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A TEXT-BOOK OF
V\ COMPARATIVE PHYSIOLOGY

FOR STUDENTS AND PRACTITIONERS OP
CoSpARATIVE (VETERINARY) MEDICINE

W E S L E Y , M I L L S

or AitnuL pH»»iou)OT, no.

WITH 476 ILLVSTBATIOm

vc^

NEW YORK
D APPLETON AND COMPANY

LONDON: CAXTOM H008B, PATEKNOSIBB SdOAEB

1890

COPTBIOHT, 18fl0,

Bt d. appleton and company
AH rights reserved.

PREFACE.

Some years of contact with students of comparative (com-
monly called veterinary) medicine, and a fair knowledge of
the actual needs of the practitioner of this department of the
medical art, have convinced me that the time has fully come
when the text-books of physiology provided for students of
human medicine, and which the former classes have hitherto
been compelled to use, should be replaced by works written
to meet their special wants and possibilities. In fact, so dif-
ferent from man are most of the animals which the veterma-
rian is called upon to treat, and therefore to understand, in
health as well as in diseac.,that only the absence of suitable
works of a special character can justify the use of those that
confessedly treat of *man alone.

Unfortunately, till within the past year the English-speak-
ing student of comparative medicine has been without a
single work in his own language of the special character re-
quired. Within that period two have appeared— the excel-
lent but ponderous Physiology of. the Domestic Animals, by
Prof. Smith, and my own Text-Book of Animal Physiology.
It has, therefore, occurred to me that a somewhat smaller
work than the latter, embodying the same plan, but with
greater specialization for the domestic animals, would com-
mend itse:. "^o both the students and the practitioners of
comparative i^edicine. In my other work I have endeavored
to set before the student a short account of what has been
deemed of most importance in g6neral biology; to furnish a
full account of reproduction; to apply these two depart-
ments throughout the whole of the rest of the work ; tobnng

COMPARATIVK FlIYblOLOUY.

before tho studoiit enough of comparative physiology in Hh
widest HuiiHe to improHs liim witli tlio imijorlunce of recog-
nizing tluit iill medicine like nil science is, when ut itn best,
eompurutive ; and to show timt tho doctrines of evolution must
apply to physiology and medicine as well as to morphology.

Comparative medicine is essentially broad. It will not do
to measure all tho animals tho veterinarian is called upon to
treat by the equine standard. This has been too much the
case in the past for the good even of the horse himself ; while
otheis, that fall to the practitioner's care, like tho dog, have
been much neglected and misunderstood.

There is no more reason, theoretically, why tho veterinn-
rian should overlook man than that tho practitioner of human
medicine should disregard the lessons to be learned from our
domestic animals ; hence the attempt has been made to exclude
references to the human subject from tho volume. Tho stu-
dent of comparative medicine may learn, by careful observa-
tion on himself, to understand much that would otherwise
never become realized knowledge; and this conviction has
been at the root of a large part of the advice given the stu-
dent as to how to study throughout tho work.

All that relates to reproduction and breeding is, in "these
days of vast stock interests, of so much practical importance,
that on this account alone the fullest treatment of the subject
seems justifiable. But, apart from this, it has become clear to
me that function as well as form can be much better and
morfe easily grosped when embryology is early considered.
This I have tested, with the happiest results, with my own
classes. Usually those taking up physiology for the first
time are, of course, not expected to master all the details of
embryology, but the main outlines prove as helpful as inter-
esting ; nevertheless, it is my experience that a considerable
number of first-year men are not content to be confined to
the merest rudiments of this or any other department of
physiology.

That a work written on so new a plan as ray Text-Book
of Animal Physiology should have met with a reception al-
most universally favorable, both in Britain and America, in

PREPACK.

>logy in its
CO of rocoj?-

ttt itH ItUHt,

liilioii niuHt
•rphology.
will not do
led upon to

much thi'
iself ; while
e dog, hnvi!

lie voterinii-
irof human
}d from our
e to exclude
. The 8tu-
tul observa-

1 otherwise
viotion has
en the stu-

80 rihort a space of time, encouragos me to ho|)e for one
equally favorable for this book, which im ollored to a pru-
fuHHiun from which I look for great things in the interests
both of maik and the lower animals within the next few
years. The time has certainly come when medicine must
leave the narrow ruts within which it has been contined, and
become essentially comparative. To hasten that consumnui-
tion, so devoutly to be wished, has been the object with which
both my earlier ami the present work have been written. Un-
less the student is infused with the broad comparative s])irit
in the earliest years of his studios, and guided accordingly,
there la no sure guarantee of tlnal success in the widest sense.
My publishers again deserve my thanks for the efforts
they have made to present this work in their best form.

Weslky Mills.

FHVSIOUMUCAL liAHURATOBY, MoGh^L UNIVGRRITV,

Montreal, Canada, Augu»t, 1800.

is, in these
mportance,
the subject
me clear to
better and
considered,
ith my own
r the first
e details of
'ul as inter-
onsiderable
confined to
artment of

Text-Book
ception al-
Vmerica, in

'?S!?sr

CONTENTS.

OiNIRAL DlOLOOT 1

Introduction 1

Tabular Htatcracnt of thu subdlviRions of Biology ... 4

Tlio Cell ,. . »

Animal and vegetable cells 8

Structure of celU

Cell-contentfi 1

The nucleus "... 8

TIbsucb 8

Summary 9

Unioellular OrganUros (Vegetable) 9

1. Yea»t »

Morphological 9

Chemical tt

Phyiiologtoal 10

Conclusions , . . 10

2. Protococcua 11

Morphological IS

PhyBiological 13

Conclusions 12

Unicellular Animals . ..,,..... 18

The proteus animalcule 18

Morphological 18

Physiological 18

Conclusions It

Parasitic Orgaulams . IS

Fungi . . . . . .IB

Huoormucedo 17

The Bacteria 18

Un'.nelluiar Animals with Differentiation of Structure ... 21

The bell-animalcule 21

Structure 21

Functions 88

Vlll

COMPARATIVE PHYSIOLOGY.

PAOB

Multicellular Organisms • • . ^»

Tlie f resli-water polyps '^^

Tlie Cell reconsidered ^'

The Animal Body— au epitomized account of the functions of a mam-
mal 28

Living and Lifeless Matter— General explanation and comparison of

their properties ^'^

Classification of the A !iimal Kingdom . . . . '. .34

Tabular statement ^*

Man's place in the animal kingdom 36

The Law of Periodicity or Rhythm in Nature— Explanations und

illustrations 37

The Law of Habit " .... 41

Its foundation *^

Instincts • • . ■ *'

The Origin of the iorras of Life *2

Arguments from :

Morphology *^

Embryology ^^

Mimicry . . . . • *'^

Rudimentary organs . ^^

Qeographical distribution *^

Paleontology **

Fossil and existing species . . • • • • • *•*

Progression

Domesticated animals * '

Summary

RgPRODCOTIOS

General . . • "l

The ovum ' ' ' ^t

The origin and development of the ovum . . > • . 67

Changes in the ovum itself . . . . . • • "8

The male cell **

The origin of the spermatozoon ''*

Fertilization of the ovum *'

Segmentation and subsequent changes . . . . , . . 64

Thegastrnia **

The hen's egg -I!

The origin of the fowl's egg '®

Embryonic membranes of birds •*

The fcBtal (embryonic) membranes of mammals .... 78

The allantoic cavity . ow

The placenta

The discoidal placenta .88

CONTENTS. ix

PAOB

The metadiscoidal placcntn ..,.,.. 84

The zonsry placenta 80

The diffuse placenta 89

The polyootyledonaty placenta 89

Tabulation of placentation 90

Hicrosoopic structure of the placenta 90

IlluBtrations 91, 98

Evolution ~ . . 98

Summary 93

Thb Detklopment or the Embryo Itself 96

Germ-layers 98

Origin of the vascular systeai 102

The growth of the embryo . . . . . . 105

Development of the Vascular System in Vertebrates . 108

The later stages of the fcetal circulation 109

Development of the Urogenital l:3y stem , . . . .112

The Physiological Aspects of Development 118

Ovulation 120

Oestrum 121

The nutrition of the ovum 123

The foetal circulation 126

Periods of Gestation . ' 127

Parturition 128

Changes in the circulation after birth 129

C!oitu8 129

OcoANic Evolution reconsidebed W

The Cbemioal Constitution or THE Animal Boot . . U2

Proximate principles 144

General characters of proteids 144

Certain non-crystalline bodies 146

The fats • M6

Peculiar fats 146

Carbohydrates • • !*•

Kitrogenons metabolites W

Non-nitrogenous metabolites 147

PuTStOLOaiCAL ^»IARCH AND PhYSIOLOOIOAL REASONING . . . 148

Tub Blood IM

Comparative IM

Corpuscles 166

Histoiy of the blood-cells 168

Chemical composition of the blood 140

Composition of serum 161

Composition of the corpuscles 162

The quantity and diatribution of the blood . . .168

X COMPARATIVE PHYSIOLOGY.

PAflB

The coagulation of the blood .168

Clinical and i)athologioal 167

Summary 169

The Contractile Tissurs 171

General 171

Comparative 172

Ciliary morementB .178

The irritability of muscle and nerve '176

Tbk Graphic Method and the Study or Muscle Pbtbioloot . .176

Chronographs and various kinds of apparatus . . .176

The apparatus used for the stimulation of muscle . . . . 179

A single muscular contraction 186

Tetanic contraction 187

The muscle-tone 189

The changes in a muscle during contraction 189

The elasticity of muscle 189

The electrical phenomena of muscle 191

Chemical changes in muscle 192

Thermal changes in the contracting muscle . . . . .196

The physiology of nerve 196

ElectrotonuB 196

Pathological and clinical 197

Electrical organs 197

Muscular work 198

Circumstances influencing the character of musular and nervous ac-
tivity 199

The influence of blood-supply and fatigue 199

Separation of muscle from the central nervous system . 201

The influence of temperature 801

Unstriped muscle 208

General 202

Comparative 802

Special considerations 808

Functional variations 804

Summary of the physiology of muscle and nerve ... 205
Till Nertohs Stbtem— GnncRAL Comsidbratiohs .... 208

ExperimenUl .810

Automatism 811

Condudons ....*. 812

Nerroos inhibition 218

Thi Oircclation of the Blood 214

General 814

The mammalian heart 816

Circuiatioa in the mammal 819

ous ac-

PAfll

168
167
169

171
172
178
■ 176
176
176
179
185
187
189
189
189
191
192
196
196
196
197
197
198

199
199
201
201
202
202

ao2

208
204
206
208
210
211
212
212
214
214
216
819

CONTENTS. ^

PAOB

The action of the mammalian heart 222

The velocity of the blood and blood-pressure . . . . .228

General . . . ^ 228

Comparatire 224

The circulation under the microscope 224

The characters of the blood-flow 226

Blood-pressure 227

Thb Heart . 281

The cardiac movements 231

The impulse of the heart 232

Investigation of the heart-beat from witliin 238

The cardiac sounds . . 234

Causes of the sounds 236

Endo-cardiac pressures 236

The work of the heart 288

Variations in the cardiac pulsation 289

Comparative 240

The pulse 241

Features of an arterial pulsc-traoing . . .242

Venous pulse 244

Pathological . . _ 244

Comparative . . . , 244

The beat of the heart and its modifications 248

The nervous system in relation to the heart 249

Influence of the vagus nerve on the heart 268

Conclusions 267

The accelerator nerves of the heart 268

The heart in relation to biood-pressuro 260

The influence of the quantity of blood . , . . .261

The capillaries 264

Special considerations 266

Pathological . , .266

Personal observations . . see

Comparative . . , . . . . 267

Evolution. . 268

Summary of the physiology of the circulation . . .269

DioBsnoN OF POO0 . 2Y4

FoodstuJTs, milk, eta ■" . .274

Embryoiogical jgo

Comparative . . . ... . 286

Structure, arrangement, and significance of the teeth . 286

The digestive juices . . . • 297

Saliva and its action 297

Secretion of the diiferent glands 298

tr-s^s^-XiESSi?-^^

xii COMPARATIVE PHYSIOLOGY.

PAOI

Comparative • < 298

Gastric juice ^'^

Bile 801

General 301

Pigments 802

Digestive action 808

Comparative 304

Pancreatic secretion 806

SuccuB entericus 807

Comparative 810

Secretion as a physiological process 811

Secretion of the salivary glands '811

Secretion by the stomach 816

The secretion of bile and pancreatic juice 316

The nature of the act of secretion . . . . 818

Self-digestion of the digestive organs . . . . 888

Comparative 824

The alimentary canal of the vertebrate 881

The movements of the digestive organs 882

Deglutition 338

Comparative 386

The movements of the stomach 836

Comparative . . . • 887

Pathological • • .887

The intestinal movements . . . . • • 837

Defecation 388

Vomiting 88»

Comparative 340

The removal of digestive products from the alimentary canal . . 841

Lymph and chyle , • • 348

The movements of the lymph — comparative . . . . 844

Pathological 862

Fteoes . 862

Pathological 868

The chains produced in the food In the alimentary canal . 864

General . . . . ' -864

Comparative .867

Pathological 369

Special considerations • • •• 369

Various 869

Evolution 868

Summary 864

Thb Respiratort Stbtbh 866

General . « 866

i 'i

824

881

882

338

386

SSff

88?

887

889

888

889

840

841

848

844

862

8B2

868

864

364

867

869

868

864

866

CONTENTS. xiii

PAtIB

Anatotniool 867

The entrance and exit of air . 870

The muBcIca of respiration 378

Types of respiration .......... 87b

Comparative * . . . . 876

Personal obHcrvation . , , 876

The quantity of air respired , . , 878

The respiratory rhythm . 379

General 379

Pathological . . . . .879

Respiratory sounds sgi

CJomparison of the inspired and the expired air . ... . 882

Respiration in the blood sss

HoBmoglobin and its derivatives ....... 386

General 886

Blood-spectra , . 887

Comparative ' . . 889

The nitrogen and the carbon dioxide of the blood . .389

Foreign gases and respiration 891

Respiration in the tissues . . 891

The nervous system in relation to respiration . . . . 898

The Influence of the condition of the blood on respiration . . . 398

The influence of respiration on the circulation 896

General . •( 396

Comparative . 898.

The respiration and circulation in asphyxia .... 399

Pathological 401

Peculiar respiratory movements 401

Coughing, laughing, etc. . . . . . . . . 401

Comparative 402

Special considerations , . . 408

Pathological and clinical 403

Personal observation 404

Evolution 404

Summary of the physiology of respiration 406

Protkotivx and Exorktort Functions ot tbb Sun .... 408

General - . . . 408

Comparative 40g

The excretory function of the skin 411

Normal sweat ' . , 411

Patholo^cal , 4II

Comparative— Respiration by the skin 412

Death from suppression of the functions of the skin . .412

The excretion of perspiration .412

xiv COMPARATIVE PHYSIOLOGY.

PAoa

Experimental *'

Absorption by the skin ....••••'***

Comparative * "

Summary *^'

EZORKTION BY THE KlDNKY ^'^

Anatoiuicai ***

Comparative .416

Urine conaidered pliysloally and cliemioally . . • . . *1*

Specific gravity *'•

Color 4»9

Reaction . *^*

Quantity *^*

CompOBition : Nitrogenous crystalline bodies .... 480

Non-nitrogenous organic bodies 420

Inorganic salts *20

Abnormal urine *^1

Comparative *21

The secretion of urine *-^

Theories of secretion 421

Nervous influence 423

Patholi^cal *28

The expulsion of urine ****

General *24

Facts of experiment and of experience 424

Pathological 426

Summary of urine and the functions of the kidneys . . . • 48*

Comparative ***

The Metabolism of the Boot 428

General remarks . • 428.

llie metabolism of the liver • . 428

The glycogenic function 429

The uses of glycogen 429

Metabolism of the spleen 429

Histological . 480

Chemical *'**

The construction of fat *^^

General and experimental 432

Histological *^^

Changes in the cells of the mammary gland . . , • . 434

Nature of fat formation 484

Milk and colostrum 436

Pathological ^^'^

Comparative • • • "

The study of the metabolic processes by other methods . . . 486

COMPARATIVE PHYSIOLOGY.

GENERAL BIOLOGY.
IMTUODnonON.

Biology (fitos, life ; Xoyor, a dissertation) is the science which
treats of the nature of living things ; and, since the properties
of plants and animals can not be explained without some knowl-
edge of their form, this science includes morphology (/m/m/ii;,
form ; Xoyor, a dissertation) as well as physiology {iftwns, na-
ture ; Xoyof).

Morphology describes the various forms of living things and
their parts ; physiology, their action or function.

General biology treats neither of animals nor plants exclu-
sively. Its province is neither zoology nor botany ; but it at-
tempts to define what is common to all living things. Its aim
is to determine the properties of organic beings as such, rather
than to classify or to give an exhaustive accoimt of either ani-
mals or plants. Manifestly, before this can be done, living
things, both animal and vegetable, must be carefully compared,
otherwise it would be impossible to recognize dififerences and
resemblances ; in other words, to ascertain what they have in
common.

When only the highest animals and plants are contem-
plated, the differences between them seem so vast that they
appear to have, at first sight, nothing in common but that they
are living : between a tree and a dog an infant can discrimi-
nate ; but there are microscopic forms of life that thus far defy
the most learned to say whether they belong to the animal or
the vegetable world. As we descend in the organic series, the
lines of distinction grow fainter, till they seem finally to all but
disappear.

COMPARATIVE PHYSIOLOGY.

But let us flrat inquire : What are the determining oharac-
teristica of living things as such ? By what barriers are the
animate and inanimate worlds separated ? To decide this, falls
within the province of general biology.

Living things grow by interstitial additions of particles of
matter derived from without and transformed into their own
substance, while inanimate bodies increase in size by superficial
additions of matter over which they have no power of decompo-
sition and recomposition so as to make them like themselves.
Among lifeless objects, crystals approach nearest to living
forms ; but the crystal builds itself up only from material in
solution of the same chemical composition as itself.

The chemical constitution of living objects is peculiar. Car-
bon, hydrogen, oxygen, and nitrogen are combined into a very
complex whole or molecule, as protein ; and, when in combina-
tion with a large proportion of water, constitute the basis of all
life, animal and vegetable, known as protoplasm. Only living
things can manufacture this substance, or even protein.

Again, in the very nature of the case, protoplasm is continu-
ally wasting by a process of oxidation, and being built up from
simpler chemical forms. Carbon dioxide is an invariable prod-
uct of this waste and oxidation, while the rest of the carbon,
the hydrogen, oxygen, and nitrogen are given back to the in-
organic kingdom in simpler forms of combination than those
in which they exist in living beings. It will thus be evident
that, while the flame of life continues to bum, there is constant
chemical and physical change. Matter is being continuoiisly
taken from the world of things that are without life, trans-
formed into living beings, and then after a brief existence in
that form returned to the source from which it was originally
derived. It is true, all animals require their food in organized
form— -that is, they either feed on animal or plant forms ; but
the latter derive their nourishment from the soil and the atmos-
phere, so that the above statement is a scientific truth.

Another highly characteristic property of all living things
is to be sought in their periodic changes and very limited dura-
tion. Every animal and plant, no matter what its rank- in the
scale of existence, begins in a simple form, passes through a
series of changes of varying degrees of complexity, and finally
declines and dies ; which simply means that it rejoins the in-
animate kingdom : it passes into another world to which ii
formerly belonged.

ng oharac-
ira are thu
e this, falls

[)articles of
their own
superficial
f decompo-
hemselyes.
to living
material in

iliar. Car-
into a very
Q oombina-
basis of all
)nly living
nn.

is continu-
ilt up from
riable prod-
the carbon,
k to the in-
than those
be evident
is constant
tntinuously
life, trans-
xistence in
I originally
1 organized
forms ; but
[ the atmoB-
li.

ring things
nited dura-
■ank-in the
through a
and finally
>ins the in-
to which ii

GENERAL BIOLOGY.

Living things alone give rise to living things ; protoplasm
alone can beget protoplasm ; cell begeto cell. Omne animal
(anima, life) ex ovo applies with a wide interppjtation to all
living forms.

From what has been said it will appear that life is a condi-
tion of ceaseless change. Many of the movements of tht priP
toplasm composing the cell-units of which living beings are
made are visible under the microscope; their united effects are
open to common observation— as, for example, in the move-
ments of animals giving rise to locomotion we have the joint
result of the movementa of the protoplasm composing millions
of muscle-cells. But, beyond the powers of any microscope that
has been or probably ever will be invented, there are molecular
movements, ceaseless as the flow of time itself. All the pro-
cesses which make up .the life-history of organisms involve this
molecular motion. The ebb and flow of the tide may symboluw
the influx and eiflux of the things that belong to the inanimate
world, into and out of the things that live.

It follows from this essential instability in living forms that
life must involve a constant struggle against forces that tend
to destroy it; at best this contest is maintained successfully for
but a few years in all the highest grades of being. So long as
a certain equilibrium can be maintained, so long may life con-
tinue and no longer.

The truths stated above will be illustrated in the simpler
forms of plants and animals in the ensuing pages, and will
become clearer as each chapter of this work is perused. They
form the fundamental laws of general biology, and may be for-
mulated as follows:

1. Living matter or protoplasm is characterized by ite chemi-
cal composition, being made up of carbon, hydrogen, oxygen,
and nitrogen, arranged into a very complex molecule.

2. Its universal and constant waste and its repair by inter-
stitial formation of new matter similar to the old.

8. Ite power to give rise to new forms similar to the parent
ones by a process of division.

4. Its manifestation of periodic changes constituting devel-
opment, decay, and death.

Though there is little in relation to living beings which
may not be appropriately set down under zoology or botany, it
tends to breadth to have a science of general biology which
deals with the properties of things simply as living, irrespective

■avnan

COMPARATIVE PHYSIOLOGY.

Biol-

The,
Hcience
of liv-
ing
things:
i. e., of
matter
in the
living
state.

Mor-

ogy.

The
science

of
form,
struct-
ure,
etc.

tially
statical.

Phyri.

dogy
Tlie

science
of

action
or

func-
tion.

Essen-
tially

djrnam-
ical.

r Anatomy. ]

Tho Holenco of Btructuro; ,
thoterm being uiuully ,
applied to tha ooaraer
and mora obvioua I
ooinposltion of plants
or anlmolii.

UUtology.
Mlcroaooplcal anatomy.
The ultimate optical
analyaiii of Htraoture
by tho aid of the ml-
oroMopo ; aeparated
nroro anatomy only oh
a matter of oonvon-
ienoe.

Taxonomy,
The classifloation of Ut-
Kna thlnipt, bused
ohlefly on phenomeni^
ofstruoture.

IHttribution.
Coniiders the position
of livins thmgti in
spaoe and time ; their
distribution over the
prosont face of'tiio
earth : and their dis-
tribution and suooes-
sion at former po-
riods, as displayed in
fossil remains.

Emhryology.
The soience of dovolop-
mont from tho gorra :
inoludes many mixed
problems pertaining
both to morphology
and physiology. At
present largely mor-
phological.

PhytMogy.
The special science of
the t\inotionii of the
individual in health
and in disease ; hence
including Ibtholoffy.

Ayehology.
' The science of mental
phenomena.

Sociology.
The science of social
life, i. e., the life of
communities, wheth-
er of men or of lower
animals.

Botany.

The
science
of veg-

et^
living
matter

or
plants.

Bid.

Zo»U
ogy.

The
science

animal

living

matter

or ani

mals.

le
science
of liv-
ing
things:
i. e., of
matter
in the
living
state.

ORNFRAL BIOLOGY.

Bidp

The
science
of liv-
ing
ihings:
i. e., oi
matter
in the
living
state.

very much a« to whether they belong to the realm of animals or
pluntH. Tlio relation of the wioncofl which may bu regarded
UM Hulxlivisions of general biology is well shown in the accom-
panying table. *

TBB 01IZX.f

All living things, great and small, are composed of cells.
Animals may be divided into those conHisting of a ningle cell
{Protozoa), and those made up of a multitude of relk (Metazoa) ;
but in every case the animal begins as a single cell or ovum
from which all the other colls, however different Anally from
one another either in form or function, are derived by processe*
of growth and division ; and, as will be seen later, the whole
organism is at one period made up of cells practically alike in
structure and behavior. The history of each individual animal
or plant is the resultant of the conjoint histories of each of its
cells, as that of a nation is, when complete, the story of the total
outcome of the lives of the individuals composing it.

It becomes, therefore, highly important that a clear notion
of the characters of the cell be obtained at the outset ; and
this chapter will be devoted to presenting a general account of
the cell.

The cell, whether animal or vegetable, in its most complete
form consists of a mass of viscid, semifluid, transparent sub-
stance (pi'oti^lasm), a cell wall, and a more or less circular
body (nttcleua) situated generally centrally within; in which,
again, is found a similar structure (nttcletdits).

. This description applies to both the vegetable and the ani-
mal cell; but the student will find that the greater proportion
of animal cells have no cell widl, and that very few vegetable
cells are without it. But there is this great difference between
the animal and vegetable cell: the former never has a cellulose
wall, while the latter rarely lacks such a covering. In every
case the cell wall, whether in animal or vegetable cells, is of
greater consistence than the rest of the cell. This is especially
true of the vegetable cell.

It is doubtful whether there are any cells without a nucleus,
whUe not a few, especially when young and moat active, poa-

* Taken from the General Biology of Sedgwick and Wilson,
f The illustrations of the sectiona follow*ng will enable the stodent to
form a generalized mental picture of the cell in all ita parts.

"VPI

COMPARATIVE PHYSIOLOGY.

■em ieverBl. The circular form may be regarded an the typical
form of both ccllri nnd nuclei, and their infinite variety in nize
and form may l)o conaidered aa in great jMirt the r«Hu1t of tJie
action of mechanical forces, such a8 mutual pressure ; this is, of
I'ourHc, more especnally true of shape. Retlucetl t4) its greatest
simplicity, then, the cell may be simply a mass of protoplasm
with a nucleus.

It Hei'mH probable that the numerous researches of reoent
years and others now in progress will open up a new world of

Fra. 1.— NnciSAii Diriiiow. A-H. ktryoklnetU of a tiMiie cell. A, nuclesr retlcnlum
In lU onltnary lUte. B, preparing for diviilon ; the contour ii leM (IpHned, and
the flbere tUlcker and lei Inftlcate. C. wroathitjije ; the ctwomatln ■ arranged
in a complicated looping ronnd the equator of the achroroatin ■pindlu. D, mo-
BMter-ttatfc ; the ciuomatin now apjpean aa centripetal eoaatorial y>a,eachof
whteh fhSuld be reprc«.nted aa don6le: K, » migration of flie half of each chrc
matin loop towarda oppoalte polee of the aplndle. V, dlaater-atage ; the chroma-
™fonM a »tar. round eacli pole of a aplndle, each aater being connected by
itrandi of achromatln. Q. dauKter-wrcath atage :«»'»"«*'' IS«2S*,HhL'LS?
paaalng through their retrogreaaire development, which is completed In the reat-
fi^'tiwe/U. a-f, karyoklnlala of •» ew-cell. fhowlngthe .mailer amount of
cfiomatln than In the tliane-cell. The atageed. #./, correapond to D, B, f, re-
apectlvely. The polar »Ur at the end of the aplndle la e2'"'S?^i"'»IL'','iS'*'^'K
manulee of the cell itaelf, and mnat not be mlatekenforthedlaaterm. The
OMuae llnea repreeent the chromatin, the Sne lines the achromatln, aud tlie dotted
ItaeaM ll-BranulS?^ (Chiefly modlfled from Plemmlng.) X-Z, direct nucLiar dlvla-
Ion in thfcells of the embryonic Integument of the KatofMn acorplon. After
Blochmann (HadtUm).

cell biology which will greatly advance our knowledge, espe-
cially in the direction of increased depth and accuracy.

OENKRAL BIOLOGY.

the typical
i«ty in Nize
Hiilt nt the
; thii it, of
tH (greatest
)rutopUuiin

I of recent
w world of

clear retlcninm
•a (loaned, and
itin li arransgd
imdiu. D, mo-
lal V'a. eacb of
If or each chiO'
I ; tbe chroma-
It connected by
rmed nuclei are
)ted In the reat-
Uler amoant of
1 to D, B, r, re-
of prtttoplaam-
aaterlF). The
aud the dotted
;tnacii)ardivla-
iorploii. After

ledge, espe-

cy.

Thoufrh many i>oiuii are Htill in dinputo, it may he iiafely
Miid that the nucleus ])liiyii, in nitml coIIh, u r6le of thu hiifhuHt
iinportatK'«s >'< ''^'^ it w^tiit* an though wu might rKgdnl tho
nuoleuH as the directive brain, ro to spealc, of the individual
cell. It frequently liu|)|)«nH that tlie behavior of thu body of
the cell tH foreshudowt'd by tlwt of the nucleus. Thus fre-
quently, if not always, division of the body of the nucleus pre-
cedes that of the coll itself, and is of a most complicated char-
acter (karyokinesia or mitoais). The cell wall is of subordinate
importance in the processes of life, though of great value as a
mechani(«l support to the protoplasm of the cell and tlie aggro-
gutions of cells known as tissues. The greater part of a tree
may be said to be made up of the thickened walls of the colls,
and these are destitute of true vitality, unless of the lowest
order; while the really active, growing part of an old and large
tree constitutes but a small and limited zone, as may bo learned
from the plates of a work on modem botany representing sec-
tions of the wood.

