starch, sugar, cellulose, etc., taken in by
the mouth, and that rejected from the body by the f.eces,
is the measure of the amount digested (see table, p. 224).

The digestibility of a food depends upon its age, growth,
mode of preparation, and condition. Well-saved hay, for
example, is better digested than hay which has been
washed by rain. The admixture of other substances with a
food also affects its digestibility ; the addition of starch or
sugar to a diet of hay and straw, if it exceeds 10 per cent,
to 15 per cent, of the dry forage, decreases its digestibility ;
small quantities of oil aid digestion, large quantities retard
it. I have found that the addition of oats to a ration of
hay increased the amount of hay digested.

Contrary to expectation, experiments made by the French
and Germans have shown that neither crushing oats nor
cutting hay increases the proportion assimilated by the
system; it is certain that, as a practical matter, both these
methods of preparing food for horses are highly appreciated
in this country, and I think with good reason. I have been
led to regard 'J lbs. of crushed oats as equal t<» 9| Lbs. to
10 lbs. of uncrushed ; these results were not obtained as
the result of scientific investigation, but as a matter of
observation.

Experiments have shown that the same amount of
proximate principles are not digested by all classes of

rorse.

Ox.

Cow.

Sheep.

69

65

57

57

59

64

65

61

08

66"

70

73

33

60

61

58

Nutrition. 235

animal ; a sheep, for instance, digests hay better than a
horse, and this digestion is not limited, as one might
expect, to the cellulose only, but is extended to the other
proximate principles, excepting the proteids, of which both
animals digested the same amount.

The following table will show the average percentage of
each proximate principle digested by animals. The figures
are the means of a mixed diet :

Albuminoids
Fatty matter
Carbo-hydrates
Cellulose and fibre

By laborious experiments, the digestive co-efficient of all
the principal feeding stuffs has been obtained. The subject
cannot here be dealt with further ; a full account is given
elsewhere.*

It is evident that every food, no matter how well-
balanced in its proximate principles, will contain a certain
proportion of digestible and indigestible matter ; the latter,
no doubt, largely depends upon the presence of cellulose
and lignin. The herbivora, though adapted to digest these,
cannot obtain from their food the full amount of nutriment
if either of them be in great excess ; but apart from
this no food is fully digested : there is a certain proportion
of proteid, fat, sugar, and cellulose which the animal can-
not extract or assimilate from the total amount given it.
This is a point of practical importance.

The digestibility of a food is affected by its Nutritive
Relation, and this term we must now explain. The nutritive
relation of a food is : (1) the proportion which the proteids
bear to the fat and carbo-hydrates, minus the cellulose ;
(2) the proportion of fats to the nitrogenous principles ;
and (3) the proportion of nitrogenous or proteid principles
to the whole of the non-nitrogenous. The first is called
the nitrogenous ratio ; the second the fatty ; the third the
complete nutritive ratio. By splitting up food into these
* ' Veterinary Hygiene.'

236 A Manual of Veterinary Physiology.

various ratios, we obtain an insight into the chemical
arrangement of its constituents, and as the proportion
which these bear to each other considerably influences the
digestion of a food, the matter is one of practical import-
ance.

The desirable nitrogenous ratio of a diet depends upon the
class of animal, the age, and, in the case of the horse, the
work which is expected. In the young and growing animal
the proportion of proteids to the carbo-hydrates, minus the
indigestible fibre, should be 1 : 2 ; at middle age it should
be 1:3; in the adult, 1 : 5. The calculation is effected by
dividing the nitrogenous material into the sum of the
starch, sugar, and digestible fibre.

The fatty ratio of a food is obtained by dividing the fat
into the quantity representing the nitrogenous portion ; the
most favourable fatty ratio should not be more than 1 : 2*2
or less than 1 : 3.

The complete nutritive ratio of a food is obtained by
dividing the nitrogenous quantity into the whole of the
non-nitrogenous ; the chief object of this ratio is to show
the proportion of indigestible fibre existing in a food. The
complete nutritive ratio should be about 1 : 87 or 1:9; if
it be 1 : 10, 1 : 12, or 1 : 15, it would indicate an undue pro-
portion of cellulose and lignin, and such a diet would be un-
fit for hard-working horses, though suitable for cattle. For
horses performing ordinary work, a ratio of from 1:8 to
1 : 8-5 is suitable; for hard-worked horses, particularly for
fast work, 1 : G or 1 : 7 is judicious.

In the determination of all these ratios, the salts of the
food are not taken into consideration.

It is important to remember that the nutritive value of
a food is not, absolutely determined by its chemical analysis ;
bran, for example, gives an excellent analysis, but its
nitrogen is useless for feeding purposes.

CHAPTER XIII.

ANIMAL HEAT.

As the result of the changes occurring in the tissues, heat
is developed. It is not necessary that carbon should be
oxidized to C02 to produce heat, though this is by far the
largest source of supply to the system : any change, hydra-
tion, tissue decomposition, muscular contraction, the passage
of blood through the vessels, the friction produced by one
articulatory surface moving on another, all result in the
formation of heat.

The chief source of continual heat production in the body
is the food supplied, and the amount of heat which different
articles of food are capable of yielding has been very care-
fully ascertained by burning them in an apparatus where
the heat given off is absorbed by water, and the increased
temperature of the water is the measure of the heat pro-
duced. This instrument is termed a calorimeter. The
measurement of beat produced in the calorimeter is known
as a heat-unit, or calorie, and one heat-unit is equivalent
to 2*2 lbs. of water raised 18° Fahr.

The following is Frankland's table of heat-units for
different substances :

1 gramme (15-432 grains) of Albumin yields 42G3 heat-units

„

Fat „

9069 „

J,

Starch „

3921 „

,,

Grape-sugar „

3277 „

,,

, Cane-sugar ,,

3348 „

,,

Urea

2205 „ ,

„

, Hydrogen „

3450 „

„

, Carbon ,,

8100 „

238 A Manual of Veterinary Physiology.

It is necessary to remember that the amount of heat
yielded by a body in a calorimeter may be much greater
than the quantity of heat which the same substance will
yield when oxidized in the body ; particularly is this the
case with albumin, which in the system is never fully
oxidized, as so much of it — one- third — passes off as urea.
The albumin in the above table has been corrected for this
loss.

Loss of Heat. — The chief seat of heat production is the
muscles ; heat is also produced in the liver and other
glands. Of the total amount produced, some is lost by
radiation and evaporation from the skin, and in other ways.

The amounts may be expressed as follows :

Warming solids and liquids 2 per cent. ) 7 . )

air of lungs -5 „ ] ' per cent- \ 15 per cent.
Evaporation from lungs, say 8 or 1) per cent. )

» ?kin I - - - 85

Radiation from skin (

Conduction (ordinarily) - - - - 0 „

100 per cent.

The bulk of the loss is due to evaporation by the skin,
and the heating of the inspired air, food, water and
feces, and only a small and varying proportion is due to
radiation.

The amount of heat lost by the skin is therefore con-
siderable. The object of this loss is to regulate the body
temperature. When animals are varnished, so as to prevent
evaporation, the heat of the body does not accumulate as
we might expect; on the other hand, a fall in temperature
occurs and death shortly follows, the explanation being
that the varnish has proved such a good conductor of heat,
that more is passing away from the animal than under
normal circumstances. If this rapid conduction of heat
be prevented by rolling the animal up in wool, death does
not follow.

The hairy covering on animals prevents loss of heat by
conduction, hair being a bad conductor. When, however,
hair is wet, as in sweating horses, it becomes a conductor of

Animal Heat. 239

heat, which is thereby lost from the body. We see here the
advantage of clipping working horses in the winter. The
effect of clipping on the body temperature has been ob-
served by Siedamgrotzky. He found that the tempera-
ture of horses rose after clipping, and fell about the fifth
day to normal. This rise in body temperature is remark-
able, and is possibly explained by supposing that an in-
creased production of heat was set up by cooling the
surface.

The Amount of Heat produced in the body is spoken of
as so many calories produced per hour per kilogramme
(2*2 lbs.) of body weight, and the hour-calorie-kilogramme
for animals is given by Colin as 2'1 for the horse ; sheep,
2-6 ; man, 2*3 ; sparrow, 3*2. The smaller the animal the
greater the production of body heat.

The quantity of heat developed by a horse in a day is
given by Colin as capable of raising by 1-8° Fahr. 4,550
gallons of water, or it will raise from freezing to boiling
point a little more than 44 gallons of water.

The Regulation of the Body Temperature is no doubt largely
produced by the skin. The respiratory passages also assist,
which is the explanation of the panting observed in the dog,
in which animal the skin practically does not sweat ; and the
remark respecting panting will apply to cattle, especially
those in show condition : here the increased respiratory
movement robs the body of heat by warming a larger volume
of air. It is more than probable that heat production may
be increased or controlled by impressions from the nervous
system ; section of the sympathetic in the neck causes a
rise in temperature on the same side, and division of the
spinal cord causes a fall in temperature ; but both a rise
and fall may be produced by the action of the nerves on
the bloo Ivessels, causing dilatation of them with increased
flow of blood into the skin, and consequently greater loss
of heat ; or constriction of the vessels of the skin, followed
by a diminished loss of heat.

A loss of heat is also produced by conversion into vapour
of the sweat of an active skin, the secretion of which is

540

A Manual of Veterinary Physiology.

wholly under the nervous system. Therefore, by the action
of the vaso-motor nerves on the vessels of the skin, and the
secretory nerves governing the sweat-glands, the discharge
of heat is regulated. But the nervous system has yet a
third effect over animal heat. It is believed that certain
centres exist in the central nervous system which are in
connection with the muscles, and which by reflex action
regulate the metabolism of the tissues, and so increase or
decrease the amount of heat produced in the part.

The normal temperature of the body in various animals
is as follows :

Horse - 100° Fahr.

Ox - - 100° to 101° (Colin).

Sheep - 103° to 104°.

Slight variations are found to occur in the temperature
during the twenty-four hours, which have been attributed
to the intake of food. The evening temperature is normally
higher than that found in the morning. Siedamgrotzky
found the highest temperature to be at six o'clock in the
evening, and the lowest at four o'clock in the mornin".

The same observer studied the influence of feeding on
temperature : he found that the temperature rose '4° to
1'4° Fahr. after feeding, falling to normal in three to five
hours. Drinking a pailful of water at a temperature of
.")0° Fahr. caused the body temperature to fall 5° to
•9 Fahr.

Feeding and drinking act antagonistically, so that one
balances the other.

Exercise raises the body temperature, but to a very
variable extent in different horses. Half an hour's trotting
raised the temperature 7° to '2-7° Fahr. After work the
temperature at first falls rapidly, and then slowly. In
horses which have sweated profusely the resulting fall in tem-
perature carries it below the normal.-

During diseased processes the temperature may run up

Bee Siedamgrotzky's interesting paper, for which [am indebted to
a translation which appeared in the Veterinary .lor, nil, vol. i., L875.

Animal Heat. 241

considerably ; 106° Fahr. is no uncommon temperature in
the horse ; a post-mortem rise in temperature has also been
frequently observed. I once found the thermometer
register 108^ Fahr. placed between the liver and diaphragm
of a horse which died from an affection of the liver.

The Distribution of Temperature throughout the body has
been made the subject of close observation by Colin. He
observed that it was common to find the temperature of the
blood in the left heart to be higher than in that of the
right. He drew particular attention to the fact that the
surface temperature of animals presents considerable differ-
ences. He found in a horse with a long winter coat (the
thermometer standing at freezing-point) that a difference of
44° Fahr. existed between the temperature of the pasterns
and that in the rectum, a difference of 35-1° Fahr. between
the knee and the rectum, and 5 "4° Fahr. between the
temperature of the skin covering the chest and that of the
rectum.

As we might naturally expect, Colin found from direct
experiment that in extremely cold weather those horses
with the longest coat had the warmest skins, the difference
being as great as 9° or 10-8° Fahr.

The power of resisting cold depends not only on the con-
dition of the skin and the means for preventing loss of
heat, but largely on the aptitude of the organism for pro-
ducing heat, and this latter depends upon the activity of
the digestion, the supply and character of the food ingested,
and the intensity of the chemical changes in the system
(Colin).

In the utilization of animal heat the expenditure must
not exceed the income. The means of regulating the
equilibrium of heat, so that no more shall be produced
than the food supplies, is through the medium of the
nervous system.

16

CHAPTER XIV.

THE MUSCULAR SYSTEM.

The actual motive-power in the body, whether it be in the
moving of the skeleton, the contraction of the heart, or
the transport of the ingesta, is performed by the muscular
system. It is one of the largest systems in the body,
representing no less than 45 per cent, of the body weight.
The movement produced by the muscles of the skeleton,
heart, and intestinal canal is very different in nature ; the
skeletal muscles soon tire, the heart and visceral muscles
never tire. We find that muscles exist in two well-marked
classes — the striated or striped or voluntary variety, and
the unstriated or involuntary ; the red muscles represent
the voluntary or skeletal muscles, whilst the white repre-
sent the involuntary or visceral. There is, however, a
remarkable exception to this rule : the muscular fibres of
the heart, though quite involuntary, are both red and
striped.

Composition. — Muscle when examined chemically is found
to consist principally of proteids and salts, in addition to
which may be found a small quantity of acid, glycogen, t races
of urea, and carbonic acid gas. J5y suitable precautions a
fluid can be obtained from perfectly fresh muscle termed
muscle plasma: this undergoes coagulation like blood, and
yields a clot termed myosin and a serum termed muscle
serum. Muscle plasma is a yellowish neutral or alkaline
fluid; after clotting and the formation of the muscle serum,
the latter is found to be acid. Myosin is a substance obtained
after the death of the muscle ; there is every reason to

The Muscular System. 243

believe that during the life of the muscle it does not exist
as myosin, any more than fibrin exists in living blood as
fibrin. The living muscle therefore contains myosinogen,
or myosin precursor, bearing the closest resemblance to the
fibrin of the blood.

Myosin only differs from the blood fibrin by being soluble
in a dilute solution of common salt and dilute hydrochloric
acid.

The muscle serum consists of three proteids, two being
globulins and one an albumin ; it possesses an acid re-
action due to the presence of lactic acid, the result of the
process of coagulation.

In muscle is also found small quantities of volatile fatty
acids, such as acetic and butyric, and an organic acid,
lactic, which exists in two forms. The importance of this
latter acid in the production of rigor mortis, or muscle
coagulation, will be dealt with presently. Carbo-hydrate
substances, such as glycogen and sugar, are also found in
muscles ; their function is the liberation of muscular
energy. The muscles of the horse contain a considerable
quantity of glycogen even after starvation (see p. 166).

Certain extractives can be obtained from muscular tissue,
such as creatin, creatinine, carnin, a variable amount of
glycogen and sugar, together with a trace of urea, and small
quantities of muscle sugar (inosite), alcohol, and lactic acid.

The salts of muscle are principally those of potassium.

A quantity of carbonic acid gas can be obtained from
muscle, together with a small proportion of nitrogen, but
no oxygen.

Changes resulting from Contraction. — The changes occurring
in muscles are remarkably active ; the so-called explosions
which result in muscular contraction, use up at every
moment the combustible material of the structure, and the
products arising from their combustion have to be got rid
of at once and repair brought about ; but changes are con-
stantly occurring even during the period of muscle rest.
Muscle activity is characterized by muscle waste ; muscle
rest is characterized by a preponderance of the process

16—2

244 A Manual of Veterinary Physiology.

of repair. We have to learn, therefore, the nature of
the waste and repair occurring in muscles, and the physical
and electrical phenomena exhibited by muscular tissue
during the period of rest and activity.

The oxygen carried to muscles by the blood is absorbed
by them in considerable quantities, and a volume of car-
bonic acid, in less quantities than corresponds to the
oxygen absorbed, is returned to the venous blood.
Whether a muscle be at rest or active, it is always absorb-
ing O and giving up C02, and, moreover, it is always storing
up oxygen. The absolute amount of 0 stored up and
COo produced varies considerably in rest and work, being
much greater during the latter than during the former
condition.

In an active muscle the bloodvessels are more dilated
than in the muscle of rest, and this dilatation corresponds
to the increased quantity of blood sent to the part, by
which alone the irritability of the muscle, or its power of
contraction, is maintained; whatever leads to a smaller
quantity of blood being sent to an active muscle, produces
partial or complete paralysis of the group or groups of
muscles affected. This is well seen in the horse when
suffering from embolism of the iliac arteries and may
readily be produced in the rabbit by compressing the
aorta.

Muscles in a state of activity contain less glycogen and
sugar than those in a state of rest, due to the amount
utilized during muscular activity. But glycogen is not
necessarily the source of the energy, since muscles free
from glycogen can work normally. Glycogen is rather ;.
convenient accessory than a necessary factor in the pro-
duction of energy in a muscle.

Active muscles present an acid reaction due to the
formation of sarcolactic acid, while the resting muscle is
alkaline.

During muscular activity heat is produced, the blood
returning from the muscle having a higher temperature
than that which supplies it. The amount o[' heat evolved

The Muscular System. 245

varies with the tension of the muscle : the higher the
tension the greater the temperature. This has been pointed
out as the probable explanation of the high temperatures
registered in cases of tetanus. Colin found that the tem-
perature of the masseter muscle of the horse rose 5° Fahr.
through feeding. The more fatigued a muscle becomes
the less heat it evolves.

Muscles possess, in common with some other tissues of
the body, the phenomenon of Irritability or Excitability,
viz., the power of contracting when irritated ; the movement
in muscle shows itself by the contraction or shortening
which occurs. The normal stimulus to muscle is imparted
to it through the nerves, but chemical, mechanical, and
electrical stimuli also lead to a contraction even in the
absence of nerves, or when applied to a muscle removed
from the body.

Through the sensory nerves the brain is made acquainted
with the position of the body and the state of the muscles,
viz., relaxed or rigid, cramped or fatigued. The amount of
ordinary sensibility in muscle is not very great unless it be
cramped or inflamed. Under these conditions acute mus-
cular pain may be manifest, as we see in the painful lameness
of embolism. The special function, however, of the sensory
nerves is communication between the exterior and the
brain, keeping the latter acquainted with the condition of
the former.

By means of the motor nerves the muscles are supplied
with the needful stimulus which brings about contraction ;
division of the motor nerves or interference with their
function leads to muscular paralysis, of which the best
example in the horse is the left laryngeal paralysis result-
ing from pressure on the recurrent nerve.

When a muscle contracts it becomes shorter and thicker ;
the exact microscopical changes which occur are disputed,
but no doubt the transverse striae are brought closer
together ; after contraction it returns to its original length.
Contraction after contraction may be produced, until at
last the muscle becomes fatigued ; it now contracts more

216 A Manual of Veterinary Physiology.

slowly, and is not capable of performing the same amount
of work. If the contractions in a muscle succeed each
other with considerable rapidity, there is no period of
relaxation, and the part is thrown into a condition of
tetanus or cramp. During muscular contraction a sound
is produced, which under suitable conditions may be
heard.

All these changes can be studied with considerable
accuracy by employing muscles isolated from the body,
and placed in contact with an apparatus on which they
can describe their movements when irritated, and at the
same time we can study the electrical phenomena in
nerves.

Muscle Currents. — Great controversy has taken place over
the question as to whether in muscle, currents of electricity
exist independently of those which make their appearance
when the muscle is stimulated. It has been found, for
instance, that a muscle isolated from the body, and placed
under suitable precautions in connection with a galvano-
meter, demonstrated the presence of electric currents which
behaved in a perfectly regular manner, viz., under certain
conditions they were always weaker, and under other con-
ditions stronger, in passing from one definite point on the
muscle to another. They are spoken of as the natural
muscle currents, or the currents of rest, and they always
pass in a definite direction, viz., from the surface of the
muscle to the cut extremity (Fig. 20). If while the gal-
vanometer is registering the direction of the natural muscle
current we stimulate the muscle preparation, a backward
swing of the needle of the instrument indicates a current
passing in an opposite direction to the natural muscle
current: it is termed the negative variation of the muscle
current, or the current of action. The existence of currents
of rest in living muscle is denied, and it would appear that
they are purely post-mortem phenomena, or when obtained
in living muscle are the result of injury due to the needful
preparation for the experiment.

But there can be no doubt that currents are developed

The Muscular System.

247

in muscle during contraction, and these are spoken of as
the currents of action.

Currents of action occur during the phase of muscular
contraction known as the latent period, a term to be presently
described. These currents are not attended by any visible
alteration in the state of the muscles, but a contraction
follows as the result of their passage ; as Foster expresses
it : ' they prepare the way for the visible change of form
which is to follow.' The current of action travels with

Fir,. 20.— Diagram Illustrating the Electric Currents of
Rest of Nerve and Muscle.

Beintf purely diagrammatic, it may serve for a piece either of nerve
or of muscle, except that the currents at the transverse section
cannot be shown in a nerve. The arrows show the direction ot
the current through the galvanometer.

a b, the equator. The strongest currents are those shown by the dark
' lines, as from a at the equator to x or to y at the cut ends. The
current from a to c is weaker than from a to y, though both, as
shown by the arrows, have the same direction. A current is
shown from e, which is near the equator, to /, which is farther
from the equator. The current (in muscle) from a point in the
circumference to a point nearer the centre of the transverse sec-
tion is shown at g, h. From a to b, or from x to y, there is no
current, as indicated by the dotted lines (Foster).

great rapidity to the nerve termination in the muscle
known as the motor end plate ; a contraction now follows,
produced by a decomposition of the muscle substance, the
contraction being in the form of a visible wave, which leads
to swelling and shortening of the muscle fibres.

24JS A Manual of Veterinary Physiology.

The electric changes in muscles are practically the same
as those occurring in nerves, and as this question has to be
dealt with more fully under the nervous system, we shall
postpone any further consideration of the subject until
then (see p. 255).

A Muscle Curve. — If a muscle preparation be arranged so
as to record its movements on a revolving drum, and a
single shock from an induced current be passed into it, a
single contraction follows which traces an upstroke on the
drum, and then the muscle relaxing makes a downstroke :
in this way is obtained a muscle-curve. But it is found on
examining it that the muscle does not contract immediately
the stimulus is applied, but that a perceptible period elapses

Fig. 21. — A Muscle Curve from the Gastrocnemius of the
Frog.

a 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 (Foster).
The curve is read from left to right ; below the muscle curve is a

curve made by a time recorder, each complete curve representing

one-hundredth of a second.

before contraction occurs; this is called the latent period
(a, b, Fig. 21). During this latent period, although the
muscle is not moving, yet it is possible to determine that
the natural muscle current is diminished and that negative
variation occurs — viz., a momentary reversal of the natural
current. The latent period differs in various muscles, and
depends also on their condition ; in the frog it is estimated
at ,,',„- of a second. Succeeding the latent period is the
stage of contraction, at first slow, then rapid, then again
slow till extreme contraction lias been produced, followed
by the third stage — viz., that of relaxation or elongation of
the muscle — which is slow at first and then rapid : while

The Muscular System.

249

the fourth stage consists of one or two small curves, due to
the elasticity of the muscle, termed the stage of elastic
vibration. All these periods are seen in the curve in Fig. 21.
As the muscle becomes fatigued the latent period be-
comes longer, and the contraction is slower and shorter ;
fatigue diminishes the elasticity of muscle. If a suc-
cession of shocks be passed into the muscle in sufficiently
rapid sequence tetanus is produced. On the recording
apparatus there is a long sharp upstroke, representing the
second stage ; the tetanic period is represented by a long
irregular line, and when the tetanus passes off there is a
sudden relaxation representing the third stage (Fig. 22).

YxG. 22. — Tetanus produced with the ordinary Magnetic
Interrupter of an Induction Machine (recording surface
travelling slowly).

The interrupted current is thrown in at a (Foster).

The irregular line shows that tetanus consists of a series of
short contractions, with an insufficient interval for complete
relaxation— in other words, it is not a single long contrac-
tion. A muscle cannot continue permanently in a tetanic
condition, fatigue occurs followed by relaxation.

Besides electrical stimuli, muscles may be excited by
mechanical stimuli — such as a prick or tap — or the appli-
cation of acids or metals to the muscle, some of which act
directly on the muscle substance, others through the
medium of the nerve.

Electrical or other stimulation of involuntary muscle
behaves much the same as voluntary, excepting that the

250 A Manual of Veterinary Physiology.

contractions are much slower and longer. The intestinal
movements seen in a horse recently destroyed exhibit per-
fectly the latent period, the stage of contraction, and that
of relaxation. If the bowels or stomach be very irritable
the lightest touch provokes a contraction, and in the case
of the stomach particularly, large weals occur on its
surface by lightly drawing the finger over it.

The Elasticity in muscle depends upon its condition. In
a resting muscle the elasticity is small but perfect — that is
to say, on being stretched it regains its natural length
when released ; a working muscle owing to fatigue is less
elastic than a resting one. The great advantage to the
animal machine of the elasticity of muscles, is the reduction
in concussion to the skeleton during progression. The
skeletal muscles in the living body are always slightly on
the stretch, at any rate they are not slack, as otherwise
great loss of time would occur before they could act.

We have certain muscles in the machine where the
strain on them is so considerable that tendinous material
is intimately mixed up with the muscular tissue : this is
well seen in the masseters, the muscles of the back, fore-
arm, and thigh. In the living animal provision is made for
the muscles of the limbs being rested without necessitating
the horse assuming a recumbent position, viz., by means of
the check ligaments in the leg ; by this means a horse
can sleep standing, and may remain standing for many
weeks without suffering.

Muscle Fatigue. — Fatigue in muscle is due to excess of
work; the products arising from muscular contraction
accumulate faster than they can escape, the irritability of
the muscles decreases, and they require a greater stimulus
to induce them to respond. The fatigued muscles are also
acid from sarcolactic acid, which probably produces the
soreness and stiffness resulting from overwork. Hand-rub-
bing and shampooing the tired body muscles, such as is
practised on both man and horse in India, and followed by
such good results, is explained by the fact that the lymph
vessels are stimulated to further absorption, and the lactic
acid and other fatigue products got rid of. This is also

The Muscular System. 251

the explanation of the value of hand-rubbing the legs of

Great difference of opinion exists as to whether fatigue
begins in the nervous system or in the muscles themselves.
I incline to the view that the nervous system fails first.

That remarkable state of the body described as ' condi-
tion,' into which horses can be brought by care in feeding
and general management, and carefully-regulated work,
must be regarded as the highest pitch of perfection into
which muscles can be brought ; it is not a permanent con-
dition : no horse can remain in it for any length of time, and
many can never be got into it at all. It is easy in the train-
ing of horses to overstep the mark and produce ' stale-
ness,' a condition due to over- training, but which, unless
it be gone too far, is in both men and horses recovered from
by a short judicious rest, when the system immediately
responds. ' Staleness ' must be regarded as having its
primary origin in the nervous system.

Laws of Muscular Work. — The material used up in muscle
as the result of contraction may be regarded as so much
fuel. Looked at from this point of view the muscles are
very superior machines, for they obtain from the fuel one-
fourth the amount of energy it is capable of producing,
whereas the best-made and most carefully-constructed
engine, cannot extract from fuel more than one-ninth the
energy it is capable of yielding ; moreover, the animal
machine gets stronger by wear instead of weaker.

The amount of work performed by the body is measured
in foot-tons, viz., the number of tons lifted 1 foot high. It
is evident that the force which can lift 1 ton 20 feet high
would be equivalent to the force which lifts 20 tons 1 foot
high (see Locomotion).

The work performed by a muscle is ascertained by multiply-
ing the weight lifted by the height to which it has been lifted.

The following are the laws of muscular work :

1. The larger the transverse section of a muscle, the
greater the load it can lift.

2. The longer the muscle, the greater the height to
which it can lift a load.

2o2 A Manual of Veterinary Physiology.

3-. A muscle at its first contraction can lift its greatest
weight ; but as the contraction continues, the weight it can
lift becomes less and less.

During progression the entire strain of the body comes
on the feet and the muscles of the limbs, and duriug such
paces as galloping the strain is enormous. By galloping
a horse over a weigh-bridge, I have observed that a weight
equivalent to that of the whole body is imposed on one fore-
leg ; it is very easy, therefore, to understand why horses
break down, for as their muscles become fatigued they lose
their elasticity, and the strain is now thrown on the flexor
tendons, which possessing but little, if any, elasticity, give
way under the weight.

Rigor Mortis. — After death a muscle passes into the con-
dition of rigor or stiffening, by which it changes both in
its physical and chemical aspect. The muscle becomes
firm and solid, loses its elasticity, and no longer responds
to electrical stimuli ; further, it loses its alkaline reaction,
and in course of time becomes acid, due to the formation
of lactic and other acids. Through the death of the muscle
the fluid myosin becomes coagulated ; it is this coagulation
which produces the stiffening. Through rigor mortis heat
is developed; some after-death temperatures are remarkably
high (see p. 241).

The rapidity with which rigor mortis sets in differs
according to the mode of death. If an animal in perfect
health be destroyed, the muscle stiffening is slow to set in
and very persistent ; where death is produced by debilitating
disease, or in cases where severe muscular exhaustion has
preceded death, the rigor mortis may occur so suddenly
and pass off so rapidly as occasionally to escape observation,
and decomposition also sots in early. The muscles of the
tongue appear to me to be the only ones where rigor mortis
does not occur, or only incompletely ; the extremity of the
tongue in a dead horse is always Qaccid, and hanging out of
the side of the mouth.

After a certain length of time rigor mortis passes oft' and
decomposition commences.

CHAPTER XV.

THE NERVOUS SYSTEM.

From the fact that the nervous system only occupies a very
subordinate position in veterinary medicine and surgery,
and also that in the lower animals its functions, so far as
the brain is concerned, are so immeasurably inferior to that
of man, I do not purpose giving more than an outline of
the physiology of the parts concerned so far as it has been
ascertained.

The physiology of the nervous system has principally
been worked out on frogs, rabbits, dogs, and monkeys.
We have no evidence that the various tracks found in
the spinal cord of man and dogs exist in the herbivora,
though there can be no doubt that some, or perhaps
even all, are present ; but the inquiry on dogs and rabbits,
which have yielded such fruitful results in determining
the paths in the spinal cord, have not been experi-
mentally applied to the horse and other large animals, and
there are no degenerative diseases of the cord, as in man,
pointing to the existence of definite tracks, so that we can
only assume the existence of much with which we have to
deal. The same may be said of the motor centres in the
cerebrum, the knowledge of which is calculated to revolu-
tionize brain surgery in the human subject. Motor areas,
no doubt, exist in herbivora, but we have no exact evidence
of their position, and even if we possessed this knowledge,
could not probably turn it as yet to any useful advantage.

The nervous system is widely distributed throughout the
body ; there are but few places where no nerves have been

254 A Manual of Veterinary Physiology.

found. It is through the medium of this system that the
blood supply to a part is governed, that the tissues are
nourished, that the part possesses sensation and power of
movement, and that those processes of life are kept up over
which we have no control, and of the existence of which,
so far as our feelings are concerned, we have but little
knowledge ; further, it endows the body with sight, touch,
smell, and hearing, and furnishes animals with whatever
intelligence they are capable of exhibiting. The nervous
system of man and the lower animals principally differs on
the ground of intelligence ; it is this latter which produces
in man his great cerebral development, and marks him out
as a superior being.

The nervous system is composed of the brain and spinal
cord, the nerves with their terminal endings, also a special
system of nerves known as the sympathetic. It is neces-
sary to the elucidation of the subject that these should be
dealt with in an inverse order, and we have first to inquire
into the function and properties of the nerves.

The Nerves.

These form the lines of communication between the
tissues and the brain and spinal cord. It is by means
of them that sensations arise, that motion is produced, that
the calibre of the bloodvessels is regulated, that secretion is
brought about, that the contraction of the heart is induced
and kept under control, that nutrition is governed, and
sight and other special senses produced. Nerves are,
therefore, spoken of as sensory, motor, vascular, secretory,
inhibitory, trophic, and nerves of special sense. These are
further subdivided into those whose duty is to convey im-
pulses from the body to the brain and spinal cord, and
hence called centripetal or afferent nerves, whilst those
which transmit impulses from the brain and spinal cord
to the body are termed centrifugal or efferent nerves.

We have no means of distinguishing these various nerves
either by their physical properties or microscopicaJ appear-
ance; and though in the body their activity is exercised

The Nervous System. 255

in one direction only, we know that removed from the
body, it is just as easy to transmit nervous impulses in
one direction as the other; and experimental inquiry has
ascertained that it is possible to join a sensory to a motor
nerve, and reverse its function,* showing that it is possible
in the body to alter the actual current through the nerve.

We have spoken of this as if the exciting influence were
due to an electrical current ; as a matter of fact, we have no
knowledge of the influence which is at work in producing
motion as the result of stimulating one nerve, sensation of
another, secretion of a third, and so on ; but we do know
that the irritability of nerves is readily manifested on the
application of electrical stimuli, and we may, therefore, at
at once consider the changes thus brought about.

Electrical Phenomena of Nerves. — If a nerve be removed
from the body and suitably applied to an instrument which is
capable of measuring delicate electric currents, the galvano-
meter, the needle of the instrument will be found to be
deflected, showing the passage of a current ; it is spoken of
as the current of rest, and by many physiologists grave
doubts have been expressed as to whether this is a natural
current in nerves or not. It is practically identical in
direction with the natural muscle current described on
p. 246. If while the current of rest is passing a shock be
sent into the nerve from an induction coil, the needle
of the galvanometer is found to indicate a momentary
current in the opposite direction to the current of rest.
This momentary opposite current is spoken of as negative
variation or the current of action. If now, instead of
passing into the nerve a shock from an induction coil, we
pass into it a continuous current of voltaic electricity,
certain phenomena will occur, to explain which we must
suppose the nerve experimented upon to be in connection
with a muscle.

The electrical stimulation employed is the make and
break of a constant (voltaic) current, such as is produced
by connecting two wires with a suitable battery, and an

* This is not generally accepted as correct by physiologists.

25(5 A Manual of Veterinary Physiology.

induced current (faradic), which is obtained by means of a
battery and an induction coil.

If a moderate constant current be passed into the nerve
by connecting it with the poles of the battery, at the
moment the connection is made the muscle gives a twitch
or contraction and then remains perfectly quiet, though the
current is still streaming through it ; if the connection be
broken by removing one pole of the battery, the muscle
gives another contraction. This is termed ' a making and
breaking contraction,' viz., a contraction produced on closing
and opening the electric circuit. If instead of a moderate
constant current a weak or strong one be used, the results
on making and breaking may not be the same.

During the period of apparent quiescence following the
closing of the circuit, though the muscle is giving no indi-
cation of the current, yet profound changes are occurring
in the nerve ; for if it be tested by passing into it an in-
duced current, it is found that the irritability is diminished
in the neighbourhood of the positive pole of the continuous
current, and increased in the neighbourhood of the negative
pole. This is known as electrotonus, the diminished irrita-
bility being known as anelectrotonus, that of increased
excitability as kathelectrotonus. .Between the increased
and reduced irritability is a zone of unaffected irritability,
known as the neutral point.

During the condition of electrotonus there is no inter-
ruption to the natural nerve current; provided the constant
current takes the same direction as the current of rest
through the nerve, the natural current is simply increased ;
but if the constant current be passing in the opposite
direction to the nerve current, the latter is diminished.