Animals, too, have their rigid ports, in the adult state espe^
cially, resulting from the thickening of a part of the whole of
the cell by a deposition usually of salts of lime, as in the case of
the bones of animals. But in some cases, as in cartilage, the
cell wall or capsule imdergoes thickening and consolidation,
and several may fuse together, constituting a matrix, which ia
also made up in part, possibly, of a secretion from the cell pro-
toplasm. In the cuter parts of the body of animals we have a
great abundance of examples of thickening and hardening of
cells. Very well-known instances are the indurated patches
of skin (eptYAe/tum) on the palms of tbe hands aud else-
where.

It will be scarcely necessary to remark that in cells thus
altered the mechanical has largely taken the place of the vital
in function. This at once harmonizes with and explains what is
a matter of common observation, that old animals are less act-
ive — have less of life within them, in a word, than the young.
Ohemioally, the cellulose wall of plant-cells consists of carbon^
hydrogen, and oxygen, in the same relative proportion as exists
in starch, though its properties are very different from those of
that substance.

Turning to cell contents, we find them everywhere made up-
•f a clear, viscid substance, containing almost alwajrs granules
of varying but very minute size, and differing in oonsistenoft

m0Lk

itti

COMPARATIVE PHYSIOLOGY.

not only in diiferent groups of cells, but often in the same cell,
so that we can distin^ish an outer portion (ectoplaam) and an
inner more fluid and more granular region (endoplasm).

The nucleus is a body with very clearly defined outline (in
Bome cases limited by a membrane), through which an irregular
network of fibers extends that stains more deeply than aay
other part of the whole cell.

Owing to the fact that it is so readily changed by the action
of reagents, it is impossible to ascertain the exact chemical com-
position of living protoplasm ; in consequence, we can only
infer its chemical structure, etc., from the examination of the
dead substance.

In general, it may be said that protc-lasm belongs to the
class of bodies known as proteids — that is, it consists chomically
of carbon, hydrogen, a little sulphur, oxygen, and nitrogen, ar-
ranged into a very complex and unstable molecule. This very
instability seems to explain at once its adaptability for the man-
ifestation of its nature as living matter, and at the same time the
readiness with which it is modified by many circumstances, so
that it is possible to understand that life demands an incessant
adaptation of internal to externa^ conditions.

It seems highly probable that protoplasm is not a single pro-
teid substance, but a mixture of such ; or let us rather say, fur^
nishes these when chemically examined and therefore dead.

Very frequently, indeed generally, protoplasm contains other
substances, as salts, fat, starch, chlorophyl, etc.

From the fsct that tha nucleus stains di£PerentIy from the
cell contents, we may infer a difference between them, physi-
cal and especially chemical. It (nucleus) furnishes on analysis
nuclein, which contains the same elements as protoplasm (with
the exception of sulphur) together with phosphorus. Nuclei
have great resisting power to ordinary solvents and even the
digestive juices.

Inasmuch as all vital phenomena are associated with proto-
plasm, it has been termed the "physical basis of life" (Hux-
ley).

TiMaes. — A collection of cells performing a similar physio-
logical action constitutes a tissue.

(Generally the cells are held together either by others with
that sole function, or by cement material secreted by them-
selves. An organ may consist of one or several tissues. Thus
the stomach consists of muscular, serous, connective, and gland-

GENERAL BIOLOGY.

ime cell,
) and an

I).

tline (in
irregular
ban any

ne action
ical com-
lan only
m of the

gg to the
lenucally
gen, ar-
rhis very
the man-
i time the
tances, so
incessant

uagle pro-
[• say, f ur^
id&oA.
Bins other

'from the
jin, physi-
D analysis
asm (with
8. Nuclei
1 even the

rith ppoto-
ife"(Hux-

ar physio-

thers with
L by them-
ues. Thus
and gland-

"^.SJ' '^r'tlSfStu »o„«* of a wall, p«M.«»i«
!^^'. « IclST The vegetable ceU hae a Umitmit

definite purposes. „-nf««lasm is hiffhly complex

SlTS'he ita^d t-Vbe ^ntial to its perfect deve^
opment a«d greatest physiological efficiency. ^

UNIOBUiUl'AR P1.AMT8.

YbIst (Toruto, Saccharomycea Cerevism).

— *• 1 ~.-* r.f the common substance, yeast, may be

The essential part of t^e ^"^ j ^^^

studied to adv^itage, ^^^^.^^^^'Z Jd^nt of physiology

'''ijS.S^'-Sir^cles of which yeast is composed
JS^TTt.^or'Z form, of an average diameter of

ote) QUed with more fl'*i'\««^*«°?-, , ^^inir mav remmn united
The various cells produced by buddmg may reiiii«
ine vart""" r ^ ,, .• „* masses composed of four

J^dT:::!. ehiefly o. »1U of ,»t.»u„. e.U.»,^
and magnesium.

COMPARATIVE PHYSIOLOGY.

The elements of which yeart is composed are C, H, O, N, S,

P, K, Hg, and Ca; but chiefly the first four.

PhyiiologioaL— If a little of the powder obtained by drying

yeast at a temperature below blood-heat be added to a solution

of sugar, and the lat-
ter be kept warm,
bubblew of carbon di-
oxide will be evolved,
causing the mixture
to become frothy ; and
the fluid will acquire
an alcoholic charac-
ter (fermentation).

If the mixture be
raised to the boiling-
point, the process de-
scribed at once ceases.

Fio. 9.— VarioMitaiiiM in the derelopment of brewer's It maybe further

yeaat, eeen, with the exception of the Urst in the _ . . j iu x • ii.

aeries, with «i ordinary high power (ZeiM,D. 4) of notioea that in the

the microscope. The flrst la greatly magnified favmanHnir aa/wlia

(Gnndhuih'aAImmeriionions). The seconfieriea »rmeilw|»g saCClMr

of four represents etages In the division of a single fine solution there is

a gradual increase of
turbidity. All of these
changes go on per-
fectly well in the to-
tal absence of sun-
light

Yeast - cells are
found to grow and
reproduce abundant-
ly in an artificial food
solution consisting of
a dilute solution of

Fia. 4.— Ftether development of the forms represented CCTtain Salts, together

with sugar.

O onelm i oa i.— What are the conclusions which may be Inti-
mately drawn from the above facts ?

That the essential part of yeast consists of cells of about the
size of mammalian blood-corpuscles, but with a limiting wall
of a substance different from the inclosed contents, which latter
is composed chiefly of that substance common to all living
things— protoplasm; that like other cells they reproduce their

cell ; and the third series a branching colony.
Bverywheie the light areas indicate vscaoles.

Fio. S.— The cndogonidi* (aaeospore) phase of repio-
dnction— i. e., endogenous division.

!, H, O, N, S,

id by drying
to a solution
, and the lat-
kept warm,
)f carbon di-
ll be evolved,
the mixture
e frothy; and
will acquire
lolic charac-
\entation).
) mixture be

the boiling-
i process de-
b once ceases,
ybe further
that in the
ng saocha-
tion there is
I increase of
. All of these

go on per-
ill in the to-
ice of sun-

- cells are
> grow and
B abundant-
irtificial food
sonmsting of
solution of
dts, together
ir.
lay be l^ti-

of about the
miting wall
which latter
o all living
roduce their

GENERAL BIOLOGY.

kind, and in this instance by two methods: gemmation giving
rise to the bead-like aggregations aUuded to above; and in-
ternal division of the protoplasm (endogenoua divmon).

From the circumstance^ under which growth and reproduc-
tion take place, it will be seen that the original protoplasm of
the ceUs may increase its bulk or grow when supplied with
suitable food, which is not, as will be learned later, the same in
all respects as that on which green plants thrive; and that this
may occur in darkness. But it is to be especially noted that the
protophasm resulting from the action of the living cells is
whoUy different from any of the substances used as food. This
power to construct protoplasm from inanimate and unorgan-
ised materials, reproduction, and fermentation are all proper-
ties characteristic of living organisms alone.

It will be further observed that these changes all take place
within narrow limits of temperature; or, to put the matter
more generaUy, that the life-history of this humble organism
can only be unfolded under certain well-defined conditions.

Pkotocoooub {Protococcus pluvialia).
The study of this one-celled plant will afford instiructive
comparison between the ordinary green phmt and the colorless
plants or fungi.

Via. 8b

ne e.ir.

Fis. 7.
PiM. 5to 7 npieMnit McceMlve stages observed in the IWe-htotory of Frotoeoeol
Fw.'^i^gJESSSttodwSaSlS^lUa.tmttng nijrtUotf of dWlsIon.

•aT nSSISS ff^otod by n«^ the cell wSF by c.w ; and the coJoring-instter by
ttl^dS* J^t oSfttSleflt of B^. 7 >n IndlTldiu may be seen that Is^evold of a
cell wall.

mmmBmmmm

B t

I i

t
V

ti;

COMPARATIVE PHYSIOLOGY.

Like TonUa it is selected because of its simple nature, its
abundance, and the ease with which it may be obtained, for it
abounds in water-barrels, standing pools, drinking-troughs,

etc.

KorphdlogiflaL— Frotococcus consists of a structureless wall
and viscid granular contents, i. e., of cellulose and protoplasm.

The protoplasm may contain starch and a red or g^^een color-
ing matter (cKUyrophyl). It probably contains a nucleus. The
oeU is mostly globular in form.

PhyuologioaL — It reproduces by division of the original cell
(fianon) into similar individuals, and by a process of budding
and constriction {gemmation) which is much rarer. Under the
influence of sunlight it decomposes carbon dioxide (COi), fixing
the carbon and setting the oxygen free. It can flomrish per-
fectly in rain-water, which contains only carbon dioxide, salts
of ammonium, and minute quantities of other soluble salts that
may as dust have been blown into it.

There is a motile form of this unicellular plant, and in this
stage it moves through the fluid in which it lives by means of
extensions of its protoplasm (ct7to) through the cell wall ; or
the cell wall may disappear entirely. Finally, the motile form,
withdrawing its cilia and clothing itself with a cellulose coat,
becomes globular and passes into a quiescent state again.
Much of this part of its history is common to lowly animal

forms.

ConolviiOlU.— It win he seen that there is much in common
in the life-history of Torula and Protococcm. By virtue of
being living protoplasm they transform unorganized material
into their own substance ; and they grow and reproduce by
analogous methods.

But there are sharply defined differences. For the green
plant sunlight is essential, in the presence of which its chloro-
phyl prepares the atmosphere for animals by the removal of
carbonic anhydride and the addition of oxygen, while for
Torula neither this gas nor sunlight is essential.

Moreover, the fungus (Tonda) demands a higher kind of
food, one more nearly related to the pabulum of anim.al8 ; and
is absolutely independent of sunlight, if not actually injured by
it ; not to mention the remarkable process of fermentation.

: i

a£NERAL BIOLOGY.

le nature, its
itained, for it
king-troughs,

:tureles8 wall

protoplasm.

r green color-

lucleus. The

) original cell
IS of budding
•, Under the
){COi), fixing
flourish per-
dioxide, salts
ible salts that

it, and in this
i by means of
ceU wall ; or
a motile form,
cellulose coat,
state again,
lowly animal

;h in common

Bj virtue of

aized material

reproduce by

^or the green
lich its chloro-
le removal of
en, while for

igher kind of
anim,als ; and
illy injured by
nentation.

UNXOBLXiUIJlR ANIMAIJI.

The Proteus AsmAuovusi (Amoeba).
In order to illustrate «nimal life in its simpler form we
choose the above-named creature, which is nearly as readily
obtainable as Protococcus and often under the same circum-
stances. . , x__

MoxphologioaL— Amosba is a microscopic mass of transpar-
ent protoplasm, about the size of the largest of the colorless
blood-corpuscles of cold-blooded animals, with a clearer, more
consistent outer zone {ectomrc), (although without any proper
ceU wall), and a more fluid, granular inner part. A clear space
(contractile vesicle, vacuole) makes its appearance at intervals
in the ectosarc, which may disappear somewhat suddenly. This
appearance and vanishing have suggested the term pulsating
or contracting vesicle. Both a nucleus and nucleolus may be
seen in Amoeba. At varying short periods certain parts of its
body (paeudopodia) are thrust out and others withdrawn.

PhytlolOgioal.— Amoeba can not live on such food as proves
adequate for either Protococcus or Torula, but requires, besides
inorganic and unorganized food, also organized matter in the
form of a complex organic compound known as protein, which
contains nitrogen in addition to carbon, hydrogen, and oxygen.
In fact, Amoeba can prey upon both plants and animals, and
thus use up as food protoplasm itself. The pseudopodia serve
the double purpose of organs of locomotion and prehension.

This creature absorbs oxygen and evolves carbon dioxide.
Inasmuch as any part of the body may serve for the admission,
and possibly the digestion, of food and the ejection of the use-
less remains, we are not able to define the functions of special
parts. Amoeba exercises, however, some degree of choice as to
what it accepts or rejects.

The movements of the pseudopodia cease when the temperar
ture of the surrounding medium is raised or lowered beyond a
certain point. It can, however, survive in a quiescent form
greater depression than elevation of the temperature. Thus, at
36° 0., heat-rigor is induced; at 40° to 45° C, death results ;
but though all movement is arrested at the freezing-point of
water, recovery ensues if the temperature be gradually raised.
Its form is modified by electric shocks and chemical agents,
as well as by variations in the temperature. At the pres-
ent time it is not possible to define accurately the functions

fB^^ _0mfgm

mum

COMPARATIVE PHYSIOLOGY.

of the vacuoles found in any of the organisms thus far consid-
ered. It is worthy of note that Amoeba may spontaneously
assume a spherical form, secrete a structureless covering, and

Vff

FlG.0.

ye-

Fia. 10.

Fie.ll.

VUi.18.

Fia.18.

•fte.

Fra.14.

'•ne- ne.

,xe

na.15.

Vf-'^f

Fia. 18.

FtoB. 8 to 16, repraaent nicceMiTe phases In the lif e-Ustonr of an Amoeboid oiniiism>
kept under constant observation for three days ; Ffs. 16 a simUar ornmlsm en;
CTSted, which was a few honrs later set free by the olslntegration of the cyst
(All the llenres are drawn under Zeiss. D. 8.) ,. ^ . .

Fio. 8.— The locomotor phase ; the eutopiasm is seen protrudlnK to form a psendopo-
dluni, Into which the endoplawm passes.

Fio. 9.~A statre in the ingestfve phase. A vegetable organism, J)7, is nndeigolng in-

Fie. 10.— A portion of the creatnre represented In Fig. 0, after complete taigeetlon of
the food-particle. .... « .n

Fio. 11, 18.-^nccesslve stages in the assimilative and excretory procesMS, Plg^
represents the organism some twenty hours later than as seen in Fig. II. Tfte
nndigested remnants of the Ingested organism are represented undergoing ejec-
tion (excretion) at/^, in Fig. 18. . . , ... ,_

Fios. 18, 14, 16, represent successive stages in the reproductive process of the same m-
dividnai, observed two days later. It will be noticed (Fig. 13) that the nucleus di-
vides first. . ... ,

In the above llgnres. vc, denotes the contracting vacuole ; nc, the nucleus ; p», pseu-
dopodlnm ; <«, diatom ; fp, food-particle.

mum

iiiiiMHiii>iimMaiiMi

B far consid-
mntaneoudy
overing, and

Fio. 10.

Fig. 18.

Fia. 18.

Qoebotd oiniiUm>
tilar OTsanisin en'
ttion of the cyet

f onn a paeadopo-

, is nndeigoing In-

iplete bigeetion of

iroceaaei. Fig. 18
I in Fig. 11. The
1 nndei^otng e]ec-

e«8of theeamein-
lat the naclens di-

inclens ; pi, psen-

GENERAL BIOLOGY.

remain in this condition for a variable period, reminding us of
the similar behavior of Torula.

Amoeba reproduces by fission, in which the nucleus takes a
prominent if not a directive part, as seems likely in regard to
all the functions of unicellular organisms.

GonollllioilS.— It is evident that Amoeba is, in much of its
behavior, closely related to both colored and colorless one-celled
plants. All of the three classes of organisms are composed of
protoplasm ; each can construct protoplasm out of that which
is very different from it ; each builds up the inanimate inor-
ganic world into itself by virtue of that force which we call
vitdl, but which in its essence we do not understand ; each mul-
tiplies by division of itself, and all can only live, move, and
have their being under certain definite limitations. But even
among forms of life so lowly as those we have been consider-
ing, the differences between the animal and vegetable worlds
appear. Thus, Amoeba never has a cellulose wall, and can not
subsist on inorganic food alone. The cellulose wall is not, how-
ever, invariably present in plants, though this is generally the
case ; and there are animals (Ascidians) with a cellulose invest-
ment. Such are very exceptional cases. But the law that ani-
mals must have organized material (protein) as food is without
exception, and forms a broad line of distinction between the
animal and vegetable kingdoms.

Amoeba will receive further consideration later ; in the
mean time, we turn to the study of forms of life in many re-
spects intermediate between plants and animals, and full of prac-
tical interest for mankind, on account of their relations to dis-
ease, as revealed by recent investigatious.

PABASmO OROAMISBU.

The Fdnqi.
Molds (PmiciUium gUtumm and Mucor mueedo).

Closely related to Torula physiologically, but of more com-
plex structure, are the molds, of which we select for convenient
study the common green mold (PenieiUium), found growing in
dark and moist places on bread and similar substances, and the
white mold (Mucor), which grows readily on manure.

The fungi originate in ^)ore8, which are essentially like
Torula in structure, by a process of budding and longitudinal
extension, resulting in the formation of transparent branches

Fia.aO.

-«»'

Fia. W.

GENERAL BIOLOGY.

FiOK. IT to JH.-

In the following flguroi, ha, donotea atrial hvpha; i/i, Rporangltim;
-■orTum; my, mycelium; mc, mucilage; el, culuniollu; «n,

jy, itygOHpore; «x

etidogonidla. . , ,. •

Vui. 17. -8poro-t)carinK hj , of Mncor. srowlng from horae-dung.
Flu. 1 .—The lame, toaned out with neediea (A, 4).

Kio*. tU, !90, 81.— SuccvhhWv utaKi'H in the development of the iporangiam.
Kio, 8St.— Isolated iporon of Mncor.
Kio. 83. — UomiinBtlnK Hporos of tliu aame mold.
Kio. 84.— Snccc'Siilvo HtOKes In tlui germination of a ilnglo spore.
Kioi. as, SB, 87. - HuccciiHlve phaiK-a In the conjuaatlve process of Mucor.
Kio. 88.— SucceMlvo vtagea oWrved during ten houra In the growth of a conldiophorc

of Penicllllam In an object^laM culture (U, 4).

or tubules, filled with protoplasm and invested by cellulose
walls, across which transverse partitions are found at regular
intervals, and in which vacuoles are also visible.

The spores, when growing thus in a liquid, gives rise to up-
ward branches (aerial hyphoe), and downward branches or root-
lets {submerged hyphce)^ These multitudinous branches inter-
lace in every direction, forming an intricate felt-work, which
supports the green powder (spores) which may be so easily
shalcen off from a growing mold. In certain cases the aSrial
hyphffi terminate in tufts of branches, which, by transverse
division, become split up into spores (Conidia), each of which
is similar in structure to a yeast-cell.

The green coloring matter of the fungi is not chlorophyl.
The Conidia germinate under the same conditions as Torula.

Kvoor mvoeoo.— The growth and development of this mold
may be studied by simply inverting a glass tumbler over some
horse-dung on a saucer, into which a very little water has been
poured, and keeping the preparation in a warm place.

Very soon whitish filaments, gradually getting stronger, ap-
pear, and are finally topped by rounded heads or spore-cases
(Sporangia). These filaments are the hyphce, similar in struct-
ure to those of Penicillium. The spore-case is filled with a
multitude of oval bodies (sporea), resulting from the subdivision
of the protoplasm, which are finally released by the spore-case
becoming thinned to the point of rupture. The development
of these spores take place in substantially the same manner as
those of Penicillium. Sporangia developing spores in this fash-
ion by division of the protoplasm are termed asci, and the spores
aaoospores.

So long as nourishment is abundant and the medium of
growth fluid, this asexual method of reproduction is the only
one ; but, under other ciroumstances, a mode of increase, known
as cor^'ugatum, arises. Two adjacent hyphae enlarge at the ex-
tremities into somewhat globular heads, bend ovm* toward each
2

WT.

COMPARATIVE PHYSIOLOGY.

i)ther, Aiul, meetinfr, their opponed faces become thinned, and
tho cMiitciitM interminffle. The result of thiH union {zygospore)
uudergoofi now certain further changefl, tho celluloHe coat being
separated into two— an outer, darlcer in color {exoaporium),
and an inner colorless one (endoaporiutn).

Under favoring circumstances these coats burst, and a
branch sprouts forth from which a vertical tube arises fhat
terminates in a sporangium, in which spores arise, as before de-
scribed. It will be apparent that we have in Mucor the exem-
plification of what is known in biology as " alternation of gen-
erations^^ — that is, there is an intermediate generation be
tween the original form and that in which the original is
again reached.

Physiologically the molds closely resemble yeast, some of
them, as Mucor, being capable of exciting a fermentation.

The fungi are of special interest to the medical student, be-
cause many forms of cutaneous disease are directly associated
with >).oir growth in the epithelium of the skin, as, for exam-
ple, con'mon ringworm ; and their great vitality, and the faoil-
ity with which their spores are widely dispersed, explain the
highly contagious nature of such diseases. The media on which
they flourish (feed) indicates their great physiological differ-
ences in this particular from the green plants proper. They are
closely related in not a few respects to an important class of
vegetable organisms, known as bacteria, to be considered forth-
with.

Thb BACrTERIA.

The bacteria include numberless varieties of organisms of
extreme minuteness, many of them visible only by the help of
the most powerful lenses. Their size has been estimated at
from Tjf „-T to Tiftrir o' ^"^ inch in diameter.

They grow mostly in the longitudinal direction, and repro-
duce by transverse division, forming spores from which new
generations arise.

Some of them have vibratile cilia, while the oause of the
movements of others is quite unknown.

As in many other lowly forms of life, there is a quiescent
as well as an active stage. In this stage (zodgloea form) they
are surrounded by a gelatinous matter, probably secreted by
themselves.

Bacteria grow and reproduce in Pasteur's sohition, rendering
it opaque, as well as in almost all fluids that abound in pinteid

'"*^

LVT».«l«.'WJfJy,i(lJ,, ,

:: U

ORNEIIAI. MOLIO^

le thinned, and
ion {zygospore}
iloHe coat being
' (exoapon'um),

1 bunt, and a
tube ariaea that
»e, as before de-
lucor the exem-
mation of gen-
Hfeneration be
the original is

» yeast, some of
mentation,
ical student, be-
rectly associated
in, as, for exam-
ly, and the facil-
i-sed, explain the
media on which
Biological differ-
troper. They are
iportant class of
considered forth-

of organisms of
ly by the help of
leen estimated at

action, and repro-
from which new

the cause of the

)re is a quiescent
^loea form) they
jably secreted by

ohttion, rendering
Bkbound in pinteid

matter. That such fluids readily piitre is uwing t ib« pres-
ence of bacteria, the vital action of whx'i ifn(>«ii tn k,.,«k asim-

{}

t^<f\

ria.».

Fio.ao.

Via. 81

Fia. as.

Fio. n.

Pio. !)B.— MicroeoooM, veiy like a ipon, bnt nnukUy mneh nmUIer.

Fia. 80.— Bacteriom.

Fia. 81.— Bacillni. The central fllunent pieeented thii Momented •ppewuiee m the

reenit of • projcM of tranivene division ocenirins Arins ten minntee' obMT-

vatlon.
Fia. 8111— Spirillnm; varions fomu. The flnt two repreaent Tibrio, which la poaalbly

only a stage of splrlllDm.
Fio. 88.— a drop of the amf ace aenm, ahowtng a aplrlUiim asgiegate In the reeling

■tate.

der complex chemical oomponnds and produce new ones. Some
of the bacteria require oxygen, as Bcusittua awlhracia, while
others do not, as the organism of putrefaction, Baeterium
termo.

Bacteria are not so sensitive to slight variations in tempera-
ture as most otlier organisms. They can, many of them, with-
stand freezing and high temperatures. All bacteria and all
germs of bacteria are killed by boiling water, though the spores

■jtiO'i'iwiPMi^jriy-i

COMPARATIVR PHYSIOIiOOY.

Are much more reiiifitHnt timii tlin nmture oi^ninmn themaelvM.
H<mic N|N)r«w <-iin roHiHt u dry hciit ot 140° C.

The HporoH, liku Torula and Pn>tococctiN, bear drying, with-
out 1<NW of vitality, for connidorahlv |)orio<lit.

That dili'i>n>nt groups of liuc-tttriu havu a Honiewhat different
life-hidtury in evident from the fatit that the ]' i>>ten(»of one
uheolu the other in the Hanie fluid, and that nikc omive Bwarnm
of ditferont kindn may flourish where othon* have ceaaed to
live.

That thcHe organisnu are enemies of the constituent cells of
the tissuuH of the highest mammals has now been abundantly
demonstrated. That tliey interfere with the normal working
of the organism in a great variety of ways is also clear ; and
(wrtain it is that the harm they do leads to aberration in cell-
life, however that may be manifested. They rob the tissues of
their nutriment and oxygen, and poison them by the products
of the decompositions they produce. But apart from this, their
very presence as foreign agents must hamper and derange the
delicate mechanism of cell-life.

These organisms seem to people the air, land, and waters
with invisible hosts far more numerous than the forms of life
we behold. Fortunately, they are not all dangerous to the
higher forms of mammalian life ; but that a large proportion
of the diseases which afflict both man and the domestic animals
uro directly caused by the presence of such forms of lifp, in the
sense of being invariably associated with them, is now beyond
doubt

I'he facts stated above oxplnin why that should be so ; why
certain maladies should be infectious ; bow the germs of dis
ease may be transported to a friend wrapped up in the folds of
a letter.

Disease thus caused, it must not be forgotten, is an illustra-
tion of the struggle for existence and the survival of the fittest.
If the cells of an organism are mightier than the bacteria, the
latter are overwhelmed ; but if the bacteria are too great in
numbers or more vigorous, the cells must yield ; the battle may
waver — now dangerous disease, now improvement— but in the
end the strongest in this, as in other instances, prevail.

I 1

'■■a..<,?«-^|L^,a.^«Wf^T"i,, ■ ^>;,VvA;-'

ORNKRAIi BIOLOGY.

sins tliemBelve*.
ar drying, wUh-

iiewliat diiTeront
l>«t«oiM!eof one

i<<;o88iveswarin«
huvo ceased to

utituout oeUi of
been abundantly
nonnal working
I alno clear ; and
)«rrttti()n in cell-
tib the tisBues of
i by the product*
•t from this, their
and derange the

land, and waters
the forms of life
[langerous to the
i large proportion
domestic animals
rms of life, in the
m, is now beyond

liould be so ; why
the germs of dis
up in the folds of

tten, is an illustra-
rivid of the fittest,
m the bacteria, the
A are too great in
Id ; the battle may
ement— but in the
8, prevail.

UmOBLLnLAR AimiALt WITH PPrmRnKTIATIOM
OF BTRUOTUIUD.

The BRLL-ANiMAtiOUUB (Vorticella).

Aincnba is an oxumple of a ono-e<!llvd animal witli little per-
ceptible differentiation of structure or corresiMtnding division
of physiological labor. This is not, luiwever, the case with all
unicellular animals, and we proceed to study one of those with
considerable dovttlnpinent of both. The Bell -animalcule id
found in both fresh and salt water, either single or in groups.
It is anchored to some object by a rope-like stalk of clear pr«v
toplasm, ihut has a spiral appearance when contracted ; and
which, with a certain degree of regularity, shortens and length
ens alternately, suggesting that more definite movement (con-
traction) of the form of protoplasm known as miucle, to be
studied later.

The body of the creature is bell-shaped, hence its name ; the
bell being provided with a thick everted lip { peristome), covered
with bristle-like extensions of the protoplasm (cilia), which are
in almost constant rhythmical motion. Covering the mouth .>f
the bell is a lid, attached by a hinge of protoplasm to the body,
which may be raised or lowered A wide, funnel-like depres-
sion (ceaophagua) leads into the softer substance within which
it ends blindly. The outer part of the animal (outicuki) is
denser and more transparent than any other part of the whole
creature ; next to this is a portion more granular and of inter-
mediate transparency between the external and innermost por-
tions (cortical layer). Below the disk is a space (contractile
vesicle) filled with a thin, clear fluid, which may be Been to en-
large slowly, and then to collapse suddenly. When the Vorti-
cellA is feeding, these vesicles may contain food-particles, and
in the former, apparently, digestion goes on. Such food vacu-
oles (v^icles) may circulate up one side of the body of the ani-
mal and down the other. Their exact significance is not known,
but it would appear as if digestion went on within them ; and
possibly the clear fluid with which they are filled may be a spe-
cial secretion with solvent action on food.

Situated somewhat centraUy is a horseshoe-shaped body, with
well-deflined edges, which stains more readily than the rest of the
cell, indicating a different chemical composition; and, from the
prominent part it takes in the reproductive and other functions
of the creature, it may be considered the nudeus (endoplaef).

22 COMPABATIVE PHYSIOLOGY.

Multiplication of the species is either by gemmation or by
flsaim. In the first case the nucleus divides and the frag-

Bto.«.

Fia.40.

Fio. as.

Fia. 80.

FisB 84 to 40.— In the figures d denote* dtak ; »,
lieriBtomo; ve, contractile vacuole; e^. fo^;
vacuole; vi, vestibule; rf, contractile fiber;
e, cyst; «e, nucleui; «/, cTllum.

Pio at.— A group of vortlcelliB ehowlng the crea-
ture In various positions (A, 8).

Fio 85— The same, In the extended and In the
retracted state. (Surface views.) ^.^^„, .

Fio. 86.^8howB food- vacuoles; one In the act or

Fio'^-A'vorticella, in which the process of
mnltlpllcatlon by fission U begun.

Fio ffi.-The resulti of fission; ^e production
of two Indivldnals of unequal size.

Fio. 89. -Illustration of reproduction by conju-

Fio.^.— An encysted yorticella.

Eio.a6.

ments toe transformed into locomotive germs; in the latter
the entire animal, including the nucleus, divides longitudi-
nally, each half becoming a similar complete, independent oiv
ganism. Still another method of reproduction is known. A
more or less globular body encircled with a ring of cUiaand
of relatively small size may sometimes be seen attached to
the usual form of Yorticella, with which it finaUy becomes
blended into one mass. This seems to foreshadow the " sexual

^Si^^'-ft^iS?^"''"

GENERA [i BIOLOGY.

emmation or by
18 and the frag-

-If*

Bto.V.

•^

•*c

r».«>.

urea d denotes diik ; 0,

ictile vacuole; vf, fooo-

e: qf, contractile flber;

«/, cillnm.

icelln showing the crea-

ona (A, 8).

lie extended and in the

rface views.)

:aoles; one in the act of

1 which the process of
lion is begun,
nsaion; the production
r unequal size,
reprodnctlou by conju-

irticella.

'ms; in the latter
divides longitudi-
«, independent or-
ion is known. A
a, ring of cilia and
seen attached to
it finally becomes
badow the " sexual

conjugation " of higher forms, and is of great biological «ig^
niilcance.

Vorticella may pass into an encysted and quiescent stage for
an indefinite period and again become active. The history of
the Bell-animalcule is substantially that of a vast variety of
one-celled organisms known as Infusoria, to which Amoeba
itself belongs. It will be observed that the resemblance of this
organism to Amoeba is very great; it is, however, introduced
here to illustrate an advance in differentiation of structure; and
to show how, with the latter, there is usually a physiological
advance also, since there is additional functional progress or
division of labor; but still the whole of the work is done with-
in one cell. Amoeba and Vorticella are both factories in which
all of the work is done in one room, but in the latter case the
machinery is more complex than in the former; there are cor-
respondingly more processes, and each is performed with greater
perfection. Thus, food in the case of the Bell-animalcule is
swept into the gullet by the currents set up by the multitudes
of vibrating ^rms around this opening and its immediate neigh-
borhood; the contractile vesicles play a more prominent part;
and the waste of undigested food is ejected at a more definite
portion of the body, the fioor of the oesophagus; while all the
movements of the animal are rhythmical to a degree not exem-
plified in such simple forms as Amoeba; not to mention its
various resources for multiplication and, therefore, for its
perpetuation and permanence as a species. It, too, like all the
unicelhilar organisms we have been considering, is susceptible
of very wide distribution, being capable of retaining vitality in
the dried state, so that these infusoria may be carried in vari-
ous directions by winds in the form of microscopic dust.

MUIiTIOEZXUUlR OROANISMa

The Frhsh-Water Polyps (Hydra viridis; Hydra fuaca).

The comparison of an animal so simple in structure, though
made up of many cells, as the Polyp, with the more complex
organizations with which we shall have especially to deal, may
be fitly undertaken at this stage. The Polyps are easily obtain-
able from ponds in which they are found attached to various
kinds of weeds. To the naked eye, they resemble translucent
massoM of jelly with a greenish or reddish tinge. They range
in size from one quarter to one half an inch ; are of an elongated

GENERAL BIOLOGY.

'25

/..-->

PfiJ

EYo.«.

'•«e

■. 41 to 40.— In the flgunw « d«note« ectoderm; fn, endodcnn; <, tentacle; Ayi,
hyiH»tome;/,foot; <», te«te«; or, ovary; m, pgendopodlnm; ec\ larger etto<lerni
cellfi; we', larger nematocygts before rupiare; ep, Kleinenbcrg's flberg; c.l, mip-

Pios.

hyp<H

cellft; we', larger i .— . ., „,

, porting lamella; rf. chlorophyl-formlng bodleg; c, clllnra. , ,. , ^

t'lo 41.— The green hydra, at the maximnm of contraction and elongation of Ito liody .

The creature is represented in the act of seizing a small crustacean (A, 8).
Flo. 48.— Transverse section across the body of a hydra, in the digestive cavity of

which a small crustacean is represented. . „^ , , ... .. ^ ,„ „> „,,
Fio. 48.— The leading types of thread-cells, after liberation from the bodv (P, 8). The

cells are represented in the active and the resting conditions; in the former all the

parts are more distinctly seen in consequence of the necessanr everslon.
Fis. 44.— Small (lortion of a transverse section across the body of a green hydra

Flo. 45.— A large brown hydra bearing at the same time bads produced asexoally and

Fio. 46.— Larger cells of the ectoderm isolated. Note the processes of the cells or

Kleinenberg's fibers (F, 8). , . . ,, ...,-„,,

All the cuts on pages 9 to 84 have been selected from Howes' Atlas of Biology.

cylindrical form; provided at the oral extremity with thread-
like tenacles of considerable length, which are slowly moved
about in all directions; but they and the entire body may short-
en rapidly into a globular mass. They are usually attached at
the opposite (aboral) pole to some object, but may float free, or
slowly crawl from place to place. It may be observed, under
the microscope, that the tenacles now and then embrace some
living object, convey it toward an opening (mouth) near their
base, from which, from time to time, refuse material is cast out.
It may be noticed, too, that a living object within the touch of
these tenacles soon loses the power to struggle, which is owing
to the peculiar cells (nettle-cells, urticating capsuUs, nemato-
cysts) with which they are abundantly provided, and which se-
crete a poisonous fluid that paralyzes prey.

The mouth leads into a simple cavity (ccelom) in which
digestion proceeds. The green color in Hydra viridis, and the
red color of Hydra fusca, is owing to the presence of cMorophyl,
the function of which is not known. Hydra is structiurally a
sac, made up of two layers of cells, an outer (ectoderm) and
an inner (endoderm): the tentacles being repetitions of the
scructure of the noain body of the animal, and so hollow and
composed of two cell layers. Speaking generally, the outer
layer is devoted to obtaining information of the surroundings ;
the inner to the work of preparing nutriment, and probably,
also, discharging waste matters, in which latter assistance is
also received from the outer layer. As digestion ti^es place
largely within the cells themselves, or is intracellular, we are
reminded of Vorticella and still more of Amoeba. There is in
Hydra a general advance in development, but not very much
individual cell specialization. That of the urticating capsules is
one of the best examples of such specialization in this creature.

tmT~yi:>r '.?3?v-a<i;^A

•Jfcx.sl

»«

COMPARATIVE PHYSIOLOGY.

A Polyp is like a colony of Amoebae in which some division of
labor (function) has taken place ; a sort of biological state in
which every individual is nearly equal to his neighbor, but
somewhat more advanced than those neighbors not members of
the organization.

But in one respect the Polyps show an enormous advance.
Ordinarily when nourishment is abundant Hj dra multiplies by
budding, and when cut into portions each may become a com-
plete individual. However, under other circumstances, near
the bases of the tentacles the body wall may protrude into little
uutsses (tea ea), in which ceUs of peculiar formation (aperma-
tozoa) arise, and are eventually set free and unite with a cell-
(ovum) formed in a similar protrusion of larger size (ovary).
Here, then, is the first instance in which distinctly sexual repro-
duction has been met in our studies of the lower forms of life.
This is substantially the same process in Hydra as in mammals.
But, as both male and female cells are produced by the same
individual, the sexes are united (hermaphroditiam) ; each is at
once male and female.

Any one watching the movements of a Polyp, and compar-
ing it with those of a Bell-animalcule, will observe that the
former are much less machine-like; have greater range ; seem
to be the result of a more deliberate choice; are better adapted
to the environment, and calculated to achieve higher ends. In
the absence of a nervous system it ia not easy to explain how
one part moves in harmony with another, except by that pro-
cess which seems to be of such wide application in nature, adap-
tation from habitual simultaneous effects on a protoplasm capa-
ble of responding to stimuli. When one proceels of an Amoeba
is touched, it'is likely to withdraw all. This we take to be due
to influences radiating through molecular movement to other
parts; the same principle of action may be extended to Hydra.
The oftener any molecular movement is repeated, the more it
tends to become organized into regularity, to become fixed in
its mode of action ; and if we are not mistaken this is a funda-
mental law throughout the entire world of living things, if not
of all things animate and inanimate alike. To this law we
shall return.

But Hydra is a creature of but very limited specializations;
there are neither organs of circulation, respiration, nor excretion,
if we exclude the doubtful case of the thread-cells (urticating
capaulea). The animal breathes by the entire surface of th^

rm^.' :,uj!ai-. ' .ni.,ttjt-a. i i iH Mjawigiw.i^*i ( Wt-

me dirision of
ogical state in
neighbor, but
ot members of

nous advance.
I multiplies by
l)ecorae acom-
nstances, near
rude into little
ition (aperma-
te with a cell-
ar size (ovary),
y sexual repi-o-
r forms of life,
sin mammals.
d by the same
m) ; each is at

p, and compare
tserve that the
r range; seem
better adapted
gher ends. In
to explain how
pt by that pro-
n nature, adap-
■otoplasm capa-
I of an Amoeba
I take to be due
ement to other
ided to Hydra,
ed, the more it
9come fixed in
this is a funda-
g things, if not
ro this law we

specializations;

1, nor excretion,

ills (urticating

surface of the

GENERAL BIOLOGY.

body ; nourishment passes from cell to cell, and waste is dis-
charged into the water surrounding the creature from all cells,
though probably not quite equally. All parts are not digestive,
respiratory, etc., to the same degree, and herein doed it differ
greatly from Amoeba or even Vorticella, though fuller knowl-
edge will likely modify our views of the latter two and similar
organisms in this regard.

THE OELL BSCX>NBIDBRBD.

Having now studied certain one-celled plants and animals,
and some very simple combinations of cells (molds, etc.), it will
be profitable to endeavor to generalize the lessons these humble
organisms convey ; for, as will be constantly seen in the study of
the higher forms of life of which tliis work proposes to treat
principally, the same laws operate as in the lowliest living creat-
ures. The most complex organism is made up of tissues, which
are but cells and their products, as houses are made of bricks,
mortar, wood, and a few other materials, however large or elab-
orate.

The student of physiology who proceeds scientifically must
endeavor, in investigating the functions of each organ, to learn
the exact behavior of each cell as determined by its own inherent
tendencies, and modified by the action of neighboring cells.
The reason why the function of one organ differs from that of
another is that its cells have departed in a special direction from
those properties common to all cells, or have become function-
ally differentiated. But such a statement has no meaning un-
less it be well understood that cells have certai|i properties in
common. This is one of the lessons imparted by the preceding
studies which we now review. Briefly stated in language now
extensively used in works on biology, the common properties of
cells (protoplasm), whether animal or vegetable, whether consti-
tuting in themselves entire animals or plants, or forming the
elements of tissues, are these : The collective chemical processes
associated with the vital activities of cells are termed its metab-
6li8m. Metabolism is constructive when more complex com-
pounds are formed from simple ones, as when the Protococcus-
oell builds up its protoplasm out of the simple materials, found in
rain-water, which makes up its food. Metabolism is destructive
when the reverse process takes place. The results of this process
are eliminated as excreta, or useless and harmful products.

COMPARATIVE PHYSIOLOGY.

Since all the vital activities of cells can only be manifested when
supplied with food, it follows that living organisms convert po-
tential or possible energy into kinetic or actual energy. When
lifeless, immobile matter is taken in as food and, as a result, is
converted by a process otcusimilation into the protoplasm of the
cell using it, we have an example of potential being converte<l
into actual energy, for one of the properties of all protoplasm is
its contractility. Assimilation implies, of course, the absori)-
tion of what is to housed, with rejection of waste matters.

The movements of protoplasm of whatever kind, when duo
to a stimulus, are said to indicate irritability; while, if inde-
pendent of any external source of excitation, they are denomi-
nated automatic.

Among agents that modify the action of all kinds of proto-
plasm are heat, moisture, electricity, light, and others in great
variety, both chemical and mechanical. It can not be too well
remembered that living things are what they are, neither by
virtue of their own organization alone nor through the action
of their environment alone (else would they be in no sense dif-
ferent from inanimate things), but because of the relation of
the organization to the surroundings.

Protoplasm, then, is contrcustile, irritable, automatic, abaorp-
k, je, secretory (and excretory), metabolic, and reproductive.

But when it is affirmed that these are the fundamental prop-
erties of all protoplasm, the idea is not to be conveyed that cells
exhibiting t^ese properties are identical biologically. No two
masses of protoplasm can be quite alike, else would there be no
distinction in physiological aemeanor— no individuality. Everj'^
cell, could we but behold its inner molecular mechanism, difPers
from its neighbor. When this difference reaches a certain de-
gree in one direction, we have a manifest differentiation leading
to physiological division of labor, which may now with advan-
tage be treated in the following section.

TBB AMIMAXi BOUT.

! lii

An animal, as we have learned, may be made up of a single
cell in which each part performs much the same work; or, if
there be differences in function, they are ill-defined as compared
with those of higher animals. The condition of things in such
an animal as Amoeba may be compared to a civilized commu-
nity in a very crude social condition. Wh :n each individual

tJ^^jU..i,IV8

f.i i ,atrJ>yjijjJSj>MtBafe"-aj«V*-i'W.

-.w;'-^-'* :

'* *

GENERAL BIOLOGY.

ids of proto-
lers in great
t be too well
i, neither by
h theantion
no sense dif-
e relation of

Mtic,ahaorp-
"odttctive.
^mental prop-
yed that cells
.Uy. No two
d there be no
lality. Everj'^
Emism, difPem
a certain de-
ation leading;
' with advan*

ip of a single
> work; or, if
as compared
lings in such
Lized conunu-
!h individual

tries to perform every office for himself, ho is at once carpenter,
blacksmith, shoemaker, and much more, with the natural ro-
sult that he is not efficient in any one direction. A community
may be judged in regard to its degree of advancement by the
amount of division of labor existing within it. Thus is it with
the animal body. We find in such a creature as the fresh-water
Hydra, consisting of two layers of cells forming a simple sac, a
slight amount of advancement on Amoeba. Its extemaF surface
no longer serves for inolosure of food, but it has the simplest
form of mouth and tentacles. Each cf the cells of the internal
layer seems to act as a somewhat improved or specialized Amoe-
ba, while in those of the outer layer we mark a beginning of
those functions which taken collectively give the higher ani-
mals information of the surrounding world.

Looking to the existing state of things in the universe, it is
pUun that an animal to attain to high ends must have powers
of rapid locomotion, capacity to perceive what makes for its in-
terest, and ability to utilize means to obtain this when perceived.
These considerations demand that an animal high in the scale
of being should be provided with limbs sufficiently rigid to sup-
jiort its weight, moved 1^ strong muscles, which must act in
harmony. But this implies abundance of nutriment duly pre-
pared and regularly conveyed to the bones and muscles. All
this would be useless imless there was a controlling and ener-
gizing systemt capable both of being impressed and originating
impressions. Such is found in the nerves and nerve-centers.
Again, in order that this mechanism be kept in good running
order, the waste of its own metabolism, which chokes and poi-
sons, must be got rid of— hence the need of excretory apparatus.
In order that the nervous system may get sufficient informa-
tion of the world around, the surface of the body must be pro-
vided with special message-receiving offices in the form of
modified nerve-endings. In short, it is seen that an animal as
high in the scale as a mammal must have muscular, osseous
(and connective), digestive, circulatory, excretory, and nervous
tissues; and to these may be added certain forms of protective
tissues, as hair, nails, etc.

Assuming that the student has at least some general knowl-
edge of the structure of these various tissues, we propose to tell
in a simple way the whole physiological story in brief.

The blood is the source of all the nourishment of the organ-
ism, including its oxygen supply, and is carried to every part of

COMPARATIVE PHYSIOLOGY.

the body ihrousfh eUwtio tubes which, continiially branching
and becomini; gradually smaller, terminate in yesselH of hair-
like finoneew in which the current is very slow — a condition per-
mitting that interchange between the cells surrounding them
and the blood which may be compared to a process of barter,
the cells taking nutriment and oxygen, and giving (excreting)
in return carbonic anhydride. From these minute vessels' thn
blood is conveyed back toward the source whence it came by
similar elastic tubes which gradually increase in size and be-
come fewer. The force which directly propels the blood in its
onward course is a muscular pump, with both a forcing and
suction action, though chiefly the former. The flow of blood
is maintained constant owing to the resistance in the smaller
tubes on the one hand and the elastic recoil of the larger tubes
on the other ; while in the returning vessels the column of
blood is supported by elastic double gates which so close as to
prevent reflux. The oxygen of the blood is carried in disks of
microscopic size which give it up in proportion to the needs of
the tissues past which they ore carried.

But in reality the tissues of the body are not nourished
directly by the blood, but by a fluid derived from it and resem-
bling it greatly in most particulars. This fluid bathes the tis-
sue-cells on all sides. It also is taken up by tubes that convey
it into the blood after it has passed through little factories
(lymphatic glands), in which it undergoes a regeneration.
Since the tissues are impoverishing the blood by withdrawal of
its constituents, and adding to it what is no longer useful, and
is in reality poisonous, it becomes necessary that new material
be added to it and the injiuious components withdrawn. The
former is accomplished by the absorption of the products of
food digestion, and the addition of a fresh supply of oxygen
derived from without, while the poisonous ingredients that
have foimd their way into the blood are got rid of through
processes that may be, in general, compared to those of a sew-
age system of a very elaborate character. To explain this re-
generation of the blood in somewhat more detail, we must first
consider the fate of food from the time it enters the viouth till
it leaves the tract of the body in which its preparation is car-,
ried on.

The food L> in the mouth submitted to the action of a series
of cutting and grinding organs worked by powerful muscles ;
mixed with a fluid which changes the starchy part of it into

MRNKRAL BIOLOGY.

|y branching

iIh of hair-

[ondition per-

nding them

of barter,

|fir (excreting)

▼easels' the

it came by

size and be-

blood in its

forcing and

low of blood

the smaller

larger tubes

e column of

Bo close as to

ed in disks of

> the needs of

lot nourished
it and resem-
laihes the tis-
I that convey
ittle factories
regeneration,
dthdrawal of
er useful, and
new material
idrawn. The
B products of
ly of oxygen
redlents that
i of through
lose of a sew-
plain this re-
we must first
^e xuouth till
.ration is car-

m of a series
f ul muscles ;
irt of it into

sugar, and prepares the whole to pass further on its course :
when this has been accomplished, the food is grasped and
squeezed and pushed along the tube, owing to the action of its
own muscular cells, into a, sac (stomach), in which it is rolled
about and mixed with certain fluids of peculiar chemical com-
position derived from cells on its inner siu^ace, which trans-
form the proteid part of the food into a form susceptible of
ready use (absorption). When this saccalar organ has done
its share of the work, the food is moved on by the action of
the muscles of its walls into a very long portion of the tract
in which, in addition to processes carried on in the mouth and
stomach, there are others which transform the food into a con-
dition in which it can pass into the blood. Thus, all of the
food that is susceptible of changes of the kind described is acted
upon somewhere in the long tract devoted to this task. But
there is usually a remnant of indigestible material which is
finally evacuated. How is the prepared materitd conveyed into
the blood ? In part, directly through the walls of the minutest
blood-vessels distributed throughout the length of this tube ;
and in part through special vessels with appropriate cells cov-
ering them which act as minute porters {villi).

The impure blood is carried periodically to an extensive sur-
face, luiually much folded, and there exposed in the hair-like
tubes referred to before, and thus parts with its excess of car-
bon dioxide and takes up fresh oxygen. But all the functions
described do not go on in a fixed and invariable manner, but
are modified somewhat according to circumstances. The for-
cing-pump of the circulatory system does not always beat
equally fast ; the smaller blood-vessels are not always of the
,same size, but admit more or less blood to an organ according
to its needs.

This is all accomplished in obedience to the commands car-
ried from the brain and spinal cord along the nerves. All
movements of the limbs and other parts are executed in obe-
dience to its behests; and in order that these may be in accord-
ance with the best interests of each particular organ and the
whole animal, the nervous centers, which may be compared to
the chief officers of, say, a telegraph or railway system, are in
constant receipt of information by messages carried onward
along the nerves. The command issuing is always related to
the information arriving.

All those parts commonly known as sense-organs— the eye,

9ftfe".S-.!8Sa8-':.

H'i

COMPARATIVE PFIYSIOLOOY.

niir, noiio, tonffue, and the entire niirfatn) of the btxly — are faith-
ful reportera of fact«. They put the inner and outer worlds in
conuiiunicutinn, and without thvni all lii^rher life at leant munt
fflttMe, for the oriyraniam, like a train directed by a conductor that
disregards the danf^r-sifrn&ls. muRt work itn own destruction.
Without laroing into further details, sufHce it t«i say that the pni-
cesaes of the various cells are subordinated to the general good
through the nervous system, and that susceptibility of proto-
pkisni to stimuli of a delicate kind which enables each cell to
adapt to its surroundings, including the inHuence of remote as
well as neighboring cells. Without this there could be no
marked advance in organisms, no differentiation of n pro-
nounced character, and so none of that physiological division
of labor which will be inferred from our brief description of
the functions of a mammal. The whole of physiology but
illustrates this division of labor.

It is hoped that the above account of the working of the ani-
mal body, brief as it is, may serve to show the connection of
one part functionally with another, for it is much more impor-
tant that this should be kept in mind throughout, than that all
the details of any one function should be known.

* till

UVIMO AMD LIFIILBSB BCATTBR.

In order to enable the student the beti' i* to realize the na-
ture of living matter or protoplasm, and to render clearer the
distinction between the forms that belong to the organic and
inorganic worlds respectively, we shall make some comparisons
in detail which it is hoped may accomplish this object.

A modem watch that keeps correct time must be regarded
as a wonderful object, a marvelous triumph of human skill.
Tltat it has aroused the awe of fiavag4)s, and been mistaken for a
living being, is not surprising. But, admirable as is the result
attained by the mechanism of a watch, it is, after all, composed
of but a few metals, etc., chiefly in fact of two, brass and steel ;
these are, however, made up into a great number of different
parts, so adapted to one another as to work in unison and ac-
complish the desired object of indicating the time of day.

Now, however well constructed the watch may be, there are
waste, wear and tear, which will manifest themselves more and
more, until finally the machine becomes worthless for the pur-
pose of its construction. If this mechanism possessed the power

i i

GRNRRAL BIOLOOT.

ily— are fnith-
itor worlds in
at least munt
conductor that
Ti deatruction.
y that the pro-
general giood
ility of proto-
« each cell to
of remote on
could be no
on of u pro-
)gical division
description of
hysiology but

ing of the ani-
connection of
I more impor-
\ than that all

realiie the na-
[er clearer the
e organic and
le oompariflons
bject.

8t be regarded
human skill,
mistaken for a
IS is the result
' all, composed
"ass and steel ;
erof different
mison and ac-
I of day.
y be, there are
Ives more and
ss for the pur-
ised the power

of adapting from without foreign matter so as to construct it
it into steel and brass, and arrange this just when required, it
.would imitate a living organism ; but this it can not do, nor is
Its waste chemically diffareht from its component metals ; it
does not break up brass and steel into something wholly differ-
ent. In one particular it does closely resemble living things,
in that it gradually deteriorates ; but the degradation of a liv-
ing cell is the consequence of an actual change in its compo-
nent parts, commonly a fatty degeneration. The one is a real
transformation, the other mere wear.

Had the watch the power to give rise to a new one like itself
by any process, especially a process of division of itself into two
parts, we should have a parallel with living forms ; but the
watch can not even renew its own parts, much less give rise to
a second mechanism like itself. Here, then, is a manifest dis-
tinction between living and inanimate things.

Suppose, further, that the watch was so constructed that,
after the lapse of a certain time, it underwent a change in its
inner machinery and perhaps its outer form, so as to be scarcely
recognisable as the same ; and that as a result, instead of indi-
cating the hours and minutes of a time-reckoning adapted to
the inhabitant* of our globe, it indicated time in a wholly dif-
ferent way ; that after a series of such transformations it fell to
pieces—took the original form of the metals from which it was
constructed — we should then have in this succession of events a
parallel with the development, decline, and death of living or-
ganisms.

In another particular o\a illustration of a watch may serve
a useful purpose. Suppose a watch to exist, the works of which
are so concealed as to be quite inaccessible to our vision, so that
all we know of it is that it has a mechanism which when in
action we can hear, and the result of which we perceive in the
movements of the hands on the face ; we should then be in the
exact position in reference to the watch that we now are as re-
gards the molecular movements of protoplasm. On the latter
the entire behavior of living matter depends ( yet it is abso-
lutely hidden from us.

We know, too, that variations must be produced in the
mechanism of time-pieces by temperature, moisture, and other
influences of the environment, resulting in altered action. The
same, as will be shown in later chapters, occurs in protoplasm.
This, too, is primarily a molecular effect If the works of
8

COMPARATIVE PIIV8I0L00Y.

waUshwi were beyond obMnmUon, we should not be able to atat*
exactly how the variationa obaerred in different kindii, or even
different individual* of tho lame kind occurred, though thew
differenoea might be of the moat marked character, luch oa any
one could recogniie. Here once niorr* we refer the differ-
ences to the mechaniani. 80 ii it with living beings : the ulti-
nwte molecular mechanism is unknown to us.

Could we but render these molecular movementa risible to
our eyes, we should have a revelation of far greater scientific
importance than that unfolded by the recent researches into
those living forms of extreme minuteness that swarm every-
where as dust in a sunbeam, and, as will be learned later, are
often the source of deadly disease. Like the movements of the
watch, the activities of protoplasm are ceaseless. A watch that
will not run is, as such, worthless — it is mere metal — has under-
gone an immense degradation in the scale of values ; ho proto-
plasm is no longer protoplasm when its peculiar molecular
movements cease ; it u at once degraded to the rank of dead
matter.

The student may observe that each of the four propositions,
embodying the fundamental properties of living matter, stated
in the preceding chapter, have been illtistrated by the simile of
a watch. Such an illustration is necessarily crude, but it helps
one to realize the meaning of truths which gather force with
each living form studied if regarded aright ; and it is upon the
realization of truth that mental growth ai well as practical
efficiency depends.

OZJUWIFIOATIOM OP THB AMIMAL XZNODOIC

There are human beings so low in the scale as not to possess
such general terms as tree, while tliey do employ names for dif-
ferent kinds of trees. The use of such a word as " tree " im-
plies generalization, or the abstraction of a set of qualities from
the things in which they reside, and making them the basis for
the grouping of a multitude of objects by which we are sur-
rounded. Manifestly without such a process knowledge must
be very limited, and the world without significance ; while in
proportion as generalization may be safely widened, is our
progress in the unifteation of knowledge toward which science
is tending. But it also follows that without complete knowl-
edge there can be no perfect classiflcation of objects ; henoey

OENRRAri BIOLOOY.

t be able to itate
i kintlii, or even
[|, thouifh theM
ter, Buoh as any
Dfer tbo differ-
einga : the ultl-

nenta riaible to
reater aoientiflo
reaearohea into
it Bworm every-
arned later, are
jvementa of the
A watch that
)tal— has under-
iluea ; ao proto-
uliar molecular
e nuik of dead

ur propositions,
g matter, stated
i>y the simile of
ide, but it helps
kthor force with
id it is upon the
ell as practical

[IN02X>M.