To state this matter more clearly, imagine a nerve
running to a muscle, Fig. 2:] ; at a certain pari of the
nerve a continuous current of electricity is passed through
it (the application and withdrawal of which gives rise to
the making and breaking contraction previously mentioned I,
but during the passage of the current the muscle is per-
fectly quiet, in spite of important changes occurring in the

The Nervous System.

257

nerve. A shock is now sent into the nerve from an induc-
tion coil at a place between the muscle and the continuous
current ; as the result of the stimulation the muscle either
responds more than it should do for the strength of the
stimulus employed, viz., there is increased excitability of
the nerve (kathelectrotonus), or the muscle does not

Fig. 23.— Diagram of Electrotonus.
n, the nerve running to the muscle M ; E, an element for the production
of a constant current, the positive pole or anode (a) in a being
placed furthest from the muscle, the current consequently flow-
ing down the nerve, and in i: being placed nearest to the muscle,
the current flowing up the nerve ; at s the nerve is stimulated
by an induced current, and its irritability determined by the con-
traction of the muscle M ; the irritability is increased in a,
kathelectrotonus, and decreased in B, anelectrotonus.

respond as strongly as it should, viz., there is decreased
excitability of the nerve (anelectrotonus). The increase or
decrease of excitability in the nerve depends upon whether
the continuous current is passed down it, as in Fig. A, or
up it, as in B ; with a descending current the excitability
is increased, with an ascending one it is decreased.

17

258 A Manual of Veterinary Physiology.

The explanation of electrotonus in nerves is that it is a
vital phenomenon, viz., the irritability of the nerve is
increased when its molecules pass from their ordinary con-
dition to one of greater mobility (kathelectrotonus), or it
is diminished when its molecules pass from their ordinary
condition to one of less mobility (anelectrotonus) (Cyon).
Hermann considers that it is a purely physico-chemical
phenomenon, due to the electric current generating acids at
the positive pole, and alkalis at the negative : the effect of
the acid being to lower the excitability of the nerve, and
of the alkali to increase it.

The practical application of this law is that the excita-
bility of a part, pain, cramp, etc., may be removed by
passing a current up the nerve, viz., by placing the positive
pole nearest the muscle, and producing anelectrotonus ; or
by reversing the process and throwing the current down
the nerve, so that the negative pole is nearest the muscle,
the irritability of the part is increased.

The Irritability of Nerves is increased by electric,
thermal, chemical, and other stimuli : it is diminished by
cold, compression, or injur}-: it is exhausted by shock or
continual excitement. Nerves are not capable of originating
in themselves any impulse ; the latter is produced by the
impressions made on the nerve terminations. While im-
pulses are being conducted along a nerve, neighbouring
nerves, though in contact, are not affected by it. This is
probably explained by the fact that each nerve fibre is
isolated from its fellow by a sheath, which acts the part of
a non-conductor. A nerve cannot be motor one moment
and sensory the next. These functions are entirely dis-
tinct, and are dependent upon the nerve terminations.

It is necessary for the transmission of an impression that
the nerve should be intact from its origin to its destination :
division of a sensory nerve means loss of sensation to all
parts supplied by it ; if, the main trunk be divided, entire
sensation is lost; if only a branch of the trunk, loss of
sensation follows to the part supplied. We sec this per-
fectly demonstrated in the ordinary operation of neurectomy.

The Nervous System. 259

If the divided end of the sensory nerve be irritated, that
portion still in communication with the spinal cord exhibits
signs of pain.

In motor nerves the reverse applies. Division of a motor
nerve means loss of power of movement ; if that portion in
connection with the tissues be irritated, movement results.
We shall have to allude to this again in speaking of the
spinal cord.

If a sensory nerve be irritated, the pain is felt in the
whole part supplied by that nerve and its branches ; and if
the motor nerve be irritated, the whole of the parts sup-
plied by this nerve and its branches exhibit movement. In
the same way division of a secretory nerve means loss of
secretion ; irritation of the extremity still in contact Avith
the gland means increased secretion. Division of a trophic
nerve may or may not be followed by loss of nutrition, as
witnessed in the comparative rarity of sloughing of the
foot after neurectomy.

The effect of dividing nerves is degeneration of that
portion either above or below the injury. Thus division of
a sensory nerve above the spinal ganglion causes degenera-
tion of that portion still in connection with the spinal cord ;
whilst division of a motor nerve means degeneration of that
still in connection with the tissues. In this way it has
been determined that the nutrition of sensory nerves comes
from above, whilst the nutrition of motor nerves comes
from below the cut extremity.

Nerves are probably nourished by the plasma which
reaches the axis cjdinder at Ranvier's nodes (M'Kendrick).

The rate of transmission of impulses through human
motor and sensory nerves has been placed at 111 to 140
feet per second.

In visceral nerves the velocity is less. Chauveau ascer-
tained that in the pharyngeal branches of the vagus the
velocity was 2G feet per second.

Ganglia. — On certain nerves are to be found nodules
termed ganglia ; they are abundant in the nerves of a
s}7stem which we have yet to consider, viz., the sympathetic ;

17—2

260 A Manual of Veterinary Physiology.

on the cerebro-spinal nerves they are to be found, though
in all cases limited to the sensory branch only. The struc-
ture of the ganglia of a sympathetic and cerebro-spinal
nerve is not identical : in the former the nerves composing
it are both medullated and non-medullated, and the nerve
cells of the ganglia are multipolar ; in the cerebro-spinal
ganglia the nerve cells are only unipolar, and the nerve
libres medullated on entering, but non-medullated on leav-
ing it. The one pole or process issuing from the nerve cell
after a time divides forming a T-piece, one end of the T
probably running to the nerve centre, and one to the
periphery. The cells are really lateral appendages to the
fibres, and we again repeat they are found on sensory and
not on motor nerves. The only known function of ganglia,
whether cerebro-spinal or sympathetic, is for the purpose of
nerve nutrition ; no impulses originate in ganglia, nor can
they serve as centres for reflex action; in other words they
are not nerve centres.

Nerve Terminations. — We have alluded to the terminal end
organs of nerves, and attributed to these the special function
of the nerve ; we must therefore briefly refer to them. A well-
known form of nerve termination is the Pacinian corpuscle ;
it is found both in connection with cerebro-spinal and
sympathetic nerves. Touch corpuscles are found in the
muzzle of the horse and other animals, and probably also
in the sensitive structures of the foot ; end bulbs are found
in the generative organs ; bodies like Pacinian exist in
tendons ; besides these, there are motor terminations, such
as the motorial end plates in muscle, and secretory fibre
terminations in the various glands ; lastly, there are endings
in the nerves of special sense, such as the rods and cones of
the retina, etc.

Spinal Cord.
The spinal cord extends from the alius to about the
second or third sacral vertebra. It is completely enclosed

by a dense membrane, the dura mater. The canal in which
it is lodged is very much larger than the cord, especially at

The Nervous System. 261

those parts where the greatest amount of movement occurs,
as in the neck. The cord is not the same shape nor the
same size throughout ; oval in the cervical region, it be-
comes circular in the dorsal, and again oval in the lumbar
portion. It is largest where any considerable bulk of
nerves is being given off, and thus there is an enlargement
corresponding to the fore, and another to the hind limbs.
We speak of the superior and inferior face of the cord, or
perhaps it would be more in accordance with comparative
anatomy to describe it as the dorsal and ventral face or
surface. On exposing the spinal canal, a large number of
nerves are found to be passing through the dura mater,
either outwards or inwards, and these gain an exit from or
entrance to the spinal canal by means of the foramen formed
at the juncture of the vertebras.

On opening the dura mater, it is easy to determine that
the nerves divide in such a way that part of them run to
the upper or superior surface of the cord, and part to the
inferior. These are spoken of as the superior and inferior
spinal nerves. In the horse the number of branches of
nerve thus formed is considerable, for both the superior
and inferior enter the cord not by a single root, but by
several. On the superior roots, but outside the dura mater,
is found a nervous body termed a ganglion ; each of the
branches of the several roots of a superior spinal nerve has
a ganglion on it. No such ganglion exists on the inferior
root, but inferior and superior roots unite after passing
the ganglion to form a mixed spinal nerve (see Fig. 24).
The function of these two sets of nerve roots is entirely
different. The superior root, containing the ganglion,
conveys sensation and sensation only ; the inferior roots
convey motion, in addition to certain other functions to be
shortly alluded to ; the superior roots are passing into the
cord, the inferior roots are passing out of it. Passing out
with the inferior root of the spinal nerve, but indistinguish-
able from it, is a branch of nerve known as the white ramus
communicans, which leaves the main trunk after the mixed
nerves have formed, and runs to a distinct system known

Fig. 24.— Scheme

Gr., grey ; W, white
matter of spinal
cord ; A, inferior ;
P, superior root ;
6, ganglion on the
superior root ; N,
mixed nerve, con-
sisting of sensory
and motor
branches with
fibres passing into
the sympathetic
system at V ; N1,
spinal nerve, con-
sisting of sensory
and motor
branches, termin-
ating in M, skeletal
muscles, S, sen-
sory cell or sur-
face, X, in other
"ways ; V, white
ramus communi-
cans uniting the
cerebro - spinal
with the sym pathe-
tic system, running
out from the cord
with the inferior
spinal nerve, and
given off from the
mixed nerve at V,
from whence it
passes to S, a gang-
lion on the sym-
pathetic chain, and
passing on at V>
to supply the more
distant ganglion
<t, then at V" to
the peripheral
ganglion a, and
ending in m, a
visceral muscle,
*, a visceral sen-
sory cell or sur-
face, .<■, other
possible visceral
endings. M

From 2 is given off a branch, r.v., known as the grey ramus com
mumcans which partly passes backwards towards the spinal cord
ana partly runs, as v.\i.. in connection with the spinal nerve to

supply vaso-constrictor fibres to the muscles, mr of bl lve«sels in

certain parts, for example, in the limb*.
Sy the sympathetic chain (gangliated cord of the sympathetic uniting
cne ganglia of the series 2. The terminations of the other nerves
arising From £. *. <i' ■.,,-,■ n..t ^i. ,,„■,,

The Nervous System. "2Go

as the sympathetic ; one part of the latter, the gangliated
cord, runs under the arch of the ribs and back as far as the
loins ; to this cord the white ramus runs, and establishes a
communication between the cerebro-spinal and sympathetic
system ; moreover, in this branch are the nerves which con-
strict all the bloodvessels in the body. A careful study
of Fig. 24 is necessary for clear elucidation of the arrange-
ment of the spinal nerves.

Arrangement of the Cord.— If a cord be suitably prepared,
it is found to consist of a superior, lateral, and inferior
column, each divided by a longitudinal groove. On the
superior and inferior surface is a fissure : the inferior fissure
is wide, and does not reach down to the centre of the cord ;
the superior fissure is very narrow, and so deep that it runs
down into the central portion of the cord.

On making a section of the cord, it is found to be made
up of both white and grey matter, the latter internally
placed, forming the medulla, is arranged something like
two commas placed back to back, the tail of the comma
being uppermost; the tail of the comma corresponds to
the incoming sensory fibres, the head of the comma to
the outgoing motor ones. The two commas are connected
by a band of grey matter, known as the commissure, in the
centre of which is a canal.

Speaking roughly, we may say that the white substance
of the cord is made up of fibres, the grey substance of
nerve cells. The white substance is not the same thick-
ness throughout, the upper portion of the cord containing
more white matter than the lower portion. In the same
way, the grey substance is not the same thickness nor the
same shape throughout the length of the cord. This grey
substance is very important. We shall have to show that
directly or indirectly both the superior and inferior nerve
roots communicate with it. The nerve cells composing it
are multipolar and of considerable size, each containing
nuclei with nucleoli. It has been ascertained that the
nerve cells of the grey matter are unequally distributed,
and can be grouped according to their position ; thus, in

264

A Manual of Veterinary Physiology.

the inferior portion of the inverted comma, or, as we shall
speak of it, the inferior cornu, they are exceedingly
numerous, there being five groups of nerve cells each
known by a separate name ; whilst the cells of the superior
cornu are not onl}- fewer in number, but the number of
groups is only three or four.

Tracts in the Cord. — The white matter of the cord can
be mapped out into columns or tracts, which are quite
distinct from the columns into which the cord is originally

Fig. 25.— DiAtiRAM to Illustrate the General Arrangement
of the Several Tracts op White Matter in the Spinal

Cokd.

The ascending tracts are shaded with dots ; the descending tracts art-
shaded with lines. The shading is in each case put on one sid<
of the cord only, the reference letters beiDg placed on the other
side. cr.i>, pyramidal tract; di\, direct pyramidal tract: C.b.,
cerebellar tract ; s.l.r. and c.r. together indicate the median
posterior tract (tract of the fibres of the superior or sensory roots
of the spinal nerves) ; asc.a.l., the antero-lateral ascending tract :
desc.l., the antero-lateral descending tract. (Foster, after Sher-
rington.)

divided. Some of these tracts are supposed to be convey-
ing impulses from the cord to the brain, and are known
as ascending tracts ; others are convoying impulses from
the brain to the cord, and arc known as descending tracts.
These descending and ascending tracts have not been mad<
out by ordinary observation, but by experimental inquiry
Tt was found that, after division of certain nerves or injuries
to certain parts of the brain, particular tracts became do-

The Nervous System. 2G5

generated either in an upward or downward direction.
By this and other means, it was ascertained that certain
paths or tracts exist in the white matter of the cord, con-
necting the brain with the cord and vice versa. It must
not be supposed that the function of a downward or
upward tract is entirely exerted in the direction given to it
by its name ; they are called upward or downward depend-
ing upon the direction of the degeneration resulting from
experimental injury.

The following are the tracts in man according to Foster :

Descending Tract*. Ascending Tract*.

Pyramidal tract. Cerebellar tract.

Direct pyramidal tract (not found Median posterior tract.

in animals). Anterolateral ascending tract.

Antero-lateral descending tract.
Comma tract (limited to cervical

and upper thoracic regions).

These paths, known to various observers by somewhat
different names, are distributed between the anterior, lateral,
and posterior columns ; an examination of the diagram
(Fig. 25) will render their position in the cord more
clearly understood. These tracts are not found throughout
the entire length of the cord, and in all cases they
diminish in size from the head to the tail.

The pyramidal tract is large in man but small in the
monkey and dog ; it is in connection with the motor region
of the brain, and its great size in man appears to bear a
distinct relation to the complexity of the motor region:
the more intricate the changes in the central nervous
system the larger the pyramidal tract. (Foster.)

Some of the tracts run from the white and terminate in
the grey matter. The tracts differ microscopically, some
being composed of coarse fibres, others of line, some of
mixed fibres.

It has not been found possible to divide the whole of the
white matter into tracts : even after all the above have
been defined, there is still much left unaccounted for.

266 -1 Manual of Veterinary Physiology.

When the various tracts in the spinal cord reach the
medulla they undergo change in form, position, and distri-
bution, in order that they may arrive at the various parts
of the brain to which they are proceeding. This will be
alluded to again when speaking of the medulla ; but we
may here mention that only two unbroken spinal tracts pass
through the medulla to the higher centres, all the others
being broken up.

The conducting paths in the cord will be studied pre-
sently, when we have learned the functions of the spinal
nerves and of the nerve centres.

Spinal Nerves. — We must now describe very briefly how
the nerves entering and leaving the spinal cord are disposed
with reference to the cord itself.

The superior or sensory roots enter the cord just by
the upper cornu ; some of the fibres run up, and some
down the cord for a short distance, and then pass hori-
zontally across it. Other fibres enter the white instead
of the gre}r substance, and after passing some distance up
the superior columns of the cord enter the grey matter.
The connection between the sensory nerves and the cells
of the grey matter of the superior cornu, is by no means
so definite as the connection of the motor nerves with the
grey matter of the inferior cornu. The motor nerve, or
inferior root, is continuous with the axis cylinders of the
cells of the inferior horn, though some fibres may be
found to be in connection with the white matter of the
lateral columns ; these later on cross over the cord and enter
the grey matter of the inferior cornu of the opposite side.

The chief difference in the behaviour of the two roots is
that the inferior is in direct connection by means of their
axis cylinders with the nerve cells of the inferior cornu,
whilst the superior root is only in connection with the
nerve cells of the superior cornu, by moans of a network of
nerve tissue known as Oerlach's.

If the sensory root before entering the cord he divided
above the ganglion, its division causes pain : irritation of
the distal extremity causes no sensation, whilst irritation

The Nervous System. 267

of that part still in connection with the cord, the proximal
end, produces pain. In course of time degeneration of the
nerve and the tracts in the cord supplied by it occurs ; but
the proximal, and not the distal, end is the part which
undergoes defeneration. If the nerve be divided below its
ganglion, then degeneration of the nerve below the ganglion
occurs. This is explained by saying that the ganglion is
the seat of nutrition of the sensory root. Another result
of the division of this root is loss of all feeling in the
parts supplied by it. When the inferior or motor roots
are cut, movement of the parts with which it is in con-
nection occurs ; stimulation of the proximal end produces
no movement, whilst stimulation of the distal extremity
provokes muscular contraction ; as the result of the
section degeneration occurs, not, however, on the spinal
cord side of the nerve, but in the distal extremity. On
irritating the proximal extremity of the divided motor roots,
it has been found in some cases that pain results. This
is due to the fact that some sensory fibres are also present
in the inferior root, being derived from the superior one after
the nerves have joined. The phenomenon is termed
recurrent sensibility.

The function of the inferior or motor roots is to supply
all the voluntary muscles with the power of movement, the
bladder and uterus with contractile power, dilator and
constrictor fibres to the bloodvessels, secretory fibres to the
sweat-glands of the skin, and nutritive nerves to the
tissues. The spinal sensory fibres supply sensation and
touch to the whole of the body, with the exception of
certain parts of the face.

The vaso-motor fibres run in the lateral columns, passing
into the ganglia of the grey matter; they leave the spinal
cord by the inferior root, and reach the muscular coat of
the bloodvessels either by the spinal nerves or the sym-
pathetic. Respiratory nerves run down the lateral columns
on the same side as the centre from which they originated,
and pass through the inferior roots to the motor nerves of
the respiratory muscles.

268 A Manual of Veterinary Physiology.

Between the spinal cord and the sympathetic system are
chains of fibres connecting the two ; these fibres originate
in certain columns of the cord, pass out through the inter-
vertebral foramen, and so establish a communication
between these two important nervous systems (see p. 261).

In order that we may understand the functions of the
nerves and spinal cord, it is necessary that the complex
acts which they are capable of producing should now be
dealt with.

Nerves by themselves are not capable of generating any
impulses ; they must be in connection with a nerve centre.
We have seen that the spinal nerves are in connection with
nerve centres in the spinal cord and brain, and we have
now to learn the nature of the various impulses these are
capable of causing.

Reflex Action. — When a horse endeavours to save himself
from falling the act is a purely reflex one — that is to say,
whether he voluntarily tries to save himself or no the result
is the same, viz., the effort is made ; he becomes conscious
of the effort, but only after it is completed. When the
eyeball is touched with the finger it is withdrawn into its
socket, the membrana protruded, and the eyelids closed ;
this is a purely reflex act, and may be found to occur
immediately after death produced by section of the medulla ;
with the exception that the eyelids are not closed, the act
in all other respects is as perfectly performed as during life.
If the hand be suddenly raised as if to strike a blow in the
face, the eyelids blink, and by no effort of the will can this
under ordinary circumstances be prevented, though the
horse may know through repeated attempts that no blow
will be inflicted; the rapid closing of the lids is a reflex
act.

The main feature of a reflex act is its apparently inten-
tional character. By means of the sensory nerves the im-
pression is conveyed to a nerve centre, and in this place
certain changes rapidly occur which load to impulses
passing out along the motor nerves. The changes in the
norvo centre are probably of a highly complex kind. The

The Nervous System. 269

impulse along the sensory nerve is not simply reflected
into a motor channel, as the name Avould imply, and there-
fore the term ' reflex,' though retained by custom, is not a
correct explanation of what really occurs.

Other reflex acts are still more complicated, as in walk-
ino-, trotting, etc. Here the animal is completely uncon-
scious of the various groups of muscles to be brought into
play ; the whole process is carried out independently of
consciousness — in fact, if the horse had to think of each
step to be taken, it would soon be worn out and certainly
blunder.

So far the illustrations we have given of reflex action are
those resulting in movement; but a reflex act is not essen-
tial a motor act, it may be a secretory or a nutritive one,
depending on the character of nerve sending out the
efferent impulse. In order, therefore, that a reflex act may
be accomplished certain conditions must be present : (1) an
afferent nerve, to convey the impression to the nerve
centre ; (2) a nerve centre, in which the outgoing impulses
are generated ; (3) an efferent nerve, to convey these impulses
outwards.

It must not be considered that reflex actions can only
take place along nerves belonging to the same system ; the
afferent or efferent nerves may be both cerebro-spinal, or
one or the other may belong to the sympathetic system, or
both may belong to the sympathetic system.

It is by the regular and apparently intelligent carrying
out of reflex actions that the normal condition of the body
is maintained. Swallowing, secretion of saliva, gastric
juice and other fluids, respiration, intestinal movements,
etc., are all examples of this condition.

There are certain reflex acts of which the animal can
take cognizance, though it can take no part in them.
These are termed ' sensori-motor '; those which it is unable
to perceive are spoken of as ' excito-motor.'

There are certain reflex movements in man which are
acquired only as the result of education — for example,
walking. In animals these so-called co-ordinated reflex

270 A Manual of Veterinary Physiology.

actions are rapidly acquired — in fact, would appear to be
more highly developed, in the same way that the limbs are
more developed in the foal than in the child. In the
former, for instance, the limbs from the elbow and stifle to
the foot are nearly their full length very shortly after birth,
and such joints as the hock are almost the same size as at
maturity.

There are other functions of nerve centres which possess
perhaps a greater pathological than physiological interest,
viz., the transference and radiation of impressions. An im-
pression is transferred, when the animal instead of per-
ceiving it as arising from its proper place, believes it to
exist in another position. Here the efferent impression,
instead of being conducted back from the nerve centre to
where the afferent impulse arose, is perceived in another
position ; thus thirst is referred to the fauces, colic is
referred to the abdominal walls, etc. Some forms of liver
disease in the horse have been known to cause lameness in
the off fore-leg, evidently referred to the shoulder as in the
human subject, in whom also stone in the bladder causes
pain in the end of the penis.

By the radiation of impressions is understood the feeling
which refers the impression from a part to exist over a much
larger area than that from which it is derived — a familiar
example in ourselves is the diffused pain of toothache. In
the horse a not uncommon example is the pain found in
the leg, generally over the flexor tendons, when pus
exists in the foot ; also the diffused pain of colic, though
probably the irritating area may be only a few inches in
length.

The majority of physiologists have ceased to describe the
radiation and transference of impressions: 1 have intro-
duced them here owing to their clinical interest.

Other functions of nerve centres are Automatism, Aug-
mentation, Inhibition, and Co-ordination. By automat ism
we understand the power possessed by a nerve centre of

originating impulses on its own account without any pre-
vious stimulation. The nerve changes resulting in the

The Nervous System.

27 1

respiratory movements and the contraction of the heart
are automatic impulses.

Augmentation and inhibition in a nerve centre is the power
it possesses of increasing or decreasing a reflex or auto-
matic movement.

Fig. 26.— Diagram of the Decussation- of the Conducting
Paths in the Cord for Sensation and Voluntary Movement.

R, right side ; L, left side of cord. Sup. r. superior root with its gan-
lion a, the fibres crossing over to the opposite side of the cord
and so reaching the medulla mo. Inf. r, inferior root, the path for
which decussates in the medulla and runs down the same side of
the cord. The arrows indicate the direction of the nervous
impulses. The places. 1. 2, 3, indicate the effect on motion and
sensation of sections made in one-half of the spinal cord at
different levels. (After Brown Srquard, and Kirke.)

B}* Co-ordination is understood the impulses proceeding
from nerve centres which regulate the action of a part, and
assist in producing a proper sequence of events : for
example, in walking the contraction of groups of muscles

272 A Manual of Veterinary Physiology.

in an exact and regular order is essential, and the same
remark applies to swallowing, and the muscles used in
respiration and other similar acts.

Conducting Paths in the Cord. — We must now examine
the paths by which impressions are conveyed between the
body and the brain, and vice versa.

Sensory impressions enter the cord at the superior roots,
and pass for a short distance along the superior columns ;
they then enter the grey matter, passing through the gan-
glion cells, and cross to the opposite side of the cord (Fig. 26) ;
from here they pass once more into the white substance.
It is supposed that, depending on the nature of the impres-
sion, the path by which it enters the brain varies, pain
being conveyed by one of the white lateral tracts of the
cord ; touch, temperature, pressure, and muscular sensi-
bility by one of the superior tracts. In this way the impres-
sion passes along the cord on the opposite side (excepting
muscular sensibility, which is on the same side) to that on
which it entered, and so enters the brain. Here the im-
pression is made and a motor impulse is generated, which,
passing out of the brain into the medulla, crosses over either
in this or the pons, and passing down the pyramidal tracts
joins the motor or inferior spinal root (Fig. 26) ; some sensory
impressions instead of crossing in the medulla cross in the
cord. The conductors of muscular sense, besides travelling
up the same side of the cord on which they entered, do not
decussate in the cord but in the medulla. Complex co-
ordinated movements are supposed to be capable of being
set up in the grey matter of the inferior cornu, either in
response to an impression from the brain, or as a reflex ad
lii-oiight about by the sensory nerves passing to the cord.

Having learned the arrangement of the nerves and spinal
cord and the functions of nerve centres, we have next to
consider the functions of the spinal cord itself.

The Functions of the Spinal Cord are to transmit motor
and sensory impulses between the body and the brain, not
only up and down the cord, hut from side to side. It is
the chief centre of reflex actions, both with and without

The Nervous System. 273

the assistance of the brain ; and it preserves by its auto-
matic action both muscular and arterial tone. In speaking
of the automatic action of the spinal cord, it is necessary
to remember that it can originate no impulses in the
same way that the brain does, and that automatic action in
the cord is due to afferent impulses.

The cord is not one large centre, but a series of centres
lying end to end, each capable to a greater or less extent of
acting independently of its neighbour, and each centre pos-
sessing its afferent and efferent roots. The white substance
may be regarded as the communicating paths between the
cord and the brain ; the grey matter as essentially the seat
of reflex actions. Experiment has shown that both the grey
and white matter is devoid of sensibility. The ganglion
on the superior root of the spinal nerve is not a centre for
automatic or reflex action, and the same may be said of all
other ganglia, cerebro-spinal or sympathetic.

So long as the pathways to the brain are open to sensory
and motor impression, so long is the animal capable of per-
forming movements and recognising sensation ; but if by
operation or accident a part or the whole of the cord be
severed, certain symptoms of what we speak of as paralysis
appear ; whether this occurs to the right or left of the body
depends upon the part injured. If the injury be inflicted
above the decussation, at the extreme superior part of the
cord, a right cord lesion leads to paralysis on the left side,
both sensor}^ and motor ; if below the decussation, the motor
paralysis corresponds to that side of the cord injured, and
loss of sensation occurs on the opposite side (see Fig. 26;.
Loss of motion may not occur immediately after an accident
or injury to the spinal cord ; but this is accounted for by the
fact that the movements observed are not those performed
through any intelligent action on the part of the animal, but
by reflex action through the spinal centres below the injury.
These reflex actions are seen very perfectly in the frog,
where after destruction of the brain, some of the actions
appear to be produced as if by reason or consciousness.
The most remarkable of these experiments is that per-
ls

274 A Manual of Veterinary Physiology.

formed by touching the skin of the body with an acid.
The animal endeavours to wipe the acid away with the
leg nearest to the injury ; and if this leg be secured
the opposite one is used for the same purpose. We see
nothing so marked as this in the higher animals, though
very characteristic reflex actions occur in the dog after
division of the cord. It is certain that in the horse, for
example, severe injury to the cord may not immediately
cause entire loss of motion, though sensation be lost. I
have known a horse walk some distance after a comminuted
fracture of the dentata, and another to walk a short dis-
tance and stand a considerable time, and even to kick, after
a fracture of the sixth dorsal vertebra. There can be no
doubt, I think, that the spinal reflexes in the larger animals
are by no means so well marked as in the dog or in the
frog.

The muscle and tendon reflexes, so well known in the
human subject, have not, so far as I am aware, been studied
in the herbivora: nor do I know whether their existence
has been demonstrated, if, perhaps, I except the immediate
lifting up of the foot, which generally follows pressure on
the so-called ' chestnut ' found on the inside of the fore- arm
of the horse.

A controlling influence may be exercised over certain
reflex acts in the human subject, which are the outcome of
moral control, and so have no counterpart in veterinary
physiology.

Under the influence of tetanus and the action of strychnia,
the reflex centres in the cord are so easily excited that even
a slight noise is sufficient to produce those purposeless
muscular movements termed convulsions.

Centres in the Cord. — Certain centres exist in the spinal
cord for the performance of functions, some of which are
partly under the control of the will, whilst the majority are
not. It is quite possible for the centres to act by them-
selves, but under ordinary circumstances they are controlled
by higher centres in the medulla.

The cilio-spinal centre has for its function the dilatation

The Nervous System. 275

of the pupil ; it is found low down in the cord, between
the cervical and dorsal portion.

The ano-spinal centre, found in the lumbar portion of
the cord, controls the act of defecation ; it would appear
to be highly developed in herbivora, which possess the
power of bringing it into play not only when the body is
at rest, but during movement. The functions of the ano-
spinal centre are rather complex, inasmuch as it has to
maintain the tone of the sphincter, and also, on receiving
the needful sensory impressions from the bowel, to relax
the sphincter, contract the wall of the intestine, and cause
a contraction likewise of the abdominal muscles.

The vesico-spinal centre, which also exists in the lumbar
portion of the cord, governs micturition ; its action is like
that of the ano-spinal centre.

The erection centre lies in the lumbar cord; the genito-
spinal centre contains the nervous apparatus employed in
the emission of semen ; the parturition centre is situated in
the lumbar part of the cord.

Vaso-motor centres, both constrictor and dilator, are
found throughout the cord; they are principally under
the control of similar centres in the medulla, but may act
independently. Sweat centres are probably closely con-
nected with the vaso-motor centres. Trophic centres for
the nutrition of the tissues also exist in the cord ; destruc-
tion of parts by ulceration follows injury of the trophic
nerves.

Centres for the maintenance of muscular tone exist in
the cord; by means of them the muscles are kept taut
and ready for immediate action.

Medulla Oblongata.
Situated at the top of the spinal cord, and forming the
connection between it and the brain, is the medulla
oblongata. It is composed of white and grey matter, but
not arranged with the regularity found in the cord. The
columns of the latter are continued into it, and give rise to
certain columns in the medulla larger and more prominent

18—2

276 A Manual of Veterinary Physiology.

than those of the cord. The inferior spinal columns form
the inferior pyramids of the medulla, the superior form the
superior pyramids, and the lateral columns dividing into
three parts help to form the restiform bodies.

As each of the main paths or highways in the cord are
either going to or coming from the brain, it is interesting
to briefly understand their distribution.

The pyramidal tract of the cord divides in the medulla
into three paths ; one proceeding to the motor areas in the
cerebrum, one to the cerebrum itself, and one to the corpora
quadrigemina. The cerebellar tract of the cord passes
through the medulla, and so reaches the cerebellum. The
antero-lateral columns run also to the cerebellum, whilst
the superior column of the spinal cord divides in the
medulla into three paths, two to the cerebellum, and one to
the cerebrum ; in this way each pathway in the spinal cord
finds either an origin or termination in the brain.

The grey matter of the cord does not maintain its charac-
teristic appearance in the medulla ; owing to the decus-
sation of fibres in the inferior pyramid the grey and white
matter get mingled up, and nuclei and masses of nerve
cells are formed as the result. From these nuclei nearly
all the cranial nerves arise.

The various tracts passing through the medulla are com-
posed of motor and sensory nerves, or, more correctly,
afferent and efferent nerves ; both of these decussate in the
medulla. But, in addition to these, we have reflex and
other centres so numerous and widespread, that it is
remarkable how the varied functions carried out by them
can be performed within such a limited area.

The decussation of the motor tracts, as previously men-
tioned, causes a right, brain lesion to produce a left body
paralysis ; and as the sensory fibres decussate in the cord,
as described when speaking of the spinal cord, insensibility
of the left limbs would result from injury or disease of the
right brain (see Fig. 26).

Centres in the Medulla. — The various centres found in the
medulla are of such importance to Life thai an injury to

The Nervous System. 277

this part generally means instantaneous death. The whole
of the brain may gradually be removed without destroying
life, but the medulla will not tolerate such interference.
The centres found in the medulla are those for mastication,
swallowing, vomiting, respiration, coughing, movements of
the heart, bloodvessels, and iris, secretion of saliva, the
diabetic centre, and a centre for the sweat glands of the
head.

The mastication and swallowing centre has for its afferent
nerves the inferior division of the fifth, glossopharyngeal,
and the superior laryngeal of the pneumogastric ; whilst its
motor branches are in the motor parts of the fifth for
swallowing, and in the facial for mastication. It would
appear that the reflex act of swallowing may be excited not
only by the presence of food in the pharynx, but even by
irritating portions of the respiratory apparatus; touching
the rima of the glottis excites the act, and so does touching
the interior of the trachea, even as low down as the bronchi.
A vomiting centre exists in the medulla, which in the horse
and ruminants is certainly most imperfectly developed.
We have previously, p. 137, drawn attention to the fact
that there is no drug which has the power of exciting
vomiting in the horse ; tartar emetic has not the slightest
action, and the effect of apomorphia is only to produce the
most alarming symptoms of cerebral excitement, but no
attempt at vomiting. Secretion of saliva is influenced by
the chorda tympani, which has its origin in the medulla
(see p. 105). A centre for dilating the pupil also exists,
the fibres for which are contained in the third nerve, and
through the sympathetic with the cilio-spinal centre in the
cervical cord.

Other centres in the medulla depend upon automatic
action, for example, the respiratory and cardiac centres.

The respiratory centre is situated close to the origin of
the pneumogastric nerves, and is divided into an expiratory
and inspiratory portion. The afferent nerve is chiefly the
pneumogastric ; but no doubt a large number of other nerves
may indirectly take part in the action, as is witnessed in

278 A Manual of Veterinary Physiology.

the inspiratory efforts of the nostril and mouth when the
medulla is divided, or in the sudden gasping produced by
throwing cold water on the body. The chief efferent nerve
is the phrenic, the diaphragm being the principal muscle of
inspiration. The vagus has a twofold action on respiration,
being capable through certain fibres of increasing and
through others of decreasing respiration. It is believed
that impulses conveyed through the vagus to the medulla
excite the inspiratory portion of the centre, whilst others
passing into it through the superior laryngeal excite the
expiratory portion. This view of the matter must not be
too rigidly adopted. Another view is that during inspira-
tion dilatation of the lungs mechanically stimulates certain
nerves, which convey to the medulla through the vagus
expiratory stimulation, and conversely during expiration
mechanical stimulation of the inspiratory centre occurs.
This is termed the self-adjusting mechanism.