IS not to possess
Y names for dif-
i as " tree " im-
f qualities from
9m the basis for
ich we are suiv
:nowledge must
ance ; while in
widened, is our
d which science
omplete Icnowl-
objects ; hence,

any classiflcation must be regarded but as the temporary creed
of wi«^nco, to be miKUflwl with the extensit)n of knowlMlge. As
a nmtter of fact this has been the history of nil wiOlojfical and
other systems of arrangement. The only purpose of grouping
is to simplify and extend knowledge ; this being the case, it fol-
lows that a method of grouping that acr€)mpIisheB this has
value, though the system may be artificial that is based on
resemblances which, though real and constuut, are associated
with differences so numerous and radical that the total amount
of likeness between objects thus grouped is often less than the
difference. Such a system was that of Liniueus, who classified
plants according to the number of stamens, etc., they bore.

Seeing that animals which resemble each other are of com-
mon descent from some earlier form, to establish the line of de-
scent is to determine in great part the classification. Much as-
sistance in this direction is derived from embryology, or the
history of the development of the individual (ontogeny) ; so
that it may be said that the ontogeny indicates, though it does
not actually determine, the line of descent (phytogeny) ; and
it is owing to the importance of this truth that naturalists have
in recent years given so much attention to comparative embry-
ology.

It will be infoiTed that a natural system of classification must
be based both on function and structure, though chiefly on the
latter, since organs of very different origin may have a similar
function ; or, to express this otherwise, homologoua structures
may not be analogout ; and homology gives the better basis for
classification. To illustrate, the wing of a bat and a bird are
both homologous and analogous ; the wing of a Imtterfiy is
analogous but not homologous with these ; manifestly, to clas-
sify batH and birds together would be better than to put birds
and insects in the same group, thus leaving other points of re-
lationship out of consideration.

The broadest possible division of the animal kingdom is into
groups, including respectively one-celled and many-celled forms
— i. e., into Protozoa and Metazoa. As the wider the grouping
the less are differences considered, it follows that the more sub-
divided the groups the more complete is the information con-
veyed ; thus, to say that a dog is a metazoan is to convey a cer-
tain amount of information ; that he is a vertebrate, more ; that
he is a mammal, a good deal more, because each of the latter
terms includes the former.

COMPARATIVE PHYSIOLOGY.

Animal
Kingdom.

Invertc-
brata.

Vertebrata.

■ Protozoa (amoeba, vortioella, etc.).
Coelenterata (spongea, jelly-flab, polyps, etc.).
Eohinodermata (star-nsb, aea-uronioB, etc.)-
Vermes (worms).

Arthropods (orabs, insects, spiders, etc.).
MolluHca (oysters, snails, etc. ).
Molluscoidea (moss-like animals).
Tunicata (ascidians).

Pisces (flshes).

Amphibia (frogs, menobranchus, etc.).

Beptilia (snakes, turtles, etc.). |

Aves (birds).

Manunalia (domestic quadrupeds, etc.).

The above classification (of Claus) is, like all such arrange-
ments, but the expression of one out of many methods of view-
ing the animal kingdom.

For the deti«il8 of classification and for the grounds of that
we have presented, we refer the student to works on zodlogy ;
but we advise those who are not familiar with this subject,
when a technical term is used, to think of that animal belong-
ing to the group in question with the structure of which they
are best acquainted.

Man's Piaoe m the Animal Sinodom.

It is no longer the custom with zoologists to place man in an
entirely separate group by himself ; but Le is classed with the
primates, among which are also grouped the anthropoid apes
(gorilla, chimpanzee, orang, and the gibbon), the monkeys of
the Old and of the New World, and the lemurs. So great is
the structural resemblance of man and the other primates that
competent authorities declare that there is more difference be-
tween the structure of the most widely separated members of
the group than between certain of the anthropid apes and man.

The points of greatest resemblance between man and the
anthropoid apes are the following : The same number of verte-
brae ; the same general shape of the pelvis ; a brain distinguish-
ing them from other mammals ; and posture, being bipeds.

The distinctive characters are size, rather than form of the
brain, that of man being more than twice as large ; a relatively
larger cranial base, by which, together with the greater size of
the jaws, the face becomes prominent ; the earlier closure of
the sutiues of the cranium, arresting the growth of the brain ;
more developed canine teeth and difference in the order of erup-
tion of the permanent teeth ; the more posterior position of the
foramen magnum ; the relative length of the limbs to each

mmm

GENERAL BIOLOOY.

, etc.).

flsh, polype, etc.).

a-urchinB, eto.)-

spiders, etc.)-

B.).

mala).

chus, eto.).
I.).

ipeda, etc.).

Q such arrange-

aethods of view-
grounds of that

irks on zodlogy ;

ith this subject,
animal belong-

e of which they

placeman in an
classed with the
anthropoid apes
the monkeys of
urs. So great is
ler primates that
re difference be-
lted members of
d apes and man.
m man and the
aumber of verte-
irain distinguish-
eing bipeds,
than form of the
rge ; a relatively
le greater size of
larlier closure of
th of the brain ;
he order of erup-
ir position of the
e limbs to each

other and the rest of the body ; minor differences in the hands
and feet, especially the greater f i-eedom and power of apposition
of the great-toe.

But the greatest distinctioti between man and even his closest
allies among the apes is to be found in the development to an
incomparably higher degree of his intellectual and moral na-
ture, corresponding to the differences in weight and structure
of the human brain, and associated with the use of spoken and
written language ; so that the experience of previous genem-
tions is not only registered in the organism (heredity), but in
the readily available form of books, etc.

The greatest structural difference between the race of men
are referable to the cranium ; but, since they all interbreed
freely, they are to be considered varieties of one species.

TBB LAW OF PBBIODZOXTT OR BHTTBM IN NATORB.

The term rhythm to most minds suggests music, poetry, or
dancing, in all of which it forms an essential part so simple,
pronounced, and uncomplicated as to be recognized by all with
ease.

The r^^ular division of music into bars, the recurrence of
chords of lie same notes at certain intervals, of forte and piano,
seeir. tf> be demanded by the very nature of the human mind.
The k-une applies to poetry. Even a child that can not under-
stand ihe language used, or an adult listening to recitations in
an imknown tongue, enjoys the flow and recurrences of the
sounds. Dancing has in aU ages met a want in human organi-
zations, which is partly supplied in quieter moods by the regu-
larity of the steps in walking and similar simple movements.

But as rhythm runs through all the movements of animals,
so is it also found in all literature and all art. Infinite variety
wearies the mind, hence the fatigue felt by the sight-seer. Be-
currence permits of repose, and gratifies an established taste or
appetite. The mind delights in what it has once enjoyed, in
repetition within limits. Repetition with variety is manifestly
a condition of the growth and development of the mind. This
seems to apply equally to the body, for every single function of
each organism, however simple or complex it may be, exempli-
fles this law of periodicity. The heart's action is rhythmical
Q)&xta) ; the blood flows in intermitting gushes from the central
pump ; the to-and-fro movements of respiration are so regular

COMPARATIVE PHYSIOLOGY.

that their cessation would arouse the attention of the least in-
structed ; food is demanded at regfular intervals ; the juices of
the digestive tract are poured out, not constantly but period-
ically ; the movements by which the food is urged along its
path are markedly rhythmic ; the chemical processes of the
body wax and wane like the fires in a furnace, giving rise to
regular augmentations of the temperature of the body at fixed
hours of the day, with corresponding periods of greatest bodily
activity and the reverse.

This principle finds perfect illustration in the nervous sys-
tem. The respiratory act of the higher animals is effected
through muscular movements dependent on regular waves of
excitation reaching them along the nerves from the central cells
which regularly discharge their forces along these channels.
Were not the movements of the body periodic or rhythmical,
instead of that harmony which now prevails, every muscular
act would be a convulsion, though even in the movements of
the latter there is a highly compounded rhythm, as a noise is
made up of a variety of musical notes. The senses are subject
to the same law. The eye ceases to see and the ear to hear and
the hand to feel if continuously stimulated; and doubtless in
all art this law is unconacwusly rc^. aized. That ceases to be
art which fails to provide for th«: nj'. ' il repose and excita-
tion of the senses. The eye will no- .,. a ; continuously one
color, the ear the same sound. Why .eeze on a warm day

so refreshing ? The answer is obvious.

Looking to the world of animate nature as a whole, it is
noticed that plants have their period of sprouting, flowering,
seeding, and decline; animals are bom, pass through various
stages to maturity, diminish in vigor, and die. These events
make epochs in the life-history of each species; the recurrence
of which is so constant that the agricultural and other arrange-
ments even of savages are planned accordingly. The* vhe in-
dividuals of each animal group have a definite period of dura-
tion is ariothsr manifestation of the same law.

Superficial observation suffices to furnish facts which show
that the same law of periodicity is being constantly exemplified
in the world of inanimate things. The regular ebb and flow of
the tides; the rise and subsidence of rivers; the storm and the
calm; summer and winter; day and night— are all recurrent,
none constent.

Elvents apparently without any regularity, utterly beyond

' -w<vwjjjfc»«iiaMyi4-?-j4^siMJ4 ' ^m:

the least in-
[the juices of
(ly but period-
along its
of the
iving rise to
at fixed
fttest bodily

nervous sys-

ils is effected

ular waves of

le central cells

kese channels.

r rhythmical,

rery muscular

movements of

1, as a noise is

ses are subject

ar to hear and

id doubtless in

lat ceases to be

)se and excita-

atinuously one

on a warm day

i a whole, it is
ing, flowering,
irough various

These events
the recurrence
other arrange-

Thfi* .he in-
leriod of dura-

ts which show
;Iy exemplified
bb and flow of
storm and the
all recurrent,

itterly beyond

GENERAL BIOLOGY.

^^mm^-^

any law of recurrence, when sufficiently studied are found to
fall under the same principle. Thus it took some time to learn
that volcanic eruptions occurred with a very fair degree of
regularity.

In judging of this and all other rhythmical events it must
be borne m mind that the time standard is for an irregularity
that seems large, as- in the instance just referred to, becomes
small when considered in relation i» the millions of yean of
geological time; while in the case of music a trifling irregu-
larity, judged by fractions of a second, can not be tolerated by
the musical organization — ^which is equivalent to saying that
the interval of departure from exact regularity seems large.

As most of the rhythms of the universe are compounded of
several, it follows that they may seem, until closely studied,
very far from regfular recurrences. This may be observed in
the interference in the regularity of the tides themselves, the
daily changes of which are subject to an increase and decrease
twice in each month, owing to the influence of the sun and
moon being then either coincident or antagonistic.

In the functions of plants and animals, rhythms must be-
come very greatly compounded, doubtless often beyond recog-
nition.

Among the best examples of rhythm in animals are daUy
sleep and winter sleep, or hibematiou; yet, amid sleep, dreams
or recurrences of cerebral activity are common — that is, one
rhythm (of activity) overlies another (of repose). In like man-
ner many hibernating animals do not remain constantly in their
dormant condition '^roughout the winter months, but have
periods of wakefukiess; the active life recurs amid the life of
functional repose.

To return to the world of inanimate matter, we find that the
crust of the earth itself is made of layers or strata the result of
periods of elevation and depression, of denudation and deposi-
tion, in recurring order.

The same l?.w is illustrated by the facts of the economic and
other conditions of the social state of civilized men. Periods
of depression alternate with periods of revival in commercial
life.

There axe periods when many more marriages occur and
many more children are born, corresponding with changes in
the material conditions which influence men as well as other
animals.

COMPARATIVE PHYSIOLOGY.

1 ;;

Finally, and of special interest to the medical student, are
the laws of rhythm in disease. Certain fevers have their regu-
lar periods of attack, as intermittent fever; while all diseases
have their periods of ^xacerhation, however invariable the
symptoms may seem to be to the ordinary observer or even to
the patient himself.

Doubtless the fact that certain hereditary diseases do not
appear in the offspring at once, but only at the age at which
they were manifested in the parents, is owing to the same
cause.

Let us now examine more thoroughly into the real nature of
this rhythm which prevades the entire universe.

If a bow be drawn across a violinnstring on which some small
pieces of paper have been placed, these will be seen to fly off ;
and if the laigest string be experimented upon, it can be ob-
served to be in rapid to-and-fro motion, known as vibration,
which motion is perfectly regular, a definite number of move-
ments occiurring within a measured period of time ^, in other
words the motion is rhythmical. In strings of the finest size
ihe motion is not visible, but we judge of its existence because
of the result, which is in each instance a sound. Sound is to us,
however, an affection of the nerve of hearing and the brain,
owing to the vibrations of the ear caused by similar vibrations
of the violin-strings. The movements of the nerves and nerve-
cells are invisible and molecular, and we seem to be justified in
r^arding molecular movementa <m constant and asaociaied
with all the properties of matter whether living or dead.

We see, then, that all things living and lifeless ai« in con-
stant motion, visible or invisible ; there is no such thing in the
universe as stable equilibrium. Change, ceaseless change, is
written on all things ; and, so far as we can judge, these
changes, on the whole, tend to higher development. Neither
rhythm, however, nor anything else, is perfect Even the mo-
tions of planets are subject to perturbations or irregularities
in their periodicity. This subject is plainly boundless in its
scope. We have introduced it at this stage to prepare for its
study in detail in dealing with each function of the animal
body. If we are correct as to the universality of the law of
rhythm, its importance in biology deserves fuller recognition
than it has yet received in works on physiology ; it will, ac-
cordingly, be frequently referred to in the future chapters of
this book.

OBNEBAL BIOLOGT.

il student, are
ive their regu-
le all diseases
nvariable the
ror or even to

iseases do not
age at which
to the same

real nature of

Lch some small
Ben to fly off ;
it can be ob-
as vibration,
aber of move-
ime^, in other
the finest size
stence because
3ound is to us,
md the brain,
ilar vibrations
ves and nerve-
be justified in
nd tusocMted
or dead.
MS are incon-
h thing in the
ess change, is
judge, these
lent. Neither
Even the mo-
irr^fularities
imdless in its
»repare for its
)f the ftTiiiif>ft l
Df the law of
r recognition
7 ; it will, ac-
« chapters of

TBB I<AW OF BABIT.

Every one must have observed in himself and others the
tendency to fall into set ways of doing certain things, in which
will and clear purpose do not come prominently into view.
Further observation shows that the lower animals exhibit this
tendency, so that, for example, the habits of the horse or the dog
may be an amusing reflection of those of the master. Trees are
seen to bend permanently in the direction toward which the
prevailing winds blow.

The violin that has experienced the vibrations, aroused by
some master's hand acquires a potential musical capability not
possessed by an instrument equally good originally, but the
molecular movements of which never received such an educa-
tion.

It appears, then, that underlying what we call habit, there is
some broad law not confined to living things ; indeed, the law
of habit appears to be closely related to the law of rhythm we
have already noticed. Certain it is tnat it is inseparable from
all biologiod phenomena, though most manifest in those organ-
isms provided with a nervojis system, and in that system itself.
What we usually call habit, however expressed, has its physical
correlation in the nervous system. We may refer to it in this
connection later: but the subject has relations so numerous
and fundamental that it seems eminently proper to introduce
it at this early stage, forming as it does one of those comer-
stones of the biological building on which the superstructure
mustiest

When we seek to come to a final explanation of habit in this
• case, as in most others, in which the fundamental is involved,
we are soon brougnt against a wall over which we are imable
to dimb, and through which no light comes to our intellects.

We must simply believe, as the result of observation, that it
is a law of matter, in all the forms manifested to us, to assume
accustomed modes of behavior, perhaps we may say molecular
movement, in obedience to inherent tendencies. But, to recog-
nize this, throws a flood of light on what would be inexplicable,
even in a minor degree. We can not explain gravitation in it-
self ; but, assuming its imiversality, replaces chaos by order in
our speculations on matter.

Turning to living matter, we look for the origin of habit in
the apparently universal principle that primary molecular

COMPARATIVE PHYSIOLWY.

movement in one direction renders that movement easier after-
ward, and in proportion to the frequency of repetition ; which
is equivalent to saying that functional activity facilitates func-
tional activity. Once accepting this as of universal application
in biology, we have an explanation of the origin, the compara-
tive rigidity, and the necessity of habit. There must be a phys-
ical basis or correlative of all mental and moral habits, as well
as those that may be manifested during sleep, and so purely in-
dependent of the will and consciousness. We are brought, in
fact, to the habits of cells in considering those organs, and that
combination of structures which makes up the complex individ-
ual mammal. It is further apparent that if the cell can trans-
mit its nature as altered by its experiences at all, then habits
must be hereditary, which is known to be the case.

Instincts seem to be but crystallized habits, the inherited
results of ages of functional activity in certain well-defined
directions.

To a being with a highly developed moral nature like man,
the law of habit is one of great, even fearful signifiqance. We
make to-day our to-morrow, and in the present we are deciding
the future of others, as our present has been made for us in part
by our ancestors. We shall not pursue the subject, which is of
boundless extent, further now, but these somewhat general
statements will be amplified and applied in future chapten.

THB ORIOIN or THB FORMS OF UFB.

It is a matter of common observation that animals originate
from like kinds, and plants from forms resembling themselves ;
while most carefully conducted experiments have failed to show *
that living matter can under any circumstances known to us
arise from other than living matter.

That in a former condition of the universe such may have
been the case has not been disproved, and seems to be the logical
outcome of the doctrine of evolution as applied to the universe
generally.

By evolution is meant the derivation of more complex and
differentiated forms of matter from simpler and more homogene-
ous oney. When this theory is applied to organized or living
forms, it is termed organic evolution. There are two views of
the ori'np of life : the one, that each distinct group of plants
and ani s was independently created ; while by " cr^tion " is

it easier after-
ititiou ; which
icilitates func-
ial application

the compara-
inst be a phys-
habits, as well
I so purely in-
re brought, in
gans, and that
mplex individ-
cell can trans-
11, then habits
e.

the inherited
1 well-defined

ture like man,
kiflqance. We
re are deciding
i for us in part
ict, which is of
Bwhat general
e chapters.

UPB.

imals originate
tg themselves ;
) failed to show *
s known to us

luoh may have
> be the logical
the universe

i complex and
ore homogene-
nized or living
B two views of
roup of plants
"creation "is

GENERAL BIOLOGY.

simply meant that they came into being in a manner we know
not how, in obedience to the will of a First Cause. The other
view is denominated the theory of descent with modification,
the theory of transmutation, organic evolution, etc., which
teaches that all the various forms of life have been derived
from one or a few primordial forms in harmony with the recog-
nized principles of heredity and vambility. The most widely
known and most favorably received exposition of this theory is
that of Oharles Darwin, so that his views will be first presented
in the form of a hypothetical case. Assume that one of a group
of living forms varies from its fellows in some particular, and
1 M ..ag with another that has similarly varied, leaves progeny
i aeriting this characteristic of the parents, that tends to be
still further increased and rendered permanent by successive
pairing Mrith forms possessing this variation in Hhape, color, or
whatever it may be. We may suppose that the variations may
be numerous, but are always small at the beginning. Since all
animals and plants tend to multiply faster than the means of
support, a competition for the means of subsistence arises, in
which struggle the fittest, as judged by the circumstances, al-
ways is the most successful.; and if one must perish outright, it
is the less fit. If any variation arises that is unfavorable in
this contest, it will render the possessor a weaker competitor :
hence it follows that only useful variations are preserved. The
struggle for exii^tence is, however, not alone for food, but for
anything which may be an advantage to its possessor. One form
of the contest is that which results from the rivalry of members
of the same sex for the possession of the females ; and as the
female chooses the strongest, most beautiful, most active, or the
supreme in some respect, it follows that the best leave the great-
est number of progeny. This has been termed sexual selection.
In determining what forms shall survive, the presence of
other plants or animals is quite as important as the abundance
of food and the physical conditions, often more so. To illustrate
this by an example : Certain kinds of clover are fertilized by
the visits of the bumble-bee alone ; the numbers of bees exist-
ing at any one place depends on the abundance of the field-mice
which destroy the nests of these insects ; the numbers of mice
will depend on the abundance of creatures that prey on the
mice, as hawks and owls ; these, again, on the creatures that
specially destroy them, as foxes, etc. ; and so on, the chain of
connections becoming more and more lengthy.

COMPARATIVK PHYSIOLOGY.

• l»o« (H), c«lf (O. wSbU (H), Md •man (M). The condlUon* ofthe thfMdiaM^
•",* ^Jf? "' deretoprnwit, which the three craw-iow* (I, n, IH) lepieMnt. are
■dec^ to correqwDd u ezaetlr u powlble. The flnt, 'or nppir oSSmow^.
renjMenU • yery ewhr eti^e, with gill-openlugi, and witbirat limbi. The second
(middle) cnMa-row, 11, ahowe a aomewhat later ataKe. with the Irat mdlmenta of
limba, while the gttl-openincs are yet retained. The third (lowest) cross-row, HI.
shows a still later stage, with the limbs more developed and the glll-openioga

GENERAL BIOLOGY.

mdincitagMt of
t the thne difluh
II) tepKMnt, are
•per croH-iow, I,
lb*. TTw Mcond
Int radlBMnt* of
It) croM-row, in,
the gill-openings

iMt. The memhranm and Appondagce of tho cmliryr.nic body (the •mninn, rclk-
Mc, allantoli) are omitted. The whole twolvn ligntvn are Klluhtly magnlfleil, the
iipiKT ones mora then tho lower. To facilitate tho comparlion, thcv are all re-
diiced to iivnrly thv name ilie in the cnti. All tho umbryoe are leen from tho loft
aide ; tho hoaa extronlty la above, the tall extremity below ; the arched back
turned to the riuht The lettera Indicate the fame parte In all the twelve flsure*,
namely: v, fore-brain; (, twixt-brain; m, mld-brain; A, hInd-braIn; n, after-ornin;
r, aplnal marrow: e, noae; <i, eve; o, ear; k, Kill-*Kne«; g. heart; tc, vertebral
column; /, fore-llmbe; ft, hlnd-limba; «, tall. (After Uaeckel.)

If a certain proportion of forms varying similarly were sep-
arated by any great natural barrier, as a chain of lofty mountains
or an intervening body of water of considerable extent, and so pre-
vented from breeding with forms that did not vary, it is clear that
there would be greater likelihood of their differences being pre-
served and augrmented up to the point of their greatest usefulness.

We may now inquire whether such has actually been the
course of events in nature. The evidence may be arranged un-
der the following heads :

1. Morphology.— Briefly, there is much that is common to
entire large groups of animals ; so great, indeed, are the resem-
blances throughout the whole animal kingdom that herein is
found the strongest argument of all for the doctrine of descent. .
To illustrate by a single instance — fishes, reptiles, birds, and
mammals possess in common a vertebral column bearing the
same relationship to other parts of the animal. It is because of
resemblances of this kind, as Well as by their differences, that
naturalists are enabled to classify animals.

2. Bmbryology. — In the stages through which animals pass
in their development from the ovum to the adult, it is to be ob-
served that the closer the resemblance of the mature organism
in different groups, the more the embryos resemble one another.
Up to a certain stage of development the similarity between
groups of animals, widely separated in their post-embryonic
life, is marked : thus the embryo of a reptile, a bird, and a mam-
mal have much in common in their earlier stages. The embryo
of the mammal passes through stages which represent condi-
tions whicbare permanent in lower groups of animals, as for
example thahel the branchial arches, which are represented by
the gills in fishes. It may be said that the developmental his-
tory of the individual (ontogeny) is a brief recapitulation of the
development of the species (phylogeny). Apart from the theory
of descent, it does not seem possible to gatiier the true signifi-
cance of such facta, which will become plainer after the study
of the chapters on reproduction.

S. Mimioiy may be cited as an instance of useful adaptation.

!i- I'J

COMPARATIVK PIIYSIOLOOY.

Thus, certain beetles reaenible bees aud wanpH, wliich latter are
protecte<l by atinga. It ia believed that auoh groupa uf beetles
aa theae ar»ae by a species of selection ; those escaping enemies
which chanced to resemble dreaded insects most, so that birds
which wore accustomed to prey on beetles, yet feared bccH, would
likewise avoid the mimicking forms.

4. BudimMltMry OrgUU. — Organs which were once func-
tional in a more ancient form, but serve no use in the creatures
in which they are now found, have reached, it is thought, their
rudimentary condition through long periods of comparative
disuHO, in many generations. Buch arc the rudimentary mus-
cleH of the ears of man, or the undeveloped incisor teeth found
in the upper jaw of ruminants.

6. OMJgpraphioal Diltribatioil.— It can not be said that ani-
mals and plants are always found in the localities where they
are best fitted to flourish. This has been well illustrated within
the lifetime of the present generation, for the animals intro-
duced into Australia have many of them so multiplied as to
displace the forms native to that country. But, if we assume
that migrations of animals and transmutations of species have
taken place, this difficulty is in great part removed.

6. Paleontology. — ^The rocks bear record to the former exist-
ence of a succession of related forms; and, though all the in-
termediate links that probably existed have not been found,
the apparent discrepancy can be explained by the natiue of
the circumstances under which fossil forms are preserved ; and
the " imperfection of the geological record."

It is only in the sedimentary rocks arising from mud that
fossils can be preserved, and those animals alone with hard
parts are likely to leave a trace behind them ; while if these
sedimentary rocks with their inclosed fossils should, owing to
enormous pressure or heat be greatly changed (metamorphosed),
all trace of fossils must disappear — so that the earliest forms
of life, those that would most naturally, if preserved at all, be
found in the most ancient rocks, are wanting, in consequence
of the metamorphism which such formations have undergone.
Moreover, our knowledge of the animal remains in the earth^s
crust is as yet very incomplete, though, the more it is explored,
the more the evidence gathers force in favor of organic evolu-
tion. But it must be remembered that those groups constitut-
ing species are in geological time intermediate links.

7. FoHil and Slilting BpeeimL— If the animals and plants

kaih

'ism-!m0 ■--Mftfeg r^

[lich latter are
mps of beetles
uping cneniie*
;, to tliat birdR
•ed becH, would

re once func-
i the creatures
thought, their
f comparative
imentary mu»-
)r teeth found

said that ani-
ie« where they
latrated within
animals intro-
ultiplied as to
t, if we assume
>f species have
id.

e former ezist-
gh all the in-
>t been found,

the nature of
ireserved ; and

rom mud that
Dne with hard
while if these
ould, owing to
itamorphosed),
earliest forms
2rved at all, be
in consequence
ve undergone.
! in the earth's
) it is explored,
organic evolu-
oups constitut-
nks.
als and plants

GENERAL DIOLOOY.

now peopling the earth were entirely different from those that
llouriHhed ii» the past, the objections U» the doctrine of descent
would be greatly Bt.-«mgthened; but when it is found that there
is in some cases :i scarcely broken succession of forms, great
force is added to the argument* by which we are led to infer
tho connection of all forms with one another.

To illustrate by a single instance: the existing group of
horses, with a single toe to each foot, was preceded in geological

Vin M — nnnM of the feet of the dlkerent K«'ncr» of Egvida (after Manh). a. Uot
"»• 1" — '!':"™ "' J"*!*^: i ."_. „# j_-*ini..j„m (l^w«r Hlocenet: c. foot of Hilh

r the dlSerent K«'ncr» of Efuiaa («rier jtannj. a, ion
'of 0»wA*p»-M (Koccne ); 6, foot of AncMihMi>m(lA>^er Miocene); e, foot of mp-
paritm (Pliocene); d, fool of the recent genu* Equui.

time in America by forms with a greater number of toes, the
latter increasing according to the antiquity of the group.
These forms occur in succeeding geological formations. It is
impossible to resist the conclusion that they are related gene-
alogically (phylogenetically).

8. Piogrwwlail.— Inasmuch as any form of specialiBation that
would give an animal or plant an advantage in the struggle for
existence would be preserved, and as in most cases when the
competing forms are numerous such would be the case, it is
possible to understand how the organisms that have appeared
have tended, on the whole, toward a most pronounced pro-
gression in the scale of existence. This is well illustrated in
the history of civilization. Barbarous tribes give way before
civiliied man with the numberless subdivisions of labor he in-
stitutes in the social organism. It enables greater numbers to
flourish, as the competition is not so keen as if activities could
be exercised in a few directions only.

9. DomestiiOSted Animftll.— Darwin studied our domestic ani-
mals long and carefully, and drew many important conclusions

COMPARATIVK PHYSIOLOGY.

1^:1

from his rcMwrchni. He waa uoiiviticed that they had all limn
derived from a few wild repreaentativea, in accordance with the
principle* of natural lelection. Breedera have lioth conicioiialy
and unoonacioualy, formed race* of animaU from Htoclu which
the new groups have now Rupplanted ; while primitive man
had tamed various speciea which hu kept for food and t4) otwiat
in the chase, or as beasts of burden. It is impossible to believe
that all the different races of dogs have originated from dis-
tinct wild stocks, for nuiny of them have been formed within
recent periods; in fact, it is likely that to the jackal, wolf, and
fox, must we look for the wild progenitors of our dogs. Dar-
win concluded that, as man had only utilized the materials
Nature provided in forming his races of domestic animals, he
had availed himself of the variations that arose spontaneously,
and increased and fixed them by breeding those possessing the
same variation together, so the like had occurred without his
aid in nature among wild forms.