An inhibitory influence is exercised over the respiratory
centre, through influences conveyed to it by either the
superior or inferior laryngeal or both, for stimulation of
these divided nerves, from that end still in contact with the
brain, produces a considerable fall in the number of respira-
tions, and even arrest of them during expiration ; on the other
hand, stimulation of the cut end of the vagus (from that end
still in contact with the brain) produces rapid inspiratory
efforts, and therefore may possibly inhibit the expiratory
centre. The respiratory centre is stimulated by blood contain-
ing a reduced proportion of oxygen, and it is this which largely
influences the automatic action of the medulla (see p. 91).

Division of the cord above the origin of the phrenic, it
is said, produces death by suffocation, though judging from
experiments on the division of the phrenic in the horse, the
suffocation is not produced by paralysis of the diaphragm
alone, but by paralysis of diaphragm and chest walls (see
p. 92); fracture of any vertebra above the phrenic does
not necessarily mean immediate' death, unless the cord be
extensively damaged.

Above the respiratory centre is the coughing centre.

The Nervous System. 279

In the medulla is situated a cardio-accelerator and cardio-
inhibitory centre. The contraction of the heart is regulated
by nerves passing from a centre in the medulla ; one nerve,
the vagus, passes down the neck, the function of which is
to inhibit or restrain the action of the heart ; it is brought
into action either by automatic impulses originating in the
medulla through the blood circulating in it, or reflexly by
impressions from without, and it is always in operation.
Accelerating influences, from a centre in the medulla, pass
to the heart through the sympathetic, the fibres for which
issue from the spinal cord in the lower cervical or anterior
dorsal region, and pass to the inferior cervical ganglion and
then to the heart ; the impulses which accelerate the heart
are not in constant action (see p. 59).

A vaso-motor or vessel-moving centre is situated in the
floor of the fourth ventricle ; by some it is considered to
•consist of two parts, a vaso-dilator and a vaso- constrictor
•centre. The vaso-constrictor centre is constantly keeping
the vessels in the condition known as ' tone ' ; if the
•centre be irritated, the vessels contract and the blood
pressure rises. Under the influence of the vaso-dilator
nerves, the vessels dilate and the blood pressure falls
{see p. 72).

The vaso-motor centre is influenced not only through the
cord from below, but directly by the brain from above ; it
is also stimulated by the character of the blood circulating
in the medulla, and under all circumstances it exercises a
control over the vaso-motor centres in the cord.

Diabetes, after puncturing the floor of the fourth
ventricle, is said to be explained by injury to the so-called
dilator centre, allowing the vessels of the liver to dilate
(see p. 1G7). The cause has, however, not as yet been
clearly made out.

The sweat centre is stated to govern the sweat centres in
the spinal cord, and to produce sweating of the head ; it
can be excited reflexly or automatically.

The medulla has no sensation ; it can originate no volun-
tary impulse ; it forms a pathway to the brain for the

Ii80 A Manual of Veterinary Physiology.

columns in the spinal cord ; gives origin to all the cranial
nerves but those of smell, sight, and the motor nerves of
the eyeball ; it is the head centre for the nerves governing
respiration, circulation, the action of the heart, and the
digestive apparatus from the mouth to the stomach.

The Pons Varolii has no definite claim to be considered
as a nerve centre ; its use is to conduct sensory and motor
impressions to and fro and up and down ; it connects the
brain with the medulla and cerebellum ; when stimulated,
pain and muscular spasms are produced. Several of the
cranial nerves obtain connection with the grey matter of
the various nuclei found in it.

The Crura Cerebri connect the cerebellum with the cere-
brum, and the basal ganglia with the pons and medulla.
They conduct both sensory and motor impulses, and are
connected with the complex movements of the eyeball.
Division of one peduncle leads to what is known as circus
movements, the animal travelling round and round in a
circle towards the opposite side to that on which the injury
was inflicted.

The basal ganglia have next to be considered ; they are
composed of the Corpora Quadrigemina, thalami optici, and
corpora striata. The corpora quadrigemina are composed
of two parts ; an anterior and posterior pair, termed the
' nates and testes.' Destruction of the corpora causes
blindness ; removal of one part causes circus movements or
rolling, or, at any rate, destruction of equilibrium and want
of muscular co-ordination ; not that these results are con-
fined to the corpora quadrigemina alone, for the same
inco-ordinate movements will occur on injury to the crura
cerebri, optic thalami, corpora striata, etc. Irritation o\
the corpora quadrigemina causes contraction of the pupil,
whilst removal of these bodies produces dilatation.

The Thalami Optici arc connected with vision ; but are
mainly supposed to be the centres for tactile impressions
which they transmit onwards to the cerebrum.

The Corpora Striata are interesting clinically on account
of the comparative frequency with which they are diseased

The Nervous System. 281

in the horse. They are considered to be the centres for
co-ordination of motor impulses ; when they are destroyed
the animal has an irresistible tendency to move forwards.

I have certainly seen this latter symptom shown in the
horse in disease of the corpora striata, but it is far from
invariable. It is remarkable how extensively the parts may
be affected and pressed upon by tumours without symptoms
being exhibited ; the gradual pressure or destruction may
account for this.

Cerebellum.

In the cerebellum is found a collection of fibres and
ganglion cells, in direct communication with the medulla
and cerebrum. It is the first piece of nervous tissue we
have studied where the surface has been folded and doubled
in on itself to a considerable extent, forming the so-called
convolutions ; it is composed of grey and white matter, the
grey being externally placed and not internally as in the
cord.

The functions of the cerebellum are principally concerned
in the co-ordination of movement, viz., harmony and rhythm
in muscular actions. It is enabled to carry out this function
through its connection with the superior columns of the
cord, which keep the cerebellum informed of the position of
the limbs. There can be no doubt that in co-ordinating
muscular movement, the cerebellum is assisted both by the
sense of sight, and by the lymph in the semicircular canals
of the ear. An animal walks with uncertainty when the
eyes are covered up, and disease of the internal ear is a
well-known cause of vertigo in the human subject.

The cerebellum possesses no sensation ; it is essentially a
motor apparatus. When sliced away in birds they lose the
power of flying, walking, or preserving their equilibrium ;
there is no loss of consciousness or intelligence, but an
inability to co-ordinate the skeletal muscles. Injury to
one of the crura of the cerebellum produces what is termed
' forced movements '; the animal rolls over and over around
the long axis of the body, and always from that side on

282 .4 Manual of Veterinary Physiology.

which the injury has been inflicted, or else circus move-
ments or somersaults are performed.

Cerebrum.
It has been considered that the larger the proportion
between the weight of the body and that of the brain, the
less the intelligence.

In Man the weight of the brain is to the body as 1 to 36
» D°g » „ „ „ 1 „ 305

» SheeP i) „ » „ 1 „ 350

» Horse „ „ „ „ 1 „ 4(10

„ Elephant „ „ „ „ 1 „ 500

» 0x » » „ „ 1 „ *G0

(Colin.)

This rule is not absolutely true. There is considerable
difference between the intelligence of a dog and a sheep.
A horse is nothing like so intelligent as an elephant, and he
is certainly not twice as intelligent as an ox. Personally I
hold a very low opinion of the intelligence of a horse.
The height of his intellect is exhibited when his stomach is
his consideration. He takes an interest in the chase and
race, but place him in a position of danger, or under any
circumstance requiring the use of reasoning powers, and he
is not only useless, but often a dangerous lunatic. He
possesses, however, an excellent memory.

The cerebrum is composed of grey and white matter, the
grey externally placed and thrown into convolutions.
These convolutions in the lower animals, at any rate the
horse, though well marked, are by no means regular in
their position or direction, thereby forming a great contrast
to the brain of man. The use of the convolutions is no
doubt to increase the surface of the brain, and the deeper
and more complex they are, the greater the intelligence of
the animal. In the horse the convolutions are compara-
tively very shallow.

Motor Areas. — Until within a few years ago, the functions
assigned to the cerebrum were simply those of intelligence
and all the higher faculties ; but experiment has shown
that the grey matter of the cortex of certain convolutions,

The Nervous System. 283

forms the motor areas for certain groups of muscles on the
opposite side of the body. By irritating these areas con-
vulsions are produced, and by observation it is found
possible to distinguish areas for the eyelids, face, mouth,
tongue, tail, flexion and extension of the limbs, and many
others. For veterinary purposes, especially dealing as we
have done almost exclusively with herbivora, a knowledge
of these motor centres is not required, nor have the exact
positions of them been determined. We are content to
know of their existence, but to the human surgeon they
have opened up a new field of surgery, and one which
promises the most important results.

After removal of the cerebral hemispheres all conscious-
ness is lost, but muscular movements and equilibrium are
retained. The cerebrum is insensitive to pain, but the
dura mater is highly sensitive.

Besides the motor centres,, sensory centres in the brain
have been described, such as a visual, auditory, olfactory,
taste, and tactile centres. A heat centre has also been
described, stimulation of which produces a rise in tempera-
ture. The definite existence of these centres has not been
agreed upon.

The respective functions of the grey and white matter
of" the cerebrum may be stated as follows : The grey
matter is the seat of intelligence and the higher faculties ;
to the cells of the grey matter run the sensory fibres, both
special and general ; from the grey matter proceed the
motor fibres supplying the voluntary muscles; the white
matter is simply the conducting area, whereby the im-
pressions made upon or issuing from the grey substance are
distributed. The fibres of the white matter are arranged
in a complicated manner, but ascending, descending, and
transverse fibres have been recognised.

It has been supposed that the majority of the sensory
impressions are implanted on the posterior half of the
cerebrum ; while from the middle and lateral portions arise
the motor impulses; and from the anterior portion con-
sciousness and intelligence.

284 A Manual of Veterinary Physiology.

Colin draws attention to the difficulty in producing
paralysis experimentally in the horse from lesions of the
hemispheres. Neither the artificial production of a clot in
the falciform sinus, nor the introduction of pieces of lead
the size of a pea into the convolutions, gave rise to
hemiplegia. This quite bears out what we know to be a
clinical fact, that horses may have in their lateral ventricles
tumours the size of an egg without producing any disturb-
ance. I have seen many such cases, the tumours being of
variable size, and the clinical history has never given more
than a few days' illness, though the growths must have
been forming for a considerable period.

The circulation in the brain is peculiar. The veins, or
so-called sinuses, are enclosed in very rigid membranous
walls, the blood being driven through them, not only by
the force behind, but by the aspiratory effect produced by
inspiration (see p. 74).

The fluid found in the ventricles is a secretion rather
than a transudation. The cavity of the ventricles com-
municates, by means of a foramen in the roof of the
fourth ventricle, with the central canal of the spinal
cord. The amount of fluid in the ventricles is normally
80 grains to 90 grains, but in disease may be as much as
7 ozs. to 10 ozs., according to Colin, who examined the
brain of several horses suffering from immobilite, and says
that in each case he found an excess of fluid in the
ventricles.

For the peculiarities in the cerebral circulation, and the
use of the cerebro-spinal fluid, see p. 73.

Nothing is known of the lymphatics of the brain.

Cranial Nerves.

These are divided into the nerves of special sense,
sensory nerves, motor nerves, mixed nerves. Altogether they
make twelve pairs, and all but Nos. 1, '2 and :> arise from
the medulla.

For nerves Nos. I and 2 see the Senses.

Third Pair, or Motor Oculi, is one of the motor nerves of

The Nervous System. 285

the eyeball ; it supplies with motor power all the muscles
(excepting the external rectus and the superior oblique),
also the muscle of the upper lid. Through its connection
with the lenticular ganglion it supplies fibres to the iris
and ciliary muscle ; it is also connected at its origin with
two other motor nerves of the eyeball, viz., the fourth and
sixth pairs.

The deep-seated origin of the third pair is from the corpora
quadrigeniina and peduncles of the cerebrum. Division of
the nerve causes the eye to turn the temporal side of the
pupil upwards and outwards, owing to the unbalanced
action of the superior oblique and external rectus ; there is
also depression of the upper lid, immobility of the eyeball,
and dilatation of the pupil. The action of the third pair
will be discussed again in connection with the physiology
of sight.

Fourth Pair, or Pathetic. — The motor nerve of the
superior oblique muscle of the eyeball ; it has a deep-seated
origin in the valve of Vieussens.

Fifth Pair, or Pars Trigemini, resembles a spinal nerve in
having two roots, a motor and sensory ; and the resemblance
is carried still further by the sensory root having a large
ganglion on it, the so-called Gasserian. The motor root
arises from the trigeminal nucleus, and is connected with
the cerebral cortex on the opposite side. The sensory
fibres arise from the sensory trigeminal nucleus ; but
fibres in connection with the origin of this branch can be
traced upwards into the cerebrum and cerebellum, and
downwards into the grey matter of the cord ; further,
it has also connections with all the nerves arising from
the medulla, excepting the abducens. In this way can be
explained the extensive connections and varied reflex acts
of the fifth pair.

The motor branches, or inferior maxillary division of the
fifth, supply the whole of the muscles concerned in masti-
cation ; by some it is considered that sensory fibres also
exist in this branch.

The sensory branch, or superior maxillary division,

286 A Manual of Veterinary Physiology.

supplies the skin of the head, face, and anterior two- thirds
of the tongue with ordinary sensation ; it supplies the
muscles of the face and jaw with sensation : it is the
efferent nerve through which many important reflex acts
are produced, and it acts as a trophic or nutrient nerve to
many parts, such as the eye.

Division of the superior maxillary division of the fifth in
the horse (Bell's experiment) prevents the animal from
grasping food with its lips; not for the reason that they
are deprived of motion, but owing to loss of sensibility
the animal is unaware of how to take hold of the food ; the
relation of the fifth to muscular movements is that it keeps
the muscles aware of the position of objects. As an
afferent nerve in reflex acts it is most important ; without
it there could be no closure of the eye, nor sneezing ; irrita-
tion of the conjunctiva would produce no tears, and no
saliva, or but little, would be secreted. By division of its
branches nutrition, taste, smell, and sight are affected.
The cornea becomes opaque and sloughs, not merely
because it is exposed to injury through the loss of reflex
acts, but because the fifth pair controls its nutrition.

The fifth pair supplies the vaso-motor fibres for the
bloodvessels of the eye.

Sixth Pair, or Abducens, arises from the floor of the fourth
ventricle, and supplies the external rectus muscle of the eye
with motor power. Paralysis of this muscle causes internal
squint.

Seventh Pair (Portio Dura), or Facial, arises from the floor
of the fourth ventricle. At its origin it is exclusively motor,
but immediately afterwards becomes sensory and motor, •
through connection with the fifth, pneumogastric, and
glosso-pharyngeal. The facial consists of two roots, one in the
auditory nerve, the other the facial proper. The branches
of the facial nerve are the petrosal, supplying motor fibres
to the spheno-palatine ganglion, branches to tho otic
ganglion, and motor fibres to the tensor palati, tensor
tympani, parotid gland, and tho stapedius muscle of the
internal ear. The important chorda tympani passes through

The Nervous System. 287

the middle ear, emerges and supplies the submaxillary gland
with sensory fibres derived from the fifth, and secretory and
vaso-dilator fibres (see p. 105) . The chorda also possesses
taste fibres for the margin and tip of the tongue, which it
reaches through the lingual ; these taste fibres are probably
derived from the glossopharyngeal.

The other branches of the facial are distributed as motor
fibres to the muscles of the face (those of expression, not of
mastication), also to the muscles of the ear.

Division of the seventh nerve leads to alterations in sight,
taste, hearing, smell, and facial expression. As it supplies
the muscle which closes the eyelids, the orbicularis palpe-
brarum, conjunctivitis occurs from exposure of the eyeball ;
hearing is affected owing to paralysis of the muscles of the
internal ear ; smell is impaired owing to the paralysed con-
dition of the nostrils ; taste is affected through paralysis of
the chorda.

The expression of unilateral facial paralysis in the horse
is characteristic ; the upper lip drawn to one side, the
elongated nostril, the pendulous lower lip, escape of saliva
and food from the mouth, the vacant look and the drooping
ear, point clearly to the extensive distribution of this nerve.

Eighth Pair, or Portio Mollis. — Arises by two roots : one
the nerve for the special sense of hearing, the other dis-
tributed to the semicircular canals, and assists through
these in maintaining the equilibrium of the body (see
' Cerebellum ').

Injury to the semicircular canals produces giddiness, not
deafness, and certain movements (termed ' pendulum-like ')
of the head occur ; the direction in which these are made
depends on the direction in which the canals have been
injured.

Ninth Pair, or Glosso-Pharyngeal, is a mixed nerve, though
at its origin it is described as a sensory one. It supplies
motor power to the muscles of the pharynx, and sensory
fibres to the posterior third of the tongue, soft palate, part of
pharynx, and anterior surface of the epiglottis. It is also a
special nerve of taste, supplying the posterior third of the

288 A Manual of Veterinary Physiology.

tongue, and having special nerve-endings, known as ' taste-
bulbs,' in the circumvallate papilla (see ' Taste ').

Tenth Pair, or Pneumogastric. — This is both a sensory and
motor nerve. At its origin it is intimately mixed up with
the ninth, eleventh, and twelfth pairs of nerves, and later
on with the sympathetic. It is the most extensively dis-
tributed nerve in the body, supplying respiration, heart,
and digestive systems.

The sensory branches of the nerve are not highly en-
dowed with sensation, probably for the reason that their
chief function as sensory nerves is as afferent channels for
reflex action. The motor fibres are joined by some from
the spinal accessory, facial, and lingual.

The various branches of the vagus may be best studied
by taking them in the order in which they are given off'.
The pharyngeal branch, through the pharyngeal plexus,
supplies motor power to the pharynx (and in the horse
supplies the cervical portion of the oesophagus with motor
power), derived, it is said, from the spinal accessory nerve.
The superior laryngeal furnishes the interior of the larynx
with sensibility. The external laryngeal supplies motor
fibres to the crico-thyroid muscle, the lower constrictor of
the pharynx, and in a minor degree the anterior portion of
the oesophagus. In the horse the crico-thyroid muscle is sup-
plied by the first cervical nerve (see ' Voice '). The inferior,
or recurrent, laryngeal is given off' from the main trunk
within the chest, on the left side winding around the aorta
from without inwards, and on the right side passing around
the dorso-cervical artery; both branches return up the neck
and supply all the muscles of the larynx (excepting the
crico-thyroid) with motor power. The branches are •'!'
great practical interest, inasmuch as they are affected (espe-
cially the left) in that common form of disease in horses
known as 'roaring,' which is generally due to paralysis and
atrophy of the muscles which dilate the laryngeal opening.
After division of the recurrent nerves death by asphyxia
is likely to follow. I have observed complete bilateral
paralysis of the larynx in horses without asphyxia being

Ttte Nervous System. 280

produced. The inferior laryngeal gives motor branches to
the cesophagus and part of the pharynx, and exercises a
controlling or inhibitory action over the respiratory centre.
The cardiac branches of the vagus contain the inhibitory
fibres of the heart, so that division of the nerve causes
the heart to beat more quickly and with increased strength.
The depressor nerve in rabbits is given off by the superior
laryngeal ; it is an afferent nerve of the heart ; if irritated,
and one vagus be intact, it slackens the heart, but only
reflexly through the cardio-inhibitory centre ; further it
dilates the arteries, and causes a fall in blood pressure
(see p. 72). The pulmonary branches supply both sensory
and motor branches to the trachea, and motor fibres to the
bronchi ; they transmit to the medulla impressions which
stimulate the respiratory and vaso-motor centres, causing
through the latter a fall in blood pressure. Division of both
pneumogastrics causes the breathing to become deeper and
more prolonged, but does not produce a sense of suffocation ;
further, it causes the lungs to become gorged with blood,
and produces a low form of pneumonia. The oesophageal
branches supply the cardiac end of the cesophagus with
motor power, the cervical portion of the tube being supplied
by the pharyngeal branches ; division of them causes the
food to accumulate in the lower end of the tube. The
gastric plexus supplies branches to the oesophagus, stomach,
and liver. According to Colin's experiment on horses,
division of both vagi does not influence either the secretion
of gastric juice or the process of digestion, but owing to the
paralysis of the lower end of the cesophagus, food is likely
to accumulate in the stomach, cesophagus, and pharynx.*

The functions of the vagus may be summarised as follows :
The vagus supplies (1) motor influences to the pharynx,
(esophagus, stomach and small intestines, the larynx,
trachea, bronchi, and lungs : (2) sensory and in part
(8) vaso-motor influences to the same regions; (4) in-
hibitory influence to the heart ; (5) inhibitory afferent

* I have to acknowledge Chauveau's experiments on the Yagus of
the horse, published in the Edinburgh Veterinary Review, 1864.

19

200 A Manual of Veterinary Physiology.

impulses to the vasomotor centre ; (6) excito-secretory to
the salivary glands; (7) excito- motor in coughing and
vomiting (Kirke).

Eleventh Pair, or Spinal Accessory, arises by two roots:
one from low down the cervical portion of the cord, the
other from the medulla. It is essentially a motor nerve,
but through being intimately connected with the pneumo-
gastric it also possesses sensory fibres. The use of this
nerve is to supply motor power to the sterno-maxillaris,
trapezius, and a portion of the levator humeri muscles. It
is supposed also to possess an influence over the larynx.
Division of it produces no difficulty in breathing, as in the
case of the recurrent laryngeal, but it causes loss of
voice.

Twelfth Pair, or Lingual, arises in the lower animals by
two roots, a sensory and a motor, the sensory having a
ganglion on it. Both roots freely communicate with the
pneumogastric, gustatory, and sympathetic. The branches
of this nerve supply the tongue with motor power, and
fibres to the muscles which depress the larynx.

The Sympathetic System.

Passing beneath the vertebra' from the cranium to the
coccyx is along chain of nerves, one on either side, com-
posed of grey nervous tissue, and possessing on them at
regular intervals a number of swellings or ganglia: these
are the two main trunks of the sympathetic system. This
remarkable system has free communication with all the
cranial nerves (excepting the first, second, and eighth), and
with the spinal nerves; the conned ion may be direct or
through ganglia. It is composed of two systems of fibres :
the grey fibres which possess no white substance of
Schwann, and the medullated or ordinary cerebro-spinal
fibres, the latter being remarkable tor their fineness, and
derived from both the superior and inferior roots of the
spinal nerves, 15y passing through the ganglia the medul-
lated become non-medullated fibres,

The characteristic feature of the sympathetic system [a

The Nervous System. 291

the extensive ganglion connections by which it is brought
into communication with the cranial and spinal nerves.

Gaskell has shown that these communications may be
classified as follows : (1) The long chain on either side of
the vertebra*, termed by him the ' vertebral ' or ' lateral
ganglia *; (2) in connection with these and with each other
are the large nervous plexuses of the chest and abdomen,
such as the mesenteric, solar, etc., and these he terms the
' collateral ganglia '; (3) ganglia situated in the substance
of organs, known as ' terminal ganglia,' and which are in
connection with the collateral ganglia (Fig. 24).

Each spinal nerve is connected by fibres proceeding from
the superior and inferior roots, with the ganglia on the
vertebral portion of the sympathetic system. By this
remarkable chain of communication, the entire nervous
system is able to work as one harmonious whole.

One of the most important functions of the sympa-
thetic, is the influence exercised over the bloodvessels by
means of the vaso-motor system of nerves.

Vaso-motor nerves are of two kinds : 1. Vaso-constrictor.
2. Yaso- dilator. Both fibres arise in the brain or spinal
cord, but possess well-marked differences.

The vaso-constrictor arise in the middle region of the
cord, viz., from the second dorsal to the second lumbar ;
running out with the inferior spinal nerve they reach, by
means of the ramus communicans, the gangliated cord of
the sympathetic (running beneath the arches of the ribs) ;
from here some pass forward to the head and neck, others
to the fore-leg, others to the thoracic and abdominal viscera,
and, lastly, others to the hind-leg ; they reach their various
destinations either directly through the sympathetic system,
or through recurrent branches of the sympathetic (grey
ramus communicans), which join the cerebro-spinal nerves
of the fore and hind legs and trunk. It is to be noted that
the constrictor fibres, after passing through the ganglia
found on the cord of the sympathetic, have, from being
medullated, now become non-medullated fibres.

It is believed that the vaso-constrictor fibres are con-

19—2

292 A Manual of Veterinary Physiology.

stantly in a state of moderate activity, by which the
general arterial tone of the body is preserved: this forms
u contrast to the dilator fibres, which are only active
occasionally.

If now we look at the vaso-dilator fibres we find that
they behave differently ; their origin from the cord is by
no means well known, but there is reason to believe that
they run in the roots of the motor-nerves to their destina-
tion, and do not pass through the sympathetic system as
we have found the constrictor fibres to do ; moreover, they
retain their medulla until near their termination.

The constrictor fibres of the whole body are under the
control of a constrictor centre in the medulla known as
the vaso-motor, though under certain circumstances inde-
pendent centres may exist in the spinal cord.

The dilator fibres are believed to have no special centre
in the central nervous system, but are affected by whatever
changes influence the centres of the motor-fibres they
accompany.

If the vaso-constrictor nerves be divided, the vessels
become relaxed through the unbalanced action of the vaso-
dilators, and a considerable quantity of blood is sent to
the part. If the vaso-constrictor nerves be stimulated, the
vessels under its influence contract and press the blood
onwards, thus relieving the physiological congestion. No
better example of this can be found than in the nervous
supply of the submaxillary gland : the chorda tympani con-
tains fibres ^which act as vaso-dilators ; if the chorda be
stimulated, the vessels of the submaxillary gland dilate and
the veins pulsate ; if now the sympathetic be stimulated.
the vessels contract and the blood stream slows down tin
sympathetic therefore acts as a vaso-constrictor apparatus.

Visceral Muscle Supply. — The next important function of
the sympathetic is the supply of nerve force to the involun-
tary muscular fibres of the body: in this way the peristaltic
movements of the stomach and bowels arc maintained.
These movements are independent of the brain and spinal
cord, and arc maintained by local ganglia.

The Nervous System. 293

The fibres supplying the visceral muscles with motor
power arise from the cervical portion of the cord, and exert
their function through the vagus nerve. The viscero-motor
nerves are in turn controlled by viscero-inhibitory ; these
pass from the inferior roots of the spinal nerves, direct to
the tissues through the abdominal spknchnics ; they are,
therefore, not connected with the vertebral ganglia.

It is probable that all the glands of the body are supplied
with sympathetic fibres, in the same way as has been
demonstrated to occur in the submaxillary gland.

Sympathetic Ganglia. —We have before noticed that when
medullated nerves pass through a sympathetic ganglion, they
lose the white substance of Schwann and become non-medul-
lated ; they also become more numerous, for nerve fibres
originate in the ganglia, arising from the ganglion cells
found in this structure. It is not known whether the
sympathetic ganglia possess the same properties as the
cerebro-spinal ganglia.

Trophic Influences. — Sympathetic ganglia also exercise
through the nerves leaving them, a trophic or nutritive
influence over parts. GaskeH's views in connection with
this matter are most important. He considers that every
tissue has nerves which excite repair, and are termed
anabolic, and others which excite waste, and are termed
katabolic. We mentioned this theory in connection with
the heart, the sympathetic nerves of which excite kata-
bolism by increasing the heart's action, whilst the pneumo-
gastric exercises processes of repair, its function being to
control the heart : it is therefore regarded as an anabolic
nerve.

Sweating is produced through the vaso-motor fibres of
the sympathetic, in conjunction with the secretory nerves:
section of the cervical sympathetic in the horse leads to
sweating on that side of the neck and head (see p. 195).

For the effect on the secretion of saliva by division of
the sympathetic, see p. 106.

CHAPTER XVI.

THE SENSES.

Sight.
The delicate structures composing the eye receive a very
thorough protection by the anatomical arrangement of the
parts. The orbital cavity, for example, is nearly entirely
surrounded by bony walls, and layers of fat within it
assist the muscles in protecting the globe and the optic
nerve ; the eyelids sweep the cornea and protect the part
from dust ; the tears keep the face of the cornea brilliant ;
the membrana nictitans removes particles of solid matter
which would otherwise produce injury; the eyeball can
also be retracted to a considerable extent to further assist
it in withdrawing from injury. The size of the orbit is such
that ordinary blows inflicted upon the eye arc expended
on the margin of the orbital cavity, and not on the eyeball
itself; so that the risk of injury to this delicate part arises
less from large than from small bodies.

The arrangement of the eye corresponds very closely with
that of a certain well-known physical apparatus the
camera, where into a dark chamber is thrown the inverted
image of an object, the inversion being produced by a
double convex lens placed in front : the amount of illumi-
nation being regulated by a diaphragm, and the focussing
power also capable of adjustment.

The eye is composed of a convex surface in front, forming
a chamber containing fluid, immediately behind which is the
iris or diaphragm, through which the light passes into a
biconvex lens; issuing from the posterior surface of the

The Senses. 295

lens, the light passes again through a fluid medium, and
comes to a focus on a delicate expansion of nerve tissue,
which takes a reduced and inverted impression of the
picture presented. The physical arrangement of the
camera and the eye are, therefore, practically identical.

The shape of the eyeball is spherical, its vertical being
somewhat longer than its transverse axis ; the optic nerve
penetrates it close to the floor, and inclined to the
temporal side of the eyeball.

The optic nerve has a deep-seated origin in the optic
thalamus, corpora geniculata externum and internum, and
corpora quadrigemina ; these unite on the base of the brain
to form the optic nerves, which decussate in the well-
known manner. This decussation, so productive of sym-
pathetic ophthalmia in man, never, in my experience, gives
rise to sympathetic ophthalmia in the horse. The nerve
runs in the substance of the retractor muscle, and makes a
distinct dip downwards before penetrating the globe.

By means of the optic nerve the impulses due to the
action of light on the retina are conveyed to the brain ;
the optic nerve conveys nothing else but luminous im-
pulses ; stimulation of the nerve causes flashes of light, but
no pain ; division of the nerve is therefore painless, but the
sheath of the nerve causes pain when cut. The optic nerve,
by its expansion the retina, collects the impulses due to the
action of light, which are then referred to the brain by
means of the nerve itself. The natural stimulus of the
retina is light ; we must therefore briefly study the changes
occurring in the rays of light while passing through the
various refracting media of the eye, which result in the
formation of images on the retina.

A beam of light is said to consist of a number of rays,
each ray running parallel to its fellow, and continuing in
this position unless it meets with a body which turns it
back in nearly the opposite direction to which it has been
travelling, viz., reflects it, or with a body which will allow
it to pass, but only on condition that the parallel rays
become bent. This bending is termed refraction.

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A ray of light passing from a rarer to a denser medium
becomes refracted ; it does not matter whether this medium
be water, glass, or diamond, a greater or less bending of the
ra}7 occurs.

A ray of light passing through a convex lens also
becomes refracted, but before we can follow exactly how this
refraction occurs, it is necessary that we should be ac-
quainted with the various parts of a lens.

A convex lens has two curved surfaces, and a line drawn
through the centre of these two surfaces is known as the

Fi<;.:>7. Fig. 28.

floures illustrating the action or lenses upon rays 01
Light passing through them.

Fig. 27. — Biconvex lens ; 0, optical centre ; m, m, chief axis ; „. h,
chief or principal rays.

Fig. 28. — Rays falling upon a lens parallel with the principal axis ,/, .-,
are so refracted that they are collected on the other side <<( the
lens at a point called the principal focus/'.- the distance Erom < >,
the optical centre, to /, is called the focal distance of the lens.
The converse of this condition is also true, viz., rays which diverge
from a focus pass through the lens, being on the other side parallel
with the principal axis without coming together (Landois and
Stifling).

principal axis of the lens. The essential idea of a double
convex lens, is that it is thicker at the centre than at the
edges.

Situated on the principal axis of a biconvex Lens a: a
point in its interior is the optical centre (Fig. ±~ ; any
straight, line passing through the optical centre is termed
a secondary axis.

Parallel rays of light passing through a convex lens, are
refracted or bent in such a way that they col!,,'- on the

The Senses. 297

opposite side of the lens at a point termed the focus; every
ray passing through the lens is refracted, excepting those
passing through the optical centre (see Fig. 28). If instead
of the rays being parallel, they diverge from a luminous
point, and that point be the focus, and pass through a
convex lens, then by passing through, they are rendered
parallel (Fig. 28).

If rays of light be passed through a convex lens from a
point beyond its focus, after passing through the lens,
and so becoming refracted, they meet again instead of
becoming parallel, and the rays cross at some point, in such
a manner that the upper ray becomes the lower one, and
the lower ray the upper one ; in other words, the image
formed under these conditions is inverted (see Fig. 29).

Fig. 29.

Rays of light passing through a convex lens from /, at a point beyond
the focus/, cross at some point r, and invert the image (Landois
and Stirling).

Applying these physical conditions to the eye, we find
that the rays of light passing into and through the cornea
are refracted ; they are further refracted passing through
the aqueous humour, considerably refracted passing through
the dense substance of the lens and vitreous humour, and
brought to a focus on the retina in such a way that the
retinal picture is upside down, and is only a miniature
though perfect representation of the object presented to
the eye (see Fig. -SO).

The rays of light passing from X Y (Fig. 30) are re-
fracted and cross in the lens ; those rays, such as a and a',
pass through the lens without refraction, as they pass
through its optical centre ; the further behaviour of the
rays is shown in the diagram, and the method by which
the inversion of the picture is produced. The angle

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X n Y is spoken of as the visual angle, and it is equal to
the angle Y n X. All objects having the same visual angle
form the same sized picture on the retina, whether they be
near or far.

The retinal image though inverted, is mentally referred
not to the retina, but to the direction from which it has
proceeded. Thus to the mind of the animal the picture is
not seen at Y A X, but referred to X ( > Y.

The optical axis of the eye is the straight line through
the eye which passes through the centre of the refracting
media.

The eye is liable to certain defects in its refracting media,
due either to its shape or errors in the curvature of the
refracting surfaces.

Fig. 30.

\.\i. Image | Foster).

a, principal ray of the pencil of light proceeding from X ; a', principal
ray of the pencil of light proceeding from Y ; the principal rays
pass through the eye without being refracted ; the other rays b, o
and b', c' are refracted. In this way the arrow X O Y forms a
smaller inverted image of an arrow on the retina Y A X.

Spherical Aberration.— The rays of light passing through
a convex lens are not all equally refracted, the rays passing
through the circumference being more bent than any
others; if the rays be derived from an object situated at
the side of the field of vision they do not all meet in the
same point, those passing through the circumference of the
lens coming to a focus earlier than those passing through
the centre. This defect, known as'spherical aberration,'
is remedied in the eye by the introduction of a diaphragm
or iris, which prevents some of the rays of light from
passing through the circumference of the lens.

The Senses. 299

Spherical aberration produces indistinctness of vision by
the production of circles of diffusion, caused by those rays
which met too early crossing each other and forming a
circle.

Chromatic Aberration is due to the decomposition of white
light into its primary colours — viz., the formation of a
spectrum — by passing through a prism or a convex lens.
The colours of the spectrum are differently refracted, the
red being the least bent, the violet the most ; when there-
fore we can see the red distinctly the eye is not focussed
for the violet. Chromatic aberration is prevented in the
eye by the unequal refractive power of the various media.

Astigmatism is due to irregularities in the curvatures
of the cornea. The curvature of the vertical meridian is
frequently greater than that of the horizontal meridian ;
by this difference in the curvatures of the refracting
surfaces whether lens or cornea, but generally the latter,
the rays of light cannot be focussed in one point, but in
two different focal points, of which the focus of rays falling
on the vertical meridian, lies in front of that for the rays of
a horizontal plane.

Emmetropia. — We shall presently have to speak of accom-
modation, or the means by which the eye is focussed ; but
it is necessary here that we should understand that by the
term 'range of accommodation' is understood the power
the eye possesses of seeing distant objects 'as far as the
eye can reach,' and also of seeing near objects distinctly
up to 8 inches. Between 8 inches and infinity parallel
rays of light should still be focussed on the retina so as
to form a distinct image ; such an eye is termed emme-
tropic.

But all eyes do not possess this range of vision ; some
are perfect for close objects, others are only perfect for
distant ones. The one eye is short-sighted, the other long-
sighted ; the explanation of these two conditions lies in the
shape of the eyeball.

Myopia, or short-sightedness, is due to the eyeball being
too long, whereby the focal points of the image, instead of

300

Manual of Veterinary Physiology.

being thrown upon the retina fall in front of it, the rays
crossing and forming a diffused circle on the retina. If in
Fig. 31 the retina lies at (I— viz., the eyeball is too long—
the rays of light will focus in front of it and diverge at
" and h.

Hypermetropia, or long sight, is due to the opposite con-
dition—viz., the eyeball being too short— whereby- the rays
of light are focussed behind the retina instead of on it.
The retina of a hypermetropic eye would be situated at
H (Fig. 31) ; the rays of light at c and/ have not yet come
to a focus. In this condition, by a great effort of accom-

Fig. 31.- Diagram to illustrate Myopia \\i» Bypermetropia.

G, the position of the retina in a myopic eye. a blurred image from
A B is perceived at e and o which are beyond the focus ; H. the
position of the retina in a hypermetropic eye. the image from
A B is blurred ate /, which are in front of the focus ; V. the
position of the retina in the emmetropic eye, the rays from A 1*.
are brought to an exact focus at </ A (Kirke).

modation (a term which will be presently explained . the
divergent rays from a near object may be caused to focus
on the retina: the parallel rays from distant objects are
generally well seen without any great effort of accom-
modation.

Since myopia and hypsrmetropia are due to the rays being
brought to a focus either in front of or behind the retina,
if we could supply horses with convex or concave spectacles,
their myopic or hypermetropic condition would bo of no
serious disadvantage.

In the normal eye the retina must be situated the proper

The Senses.

301

focal distance from the lens ; if too close long sight results,
if too far away short sight is produced.

Accommodation. — We must now consider the question of
accommodation, and the manner by which it is brought
about.

The near point of the eye lies at about 8 inches from it ;
the far point in the emmetropic eye is infinity. It is not
necessary, however, that the eye should be capable of
focussing, adjusting, or accommodating itself for any and
every range between 8 inches and infinity, for at a point a
little over 200 yards from the eye the rays of light for all

Fig. 32.

FAR
Diagram t<

NEAR

ILLUSTRATE ACCOMMODATION.

C.P., ciliary process ; T, iris ; Sp.l., suspensory ligament ; l.c.m., longi-
tudinal ciliary muscle ; c.c.m., circular ciliary muscle ; c.S., canal
of Schlemra (Foster after Helmholtz).

The left half represents the shape of the lens for viewing far objects,
and the right half that for viewing near objects.

practical purposes are parallel, and no effort of accommoda-
tion is required. From S inches up to 200 yards the eye
has to be capable of focussing itself, and the mechanism by
which this is produced we will now study.

The rays of light passing through a convex lens, will be
brought to a focus at a greater or less distance behind the
lens, depending upon its curvature ; thus, the thicker the
lens the shorter the focal length, and vice versa. It is
obvious, therefore, that any mechanism which can alter the
curvature of the crystalline lens of the eye, will adjust it for
distant or near vision ; such an arrangement exists. The

302 A Manual of Veterinary Physiology.

crystalline lens may be made natter or more convex, and the
process which brings this about is termed the ' mechanism
of accommodation."

The crystalline lens is contained within a capsule ; to this
capsule is attached the zonula ciliaris, which in turn is
attached to the choroid. So long as the zonula is tense the
lens is flattened; but if the tension be removed, the natural
elasticity of the lens causes it to bulge forward and become
more convex. The tension of the zonula is removed from
the lens by means of the ciliary muscle, which draws forward
the choroid coat, relaxes the zonula, and the lens becomes
convex. In this way the accommodation of the eye is
adjusted (Fig. 32).

Whilst on this point mention may be made of the refiec-

A B C

Fig. 33. — Diagram of the Katoptrk Test.

A, from the anterior surface of the cornea: B, from the anterior face
of the lens : and C, from the posterior face of the lens.

tions obtained when examining the eye with a candle — the
so-called katoptric test. When a candle is held opposite
the eye three images of the name are seen: one a very sharp
bright one, obviously reflected from the cornea ; a second
much duller, but also large, reflected from the anterior sur-
face of the lens; and a third very small, brighter than the
middle one, and inverted, reflected from the posterior part
of the lens. In a normal eye these are seen perfectly, and
move in a definite direction when the candle is moved, the
inverted one in an opposite direction to the two erect images,
and all are equally visible at any surface of the lens ' see

' The blurring or duplicature of the images, especially the second
one, is a good ordinary test for opacities of the leas,

The Senses. 303

Fig. 33). The eye all this time we must suppose to have
its accommodation relaxed, and to be looking into distant
space ; if now it be focussed on a near object, the lens
becomes convex, and the second image of the candle
advances and it becomes smaller and clearer.

At the moment when the ciliary muscle acts the pupil
contracts, and when the muscle is relaxed it dilates. This
is due not only to the intimate connection existing between
the ciliary muscle and the iris, but also both are supplied
by the same nerve — viz., the third cranial.

The Iris, or diaphragm, performs the same function as a
shutter : it regulates the amount of light entering the eye,
and, as pointed out in speaking of spherical aberration, it
cuts off' those rays entering at the circumference of the
lens, and so introduces a correction for spherical aberration.

The movements of the iris are brought about by two sets
of muscles — a sphincter and a dilator (?). The former sur-
rounds the pupil, and by contracting closes it ; it is supplied
with nervous power through the third pair. The dilator by
contracting opens the pupil, and its nervous supply is fur-
nished chiefly by the sympathetic. The existence of a
dilator muscle, though very probable, is not absolutely
proved ; but it is certain that the contraction of the pupil
is under the control of the third pair of nerves, whilst its
dilatation is produced by the sympathetic.

The ordinary contraction of the pupil due to light is a
well-marked reflex action.

The iris would also appear to be affected by the action of
light. In a horse, for instance, just destroyed, the pupil
dilates considerably, and yet in a few hours' time it has
undergone extensive contraction. It is said that if the eyes
remain covered up the subsequent contraction does not
occur. It is important to note that the pupil of the horse
dilutes under artificial light, a point to be referred to
presently.

The opening in the iris— termed ' the pupil' — is elliptical
in herbivora. The range of movement is extensive, from a
mere ring of iris, such as may be obtained under atropine,

304 A Manual of VeUrinary Physiology.

to a simple slit of pupil, such as is seen in sunlight ; in fact,
owing to the presence on the edge of the iris of some large
pigmentary bodies, which completely block up the centre
of a powerfully contracted pupil, it is wonderful how
sufficient light finds its way into the retina during sun-
light.

The function of these black bodies (which are sometimes
so large as to cause serious apprehension about the vision)
is obscure; that they assist in absorbing rays of light
appears certain, but their position in the centre of the
pupillary opening would certainly not be the most suitable
position for a light-absorbing substance, and therefore they
must have some other function. We believe that they may
assist in rendering vision binocular when both eyes are
turned to the front ; but this point will be touched upon
later. It only remains here to note that the horse appears
to be the only animal possessing them.

The colour of the iris is brown in the horse, occasionally
bluish white, as in : wall-eyed ' horses. It is of a brighter
brown in the ox, and is of a brownish yellow in the
sheep.

The Retina— The expansion of the optic nerve within the
eye is termed the retina ; it is a thin, delicate membrane,
covered by the vitreous humour in front and the choroid
behind. Microscopically, it consists of several layers, of
which the so-called rods and cones is the most important,
for the reason that the cones are the parts most concerned
in vision. The entrance of the optic nerve is a good example
of this; there are neither rods nor cones over the optic
nerve at its entrance, and in consequence the part is quite
blind. There is no yellow spot or area of intense vision in
the horse or other herbivora; it is possible that the region
of the tapetum is the area of the retina which is most
excited by light.

The Tapetum Lucidum is part of the choroid coat ; it is of a
remarkably brilliant, colour, being in the horse of a greenish
vellow, and occupying a somewhat semi-lunar spare above
the optic nerve. It is formed of 'numerous undulating

The Senses. 305

bundles of connective tissue, giving a metallic lustre to the
eye. The colour is not due to pigment, but is iridescence
caused by interference of waves of light' (M'Kendrick).
Over this region there is an entire absence of the pigment
so characteristic of the inner surface of the choroid, and
the appearance of the fundus of the horse when examined
by the ophthalmoscope is an extremely beautiful object.

The Ophthalmoscope. — We may here describe in outline
the theory of this instrument, and the appearance of the
picture presented by it.

To examine the eye, a mirror with a hole in the centre
is applied to the eye of the observer; from a suitable
source of light rays are thrown through the pupil on to the
retina to be examined.

When a light is thrown into the eye, the rays are re-
flected back through the pupil in the direction in which
they entered, and pass through the hole in the mirror into
the eye of the observer.

This is the principle of the ophthalmoscope. On looking
through it at the retina of the horse, a remarkable golden-
yellow or greenish-yellow surface is illuminated studded
with minute dots ; this is the tapetum. Examination shows
this surface to be situated above the optic papilla, and to
be half-moon in shape ; below it the optic papilla comes out
of a reddish or pink colour, with a slightly raised whitish
margin. It is so difficult to study the eye, owing to its
frequent movement, that only occasional glimpses of the
papilla can be obtained. From the optic papilla several
vessels may be seen radiating, but extending no great dis-
tance from it. This is characteristic of the retina of the
horse. The remainder of the fundus is purple or brown,
the shading in it resembling that employed for representing
mountains in a map.

Owing to the presence of the tapetum in the horse, a per-
fect examination of the lens, and a fair examination of the
fundus may be made without the aid of artificial light;
under the influence of artificial light the pupil dilates so
much that there is no need for the use of atropine.

20

306 A Manual of Veterinary Physiology.

As before noticed, there is no yellow spot in the eye of
herbivora, and the tapetum is probably the area of the most
acute vision.

In the rods of the rod and cone layer of the retina is a
peculiar pigment known as the visual purple ; it can be ob-
tained from eyes kept in the dark, but in those exposed to
light it rapidly becomes bleached, though it reappears
when the light is again excluded.

Pictures have been printed on the retina through the aid
of the visual purple ; its exact use is not known, though
the photographer's process is suggestive of its probable
use. Unfortunately for this theory it is absent from the
cones, which are known to be the instruments of the most
acute vision.

Movements of the Eyeball. — We have now to consider the
mechanism by which the eye is brought to bear on any
desired point, and the subject is somewhat complicated by
the fact that with most quadrupeds the eyes occupy a
lateral position in the head, in such a way that in
many cases vision is only one-eyed, and not two-eyed as
in the human subject. Further, the chief movements of
the head are not from side to side as with us, but up and
down, and as the pupil remains horizontal, no matter what
the position of the head, it is evident that rotation of the
eyeball must occur. If it were not for this rotation the
pupil in the uplifted head would be vertical instead of
horizontal, and, in the depressed head, it would be obliquely
instead of horizontally placed.

The muscles working the eyeball are seven in number :
four recti, two oblique, and one retractor. The use of the
recti is clear enough ; they turn the eye in four directions,
outwards, inwards, downwards, and upwards. The two
oblique muscles rotate the eye in opposite directions; tin.'
superior oblique turns the nasal side of the pupil down-
wards, and the eye can rotate upwards until the pupil,
with the head in the normal position, becomes vertical
instead of horizontal; the inferior oblique turns the nasal
side of the pupil upwards. The retractor pulls the eye

The Senses. 307

backwards into the socket. The following table shows the
action of the ocular muscles :

Eye turned upwards aud inwards ... Sup. rectus, int. rectus,

and inf. oblique.
Eye turned downwards and inwards ... Inf. rectus, int. rectus,

and inf. oblique.
Eye turned upwards aud outwards .. Sup. rectus, ext. rectus, .

and sup. oblique.
Eye turned downwards and outwards ... Ext. rectus, inf. rectus,

and sup. oblique.

When the head is elevated the superior oblique renders
the pupil horizontal, when depressed the pupil is horizontally
placed by the inferior oblique.

With the exception of the external, all the recti muscles,
the inferior oblique, and the retractor, are supplied with
nerves by the third pair ; the fourth pair supplies the
external rectus, and the sixth pair the superior oblique.
The orbicularis palpebrarum, which closes the eye, is sup-
plied by the seventh nerve, and the muscle which raises
the upper lid derives its nerve supply from the third pair.

It will be observed that the muscles of the two eyes em-
ployed in any movement may be the corresponding muscles
in both eyes or not ; both eyeballs may, and commonly are,
directed to the front, producing what would be known
in man as a decided internal squint : in this case the same
group of muscles in each orbit are employed ; but if the
left eye moves backwards, the right eye goes forwards, and
vice versa. Here the groups of muscles employed are
different in each eye, for Avhile the external rectus is acting
on the left eye and drawing it back, the internal rectus is
drawing the right eye forwards.*

Monocular and Binocular Vision. — When a horse looks
direct to the front (Fig. 34), he is capable of seeing an
object with both eyes ; he produces a marked internal
double squint, the eyes being rotated inwards and upwards
by the combined action of the superior and internal rectus,

* The terms employed here of backwards and forwards, express the
same condition as outwards and inwards when applied to ourselves.

20—2

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A Manual of Veterinary Physiology.

and inferior oblique muscles, the object being to bring the
pupillary opening as far as possible to the front. That the
horse succeeds in this can be readily determined by simple
inspection ; the inner part of the iris, as far as the edge of
the pupil, may often be seen in both eyes to disappear
beneath the folds of the eyelid, in the powerful endeavour
to concentrate both eyes on an object situated directly to

Fig. 34.— The P<

Eyes

BlNOCULAB

the front. In no other position has the horse binocular
vision (that is to say, single vision resulting from the em-
ployment of a pair of eyes), and to direct the rays of Light
into the outer half of each lens, the corpora nigra appeal
to be placed in the centre of the pupillary opening.*

* The greal argument which tells against tins theory is thai rami
mints, which bave also binocular vision, have no corpora nigra. Their

The Senses. 309

Whether this be the function of these black bodies or
not, does not affect the accuracy of the statement that
binocular vision in the horse can only occur when a
powerful internal squint is produced, and the eyeballs
directed well to the front. Monocular vision is otherwise
the only one of which animals with their eyes situated on
the lateral side of the head are capable, when from the
position of the object both eyes cannot be directly concen-
trated upon it. Monocular vision would appear to be as
perfect as binocular, though on this point it is difficult to
speak with certainty. Though ordinary vision is mono-
cular, yet the right eye will blink when an attempt is made
to strike the left, though the left cannot possibly see what
is going on.

In man binocular vision is perfect, and the explanation
afforded is that any part of one retina corresponds to the
same part of its fellow ; so that if the retinae be laid over
one another, the left portion of one will lie exactly over
the left portion of the other, and their right upper and
lower parts will equally correspond. But the temporal
side of one eye corresponds to the nasal side of the other.
For instance, in Fig. 35, the two circles represent the two
retina? divided into quadrants, L being the left, and R the
right eye ; a and c in the left eye, correspond to a' c' in the
right eye ; and b and d in the left, correspond to b' and d'
in the right eye.

When the two images of an object fall on corresponding
points of the retina, then vision is binocular and only one
object is seen ; thus, if the rays fall on the right side of one
retina, they must fall on the right side of its fellow; in
Fig. 35 this is shown, v 1 from x to x', and x to x are the
two visual axes. If the centre x of an object be looked at
the corresponding points which lie on the right side of one
retina, lie on the right side of the other also, and con-
versely. Owing, then, to the manner in which the human

eyeballs are so prominent that it is possible that here they are not
needed.

310

A Manual of Veterinary Physiology.

eyes are placed in the head, and the convergence of axes
of the eyeball, a ray of light from any point is imprinted
upon the same part of the retina in both eyes, and we see
it not as a double image, but as a single one.

This explanation does not apply to the horse or ox ; no

Fig. 35. — Diagram illustrating Corresponding Points. (Fostek.)

z' x' yf are points in the right eye corresponding to z x y in the left
eye ; v 1, visual axis. The two figures helow illustrate the cor-
responding points on the retina, described in the text.

matter how greatly the eyes may be converged in order to
see an object, the rays of light do not fall on the same sido
of the retina, but on opposite sides of it. The diagram
( Fig. 36) will make this point clear.

The outer part or temporal side of the retina in the

The Senses.

311

horse, corresponds with the temporal side of the opposite
eye ; while the nasal side cannot correspond with the nasal
side of the other eye, as it is not possible for a ray of light
from an object to strike both nasal sides at one time (see
Fig. 36).

Cartilago Nictitans.— The retractor muscle of the eye with-
draws the eyeball within the orbit, and the pressure thus
produced within the cavity forces the cartilago nictitans

Fig. 36. — Diagram of Horizontal Section of the Head passing
through both eyeballs, to illustrate corresponding
Points in the Retina of the Horse.

x x, the frontal bones ; p p, portion of malar bone entering into the
formation of the outer rim of the orbit ; s, the nasal septum.
Rays of light proceeding from A are seen by both eyes, being
imprinted on the temporal side of each retina at a ; rays from B
are seen at b in the left eye, but are not seen with the right eye.
In the same way rays from C are imprinted at c in the left eye,
but cannot be seen with the right eye.

forward to such an extent, that it may be made to sweep
nearly the whole corneal surface.

The reason why the cartilage is pressed forwards is due
to the fact that, naturally curved, it becomes flattened by
the pressure caused by retraction, and shoots forward ;
when the pressure is removed it retires through its own
elasticity, becoming curved once more.

312 A Manual of Veterinary Physiology.

On the cartilago of some animals is a small gland termed
the Harderian ; its use is to prepare an unctuous secretion,
probably of a protective nature.

In the eyelids are found numerous glands, the MeiDo-
mian, which furnish an oily secretion, and prevent the
overflow of tears.

The Tears are secreted by the lachrymal gland, placed on
the upper surface of the eyeball ; they find their way into
the conjunctival sac by several small tubes. The use of
the tears is to keep the cornea moist and polished, and to
wash away foreign bodies. The tears find their way
through the narrow puncta into the lachrymal sac, and so
into the nostril ; once in the sac the descent to the nostril
is readily understood; but it is not clear why the tears
prefer passing through a narrow slit in the eyelid to
running over the side of the face; probably the only
explanation is the unctuous secretion mentioned above.

The Eyelashes of the horse are peculiar. Those on the
lower lid are very few and fine, whilst on the upper lid they
are abundant, and exist not in one single row but a double
one ; the rows crossing each other like a trellis-work, but
without interlacing ; these eyelashes are very long and
strong. A few protective hairs grow from the brow and
below the lower eyelid ; in some horses they are four or
five inches in length. They appear to be in connection
with nerve terminations, for their delicacy to the sense of
touch is remarkable. They are doubtless protective, and
give the eyes previous warning of danger.

Smell.
In order that the sense of smell may be obtained, it is
necessary that a sensory surface specially endowed should
exist, the connection of which by a nerve with the brain
should be intact. The special nerve of smell is the olfac-
tory, and the special smell centre in the brain is (according
to Ferrier) in the tip of the uncinate gyrus, on the inner
surface of the cerebral hemisphere. The olfactory bulbs
are hollow in the horse, filled with fluid, and communicate

The Senses. 313

with the lateral ventricles. From the olfactory lobes is
given off the olfactory nerves, which pass out through the
cribriform plate of the ethmoid bone, and ramify over the
middle meatus and superior turbinated bone. Owing to
the fact that the olfactory nerve is not distributed over the
entire area of the nasal chambers, it is usual to divide this
cavity into two areas — an olfactory and a respiratory portion.
The special nerves of smell ramify in the mucous membrane
covering the parts named, but they have no special end
organs. In appearance the olfactory, owing to the greyness
of its fibres, resembles the sympathetic nervous system.

In all animals in which the sense of smell is acute the
turbinated bones are remarkably convoluted ; this is more
marked in carnivora than in herbivora. There are certain
substances which excite the olfactory organs more readily
than others : thus, in carnivora, flesh, blood, or any animal
matter, has a remarkably stimulating effect ; in herbivora,
plants, grasses, and vegetable products have a characteristic
effect, while the odour of blood is evidently repulsive, and
often causes nervousness and fright. Some of the herbivora
have remarkably keen scent ; antelopes and deer have the
power of smelling the presence of man when even a con-
siderable distance away. The sense of smell plays an
important part in the sexual relations of animals, for the
female in the 'rutting' period may be distinguished at a
considerable distance.

The organ of Jacobson, which is well marked in her-
bivora, is said to have some connection with the sense of
smell. Cuvier regarded it as the means by which the
herbivora distinguished between poisonous and non-
poisonous plants. This can hardly be correct; cattle
poisoning is comparatively common.

Before a substance can be perceived by the olfactory
nerves, it has to become dissolved in the mucous coating of
the part— in fact, it is considered that substances can only
be perceived by the sense of smell either in the form of a
vapour or liquid, as the sense is nearly or entirely lost if
the membrane be dry.

314 A Manual of Veterinary Physiology.

The odour of a body can be more certainly obtained by
' sniffing.' This is an inspiratory act, producing a rarefac-
tion in the nasal chambers, which is overcome by more air
rushing in to restore equilibrium ; by this rushing in the
air is forcibly brought into contact with the olfactory area.
The sense of smell rapidly becomes blunted, the olfactories
apparently get used to an odour ; an unpleasant smell is
always more offensive when first detected than it is a few
minutes later.

In connection with the nasal chambers are the facial
sinuses, which in horses and cattle are very extensive cavi-
ties filled with air, (which they derive from the nasal
chambers), and lined by a mucous membrane derived
from the Schneiderian. This membrane cannot distinguish
smell, according to Colin's experiments, nor should we
expect it to.

The use of these sinuses is to make the head larger with-
out being heavier, and thus afford more surface attachment
for the muscles. During health the membrane lining the
cavities is moistened with a watery fluid ; but under
diseased processes, which are very frequent, the cavity
becomes filled with pus.

By the sense of smell animals have the power of distin-
guishing good from bad, eatable from uneatable : and,
moreover, through this sense sexual activity is excited.

Sensibility is supplied to the nasal chambers by the nasal
branch of the fifth nerve, not by the olfactory.

Taste.

The special nerve of taste is the glossopharyngeal, and
the portion of the mouth where the sense principally lies,
though not fully agreed on by physiologists, is the root of
the tongue and soft palate. The part of least taste, or no
taste at all, is the dorsum of the tongue ; this is due to the
dense coating of epithelium.

The glosso-pharyngeal nerve consists of medullated and
non-medullatcd fibres ; the former terminate in end bulbs,
the latter in taste goblots (M'Kondriek).

The Senses. 315

The taste goblets are balloon-shaped bodies, found prin-
cipally in the circumvallate papilla ; in the top of the
balloon or goblet is a depression or funnel, termed a ' taste-
pore.'

With reference to the position of these taste goblets in
the lower animals, M'Kendrick gives the following details :
The taste goblets appear principally on the side of the
circumvallate papilke — 1,760 taste goblets were counted in
a papilla of the ox ; in the papilla foliata of the sheep 9,500
goblets, and in the ox as many as 30.000 goblets have been
observed. There can be no doubt that taste is due to these
bodies acting through the glossopharyngeal nerve, for
division of this nerve causes the goblets to degenerate.

All the papillae of the tongue are made up on much the
same lines, viz., an elevation of the mucous membrane,
with vessels and nerves ramifying in its substance. In the
coating of epithelium which the circumvallate papillae
receive are to be found the taste goblets.

In herbivora taste produces an abundant secretion from
the submaxillary and lingual glands, but not from the
parotid (Colin).

The papilla? in the mouth of the ox appear to serve the
purpose of retaining the food in the mouth ; the hard rough
coating to the dorsum of the tongue is for cleaning pur-
poses, and to retain grasp of the food in grazing. This
condition is absent in the horse, who feeds with his lips
and teeth.

The nerve of taste does not supply the tongue with
sensation ; the latter is derived from the lingual branch of
the fifth pair. It is quite possible for a tongue to have lost
its touch, and not its taste. The motor power is derived
from the twelfth pair of nerves, or hypoglossal.

Hearing.

The arrangement of the ear is best understood if we
describe it as consisting of two cavities containing air,
placed side by side but separated by a partition, one of the
cavities being brought into contact, by means of a flexible

316 A Manual of Veterinary Physiology.

bridge, with a membranous and rigid apparatus containing
fluid. The cavities are the external and middle ear ; the
apparatus containing fluid is the internal ear ; the partition
between the external and middle chamber is the tympanum ;
and the flexible bridge connecting one air chamber with the
internal ear is composed of the bones of the ear or auditory
ossicles.

The vibrations of sound are collected by the external ear,
which from its funnel shape is eminently calculated to con-
centrate them. From here they are directed on to the
tympanum ; this being set in vibration, the handle of the
malleus, then the incus, and lastly the stapes, are also
moved ; and the latter being attached to a membrane in
contact with fluid, the vibrations of the stapes are trans-
ferred to the fluid or perilymph, by which means a special
impression is made on the nerve endings in the cochlea
and so conveyed to the brain.

It is therefore in the internal ear where the proper organ
of hearing is contained, and to which the eighth pair of
nerves is distributed ; and the arrangement is so peculiar
that we must momentarily glance at it.

The internal ear consists of a cavity termed ' the laby-
rinth,' composed of the vestibule, cochlea, and semicircular
canals. All these, with the exception of two small surfaces,
are entirely covered with bone, yet within it we find a
membranous labyrinth containing a fluid termed ' the endo-
lymph,' and in the space between the membranous and
osseous labyrinth is a second fluid termed ' the perilymph."
Within the coils of the cochlea are spread out on a special
membrane some remarkable cells or organs, termed ' the
organs of Corti '; their general arrangement resembles the
keyboard of a pianoforte, and in connection with them,
through the medium of the auditory epithelium in which
they terminate, are fibres of the special nerve of hearing.

The eighth pair of cranial nerves supplies the special sense
of hearing. The nerve is remarkably soft, and its fibres
very fine. It gives off branches to the vestibule, cochlea,
and semicircular canals.

The Senses. 317

The tympanic membrane is placed obliquely across the
canal of the external meatus, and owing to its attachment
to the malleus on the opposite side, it does not present a
plane, but a concave surface towards the external ear. It
is not tightly stretched across the space ; by its attachment
to the malleus excessive vibration is prevented, for this
connection acts the part of a damping apparatus.

The bones of the ear transmit the vibrations from the
tympanic membrane to the internal ear. The small bones
have a certain amount of movement on each other, and
there are special muscles for bringing it about ; by means
of these movements the tension of the membrane may be
altered. As before mentioned, this chain of bones lies in
the middle ear, which is also an air cavity deriving its
supply through the Eustachian tube. It is necessary for
the perfect production of sound that the same atmospheric
pressure should exist on both sides of the tympanic mem-
brane, and this is provided for by the Eustachian tube.

Whatever part those remarkable sacs (confined solely to
solipeds) are intended for — viz., the guttural pouches — it is
probable, from their anatomical connection, that they take
some part in the sense of hearing, perhaps that of supplying
the needful amount of air to the middle ear. The actual
use of the guttural pouches is involved in obscurity, but we
may provisionally consider them as part of the middle ear.
In man, acuteness of hearing is produced by listening with
an open mouth ; the fact that the horse cannot breathe
through the mouth may explain the presence of these large
air-sacs beneath the skull ; in other words, they are pro-
bably associated with acuteness of hearing.

The tension of the tympanic membrane, produced by the
muscles acting on the small bones of the ear, assists in pro-
tecting the internal ear from violent noises, and the same
movement which slackens or tightens the drum-head in-
creases or decreases the pressure on the perilymph of the
internal ear.

The stapes being fixed against the membranous labyrinth
through a foramen in the osseous structure, every alteration

31S A Manual of Veterinary Physiology.

in the pressure it exercises transmits movement to the fluid
of the internal ear, and excites the terminal organs of the
auditory nerve which are lying free in the endolymph.

In the cochlea the nerve endings of the eighth pair are
distributed over a large surface, which is one explanation of
the peculiar shape of the part, and in connection with the
nerve endings are the peculiar rods of Corti ; these are so
arranged that they are supposed to each be capable of
vibrating to its own particular tone, and thus really striking
its own note.

The excessively hard bone in which the internal ear is
lodged, with its central fluid medium, are both of the
highest acoustic value.

The semicircular canals, though they undoubtedly take
some part in hearing, are particularly connected with
maintaining the equilibrium of the body, and of keeping
the mind acquainted with its position. This remarkable
function is probably carried out by alterations in the position
and pressure of the fluid contained within them, which
results from every movement of the head (see p. 2S1).
Division of these canals causes the most remarkable irregu-
larity in the movements, and a side-to-side or upward
movement of the head.

In certain parts of the vestibule are found small particles
of calcareous matter termed otoliths. They are brought
closely in connection with the nerves in the labyrinth,
and produce upon them more intense impressions than
would be produced by fluid alone.

Touch.

The sense of touch in the lower animals is developed to a
considerable degree in those parts of the body used for con-
tact purposes, such as the muzzle and the feet (where pro-
bably special nerve endings exist), and generally through-
out the skin, especially in the horse, in which a wry acute
sense of touch exists, though no special touch organs have
been found in connection with the nerves of the skin.

The sense of touch is for the purpose of rendering the

The Senses. 319

animal acquainted with its surroundings. In the lips,
where we find the most exquisite sensibility, this sense is
developed not only for the purpose of distinguishing the
different varieties of food, but for ordinary touch purposes,
the lips of animals corresponding to our fingers. In the
horse the nerves supplying the long papillae of the skin of
the lips run to their extreme termination, the papillae being
thrown as finger-like processes into the substance of the
epithelial layers, and almost reaching to the free surface.

The tactile sensibility in the foot of the horse enables
him to be acquainted with the nature of the ground over
which he is travelling, though that this is not absolutely
essential to his safety in progression, is proved by the results
of plantar neurectomy. I have suspected the presence of,
but not yet found, definite touch organs in the foot.

The long feelers, or hairs, growing from the muzzle are all
endowed with extreme sensibility; this is brought about
through their close connection with the nerves of the
skin.

We cannot explain why it is that the different impressions
of touch or pain can be so accurately defined by the pecu-
liarity of the impression conveyed. The impression of a
prick, a cut, or a burn, touch, itching, etc., produce unmis-
takable evidence of the nature of the substance causing the
impression.

Through the nerves of the mucous membrane of the
mouth impressions are carried to the brain, impressions
which in horses convey unmistakable evidence to the animal
of the strength of will or weakness of his rider.

CHAPTER XVII.

THE LOCOMOTOR APPARATUS.

The muscles are attached to bones, which form by their
movements on each other angles of varying size. These
angles are opened and closed during progression, and the
mechanical aid which is introduced to effect this is that of
the lever.

The lever is composed of a power, fulcrum, and weight,
and, according to the relative position which these occupy,
we have formed a lever of the first, second, and third
order.

In a lever of the first order the power is at one end, the
weight at the other, and the fulcrum between the two. If
we try to move a heavy box by placing a crowbar beneath
it, and a block under the crowbar, we are employing a
lever of the first order, the box beiDg the weight, the
block the fulcrum, and the hand of the operator through
the crowbar the power. The muscles which extend the
head act also as a lever of this order, the head being the
weight, the occipito-atloid articulation the fulcrum, and the
muscles of the neck the power. When the angle formed
between the scapula and humerus is reduced, the triceps
forms a lever of the first order, the muscle being the power,
the elbow the fulcrum, and the limb below the weight. In
extension of the hind-leg the gastroc muscles are the power,
the hock-joint the fulcrum, and the leg below the hock the
weight.

This is principally a lever of extension, and exists all <>\ Ti-
the body. It is a lever of power, lor if the long-arm be

The Locomotor Apparatus. 321

5 feet, and the short-arm 1 foot, a power of 1 lb. at the long-
arm will support a weight of 5 lbs. on the short-arm ; but
it is to be noted that as a lever increases in power it loses
in speed.

In the second lever, which is a rare one in the body, the
weight is placed between the fulcrum and the power, as in
a wheelbarrow, the wheel being the fulcrum.

When the leg is fixed on the ground the muscles of the
olecranon act as a lever of the second order, the ground
being the fulcrum, the triceps the power, and the body
through the elbow-joint the weight. The same applies to
the gastrocs when the weight is on the limb and the foot
on the ground.

In the third order of lever the power is between the ful-
crum and weight. It is the lever of speed, and what it
gains in speed it loses in power. It is also the lever of
flexion, and examples abound in the body ; the flexor
brachii is one, the weight is the leg below the elbow, the
power the muscle at its insertion into the radius, and the
fulcrum the elbow-joint above. This is a wasteful lever,
but an essential one in the limbs. The nearer the power is
to the fulcrum, the greater the flexion obtained with the
least amount of muscular force, and the same remark will
apply to the first lever. Other examples are the masseter
muscles, flexor metatarsi, the psoas magnus, the muscles
which flex the head, etc.

In nearly all cases the fulcrum of the lever is formed by
a joint, which is fixed or rendered rigid by other muscles
during its action. Antagonistic muscles are not relaxed
during the contraction of their opponents, nor are they
contracted. They may help the antagonistic muscles to
return to their position of rest.

Groups of muscles act together ; this co-operation admits
of certain points being fixed, or increases the effect, or
gives the movement a special direction (Foster).

The reason why the third lever is more frequent than
the others, is due to the fact that the chief movements of
the limbs are directed to moving comparatively light weights

21

322 A Manual of Veterinary Physiology.

through a great distance, or through a certain distance with
great precision, rather than moving heavy weights through
a short distance (Foster). In connection with this we may
say that the weight of the fore-leg, cut off at the elbow, of
a cavalry horse was found to be 17 lbs. 8 oz. : cut off at
the knee, through the upper row of bones, it was found to
weigh 7 lbs. 10 oz. : one fore-foot with corona weighed
2 lbs. 3 oz., and the hind-leg, cut off' at the hock-joint,
weighed 10 lbs. 9 oz.

It is very necessary to be clear on this question of levers,
and not to adopt too rigid a mechanical view of them. The
point of importance to which I would draw attention is,
that what will form a lever of one order in a certain posi-
tion of limb, forms a lever of another order in a new
position. We have given examples of this in the triceps
extensor brachii acting in the one instance as a lever of the
first order, and then as one of the second. The nature of
the lever depends upon the position of the body, so that
Colin proposes the term ' alternative lever.' He also speaks
of a ' composite lever,' where the power in the same position
of limb acts in two distinct ways, and he gives as an
example the flexor metacarpi externus acting as a lever of
the first order above the knee through its insertion into
the trapezium, and as a third order of lever below the knee
through its insertion into the external metacarpal bone.

The same care must be taken also in viewing muscles
simply as extensors or flexors. Stillman points this out
very clearly, and lays stress on the fact that some muscles
may act as flexors and extensors at the same time, and he
very rightly impresses the importance of taking into con-
sideration in animal locomotion some other action of
muscles than that of flexion, extension, adduction, and ab-
duction, viz., the function. of propelling, which he believes to
represent 85 per cent, of the work of the horse's muscles.