Evolutionists are divided as to the origin of man himself ;
some, like Wallace, who are in accord witlt Darwin as to the

Fia, 46.— Skeleton of hand or fore-foot of ilz mammali. I. man; IT, doK; ITI, pig;
IV. ox; V, tapir; VI, hone, r, ladlna; u, nina: a, icaphold; b, leinl-lunar; e,
triqaetmm (cnnciform); rf, trapeilniii: «, tmpeaold; f, capitatum (unciform pro-
o«*a); g, hamatiim (unciform bone); p, pialform; 1| thumb; 8, digit; 8, miadle
flnger; 4, rlng-flnger; B, little flnger. (AfMr Gogenbaur.)

origin of living forms in general, believe that the theory of
natural selection does not suffice to account for the intellectual

ey had all been
nknce with the
nth conm-iously
n Htoclu which
priiniiive man
Oil and t4) ombt
Mible to believe
lutod from dla-
formod within
tckal, wolf, and
lur dogs. Dar-
1 the ninterials
itio aniniab, he
■pontaneouflly,
B poMMMing the
red without hia

' man himself ;
irwin ao to the

in; IT, doft; ITT, pig:
lid; 6, teml-lunar; c,
■turn (nnclfonn pro-
i; », digit; 8, middle

t the theory of
the intellectual

(IKNKUAI. niOLOOY.

1 1,

^ 'i

i i

j'lj

j,(

i'l

1 1

I'M

1 ii

lii

i
1

1 '

i !{||

1 1

■

III

■ 1

1 1

1 i ,

"^ 1

1 ^

COMPARATIVE PHYSIOLOGY.

and moral nature of man. Wallace believes that man's body
has been derived from lower forms, but that his higher nature
is the result of some unknown law of accelerated development;
while Darwin, and those of his way of thinking, consider that
mau in his entire nature is but a grand development of powers
existing in minor degree in the animals below him in the scale.
Bnmmary. — Every group of animals and plants tends to in-
crease in numbers in a geometrical progression, and must, if
unchecked, overrun the earth. Every variety of animals and
rlants imparts to its offspring a general resemblance to itself,
but with minute variations from the original. The variations
of offsprings may be in any direction, and by accumulation
constitute fixed differences by which a new group is marked
off. In the determination of the variations that persist, the law
of survival of the fittest operates.

Eit man's body
higher nature
, development ;
, consider that
aent of powers
m in the scale,
its tends to in-
i, and must, if
f animals and
lance to itself,
The variations
accumulation
oup is marked
persist, the law

REPRODUCTION.

As has been already noticed, protoplasm, in whatever form,
after passing through certain stages in development, undergoes
a decline, and finally dies and joins the world of unorganized
matter ; so that the permanence of living things demands the
constant formation of new individuals. Groups of animals
and plants from time to time become extinct; but the lifetime
of the species is always long compared with that of the indi-
vidual. Reproduction by division seems to arise from an exi-
gency of a nutritive kind, best exemplified in the simpler or-
ganisms. When the total mass becomes too great to be supported
by absorption of pabulum from without by the surface of the
body, division of the organism must take place, or death ensues.
It appears to be a matter of indifference how this is accom-
plished, whether by fission, endogenous division, or gemmation,
so long as separate portions of protoplasm result, capable of
leading an independent existence. The very undifferentiated
character of these simple forms prepares us to understand how
each fragment may go through the same cycle of changes as
the parent form. In such cases, speaking generally, a million
individuals tell the same biological story as one ; yet these
must exist as individuals, if at all, and not in one great united
mass. But in the case of conjugation, which takes place some-
times in the same groups as also multiply by division in its
various forms, there is plainly an entirely new aspect of the
case presented. We have already shown that no two cells, how-
ever much alike they may seem as regards form and the cir-
cumstances under which Uiey exist, can have, in the nature of
the case, precisely the same history, or be the subjects of ex-
actly the same experiences. We have also pointed out that aU
these phenomena of cell-life are known to us only as adapta-
tions of internal to external conditions; for, though we may not
be always able to trace this connection, the inference is justi-

COMPARATIVE PHYSIOLOGY.

flable, because there are no facts known to us that contradict
such an assumption, while those that are within our knovledgf,
bear out the generalization. We have already learned Utui ' iv-
ing things are in a state of constant change, as indeed -a-e all
things ; we have observed a constant relation between certain
changes in the environment, or sum total of the surrounding
conditions, as, for example, temperature, and the behavior of
the protoplasm of plants and animals; so that we must believe
that any one form of protoplasm, however like another it may
seem to our comparatively imperfect observation, is diiferent
in some i-espects from every other— as different, relatively, as
two human beings living in the same community during the
whole of their lives ; and in many cases as unlike as individuals
of very different nationality and history. We are aware that
when two such persons meet, provided the unlikeness is not so
great as to prevent social intercourse, intercommunication may
prove very instructive. Indeed, the latter grows out of the
former; our illustration is itself explained by the law we aro
endeavoring to make plain. It would appear, then, that con-
tinuous division of protoplasm without external aid is not pos-
sible; but that the vigor necessary for this must in some way
be imparted by a particle (cell) of similar, yet not wholly like,
protoplasm. This seems to furnish an explanation of the neces-
sity for the conjugation of living forms, and the differentiation
of sex. Very frequently conjugation in the lowest animals and
plants is followed by long periods when division is the prevail-
ing method of reproduction. It Js worthy of note, too, that
when living forms conjugate, they both become quiescent for a
longer or shorter time. It is as though a period of preparation
preceded one of extraordinary activity. We can at present
trace only a few of the steps in this rejuvenation of life-stuff.
Some of these have been already indicated, which, with others,
will now be further studied in this division of our subject, both
because reproduction throws so much light on cell-life, and be-
cause it is so important for the understanding of the physio-
logical behavior of tissues and organs. It may be said to be
quite as important that the ancestral history of the cells of an
organism be known as the history of the units composing a
community. A, B, and C, can be much better understood if
we know something alike of the history of their race, their an-
cestors, and their own past; so is it with the study of any indi-
vidual animal, or group of animals or plants. Accordingly,

REPRODUCTION.

lat contradict
r knov'ledgfi
imed tiibi 'iv-
indeed ^-e a]l
ween certain
surrounding
|e behavior of
must believe
lother it may
is different
, relatively, as
ty during the
as individuals
re aware that
mess is not so
iinication may
ws out of the
le law we are
hen, that con-
aid is not pos-
in some way
>t wholly like,
m of the neces-
differentiation
st animals and
1 is the prevail-
note, too, that
quiescent for a
of preparation
can at present
n of life-stuff,
h, with others,
\r subject, both
)ll-life, and be-
of the physio-
' be said to be
the cells of an
s composing a
understood if
race, their an-
ly of any indi-
AccordingJy,

embryology, or the history of the origin and development of
tissues and organs, will occupy a prominent place in the vari-
ous chapters of this work. The student will, therefore, at the
outset be furnished with a general account of the subject, while
many details and applications, of principles will be left for the
chapters that treat of the functions of the various organs of
animals. The more knowledge the student possesses of zoology
the better, while this science will appear in a new light under
the study of embryology.

Animals are divisible, according to general structure, into
Protozoa, or unicellular animals, and Metazoa, or multicellular
forms — that is, animals composed of cell aggregates, tissues, or
organs. Among the latter one form of reproduction appears
for the first time in the animal kingdom, and becomes all but
universal, though it is not the exclusive method ; for, as seen in
Hydra, both this form of generation and the more primitive
gemmation occur. It is known as sexual multiplication, which
usually, though not invariably, involves conjugation of two un-
like cells which may arise in the same or different individuals.
That these cells, known as the male and female elements, the
ovum and the spermatozoon, are not necessarily radically dif-
ferent, is clear from the fact that they may arise in the one in-
dividual from the same tissue and be mingled together. These
cells, however, like all others, tell a story of continual progress-
ive differentiation corresponding to the advancing evolution of
higher from lower forms. Thus hermaphroditiam, or the coex-
istence of organs for the production of male and of female cells
in the same individual, is confined to invertebrates, among
which it is rather the exception than the rule. Moreover, in
such hermaphrodite forms the union of cells with greater differ-
ence in experiences is provided for by the union of different in-
dividuals, so that commonly the male cell of one individual
unites with (fertilizes) the female cell of a different individual.
It sometimes happens that among the invertebrates the cells
produced in the female organs of generation possess the power
of division, and continued development wholly independently
of the access of any male cell {parthenogenesis) ; such, how-
ever, is almost never the exclusive method of increase for any
group of animals, and is to be regarded as a retention of a more
ancient method, or perhaps rather a reversion to a past biologi-
cal condition. No instance of complete parthenogenesis is
known among vertebrates, although in birds partial develop-

COMPARATIVE PHYSIOLobv.

ment of the egg may take place independently of the influence
of the male sex. The hest examples of parthenogenesis are to
be fouhd among insects and crustaceans.

It is to be remembered that, while the cells which form the
tissues of the body of an animal have become apecialized to
discharge one particular function, they have not wholly lost
all otliers ; they do not remain characteristic amceboids, as we
may term cells closely resembling Amoeba in behavior, nor do
they wholly forsake their ancestral habits. They all retain the
power of reproduction by division, especially when young and
most vigorous ; for tissues grow chiefly by the production of
new cells rather than the enlargement of already mature ones.
Cells wear out and must be replaced, which is effected by the
processes already described for Amoeba and similar forms.
Moreover, there is retained in the blood of animals an army of
cells, true amoeboids, ever ready to hasten to repair tissues lost
by injury. These are true remnants of an embryonic condition ;
for at one period all the cells of the organism were of this un-
differentiated, plastic character. But the cell (pvum) from
which the individual in its entirety and with all its complexity
arises mostly by the union with another cell ispermatozodn),
must be considered as one that has remained unspecialized
and retained, and perliaps increased its reproductive functions.
They certainly have become more complex. The germ-cell
may be considered unspecialized as regards other functions, but
highly specialized in the one direction of exceedingly great ca-
pacity for growth and complex division, if we take into account
the whole chain of results ; though in considering this it must
be borne in mind that after a certain stage of division each
individual cell repeats its ancestral history again ; that is to
say, it divides and gives rise to cells which progress in turn as
well as multiply. From another point of view the ovum is a
marvelous storehouse of energy, latent or potential, of coun^^,
but under proper conditions liberated in varied and unexpected
forms of force. It is a sort of reservoir of biological energy
in the most concentrated form, the liberation of which in sim-
pler forms gives rise to that complicated chain of events which
is termed by the biologist development, but which may be ex-
pressed by the physiologist as the transformation of potential
into kinetic energy, or the energy of motion. Viewed chemi-
cally, it is the oft-repeated story of the production of forms, of
greater stability and simplicity, from more unstable and com-

RKPRODUCTION.

the influence
genesis are to

lich form the
specialized to
t wholly lost
»boids, as we
avior, nor do
all retain the
in young and
production of
mature ones,
fected by the
juilar forms.
Is an army of
,ir tiusues lost
uic condition ;
re of this un-
{ovum) from
ts complexity
)ermatozoSn),
unspecialized
ve functions.
?he germ-cell
Functions, but
igly great ca-
» into account
g this it must
division each
n ; that is to
ess in turn as
he OTum is a
ial, of cours*^,
id unexpected
}gical energy
which in sim-
events which
a may be ex-
a of potential
iewed chemi-
n of forms, of
ble and com-

plex ones, involving throughout the process of oxidation ; for
it must ever be kept in mind that life and oxidation are con-
comitant and inseparable. The further study of reproduction
in the concrete will render the meaning and force of many of
the above statements clearer.

THB OVX7M.

The typical female cell, or ovum, consists of a mass of pro-
toplasm, usually globular in form, containing a nucleus and

nucleolus. ,

The ovum may or may not be invested by a membrane ; the
protoplasm of the body of the cell is usually highly granular,
and may have stored up within it a varying amount of proteid
material (food-yelk), which has led to division of ova mto
classes, according to the manner of distribution of this nutri-
tive reserve. It is either concentrated at one pole (telolecith-
at); toward the center (centrolecithat); ct evenly distributed
throughout {alecithal).
During development this ^

material is converted by -^-^
the agency of the cells of
the young organism {em-
bryo) into active proto-
plasm ; in a word, they
feed upon and assimilate
or build up this food-stuff
into their own substance,
as Amoeba does with any
proteid material it appro-
priates.

The nucleus (germinal
vesicle) is large and well
defined, and contains with-
in itself a highly refractive

nucleolus (germinal spot). „ , . *„.

These closely resemble in general the rest of the^cell, but stam
more deeply and are chemically different in that they conuim
nucleine (nucleopUism, chromatin).

It will be observed that the ovum differs in no essential par-
ticular of structure from other ceUs. Its differences are hidden
ones of molecular structure and functional behavior. In ac-

Fio. 55.— Semi-dt»P«nini«tic repreeen ration of
» mammalian ovum (SchMcr). , Highly niM-
niflod. a>. isonapfillacida; vi, vlteUu8(yelk);
ffv, germinal vesicle; gs, germinal epot.

■y.¥'m.

COM PA RATI VE I'U YSIOLOG Y.

cordance with the diverse circumstances under which ova ma-
ture and develop, certain variations in structure, mostly of the
nature of additions, pi-osent themselves.

Thus, ova may be naked, or provided with one or more cover-
ings. Tn vertebrates there are usually two membranes around
the protoplasm of the ovum : a delicate covering (Vitelline
membrane) beneath which there is another, which is sieve-like
from numerous perforations (zona radiata, or z. pellucida).
The egg membrane may be impregnated with lime salts (shell).
Between the membranes and the yelk there is a fluid albumi-
nous substance secreted by the glands of the oviduct, or by other
special glands, which provide proteid nutriment in different
physical condition from that of the yelk.

The general naked-eye appearances of the ovum may be
learned from the examination of a hen's egg, which is one of

eAJ

Fiu. 56.— DiagMmmatic section of an unimpregnated fowl's egg (Poster and Balfonr,
after AH n Thomson), bl, blastoderm or cicatricula; w. y, whlto yelk; y. y. yel-
low yelk; eh.l, chalazs; i.g. m, Inner layer of shell membrane; ». m, outer layer
of shell membrane; ». shell; a.c. k, air-Bpace: w. the white of the egg; ». /, vitel-
line mcmbrauu ; x, the denser albuminous layer lying next the vltellino mem-
brane.

the most complicated known, inasmuch as it is adapted for
development outside of the body of the mother, and must, con-
sequently, be capable of preserving its form and essential vital
properties in a medium in which it is liable to undei-go loss of
water, protected as it now is with shell, etc., but which, r.t the

REPRODUCTION.

fhich ovu iim-
niostly of the

T more cover-
tranes around
ng {Vitelline
I is sieve-like

pellucida).

salts (shell).
fluid albumi-
ct, or by other

in different

)vum may be
ich is one of

'o«ter and Balfonr,
itc yelk; y. y, yel-
; t. m, outer layer
:bo eeg; v. t, vitel-
he vitellino mem-

i adapted for
ad must, oon-
essential vital
idergo loss of
which, r.t the

same time permits the entrance of oxygen and moisture, and
conducts heat, all being essential for the development of the
germ within this large food-mass. The shell serves, evidently,
chiefly for protection, since the eggs of serpents (snakes, turtles,
etc.) are provided only with aVery tough membranous cover-
ing, this answering every purpose in eggs buried in sand or
otherwise protected as theirs usually are. As the hen's egg is
that most readily studied and most familiar, it may be well to
describe it in somewhat further detail, as illustrated in the
above figure, from the examination of which it will be ap-
parent that the yelk itself is made up of a white and yellow
portion distributed in alternating zones, and composed of cells
of different microscopical appearances. The clear albumen is
structureless.

The relative distribution, and the nature of the accessory or
non-essential parts of the hen's egg, will be understood when it
is remembered that, after leaving its seat of origin, which will
be presently described, the ovum passes along a tube (oviduct)
by a movement imparted to it by the muscular walls of the
latter, similar to that of the gullet during the swallowing of
food ; that this tube is provided with glands which secrete in
turn the albumen, the membrane (outer), the lime salts of the
shell, etc. The twisted appearance of the i-ope-like structures
{chalaza) at each end is owing to the spircJ rotatory movement
the egg has undergone in its descent.

The air-chamber at the larger end is not present from the
first, but results from evaporation of the fluids of the albumen
and the entrance of atmospheric air after the egg has been laid
some time.

THB ORIOIN AND DBVBLOPBOZINT OF THB OVUM.

Between that protrusion of cells which gives rise to the bud
which develops directly into the new indiAddual, and that which
forms the ovary within which the ovum as a modified cell arises,
there is not in Hydra much difference at first to be observed.

In the mammal, however, the ovary is a more complex struct-
lure, though, relatively to many organs, still simple. It consists,
u the main, of connective tissue supplied with vessels and nerves
inclosing modifications of that tissue {Oraafian follicles) within
which the ovum is matured. The ovum and the follicles arise
from an inversion of epithelial cells, on a portion of the body

/ ■'.

t'OMPARATlVR PIIVSIOLOGY.

cavity (germinal ridge), whicli give rise to the ovum itself, and
the other cells surrounding it in the Graafian follicle. At Hrst

these inversions form
tubules {egg-tubes) which
latter become broken up
into isolated nests of
cells, the forerunners of
the Graafian follicles.

The Graafian follicle
consists externally of a
fibrous capsule {tunica
flbroMi),ia close relation
to which is a layer of cap-
illary blood-vessels {tu-
nica vasculoaa), the two
together forming the gen-
eral covering {tunica
propria) for the more
delicate and important
cells within. Lining the

Fio. 57.-Sectlon through portion of theovaryof . . • i_^-_ „» ama\}

tnammal. illiiKtrntlng n. .10 of development of tumc IS a layer Of smau,

the Oraaflan follicleii (Wledirshcim). />, dig- -nmnwliftf Aubioal cells

CUB prollgcnw ; Ei, ripe ovum; 0, follicular SOmewnai CUDlcai ctJiiB

cellnof germinal epithelium; fir, blood-vog»elH; (^igjn&rona oranulofM),

K, germinal vesicle (nucleus) and germinal V"«"*"' """ V '1

Ppot (nucleoluH) ; KE. germinal epithelium; yrhlch at one part mvest
jy, liquor foUieull; il/f/, membrana or tunica
luTo

jy; liquor foUleull; iWfir.memorana or luuicB , . i„_.««.

gTanuTm-a. or follicular epithelium; Mp. Mna the ovum several layers
l?^;!ia?^.aiiTZi!;S/b7mel'n".Sr'ra deep {discm proUgerus),

■onif of the neste retain their connection with while the remainder of

the epithelium; S. cavity which apiicani with- wuiio wio »^iji««»* «

in the Graafian follicle; So, stroma of ovary; ^q space IS filled by a

77, theca folllculi or capsule ; t'. primitive „ -Ji n- *^JU^.].'\

ova. When an ovum with its giirroundlng "— "^ "— "~ f^iu^.M
cells has become separated from u nest, it ii
known as a (iraaflan fullicle.

fluid {liquor folliculi)
probably either secreted
by the cells themselves,
or resulting from the disintegration of some of them, or both.

In viewing a section of the ovary taken from a mammal at
the breeding-season, ova and Graafian follicles may be seen in
all stages of development— those, as a rule, nearest the surface
being the least matured. The Graafian follicle appears to pass
inward, to undergo growth and development and .again retire
toward the exterior, where it bursts, freeing the ovum, which is
conducted to the site of its future development by appropriate
mechanism to be described hereafter.

Change! in the Ovum itedf.— The series of transformations
that take place in the ovum before and immediately after the

RKPRHDUCTION.

vum itself, nnd
Hide. At tlntt
reraions form
jy-ttibea) which
Dine broken up
ated nests of
forerunners of
ian follicles,
raafian follicle
ixternally of a
apsule {tunica
n close relation
su layer of cap-
Mxl-vessels (tu-
uloaa), the two
ormingthegen-
ering (tunica

for the more
and important
in. Lining the
layer of small,
; cubical cells
na granulom),
one part invest
1 several layers
cua proligerus),
e remainder of
3 is filled by a
quor fcHliculi)

either secreted
Ellis themselves,
bhem, or both,
n a mammal at
may be seen in
rest the surface
I appears to pass
and again retire
) ovum, which is
; by appropriate

transformations
liately after the

accefw of the male element is, in the opinion of many biologists,
of the highest significance, as indicating the course evolution

0*:

(.J. n/-

ot.

.V/.

^'i'.^i'H

.tri

'•yyj-v;;!

hyii

■1>/-

b.«-

f-m

[^■■1

f.c-

^-iS^^-iZ.^:i:i

inm

^!^

f:>^r;A

e.t.

Fio. I«.-S«plttal iecMon of the ovnry of an adult bitch (after Waldeycr). o.f.ov^
rian eiilthenmn; o.t, ovarian tube*; y.f, vonngcr fplllclc»; o.f, older follicle,
d. p. diDcua prollgcrua, with the ovnm: «, epithelium of a Becond oviim In the Mme
follicle: /.eT fibrong ooat of the follicle; p. c, proiwr coat of the fuH'c e; j/j ep'"
thellum of the follicle (membrana granuloaa); a./, col lapred atrophied foUlcle.
ft.D.blood-voseelH; c.t, ccll-tnbea of the imrovarinm diviaed longitiidlnally and
tranaverwly; (. d. tiibniar depreialonof the ovarian epithelium In the tlwue of
the ovary; ft! «, beginning of the ovarion epithelium, close to the lower border of
the ovary.

has followed in the animal kingdom, as well as instructive in
illustrating the behavior of nuclei generally.

COMPARATIVK PHYSIOLOGY.

The germinnl voiicle may acquire iKtworeof hI«)w iiiovemotit
(amceboid), ami the (yerininul BiM)t disapiM-ar : tlio f«»nner paasea
U) OHO surface ([)*>/♦') of the ovum ; both these Htructuros may
undergo that peculiar form of rearrangement {karyokineaia)
which may occur in the nuclei and nucleoli of other cells prior
to divinion ; in other words, the ovum has featuren common to it
and many other cells in that early stage which precedoH the com-
plicated transformationB which constitute the future history of

the ovum.

A portion of the changed nucleus (aster) with somo of the
protoplasm of the cell accumulates at one surface {pole), which
is termetl the upi)er pole because it is at this region that the epithe-
lial cells will be ultimately developed, and is separatwl. This pro-
cess is repeated. These bodies (polar cells, polar globulea, elfi.>,

■ • ^iii'irli ; -

■■■.^'^'^-

Fio

BO -Formation of polar cell* In a «tar-flih (.Atteriat glaHnlit) (from. OfW**-

A-K after Fol. L afler O. HertwlR). A. r |)e oynm with ec"'"'"" 8«™ "j' ^'•
clo andVpot; B-D. Kradual metamorpliosle of Kcrmlnsl vesicle and ipotMaeen
In the llXi Vkk, into two asten.; F. formation of flrat polar cells and withdrawal
of remalnlns partof nuclear spindle within the ovum: V'J'I.":f,".'=r»''u.i!j ii^e^
Xvnm in thiTflrnt Dolarcell; II. comp oton of second polar cell; I, a later stage,
lowing the "ena nlng Interna half of the spindle In tihe form of two clear vesl-
rr«*I^ ovum witl two polar cells and radial atrln round female pronucleus. a»

ovum'lnThrnrit'iwlarceriT'lircomplot^^^^^

' • ' temal half of the spindle In the

mlar ' -^'-' -—

e)K(E.F,H,
of the first irolafcell. (Haddon.)

then, are simply expelled ; they take no part in the development
of the ovum •, and their extrusion is to be regarded as a prepar-
ation for the progress of the cell, whether this event follows or
precedes the entrance of the male cell into the ovum. It is wor-
thy of note tliat the ovum may become amceboid in the region
from which the polar globules are expelled.

The remainder of the nucleusC/emafepronMctetw) now passes
inward to undergo further changes of undoubted importance,
possibly those by virtue of which all the subsequent evolution
of the ovum is determined. This brings us to the consideration
of another ceU destined to play a brief but important rdle on the
biological stage.

RKPRODL'CTION.

ilow iiiovemont

former paaaes
HtructureH mfty

ikoryokineaia)
ther coIIb prior
OH coiumou to it
•eccdoH tho i'om-
iture hiatory of

th soino of the
36 (po/c), which

1 that the epithe-
mtwl. ThiHpro-
r globules, etc.),

HalU) (from Geddes,
pi'iitrlc gormliial veal-
ilrlcandipot, aa seon
r ct- 111* and withdrawal
surface view of living
cull; I. a later stage,
irni of two clear veil-
female pronucleus, as
rations); L, vxpuliion

the developmeut
xled as a prepar-
jvent foUowB or
3vum. It is wor-
oid in the regfion

cleua) now passes
bled importance,
equent evolution
the consideration
ortantrdteonthe

THB MALB OBLL (BPBRMATOZOdN).

This cell, almost without exception, consists of a nucleus
(head) and vibratile oiliuni. However, as indicating tlu»t the

F,o. «..-4,perm«to.oa (after Haddon) Not d^^^^^^

?;.";n'SSy"'^riiSo2.".i ?u •jSSl'.'Tk^dtlSiTxtrlm'et delicate' vlbratUe band is
present.

latter is not essential, spermatozoa without such an appendage
do occur The obvious purpose of the cilium is to convey the
male cell to the ovum through a fluid medium-either the water
in which the ova are discharged in the case of most invertebrates,
or through the fluids that overspread the surfaces of the female
generative organs.

The Origin of the Spennatoioai.— The structures devoted to
the production of male cells (teatea), when reduced to their e^
aentials, consist of tubules, of great length in mammals, Imed

CH'

COMl'ARATIVK PIIVHIOIAKJY.

V'i :!' . aelpauxl opitlivliul coUh, from which, by a Horien of
Ciiniigefl flifuivd above, a ({eneral idea of their tloTelopmnnt may
be obtuinml.

It will )m^ r)lMerveil that throughout the aeries the nuclega of
the cell in in every eaae preserved, and Anally becomes the head

Via. 61.— SMniwtoMDMls. A— H, bolated mnn-celli of the rat, ithowing the devel-
opment of the RpermatocoOn and the gndusl tiMMfonnatlon of the nncieoi into
the epermatoEoSn head. In O the Mminal grannie ii bcint; cast off (after H. H.
Brown). I— M, ipermcellB of an Elaamobranch. The nucleiiR of each cell dlv/des
Into a large nnmber of danghter-nuclei, each one of which in convcrtrd Into the
rod-like head of '^ spermatozoon. N, tranivene wction of a ripe cell, ihowlne
the bnndle of Rpermatosoa and the paetlve nucleus (I— N, after Semper). <>— 8.
spermatogenesis In the earth-worm; O, jonng epcrm-ccll; F, the same divided
Into fonr; Q, epermatosphero with the central sperm-blastophure; K, a later stage;
8, nearly matarc spermatozoa. (After Blomfleld.)

t, nhowlng the devel-
of the nacleni into
csRt off (after H. H.
iH of each cell divide*
» converted Into the
a ripe cell, ihowlng
rter Semper). O— S
P, the aame divided
lore; H, a later stage;

F.rm

t'Ki. tH.

UKrUOlU'CTloN.

«f th« nmlo cell. Onco more wo ar« Itxl to iwo the importar.co
of thiH Htnicturc in the life «)f the toll.

Fsrtilintlon of the Orum.— The H|)cnimt<)zo«»u, hwhiiiK itH
way uloiiK. when it lueetH the ovum, enU^n* it either ihroujfh tt
•liecial iniimtc Kiitevlruy (mi>w/»tf/«'), or, if thi« b«. not pronent-
im it is not in the ova of all aniinaU-uctimlly |wnetruteH the
memhruncB and Bub«tuiuoof the female «ell. and lontinucH uct
ive till the female pronuclei^ iw reooheil. when the head cntera
And the Uil Ib ab«)rbed or bleiulH with the female tell. The nu-
cleiw of the male cell prior to union with the nucleui of the

V.l'N:

-M.pfr.

o*.-Krrtillr.«tlon of ovnm of a mollnok {Khirta riridUl A. Ovnm tending np a
nroliibemncc to meet the »iiermBloj!i«n. ft. Approach of m«l« oroniicleua lo
m"i" iheftiiialepronuclBM. F.J'N, fimale proimclfua; M. VN. male pronucleut.
S, ipcrmatozoOn.

ovum undergoes chanpfes similar to those that the nucleus of the
ovum underwent, and thus becomes fltte<l for its special func-
tions as a fertilizer ; or perhaps it would be more correct to say
tliat these altered masses of nuclear substance ntutually fertil-
ize each other, or initiate chanjfes the one in the other which
conjointly result in the subsequent stages of the development
of the ovum. The altered male nucleus {male pronticlem), on
reaching the female pronucleus, finds it somewhat amteboid,
a condition which may be shared in some degree by the entire
ovum. The resulting union gives rise to the new nucleus (seg-
mentatum nticleus), which is to control the future destinies of
the cell ; while tho cell itself, the fertilized ovum {oosperm,), en-
ters upon new and marvelous changes.