It, is most important, however, to remember thai pro-
pelling is not a power apart from flexion and extension, but
the result of them.

The difference existing between the articulation of the

The Locomotor Apparatus. 323

fore and hind limbs with the body, has until recent years
been the cause of considerable error being promulgated.
It was previously supposed that the muscular attachment
of the fore-leg to the trunk indicated that the body was
simply slung between the fore-legs, the latter acting as
props whilst the hind-limbs did the work. Instantaneous
photography has shown us that the fore-limbs not only act
as props, but also as most efficient propellers of the body,
especially in the gallop, where by measurement it has been
shown that one fore-leg will propel the body a distance of
10 feet and raise its centre of gravity 4 inches.*

By means of the fore -legs the horse is enabled in draught
to assist his hind-legs in stopping weights.

Joints are formed wherever two bones come into contact.
Dealing only with those joints found in the limbs, which
are of the most practical interest, we find we have ball-and-
socket joints (as in the hip), hinge-like joints (as in the
hock), gliding joints (as in the knee), and spiral joints (as
in the stifle). All these joints are coated with articular
cartilage and lubricated with synovia.

Synovia is a viscid, yellow, alkaline fluid containing pro-
teids, mucin, and salts. The viscidity of synovia is due
entirely to the mucin it contains, and it confers on synovia
its slippery nature. There is no difference between the
synovia of joints and that of bursse.

It is said that the amount of synovia in a joint is greater
in animals at rest than in those at work, but its bulk
appears to be due to an increase in the watery material,
whilst the proteids are decreased ; the salts, on the other
hand, especially those of sodium, exist in a larger propor-
tion than in the synovia of working animals.

The bursas in the limbs of the horse are very important
structures. They are placed where the tendons pass through
bony channels, as at the back of the knee, and also may be
turned to useful advantage as pulleys, as in the sesamoids
at the fetlock, or the calcis in the hock. Without them
the rapid movements of the limbs would be impossible,

* < The Horse in Motion ' (Stillman).

21—2

324 A Manual of Veterinary Physiology.

and that the strain and wear and tear is considerable we
know from practical experience.

The only joint I propose dealing with in detail is one the
action of which I believe to be universally misunderstood.
I refer to the perfect hinge-joint formed by the articulation
of the tibia with the astragalus.

Hock Joint. — Solipeds appear to stand alone in having
the ridges of the astragalus obliquely placed, instead of
vertically as in ruminants. The ridges are oblique in the
horse, and some considerable difference in the action of the
limb is the result. It is usual to speak of the screw action
of the hock produced by the oblique ridges of the astrag-
alus. This screw action I believe to be an entire mis-
conception ; the ridges on the astragalus do act as a screw,
but not on the hock. The effect is on the stifle, and
produces that remarkable stifle action particularly well
seen in trotters. If the ridges on the astragalus turned
the hock outwards, every horse would travel as if he were
'cow-hocked.' I hold that the leg below the astragalus
is carried directly forwards ; when, however, it comes to
the ground, and the body passes over it, it is not un-
common in some horses to observe a considerable twist
outward* of the hock-joint, the toe being turned in ; this
is due to the ascent of the tibia on the astragalus turning
in the stifle, the result of the leg being fully extended.

The cuneiform bones of the hock have a movement on
each other and the astragalus, which is always in the one
direction, viz., obliquely outwards.

The object of the stifle being turned outwards during
the flexion of the leg is to clear the abdominal wall, and
the reason why solipeds have oblique ridges on the astrag-
alus, and ruminants vertical ones, is that the ribs of the
latter class are short, and do not come near the pelvis (as
in the horse), and therefore the abdominal wall is not in
the way.

A spring or automatic flexion action in the hock has
been described, such as may be readily observed in the dead
leg, when if the hock be flexed slightly it cither flics back,

The Locomotor Appa/ratus. «S25

or completes its revolution with a jerk. This condition
does not exist during life, nor after death until rigor mortis
occurs ; it is produced by the lateral ligaments of the hock-
joint, and is purely a post-mortem condition.

The flexor metatarsi muscle is remarkable in having a
tendon running its whole length, so that from the origin
at the femur to the insertion at the front of the hock is a
stout tendinous cord. When the muscle acts the hock is
flexed, but the use of the tendon running from origin to
insertion is not at first sight quite clear. Chauveau con-
siders that it automatically flexes the hock, but tendons
are devoid of any such power ; and it appears to me that
its sole function is to relieve the muscle when the animal
is standing or sleeps standing. Though a flexor of the
hock, we must remember that when muscles which per-
form flexion and extension are acting together with equal
force no movement results. Such is the case when the
weight is on the limbs and the animal at rest. When a
horse is at rest his gastroc muscles and flexor metatarsi are
acting in opposite directions, and equally — the one is trying
to close the femoro-tibial angle, the other is keeping it
open; it is the function of the tendinous portion of the
flexor metatarsi to keep this angle open without any
muscular effort.

Briefly reviewing some of the other joints, we find that
the Stifle is the largest in the body ; the cause of its rota-
tion has just been described. One chief function of this
joint is that of rendering the limb firm and rigid when the
foot is on the ground while the body is at rest, and this it
does by the contraction of the muscles inserted into the
patella ; if the latter bone be kept fixed on the upper part
of the trochlea of the femur, no flexing of the hock or stifle
can occur. This experiment can be readily tried on a horse
just destroyed ; the limb having been extended, the simple
pressure of the hand on the crural muscles is sufficient to
prevent the bending of the hock unless considerable force
be employed. No bending of the hock can occur if the
foot be kept extended ; the first movement in the advance

:!2G A Manned of Veterinary Physiology.

of the leg and the flexing of the hock and stifle, is that the
foot is flexed. In a certain surgical condition, commonly
known as dislocation of the patella, the limb is rigid from
the stifle to the hock ; but, though the foot may be flexed,
neither hock nor stifle responds, owing to the patella being
fixed. I believe, in the majority of these cases, that the
patella is not fixed from dislocation but from spasm of the
patella muscles.

The amount of movement in the stifle is so considerable,
that to admit of it being carried out with perfect freedom
the convex condyles of the femur play in cups formed of
cartilage on the upper surface of the tibia. It will be
noticed that the patella does not play up and down on the
femur, as at first sight we might expect, but rather that
the femur plays on the patella by the opening and closing
of the femoro-tibial angle.

The Hip is a cup and ball joint ; the range of movement
obtained by it in the horse is limited by the insertion of
the ligamentum teres and pubio-femoral ligament into the
inner side of the head of the femur, and not into its centre
as in most other animals. This is said to be the reason
why the horse rarely ' cow-kicks.' The lengthening of
these ligaments, according to my unpublished observations,
accounts for ' cow-hocks ' in horses.

The Shoulder-joint is remarkable for the considerable
surface afforded by the humerus and the small surface of
the scapula, the object being to obtain a large range of
motion.

The Elbow presents an articulation with ridges which
influence the turning outwards of the knee in progression ;
if the knees are turned out too much the leg below is
thrown in as it is brought forward, and in this way ' brush-
ing ' and ' speedy cutting ' is produced : but in the knee-
joint a provision exists to counteract this movement.

The Knee consists of three main joints ami numerous
minor ones ; the upper joint possesses the largest range of
motion, whilst the lower joint, practically dors not open1.
Probably such defects as speedy cutting and its opposite

The Locomotor Apparatus. o27

condition, ' dishing,' are influenced not only by the elbow,
but by the shape of the articular surfaces between the
radius and upper row of bones.

The radius is peculiar in presenting on that articular
surface next the knee a concave surface anteriorly and a
convex one posteriorly ; these form two condyles, of which
the inner is more curved than the outer. The outer
condyle plays on the trapezium, cuneiform, and lunar : the
inner condyle plays solely on the scaphoid. When the
knee is flexed the influence of the condyles is seen ; the
concave articular surface of the radius is removed from
the surface of the bones of the knee, and the convex
articular surface appears as the joint grows wider. The
inner condyle being larger than the outer depresses the
scaphoid, so that a very important movement occurs
between the scaphoid and lunar ; this action of the radius
on the scaphoid throws the foot slightly outwards, probably
with the object of enabling it to clear the opposite limb.
I believe that an examination of the knees of ' dishing '
horses will show that extreme curvature of the inner
condyle of the radius is the cause of the action, in the same
way that turned-in elbows and alterations in the curvatures
of the radius and humerus will probably account for horses
throwing the lower part of the leg inwards, and thus
' brushing ' or ' speedy cutting.'

The Fetlock forms a flexible articulation : in a state of
repose the greater part of the horse's weight is borne on
the posterior half of the metacarpal articulation, and the
articular surface of the sesamoids. The influence exercised
by the sesamoids by being attached both above and below
to ligamentous structure is dealt with in the next para-
graph. For the movements of the foot-joint, see the
Chapter on the Foot.

The Function of the Suspensory Ligament has been a
fruitful source of discussion. Its chief use, no doubt, is to
support the fetlock ; in no other way could a joint placed
in such a part of the limb, possessed of so much motion,
and exposed to such concussion, be supported. Though

328 A Manual of Veterinary Physiology.

ligaments and tendons are held to be non-elastic, yet
we must claim for the suspensory ligament a little more
elasticity than would be obtained if the sesamoids were
united by bony tissue to the metacarpal ; and the pleasant-
ness and freedom from jar experienced in the riding-horse
is due to the suspensory ligaments. But Stillman
claims for it a function which he believes to be demon-
strated by instantaneous photography, viz., that it acts the
part of a spring, flexing the fetlock sharply when the weight
is taken off it, and explaining why the dirt is thrown out of
the feet of a galloping horse. The sharp picking up of the
foot from the ground in walking (a movement so rapid as
almost to defy detection) is probably assisted by the sus-
pensory ligament. Besides these functions, the suspensory
ligaments assist the horse to stand whilst sleeping.

Function of the Check Ligaments.— Horses are enabled
to sleep standing, and remain for some considerable time
without lying down, by means of a singular arrangement
of check ligaments which exists in both fore and hind
limbs. The flexor tendons support the weight, the ex-
tensors keep the limbs rigid. In order that the strain of
supporting the weight may not be placed on the muscles
of the arm, both flexor tendons, one above and both
below the knee, receive a large branch of ligament from the
radius and metacarpus respectively. These are attached
below the muscular portion, and so cut off the latter
entirely from the strain of standing in one position for any
length of time. This is also assisted by the suspensory
ligament running from the metacarpus to the back of the
fetlock. If the suspensory ligament be divided, the
fetlock does not come to the ground : if the perforans be
divided, a slight sinking of the fetlock is the only change.
To bring the fetlock to the ground, both flexors and sus-
pensory ligament must be divided, which demonstrates that
all three support the weight while standing, and by their
peculiarity in attachment enable the animal to sleep in the
upright position.

Further, the horse is enabled to stand whilst sleeping by

The Locomotov Apparatus. 329

means of the fascia of the arm and thigh ; both of these
are attached to the muscles and tendons of the part,
affording them considerable support of a non-muscular
nature ; particularly is this the case with the fascia of the
thigh.

Centre of Gravity. — Whether the horse be at rest or in
motion, the position of his centre of gravity is an important
one for our consideration. The centre of gravity at rest is
fixed, but during motion it oscillates from side to side,
depending on the position of the body and the pace.

At rest the centre of gravity must always fall within the
base formed by the four feet, or the body is no longer in
stable equilibrium. Owing to the fact that more weight is
carried on the fore than on the hind legs, the centre of
gravity lies nearer to the elbow than the stifle. If a vertical
line be dropped just behind the ensiform cartilage of the
sternum, and intersected by a horizontal one passing
through the lower part of the middle third of the body, the
point of intersection is the centre of gravity ; this is the
rule given by Colin. We may say, speaking roughly, that
the vertical line passes about six inches behind the elbow,
the horizontal just below the shoulder-joint ; the centre of
gravity is where these intersect. It is obvious that the
position of the centre of gravity will vary with different
horses, but not to such an extent as to seriously affect the
truth of the above statement.

Distribution of the Weight of the Body. — The fore-legs
carry more weight than the hind, which is perhaps, the
reverse of what might be expected ; but if a horse be
carefully weighed, it is found that the fore-legs take
more than one-half the body weight. The position of
the head considerably affects the weight on the legs.
Thus, if the head be raised up when the fore-legs are
weighed, the latter will be found to be carrying over
20 lbs. less weight than if the head were dependent.
The practical application of this fact is obvious — keep a
stumbler well in hand. A horse's head weighs between
40 and 50 lbs.

330 A Manual of Veterinary Physiology.

When a man is on the horse's back, it is found that 66
per cent, of his weight is carried on the fore-legs, and
34 per cent, on the hind; the amount of weight on the
fore-legs is increased by leaning forward in the saddle, and
decreased by leaning back.

An explanation why fore-legs are worn out earlier than
hind is afforded us by Avhat we now know of the physiology
of locomotion, viz., the fore-legs act as propellers of the
body, and owing to their being close to the centre of
gravity, they bear the largest share of the weight of the
body and the weight of the rider.

In the act of standing the body is supported on four
props ; two of them have only a muscular attachment to the
trunk, the other pair are united by a ball and socket joint.
It is unnecessary to allude by name to the muscles con-
necting the fore-leg with the trunk, excepting to mention
the serratus magnus, through the medium of which the
body is principally slung on the scapula.

No matter what the position of standing may be, or the
condition under which the horse is standing, he never in a
state of health keeps his fore-feet in any other position
than together ; one fore -limb advanced in front of the other
is abnormal. On the other hand, it is very rarely that one
ever sees a horse standing square on both hind-legs, he is
invariably resting the limbs alternately. Some years ago I
drew attention* to this as being an explanation of the
exemption of the hind-limbs from navicular disease. By
this process of resting, the compression of the navicular
bone between the body and the perforans is relieved. The
horse only learns to do it in the fore-legs when too late.

When the horse is feeding off the ground, he always has
to advance one fore-leg a considerable distance in front of
the body, owing to the shortness of his neck.

In the act of standing the rigidity of the bony column of

the leg is maintained by the extensor tendons, each phalanx

having an extensor attached to it, viz., the extensor meta-

carpi leading to the large metacarpal bone, extensor pedis

* Veterinary Journal, 1886.

Fig. 37.— Tin: Walk.

From instantaneous photographs by Ottomar Anschiitz. (Elh nil rgi r'
' Phy.nologie.')

The Locomotor Apparatus. 333

to the corona and pedis, receiving also a slip from the sus-
pensory ligament, and extensor suffraginis to the suffraginis.
This latter receives a strong slip of ligament from the out-
side of the carpus, which entirely takes off the strain from
the muscle, and keeps the tendon taut during sleep. The
action of the tendons and ligaments of the hind- leg in the
act of standing has been described on p. 325.

When a horse falls at a walk or trot, he injures his knees ;
but when he falls (which is sometimes the case) through
sleeping standing, he invariably damages his fetlocks.

Locomotion. — We have next to study the question of
locomotion in the horse, and describe how the legs are
moved during the different paces. It will be remembered
that our knowledge of this subject chiefly depends upon
instantaneous photography, the pioneers in the field being
Stillman and Muybridge.*

The axiom laid down by Stillman is that ' perfect
quadrupedal locomotion requires uniform support to the
centre of gravity, and continuous propulsion by each
extremity in turn.'

The Walk is the slowest pace, and is executed in a per-
fectly definite manner. In the first stage the body is
balanced on three legs, in the second stage on two diagonal
legs, in the third stage on three legs, and in the fourth on
two lateral legs, and the next movement brings us back to
the first stage, only with different legs employed (Fig. 37).

We will now trace the movements in each stage : The
horse advances one fore-leg — say, the off (1) — and he is
left standing on the near fore, near hind, and off hind —
this is the first stage ; in the second stage the near hind is
picked up, and the animal is standing on the near fore and
off hind, viz., on diagonal legs (2) ; in the third stage
the off fore has come to the ground, and the animal is
balanced on both fore and the off hind legs (3) ; in the
fourth stage the near hind is advanced to be placed over,
or in advance of, the track of the near fore ; to make room
for it the near fore is advanced, and the horse is left stand-
* ' The Horse in Motion.'

334 A Manual of Veterinary Physiology.

ing on two lateral legs, viz., off fore and off hind (4; : the
next movement brings the horse into the first position,
the hind-leg coming to the ground first leaves him on
the off fore and both hind-legs, and the near fore is being
advanced to be followed by the off hind — it is simply the
first stage with the near fore leading instead of the off fore.

The fore-leg remains on the ground for a longer period
than it takes passing through the air ; this can be seen
perfectly in watching the animal, and comprises the period
during which the body is passing over the limbs. The
movement in the air both of fore and hind legs is so
extremely rapid as almost to defy detection, so far as de-
fining the changes in the direction and shape of the limb.*
The snatching up of the foot from the ground is the quickest
movement. Stillman refers the snatching up to the spring
or rebound of the suspensory ligament.

In walking, the majority of horses rarely extend the knee
any great distance beyond a vertical line dropped from the
shoulder. A sudden movement of the extensors now
straightens the leg, and the foot is placed down flat or heel
first. If the leg is not fully straightened by the extensor
muscles, the foot comes to the ground toe first, with the
knee slightly bent, and a stumble follows.

It appears to be a matter of indifference which fore-leg
an animal starts the walk with.

Figs. 38 and 39 show the curves or paths described by
both fore and hind limbs in the walk, after Marey and
Pages. Examining these curves from the time the foot
lea ccs the ground until it touches it again (Fig. 38, B),
we find that the shoulder-curve runs slightly upwards, due
to the limb being advanced ; the elbow-curve runs rather
downwards, due to the limb being extended ; the knee
shows a marked upward curve, and then a fall as extension
occurs ; the fetlock also shows a well-marked curve, due
to its flexion and then extension. The curve shown by the

* Stillman states that if the speed of the horse be "J.") miles an hour,
the foot which is in the air and travelling forward is moving at the
rate of 50 miles an hour.

\

XX x

Fig. 38. — Path Described by the Joints of the Fore-limb at
the Walk : A, while the Foot is on the Ground ; B,
during the Time it is in the Air.

S. scapula ; H, humerus ; R, radius ; M, metacarpus ; F, fetlock ; A — o
is the position in which the leg makes contact with the ground ;
4, the position at which it leaves it ; B — O is the position in
which the limb leaves the ground, and 4 at which it meets it ; ? x
is the foot ; 1, 2, and 3, various phases during progression. Ob-
serve the sinking of the fetlock at A, 1 and 2, as the weight comes
on the limb. (Marey and Pages.)*

O 1

u

Q !

2 3 4

J-LA.

U_^_

FIG- 39.— Path Described by the Joints of the Hind-leg

DURING THE WALK.
P, pelvis ; F, femur ; T, tibia ; M, metatarsus ; f', fetlock ; x,~foot.
In other respects the description of Fig. 38 applies. (Marey and
Pages.)

* Goubaux and Barrier, ' L'Exterieur du Cheval.'

The Locomotor Apparatus. 337

foot is a large and gradually increasing one ; it then rapidly
descends as extension occurs.

Marey and Pages' foot-curve, which is the only one I
have worked out, agrees with rny results, which were
obtained by walking the horse past a vertical piece of
prepared canvas, and a blacklead pencil being attached
laterally to the foot the path was readily traced on the
canvas.

The curves described by the fore-limb from the time it
touches the ground until it leaves it are shown in Fig. 38, A.
The shoulder sinks, the joint coming nearer the ground
due to the forward movement of the body, which, from my
observation, is the cause of collar-galling when collars
are too wide, for the depression of one shoulder and the
elevation of the opposite one produces considerable side-to-
side movement, and consequently great friction. While the
body is passing over the leg the elbow slightly rises, due to
the ascent of the fetlock ; this also produces a well-marked
curve in the path of the knee, the fetlock-curve is naturally
the steepest ; we notice that there is first a sinking back-
wards in the fetlock curve before it rises ; this occurs at
the moment the weight of the body commences to pass
over the foot (Fig. 38, A, 1 and 2).

Following now the curves of the hind-limb from the time
it leaves the ground until it meets it again (Fig. 39, B), we
find the stifle-curve rises and then slightly falls as the leg
touches the ground ; the hock-curve is highest at the first
half of the movement, and then falls; the fetlock-curve
rises, being greatest at the middle of the movement, and
then falling; the foot-curve is greatest at the commence-
ment of the movement.

In examining the curves of the same limb from the time
it reaches until it leaves the ground (Fig. 39, A), there is a
well-marked up-and-down curve in both hip and stifle, that
of the stifle being particularly marked towards the end of
the movement, and due to the extension of the leg; the
hock-curve rises the whole way, whilst the fetlock- curve is
rather a flat one compared with the fore-leg.

99

338 A Manual of Veterinary Physiology.

The Trot is a very simple pace to analyse (Fig. 40), for
the body is supported on diagonal legs (1), which by their
propulsion drives it off the ground, so that there is a period
during which there are no legs on the ground (2). When
the body comes to the ground again the next pair of
diagonal legs receive it (3), and once more propel it off the
ground. There are thus three stages to the trot ; the body
in two of them is supported by diagonal legs, and in one of
them the body is in the air.

The trot appears to be the only pace in which instan-
taneous photography has supported the conventional
notions of this movement. We can see the trot, first,
because it is a simple pace, and secondly, because the body
is comparatively so long in the air. When a horse falls at
the trot, he does so through not bending his knee suffi-
ciently in bringing the leg forward, and the toe touches the
ground, or if the extension of the knee is not perfect he
also falls. When the knee has been well bent and the leg
brought forward, the limb is then sharply extended and the
foot placed down flat or heel first.

Marey and Pages' curves of the fore and hind limb
during the trot are seen in Figs. 41 and 42. Observe the
knee-curve as the limb is in the air. The hock-curve in
Fig. 42 is much flatter than one would have expected,
whilst the foot-curve is a big one.

In the Amble the horse, instead of using diagonal legs
uses the lateral limbs, so that off' fore and off' hind are on
the ground instead of off fore and near hind. A horse may
amble both at the walk and trot, in this respect resembling
a camel. There is no doubt that it is perfectly natural for
some horses to amble ; many others are taught the pace, as
it is a particularly pleasant one for the rider.

In the Canter (Fig. 43) the body is pushed upward off
the ground by one fore-leg — we will say the off' fore (1) —
the near fore leading, and both hind being off the ground ;
in the next stage all the legs are off the ground though the
feet are no great distance from it (2); in the third stage the
body returns to the ground, alighting on the near hind-leg,

Fig. 40.— The Trot.
From instantaneous 'photographs by 0 AnscMtz. {Ettenbt rger. )

22—2

XX x

Fig. 41.— Curves Described by the Fore-leg during the Trot.
The description of Fig. 38 applies. (Marey and Pages.)

xx x

Fig. 42.— Curves Described by the Hind-leg during the Trot.
The description of Fig. 39 applies. (Marey and Pages.)

Fig. 43.— The Canter.

From instantaneous photographs % 0. Anschiitz. [Ellenberger.

■6 6

Pig. 4 1. Tin: Gallop.
After Stanford, Muybridge, and JStiUman. (' T% Horn m Motion.')

The Locomotor Apparatus. 347

which is not placed under the centre of gravity, as in the
gallop, but behind it, the animal being balanced on one
limb only (3) ; in the fourth stage the off' hind and near
fore come to the ground together, so that the body is now
balanced on three legs, viz., near fore and both hind (4) ;
in the fifth stage the off fore comes to the ground, but as it
does so the near hind rises — the animal is still left on three
legs, viz., both fore and off hind (5) ; in the sixth stage the
near fore and near hind, and, slightly later, off hind, leave
the ground, the horse being balanced on the off fore only
(0) ; the next movement is a repetition of the first, the off
fore pressing the body upwards.

The Gallop is a very difficult pace to describe, and the
analysis I give of it here is from one of Mr. Muybridge's
numerous and beautiful instantaneous photographs (Fig. 44).
To this gentleman the scientific world is indebted for an
accurate knowledge of how animals use their legs in pro-
gression.

The Gallop consists of seven stages. We will elect to
describe it from the time the animal is in the air, no legs
being on the ground, but all four of them brought well
under the body; this is the first stage (1). In the second,
one hind-leg, say the off, comes to the ground (2) ; in the
third stage the near hind comes to the ground, the horse
now being balanced on two hind-legs, both fore being in
the air (3) ; in the fourth stage the off fore comes to the
ground, but the horse is not balanced on three legs as in
the canter, for at the moment the off fore came to the
ground the off hind was extended, leaving the animal on
diagonal legs, viz., off fore and near hind (4) ; in the fifth
stage the near hind leaves the ground, the animal being
balanced on one fore leg, in this case the off fore (5) ; in
the sixth stage the near fore comes to the ground (6a), and
the off fore leaves it (Job) — the body is, therefore, again
supported on one fore leg ; in the seventh stage the body
passes over the near fore leg (7), and by a contraction of
its muscles the entire weight is lifted off the ground, and
the body propelled forwards and upwards (1).

34S A Manual of Veterinary Physiology.

The points of importance to observe in the gallop are :
that the heel of the foot comes to the ground first, that the
hind-legs break the shock of the falling bod)T, and that the
fore-legs share in propelling the body as much as the hind.
The latter is a truth which was never anticipated until
Mr. Muybridge published the results of his labours.

In examining the track of a galloping horse it is remark-
able to observe what a very straight line the hoof-marks
leave, showing that each foot is brought well under the
centre of the bod}\

When a horse gallops, no matter how fast the pace, the
fore-feet never extend beyond a vertical dropped from the
muzzle.

In the Jump (Fig. 4-5) the horse rises to it by the pro-
pulsion upwards which the fore-legs give to the body (1) ;
both hind-legs now being fixed on the ground, he gives
the propulsion through these to his bod}-, the hocks at
the same time being greatly flexed to enable the feet to
clear the obstacle (2). In alighting on the other side he
does so through the medium of both fore-legs, one follow-
ing the other (-S) : instantaneous photography appears to
disprove the theory that in the jump a horse alights on
the hind-legs.

In Rearing the hind-legs are brought well under the body,
the head and neck thrown up, and the propelling power of
the fore-legs directs the bod}T upwards, where it is sustained
by the muscles of the back and loins. So long as the
centre of gravity falls within the base formed by the hind-
feet, the body is in a position of stable equilibrium ; but if
it passes outside this base, the horse comes down on to the
point of both hocks, and may either roll over on his side or
go directly backwards. If the latter, the first part of the
body to strike the ground is the occiput. In this way I
have met with many fractures of the base of the skull
through aontre cov. />, and also a fracture of the dentata from
direct violence.

In Kicking with both hind-legs the head is depressed,
and a powerful action of tin' muscles of the quarter and

Fig. 45.— The Jump.
From instantaneous photographs by O. Anschiitz. (EUeriberger.)

350 A Manual of Veterinary Physiology.

back throws the hind-part upwards, and at the same time
both legs are violently extended. A horse appears to have
little or no power of kicking if his head be kept up, or his
tail be fixed down.

In Buck-jumping the animal springs bodily off the ground,
the back is violently arched, and the head depressed
between the fore-legs.

In Lying- down the horse brings his four legs together
under his body, bends both knees and hocks, the knees
and chest touching the ground before the hind- quarters.
Whilst down he either lies extended on his side, or seated
on his chest, two lateral legs being under the body, and
two outside it; if on his near side, the near fore-foot is
close to the breast-bone, the elbow resting on the ground,
the hind-foot under the abdomen, the off fore-foot lying
close to the off elbow, but outside it as a rule, and the
point of the off hock is touching the ground. A horse
does not lie long in one position, owing probably to the
enormous weight of his body.

In Rising he can only get up by extending both fore-feet
in front of him. The hind-quarters are now pressed up-
wards, assisted by the muscles of the back, and the animal
is immediately on his feet, the fore-part always rising before
the hind.

The cow rises quite differently — in fact, the reverse of the
horse, the hind-quarters being the first to ascend. The
camel rises in the same manner.

The Normal Daily Work of Horses, the rate at which
they are capable of performing it, and the power the)"
exercise in doing so must now be briefly considered.

Rankine has laid down that the mechanical daily work
is the product of three quantities: (1) the effort : (2) the
rate; (3) the number of units of time per day during
which the work is continued. Our only difficulty here is
obtaining the value of the effort, which it is clear must
depend upon the nature of the work, the character of the
ground, the weight carried or drawn, and the physical fit-
ness of the animal. I have dealt with this question

The Locomotor Apparatus. 351

elsewhere,* as fully as is possible in our present state of
knowledge. The whole subject requires to be gone into
carefully, both mathematically and by direct experiment.
In the work alluded to will be found formulae for calculat-
ing the foot-tons of work performed both in saddle and
draught, though the results can only be regarded as
approximately true.

The normal work of horses would appear to be 3,000
foot-tons per diem ; a hard day's work is equivalent to
4,000 foot-tons, and a severe day's work is 5,000 foot-tons.
Redtenbacher places the daily work of a horse for 8 hours
at 6,700 foot-tons, and Rankine's tables showf that a
draught horse exercising a force of traction of 120 lbs. for
8 hours a day, performs G,20U foot- tons of work. I think
both these estimates are without doubt too high. The
co-efficients of resistance I have employed in my calcu-
lations, were those determined for man by the Rev. Professor
Haughton. I know of none especially calculated for the
quadruped. Assuming the weight of the animal, plus the
weight carried or drawn, to be equal to 1,000 lbs., then
3,000 foot-tons of work will be obtained by the following :

Walking at 3 miles per hour for rt-7 hours.

„ 4 „ „ 5-3 „

» 5 „ „ 3-7 „

Trotting „ 8 „ „ 1'5 „

Cantering „ 11 ,, ,, 1 „

This table is only given as a means of conveying to the
mind the value of 3,000 foot-tons of work.

The Velocity of the gallop has been variously stated, but
it is certain that no horse has galloped 1 mile in 1 minute
as is reported of Flying Guilders. Firetail's mile in
1 minute 40 seconds in 1772, was beaten in 1890 in the
United States by Salvator's mile in 1 minute 35£ seconds.
This horse was galloped on a straight course against time,
the weight carried being 7 stone 12 lbs., the age of the animal
four years. The best time in a race has been quoted at

* ' Veterinary Hygiene.'

f 'Encyclopaedia Britannica,' art. 'Animal Mechanics.'

.4 Mi

rcmual of Veterinary Physiology.

1 minute 39£ seconds for 1 mile. The most severe
galloping ever recorded was at Carlisle in 1761, where,
owing to six heats being run, the winner galloped 24 miles.
Quibbler, in 1786, galloped 23 miles round the flat at New-
market in 57 minutes 10 seconds.

The fastest pace at which trotting has been performed is
1 mile in 2 minutes 8] seconds. The horse was Sunol, the
match taking place in the United States in October, L891.
The celebrated American trotting-horse Tom Thumb
trotted 100 miles in 10 hours 7 minutes, including a stoppage
of 37 minutes , an English mare did the same distance in
10 hours 14 minutes, including a stoppage of 13 minutes.
Sir E. Astley's Phenomenon trotted 17 miles in 53 minutes.

The walking performances are not. numerous. Twenty-
two miles in 3 hours 52 minutes was done by Sloven in 1793.

All the old performances here quoted are from Youatt's
work on ' The Horse.'

Turning now to what may be expected of ordinary
horses, we find that the average walk of a cavalry horse is
375 miles per hour ; the average trot is 7"5 miles per hour,
or a mile in 8 minutes ; and a fast trot is 8| miles per hour.
A cavalry gallop is at the rate of 12 miles per hour.*

The stride of horses at various paces was measured in a
very ingenious manner by StiUman and Muybridge.f They
give the stride at the walk as 5 feet 6 inches ; at the trot
between 7 feet and 8 feet ; at the canter about 10 J, feet ;
and the gallop varying between 16 feet and 20! feet, and
they even speak of a stride of 25 feet.

The question of the Weight which a horse can carry is one
affecting the vital interests of the cavalry service : there is
a great difference between the weight a horse can carry and
the effective weight he can carry. It has been stated by
Desaguliers": that a horse at Stourbridge carried 1,232 Lbs,
of iron for a distance of s miles ! This either exceeded or
must have equalled his own body-weight, and the case i^
probably without parallel.

* ' The Soldier's Pocket-Book,' Viscount Wolseley.
t Op. cit. : ■ Bxpt. Philos.,' vol. i.

The Locomotor Apparatus. 353

The entire question of the weight a horse can carry
must depend upon the pace at which he has got to carry it,
but under any circumstances is largely influenced by the
weight of the animal's own body. We are not far from the
truth in saying that the mean weight of a riding horse is
1,000 lbs., and the question is what proportion should the
weight he carries bear to his own body- weight. On this
point I have made some careful observations, through its
important bearing on the cavalry service, and have shown
that cavalry horses should not be asked to carry more than
one-fifth of their body-weight, and this conclusion will
doubtless apply to all saddle horses. The one-fifth of the
body-weight of a cavalry horse is roughly 14| stones.
Instead of carrying this, they carry at least 20 stone. I
found in a cavalry regiment that the effective carrying
capacity of the horses was between the one-fifth and one-
sixth of their body- weight, and that if the horse's weight
be divided by 5 6 7 we got a figure which represented the
weight it should carry. These results were arrived at
by weighing a large number of horses, the weight each
being 'up to' having been previously estimated by an
expert.

The physiological features of Draught can only be glanced
at. The subject of draught is a very big one, and our
information is still very incomplete.

Quadrupeds appear to be designed for the purpose of
draught. A horizontal spine is not intended for carrying
weight. This can only be satisfactorily met by an upright
column, as in man, who, from his conformation, is essentially
devised for carrying a burden ; the horse, on the other hand, is
constructed for hauling or draught. Youatt, in his article on
' Draught,'* points out that the reason why a horse is more
suited for draught than for carrying weight, is that he can
throw his weight considerably in front of his centre of
gravity, the feet forming the fulcrum, and 'allowing the
weight of the body in its tendency to descend to act
against the resistance applied horizontally, and drag it

* ' Book of the Horse.'

23

354 A Manual of Veterinary Physiology.

forward. As the resistance yields, the feet are carried for-
ward, and the action continued.'

Such is the theory of draught. The nature of the
vehicle, the condition of the roads, the angle the trace
forms with the horizontal, the presence or absence of
springs, four wheels or two, high or low front wheels, and
the width of the track, so complicate the question as to
take it at once into the domain of pure mechanics, into
which we cannot follow it.

In the light or mail stage-coach, where 10 and 11 miles
an hour were attained, the strain or force of traction em-
ployed by each horse was only 40 lbs. ; in the heavy coach
it was 621 lbs. for each horse.

For slow draught work at 2£ to 3 miles per hour, and for
8 hours a day (which appears to be the most suitable pace
and duration of labour), a force of traction of from 100 lbs.
to 125 lbs., or 150 lbs., is quoted by Youatt as being the
most suitable. I have previously stated (p. 351) that I
consider it probable that a force of traction of 120 lbs. for
8 hours a day is too much to expect from a horse. The
higher the velocity the less the force of traction which
can be employed, and the shorter the duration of labour.

It has been stated (Landois) that a horse can only drag
three times his own weight, and taking as a matter of con-
venience his weight at 1,000 lbs., it is probable that
3,000 lbs. is the limit of his strength if tested against a
dynamometer. Yet this amount is far above what it is usual
to regard as the power of a horse. I have been credibly
informed that a big railway horse could only exercise
1,<S40 lbs. when tested against the dynamometer. The limit
of a horse's power is therefore a very doubtful point.

Watt found that a horse could raise a weight of 150 Lbs.
passed over a pulley, 220 feet per minute ; this, as applied
to engines, is termed 'horse power,' and is equal to
33,000 lbs. lifted 1 foot high per minute, viz., 33,000 foot-
pounds per minute. This standard of comparison cannot
be applied to animal labour, as it is much too high. A
horse could only perform this amount for :\\ hours per
diem, whereas his most useful work is performed in S hours.

CHAPTER XVIII.

THE FOOT.

Veterinary literature has been remarkably barren on every
other subject than the foot and shoeing. It was natural,
perhaps, that this subject should excite considerable interest,
considering its vast importance.

The first thing which strikes one in the foot is its re-
markably small size in proportion to the size of the body.
Comparing the horse's foot, so far as size is concerned, with
our own, the advantage in the majority of cases lies on the
side of the biped. The most interesting fact which physi-
ology has to demonstrate is that, though the foot presents
a small circumference, in reality it encloses a vast area, due
to the anatomical arrangement of the parts.

The amount of moisture contained in the horn of the foot
is something considerable, and the rate at which it evapo-
rates is quite extraordinary. If portions of the frog be
enclosed in a bottle, in a short time the interior will become
bedewed with moisture. The use of this moisture is to
keep the foot elastic and prevent it from becoming brittle,
and the agencies which are at work to assist this are a
coating over the wall of a thin varnish-like layer of horn,
which can only be seen in the unmutilated foot, and in the
case of the sole by the layers of exfoliated material which
accumulate as the result of the shedding of the superficial
layers.

We are bound to recognise that horn containing but little
moisture is in an abnormal condition ; it is rigid and brittle,
nails driven into the part cause it to crack, and that

23 2

356 -1 Manual of Veterinary Physiology.

elasticity on which so largely depends the natural shape
and usefulness of the foot becomes impaired, or even
destroyed. A museum specimen of a foot will very clearly
illustrate our meaning. In its dried condition it is so
brittle that, if dropped, it will occasionally fracture like a
piece of glass ; place the foot in water for a few days, and
it comes out as fresh and elastic as though it had just been
removed instead of being probably 20 years old. All the
horn has done is to imbibe water, which has entered the
minute canals by capillary attraction, and the brittle
substance now becomes yielding and elastic.

We can see how necessary elasticity is in the foot,
when we consider the concussion to which it is exposed
during work, and which would inevitably lead to its de-
struction by fracture or otherwise unless this provision
were present. Clinically we are perfectly acquainted with
the fractures which do occur in the wall of the hoof from
violence.

One of our main objects in shoeing should be to protect
the wall from unnecessary interference ; the removal of the
varnish layer of the wall, and the cutting across of some
thousands of horn-fibres by the unnecessary use of the rasp,
lead to considerable destruction. Even, however, in the
most brittle foot that portion of horn nearest to the vascular
structures still maintains its elasticity.

Here is an analysis of the horn of the foot :

Wall.

Sole.

Fro;/.

Water

- 24-735

::7-065

42-54

Organic matter

- 74-74(1

62-600

57 "27

Salts

•f>25

•335

•19

100-oon 100-OQO 10000

The frog contains the largest amount of moisture, and the
wall the least.

The salts are small, and consist of sodium, magnesium,
iron, and silica.

The foot may be regarded as a duplicate structure, one
being a complete counterpart of, and fitting into the other.

The Foot. 857

The internal one we speak of as ' the sensitive foot/ the
external cover as ' the horny foot.'

The physiological interest in the sensitive foot lies in the
arrangement of its bloodvessels, the provision which exists
for saving the parts from destruction by concussion, the
means by which the weight ofHhe body is supported, and
the remarkable manner in which the area of the foot is
increased without adding to its surface.

Vascular Mechanism. — Taking the bloodvessel arrange-
ment, we recognise that the enormous amount of blood
sent to the foot is for the purpose of growing the needful
quantity of horn. There is hardly an}^ other part of the
body so vascular; even the bone of the foot is a rarified
structure, like so much pumice-stone, to afford passage and
protection to the vessels.

Lying as the foot does furthest from the heart, added
to which is its position at the lowermost part of the body,
we are led to inquire why it is that the blood is able to
circulate through it so thoroughly, and if other means are
at hand for assisting the force of the heart in facilitating
the circulation : such means, we know, do exist. The
arterial blood pressure in the foot is high, for we have
gravity assisting the action of the heart and powerful
elastic walls to the vessels. But though the contraction of
the left ventricle is sufficient to bring the blood back to the
right side of the heart from any part of the body (as we
have pointed out in dealing with the circulation), it is
doubtful whether this would be wholly sufficient to empty
the foot of blood and keep the considerable plexus of veins
full.

The venous circulation is assisted by two movements in
the foot, viz., the expansion and contraction of its posterior
half, and the descent and elevation of the inner foot under
the pressure of the body.

There is no point in the physiology of the foot which
has given rise to greater controversy than its elasticity ; but
we submit that it is not only anatomically provided for, but
amply proved within recent years. Its provision exists in

358 ^4 Manual of Veterinary Physiology.

the elastic nature of the horn, the existence of large elastic
cartilages at the posterior and lateral part of the foot, and the
fact that though the internal foot is a solid mass anteriorly,
yet it is soft and yielding posteriorly.

The amount of movement occurring in the foot under the
influence of the body- weight increases no doubt with the
velocity at which a horse may be travelling ; it is very small
at the walk, and still less when he is made to throw all his
weight on to one foot by lifting up its fellow. But even with
this simple test special and delicate instruments are capable
of registering the movement, and, moreover, of measuring it.
I cannot here enter into a description of the apparatus em-
ployed ; that used by Lungwitz is fully described,* also
that employed by myself, f

There is no difficulty in seeing the movement imparted
to a column of rluid circulating in these parts ; for if we
divide a plantar vein, and make the horse walk, eveiy time
the foot comes to the ground expansion occurs, and the jet
of blood is considerably increased, and when the foot is
taken off the ground the jet of blood becomes reduced.

We must accept it, therefore, as a proved fact that the
venous circulation is largely facilitated by the expansion
and contraction of the posterior part of the foot — during
expansion the blood being driven upwards, and during con-
traction the veins relaxing aspirate the blood into their
interior.

So perfect are these changes that there are no valves in
the veins of the foot, and none are found until near the
middle of the pastern. To assist the circulation, the large
venous trunks at the postero-lateral part of the foot are in
close connection with the lateral cartilages, and some pass
through its substance.

Sensitive Laminae. — We have now to consider the means
by which the weight of the body is supported within the
foot. It is universally recognised that this is carried out
by the union of the horny with the sensitive lamina'. That

* The Journal of Comparative Pathology and Therapeutics, vol. iv. 3.
f The Veterinary Record, January, L892.

Fig. 46.— Diagrams to illustrate the direction taken by the
Laminae at different parts of the Foot, as seen in Vertical
Section.

In the top figure the section is made through the toe of the foot :
a, being part of the pedal bone ; b, the horny wall ; c, the laminae,
which are practically straight, the weight being imposed from
top to bottom in their length. The middle figure is a vertical
section just behind the point of the frog : the lamina?, c, give the
appearance of being placed above one another ; they are rather
more obliquely placed than is shown in the drawing. The lower
figure is a vertical section through the posterior part of the foot :
a, being the lateral cartilage, and c, the laminae, which should
slope rather more than is shown in the figure : it will be observed
that the lamina?, as in the previous figure, are placed one above
the other — this arrangement gives strength.

360 A Manual of Veterinary Physiology.

the enormous weight of the horse's body should be carried
upon — or, rather, slung upon — these delicate strips of sensi-
tive material on the one hand, and correspondingly delicate
strips of horn on the other, is perhaps the most remarkable
feature in the physiology of the foot. We know how firm
the union is, we know the extreme difficulty of separating
these two parts even by mechanical means in a state of
health, and we readily recognise the delicate structure of
the parts yielding this firm yet flexible union.

The horse's weight is supported in the foot by the dove-
tailing of 500 or more sensitive lamina? with 500 or more
horny lamina.', the union being made the more complete by
each primary sensitive and horny lamina containing 100 or
more secondary lamina?. These lamina^ afford an immense
surface of support, which is longest at the toe, shorter at
the quarter, and still shorter at the heel ; but though the
slinging surface is so much shorter at the quarters and heels,
yet its strength is increased by the direction in which the
weight of the body comes upon it. Instead of bearing the
weight on the length of the lamina?, as at the toe, it bears it
on the width in such a manner that where we have, say, one
lamina at the toe, there are twenty at the quarter. It is
not possible to clearly describe this, but Fig. 46 will ex-
plain.

These lamina? are attached at the anterior and part of
the lateral face of the foot to bone, but for the remaining
lateral face and posterior part of the foot they are attached
to stout cartilage ;* if a line be drawn through the foot
separating the osseous attachment of the lamina? from the
cartilaginous attachment (see Fig. 49), it will be found that
roughly speaking one-half is cartilaginous and one-half
osseous ; the cartilaginous portion is situated just where
elasticity is required, viz., the posterior face of the wall ; one
function of the lateral cartilages of the foot is to afford an
elastic wall attachment to the sensitive lamina1.

A horse's sole carries but little of his weight, only the

* Some of the laminae axe attached to the tendon of the extensor
pedis, and the lateral ligaments of the foot joint.

The, Foot. 361

margin which is immediately in contact with the wall
assisting. When we remember that the sole is concave, it
will be clear that it has some other function than that of
weight-bearing to perform : its function is to protect the
sensitive sole and pedal bone.

The folding up of the horny and sensitive leaves in the
foot, in the manner above described, has another function
besides that of merely supporting the weight and rendering
the union firm.

It is clear that by folding up this amount of material
the surface of the foot is considerably increased. In
other words, by this arrangement the foot has been kept
within small proportions, without affecting its stability.
A book, say of 500 pages, may, by placing one leaf on the
other, be made to occupy a bulk represented by a few
inches; but if each page be laid out separately on the
ground, and made to touch one another, the surface covered
will be considerable. This is exactly what occurs in the
foot. The horny and sensitive leaves by their singular
arrangement increase the surface of the foot, and yet keep
it within reasonable bounds. Bracy Clarke, who first had
a calculation made as to the increased surface afforded by
this arrangement, came to the conclusion that it was equal
to H square feet ; but Moeller* has estimated that it is
equivalent to 8 square feet ; whilst Gader's estimatef is
lOf square feet. For safety we will adopt Moeller's
number.

The bearing surface afforded by each foot is equivalent to
8 square feet, affording a total area for the pedestals of
32 square feet.

The physiological function of the leaves of the foot is
demonstrated by pathological observation. Inflammation
of the leaves occurs either through over-work, or through
an animal standing too long in one position ; in either case
they get strained, and resent it. We all know the practical
value of exercising horses which from any reason have to

* Veterinary Journal, vol. v.

+ Quoted by Goubaux and Barriere.

362 A Manual of Veterinary Physiology.

stand up for any length of time, the exercise overcoming
the tendency of the laminae to congestion from continual
strain ; and the feet not only become cool, but the animal
may continue standing for a considerable time if daily
exercised. The value of exercise in the treatment of
laminitis, first taught us by Mr. Broad, of Bath, is based on
the most satisfactory physiological basis.

If any doubt exists as to the function of the laminse in
supporting the weight of the horse's body, we have only to
look at the processes which occur in them as the result of
disease. Laminitis is often attended by separation of the
horny and sensitive lamina}, when the horse's weight being
no longer properly supported, the pedal bone under the
influence of the animal's weight is actually forced through
the sole of the foot.

Anti- concussion Mechanism. — The arrangements which
exist to save the foot from concussion are numerous. We
have, in the first instance, the highly elastic and india-
rubber-like horny frog, the fibro-fatty or plantar cushion,
the elastic cartilages of the foot, the elastic posterior wall,
and, moreover, the descent of the sensitive foot within its
glove, the horny foot.

The descent of the sensitive foot has been as strongly
denied as the expansion of the posterior wall, but there is no
difficulty in demonstrating it,* and we can see the value of
this function. The foot comes to the ground either flat or the
frog first ; I believe that in the slower paces it comes to the
ground nearly flat, but in the faster paces there is no doubt
whatever but what the frog comes first to the ground, viz.,
the posterior part of the foot first, the anterior part last.
The frog, from its peculiar physical condition, is not only
adapted to prevent the horse from slipping, to give him a
grip on the ground, but also to save the foot and leg from
concussion ; that is the reason why it comes first to the
ground. Concussion to the anterior part of the foot is
prevented by a slight up-and-down play between the
lamina- and the pedal bone, through the medium of the
* See the articles alluded to on [>. 358.

The Foot. 363

extensive layer of elastic tissue found at this part ; as the
weight comes on the foot, the pedal bone slightly descends,
to rise again when the weight is taken off it. As the pedal
bone descends, the sole on which it is resting also slightly
descends and comes nearer to the ground, which is the
reason why the sole is concave instead of flat. The descent
avoids concussion, in the same way that it is easier to
catch a cricket-ball with a retreating movement of the
hand than by rigid opposition.

Much more might be said of practical importance on this
subject, but we have other points which press for our
consideration.

The Frog. — The function of the horny frog and its
peculiar physical features we have already alluded to. The
manner in which it protects the important navicular bursa
is also no insignificant part of its function. The soft and
elastic condition of the horn of the frog has been attributed
to certain perspiratory glands which are found in that part
of the sensitive frog on either side of the frog stay ; how
far these actually contribute to the elastic condition of the
frog is not clear, especially as the surface over which they
are distributed is of very limited area.

The frog is peculiar, inasmuch as it needs for its perfectly
healthy condition contact with the ground. It is strange
that in this respect two structures situated side by side,
viz., the sole and frog, should be so opposed in function.
We know practically, that if the frog be kept off the
ground, the part atrophies, the heels contract, viz., the foot
is rendered smaller, and the frog becomes diseased. This
wasted condition of the frog may be restored by pressure,
but that pressure must be ground pressure. It is possible
by means of a bar- shoe to throw considerable pressure on
the frog and heels, but the foot still contracts ; it is only
when the frog is touching the ground that it continues in a
healthy condition, and retains its normal size. Frog
pressure is therefore one of the golden rules in shoeing if
the frog is to exercise its natural functions.

The Wall. — From what we have previously said, it can

3(34 A Manual of Veterinary Physiology.

be seen that it is on the wall of the foot where the horse's
weight is supported. On examining the horny wall, we
find that it is thickest at the toe, thinner at the quarter,
and thinnest at the heels. It is thickest at the toe owing
to the wear and tear of the foot at this part. As the frog
is the first to come to the ground, so is the toe of the wall
the last to leave it ; and when, as we have seen in studying
locomotion, the propulsion is given to the body by the toe
of the foot, we can understand how necessary it is to thicken
the part here. The toe of the wall appears to grow faster
than either the quarter or the heels, but this is more
imaginary than real. It is the tendency of the foot to grow
forward as well as downward which produces the illusion.
That the foot does grow forward may readily be determined
by experiment, for if we cut or saw a groove in the wall at
the coronet, say an inch or so from the heels, that groove
will in course of time be carried some considerable distance
forward. The exact amount can be determined b}T observ-
ing the obliquity of the horn fibres. The object of the wall
becoming thin towards the posterior part of the foot is to
allow of the elastic movement which we have described as
expansion and contraction.

Two physical conditions have to be provided for in the
wall, viz., elasticity of the posterior part, and toughness of
the anterior portion. Some of the methods by which the
needful provision is made we have spoken of, but here is a
general summary of the subject :

The posterior portion of the foot first receives the weight
of the body (certainly in all fast paces) : the expansion of
this part saves it from destruction, and the various pro-
visions which exist are considerably assisted by the fact
that the wall is thinner at the heels than elsewhere, and so
yields outwards ; but besides being thinner the wall of the
heel contains more moisture than the wall of the tot.', and
this moisture ensures its elasticity. The younger the horn,
viz., the nearer to the coronet at which the horn is taken,
the more moisture it contains, the further away from the
coronet the less moisture it contains, and the tougher and
more resisting the horn.

The Foot. 060

Let us observe how perfectly horn of various degrees of
moisure, viz., of varying degrees of toughness and elasticity,
is provided for in the foot.

1. The anterior part of the wall is longer than the
posterior, therefore the anterior is tougher than the pos-
terior, for the reason that the horn is much older at the
extremity of the toe than at the heel, and it is further
away from the coronet, and therefore contains less moisture.

2. The wall at the heel is some months younger than at
the toe ; it is thinner, and contains more moisture, there-
fore it is more elastic, but not so tough.

^' b''c' dJ e' /
Fig. 47.— Diagram illustrating the Age of the Wall.

a, b, c, d, e,f, are circles drawn around the hoof parallel to the coronet :
in this way we ascertain that the age of the wall at a is the same
as the heel at a', the age of the wall at d corresponds with the age
of the quarter at d'. Every portion of the ground surface of the
wall is of a different age, being oldest and hardest at f, and
youngest and most elastic at a'.

The age of the wall is, therefore, an important factor in
the wear of the foot. The horn of the quarter is older
than the horn of the heel, and the horn of the toe older
than that of the quarter. This excellent provision for
wear admits of that considerable friction between the
ground and the toe which occurs during progression, and
allows of the expansion of the younger and moister horn of
the posterior part. I am not aware that this explanation
of the different ages of the wall has ever before had atten-
tion directed to it.

The expansion of the wall is aided by the lateral car-
tilages, which carry outwards the sensitive lamina?, and so

366 A Manual of Veterinary Physiology.

keep them in connection with the horny ones, without
which provision a drag on the dovetail arrangement would
occur. The fact of the lateral cartilages affording attach-
ment to about half of the sensitive laminae has been pre-
viously mentioned. As the posterior wall contracts the
lateral cartilages are carried inwards.

At the heels the wall is turned in to form the bars, which
run some distance under the foot towards the apex of the
frog. The bars are part of the wall, and their function is
the same, viz., to support weight, for which purpose they
have the usual dove-tailed sensitive and insensitive lamina).

The elastic movement of the foot must now occupy our
attention. The mechanism which brings this about has
already been touched on ; it only remains for us to briefly
describe the changes in shape which the foot undergoes as
the result of the body- weight.

When the weight comes on to the foot, it is received by
the posterior part of the foot, viz., the posterior wall, bars,
frog, and through this the plantar cushion. The elastic
posterior wall is pressed outwards by the compressed india-
rubber-like frog, and it expands from the coronet to the
ground surface for about 7>L- of an inch; sometimes the
expansion at the coronet is not so marked as it is at the
ground surface, but in the majority of feet it exists. At
the moment of expansion the bulbs of the heel of the foot
at the coronary edge sink under the body weight, and come
nearer the ground ; and as a result of this, the anterior
coronary edge, that corresponding with the toe of the wall,
retracts, and the pedal bone slightly descends through its
elastic connection with the sensitive lamina1, and presses
the sole down with it. Under these conditions the blood
pressure in the veins of the foot rises, and the vessels are
emptied. When the weight is removed from the foot the
bloodvessels till, the frog retracts, the posterior walls con-
tract and become narrower from side to side, and the bulbs
of the heel rise; at the same time the anterior edge of the
coronet goes forward, and the pedal bone and sole ascend.

Lungwitz lays stress upon the tense condition of the

The Foot.

367

coronary edge of the foot at the moment of the greatest
weight, and describes it as an elastic ring. Dr. Macdonald,*
in this country, who has devoted attention to the vascular
mechanism of the horse's foot, considers that the swelling
up of the coronary cushion can only be regarded in the

Fig. 48.— Diagrams illustrating the Expansion of the Foot.

In the top figure the solid outline indicates the position of the foot at
rest : the dotted outline shows the retreat of the coronet, and
descent of the heels under the influence of the body weight ; the
shaded portion of the wall indicates the area of expansion. The
two lower figures are after Lungwitz : the left-hand one supposes
the observer to be looking down on to the foot ; the dotted outline
indicates the retreat of the coronet and descent of the heels ; the
dotted outline of the right-hand figure indicates the expansion of
the wall.

light of a powerful hydraulic ligament, which supports the
joint under the immense strain to which it is exposed.
The value or existence cf this hydraulic support has yet
to be demonstrated.

Lateral Cartilages. — We have dealt with certain functions
* Veterinary Record, No. 145, 1892.

368

A Manual of Veterinary Physiology.

of the lateral cartilages, but it will not be amiss to here
summarise our knowledge of their use.

1. They form an elastic wall to the sensitive foot, and
afford attachment to the sensitive laminre.

2. As the foot increases in size the cartilages carry out-

Fig. 49. — Portion of the Wall Removed, to show the position
of the Rigid and Elastic Sensitive Foot.

a, wall of the foot ; b, the lateral cartilage ; G, a line which represeuts
the coronet ; c, the pedal bone — the line of union between the
pedal bone and lateral cartilage is well seen ; P, is a portion of the
os corona; D, a portion of the sole exposed by the removal of the
wall ; E, the heel of the wall left at its plantar surface to show the
arrangement of the bar, n, which passes behind and within the
lateral cartilage B. The figure, which is accurately drawn from a
photograph, is intended to show what an extensive surface the
lateral cartilage presents, and the variety of surfaces to which the
sensitive laminie are attached; they cover B, C, and f, the latter in
the living animal being the position of the extensor pedis tendon
and lateral ligament of the foot, to which the lamina) are attached.
Further, the figure shows the division of the internal foot into an
elastic and a rigid portion.

wards the sensitive laminae which are attached to them,
and so prevent any disturbance of the union of the horny
and sensitive lamina;.

3. Large venous trunks pass through, and close to, the
cartilages of the foot, and the movements of the cartilages
assist the venous circulation. The function of the lateral

The Foot. 369

cartilages has light thrown on it by diseased processes.
When this elastic cartilage becomes converted into bone,
its functions are destroyed, and lameness occurs. I have
shown that by a simple operation relief from this lameness
may, in a large proportion of cases, be secured, and demon-
strated that by surgical interference it is possible to make
the horny foot larger, and thereby render it capable of
accommodating, without inconvenience to the animal,
lateral cartilages which have undergone the process of ossi-
fication, and thus increased in size. This operation is
based on physiological principles.

4. The object of having elastic cartilages at this part of
the foot is to allow of expansion.

Navicular Bursa. — The pedal bone presents a remarkably
small articulatory surface, much smaller than the surface
of the bone which rests on it. In order to increase this
articular surface a sesamoid bone is introduced, known as
the Navicular ; by this means the corona rests on an articu-
lation which anteriorly is rigid, but posteriorly is flexible.
Under this yielding sesamoid bone passes the perforans
tendon, and the weight on the bone is supported almost
solely by this tendon. I have shown* that the compression
to which the navicular bone is thus exposed by the weight
of the body from above, and the pressure of the perforans
from below, is the chief factor in the production of that
serious and common lameness, navicular disease. I do not
consider, as is generally believed, that the navicular bone
acts the part of a pulley.

When the foot comes to the ground the weight of the
body comes first on to the flexible articulation in the pedal
joint, viz., the navicular bone and its supporting tendon,
the perforans ; the corona is then rotated in such a manner
that the wTeight of the body is transferred to the pedal bone,
and through this to the laroime.

Wherever we look in the foot we find the same provi-
sion maintained for an elastic posterior and rigid anterior
foot.

* Veterinary Journal. 1886, 'The Pathology of Navicular Disease.'

24

.370 A Manual of Veterinary Physiology.

Such are the physiological features of the foot which
facilitate circulation and. destroy concussion. Foot-lame-
ness is only too frequent, but if it were not for the
mechanism we have described, it would not be possible
for us to work horses for a single day. It is no argument
against expansion that it requires delicate apparatus to
detect it, owing to its minuteness ; small as it is in the
slower paces, it yet suffices to convert what would be a
rigid, unyielding block into an elastic and yielding one ; and
at the gallop the expansion must be considerable, probably
more than double what it is under ordinary conditions.

Physiological Shoeing. — It is impossible to conclude this
chapter on the foot without some mention of what we
might term physiological shoeing.

We all recognise the evil of shoeing as strongly as we
recognise its necessity. By bearing in mind the functions
of the various parts of the foot, we can certainly reduce the
evil of shoeing to comparatively narrow limits, and in a few
words we will state what constitutes physiological shoeing :

1. The reduction of the wall to its proper proportions,
such as would have occurred through friction had no shoe
been worn.

2. Fitting the shoe accurately to the outline of the foot,
not altering the latter to lit the shoe. Rasping away the
crust to fit the shoe not only renders the horn brittle, but
is so much loss of bearing surface.

3. Leaving the wall intact, so far as its varnish -like
layer is concerned. The practice of rasping the wall for
appearance' sake destroys the horn tubes, and allows of so
much evaporation from the surface of the foot that the
wall becomes brittle.

4. The sole not to be touched by the knife ; it cannot be
too thick ; it is there for the purpose of protection.

.*>. The bars not to be cut away ; they are part of the
wall, and intended to carry weight. The shoe should rest
<>n them.

(i. The frog to be uncut and left to attain its full growth,
which can only occur through resting on the ground. No

The Foot. :*71

frog can perform its function unless on a level with the
ground surface of the shoe.

7. The pattern of shoe is immaterial so long as it has a
true and level bearing, and rests well and firmly on the wall
and bars. I believe the simpler the shoe the better, viz., one
plain on both ground and foot surface, to be secured with
no more nails than necessary, as the nails destroy the horn,
and these are not to be driven higher than needful, for high
nailing is ruinous to feet.

Such, briefly, are the conditions which fulfil physiological
shoeing.

24

CHAPTER XIX.

THE VOICE.

The voice of each class of animal — horse, ass, ox, sheep, etc.
— is so distinctive that we may recognise their presence
without seeing them ; yet, though the larynx in all these
animals differs more or less, the difference is not sufficiently
great to offer an explanation of why the sounds it emits are
so entirely distinct.

The voice of male and female animals differs in intensity.
The wild neigh of the stallion is very different from the
neigh of the mare, and the bellowing of the bull is distinc-
tive from that of the cow.

The operation of castration has a remarkable effect on
the voice, the neigh of the gelding resembling that of the
mare.

In the horse the voice is used during sexual excitement,
also during fear or especially loneliness, during pain, anger,
and as a mark of pleasure. It is not possible to convey in
words the difference in the notes produced, but they are
easy to recognise.

The horse is essentially a sociable animal. When he is
used to being in the company of others he hates separation,
and he shows it by persistent neighing. This is perhaps
more noticeable amongst army horses than any others.

The neigh of pleasure is often spoken of as the ' whinny."
The word rather conveys an idea of the sound made.

Sounds which can only be described as screams are often
evoked during ' horse-play ' and temper, or by mares during
cpstrum. It is not a scream as we know it in the human

The Voice. 373

subject, but no other word conveys an idea of its shrill-
ness.

If a horse cries from pain (which is very rare) as during
a surgical operation, the cry is a muffled one and short ; it
is a groan rather than a cry.

The larynx is divided into a respiratory portion and
a vocal portion; the latter comprises the region of the
vocal cords and their attachment, the former the glottal
opening formed by the arytenoid cartilages.

Production of Sound. — If air be forced between the vocal
cords so as to cause them to vibrate, sound is produced.
The various modifications of that sound are produced in
the air-passage anterior to the larynx, such as the posterior
nares, the nostrils, and in the horse the false nostril and
perhaps the guttural pouch. How far the latter assists in
producing the voice is not clear ; but it has been considered
that it plays some part in the process, though Colin men-
tions that, when he opened the guttural pouches, the horse's
neigh had lost but little, if any, of its ordinary character.
I have previously expressed myself that this remarkable
pouch is perhaps more intimately connected with the sense
of hearing. In the false nostril sounds are certainly pro-
duced of an expiratory character, such as the peculiar snort
of a frightened or ' fresh ' horse. The sacs during these
sounds are considerably dilated.

During ordinary respiration, the vocal cords are apart,
but when voice is produced, the edges of the cords are
approximated and made parallel, so that the rush of air
passing between them causes them to vibrate, the tone
produced depending on the tension of the cords. If air be
forced through a dead larynx, and the tension of the cords
increased and decreased, a sound remarkably like a neigh
may be produced.

The ventricles of the larynx, cavities of the mouth, nose,
and pharynx, act as resonators, being tilled with air. The
ventricles of the larynx also allow of the free vibration of
the vocal cords ; they are very large in the horse and
howling monkeys.

•S74 A Manual of Veterinary Physiology.

The cartilaginous box, the larynx, undergoes at its
glottal opening certain changes in shape during inspiration
and expiration. During ordinary inspiration it slightly
opens, and the vocal cords, which were towards the centre
of the tube, retire towards the side. During expiration the
glottal opening becomes smaller and the cords approxi-
mate.

Movements of the Larynx. — These movements are carried
out by certain muscles in connection with the cartilages of
the larynx and vocal cords, and the muscles may be divided
into those which dilate the cavit}- and those which close it.
The sole dilator is the crico-arytenoideus posticus, a muscle
of considerable power, and strengthened by tendinous fibres
in its substance. Its function is to lift the arytenoid carti-
lage upwards and outwards, more especially during forced
respiration, when the glottis is dilated to its utmost. It is
the muscle of the larynx, and paralysis of it causes laryngeal
' roaring,' owing to the immobile arytenoid cartilage being
drawn into the glottis, instead of being lifted up out of the
way of the incoming air. The paralysed vocal cord takes
no part in the production of the sound, which, it is to be
noticed, is almost invariably an inspiratory one.

The larynx having been dilated, it is then closed partly
by its elastic recoil, but also through the medium of the
muscles antagonistic to the dilator, viz., the constrictors, or,
more correctly, the adductors, of which there are four on
either side, viz., the arytenoideus, thyro - arytenoideus
anticus and posticus, and crico-arytenoideus lateralis. By
the contraction of these muscles the glottis is closed, the
arytenoid cartilages depressed, their glottal surfaces closely
applied, and they also bring the vocal cords together, or
nearly so, forming a simple slit between them.

The vocal cords, lying in close apposition to the thyro-
arytenoideus posticus muscle, are relaxed by a contraction
of this muscle, which approximates the arytenoid and
thyroid cartilages ; whilst the crico-thyroid places the cords
on the stretch, or renders them tense by the manner in
which it rotates the cricoid on the thyroid cartilage. The

The Voice. 375

vocal cords by being stretched and relaxed produce the
pitch of the note emitted; the pitch of the note produced
thus depending on the tension of the cords.

The nerve supply of the larynx is peculiar, and of con-
siderable practical interest. Sensation to the mucous
membrane, and portion of the epiglottis and glottis, is sup-
plied by the superior laryngeal division of the tenth nerve.
Motor power is supplied to all the muscles of the larynx,
excepting the crico-thyroid, by the inferior laryngeal or
recurrent nerve, which is given off from the pneumogastric
in the chest : that on the right side winding around the
axillary artery and passing up the neck supplies the right
larynx, whilst on the left side it passes around the aorta and
returns up the neck, in its passage being exposed to aortic
pressure and any pressure arising from diseased bronchial
lymphatic glands, through the substance of which it passes ;
it thus reaches the left side of the larynx and supplies it with
motor power. It is this branch of nerve which supplies the
muscles implicated in 'roaring,' especially, of course, the
inspiratory muscle of the larynx — the crico-arytenoideus
posticus.

The crico-thyroid muscle in the horse is supplied with
motor power by the first cervical nerve ; this, according to
the experiments of Moeller, is beyond all doubt.* We
know that in the most acute case of laryngeal paralysis this
muscle is quite sound. Chauveau and others have shown
that the spinal accessory supplies the superior laryngeal
division of the tenth nerve with motor fibres.

Swallowing may be excited by touching the vocal cords,
but especially the anterior extremity of the arytenoid carti-
lages ; the adductor muscles then close and depress the
glottis, and the free mucous membrane of the ary-epi-
glottic folds, together with the epiglottis, close the entrance
into the larynx. The presence of the arytenoid cartilage is
not essential to swallowing, or, rather, its presence is not
necessary to prevent food passing into the trachea.

Neighing in the horse is produced by an expiration,
* Fleming's ' Roaring.'

376 A Manual of Veterinary Physiology.

whilst the braying of the ass is both an inspiratory and
expiratory effort. In both cases the sound partly comes
through the mouth.

In the ox, sheep, and goat there are no ventricles in the
larynx, and only rudimentary vocal cords. In the ass the
ventricles are very large.

Yawning is a deep, slow inspiration, and though the horse
opens the mouth and slightly crosses the jaws, I am not
certain whether the whole of the air or only part of it
passes by the mouth.

Sneezing and coughing are expiratory efforts, the former
occurring through the nostrils, the latter through the
mouth ; but in both yawning and coughing the long soft
palate of the horse must be raised to allow the air to pass
into the mouth.

CHAPTER XX.

GENERATION AND DEVELOPMENT.

The seminal fluid is secreted by the testicle, and constitutes
the fecundating material of the male. As discharged
from the urethra, it is mixed with the secretion of the
prostate and vas deferens. It is not known what part the
accessory secretions play, but they appear to be essential to
fertility.

The spermatic fluid is alkaline or neutral in reaction, of
gelatinous consistence, and was found by Lassaigne, who
examined the material taken from the vesiculte seminalis of
the horse, to contain a large quantity of water, an abund-
ance of a substance termed by him spermatin, mucus, soda,
chloride of sodium, and phosphate of lime. Colin describes
the spermatic fluid of a bull after standing to consist of
two parts — the upper colourless and transparent, the lower
stratum milky and opaque. He regards the former as
prostatic fluid, the latter as spermatic. More recent
analyses of this fluid show it to contain serum and alkali
albumin, nuclein, lecithin, cholesterine, fat, leucin, tyrosin,
kreatin, inosit, sulphur, alkaline earths, and phosphates.

The essential element of the spermatic fluid is the
spermatozoa, without which the fluid is not fertile. They
are developed in the seminal tubes of the testicle from
the so-called spermatoblasts. These are projections from
the wall of the tube, which, when ripe, leave the wall,
and are carried along in the fluid. They exhibit spontaneous
movement, the long tail moving from side to side, by which
means the organism is propelled when placed in the body

•S7<S .1 Manual of Veterinary Physiology.

of the female. The vitality of the spermatozoa is consider-
able under suitable conditions ; and when placed in the
body of the opposite sex they have been found vary active
seven or eight days after copulation. Colin has found
them in a similar state in the vesicuhe seminales eight
days after castration. The spermatozoa are readily killed.
Colin says that those of the ox, horse, and carnivore
are killed immediately by ordinary or acidulated water,
glycerine, etc.

The prostatic fluid precedes the spermatic in ejaculation,
and in stallions and bulls, when excessive daily demands
are made, the fluid ejaculated is largely prostatic and
infertile.

The testicular products of hybrids, such as the mule, are
said to be devoid of spermatozoa.

The act of copulation consists in the introduction of the
penis of the male into the vagina of the female. With
some animals, as in the dog, the introduction is facilitated
by the presence of a bone in the substance of the penis ;
but in all animals the penis has to become erect and larger
before it is fit for penetration.