In reality this process was foresliadowed in the dim past of
the history of living things by the conjugation of infusoria
and kindred animal and vegetable forms. When lower forms
(unicellular) conjugate they become somewhat amoeboid sooner
or later, and division of cell contents results. In some cases
(septic monads) the resulting cell may burst and give rise to a

COMPARATIVE PnYSIOLOQV.

shower of animal dust visible only by the highest powera of the
microscope, each particle of which proves to be the nucleus
from whicli a future individual arises.

The study of reproduction thus establishes the conception of
a unity of method throughout the animal and, it may be added,
the vegetable kingdom, for repixxluction in plants is in all main
points parallel to that process in animals.

But why that costly loss of protoplasm by polar globules ?
For the present we shall only say that it appears necessary to
prevent parthenogenesis ; or at least to balance the share which
the male and female elements take in the work of pixxlucing a
new creature. It is to be remembered that both the male and
female lose nmch in the process — blood, nervous energy, etc., in
the case of the female, while the male furnishes a thousand-fold
more cells than are used. But the period when organisms are
best fitted for reproduction is that during which they ,ire also
most vigorous, and can best afford the drain on their super-
fluous energies.

SBOMBNTATION AND SUBSBQUBNT OBANOBS.

After the changes described in the last chapter a new epoch
in the biological history of the ovum — now the oosperm (or fer-
tilized egg)— begins. A very distinct nucleus {segmentation
ntteleus) again appears, and the cell assumes a circular outline.
The segmentation or division of the ovum into usually fairly
equal parts now commences. This process can be best T/atched
in the microscopic transparent ova of aquatic animals which
undergo perfect development up to a certain advanced stage
in the ordinary water of the ocean, river, lake, etc., in which
the adult lives.

Segmentation among invertebrates will be first studied, and
for this purpose an ovum in which the changes are of a direct
and uncomplicated nature will be chosen.

The following figures and descriptions apply to a mollusk
(Elysia viridis). We distinguish in ova resting stages and
stages of activity. It is not, however, to be supposed that abso-
lute rest ever characterizes any living form, or that nothing is
transpiring because all seems quiet in these little biological
worlds ; for we have already seen reason for believing that life
and incessant molecular activity Ure inseparable. It may be
that, in the case of resting ova, changes of a more active char-

REPRODUCTION.

t powera of the
[)e the nucleus

e cuuception of

may be added,

iS is iu all main

Hilar globules ?
.rs necessary to

le share which
of producing a
1 the male and

energy, etc., in
a thousond-fold

organisms are
h they are also
ou their super-

OBANOSS.

ter a new epoch
odaperm (or fer-
I {segmentation
sircular outline.
» usually fairly
be best v/atched
: animals which
advanced stage
i, etc., in which

Irst studied, and
i are of a direct

ly to a mollusk
ting stages and
posed that abso-
that nothing is
little biological
[ieving that life
ble. It may be
ore active char-

acter than usual are going on in their molecular constitution ;
but, on the other hand, there may be really a diminution of

Fie. OS.— PrimitlTe eggs of variona antnuUt, performing amoeboid movemenu (very
much enlarged). All primitive egm are naked cellg, capable of change of form.
Within the dark, finely granulafid piotoplaam (egg-yelk) lies a large vesicular
kernel (the germ-vesicIc), and in the latter is a nncleolnR (gertn-gpot); in the nv-
cleolas a germ-point (nucleolng) is often visible. Fig. A I— A 4. The primitive
egg of a chalk sponge (£«ucu/mi« eehinu*), in fonr consecutive eonditiona of mo-
tion. Fig. B 1—B 9. The primitive egg of a hermlt-enb (C/tondracanthu» cnmu-
tut), in ofght consecutive conditions of motion (after E. Van Beneden). V'-e. V 1
— C5. Primitive egg of a cat in tour different conditions of motion (after Pfltger).
Fig. D. Primitive egg of a trou*. Fig. E. Primitive egt; of a hen. Fig. F. Primi-
tive human egg. (IlMckcl.)

these activities in correspondence with the law of rhythm. This
seems the more pi-obable. The meaiing, however, of a " resting
6

f"" MUJUISO?

\ - -v

COMPARATIVE PHYSIOLOGY.

stage" is the obvious one of apparent quiescence— cessation of
all kinds of movement. Then ensues rapidly and in succession
the following series of transformations : The nucleolus divides,
later the nucleus, into two parts. These new nuclei then wan-
der away from each other in opposite directions, and, losing
their character as nuclei and nucleoli, are replaced by asters
{polar stars), which seem to arise in the protoplasm of the body

Fio 64.— Early stageg of gegmentation of a molluak. Elyria elrWte (drawn from the
Uvine em). A, oOgperm in Rtote of reat after the extnuion of the polar celU; B,
the nncfwluB aloneTiag divided; C, the nucleus 1» dividing; D, the nuclens, as
Buch, has disappeared, flrst gegmentaUon fjirrow appear* ; E, later »tage; F,
oosperm dlvidedtato two distinct segmentation spheree, the clear nuclear space
In the center of the aster of giannles is growing latger; O, rertlng stage of ap-
pressed two spheres: H,I, similar stages In the production of four spheres; n.,
format' on of eight-celled stage. (Haddon.)

of the cell, and which are in close juxtaposition at first, but later
separate, the oosperm becoming amoeboid in one region at least.
A groove, which gradually deepens, appears on the surface, and
finally divides the cell into two halves, which at once become
flattened against each other. The nucleus may again be recog-
nized in the center of each polar star, while a new nucleolus
also reappears within the nucleus, when again a brief period of
rest ensues. In the division and reformation of the nucleus,
when most complicated {karyokinesis), the changes may be gen-

! — cessation of
1 in succession
sleolus divides,
clei then wan-
ns, and, losing
iaced by asters
sm of the body

idi» (drawn from the
>f the polar celU; B,
; D, the naclena, m
; E, later stage; F,
9 clear nnclear epace
reating stage of ap-
of fonr spheres; K,

ii first, but later
I region at least,
the surface, and
at onoe become
again be recog-
, new nucleolus
I brief period of
of the nucleus,
iges may be gen-

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REPRODUCTION.

eralized as consisting of division and segregation, followed by
aggregation.

The subdivision (segmentation) of the cell, after the quies-
cence referred to, again commences, but in a plane at right
angles to the first, from which four spheres result, again to be
followed by the resting stage. The process continues in the
same way, so that there is a progressive increase in the number

;■<

KiG. (a,

The cleavage of a frog's em; (10 times enlarged),
flret twooleavage-celU; C, 4 colls; D, 8 cells (4 animal and 4 vegetative);

A. the parent-cell; J, the
I and 4 vegetative); E, la
cells (8 animal and 4 vegetative); F. 16 cells (8 animal and 8 vegetative); O, Hi
cells (16 animal and 8 vegetative); H, 83 cells; /, 48 cells: A', 64 cell's; L, 96 cleav-
age-cells; if, 160 cleavage-cells (138 animal and 88 vegetative). (Haeckel.)

uf segments, at least up to the point when a large number has
been formed. This is ra-her to be considered as a type of one

iMtaMBiB::^

COMI'ARATTVE PHYSIOLOGY.

form of segmentation than as applicable to all, for even at
this early stage differences are to be noted in the mode of seg-
mentation which characterize effectually certain groups of ani-
mals ; but in all there is segmentation, and that segmentation
is rhythmical.

Segmentation results in the formation of a multicellular
aggregation which, sooner or later, incloses a central cavity
(segmentation cavity, blastocele). Usually this cell aggrega-
tion {blaatuia, blastophere) is reduced to a single layer of invest-
ing cells.

The Gaitrola.— Ensuing on the changes just described are

Fio. 66.— fliMtiila and gaatrnls of amphioxus (Olaua, after Hatschek). A, blaetula
with flattened lower pole of larger cells; B, commencing Invagination; C.rartru-
lation completed; the blastopore ia still widely open, and one of the two hinder-
pole mesoderm cells is seen at ite ventral lip. The cilia of the epiblast cells are
not represented.

others, which result in the formation of the gastrula, a form of
cell aggregation of great interest from its resemblance to the
Hydra and similar forms, which constitute in themselves inde-
pendent animals that never pass beyond that stAge. The blas-
tula becomes flattened at one pole, then depressed, the cells at
this region becominir more columnar (kistohgicdl differentia-
tion). This depression {invagination) deepens until a cavity is
formed (as when a hollow rubber ball is thrust in at one part
till it meets the opposite wall), in consequence of which a two-
layered embryo results, in which we recognize the primitive
mouth {Uastop&re) and digestive cavity (archenteron), the outer
layer (ectoderm) being usually separated from the inner (endo-
derm) by the almost obliterated segmentation cavity. Such a
form mey be provided with cilia, be very actively locomotive,
and bear, consequently, the greatest resemblance to the perma-
nent forms of some aquatic animals.

The changes by which the segmented oosperm becomes a
gastrula are not always so direct and simple as in the above-

1, for even at

LB mode of seg-

groups of ani-

b segmentation

I multicellular
central cavity
I cell aggrega-
layer of invest-

t described are
C

ichek). A, blastula
iglnation; C.gaatrn-
e of the two ninder-
he epiblast cells are

Tula, a form of
mblance to the
lemselves inde-
tge. The bias-
sed, the cells at
eal differentia-
mtil a cavity is
in at one part
)f which a two-
) the primitive
eron), the outer
he inner (endo-
javity. Such a
ely locomotive,
e to the perma-

erm becomes a
s in the above-

REPRODUCTION.

described case, but the
behavior of the cells of
the blastosphere may Oe
hampered by a burden
of relatively foreign
matter, in the form of
food-yolk, in certain in-
stances ; so much so is
this the case that dis-
tinct modes of gastrula
formation may be rec-
ognized as dependent on
the quantity and ar-
rangement of food-yelk.
These we shall pass by
as being somewhat too
complicated for our pur-
pose, and we return to
the egg of the bird.

The Hen's Egg.— By
far the larger part of
the hen's egg is made
up of yelk ; but just
beneath the vitelline
membrane a small, cir-
cular, whitish body,
about fotu* millimetres
in diameter, which al-
ways floats uppermost
in every portion of the
egg, may be seen. This
disk (blastoderm, cica-
iricula) in the fertilized
egg presents an outer
white rim (area opaca),
within which is a trans-
parent zone (area pellu-
oida), and most centrally
a somewhat elongated
structure, which marks
otf the future being
itself (embryo). All

Flo. 67.— Female generat'-.-e organt of the fowl
(after Dalton). .4, ovary; B, Sraa an follicle,
from which the egg lias Just been discharged;

C, ycik, entering 'ipon extremity of ovidnct;

D, E, second portion of ovidnct, in which the
chalaziferous membrane, chalazffi. and albumen
are formed ; F,th\Ti portion,in which the fibrous
shell membranes arc produced; O, fonrth por-
tion laid open, showing the egg completely
formed witn its calcareous shell; H, canal
through which the egg is expelled.

COMPARATIVE PHYSIOLOOY.

these parts together constitute that portion (blastoderm) of the
fowl's egg which w alone directly concerned in reproduction,
all the rest serving for nutrition and protection. The appear-
ance of relative opacity in some of the parts marked off as above
is to be explained by thickening in the oell-layen of which they
are con^posed.

The Origin «f the Fowl'i Bgg.— The ovary of a young but
mature hen conaists of a mass of connective tissue {stroma),

1 1

Fie. 88.— VarioaB «tagM In the «egmentstlon of a fowl's egg (KOIliker).

abundantly supplied with blood-vessels, from which hang the
capsules which contain the ova in all stages of development, so
that the whole siiggests, but for the color, a bunch of grapes in

REPRODUCTION.

rm) of the
>roduction,
he appear-
ff 08 above
vhich they

jroung but
(atroma),

Uliker).

I hang ^6
opment, so
f grapes ia

an early stage. The ovum at first, in this case as in all others,
a single cell, becomes complex by addition of other cells (dia-
eua proligerua, etc.), which go to make up tlie yelk. All the
other parts of the hen's egg are additions made to it, as ex-
plained before, in its passage down the oviduct. The original
ovum remains as the blastoderm, the segmentation of which
may now be described briefly, its character being obvious from
an examination of Fig. 68, which represents a surface view of
the segmenting fertilized ovum (oosperm).

A segmentation cavity apv^ears early, and is bounded above
by a single layer of epiblast cells and below by a single layer of
primitive hypoblast cells, which latter is soon composed of sev-
eral layers, while the. segmentation cavity disappears.

The blastoderm of an unincubated but fertilizei! egg consists
of a layer of epiblastic cells, and beneath this a mass of rounded
cells, arranged irregularly and lying loosely in the yelk, consti-
tuting the primitive hypoblast. After incubation for a couple
of hours, these cells become differentiated into a lower layer of
flattened cells {hypoblast), with mesoblastic cells scattered be-

Fio. 99.— Portion of section throngh an nnlneubated fowl's oOapenn tafter Klein),
a. epIblMt composed of • single layer of colnninar cells; b, inegnlarly disposed
lower lajrer cells of the primitive hypoblast; e, larger formative cells resting on
white yelk; /, aichenteron. The segmentation cavity lies between a and b, and
is nearly obliterated.

tween the epiblast and hsrpoblast. It is noteworthy that, in the
bird, segmentation will proceed up to a certain sta^ independ-
ently of the advent of the male cell, apparen*'^ indicating a
tendency to parthenogenesis.

The fowl's ovum then belongs to the class, a portion of which
alone segments and develops into the embryo (merobkutic), in
contradistinction to what happens in the mammalian ovum, the
whole of which undergoes division (holoblcutic) ; a distinction
which is, however, superflcial rather than fundamental, for in
reality in the fowl's egg the whole of the original ovum does
segment. This holoblastic character of the mammalian ovum

COM I'A RATI VK

and it8 reHemblance to the Beg:
forms previouBly described maj
amination of the accompanying

tnt.

^"•^zp.

ectr'

Fio. 70.— Sectlonii of ovum of a rabbit, lit
cle (after E. Van Boncden). A, B, C,
mtot. q>, lona pellucida; eel, octom
cellR.

We shall return to the deve
later; in the mean time we prei
ment in the bird.

Remembering that the de^
takes place within the pellucid
area opaca gradually extends o^
yelk, so that the original disk
the rest of the ovum, has gro'
of this area nearest the pelluci
blood-vessels that derive the f
blood as it is exhausted, from 1

UKrUODUCTION.

DO invertebrate
t from an ex-

Tli( first indications of future Btructural outlines in the em-
bryo is the formation of the primitive streak, an opaque bantl

-ent.

■•ap.

he blastodermic veii-
'e 8ta^ci of develop-
', entomeree, or inner

immalian ovum
ures of develoj)-

embryo proper
>int out that the
tn, inclosing the
I watch-glass on
. That portion
nUoaa) develops
sh replenish the
lie area opaca.

M.e-

« f.< T>i...Mmn<iiHo tntiiavprM ■ectloni throuffh b hypothotlcal mammM oflcpcnp
'^'°;iU,Wo ,>'^A The ycTof TheTf ml lv« m«mm.ill«n oO»i..t,u I. i.ow lo.t. B.

pStlve l.ypoblMt; y. ; y«lk-ittc, or blo.to<lCTmlo ve^lde.

the long diameter of the peUucid area, opaque in consequence

, coll accumulation in that region. Very soon a groove {primi-
tive groove) extends through-
out this band, wliich gradu-
ally occupies a more central
position. The relative thick-
ness of the several parts and
the arrangement of cells may
be gathered from Fig 72.
These structures are only
temporary, and those that re-
place them will be described
subsequently.

We have thus far spoken
of cells as being arranged in-
to epiblast, hypoblast, and

raesoblast. The origin of the

first two has been sufficiently

indicated. The mesoblast

forms the intermediate ger-
minal layer, and is derived

from the primitive hypoblast,

which differentiates into a

stratum of flattened cells,

situated below the others,

and constituting the later

Fiu. ra.-Sarface view of pellucid area of
blastoderm of eighteen bonrs (Foater and
Balfour). If, mednllary folda ; me, mc-
dnllary groove; pr, primitive groove.

COMPARATIVE I'HYSIOLOOY.

hypoblaat, and intermediate leu clo«ely arranged cell*, termed,
from their puHition, meaoblast.

It will be noticed thut ull future growth of the embryo be-
gins axially, at least in the early stages uf iU development.

As the subsequent growth and advance of the embryo de-
pend on an abundaiit and suitable nutritive supply, we must
now turn to those arrangements which are temporary and of
subordinate importance, but tlill for the time essential to devel-
opment.

. TBB miBRTOinO MBMBBfVMTIi OF BIRDS.

It will be borne in mind throughout i .•;* the c.i. / food-sup-
ply for the embryo birtl is derived from th«, ycU( ; and, as would

■•1--H»

-«»

Fio. 73.

Fioi. 78-75.-A MriMof diagrams lntei;dcd to racilltato the comprohen»Jon of the
Klatlons of the membnuiea to other parts (after Foster and Balfour). A, B, C,D,
K, F are vertical aectlons lo the long axis of the embno at different perioda, yhow-
lag the itagea of devolopnent of the amnion and of the Telk-aac. I, }}',}yijj^
are ttaniTerso aections at abont the same stages of development. 1. i, "l.,Po«-
terlor part of longitudinal section, to Illustrate three stages In formation of the
Bllantols. «, emhiyo: y, yelk; pn, plenroperltoneal cavlu: «i, vitelline mem-
brane of amniotic fold; al, allantols; a, amnion; a', alimentary canal.

be expected, the older the embryo the smaller the yelk, or, as it
is now called when limited by the embryonic membranes, the

, celU, temieil,

ho oinbry«» be-
ilopinoiit.
he embryo de-
)ply, we must
IM>rary aiid of
ntial lo devel-

BIRDS.

a. / food-mi 1)-
aud, as would

-«»

iprchenslon of the
Ifour). A, B, C, D,
innt periods, ihow-
:-««c. I.IlJlI.IV
nent. 1, li, ill, po«-
n formation of the
tt, vitelline mem-
7G«nai.

i yelk, OP, as it
lembranes, the

liiijiir rr-----|- ■

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s. • >

COMPARATIVE PHYSIOLOGY.

yeOc-aae (umbilical vesicle of the mammalian embryo). The
manner in wiiich this takes place will appear upon an inspec-
tion of the accompanying figures.

Very early in the history of the embryo two eminences, the
head and the tail folds, arise, and, curving over toward each

Fio. 76.— Biagitmmatic longitadimU Mction throngli tbe azts of an embryo chick
(after Fpater and Balfonr). N. C, Neural canal; Ch, notochord; Fg, forcgnt;
F". So, «oinatoplenre; f". 8p, iplanchnopleare; Sp, aplanchnopleare, forming lower
wall of foregut; Ht, Iteart; m plenroperitoneal cavity; Am, amniotic fold; E,
eptblast; M, mesoblaat; H, bypoblaat

other, meet after being joined by corresponding lateral folds.
Fiision and absorption result at this meeting-point, in the
inclosure of one cavity and the blending of two others. These
folds constitute the amniotic membranes, the inner of which

Fig. 77.— Diagrammatic longitndinal section of a cbick of the fonrth day (after Allen
Thomson}, ep. epiblaat; Ay, hypoblast; «m, aomatoplenre; vm, aplanchnopleore;
qf, pf, folds of the amnion; pp, pleoroperitoneal cavity; am, cavity of the am-
nion: al. allantois; a, position of the fninre anas; h, heart; i, intestine; vi, vitel-
line duct; y$, yelk; «, foregnt; m, position of the month; m», mesentery.

forms the trite amnion, the outer the false amnion {serous memr
brane, subzonal membrane). Within the amnion proper is the .
amniotic cavity filled with fluid (liquor amnii), while the space
between the true and false amniotic folds, which gradually in^

embryo). The
upon an inspec-

) eminences, the
er toward each

of an embiyo chick
ichord; Fg, fofcgnt;
pleare, forming lower
n, unniotic fold; B,

ig lateral folds,
ig-point, in the
) others. These
inner of which

nrth day (after Allen
Dm, splanchnoplenre;
N, cavity of the am-
i, intestine; vi, vitel-
I, meMnteiy.

m («erotMm«m-
on proper is the
while the space
ih gradually in-

REPRODUCTION.

creases in size as the yelk-sac diminishes, forms the pUwro-
peritoneal cavity, body cavity, or coeUm. The amniotic cavity
also extends, so that the embryo is surrounded by it or lies
centrally within it The enlargement of the coelom and exten-
sion of the false amniotic folds lead finally to a similar meeting
and fusion like that which occurred in the formation of the true
amniotic cavity. The yelk-sac, graduaUy lessening, is at last
withdrawn into the body of the embryo.

Fig. 76 shows how the amniotic head fold arises, from a
budding out of the epiblast and mesoblast at a point where the
original cell Uiyers of the embryo have separated into two folds,
the 8tmatopleure or body fold and the «ptonc/mopfettre or vis-
ceral fold, owing to a division or cleavage of the mesoblast
toward the long axis of the body. Remembering this, it is
always easy to determine by a diagram the composition of any
one of the membranes or
folds of the embryo, for
the components must be
epiblast^ mesoblast, or
hypoblast ; thus, the
splanchnoplenre is made
up of hjrpoblast internally
and mesoblast externally
—a principle of great sig^
niflcance, since, as will be
learned later, all the tis-
sues of the body may be
classified simply, and at
the same time scientifi-
cally, according to their
embryological origin.

The allantoia is » .DlagmnmatTc longitudinal action

structure of much physi- thnitigh iJ» egg of a fowl (•»"» d>"^-

, . , . . Ti. J3 cavity of alUmtoi«;a», albumen; o«.me8-

ological unportance. It Steron;«m,cavityof amnion; «n6,embryo;

arises at the same time as «*. ^"^^'^ "• »»• '"«"»»« '°*'"''"°*-
the amniotic folds are . , . . x • * iu

forming, by a budding or protrusion of the hm*gut mto the
pleuio-peritoneal cavity, and hence consists of an outgrowth of
mesoblast lined by hypoblast

.v.m.

COMPARATIVE PHYSIOLOGY.

TBB iHBTAXi (BMBRTONIO) MBBIBIUNBS OF

The differences between the development of the eggf mem-
branes of iTi i^mmftl* and birds are chiefly such as result from

the absence in the
'^ • ^ former of an eggnshell

and its membranes, and
of yelk and albumen.
The mammalian orum
is inclosed by a zona
radiata (zona peUuci-
da) surrounded by an-
other very delicate cov-
ering {vitettine mem-
brane).

The growth of the
bkutodermic vesicle
(yelk-sac) is rapid, and,
being filled with fluid,
the zona is thinned and
soon disappears.

The germinal area
alone is made up of
three layers of cells
(Fig. 100), the rest of
the upper part of the
oSsperm being lined
witii epiblast and hyp-
oblast, while the low-
er zone of the yelk-sac consists of epiblast only.

Simple, non-vascular villi, serving to attach the embryo
to the uterine walls, usually project from the epiblast of the
subzonal membrane. In the rabbit they do not occur every-
where, but only in that region of the epiblast beneath which
the mesoblast does not extend, with the exception of a patch
which soon appears and demarkates the site of the future plar
centa. The amnion and allantois are formed in much the same
way as has been described for the chick.

At about the same period as these events are transpiring the
vascular yelk-sac has become smaller, and the allantois with
its abundant supply of blood-vessels is becoming more promi-

Fio. 79. — DUgnunoutlc lonxitndtnal Mction of
oOspenn of rabbit at an advanced itaRe of prec-
nancy (KAIIiker, after Biacholt). a, amnion; <u,
•llantoiR with iU blood-veHela; «, embirp ; (b.
yelk-aae ; €d, «d', td", hypoblaatic cplthelinm of
the vellc-Mc and its atalk (ambllical veaiele and
cord); /d. vaicniar meiobUiatic membrane of the
nmbtlical cord and voaicle ; n{, placental villi
formed by the alUmtoi* and anbconal mcmbrano;
r, apace fllled with flnid between the amnion,
the allantoi*. and the yellc-iiac ; tt, sinoa terml-
nalia (marginal vitelline blood-veaaci); u, nrach-
ne, or atalk of the allantoia.

Mar-ai i t(. i , i BM-i . )WM(! i

RBPRODUCTION.

MBS OF

the egg mem-
OB result from
lence in the
if an eggHshell
tembranefi,and
and albumen,
nmalian ovum
ed by a zona
(zona pettuici-
Dunded by an-
ry delicate cov-
ntettine mem-

prowth of the
rmic veaide
;) is rapid, and,
[led with fluid,
is thinned and
appears,
germinal area
I made up of
ayera of cells
9), the rest of
er part of the
L being lined
[blast and hyp-
irhile the low-

ih the embryo
epiblast of the
>t occur every-
beneath which
»tion of a patch
the future pla-
much the same

transpiring the
! allantois with
ig more promi-

,an.
m.m.

an.

nent, and extending between the amnion and subsonal mem-
brane.

The formation of the chorion marks an important step in

the development of mammals in which it plays an important

functional part. It is

the result of the fusion

of the allantois, which

is highly vascular,

with the subional

membrane, the villi of

which now become

themselves vascular

and more complex in

other respects.

An interesting re-
semblance to birds has

been observed (by Os-

bom) in the opossum
(Fig. 83). When the
allantois is small the
blastodermic vesicle
(yelk-sac) has vascular
villi, which in all prob-
ability not only serve
the purpose of attach-
ing the embryo to the
uterine wall but derive
nourishment, not as in

birds, from the albumen of the ovum, but directly in some way
from the uterine wall of the mother. It will be remembered
that the opossum ranks low in the mammalian scale, so that this
rtisemblanoe is the more significant from an evolutionary point
of view.

The term chorion is now restricted to those regions of the
subional membrane to which either the yelk-sac or the allan-
tois is attached. The former zone has been distinguished as the
false chorion and the latter as the true chorion. In the rabbit
the false chorion is very large (Fig. 79), and the true (placen-
tal) chorion very small in comparison, but the reverse is the
case in most mammals. It will be noted that in both birds
and mammals the allantois is a nutritive oi^gan. Usually
the more prominent and persistent the yelk-sac, the less so

Fie. 80.— Dlagnunowtic donal view of an embno rab-
bit with Tta membnuiM at the stage of nine io-
mltes (Haddon, after Van Bcnedan and Jalln).
at, alUntoli, showInK from behind the tall fold
of tho embryo; am, anterior border of tme am-
nion ; a. «. area vaacnioea, the outer border of
which indieatea the farthest extension of tho
mesobhwt; M, blastoderm, here consisting only of
, ompliaio-mesen-
„ . , proamnion ; pi,

non-vascoiar qplbiastic ViOi of the future pUcen-
ta ; «. f, Sinn* termlnalis.

mesoblast; M, blastoderm, here cor
epiblast and hypoblast; o. m. v, oi
terio or Titeliino veins ; ». am, t
non-vaseolar epibiastic viul of Inc

".Hi*

COMPARATIVE PHYSIOLOGY.

the allantoia, and vice versa; they are plainly supplementary
organs.

Th« Allutoio Cavity. -The degree to which the various em-
bryonic membranes fuse together is very variable for different
groups of mammals, including our domestic species.

In ruminants, but especially in solipeds, the allantois as it
grows spreads itself over the inner surface of the subzonal

Fi«. 81.-Embnro of dog. twentyflvo im old. opened on the vtntni side. Che«t
•nd vontral waIIb havo been removca. a, noee-pito; ft, eyet; e, nnder-J«w (flnt
gill-arch); d, oecoiid gill-arch; <>./, a, A. heart («. right,/ left auricle; gr, right, h,
left ventricle); i, aorU (origin of); kL liver (in the middle between the two lobea
is the cut yelk-'Veim: /, Rtomaeh; m, intestine; n. yelk-aac; o, urimitlve kidneys:
p,allantol«: 9, fore-limbs; A, hlnd-llmbi>. The croiAedemhiyo has been stretched
straight. (Haeckcl, after Bischoff.)

membrane, often spoken of as the "chorion," while it also
covers, though capable of easy detachment, the outer cniriace of
the amnion ; and thus is formed the allantoic cavity. The por-
tion of the allantois remaining finally within the foetus beoomea
the bladder, which during embryonic life communicates by its
contracted portion (uraehua) with the general amniotic cavity.

i. ii .j. I i ii ,m i -i> ii

«l l l|iii in i |[i ii»>>|<f|iiiwiMH ||«»» i niri iiiiiii

REPRODUCTION.

upplementary

te varioiM em-
e for different
es.

allantois aa it
the subzonal

nttiml side. Cheat
e, nnder-J«w (flnt
wricle; g, right, k,
*een the two lobe*
urimitlve kidneyi:
OMbeeaetretched

while it also
jtercniriaceof
ity. The por-
FoetiiB beoofiiiea
inicatesby its
miotic cavity.

■am.

Fia. 8>.— DIamm of wi embryo ehowlns the relstloM of the ▼••calu- allMtole to the
villi of the chorion (OadiM). «, embryo lying In the cavity of the unnlon; y«,
yell(-ue: al, alluitoli; A. V, allantoic veeaele dipping into the vUli of the chorion;
eh, chorion.

In the mare especially these parts can be readily distin-
gfuished. From the connection of the portion' that ultimately
forms the bladder with the
main sac, as indicated
above, there is ground for
regarding the allantoio
fluid in the later stages of
gestation, at all events, as
a sort of urine.

This fluid is at an ear-
ly period abundant and
colorless, later yellowish,
and finally brown. Since
at one thne it contains
albumen and sugar, it
inay serve some purpose
in the nutrition of the
foetus.

When most suggestive
of urine in the latest stages
of gestation, it contains
«

Sto. 88.— Diagram of the fatal membnuiea of
the Vlntlnian opoesam (Haddon, after Oa-
bom). Two villi are shown greatly enlarged.
The proceaeea of the cells, which have been
ezamerated, donbtlcM coneapond to the
peendopodia deaerlbed by Caldwell, al,
allantob ; am, amnion; «. t, ainns tenni.
nalia; «.a, anbaonal membrane: v, villi on
the anbaonal membrane In the region of
the yelk-aae ; ya, yelk-eac. The vaacolar
aplanchnoplenre (hvpobbat and mesoblast)
is indicated by the blMk line.

COMPARATIVE PBT8I0L001.

i ;

• oharaoteriitio body, aUantoin, reUtod to urio acid, una,
etc.

Certain bodiei, being probably intpiaiated allantoic fluid,
have been termed "bippomanea." They may either float free
in the fluid or be attached to the allantoii by a slender pedicle.

The relation of the parta deaoribed above will become clearer
after a study of the accompanying outa and thoae of preceding
pagea, in which the allantois ii flgured.

Fia. M.— Bst«rior of ohorU lae; mate. (CIuniTMn.) A, body; B. 0. oonitw.

Tht TlMOlta.— Thia itmcture, which variea greatly in com-
plexity, may be regarded as the result of the union of structures
existing for a longer or shorter period, free and largely inde-
pendent of each other. With evolution there is differentiation
and complication, so that the placenta usually marks the site
where structures have met and fused, differentiating a new or-
gan; while corresponding atrophy, obliteration, and fusion take
place in other regions.

AU placentas are highly vascular, all are villous, all dis-
charge similar functions in providing the embryo with nourish-
ment and eliminating the waste of its cell-life (metabolism).
In structural details they are so different that classiflcationB of
wa mm fl l* have been founded upon their resemblances and dif-
ferences. They will now be briefly described.

In marsupials the yelk-sac is both large and vascular; the
allantois small but vascular; the former is said (Owen) to be
attached to the subaonal membrane, the latter not; but no villi,
and consequently no true chorion, is developed. All mammals

tm m I —I ■^ ■ ■1 ■■ ! ■

tm mx 'im^mmmmitmm*

REPRODUCTION.

rio acid, una,

alUmtoio fltiid,
ither float free
lender pedicle,
become clearer
« of preceding

ly; B. 0. conn*.

greatly in com-
on of structures
id largely inde-
I di£Perentiation
marks the site
iating a new or-
and fusion take

villous, all dis-
fo with nourish-
fe (metabolism),
slaarifloations of
blances and dif-

id vascular; the

id (Owen) to be

iot; but no villi,

All mammals

Fio. 86.— FottM of in«N with lit envelopM. (CbkOTMo.) A, chorion; 0, Mnitloii n-
novad from allantold cavity and opened to ezpoM fcetw; D, infundlbnlamjDf
nrachoa; B, atlantold portion of ambllical cord.

other than the monotremes and maisupials have a true allan-
toic placenta.

Thib IMieaidal IlMWiita.— This form of placenta is that exist-
ing in the rodentia, inseotivora, and cheiroptera. The condition
found in the rabbit in that which has been most studied. The
relation of parts is shown in Fig. 79.

The uterus of the rodent is two-homed; so we find in gen-
eral several embryos in each horn in the pregnant rabbit.
They are functionally independent, each having its own set of

wmm>*

■fw

COMPARATIVE PHYSIOLOGY.

membranen. It will be obMnred from the figure that the true
yilloua chorion ii oonttned to a comparatively Muall regiou;
there is, however, in addition a falM chorion without villi, but
highly vaacukr. Thii blending of forma of plaoetatation which
exist aeparately in different groupa of animals is significant.
In the rabbit at a later stage there is considerable interming-
ling of foetal and maternal parts.

rio. 8A.— Seriea of dlagnuni rapreMntlng the ralttloM of the dccldoa to the ovnin. at
different periode, In the human enbiect. The dectdn* Me dark, the ovam ihadM
trantvereely. In 4 and 5 the chorionic vaecniar proeeeiiec are flgnred (after Dal-
ton). 1. Omm reatimr on the decidna eerotlna; >. Decldoa refleia growInK round
the ovum: S. Complotion of the decidna aronnd the omm; 4. Villi, mwlng out
all around the chorion; 6. The villi, epeclally developed at the site of the future
placenta, having atrophied eieewhere.

The MatadiiooidBl FlMOita.— This type, which; in general
naked-eye appearances, greatly resembles the former, is found
in man find the apes. The condition of things in man is by no
means as well understood as in the lower mammals, especially
in the early stages; so that, while the following account is that

REPRODUCTION.

•5

re that the true
f aaiall ragioq;
ithout villi, but
uekitation which
In ia Blgnifloant.
«bl« interming-

•cldna to the ornm. at
lark, the ovam ihaM
•re flgnred (after DaU
reflexa Browlne roand
4. Villi, mWlnR oat

t the site or the fntote

rhioh; in general
former, is found
in man la by no
nmals, especially
ig account is that

usually given in worka on embryology, the atudent may aa well
underatand that our Icnowledge of human embryology in the
very earlieat atages ia incomplete and partly conjectural. The
reaaon of thia is obvious: s^jccimens for examination depending
on accidents giving rise to abortion or sudden death, often not
reaching the laboratory in a condition permitting of trust-
worthy inferences.

It is definitely known that the ovum, which ia usually fer-
tilised in the oviduct (Fallopian tube), on entering the uterus
becomes adherent to its wall and encapsuled. The mucous
membrane of the uterus is known to undergo changes, its com-
ponent parts increasing by cell multiplication, becoming in>
tensely vascular and functionally more active. The general
mucous surface shares in this, and is termed the deeidua vera ;
but the locality where the ovum lodges is the seat of the great-
est manifestation of exalted activity, and ia termed the deeidua
aerotina; while the part believed to have invested the ovum by

Fio. 87— Vancalar ayatem of the haman tatna, repreiented dUgrammatieally (Hnx-
ley). J7, heart; TA, aoitle tmnk; e, eonmon carotid artery; «', eztamal carotM
artery; e", Internal carotid artery; «, anbclavian artery; v. vertebral artery; 1. 9,
S. 4. 5, aortic arehea; A', donal aorta; o. omphalo-meaenteric artery; ilv, Vitelltne
duct; 0', omphalo-ineaenterU) rein; v', nmbillcal Tealele; vp, portal vein: X. liver;
II. M, nmbllleal arterlea: u", u", their endlnga In the placenta; «', nmbillcal vein;
Df), doetna vcnoana; vA. hepatic vein; «e, inferior vena cava; vU, Iliac velna; Of,
vena aiygoa; vc', poaterior cardinal vein; DC, dnct of Covier; P, long.

COMPARATIVE PHYSIOLOGY.

fused growths from the junction of the deoidua y«nt and aero-
tina is the decidua reflexa.

The decidua serotUia and reflexa thus become the outermost
of all the coverings of the ovum. These and some other devel-
opments are figured below. It is to be remembered, however,
that they are highly diagrammatic, and repiresent a mixture of
inferences based, seme of them, on actual obnrvation and others
C2l analogy, etc.

The figures will convey some information, though appear-
ances in all such cases must be interpreted cautiously for the
reasons already mentioned.

During the first fourteen days villi appear over the whole
surface of the ovum ; about this fact there is no doubt. At
the end of the first month of foetal life, a complete chorion
has been formed, owing, it would seem, to the growth of the
allantois (its mesoblast only) beneath the whole surface of the
subzonal membrane. From the chorionic surface vascular pro-
cesses clothed with epithelium project like the plush of velvet.
The allantois is compressed and devoid of a cavity, but abun-
dantiy supplied with blood-vessels by the allantoic arteries and
veins, which of course terminate in capillaries in the villi.
Compare the whole series of figures.

Flo. 6B.-Hniiu« on during Mriy ttagM of d«TC)opiiwnt A Md B, front and Bide

view of an ovnm anppoaed to be abont thirteen day* old; «. embrronic am

(Qoaln, after Helchert); C. o»»m of four io tm wedti. ahowlng the nmcral

■ atiractnte of the ovnm before formation of the plaeenta. ..«»*of the w^ITof the

ovam ii removed to show the embryo in poeltlon (after Allen Thomaon).

At this stage the condition of the chorion suggests the type
of the difiPuse placenta which is normal for certain groups of
animals, as will presentiy be learned.

The subsequent changes are much better understood, for
parts are in general no longer microscopic but of considerable
sin, and their real structure less readily obscured or obliterated.

The amniotic cavity continues to enlarge by growth of the
walls of the amnion and is kept filled with a fluid; the yelk-sac

REPEODUCTION.

ytm aadBero-

i the outermost
me other devel-
Mred, however,
it m mixture of
ttion and others

though appear-
itioudy for the

over the whole
no doubt. At
implete chorion
growtli of the
e surface of the
ce vascular pro-
plush of velvet,
mty, but abun-
oic arteries and
Bs in the villi.

■ad B, front and side
Id; «. embrronlc we*
•howlng "»«.^I™*P'
tetcrf thewwof ttM
m TbomMm).

luggests the type
ertain groups of

understood, for
t of considerable
ad or obliterated.
>y growth of the
aid; thes^elk-sao

is now very small ; the decidua reflexa becomes almost non-
vascular, and fuses finally with the decidua vera and the cho-
rion, which except at one part has ceased to be villous and vas-
cular ; so that becoming thinner and thinner with the advance
of pregnancy, the single membrane, arising practically from

Fia. 80.— HnniMi embrTo, twelve weeks old, with tto eoverinc*; lUttana siae. The
navel-cord imutm mm the navel to the placenta, b, amnion; «, chorion; a, pla-
cenU; d', lemalna of tufta on the amooth chorion; /, <t»eUua fv**" (Inner); g,
dwkhMi Mrs (oater). (Uaeckel after Berahard SchiUtie.)

this fusion of several, is of a low type of struotuie, the result of
gradual degeneration, as the rdfe they once played was taken
up by the other parts.

But of paramount importance is the formation -of the pla-
centa. The chorion ceases to be vascular except at the spot at
which the villi not only remain, but become more vascular and
branidi into arborescent forms of considerable complexity. It
is discoidal in form, made up of a foetal part just described and
a maternal part, the decidua serotina, the two becoming blended

t-'

COMPARATIVE PHYSIOLOGY.

so that the removal of one inTolves that of more or leas of the
others. Theoonneciionof parts is far closer than that deocribed

Fi«. W.— DUgnm illmtnting the decidna, placenta, etc. (after LMgeoia). e, embryo;
i, Intestine; p, pedicle orthe amblllcal vesicle; u. «, ombilical ▼eelcle; a, amnion;
eh, chorion; «. t, vaacnlc; tafta of the chorion, conitltatlng the fcetal portion of
the placenta; m. p, maternal portion of the phwenta; a. t, decidna vera; a. r, de-
cidna rMeza; al, allantols.

for the rabbit ; and, even with the preparation that Nature
makes for the final separation of the placenta from both foetus
and mother, this event does not take place without some rupture
of vessels and consequent hsemorrhi^.

It is difficult to conceive of the great vascularis of the
human placenta without an actual examination of this structure
itself, which can be done after being oast off to great advan-
tage when floating in water; by which simple method also the
thinness and other charaoteristics of the membranes can be
well made out.

The great vessels conveying the foetal blood to and ft»m the

RBPRODUOTION.

ire or leas of the
ui that described

LWgmte). e, embryo;
eal TMicle; a, •mnion:
I the total portion of
aeeidu vera; a. r, <1e-

ion that Nature
from both foetus
[>ut some rupture

scularity of the
I of this structure
' to great advan-
method also the
tmbranes can be

to and ttom the

placenta are reduced to three, two arteries and one vein. The
villi of the placenta (chorion) are usually said to hang freely
in the blood of the large irregular sinuses of the decidua sero-
tina; but this is so unlike what prevails in other groups of
animals that we can not refrain from believing that the state-
ment is not wholly true.

The Zonary FlMsenta.— In this tjrpe the placenta is formed
along a broad equatorial belt, leaving the poles free. This form
of placentation is exemplified in the camivora, hyrax, the ele-
phant, etc.

In the dog, for example, the yelk-sac is large, vascular, does
not fuse with the chorion, and persists throughout A rudi-
mentary discoid placenta is Brst formed, as in the rabbit; this
gradually spreads over the whole central area, till only the ex-
tremes (poles) of the ovum remain free; villi appear, fitting into
pits in the uterine surface, the maternal and foetal parts of the
placenta becoming highly vascular and closely approximated.
The chorionic zone remains wider than the placental. As in
man there is at burth a separation of the maternal as well as
foetal part of the placenta— i. e., the latter is deciduate; there is
also the beniming of a decidua reflexa.

The Dimue PlMenta.— As found in the horse, pig, lemur,
etc., the allantois completely incloses the embryo, and it be-
comes villous in all parts, except a small wea at each pole.

The Fdlyootyledoiiaxy FlMenta.— This form is that met with
in ruminants, in which case the allantois completely covers the
surface of the subconal membrane, the placental villi being
gathered into patches {chorial cotyledons), which are equivalent
to so many independent placoaitas. The component villi fit into
corresponding pite in the uterine wall (uterine cotyledons),
which is specially thickened at these points. When examined
in a fresh oondi^on, under water, they constitute very beautiful
objects. The pits referred to above into which the foetal villi fit
are, as shown in the figures on page 91, essentially the same in
structure as the villi themselves. In the cow the uterine cotyle-
dons are convex ; but in the sheep and goat they are raised con-
cave cups in which the openings for the foetal villi may be seen
with the naked eye. The differences are not essential ones.

Between the uterine cotyledons and the foetal villi which
fit into them a thiokish, milky-looking fluid is found, the
" uterine mUk " elaborated, no doubt, by the cells which line the
cotyledonous pits.

COMPARATIVH PHYSIOLOGY.

The placentation of certain of our domeatio animals may be
thus expressed in tabular form (Fleming) :

( General.

Simple placenta.

(Man.
J Sow.

( Local and olnmUr. < B"<*-

Multiple placenta.

ICat.

(CAw.
i Sheep.
(Goat

Oomparing the formation, complete development, and atro*
phy (in some cases) of the various foetal appendages in mam-
mals, one can not but perceive a common plan of structure,
with variations in the preponderance of one part over another
here and there throughout. In birds these structures are sim-
pler, chiefly because less blended and because of the presence
of much food-yelk, albumen, egg-shell, etc., on the one hand,
and thelibsence of a uterine wall, with which in the mammal
the membranes are brought into close relationship, on the other ;
but, as will be shown later, whatever the variations, they are
adaptations to meet common needs and subserve common ends.

BIZOROSOOFIO 8TRU0TUBS OF THB FZtAOSNTA.

This varies somewhat for different forms, though, in that
there is a supporting matrix, minute (capUlary) blood-vessels,
and epithelial coverings in the fcetal and maternal tnrtaeea, the
several forms agree.

The jng ixMsesses the simplest form of placenta yet known.
The vOli fit into depressions or crypts in the maternal uterine
mucous membrane. The villi, consisting of a core of connective
tisnie, in which capillaries abound, are covered with a flat epi-
thelium; the maternal crypts correspond, being oompoMd of
a similar matrix, lined with epithelium and permeated by
oapillMy vessels, which constitute a plexus or mesh-work. It
thus results that two layers of einthelium intervene between
the maternal and foetal capillaries.

The arrangement is substantially the same in the diffuse and
the cotyledonary placenta.

In tlie deciduate placenta, naturally, there is greater compli-
cation.

In certain forms, as in the fox and cat, the maternal tissue
shows a Bjrstem of trabeculee assuming a meshed form, in
which run dilated capillaries. These, which are covered with

inimals may be

«h.

eep.
at.

nent,and atro*
dagesin mam-
n of Btruotttre,
rt over another
ctturesare sim-
>f the presence

the one hand,
a the mammal
p, on the other;
itiona, they are

common ends.

3LAOBHTA.

hough, in that
) blood-veaeels,
ialBurfooeB,the

nta yet known,
latemal uterine
re of connective

with a flat epi-
ig compoeed of

permeated by
mesh-work. It
Bnrene between

. the diffuse and

greater compli-

maternal tissue
eshed form, in
recovered with

COMPARATIVB PHYSIOLOGY.

In the placenta of the
apes and of the human sub-
ject the most marked depart-
ure from simplicity is found.
The maternal vessels are said
to constitute' large intercom-
municating sinuses; the villi
may hang freely suspended in
these sinuses, or be anchored
to their walls by strands of
tissue. There is believed to
be only one layer of epithe-
lial cells between the vessels
of mother and foetus in the
later stages of pregnancy.
This, while closely investing
Fia. M.— Placenta of • tiotb. Flat matemai the foetal vessels (capillaries),

•pltheltal cellf) ihown In poaitlon on n v i x aiT i.

rbriitaide; on left thqr an removed and really belongs tO the mater-

feiere^S:ld.-'*' "'"^ '^ "'^' nal structures. The signifl-

Via. 97.— Stractnre of bnman placenta; 0$, decidna seiotina; t. tr^Mcnla of MX^ln*
paMbur to fatal vlUi; ea, corilnx arterr; vp, nteio-plaeenta] Teln; «, prolon gaUon
of miMerAal tiMue im exterior of vUIm, ootaide celinlar lAyer r, whlcn mar npRK
aent either endothelhun of matemai blood-veMele or delieato connaetite tlaane or
tbe lerotina or both; e', matemai cell* of the seiotina.

REPRODUCTION.

lacents of the
^e human sub-
marked depart-
plioity is found.

vessels are said
large intercom-
inuses; the villi
ely suspended in
, or be anchored
s by strands of
B is believed to
layer of epithe-
reen the vessels
id foetus in the

of pregnancy,
loeely investing
lels (capillaries),
pi to the mater-
«. The signifl-

,tnbecDl««rfMK>Uii»
1 Teln; «, prolongation
Br if, wUch nwT npre-
ito conneetiTe tuane of

canoe of this general arrangement will be explained in the
chapter on the physiological aspects of the subject.

It remains to inquire into the relation of these forms to one
another from a phylogenetio (derivative) point of view, or to
trace the evolution of the placenta.

BfOLntion. — Passing by the lowest mammals, in which the
placental relations are as yet imperfectly understood, it seems
clear that the simplest condition is found in the rodentia.
Thus, in the rabbit, as has been described, both yelk-sac and
allantois take a nutritive part ; but the latter remains small.
In forms above the rodents, the allantois assumes more and
more importance, becomes laiger, and sooner or later predomi-
nates over the yelk-sac.

The discoidal, zonary, ootyledonary, etc., are plainly evolu-
tions from the diffuse, for both differentiation of 8truct\u*e and
integration of parts are evident. The human placenta seems
to have arisen from the diffuse form ; and it will be remembered
that it is at one period represented by the chorion with its villi
distributed universally.

The resemblance of the embryonic membranes at any early
stage in man and other mammals to those of birds certainly
suggests an evolution of some kind, though exactly along what
lines that has taken place it is difficult to determine with exact-
nefB ; however, aa before remarked, nearly all the complica-
tions of the higher forms arise by concentration and fusion, on
the one hand, and atrophy and disappearance of parts once
functionally active, on the other.

Snnunary. — ^The ovum is a typical cell ; unspecialized in most
directions, but so specialized as to evolve from itself compli-
cated structures of higher character. The s^mentation of the
ovum is usually preceded by fertilization, or the union of the
nuclei of male and female cells, which is again preceded by the
extrusion of polar globules. In the early changes of the ovum,
including segmentation, periods of rest and activity alternate.
The method of segmentation has relation to the quantity and
armngement of the food-yelk. Ova are divisible generally
into completely segmenting (holoblastic), and those tiiat under-
go s^^entation of only a part of their substance (meroblastic) ;
but the processes are fundamentally the same.

Provision is made for the nutrition, etc., of the ovum, when
fertilized (ofisperm) by the formation of yelk-sac and allan-
tois; as development proceeds, one becomes more prominent

COMPARATIVE PHYSIOLOGY.

than the other. The allantoii may fine with adjacent mem-
branea and form at one part a condensed and hypertropbied
chorion (placenta), with corresponding atrophy elsewhere.
The arrangement of the placenta yaries in different groups of
animals so constantly as to furnish a basis for classification.
Whatever the variations in the structure of the placenta, it is
always highly vascular ; its parts consist of villi fitting into
crypts in the maternal uterine membrane— both the villi and
the crypts being provided with capillaries supported by a con-
nective-tissue matrix covered externally by epithelium. The
placenta in its different forms would appear to have been
evolved from the diffuse type.

The peculiarities of the embryonic membranes in birds are
owing to the presence of a large food-yelk, egg-shell, and egg-
membranes; but throughout, vertebrates follow in a common
line of development, the differences which separate them into
smaller and smaller groups appearing later and later. The
same may be said of the animal kingdom as a whole. This
seems to point clearly to a common origin with gradual diver-
gence of type.

L ' JMH « ft'W'H t» ' » | i l'

adjacent mem-
1 hypertrophied
phy elaewhere.
ferent groups of
tr olaaaiflcation.
le placenta, it is
rilli fitting into
th the villi and
orted by a con-
pithelium. The
r to have been

nea in birds are
If-shell, and egg-
Mr in a common
arate them into
md later. The
a whole. This
h gradual diver-

THB DEVELOPMENT OP THE EMBRYO ITSELF.

We now turn to the development of the body of the animal
for which the structures we have been describing exist. It is
important, however, to remember that the development of
parts, though treated separately for the sake of convenience,
really goes on together to a certain extent; that new structures
do not appear suddenly but gradually ; and that the same law
applies to the disappearance of organs which are being super-
seded by others. To represent this completely would require
lengthy descriptions and an unlimited number of cuts; but
with the above caution it is hoped the student may be able to
avoid erroneous conceptions, and form in his own mind that
series of pictures which can not be well furnished in at least
the space we have to devote to the subject. But, better than
any abstract statements or pictorial representations, would be
the examination of a setting of eggs day by day during their
development under a hen. This is a very simple matter, and,
while the making and mounting of sections from hardened
specimens is valuable, it may require more time than the
student can spare; but it is neither so valuable nor so easily ac-
complished as what we have indicated ; for, while the lack of
sections made by the student may be made up in part by the
exhibition to him of a set of specimens permanently mounted
or even by plates, nothing can, in our opinion, take the place
of the examination of eggs as we have suggested. It prepares
for the study of the development of the m a mm a l , and exhibits
the membranes in a simplicity, freshness, and beauty which
impcut a knowledge that only such direct contact with nature
can supply. To proceed with great simplicity and very little
apparatus, one requires but a forceps, a glass dish or two, a
couple of watch-glasses, or a broad section-lifter (even a case-
knife will answer), some water, containing just enough salt to
be tasted, rendered lukewarm (blood-heat).

COMPARATIVB PHYSIOLOGY.

Holding the egg longitudinally, crack it aoroM the center
tranivenely, gently and carefully pick away the ehell and ito

1 « 8 4 »

® # © ® •

Fio. W.— VuioDi ttasM In the developmnit of the frog from Um en (wtOT I
1. The Mainentliic OAiiin, ihowlns Bnt clearage funow. «. Section of tfc
•t risht angle* to the fnnow. 8. iSaaie, on •ppeMsnee of Moond farrow,

plightlT from above. 4.

•nee of first hciriaontal_fnrrow.

•ection " " " • ■ —

fifth fnrrowe

above.

The latter aeen from Deneath. 5.

S. The fame, teen ffom above,

(after Howea).

' the above

viewed

The Mune, on appear-

7. Longttmlinal

'Mrth and
than the

U. Later ph

»'M'(aII oltiere K 6). W.' Ixmgitn3rn5Terticar_iS5iM'^ m^o rt

15. Caqgltudlnal vertical section of i

than 14 a * 10). ne, nuclena; «. e, eteavage cavity; m>. epiblasf: LI, jrolk-bearing
tower-larer cells; « bUstopore; at, aichenteron (mYd-gnt): *6, hypoblast; m$.
nwUfleientlated mesoblast; «*, notochord; n. a, neuid (eerebro-spinal) asU.

membranes, when the blastoderm may be seen floating upward,
as it always does. It should be well examined in position,

TUB DEVBLOPMENT OF THK BMHRYO ITSELF. 97

oroM the oentor
he ihell and its

n Um cog (aflOT Howm).
9. Section of the aboTe
f Moond fnrrow, viewed
5. The Mune, on appear-
above. 7. LongitMUniU
ippaaranoe of fourth and
hti)' later ttaoe than the
m«te mptdljrlhan lower.
9 of It. 14. Becmentlns
tlon of Mme. 18 and 15
>f embryo at a itaoe later
iplblaan U, yolk-bearing
lut): W, hypoblaat; m«.
^bio-sptnal) asU.

n floating upward,
oined in pontion,

using a hand lens, though thia ii not eaential to getting a fair
knowledge; in fact, if Uie exam-
ination goes no further than tlie
naked-eyo appearances of a doien
eggs, selecting one every twenty-
four hours during incubation,
when opened and the shell and
membranes well cleared away,
such a knowledge will be sup-
plied as can be obtained fnmt no
books or lectures however good.
It will be, of course, understood
that the student approaches these
examinations with some ideas
gained from phites and previoiu
reading. The latter will furnish
a sort of biological pabulum on
which he may feed till he can
supply for himself a more natu-
ral and therefore more healthful
one. While these remarks apply
with a certain degree of force 'to
all the departments of physiolo-
gy, they are of special impor>
tance to aid the constructive fac-
ulty in building up correct no-
tions of the successive rapid
transformations that occur in
the development of a bird or
mftmmal.

Fig. 99 shows the embryo of
the (bird at a very early poiod,

when already, however, some of Fi«. ».— Kmbwo fowl 8 mm. long, of

., '',. . _, , about twMiCT-foarboata, lean mm

the mam outlines of structure ^ - ' — — — -

are marked out. Development
in the fowl is so rapid that a few
days suffice to outline all the
principal organs of the body. In
the mammal the process is slow-
er, but in the main takes place in
the same fashion.

As the result of long and pa-
1

above. 1 K 10. (Haddon, aft«r
KSIIiker.} JN, onion of the med-
nllaiy folda In the realon of the
htnd-brain ; fr, primlUve streak;
A. parietal sone; I(f, posterior
portfon of widely open nenral
groove; H/', anterior part of neu-
ral groove ; Bv, neaial ridge ; 81*,
tmnk-sone ; vAf, anterior amni-
otic fold ; vD, anterior umbilical
■inni showing throoch the blasto-
derm. His divides the embryonic
rudiment into a central .tmnk-ione
and a pair of lateral or parietal
■ones.

COMPARATIVK PIIVSIOUKlY.

tient nbwrvaUtni, it ii now Mttled that all tli( ]^tia of the moit
coinplirutetl organUm ariw fmtn the three-la;yi>ivd blaatoderm
provioualy flfrured ; every part may be traced buck ao ariaing in
one or other of these layer* of cellit — the epiblunt mesubluMt, or
hypoblaat. It frequently happens that an organ la made up ot
cella derived from more than one layer. Rtruoture« rmiy, ac-
cordingly, be oUuNifled um epiblastlc, meeoblaKi : , or hjrpoblastic ;
for, when two atrata of oella unite in the formation itt any part,
one ia alwaya of aubordinate importance to the other : thua the
digeative organs are made up of meaoblaat aa well aa hypo-
blaat, but the latter oonatitutea the eaaential aecreting cell mech-
aniam. As already indicated, the embryonic membranea are
alao derived from the aame aouroe.

The epMaat gives rise to the akin and its appendages (hair,
naila, feathers,* etc.}, the whole of the nervous system, and the
chief parts of the organs of special sense.

The tneadbkut originates the vascular syntem, the skeleton,
all forms of conneotive tissue including the framework of
glands, the muscles, and the epithelial (endothelial) structures
covering serous membranes.