The Phenomena of Erection is produced by a gorging of
the vessels of the penis, caused by a dilatation of the
arteries, increased blood supply, and pressure on the veins.
This is brought about by the nervi erigentes, the fibres
of which contain both dilator and constrictor nerves for
the walls of the bloodvessels. An erection centre also
exists in the spinal cord, normally under the control of the
vaso-motor centre in the medulla, though it may act inde-
pendently of it, as in persistent erection after laceration of
the cord. The stimulation of the centre in the medulla
may even at the moment of death lead to erection and
ejaculation. Colin has observed this in stallions destroyed
by section of the medulla, injuries to the head, or even simply
by bleeding. The emptying of the bladder and evacuation
of the contents of the intestines, in horses destroyed by
shooting through the head, is a regular accompaniment of
this mode of death, and the same prooe8S which empties

Generation and Development 379

the bladder and elongates the penis of the castrated animal,
no doubt produces what Colin has recorded of stallions.

The influence of the cerebrum on the mechanism of
erection, viz., in stimulating the centre in the cord and
medulla, is well known.

The first portion of the penis which receives the excess of
blood in erection is the corpus cavernosum ; the spongiosum
and glans are not fully erect in the stallion until the penis
is introduced into the vagina; at the moment of ejacu-
lation the glans swells enormously, apparently to cover
or grasp the os uteri. The blood sent to the penis for the
purpose of erection is practically imprisoned by the com-
pression exercised by the muscles of the perinseum on the
veins of the part, and this mechanism further maintains
the blood pressure.

If the nerves of the penis be divided in the horse, erec-
tion is impossible, though desire may be intense. Gunther's
and Colin's experiments have placed this beyond doubt.

Though the organ in the horse assumes such considerable
proportions, in the bull this is not so marked. The penis
in this animal comes to a narrow point without any of the
swelling observable in the stallion. In the ram, also, the
penis is narrow and pointed, and the peculiar vermiform
appendage at its extremity appears essential for successful
impregnation, for if removed the animal proves sterile.

Sexual Intercourse is of short duration in the majority of
animals, excepting the dog and pig. Colin places it at 10
to 12 seconds for a vigorous stallion ; it is exceedingly rapid
in the bull and ram, probably from the peculiar shape of
their intromittent organ.

The spermatic fluid is forced into the vagina, or even
directly into the uterus ; the peculiar termination of the
urethra of the horse, and the bulbous enlargement of the
glans during the act of coition, would rather point to the
fluid in this animal being directly passed, at any rate to
some extent, into the os uteri, and the pointed penis of the
bull and ram makes it nearly certain that much of the
fecundating fluid passes directly into the uterus.

3<so A Manual of Veterinary Physiology,

At the moment of intercourse, the uterus becomes erect,
and the introduction of the male element into it is assisted
by the aspiration following its subsidence. It would appear
necessary in the lower animals for the fluid to pass into the
neck of the uterus, and there is probably a great deal to
say in favour of the common practice of preventing the
mare from straining immediately after copulation, and
thus rejecting the spermatic fluid.

The actual mechanism of ejaculation is produced by the
contraction of the vesiculse seminales, and probably of the
vasa deferentia, through the reflex action of the ejaculation
centre in the lumbar and sacral portions of the cord ; by
this means the seminal fluid is forced out of the vesiculse
into the urethra, and by means of the muscles of the
perinaeum is forcibly ejected from the urethra.

The amount of seminal fluid ejaculated by the stallion
and bull is estimated by Colin at 770 grains to 930 grains.

The Ovum. — The ovaries prepare the female element, the
ovum. The ovum is exceedingly small ; it is contained in a
thick envelope, the zona pellucida, within which is the yelk,
and at one part of the yelk is the germinal vesicle ; within
the vesicle is the germinal spot. When the ovum is about
to ripen, it passes from the periphery of the gland towards
the centre and undergoes certain changes, becoming large
through the accumulation of thud within the Graafian
follicle; it now passes to the surface of the gland once
more, preparatory to bursting.

As the ova ripen, changes take place in the system of the
animal, known as ' heat ' or ' rutting.' It manifests itself by
uncontrollable sexual desire, which comes on at fairly
definite periods, and lasts for a certain number of days. In
the lower animals it is not accompanied by anything
approaching the menstruation in the human female
Although slightly blood-coloured discharges have been
observed in animals, wo may fairly say that menstruation
proper is not a normal occurrence, due probably to the tact
that neither horses, cattle, nor pigs have anything of the
nature of a uterine decidua.

Generation and Development. 381

The ripened bladder-like Graafian vesicle comes to the
surface of the ovary and bursts ; but before this occurs, the
fimbriated expansion of the Fallopian tube has embraced
it, the ovum passes into the canal, and, by means of the
cilia which line it, is impelled towards the uterus. In the
Fallopian tube it meets with the male element, and impreg-
nation of the ovum occurs in a manner which will be
presently described. Should the fimbriae of the Fallopian
tube fail to grasp the vesicle, the ovum falls into the
abdominal cavity and there perishes, or, if it has already
met with the male element, an extra-uterine foetation
occurs.

The period of heat manifests itself at different times :
the mare is ' in season ' during the spring and summer, the
period lasting two to four days, and recurring every three
or four weeks ; during the interval the male is not accepted.
The cow is much the same as the mare ; sheep take the
ram in the autumn.

The male is attracted to the female by a peculiar smell,
which can even be detected by the former at some con-
siderable distance.

The number of ova discharged at each period varies :
generally one for the mare and cow is the rule, though two
may be discharged ; one to four for the sheep ; whilst the
pig may discharge ten or more ova at one time.

The Period of Puberty, or that time in the animal's life
when it is capable of procreation, has been put at 3 years
for horse and ox, and 12 months for the sheep ; the
females may conceive at an earlier period than this — in
fact, commonly do. A mare may conceive between 12
months and 2 years, a cow 12 to 18 months, sheep and
goat 8 to 12 months. The use of immature mares for

o

breeding stock is the explanation of a great deal of the
worthless material in the shape of horseflesh which may
be seen in this country. In my opinion, neither mare nor
horse is fully developed, mature, or fit for procreation until
5 years old.

The advent of maturity is marked by certain changes in

382 A Manual of Veterinary Physiology.

form, particularly in horses. They lose their awkwardness,
the outline of the frame becomes more consolidated and in
greater unison. In the male the neck becomes thick and
curved, the voice deepens, and the whole appearance
denotes life and vigour ; the temper is usually irritable and
uncertain, and often extremely vicious.

The age at which procreation ceases is not known.
Fleming* says that mares have been known to produce
foals at 28, 32, and 38 years of age, and it is certain that
some of our best stallions are well advanced in years.

Changes in the Ovum. — Before impregnation the germinal
vesicle and spot undergo changes, and the place of the
vesicle is taken by a spindle-shaped body ; at each end of
the spindle the elements of the yelk arrange themselves
in the form of a star. The peripheral pole of the spindle
projects outside the wall of the ovum, and is cut off; the
remaining pole is termed the female pro-nucleus.

The ovum is impregnated in all probability in the
Fallopian tubes or tube. The spermatozoa passing through
the yelk envelope, or zona pellucida, and forming the male
pro-nucleus, which passes deeper into the ovum, and
approaching the female pro-nucleus, causes it to become
active. The change which now follows is segmentation of
the p-erminal vesicle, which divides and subdivides into an
indefinite number of small bodies. Next, the yelk in which
the small bodies of the germinal vesicle are distributed
begins to become segmented in twos, fours, eights, etc.,
until the whole surface of the yelk is converted into
a mulberry-looking mass, consisting of minute spherules,
termed vitelline spheres. These now pass to the wall of
the vitelline membrane, and arrange themselves on its
inner surface, while the central portion of the ovum becomes
clear and transparent, The vitelline spheres which have
thus passed to the wall arrange themselves into a kind of
membrane termed the blastodermic or germinal membrane.
The cells of the germinal membrane accumulate at one
point and form an Opaque spot, the germinal area, which in
* ' Areterin:uy Obstetrics.'

Generation and Development. 383

time becomes pear-shaped, and corresponds to the direction
of the future embryo.

At the posterior part of the germinal area the primitive
streak appears, and soon becomes a groove termed the
primitive groove.

Leaving the ovum for the moment, we must describe the
changes which have occurred in the blastodermic layer
which was left on the inside of the vitelline membrane. It
is found that this layer divides at first into two, and then
into three layers. The outer, called the ectoderm, epiblast,
or serous layer, grows the central nervous system and
epidermal tissues, including hoof. The inner or lower
layer is termed the endoblast or hypoblast, and grows the
intestinal canal and the glands opening into it. The
middle layer, or mesoblast, forms the bloodvessels, and
constitutes a part termed the area vasculosa : it also grows
the muscles and skeleton, generative and excretory organs.
Returning to the primitive groove, it is found that in
front of it is formed another groove, the medullary, which,
extending back and opening out, encloses the primitive
groove and causes it to disappear. The growth of the
medullary groove has given rise to a part termed the area
pellucida, surrounded by an opaque surface, termed the
area opaca. In the pellucid area is formed the embryo.
The medullary groove grows from the epiblast ; from either
side of the groove rises up a structure termed the lamina
dorsales, which, growing over the groove, meet, and thus
form a canal termed the neural canal ; in this is developed
the brain and spinal cord.

Underneath the medullary groove is formed from the
mesoblast a cord termed the notochord, from and around
which are developed the vertebrae. From another portion
of the mesoblast is formed the pleuro-peritoneal cavity.
Two important structures appear at this time, developing
from one or other of the layers into which we have seen
the blastodermic membrane is divided. By the union of
certain layers of the mesoblast with the epiblast a structure
termed the somatopleure is formed, and from a layer of the

o84 A Manual of Veterinary Physiology.

mesoblast with the hypoblast is formed the splanchnopleure.
From the somatopleure is formed the skin, muscles, and
bloodvessels ; from the splanchnopleure is formed the
intestinal canal.

The embryo now undergoes a change in shape, for at
each end an inflection or tucking in of the layers surround-
ing it occurs. These inflections are spoken of as the head
and tail fold. As this folding under the body occurs, the
embryo (ventral surface downwards) is raised higher and
higher, so that at last it rests at the future umbilicus on a
narrow stalk or pedicle, termed the vitelline duct, which
communicates with a sac outside the body of the embryo
termed the umbilical vesicle ; in the body of the embryo
the vitelline duct communicates with the primitive intes-
tinal canal.

From the splanchnopleure is now developed the heart,
then the aorta, from which is given off several vessels
termed omphalo-mesenteric arteries, which form, by passing
through the vitelline duct, a vascular network within the
umbilical vesicle, and from here arises the omphalo-
mesenteric veins, which return to the body of the embryo
by the vitelline duct, and terminate in the heart.

This is the primary embryonic circulation. The um-
bilical vesicle is furnishing the embryo with nutriment, but
this does not last for long, for when the placental circula-
tion is established, the umbilical vesicle has no longer any
function to perform, and it gradually disappears.

We must now describe the formation of two sacs which
are found outside the body of the embryo, which at this
time are destined to perform important functions, and in
their arrangement are different from those occurring in the
human subject.

The Amnion is formed from the somatopleure, growing
over the embryo from all sides, meeting, and then forming
a cavity termed the amniotic, which eventually contains
a quantity of fluid in which the embryo resides. The
amnion surrounds the duct of the umbilical vesicle, and
we may describe it as terminating at the umbilicus, where

Generation and Development. 385

it eventually forms the amniotic portion of the cord. The
liquor amnii i« an albuminous alkaline fluid, yellowish in
the early period of gestation, reddish toward the end of it,
probably due to discoloration with meconium. It consists
of albumin, mucin, globulin, sugar, urea, lactic acid, keratin,
calcium sulphate, phosphates, and sodic chloride ; it con-
tains also portions of hoof, epithelium, etc.

Gurlt, quoted by Fleming, puts it at 2 lbs. 12 ozs. at the
twenty-first week of pregnancy in a mare, and at the
fortieth week the amniotic and allantoic fluids amounted to
19 lbs. The function of this fluid is protective to mother
and foetus, and during parturition it dilates the os and
lubricates the passage.

The Allantois is formed from the splanchnopleure, grow-
ing out from the body of the embryo at the future um-
bilicus. As it grows from the umbilicus it spreads out, and
in the mare completely envelops the amnion, though in
ruminants it only partially envelops it. The part of the
allantois within the body of the embryo becomes the bladder,
and this is brought into communication with the allantois
outside the body, by means of the urachus, which passes
through the umbilicus ; the urine from the bladder passing
through the urachus, distends the allantoic sac with this
fluid. The outgrowth of the allantois is to establish com-
munication with the vascular covering of the embryo, the
chorion ; in the mare it lines the chorion as well as being
reflected over the amnion.

The allantoic fluid of the mare is at first colourless or
turbid, but later becomes brown ; it contains albumin,
sugar, urea, lactic acid, phosphate of lime, soda, and
magnesia, and in the cow allantoic acid.

Floating in the allantoic fluid of the mare are certain
peculiar bodies of a brownish colour, termed hippomanes ;
they contain much oxalate of lime. Some of these bodies
are attached to the wall of the allantoic sac. Their use is
unknown.

In ruminants the allantois is smaller, and only partially
envelops the amnion ; it is attached to the chorion between

25

386 A Manual of Veterinary Physiology.

the horns of the uterus. The urachus communicates with
the allantois as in the mare ; but, unlike the latter, it is
constantly found to be pervious at birth.

Surrounding both these sacs we have the Chorion, which
forms the connection, through the medium of the umbilical
cord, between the mother and embryo. It is developed
from the outer or vitelline covering of the embryo, and
important differences are observable between its arrange-
ment in the mare and in ruminants. In the former the
chorion is attached all over the inner surface of the uterus,
excepting at the os ; in ruminants the chorion is attached
to the uterus by cotyledons, dotted here and there over the
surface, about 60 or 80 in number ; while in the pig the
placenta is like that of the mare.

The development of the chorion from the vitelline layer
occurs by tufts of vessels forming on its exterior, either all
over as in the mare, or dotted here and there as in the
cow. These villi project themselves into the mucous mem-
brane of the uterus, not through the medium of a decidua,
as in the woman, but directly into the wall of the uterus, as
solipeds and ruminants possess no decidua. As the um-
bilical cord forms the connection between the embryo and
the chorion, a perfect communication is kept up between
the mother and embryo, not by the direct passage of blood
from mother to foetus, but through the capillary Avails only,
for the vessels of the one do not directly communicate with
the vessels of the other.

The umbilical cord is composed of two portions : an
amniotic, which is nearest the foetus, and an allantoic,
which is next the chorion and outside the amniotic cavity j
this is the arrangement in the mare. The umbilical cord
in ruminants has no fold of allantois, owing to the anatomical
difference in the arrangement of this sac, but it directly
enters the chorion from the amnion. In both classes of
animal the cord is made up of a gelatinous material, known
as ' Wharton's jelly,' containing the umbilical arteries and
veins passing to and from the chorion. The cord is about

p. It.

L

Fk;. 50.— Diagram of the Fcetal Circulation.

(Ellenberger— Bonnet.)

, umbilical vein ; d. v., ductus venosus ; pt. v., portal vein ; /., liver :
r. h., hepatic veins ; p. r. c, posterior vena cava ; r. a., right auricle :
/'. (,., foramen ovale ; r. v., right ventricle : p. a., pulmonary artery ;
d. a., ductus arteriosus ; /. a., left auricle ; /. v., left ventricle ; a., the
aorta; a. a., arch of aorta; ant. a., anterior aorta ; i. v., innominate
veins ; a. v. c, anterior vena cava ; po. a., posterior aorta : i. a., illiao,
artery; h. a., hypogastric artery ; u. a., umbilical arteries ; i. ve., illiao
veins; h. v., hypogastric veins ; */. p., umbilical cord. The diagram

actually represents the foetal circulation in ruminants: to make it

applicable to the horse the ductus arteriosus (</. v.) must be supposed

to be removed, the whole of the hlood then traverses the liver by
the union of the umbilical vein (11. r.) with the portal vein (pt. [>.).

The arrows indicate the course taken by the blood : observe how
i he stream entering the tight auricle divides, pan passing into the

right, ventricle, and part into the left auricle through the foramen
ovale (/. o. ).

Generation and Development 389

3 feet in length, and the amniotic portion is twisted very
much like the strands of a rope.*

We have traced the development of the ovum from the
period of impregnation to the development of the primary
circulation and investing membranes. It is not our inten-
tion to follow out the development of the various parts of
the body, until the foetus is completely formed, as ample
information on these points can be obtained in works on
anatomy and embryology. t We will here only mention the
peculiarities of the foetal circulation, as these are of physio-
logical interest.

Foetal Circulation. — The blood of the foetus, returning from
the placenta in a purified condition, passes by means of the
umbilical vein to the umbilicus, then turns and runs along
the floor of the abdomen, reaches the liver, and opens into
the vena porta ; from the union of the umbilical and portal
veins, a single vessel results, which breaks up in the liver,
and the blood passing through this gland, reaches, in course
of time, che posterior vena cava through the medium of the
hepatic veins. So that in the foetal circulation of the horse
the whole of the blood first passes through the liver. (See
Fig. 50.)

In ruminants the umbilical vein on reaching the liver
joins the vena porta, from which a canal — the ductus
venosus — takes a portion of the blood direct to the posterior
vena cava ; the other portion, traversing the liver through
the hepatic veins, eventually reaches the posterior vena
cava; from here in both animals it passes to the right
auricle of the heart, where it meets with the blood which
has been circulating through the head, neck, and fore ex-
tremities. Here occurs a remarkable change characteristic
of the foetal circulation in all animals : that portion of blood
which reached the right auricle by the posterior cava divides ;

* To Fleming's ' Veterinary Obstetrics ' I am indebted for the
account of the masterly foreign researches on the formation of the
membranes in solipeds and ruminants.

f The development of the ovum and the various parts is fully
described in Chauveau's 'Anatomy' (Fleming), and in Fleming's
' Veterinary Obstetrics.'

390 A Manual of Veterinary Physiology.

part passes from the right auricle into the left auricle
through a foramen in the auricular septum, known as the
foramen ovale ; from the left auricle it passes into the left
ventricle, and from here to the aorta, and thence over the
body, especially to the head and neck ; that portion of
blood which reached the right auricle by the anterior cava,
passes into the right ventricle in conjunction with the
balance of the blood received by the posterior cava, thence
into the pulmonary artery, a small portion passing on to
the lungs and behaving as in the adult, whilst the major
portion passes from the pulmonary artery direct into the
aorta by means of the ductus arteriosus, and is distributed
by means of the aorta to the posterior part of the body.
From the external iliac arteries arise the umbilical arteries,
which run along the sides of the bladder, pass out at the
umbilicus, traversing the substance of the cord to the
placenta, where the impure blood it conveys becomes re-
vivified by the maternal placenta, and in a purified con-
dition it returns once more to the body of the foetus by the
umbilical vein.

Thus it will be seen that the blood circulating in the
foetus is a mixture of arterial and venous, arterial up to the
liver, where it mixes with the portal ; another mixture occurs
in the right auricle, but the greater part of that blood, as we
have seen, after performing work in the anterior extremities,
is sent by another channel to assist in the nutrition of the
posterior extremities, whilst the purest blood in the body is
principally directed to the head, which needs it the most.

After birth the circulation changes : the ductus venosus
closes, the septum in the auricles becomes filled in, the
ductus arteriosus is obliterated, the umbilical arteries be-
come the lateral ligaments of the bladder, whilst the
umbilical vein becomes the round ligament of the liver.

The Duration of Pregnancy for the mare is about 11
months, though it may vary within wide limits ; for the
cow, about J) months ; sheep and goat, 5 months ; pig,
4 months ; and bitch, 2 months.

Among the changes which the uterus undergoes after

Generation and Development. 391

impregnation may be mentioned the great increase in the
elements of the muscular wall, enlargement of the broad
ligaments of the uterus, and the formation in the mucous
membrane of depressions, or ' crypts,' in which are lodged
the villi of the chorion.

The Nutrition of the Embryo is in the first instance carried
out by the umbilical vesicle; later, when the membranes
are formed, and connected with the interior of the uterus,
nutrition is carried on by the interchange of material oc-
curring in the villi of the chorion, and the capillary vessels
surrounding the follicles or crypts in the uterine mucous
membrane. The capillary vessels of mother and foetus
here come in contact, though there is no communication
whatever between them ; carbonic anhydride passes through
the vessels from the foetus to the mother, and in return the
vessels of the latter give up oxygen to the foetal villi, by
which it is conveyed to the umbilical vessels, and so enters
the body of the foetus.

Uterine Milk.— If the villi of the chorion be separated
from the tubular depressions of the mucous membrane of
the uterus, a milky fluid can be expressed, known as uterine
milk. This is particularly observable in separating the
foetal and maternal cotyledons.

Uterine milk is of a white or rosy-white colour, creamy
consistence, and contains proteids, fat, and a small propor-
tion of ash. Examined microscopically it is found to con-
tain globules of fat, leucocytes, and rod-like crystals of
albumin-crystalloids, besides structureless masses of proteid
containing chromatin* The use of the fluid is described
by this authority as for the nourishment of the epithelial
cells of the chorion.

Parturition.— The foetus having reached its full stage of
development, changes of an obscure nature take place,
which lead to it being expelled. Preparatory to this pro-
cess the foetus changes position ; for, from lying on its back
on the floor of the mare's abdomen, with its chin on its
chest, the fore-legs bent at the knee, and the hind-legs in
* Ellenberger, ' Physiologic'

392 A Manned of Veterina/ry Physiology.

the largest of the two cornua, the fujtus now assumes first a
lateral position, and lastly an upright one, Iry which the
fcetal and maternal spines are brought nearer together. To
assume this position, the foetus has had to make a complete
revolution ; it is now brought with the muzzle and fore-legs
in the direction of the pelvis, and the dilatation of the
os uteri follows. In the cow the foetus lies on its back on
the floor of the abdomen as in the mare, but lies somewhat
crooked, viz., the head inclining towards one side, and the
hind extremities towards the other ; in all other respects it
resembles the mare. The alteration in the position of the
foetus does not occur through its own movements, but by
the contraction of the uterus; on the other hand, the
stretching of the limbs is the result of foetal movement.*

The dilatation of the os is assisted by the amniotic and
allantoic fluids ; each contraction of the uterus is accom-
panied by a pain ; the pains last from 15 to 90 seconds,
and the interval between them is from 2 to 4 minutes.

The mare is remarkable for the rapidity with which
delivery is effected ; ruminants, on the other hand, are
often very slow, and in labour for hours. The rapid de-
livery of the mare is accompanied by a complete separation
of the chorion from the uterine walls ; this is the explana-
tion why any difficulty in foaling invariably sacrifices the
life of the foal. In ruminants, on the contrary, the circula-
tion between the mother and foetus is kept up to the last
by the gradual separation of the cotyledons, so that, though
calving may be delayed several hours, the calf may, and
commonly is, born alive.

The contractions of the uterus occur through a centre
in the lumbar portion of the cord ; it is not under the
control of the will, and has the power of acting even
though the animal be unconscious.

Mammary Secretion.
As the period of parturition approaches the mammary
glands become swollen, owing to the active changes occur-

* The description of the change in the position of the foetus pre-
paratory to birth is takon from Bllenb xger's ' Physiologies

Generation and Development. 393

ring in them, culminating in the production of milk at the
birth of the young animal.

The earliest milk is termed the Colostrum. It is a peculiar
yellowish-white fluid, of alkaline reaction, sweetish taste,
and remarkable for the amount of proteid it contains ; for
instance, in the cow, the colostrum contains 15 per cent, of
proteid, whilst the normal milk only contains 4 per cent,
to 5 per cent.

If the fluid be examined microscopically, it is found to be
filled with bodies termed 'colostrum corpuscles.' These
are large granular corpuscles filled with fat, which has not
yet escaped from the parent cell.

The use of colostrum is to act as a natural purge, and so
clear out the intestinal canal of the young animal.

Milk. — This follows the secretion of colostrum. It is a
slightly alkaline fluid, soon showing an acid reaction, with
a specific gravity in the cow of 1028 to 1034 The following
analysis of cow's milk and colostrum from the same animal
is given by Halliburton :

Milk. Colostrum.

Water- - - - 84-28 787

Solids- - - 15-72 21-3

Casein - - - 3-57 7"3

Albumin - - - '75 7'5

Fat - - - - 6-47 4-0

Lactose - - - 4*34 1*5

Salts - - - - -63 1-0

Specific gravity - - 1028-1034 1046-1065.

The same authority also quotes analyses of the milk of
other animals :

Mare. Sheej>. Ass.

Water - - 92*5 - 18-24 - 90-5

Solids - 7-5 15-17 - 9-5

Casein - - 1*3 )

Albumin - "3 )

4-7 - 1-7

Fat - -6 4-8 - 1-4

Lactose - 4'7 - 3-4-6 )

Salts - - -3 - -6 .•

f.--'

The proteids of milk are casein (which clots on the

3D4 A Manual of Veterinary Physiology.

addition of the rennet ferment) and ordinary milk albumin.
Milk acted upon by rennet is divided into clot and whey.
The casein of mare's milk is more like human tlian cow's
casein.

If milk be microscopically examined, it is found to be
tilled with minute oil globules, which form in the milk a
perfect emulsion, and so never run together. After the
fluid has stood some time the fat globules rise to the sur-
face as cream, though still forming an emulsion. The fat in
milk consists of several fatty acids. If the fat be liberated
from the globules by beating, butter is formed, consisting
of G8 per cent, of palmatin and stearin, 30 per cent, of olein,
and 2 per cent, of specific butter-fats (Halliburton).

The sugar of milk is known as lactose ; the salts of milk
have been dealt with on p. 18.

CHAPTER XXI.

GROWTH, DECAY, AND DEATH.

Growth. — The young of the herbivora very rapidly shake
off the helpless condition in which they first find them-
selves in this world. This is largely due to the fact that
they are born with a nervous system in a high state of
development ; in the course of a few hours they learn to
stand and walk, and in a day or two can skip and run. The
young animal, moreover, is born in full possession of its
senses, such as sight, touch, hearing, smell, taste, and with
an amount of intelligence which nearly, if not quite, equals
its parent; it practically has nothing to learn but obedience
to man.

Not only is the nervous system in an advanced condition,
but also the locomotor : the legs of the foal are remarkably
long, some of the bones being nearly their full length,
though, of course, not of their full weight; such joints as
the knee and hock are nearly their full size. We can
understand the reason of this development of the limb
from what we have previously said, and the length of leg
in the foal is undoubtedly for the purpose of enabling the
animal to reach the mammary gland.

The limb, however, is only partially developed ; from the
knee and hock to the ground it is nearly the length of the
adult ; from the knee and hock to the elbow and stifle it is
decidedly below the adult ; whilst from the elbow to the
withers, and the stifle to the croup, the body has a con-
siderable amount to grow. It has been said, and the state-
ment appears to be true, that the future height of the foal

896

A Manual of Veterinary Physiology.

may be ascertained by measuring the fore limb from the
fetlock to the elbow and multiplying it by two.

Table Showing the Length of the Bonks of the Limbs of
the Foal and Adult House.

Scapula -

Adult Home.
15 in.

Foal of
Six ]\'<> /.•-•.

Diffen nee.

84, in.

6| in.

Humerus -

12 in.

8 in.

4 in.

Radius and ulna

18 in.

12 in.

() in.

Knee-joint

34, x 3| in.

3x3 in.

\ in.

Metacarpal

" 94 in.
3|in.

8f in.

\ in.

Suffraginis -

3 in.

4 in.

Femur -

17 m.

104 in.

6| in.

Tibia -

134 in.

94 in.

4 in.

Calcis to metatarsal bone-

Gin.

5 in.

1 in.

Metatarsal

11 in.

10 in.

1 in.

Suffraginis -

34 i„.

3 in.

u.

The hind quarters of the foal are in a more advanced
state of development than the fore ; the shoulders are very
oblique, the chest contracted and shrunken-looking, and
neither contains much muscle. The oblique position of the
scapula is due to the weight of the body on the limbs, the
weakness of the muscles at this part allowing the angle
formed by the scapula and humerus to be considerably
closed, and the shoulder joint to bulge.

The head of the foal is prominent over the brain, and
depressed over the nasal bones ; the hair is fully developed,
that of the mane being scanty, and of the tail curly : whilst
the colour of the body is light of its kind.

The rate at which the foal increases in weight, and other
circumstances connected with its nutrition, were made the
subject of inquiry by Boussingault.* He found that the
mean weight at birth was 112 lbs., that during the first
three months the daily increase in weight was 2"2 lbs.; from
three up to six months the daily increase was 1*3 lbs., and

(Juou-d by Coli

Growth, Decay, and Death. :i(.i7

from six months up to three years of age the increase was
at the rate of -7 lb. per diem.

With calves, according to Torcy,* the mean weight at
birth is 77 lbs,, the daily increase during the first year is
1*5 lbs., during the second year 15 lbs., during the third
year T43 lbs., during the fourth year 1*32 lbs.

With sheep the daily increase in weight is still more
rapid : a lamb will in ten days gain 50 per cent, on its
original weight, will double its weight at the end of the
first month, and triple it at the end of the second.

Swine present, however, the most rapid increase in
weight, for, according to the authorities quoted, a pig will
increase 20 per cent, in its weight per diem during the
first week, and up to the end of the first year is adding
•44 lbs. daily to its body weight.

The growth of the body implies an increase in weight and
height ; from what we have said respecting the limbs, it
may be judged that the amount of growth of each part is
not the same : the eyes, ears, brain, kidneys, and liver grow
less rapidly than the other parts, owing to their com-
paratively large size at birth ; the greatest increase is in the
skeleton and muscles, and the rate of this increase we have
just alluded to ; the least increase is in the eyes and the
ears, and the limbs below the knee and hock.

But few observations have been made on the rate of
growth. Percivalf many years ago drew up a table, which
he considered very imperfect, as to the rate at which some
horses of his regiment grew, from which he showed that the
increase in height between 2 years and 3 years was on
an average one inch, between 3 years and 4 years one-third
of an inch, and between 4 years and 5 years one-third
of an inch. Of 35 two-year- olds, 2 did not grow in the year ;
of 144 three year-olds, 17 did not increase in height during
the year ; of 48 four- year-olds, 7 did not grow during the
year ; and of 11 five-year-olds, only 9 grew during the year.

These numbers are too small to generalize from ; there

* Quoted by Colin.

f 'Lectures on Form and Action.'

398

Manned of Veterinary Physiology.

can be no doubt that many horses grow much more than
two-thirds of an inch between three and five years old. It
is probable that many grow up to their sixth or seventh year.

During the time the young animal is receiving its
mother's milk, the urine is acid ; it is practically carni-
vorous ; once a vegetable diet is taken the urine becomes
alkaline, and, it is probable, decreases in quantity.

The activity of certain glands, such as the thymus, be-
comes considerably reduced as the animal grows,, until they
disappear at the adult period.

One characteristic of the young animal is the necessity
for sleep ; it is probably during slumber that the tissues
make the immense strides noticeable during the first few
weeks of life.

The period of dentition commences immediately at birth,
if it has not already commenced in utero ; the following
table from Gamgee* shows the changes taking place in the
teeth from birth to adult life :

Kreutzer's Table of Dentition.

Horse.

Ruminants.

Eruption.

Change.

Eruption.

Change.

Incisors :
Central

Lateral

Outer lateral

Corner
Tushes -
Molars :

First -
Second

Third -
Fourth
Fifth -
Sixth -

(Before or a
few days
( after birth
4 to 6 weeks

6 to 9 months
4 to 5 years

Before or a
few days
after birth

10 to 12 months
\\ to 2 years
4 to 5 years

ylk years
3i years

4J years

1 2i years
3$ years

1 Before or a
-j few days
( after birth

14 days
2 to 3 weeks

' Be fore or a
-; few days
[ after birth

t) to D months

2 J. years

1 to ."» years

1 1 A yea ra

•_'.', years

3i years
4i years i

1 1 years
2| years

ill years

* 'Our Domestic Animals.1

Growth, Decay, and Death. 399

The influence of feeding on development is most remark-
able : not only does the body increase in size and weight,
but the animal presents the appearance of the adult, so
that a thoroughbred at two years old is furnished and looks
as old as an ordinary horse at four years old.

The completion of dentition marks the age of maturity ;
the uncastrated animal presents very distinctive features
from the female, viz., greater bulk, a heavy crest and neck,
and a harsher voice; the castrated horse more closely
resembles the mare. No such difference as is observable
in the human family exists between the male and female
of the horse tribe : the mare arrives at maturity at the
same time as the horse ; and the castrated animal is not
deficient in stamina, strength, or capacity for work ; more-
over, castration in the horse does not lead to a deposition of
fat in the body.

Decay. — It is doubtful what age a horse would live to if
not subjected to civilization ; we may safely say that at
seventeen years old the powers of life in the majority of
animals are on the wane, though many at this period may
be found in full possession of life and vigour; these are
probably cases of the survival of the fittest, and cannot be
taken as a general guide.

Doubtless the work performed by horses is the chief
cause of their rapid decay ; but apart from this, changes
in their teeth, such as the wearing away of the molars,
appear to preclude many of them from reaching a ripe old
age, though instances are on record of horses attaining the
age of thirty-five, forty-five, fifty, and one animal is known
to have lived to sixty-two years of age.

Blaine* appears to have gone very carefully into the
question of old age in equines, and he drew the following
comparison :

' A parallel drawn between the ages of horses and of men

will fully convince us of the error of fixing the decay of the

horse at eight years from his birth. A very considerable

attention to the subject, over a wide field of observation, has

* ' Encyclopaedia of Rural Sports.'

400 ^4 Man /'a/ of Veterinary Physiology.

impressed the writer with the propriety of drawing the
following comparison between the ages of horses and men :

' The first five years of a horse may be considered as
equivalent to the first twenty years of a man ; or thus, a
horse of five years may be comn/paratively considered as old
as a man of twenty ; a horse of ten years as a man of forty ;
a horse of fifteen as a man of fifty ; a horse of twenty as a
man of sixty ; of twenty-five as a man of seventy ; of thirty
as a man of eighty ; and of thirty-five as a man of ninety.

' So far from this comparison being too much in favour of
the horse, we are disposed to think it too little so.

' Horses of thirty-five years of age are as common as men
of ninety, provided it be taken into account there are at
least fifty human subjects for every horse ; and, unquestion-
ably, a horse of forty-five is less rare than a man of a
hundred and ten.'

Death. — Death from natural causes in the horse is a
matter of rare occurrence ; it is seldom that an animal is
taken such care of that the tissues are worn out by age and
decay, and the breath of life passes gradually from the b< >dy :
by far the majority of horses meet either with a violent
death or one the result of disease.

Natural death is described as commencing either at the
heart, lungs, brain, or blood. Probably in the main most
cases of natural death may be attributed to a failure of the
heart's action ; but from what we know of the physiology of
the heart, respiration, and blood, it is very difficult to separate
these in discussing the causes of natural death, knowing as
we do how completely one is dependent on the other. The
cessation of the heart's action may be looked upon as the
termination of life.

We cannot enter upon the causes of death the result o\'
disease, excepting to notice the interesting fact that no
matter what the cause of death may be, horses seldom die
quietly ; by far the majority of them leave this world
in powerful convulsions, lighting or struggling to the last,
lying on their side, and galloping themselves to death.
Rarely, indeed, does one witness a quiet death in horses,

Growth, Decay, wnd Death. 401

and the subject presents a problem for the solution of the
physiologist.

Shortly after death rigor mortis appears (see page 252),
and within an hour or two tympany of the abdomen is
apparent, reaching such a degree in a few hours, that post-
mortem rupture of the diaphragm is exceedingly common.
The explanation of this disturbance is the enormous amount
of gas generated by vegetable food.

20

IXDEX.

Abdominal muscles in respiration, 80
Aberration, chromatic, 299

spherical, 298
Abomasum, 133
Absorbents. See Lymph
Absorption, 175, 183

from cellular tissue, 184

from conjunctiva, 185

of fats, 188

from intestines, 1S6

from peritoneum, 185

from the pleura, 185

of proteids, 189

from respiratory passages, 183

by the skin, 185

from the stomach, 133

of sugar, 189
Accommodation of the eye, 301
Achroodextrin, 104
Acid, acetic, 17, 121

amido, 12

benzoic, 12, 203, 21 6

bile. 13, 162

butyric, 17, 121

carbonic. See Carbonic acid

carbolic, 17, 151, 203, 214

cholalic, 162

fatty, 13, 17, 243

formic, 1 7

glycocholic, 1G2

hippuric, 12, 202

hydrochloric, in stomach, 121,
122, 130, 133

lactic, 17, 121, 122, 130, 133,
244

lactic, conversion of starch into,
129

lactic ferment, 126

lactic, in muscle, 243

lactic, in gastric juice, 133

nitrogenous, 12

organic, 1 7

oxalic, 17

phosphoric, 200, 218

Acid, sarco-lactic. 92, 244

stomach, 114, 121, 125, 130, 133

sulphuric, 203, 20 *i, 218

sulphuric conjugate, 168, 218

taurocholic, 162

uric, 201, 216
Age, old, 397

Air, changes in, during respiration,
83

composition of, S3

expired, comjjusition of, 93

inspired, composition of, 93

quantity breathed, 92
Albumen, 6

acid, 7

alkali, 7

conversion into peptones, 127

serum, 27

tests for, 10

in urine, 211

in urine, tests for, 212
Albuminoids, 10
Albumins, derived, 7
Albumose, 8, 127
Alimentary canal. See Intestines
Allantoic fluid, 385
Allantois, formation of, 385
i Amble, the, 338
Amides, 1 2
Amido acids, 1 2
Ammonia in mine, 206
Amnion, 382

Amylolytic action of saliva, 104
Amylopsin, 170
Amy lose, 15
Anabolism, 226
An electro tonus, 256
Animal body, composition of, 1, 220

expenditure of, 220, 222

income of, 220, 222
Animal heat, 237

regulation of, 239
Animal starch, 165
Ant i -albumose, 128

4(14

Index.

Anti-peptone, 127

Aorta, pressure in, 57
Apncea, 90

Arteries. See Circulation
Arterial pressure, 64
Asphyxia, 90
Astigmatism, "299
Auditory canal, 316

centre, 283

nerve, 316
Augmentation in nerve centres, 271
Auricles of heart, 48
Automatism in nerve centres, 270
Automatic action, 270

Benzoic acid, 12, 203, 316

Bile, 159

Bile acids, 13, 162

action on food, 164

analysis of, 159, 160

pigments, 161

quantity of, 163

reaction of, 159, 164

salts of, 159, 162

secretion of, 163

specific gravity of, 159

in urine, 213

use of. 163
Bilirubin, 161
Biliverdin, 161
Birth, 391
Bladder, urinary, 210

gall, 159, 163
Blastodermic membrane, 382
Blind spot, 304
Blood, 24

analysis of, 44

arterial, 40

buffy coat, 36

changes in, during respiration, 83

circulation of, 51

coagulation of, 35

compared with lymph, 178

composition of, 25, 44

corpuscles, 28, 33

distribution of, 42

effect on respiratory centre, 92

extractives of, 40

fibrin in, 37

ferment, 38

gases of, 12

haemoglobin in, 29, 30

laky, 29

liquor sanguinis, 26

physical characters of, 24

plasma, -Jii

plasma, carbonic acid in, 88

plates, 85

pressure, 57, • > I

proteios of, 26

Blood, quantity of, 12

salts of, 40

serum, 26

sugar in, 165

in urine, 21 1

velocity of, 68

venous. 40
Bloodvessels, 62. See Circulation

influence of nerves on, 71

tension in, t',."
Body, composition of, 1, 221

metabolic processes in. 226
Brain, circulation in, 7;!, 28*4

comparative weight of. 282

ventricles of, _' s 1

See Nervous System
Breathing. See Respiration
Butter, formation of. 394
Butyric acid, 121

Caecum, 14.">, 146

digestion in. 1 16-148
Calcium in urine, 205, 218
Calorimeter, 237
Canter, physiology of, 338
Carbo-hydrates, classification of. 14
Carbo-hydrates, formation of fat from.
229

source of energy. 165, 167
Carbolic acid, 17, 151, 203, 211
Carbon in the body, 1
Carbonates in body, 22
Carbonic acid in the air, :■:;
Carbonic acid in blond plasma, S8

diffusion of. from blood. 89

in expired air, 93
Caitilago nictitans, 311
Casein, action of rennin upon, 126, ;;'-' 1
Cellulose, 16, 129

digestion of, 16, 129, 1 16, 149,
150
Cellular-tissue, absorption from, Is 1
Centre ano-spinal, 275

cardio accelerator, 27'.'

cardio-inhibitory, 279

cilio-spinal. 27 1

for coughing, 278

for defiecation, 157

for dilating the pupil, 277

for erection, 27."

genito-spinal, 275

tor heat, 288

auditory, 283

olfactory, 288
parturition, 275
respiratory, 277

swallowing, 277
for sweating, 27'.*
tactile, 288
< f taste, 288

Index.

405

Centre, vasomotor, 275, '271'

vesico-spinal, 275

visual, 283

for vomiting, 277
Cerebellum, 2S1

effect of removal of, 283

functions of, 281
Cerebrum, 282

composition of, 282

convolution of, 2S2

functions of, 283

motor areas in, 282

sensory centres in, 283

ventricles of, 284
Chlorides in urine, 206, 217
Chlorine in body, 3, IS
Cholesterine, 16, 160, 196
Chorion, 386
Chyle, 181

analysis of, 182

colour of, 183

comparison with lymph, 181

gases of, 183
Chyme passage through small intes-
tines, 1-15

passage of, from stomach, 114

physical characters of, 144
Circulation, arterial, 69

of blood, 51

in brain, 2S4

capillary, 70

duration of, 69

ffetal, 389

influence of respiration on, 64, S2

mechanics of, 62

peculiarities in, 73

venous, 70
Colon, 148

absorption from, 150

condition of ingesta in, 1 18

description of, 148

digestion in, 149

fermentation in, 149

single, contents of, 150
Colostrum, 393

Conjunctiva, absorption from, 185
Contraction of muscle, 243
Co-ordination in nerve centres, 271
Copulation, act of, 378, 379
Cord, umbilical, 386

spinal. Sat Spinal cord
Cornea, 297
Corpora nigra, function of, 304

quadrigemina, 280

striata, 280
Corpuscles in blood, 28

colostrum, 393

destruction of, 34

number of, in blood, 29

Pacinian, 260

Corpuscles, third, 35

touch, 260

red, 28

white, 33, 34
Cotyledons, use of, 386, 391
Crura cerebri, 280
Currents in muscle, 247

nerves, 255
Cycle, cardiac, 51

Death, 400
Decay, 399
Decidua, 386
Defsecation, 156

centre for, 157
Deglutition, 99

influence of saliva on, 100
nervous mechanism of, 100
in ruminants, 100
voluntary control of, 99
Dentition, table of, 398
Depressor nerve, 72
Development of ovum, 382
Dextrin, 15
Dextrose, 14
Diaphragm, during rumination, 140

movements during respiration, 79
Diet. See Food
Diffusion in air of lung, 87
laws of, 86

of oxygen into tissues, 87
Digestibility of food, 234
Digestion, 96

changes, 104

amylolytic, 128, 149

of cellulose, 16, 129, 146, 149,

150
changes in gastric glands during,

123
in caecum, 146, 147, 148
in colon, 149

comparison of peptic and pancrea-
tic, 171
food, comparative time occupied
by different varieties of, 113,
115, 116
food, prehension of, 96
gastric juice, secretion of, 122,

124
of hay, 114
intestinal, 141

small intestines, 141
large intestines, 145
mastication, movements of jaw

during, 97
movements of stomach during,

114
of oats, 116
palate soft, use of, 99

40i;

Index.

Digestion, pancreatic, 170

(if peptones, 127

post-mortem of stomach, 134

stomach, 109

stomach acids, 121

stomach, effect of gastric juice
upon colour of food, 114

stomach, periods of, 129

stomach, in the pig, 133

stomach, in ruminants, 130
Draught, force exercised during, 354

physiology of, 353
1 hictus arteriosus, 390

venosus, 389
Duodenum, effect of pressure upon,
113

pyloric curve of, 113
use of, 1 1 .".
Dyspnoea, 90

Ear, cochlea of, 316, 318

internal, bones of, 316

internal, muscles of, 317

labyrinth of, 316

lymph of, 316

nerves of, 316, 318

organs of Corti, 318

otoliths, 318

semi-circular canals, 316, 318

tympanum, 317

vestibule, 316, 318
Ejaculation, mechanism of, 380
Electrotonus, 256
Embryo, development of, 382

nutrition of, 391
Eminetropia, 299
Endo-cardium, 49
Kudo. lymph, 316
Epidermis, 192

effect of grooming upon, 192
Epiglottis in deglutition, 99, 375
Erection, phenomena of, 378
Ervthrodextrin, 104
Eustachian tube, uses of, 317
Excretion, 197
Exercise, effect on muscles, 21:;

on respiration, 81, 91

on secretion of urea, 201

on production of heat, 240, 2 1 I

on production of carbonic acid, 98
Exertion, effect upon respiration, 9 1
Expiration, 79
Eye, 2'.' I

optical axis <>f, 298

pupil of, 303

&'<■ Sight
Eyeball, movements of, 306

muscles of, 306
Eyelashes, 312

Faeces, 153

analysis, 151, 155

amount of, 156

colour of, 154

composition of, 154

consistence of, 154

expulsion of, 156

meconium, 157

odour, 156
Fallopian tube, use of, 381
Fat, 13

a! sorption of, 188

in chyle, L81

emulsion of, 171

formation of. 229

saponification of, 172

unacted upon in stomach, 129
Fatigue, muscle, 250
Fatty acids, 13

nitrogenous matters, 12
Feeding, Ellenberger's views upon, 1 I'.'

effect of water after, 1 1 9

fluid in stomach after, 1 21 >
Ferments, 10

amylolytic, development of From
food, 128

blood, 38

cellulose, 129

cyto-hydrolytic. 129

gastric, 125, 129

of succus intericus, 143
Fibrin, 7

in blood, 37

ferment, 38
Fibrinogen, 38
Foetus. Set Embryo
Fietal circulation, 389
Food, absorption of, 186

acidity of, in stomach, 11 !

amount required, 232

acted upon by saliva, 103, 101
gastric juice, 127
bile, 164

pancreatic juice, 1 70
succus entericus, 143

appearance of in stomach, 119

arrangement of in stomach, 117.
118, 11'.'

digestibility of, 2:: 1

effect of gastric juice on, 111, 127

inorganic, 229

length of time occupied bj diges
tion of, [18, 115, lit!

nitrogenous, 227

non-nitrogenous, 228

passage from stomach of, l L8

prehension of, 96

time occupied in consumption of,

Foot, anti concussi

•hani-m 362

Index.

407

Foot, composition of, 356

elastic movements of, 366
expansion of, 366
the frog, 363
laminae of, 358
lateral cartilages of, 365, 368
moisture in, 355
navicular bursa of. 369
physiological shoeing, 370
sole of, 360

vascular mechanism of, 357
the wall, 363
Foramen ovale, 390

Gall bladder, 159, 163
Ganglia, 259

cardiac, 60

Gasserian, 285

spinal, 261

structure of, 260

sympathetic, 293

trophic influences of, 293
Ganglion cells. 260
Gallop, physiology of, 347
Gas, blood, 42
Gases, absorption of, by fluids, 85

dissociation of, 89

in body, 18

intestinal, 153

partial pressure of, 85-89

of respiration, 95

of stomach, 135
Gastric juice, 124

acids of, 114, 121, 125

action of, 127

ainylolytic action of, 12S

colour of, 125

composition of, 124

effect upon food of, 114, 127

mucin in, 125

pepsin in, 125

rennin in, 125

of the pig, 133

secretion of, 122

specific gravity of, 125
Generation, 377
Germinal vesicles, 382
Gestation, period of, 390
Glands, gastric, 122

gastric changes in, during diges-
tion, 123

Harder ian, 312

fundus, 122

mammary, 292

thymus. 77

pineal, 77

pituitary, 77

pyloric, 123

salivary, 101

sebaceous, 195

Glands, small intestines, 142

sweat, 193

changes in cells of, 195

thyroid, 77
Glands, vascular, 76
Globin, 33
Globulin, 6

Glottis, movemeuts of, 182
Glucose, 14

test for, 14
Glycerine, 17
Glycin, 162
Glycocoll, 162
Glycogen, 15, 165

in muscle, 166, 167, 243

source of, 167

use of, 167
Graafian follicles, 380. 381
Growth, 395

rate of, 395
Gums, animal, 16
Gustation. See Taste
Gutteral pouches, 317

Hannatin, 33

Haematoblasts, 35

Hamiatoidin, 33, 161

Hamiatoporphyrin, 33

Hiemin, 33

Hiemochromogen. 33

Haemoglobin, amount of in body, 31

in blood, 29

carbonic oxide, 33

compounds of, 32

nitric oxide, 33

union with oxygen, 87
Hair of skin, 192

shedding of, 192
Hay, digestion of, 114
Hearing, nerves of, 316, 318

physiology of, 315
Heart, 47

capacity of, 56

daily work of, 57

fibres of, 49

ganglia of, 60

movements of, 52, 54

nervous mechanism of, 57

position of, 48

pressure within, 56

revolution of, 51

sounds of, 54

valves of, 48, 50, ">:;
Heat, animal, 237

amount of, 239

loss of, 238

regulation of, 239

sources of, 237

unit, 237
Hemi-albumose, 128

40S

Inch

Eemi-peptone, 127

Hippomanes, 385
Hippuric acid, 12, 202

in urine, tests for, 21b
Hydrochloric acid in stomach, 121,

"122
Hydrogen in body, 2
Hypernietropia, 300

Images, retinal, 298

Income and expendituie, 220, 222.

224
Indigo, 13

in urine, 21 ti
Indol, 13, 151
Infusoria in stomach, 152
Inhibition in nerve centres, 271
Inhibitory nerves, 59, 289
Inosite, 14
Inspiration, 78
Intelligence, comparative, of animals,

282
Intestines, absorbent surface of, 187

absorption from, 186

circulation in, 74

digestion in, 141

gases of, 153

large, 145

caecum, 145, 14ti

colon, 148

duration of digestion in, 149

nervous mechanism of, 157

putrefactive processes in, 150, 152

reaction of contents of, 143

small, 141

glands of, 142
Iron n body, 3, 23
Iris, the, 303

action of light upon, 303

colour of, 303

movements of, 303
Irritability, 24 5, 25s

Joint, elbow, 326

fetlock, 327

foot, -"b:>

hip, 32i)

hock, 324

knee, 32b

shoulder, 32b

stifle, 325
Joints, synovia of, 328
•lump, the, 348

Katabolism, 226
Kathelectrotonue, 256
Kicking, physiology of, 348

Kidney, function <,f, 197
nci \ ■• supply of, 198
structure of, l!'7

Labyrinth of ear, 316

Lact.-als, 183, 186, 188

Lactic acid in stomach, 121, 122

Laminae arrangement of. 360

foot, use of, 358
Lanolin, 196
Larynx, during deglutition. 99

movements of. 37 I

muscles of, 371

nerve supply of, 3 75

physiology of, 373

ventricles of, 373, 376

vocal cords of, 37-, 37 1, 376
Lecithin, 4, 34, 160
Lens, convex, passage of light through,
296

crystalline, 302

optical, centre of, 296

principal axis or, 296

refraction in, 297

secondary axis of, 296
Leucin, 5, 168, 170, 201
Leucocytes, 33
Levers, theory of, 320
Levulose, 14
Ligaments, check, 328

suspensory, 327
Lips. iSee Prehension
Liver, 159

destruction of red corpuscles in,
36

nervous control of glycogenic
function, 1 1 > 7

conversion of leucin into urea in.
16S

summary of changes in. 168

uses of, 168
Locomotion, the amble, 338

apparatus of, 320

buck jumping, 350

the canter, 338

centre of gravity, 329

check ligament, use of, 328

daily work of horses, 350

draught, physiology of, 353

the gallop, 347

joints, structure of, 323

the jump, 3 18

kicking, .(48

lying down, 350

muscles, action of, 321, 322

rearing, •". 18

rising, 350

standing, act of, 330

suspensory ligament, use of, 327

the trot, 388

\ elooity of paces, 351
the walk, 333

tin- weight carried, 352
weight on the limb-. 829

Index.

40 V)

Lung, position of, 78

respiratory changes in. Set Res-
piration

Lying down, act of, 350
Lymph, 175

analysis of, 177

analysis of, compared with that of
blood, 178

cells, 176

comparison of, with Chyle, 181

gases of, 176

movements of, ISO

quantity of, 17S

reaction of, 176

salts of, 1 76

spaces, 175

specific gravity of. 176

transudation of, 179
Lymphatic glands, 180, 186, 189

Making and breaking currents, 251;
Magnesium in body, 22

in urine, 205, 218
Malpighian bodies, 198
Maltose, 15, 104
Mammary gland, 392
Mastication, 97

muscles of, 98, 100
Meconium, 157
Medulla, 275

centre for deglutition in, 100

centres in, 276

centre for rumination, 140

cerebella, tract in, 276

columns of, 275

decussation of fibres in, 273, 276

function of, 280

grey matter of, 276

pyramidal tract in, 276

respiratory centre in, 91

tracts in, 266

vaso motor, centre in, 72
Metabolism, 226
Methsemoglobin, 32
Micturition, 210

Milk, action of stomach, juice upon,
129

composition of, 393

globules, 394

proteids of, 394

salts in, 18

uterine, 391
Movement, coordination of, 281
Mucous, secretion of, by stomach, 112,

120, 122, 125, 126
Mucus in urine, 214
Muscle, acid of, 243, 244

cardiac, 49

composition of, 242

contraction of, 243

Muscle, currents, 246

curves, 248

elasticity of, 250

excitability of, 245

fatigue, 250

glycogen in, 166

laryngeal, 374

nervous mechanism of, 245

pharyngeal, 99

respiratory, 80

rigor mortis in, 252

skeletal, proportion in body, 212

tetanus of, 249

varieties of, 242

exertion, effect of, upon nutrition,
232
Muscular system, 242

work, laws of, 251
Myopia, 299
Myosin, 243

Nasal chambers, 82, 313
Neighing, physiology of, 376
Nerve cells, 260
endings, 260
centres, augmentation in, 271

automatism in, 270

co-ordination in, 271

inhibition in, 271

radiation of impressions from,
270

transference in, 270

terminations, 260
Ner\ es, 254

the bladder, 211

bloodvessels, 69, 71, 267, 279,

291
chorda-tympani, 105, 106
cranial, 2S4
cardiac, 57
decussation of, 295
depressor, 72
effect of division of, 259
effect of stimuli on, 259
eighth pair, 287
electrical phenomena of, 255
of the eyeball, 285, 286
facial, 286
fifth pair, 285
glosso-pharyngeal, 287
of hearing, 287, 316, 318
inhibitory, 59
intestinal, 157
irritability of, 258
of kidney, 198
laryngeal, 288, 375
lingual, 290
of mastication, 285
motor-oculi, 284
<>f muscle, 245

410

I nth.

N< rvea, nutrition <>f, 259

of thr oesophagus, 289

olfactory, 313

optic, 295

of pancreas, 1 71

pathetic, 285

pharyngeal, 287, 288

phrenic, effect of division of, 91

pneumogastric. 58, 92, 288
branches to intestine*, 157
branches to stomach, 141
influence on circulation, 72
influence on heart, 58
summary of functions of, 289

of respiration, 289

sensory roots, function of, 2*57

seventh pair, 286

sixth pair, 286

of the skill, 191

spinal, 266
accessory, 290

'splanchnic, 141

of stomach, 140
in rumination, 140

sympathetic, influence! on heart,

of taste, 287, 314

of the tongue, 286. 290, 287

vaso-motor, 69, 71, 267, 279,
291

velocity of impulses through,
259
Nervous system, 253

etrebrum, the, 281, 282

corpora quadrigemina, 280

corpora striatn, 280

crura cerebri, 280

medulla oblongata, 275

pons varolii. 280

reflex action in. 268

spinal cord, 260

sympathetic system, 290

thalami optici, 280
Xitrogen in body, 2
Nitrogenous acids, 12

bodies, 1
Non- nitrogenous bodies, 6
Nostrils, movements of, 82
Nutrition, 220

amount of food required for, 232

effect of nitrogenous food upon,
227

effect of inorganic food upon, 229

effect of muscular exertion upon,
232

i [feet of non-nitrogenous food

upon, 248
effect of starvation upon, 230
effect of Income and expenditure

on, 220. 222. 221, 225

Nutrition lie embryo, 391

of nerves, 259
Nutritive ratio, 235

Oats, digestion of, 116, 120
Odour, perception of, 313
(Edema-, cause of, 1 79. 1 B 1
(Esophageal groove in rumination,

138
(Esophagus dining deglutition, 99

during rumination, 101

nerve supply of, 288

Btfucture of, 100
Oil, olein, 13

palmitin, 13

stearin, 13

emulsitica tion of, 170, 189

saponification of, 170
Old age, 399
Olfactory lobes, 313

nerves, 313

sensations, 313
Omasum, 132

condition of food in, 132

function of, 132

reaction of. 133
Ophthalmoscope. .'105
Optic nerve, 295
Orbit, 294

: Organ of Jacobson, 313
Organism, constituents of, 1
Ovum, 380

changes in, 382

development of, 382

impregnation of, 382
Ovary, 380
Oxygen, diffusion of, into tissue-, 87

in body. 2

of inspired and expired air, 93

union with haemoglobin, 87

uses of. in tissues, 88

absorption of, by blood, not
according to law of pressure,

Palate, soft, during deglutition, t.>'.'

nerves of, 100
Pancreas, 159, 169

changes in colls of, 172

nervous mechanism of, 171
Pancreatic digestion compared with
that of stomach, 1 7 1

juice, 169

action on plot. ids. 170

action on tats, 170
action on staieli, 1 71
amount of, 173
analysis of, 169

emulsifj Lng action of, 17 1
ferments of, 170, 172

Index.

41

Pancreatic juice, salts of, 170

specific gravity of, 169
uses of, 170
Papillae of tongue, 31 f>
Parotid gland, 101
Parturition, 391
Penis, circulation in, 74
Penis, erection of, 378
Pepsin in gastric juice, 12f>

action of, 126
Peptone, 7, 8, 127
Pericardial fluid, 2
Peritoneum, absorption from, 185
Perspiration, 193
Phaiynx, nerves of, 100

during deglutition, 99
Phenol, 17, 151, 203, 214
Phosphates in body, 3, 22
Pigments, 11
Pigments, bile, 161

urinary, 204
Pineal gland, 77
Placenta, 386

Pleura, absorption from, 1S">
Plexus, gastric, 289
Pneumogastric nerve, gastric branches
of, 141, 157

nerve in rumination, 140

nerve, respiratory fibres of, 91
Pons varolii, 280
Portal vein, 389
Potassium in body, 19

urine, 205
Pouches, guttural, 317
Pregnancy, duration of, 390
Prehension of food, 96

of liquid, 97
Prostatic fluid, 378
Proteids, 6

absorption of, 189

decomposition of, 151

gastric digestion of, 130

intestinal digestion of, 143

of sweat, 193

tests for, 10
Proteose, 8
Ptyalin in saliva, 104
Puberty, period of, 381
Pulse, 67

wave, 67
Pupil of the eye, 303 .
Purple visual, 306
Putrefaction in intestines, 150, 152
Pylorus, duodenal curve of, 113

of stomach, 113
Pyramidal tracts, 265

Ratio, nutritive, 235
Rearing, physiology of, 348
Rectum, absorption from, 150

Rectum, contents of, 150

reaction of, 150
Reflex action, 268

as a motor act, 269

as a secretory act, 269
Refraction, 295
Renal capsule, 77
Rennin in gastric juice, 125, 126

action of, on casein, 126, 394
Respiration, 78

carbon of, 93

carbonic acid of, 88

centre for, effect of blood upon,
92

centre for, in medulla, 91

changes in air during, 83, 93

changes in blood during, 83

chemical aspects of, 85

during rumination, 81

effect of muscular exertion on, 81,
94

gases of, 84, 94, 95

influence on circulation, 64, 82

movements of diaphragm in, 79

movements of nostrils during, 82

muscles employed in, 80

nervous mechanism of, 91

number of, 81

oxygen absorption during, 87

pressure in trachea during, 81

quantity of air breathed, 92, 94
Respiratory passages, absorption from,

183
Respiratory quotient, 84, 93
Reticulum, function of, 132

reaction of, 131
Retina, the, 304

action of light on, 295

corresponding points of, 309

rods and cones of, 306
Rigor mortis, 252
Rising, act of, 350
Rumen, 130

cellulose digestion in, 132

function of, 132

muscular action of, 131

reaction of, 131

use of, 131
Rumination, 138

effect of saliva on, 103

muscular assistance in perform-
ance of, 140

nervous mechanism of, 140

(esophageal groove in, 138

respirations during, 81

salivary secretion during, 140

Saliva, 101

action on starch, 103, 104
amylolytic action of, 104

412

rndex.

Saliva, analysis of, 102

characters and properties of, 1-10
during deglutition, 100
effect of rumination on, 103
effect of fasting on secretion of,

io:;

gases of, 102

-lands producing, l«il

nervous mechanism concerned in
secretion of, 105

physical properties of, 10-'!

ptyalin in, 104

reaction of, 102

secretion of, 101, 105, 114

specific gavity of, 102

in stomach, 120

unilateral secretion of, 103

use of, 103
.Salivary glands, mucous and serous.
101, 107

changes in cells of, 107
Salts, bile, 162

in body, IS

in milk, 18

various in nutrition, 229
Schneiderian membrane, 314
Sebaceous secretion, 195
Sebum, 195
Secretion, gastric juice, 122

of saliva, 105

changes in albuminous cell-, 108

changes in mucous cells, 10s

by cells of stomach, 1 22

of pancreatic juice, 169

of bile, 159

of urine, 209

of sweat, 193

of milk, 392

of semen, 377
Segmentation of ovum, 382
Self digestion of stomach, 134
Semen, chemical composition of, 377

emission of, 380
Semilunar valves, 51
Semicircular canals, use of, 318
Sensations special, auditory, 316

olfactory, 312

of taste, 314

visual, 294
Senses, 294

touch, 1!H
Sensibility, recurrent, 2(17
Serous cavities, 181, 185
Serum, 26

albumen, 4, 6, 26
Sexual desire, 380

Shoeing, physiological, 370
Sight, 294

accommodation, 301

astigmatism, 299

Sight, cartilago nictitans, 311

chromatic aberration, 299

cornea refraction, l'!<7

corpora nigra of iri-, :;04

crystalline lens, 302

emmetropia, 299

fundus, appearance of, 305

hypermetropia, 300

the iris, 303

katoptric test, 302

lens, refraction of, 2 '.'7

movements of eyeball,

myopia, 299

muscles of eyeball, 306

optical axis of the eyi _

refraction, 295

the retina, 304

retina, corresponding points of,
309

secretion of tears, 312

spherical aberration. 298

tapetum lucidium, 304

vision, binocular, 307

vision, monocular, 307

\ isual angle, 298

visual purple, 306

yellow spot, 306
Silicon in body,
Sinuses, facial, use of, 31 1

lymph, 175
Skatol, 13, 151
Skin, 191

absorption by, 185

area of, 191

as an organ of touch, 191

hair of, 192

nerve endings in, 191

respiratory function of, 196
Sleep, 328, 333, 350
Smegma, 195
Smell, in choice of food, 96

seat of, 312

turbinated bones, use of, 313
Sodium in body. 19

glycocholate and taurocholate, 1 62

in urine, "206
Solar plexus, 2!>1
Sound, 316
Spermatozoa, :i77

action of, on the ovum, 382
Spermatic fluid, 377, 878, 379, 380
Sphygmograpb, 66
spinal cord, 260

arrangement of, 268

centres in, 27 I

conducting paths in, 272

connection with sympathetic
system, 268

decussation in, 272

effect of injuries upon, 27:'.

Index.

413

Spinal cord, functions of, 272

ganglia on superior roots, 261
superior and inferior roots of, 261 J
tracts in, 264

variations in shape of, 261
white and grey matter in, 263

Sphincter ani, 156

Splanchnic nerves, 292

Spleen, 76

corpuscles in, 76

Standing, act of, 330

Starch, 15

action of pancreatic juice on, 171
action of saliva on, 103, 104
amylolytic action of gastric juice

on, 128
conversion in small intestines, 143
conversion in stomach, 130

Starvation, 230

Steapsin, 170

Stearin, 13

Stercobilin, 165

Stomach, absorption from, 133
acids, 121, 122, 130
acidity of contents, 114, 120
action upon fats, 129
amylclytic changes in, 128
appearance of food in, 119
arrangement of food in, 117, US,

119
bile in, 120

capacity of horse's, 111
cellulose fermentation in, 129
diastatic ferment in, 129
digestion compared with pan-
creatic, 171
digestion in, 109
digestion of oats in, 120
digestion in ruminants. 130
digestion effected by pressure on

duodenum, 113
fluid in, after feeding, 120
gastric juice, secretion of, 122
gases of, 135
glands of, 122
gland cells of, 122
hay digestion, duration of, 114
horse's, points in structure of, 113
infusoria of, 152
movements of, during digestion,

114
mucous membrane of, in horse, 112
muscular coats of, in rumination,

131
nervous mechanism of, 140
passage of chyme from, 114
passage of food from, 118
passage of water to caecum, 145
peptone in, 127
periods of digestion in, 129

Stomach, of the pig, 133

proteid digestion of, 130

pyloric orifice of, 113

in ruminants, 130, 140

secretion of mucin by, 112, 120,
122

self digestion of, 134

starch conversion in, 130

st.ucture of, 112, 113

voinition with rupture of, 137
Succus cntericus, 142

analysis of 142

function of, 143
Sugar, absorption of, 189

course taken by, during diges ion,
165

in the blood, 165

in urine, 213

its conversion into glycogen, 166

its value in diet, 234

used up by muscle, 166
Sulphur in body, 2, 22

in urine, 203, 206
Suspensory ligament, use of, 327
Swallowing, mechanism of, 99
Sweat, 193

amount of, 193

analysis of, 193

glands, 193, 195

glands, action of pilocarpin on,
194

reaction of, 193

specific gravity of, 193
Sweating, effect on condition, 192

nervous mechanism of, 194
Sympathetic system, 290
Sympathetic system, connection with
spinal cord, 268, 290

system, ganglia of, 291, 293

system, vaso-motor nerves of, 291

system, visceral branches, 292
System, muscular, 242

nervous, 253
Systole, 51

Tapetum lucidum, 304
Taste goblets, 315

nerves of, 314
Tears, secretion of, 312
Teeth, 97, 98, 398

Temperature, distribution of, in the
body, 241

regulation of, in the body, 239
Tetanus of muscle, 249
Thalami optici, 280
Thorax, 78
Thymus gland, 77
Thyroid gland, 77
Tongue of horse, 96

nerves of, 100

414

Index.

Tongue of ox, 96

papillae of, 315
Touch, 318

Trachea, pressure in, daring respira-
tion, 81
Tracts in cord, 272

medulla, 27 b'
Transudation of white corpuscles?, 3 I

lymph corpuscles, 17b"
Tricuspid valves, 48, 50
Trot, physiology of, 338
Trypsin, 170
Trypsinogen, 172
Tympanum of ear, 3 17
Tyrosin, 9, lb'8, 171

Umbilical cord, 386
Urea, 201

conversion in the liver, 168

in urine, tests for, 215
Uric acid, 201

conversion in liver, 168
Urine, 197

abnormal constituents in, 211

analysis of, 207, 208

ash analysis of, 204

of the calf, 208

clinical examination of, 211

colour of, 200

colouring matter of, 204

composition of, 198

of horse, 199

odour of, 200, 207

of the ox, 207

physical characters of, 200

of the pig, 209

quantity of, 199, 207, 208

reaction of, 199

secretion of, 209

sheep, 208

solids of, 201

specific gravity, 199

testing of, 21 1

Urobilin, 16',, 204
Uterine milk, 391
Uterus during intercourse, 379

Vagus. See Pneumogastric Nerves
Valves of heart, 48, 50

of lacteals, 183

of lymphatics, 180

veins, 70
VasQ-motor, nerves, 71, 29]

centre, 72, 279
Wins See Circulation

of foot, 75, 358
Velocity of paces, 351
Ventricles of brain, 284

of heart, 48
Vestibule of ear. 316
Vision. Sc< Sight
Vocal cords, 373, 374, -1 7»;
Voice, the, 372

coughing, 376

neighing, 375

sneezing, :J76

sound, production of, 37:;

yawning, 376
Vomiting, 136

in the horse, bio, 137

in ruminants, 136

with ruptured stomach, 137

Walk, physiology of, 3:;:;

Water in body, 18

passage of, to caecum, 145
after feeding, effect of. 119

KUenbei

gers vu-w upon, ll!<

Weight carried by horses, 352

increase during growth, 396

Work of horses, 350

Pawning, 376

yelk, segmentation of, 385

-/ C«>.i, A7«v /('/.', '/,»/« Street, Strand.

>

WILLIAM R. JENKINS'

Veterinary Catalogue.

1893.

(*) Single asterisk designates New Book.

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Agassiz and Gould. "Outline of

COMPAKATIVE PHYSIOLOGY." $1.50

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American Trotting Association,
and the names of all horses with
records of 2 :30 or better, trotting
or pacing to the close of 1887.
Price i.oo

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HAYES. "Soundness and Age of

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Hayes. "The Points of the House."
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HA YES. "Illustrated Horse Break-
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12mo, cloth, illustrated

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1.25

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C. V. S. 12mo, cloth

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Cloth 10.00

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Sheep

HOLCOMBE. ' Laminitis." A

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LIAUTAIID. "Yiide Mecum of
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LIAUTAIiD. "Translation of
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Martin. " The Family Horse."
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Marvin. "TBABONa the Troth n«.
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Maudsley. "Highways ihdHobses."

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MF n>) i: I \. "Anatomj of the

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Ml .1 ) in: iv. « Comparative
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M. D., V. S. It tells how to
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Paper $0.26

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Navin . " The Explanatory Stock
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Percival. Works by William Per-
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" Hippopathology." A Systematic
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Roget. "Animal and Vegetable
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Rolleston. " Forms oi- Animal
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Russell. " Horse - Keeping for
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Rush, Dr. John. "Veterinary
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Sanders. "Horse Breeding." Being
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Schseffer. "New Manual of Homceo-
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<*) STRANGE WAY. 'Veterinary
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Struss. " Ring Riding." Being a
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