The hypobkut furnishes the secreting cells of the digestive
tract and its appendages— as the liver and pancreas— the lining
epithelium of the lungs, and the cells of the secreting mucous
membranes of their framework of bronchial tubes.

It is difficult to ovenate the importance of these morpholog-
ical generalisations for the physiologist ; for, once the origin of
an organ is known, its function and physiologiaal relations gen-
erally may be predicted with considerable certainty. We shall

Fta. 100.— TnuMTMM Mction thfongh the uMdnllMy

of a chiek of eltfhiMn hoan (fntter and Balfob;. a, vyin....^ ., •««
H, hypobbwt; nff, m edu lU ry foM; mg, iiMdollwjr groove; eh, nbtocbord.

and half the bUwtodgnn
K, epIblMt; M, nwMbhift;

endeavor to qiake this prominent in the future chapters of thi^
work.

Being prepared with these generalisations, we continue our
study of the development of the bird's embryo. Before the end

THE DKVKIiOPMBNT OF TIIK KMBRVO IT8KI.F. y9

irta of the mott
rpd blaatuderm
ok aa aruing in
t, ine«ubliM«t, or
L 18 made up ot
lotureti rriftjr, ao-
or hypoblastk' ;
ion of any i»art,
other : thus the
I well aa hypo-
sting cell mech-
membranea are

ipendagea (hair,
tiyatem, and the

m, the skeleton,
I framework of
lelial) structurea

of the digestive
sreaa-the lining
ecreting mucoua
ibes.

heae morpholog-
nee the origin of
sal relations gen-
linty. We shall

tug

ad hiUf the btartodsim
iplMMt; M, mMoblMt;
; eh, nbtocbora.

■e chapters of this

I, we continue our
>. Before the end

of the flmt twenty-four hours such an appearance as that repre-
sented ill Fig. 100 is preaonted.

The mounds of cells forming the metlullary foldn are sct>n
coming in contact to form the medullary (neural) canal

tia 101 -Tnnwvdrw lectlon of embryo chick at end of jjrit lUy (afU-r KOlllker). M,
mSiibuitrW. hViM.blMt; m. roeduitary pl»t.;; ^..plblMt; m. j,, mwlullary irroove;
mTm«SnlSry fl)ld; cA. chord* dorwIU ; l\ proioverlcbr.l pUte; </. »/i. JIvlilon
of mcioblMi.

The notoehord, marking out the future bony axis of the
body, may also be seen during the first day as a well-nmrkttl
linear extension, just beneath the medullary groove. The clea v-

Fio. «».-TrMi«vww •wstloii of chkk ftt and of tecond day (KBUlker). E, eplbl«»«;
ffl^poblMt; t. m, extenuU pkrte of mcMblsit dividing (cleavage of nieeoblaat);
m./m«ln"wy '»M; m. g, ■ladullary groove; ao, aorta; p. plenroperltoneal oavl'y;
P, protovertebral plate.

age of the meaobhist, randting in the commeneement of the
formation of mmatopkure (body-fold) and the apUinchnopleure
(visceral fold), is also an early and important event These
give rise between them to the plmro-peritoneal oavity. The
portions of mesoblast nearest tlie neural canal form masses (per-
tdtral plates) distinct from the thinner outer ones (lateral
plates). The vertebral plates, when distinctly marked off, aa
represented in the figure, are termed the protovertebra (meao-
blastic mmiites), and represent the future vertebrse and the vol-
untary muscles of the trunk: the former arising from the inner
subdivisions, and the latter from the outer (muscle-plates). It
will be understood that the protovertebne are the results of

100

COMPARATIVE PHYSIOLOGY.

transverse division of the columns of mesoblast that formed the
vertebral plates.

Before the permanent vertebrsB are formed, a reunion of the
original protovertebrsB takes place as one cartilaginous pillai',

followed by a new segmen-
/•'*• tation midway between the

original divisions.

It is thus seen that a
laige number of structures
eitiier appear or are clearly
outlined during the first
day of incubation : the
primitive streak, primitive
groove, medullary plates
and groove, the neural ca-
nal, the head-fold, the
cleavage of the mesoblast,
the protovertebras. with
traces of the anmion and
areaopaca.

During the second day
nearly all the remaining
important structures of the
chick are marked out, while
those that arose during the
first day have progressed.
Thus, the medullary folds
close ; there is an increase
in the number of protover-
tebrse ; the formation of a
tubular heart and the great
blood-vessels ; the appear-
ance of the Wolffian duct ;
the progress of the head re-
gion ; the appearance of the
three cerebral vesicles at the anterior extremity of the neiwal
canal ; the subdivision of the first cerebral vesicle into the optic
vesicles and the beginnings of the cerebrum ; the auditory pit
arising in the third cerebral vesicle (hind-brain); cranial flex-
ure commences ; both head and tail folds become more dis-
tinct ; the heart is not only formed, but its curvature becomes
more marked and rudiments of auricles arise ; while outside

Fia. 103.— Embryo of chick, between tiiirty
and thMy-tix honn, viewed from above
as an opaque object (Foster and Balfour).
/. b, forebrain; m. ft, midbrain; A. b, hind-
Drain; cp. V, optic vesicle; au.p, anditory
pit ; o./, vitelline vein ; p. v, mesoblastic
somite; m.f. line of functioo of mednlla-
' TV folds above^medullaiT canal ; s. r, ainus
rhomboidalis; t, tail-fold; p.r, remains of
primitive groove ; a. p. area pellnclda.

•owaMiaMM

iiMMtli

that formed the

% reunion of the
ilaginouB pillai*,
r a new segmen-
way between the
itdons.

lus seen that a
ler of structures
ar or are clearly
uring the first
icubation : the
itreak, primitive
ledullary plates
), the neural ca-
head-fold, the
f the mesoblast,
tvertebree. with
he amnion and

the second day
the remaining
structures of the
larked out, while
arose during the
liave progressed,
medullary folds
re is an increase
iber of protover-
i formation of a
art and the great
ds ; the appear-
B WolfBan duct ;
Bs of the head re-
appearance of the
ity of the neural
icle into the optic
; the auditory pit
in); cranial flez-
lecome more dis-
irvature becomes
e : while outside

THE DEVELOPMENT OP THE EMBRYO ITSELF. 101

the embryo itself the circulation of the yelk-sac is established,
the allantois originates, and the amnion makes rapid progress.

It may be noticed that the cerebral vesicles, the optic vesi-
cles, and the auditory pit are all derived from the epiblastic
accumulations which occur in the anterior extremity of the
embryo ; and their early appearance is prophetic of their physi-
ological importance.

The heart, too, so essential for the nutrition of the embryo,
by distributing a constant blood-stream, is early formed, and
becomes functionally active. It arises beneath the hind-end of
the fore-gut, at the point of divergence of the folds of the

B _*

Fio. 104.— Dtagrwn repreaenting under larface of an embryo rabbit of nine days and
thrw hoS old. Ifluatrattag development of the h«?« <»^ie' *"«» Tlw?'""'')- , *.
view ^^ enttoe embryo^ B, an enlaised outUne of the heart of A: C, later etaffe
of ttedevdo^tof B; XaI minnitel heart; oo, aorts; vv, vltilllne veins.

splanchnopleuie, and so lies within the pleuro-peritoneal cav-
ity, and is derived from the mesoblast. At the beginning the
heart consists of two solid colimms ununited in front at first ;
later, these fuse, in part, so that they have been compared
with an inverted Y, in which the heart itself would correspond
to Oie lower stem of the letter (a) and the fjreat veins (vitel-
line) to its main limbs. The solid cords of mesoblast become

102 COMPARAT E PHYSIOLOGY.

hollow prior to their ooaleacenoe, when the two tubes become

one.

The entire blood-vascular system originates in the mesoblast
of the area opaca especially ; at first appearing in isolated spots

Fio. 105.-Chick on thliddaj, (Men froni bwiMUi aa ateMitiMrent object, the hMd
being tamed to one side {Poater wd Balfoor). <^. f«lM Mnnfcm: a, amnkni; CH,
eerSSnX hemiqtheie; FB, MB.HB, anterior, middle, and poateriorMtebial »^-
dee; OP. M»tlc Teelcle; ot, andltonr TeeloUs; (JfV, omphal»meaenterie rein*; JSB,
heart; iti, bnlboa arterioaoa; eft, notodiord: (M'.a.ompbalo^Maenterte artertoa;
Pt, protoTertebne: <r, point of diveigence of the eplanchnoplettnl folda; y, ter-
mination ot the foie-gut, V.

which come together as actual veeselB are formed. The student
who will pursue the plan of examining a series of incubating
eggs will be struck with the eariy rise and rapid progress of the
vascular system of the «nbryo, which takes, when complete,
such a form as is tepKwented diagramatioally in Fig. 109.
The blood and the blood-vessels arise simultaneously from

wo tubes become

3 in the meaoblast
g in isolated spots

-Pr

-tk

—Oftt,

•parent object, the heed
iBiikm; a, amiiioii; CH,
d poeterior oefebiel vesl-
Uo-meeenteric reiiu; Ht,
baloHiMeenteric atteriee;
ihnopleutel folde; y, ter-

med. The student
tries of incubating
pid pn^rreos of the
«, when complete,
r in Fig. 109.
nultaneously from

THE DEVELOPMENT OP THE EMBRYO ITSELF. 103

the cells of the mesoblast by outgrowths of nuclear proliferar
tion, and in the case of vessels (Fig. 143) extension of processes,
fusion, and excayation.

aJ's'^^WSiSfi bilbTiTSitaiftlw e&t., «.«, «»ph.lo.me.e«ter.e
uieriM;ul,niiltedaaft».

The fwoijut is formed by the union of the folds of the
splanchnopleure from before backward, and the hind-gut in a
nmilar manner by fusion from behind forward.

Y^^HV

SjKJibAft h3L»%SSSittoi B. fitSitU. wWtwo pelri of aor^e archer
MtaS?^t«to£iVol hSST*. vltelHn* vShtt; 1-6. the aortic archee. The
diMM UM^tadSS* & pmMob of the futiin archee.

104

COMPARATIVE PHYSIOLOGY.

The excretory system is also foreshadowed at an early period
hy the Wolffian duct (Fig. 110), a mass of mesoblast cells near

which the cleavage of the mesoblast
takes place.

During the latter part of the sec-
ond day the vascular system, includ-
ing the heart, makes great progress.
The latter, in consequence of excessive
growth and the alteration of the rela-
tive position of other parts, becomes
bent up on itself, so that it presents
a curve to the right which represents
the venous part, and one to the left,
answering to the arterial. The rudi-
ments of the auricles also are to be
seen.

The arterial system is represented
at this stage by the expanded portion
of the heart known as the bulbua ar-
teriosua, and two extensions from it,
the aortffi, which, uniting above the
alimentary canal, form a single poste-
rior or dorsal aorta. From these great
arterial vessels the lesser ones arise,
and by subdivision constitute that
great mesh-work represented diagram-
matically in Figs. 108, 109, from which
the course of the circuli^on may be
gathered. The beating of the heart
commences before the corpuscles have

StTm^iAu/SumMle^' become numerous, and while the tub-

^^SSSr^i!^^ isto^edriven>»ffllve»ymcomplete
cnvieri (preckvai veinin B. The events of the thtrd day are of
ext»n>.i iUM«t«ie..: S.e, ^^ ^^^ ^^ ^^ extension of paHs

already marked out rather than the
formation of entirely new ones. The
following are the principal changes :
The bending of the head-end down-
ward (cranial flexure) ; the turning
of the embryo so that it lies on its
the completion of the vitelline circulation ; the in-

Fio. 108.— DIagnun at the em-
bryonic vMGular ayitem
(Wiedenhelm). A, atriooi;
A', A'. doiMJ aorte ; Ab,
bimneUal veeaelB:

pocterior cardinal vein: 7«.
common Iliac arteriea; K, L.
Ml cleft* ; S. A, right and
left roota of the aorta; S. S",
branchial collecting tranks
nr vein* ; 8b, subcUman ar-
tery ; Sb', inbclavian Teln;
Si, siona venoma; Fi'*eDtri-
cle: VC, anterior cardinal
vein; Km, vitelline velna.

left side

:s*talmtiii^>tteiaeBaaMmMit m*a ii mma nmmim

TT1"

at an early period
Moblast cells near
of the mefloblast

r part of the sec-
EU* system, includ-
es great progress,
uenoe of excessive
ration of the rela-
er parts, becomes

that it presento
which represents

d one to the left,
terial. The rudi-
es also are to be

iem is represented
expanded portion

1 as the bulbuB ar-
Ktensions from it,
niting above the
irm a single poste-

From these great
lesser ones arise,
n constitute that
>ree6nU!d diagram-
)8, 109, from which
irculation may be
kting of the heart
tie corpuscles have
md while the tub-
ti which the blood
11 very incomplete.
le third day are of
sxtension of parts
t rather than the
y new ones. The
rincipal changes :
i head-end down-
ire) ; the turning
hat it lies on its
rculation ; the in-

THB DEVBLOPMBNT OP THE BMBRYO ITSELF. 106

crease in the curvature of the heart and its complexity of struct-
ure by divisions ; the appearance of additional aortic arches
and of the cardinal veins ; the formation of four visceral clefts
and five viaoend arohes ; a series of progressive changes in

AAA

Fi«. 10B.-Di«ai«m of ciicaUrtioii of yrik-Me at m« <rf ttM d» (?»«« ■«< BjJ-
foar> BUModiom Mm from below. ArteriM inMle blMk. Abewt: ^il.iM-

ytSi M-or, right TiteUlne veto; 6. V, ■tonajrOMNai />•_£.«»»"» CuTleri;
* A%. V, Mpwfor CMdtotf or Jugnlwr v^n; V.Ca, tnfwlor ewdta^ vein.

the organs of the special senses, such as the formation of the
lens of the eye and a secondary optic vesicle ; the dosing in of
the optic veddo ; and the formation of the nasal pita. In the
region of the future brain, the vesicles of the oerebtal hemi-
spheres beoome distinct ; the hind-brain separates into cere-

106

COMPARATIVE PHYSIOLOGY.

Fia. HI.

ri«.llS.

dw (Forter and Balfour). nrcTnwinJ cmrt; pr. potterior root ^ f^ nwje
irttti «ngU«r«r, witoHor root; A. O. C. Mteffor ar»J colmnn of S»«Mj^«»4s
T. Jf. ftantwlor white colnnm to couwe of focinatioii; m. P< B»;^Pl^i„«ii
notochoid: rA; WoMBm ridge ; AO, domU eorta : v.e. a. pwrterior ^dlB^
?Sto; Til. W^toi duct; wr», WoiAm body, conttottag ol tabnlee and Hal-

THE DEVELOPMENT OP THE BMBBTO ITSBLP. 107

PiS ^nS^ *!0, •om.lopleaw; HP, ■pUnehnoptonre ; V, blood • veweU ;

,'f{l^-^SS^^T^A dlgeitiw tnict of chick on fourth d.y (after G«to).
*TT^iblick1i;"wpiS«.iiUh»poblMt; the .Uded P«rtlon. me«.blMtiJj. loiw df-
vertlculnm. expimding at bMei Into primary lung veaicle; tt, •lomach; /, Hver;

Fio.'ilS^uSdof chick of third day. viewed •Wewlw m a tfawp^nt obje^^^^^^
lev* /•. cerebral hemiapheree; A, veelcio of third Teptrtcla: II, mld-braln; III,
h(;ia-brJni%opUcve.loIe; a.'naaal pit; b, otic yealcle: i, Infundlbnium : «.
SlnMl bSy; A, notochoidiV, flfth nerve ; VU.ievmtii nenre ;Vni, united
gloHophaivi^ and pnemnosutrle narvea. 1, S, >, 4, S, the flva viMeral foldi.

bellum and medulla oblongata ; the nerves, both cranial and
gpinal, bud out from the nervous centers. The alimentary ca-
nal enlarge!, a fore-gut and hind-gut being formed, the former
being divided into oecophagus, stomach, and duodenum ; the
latter into the large intestine and the doaoa. The lungs arise
from the alimentary canal in front of the stomach ; from simi-
lar diverticula from the duodenum, the liver and pancreas orig-
inate. Changes in the protovertebrsB and muscle-plates con-
tinue, while the Wolffian bodies are formed and the Wolffian
duct modified.

Up to the third day the embryo lies mouth downward, but
now it comes to lie on iti left side. See Fig. 106 with the ac-
companying description, it being borne in mind that the view is
from below, so that the right in tho out is the left in the em-

KB.

v.. 1M UmiI of ahiek of fourth day, viewed from below aa an opaque object (Foi-

arohc8;^;lMaalptt.
bryo itodf. Fig. 110 gives appearances furnished by a vertical
transverse section. The relations of the parts of the digestive
tract and the mode of origin of the lungs may be learned from
Fig. HI.

108

COMPARATIVE PHYSIOLOGY.

An examination of tlie figure* and subjoined deacriptioni
must BufHce to convey a general notion of the lubMquent prog-

a.ph.

yjt.

If.

C.b.

'to.

tfV

-««.

fit.

•ehM.

-CU.

Wr'

th.

^l.

'BJ^

Fio. 114.-Kmbi7o "t end of fonrth (toy. •«« w • tmiwpMent »I»J«!.» }'!"•»«' «*^
Balfonr). Off, cerebnU bemltpliere; r. B. fora-bmin, or vmIcIc of thIM ventricle
(thalwnencephalon), with plne«l Blwid (/V.) projecting; JT. A MW-b>«lnv,,^*.
cecebellam; VK. F, fonrth ventricle; t, lent; eh». choroid ullt; Cm. V, •udltorr
vesicle; tm, raperior nuiilllMT prooM*; IF, «^etc., lint, Mcond. etc.. vlicend
folda ; V, llfth nerve; 17/, eeventb nerve; a. Ph, KloHopluraisMl nerve: Pg,
pnenmonitric. The dirtribntion of thiMe nervwle abio Indloited: e*. noto-
chord; jKTheMt: MP. mi»cle.ptate.; W' *J»B-. H. L, }^vAA\mb. llie .innlon
bM been removed. At, allantoli protmding f nnn cat end of aonuktlc (tiUk SS.

resB of the embryo. Special points will be considered, either in
a sepamte chapter now, or deferred for treatment in the body
of the work from time to time, as they seem to throw light
upon the subjects under discussion.

DBTBUPOIIBIIT OF THB V AaOOIAR STBTBM Of VBBr

TBBRATBS.

This subject has been inddentally considered, but it is of
such importance morpholopcal, physiological, and {lathological,
as to deserve special treatment.

In the earliest stages of the circulation of a vertelnato the
arterial system is made up of a pair of arteries derived from the
single buJbua arteriosus of the heart, which, after passing for-

satass:

ned deocriptioiM
subsequent prog-

ent object {Vimler and
mlclc of third ventriele

M. B, mid-bi«in: C.»,
d *llt; Clfii. V, audilorr
It, MRoad, etc., viiceru
DpharrngMl mnre; Pg,
M Indlcatiid: eh, noto-
lind-limb. The aronion

of fomatlo atalk SS.

osidered, either in
nent in the body
n to throw light

imc nr

lered, hut it is of
and pathological,

' a vertebrate the
I derived from the
after paoring for-

THE DEVELOPMENT OF THE EMBRYO ITSELF. 109

ward, bends round to the dorsal side of the pharynx, each giving
off at right angles to the yelk-sao a mteUine artery ; the aortie
un'*<< dorsally, then again separate and become lost in the pos-
ter, md of the embryo. The so-called arohea of the aorta are
large branches in the anterior end of the embryo derived from
the aorta itself.

The venous system corresponding to the above is composed
of anterior and posterior pairs of longitudinal (cardinal) veins,
the former (jugular, cardinal) uniting with the posterior to form
a common trunk (duc(tM Cuvieri) by which the venous blood is
returned to the heart The blood from the posterior part of the
yelk-sao is collected by the viteiline veins, which terminate in
the median m'ntM venoaus.

TlM Lator BtagM of th* Festal Oironlatioii.— Corresponding
to the number of visceral arches Ave pairs of aortic arches arise ;
but they do not exist together, the first two having undergone
more or less complete atrophy before the others appear. Figs.
115, 116 convey an idea of how the permanent forms (indicated by
darker shading) stand related to the entire system of vessels in
different groups of animals. Thus, in birds the right (fourth)
aortic aroh only remains in connection with the aorta, the left
forming the subclavian artery, while the reverse occurs in
mammals. The fifth arch (pulmonary) always supplies the
lungi.

Fia. 115.— Dlamma of the aortie archee of mammal (tandois and StIrllnB, after
Bathke). I. Arterial tmnk with one pair of archee, and an Indleatlon where the
•econd and third paira will develop, i. Ideal itago of Ave complete archee: the
fonrth clefta are shown on the left fide. 8. The two anterior pain of archee have
dlMppeaied. 4. Tranaltlon to the flnal at^te. A, aortic arch; ai, donal aorta;
oar, anhcUiTlan or axillaij arterjr; Ot, external carotid; d. Internal carotid: dB,
dnetna arteriaeuf Botallt; P, polmonaiy artery; 8, inbclavian artery; la, tnincus
arterkwDs; c, vertebral artery.

The arrangement of the principal vessels in the bird, mam-
mal, etc., is represented on page 110. In mammals the two prim-

Haaimw-J!/-!}.. ,..'-■ ■ -..i>^\v. ' .mfn ■

*:h..'---y>- ' 'i'!« ' ■■ • '■ > "Ji ' Mmj " I MWBWjK'i ' Wi

110

COMPARATIVE PHYSlOLOOy.

iUve anterior abdominal (aUantoie) veimi develop e«rly and
unite in front with the vitelline: but the right allantoic vein
and the right vitelline veinanoon dimppear, while the long com-
mon trunk of the allantoic and vitelline vefaw (duetu* venoaun)
paMNfl through the liver, where it i» Mid the ductus venoeun
gives oir and receive* branches. The ductus venosus Arantii
penisU throughout life. (CompM« the various figures iUustrat-
ing the circulation.)

*ia 116 — DlacnuB lllutratins tnuwformatioiif of aortk w^M tn • llMid. A ; •
•iike, bT*S^ cTimimintl, D. .Seen fiom below. . (li«Woi. •'««» Rethke.
™i,tinii cMotid; \ exttrniU e«otld; «. emnmon owotM A. rf. doctw WmM
b tween the third an^ fourth Mcbise; «. right •ortic jiKh^. •n»«'*»]"L?'*SBii
•oita; A, loft aortic aich; I. pulmmiwy Mtenf; *• "«>'^' »LS^? SSSu .5*?^i
between the palmonanr nrtery end the aortic mchee. B. Aright aortic areh.*.
vMta^turt«n^:Tlen aortic aich: A, palmonarjr arteiy: <. dnctua Botalll of the
Urtttr. C.TSlgta "aorta; «. fourth arch of the' right side (root of doiaal aorta) :
/ Tteht wbiSJCm; kdMMl aorta: *. left Mbetavlan tfouiih a«A of the left
■Idet • ( ralinon«7 aHenfTTaMl I. right and left dnctu Botal I of the imlmpaarT
SteHellnTrfTwlKtacS aortoj i, ftnrth arch of the loft .Ide (roof of dotyia
Srta)T>, dorwJ ao&; a, left mrtebral artery; », Wt •obclavtan; i.rijW w^:
ffliWurth arch of'tK; right eMc); *. right vertebral artenr: '.«««"»•««»»'
the right iubclavlan: m. pulmonary art»ry; », dnctua Boialll of the latter (usually
termia dueUu artmomi).

With the development of the placenta the allantoic circula-
tion renders the vitelline subordinate, the vitelline and the larger
mesenteric vein forming the portal. The portal vein at a later
period joins one of the venae advehmtea of the allantoic vein.

At first the vena cava inferior and the ductus venosus enter
the heart as a common trunk. The ductus venosus Arantii be-
comes a small branch of the vena cava.

THE I' ELOPMENT OP THK EM H\ ITSELF '\\

evelop early and

ht allantoio vein

bile the long oom-

(duetus venoauM)

) ductus venmus

yenomis Arantii

LIS flgurw illustrat-

iKbM ta • llMid. A ; •
lllwld»n, after Rathlui.)
tid. A. (/, doctM BoUIII
i; /, labclAvlu; g, dmaal
MM of tbo dnciM Botalll
B. a, right aortic arch; «,
rs i, doctM Botalll of th«
lide (root of donal aorta) :
(fourth arch of th« left
Botalll of thcpalmonarT
loft (Ide (root of dond
mbclavian; i, right rab-
artnrjr: /, contlnnation of
>lalll of the latter (nanally

le allantoio circula-
Qine and the larger
rtal Vein at a later
le allantoic vein,
ictus yenomis enter
^enosus Arantiibe-

The allaiii< ' vc i'
form as a solid <ord c
ply of the liver bcinir <l

The developmvnt nf
fowl up to a certain po

lally repn >nt«<l .n Am deigenerated
id ligamt' tht< uui -^ venous sup-
vtKl from M portal vein.
* h«irt Ilk ilready been traced in the
In th'- •uMiumal its origin and early
progress are similar aiul it* furth»>r history may be gathered
from the following series of representations.

In the fowl the heart shows the commencement of a division
into a right and left half on the third day, and about the fourth
week in man, from which fact alone some idea may be gaiK-xl
as to the relative rate of development. The division is effected
by the outgrowth of a septum from the ventral wall, which rap-

Via. 118.

Fm. 117.

la-JIT.-Develaiiiiieiit of the heart In the haman embryo. fKn the fourth to the
alsthweek, A. Rmbryo of four waeka (KOIIIker, after Coate). B, aatarior, 0,
poeterior viewi of the heart of an embryo of ilx weeke (KMIIker. after Bcker).
a. npper Umlt^of buccal cavity ; e, buccal cavity; A, Ilea between the ventral endi
of aecond and third branchial archea; <f, bnda of apper llmba; », liver; /, Intee-
tlne; 1, aoparlor vena cava: 1', left eoperlor vena cava; 1", opening of Inferior
vena cava; •, V, right and left aartclee; 8, S', right and left ventrtofae; 4, aortic
bolb

Fio. 11&— Hnman embryo of about three weeka (Allen Thameon). «it, yelk-eae; al,
allantole; am, annkm; at, anterior extremity; p$, poeterior extremi^.

idly reaches the dtwiial side, when the double ventricle thus
formed communicate by a right and a left auiiculo-ventricular
opening with the large and as yet undivided auride. Later an
incomplete septum forms similar divisions in the auricle ; the
aperture (foramen ovale) left by the imperfect growth of this
wall persisting throughout foetal life.

The Eustachian valve arises on the dorsal wall of the right
auricle, between the vena cava inferior and the right and left

119

COMPARATIVK PnY8I0U)0T.

Venn cavas •uperiorai; but in many nwDimabi, among which ia
man, the left vena cava Bupttrior diaappeani during foetal life.

For the preaent wo may tiimply My that the hiatoriea uf the
derelopment of the heart, thu blood-veMeb, and the bluud itaelf
are cloaely related to each other, and to the nature and ohangea
of the various metboda in wliich oxygen ia aupplied to the blood
and tiaauea, or, in other wordH. to the development of the respir-
atory ayatem.

THB OIVBIiOnUMT OF TBI USOOBMlTAZi STBTSBI.

Without knowing the hiatory of the organa, the anatomical
relatione of parta with uaes ao unlike aa reproduction on the one
hand and excretion on the other, can not be comprehended ; nor,
aa will be abortly made clear, the fact that the aame part may
aerve at one time to remove waste matters (urine) and at an-
other the generative elementa.

The vertebrate excretory ayatem may be divided into three
parta, which result from the differentiation of the primitive kid-
ney which hum been effected during the alow and gradual eve-
lution of vertebrate forma:

1. The head-kidney (pnmephrM).

i. The Wolffian body (memmephroa).

8. The kidney proper, or inetatufpAroa.

But in thia inatance, as in others to some of whidi alluaion
has already been made, these three parta are not funotiooal at
the same time. Hie pronephros arises from the anterior part
of the segmental duct, pronephrio duot, duct of primitive kid-
ney, and archinephric duot, and in the fowl is apparent on the
third day; but the pronephros ia beet developed in the ichthy-

Fio. lis.— DUmmi lllnttnitiiig developmeiit of nmnaphro* In th* fowl (Haddim).
ao, aorU; b. e, body-cavity; tp, •plbuwt with It* epitrlcblal (fl«ttcn«d) layer; Ay,
hypoblaat: m. «, meaoblaatie aonute; ii. e, neural canal; neh, notoebord; p. <., pro-
nepbric tnbnle; m, 10018110, and ip, ephuichnlo niMob^wt.

jvumm

tmtmmun iiir

among which ia
ring foetal life,
hiatohm i>f the
the blutid itself
ture and ohangea
plied to the blood
lent of the r«apir-

nTAL ■TtTHM.

1% the anatomical
notion on the uuo
nprehended; uor,
le aame part may
(urine) and at an-

divided into three
the primitive kid-
and gradual eve-

of which allusion
not funotional at
the anterior part
. of primitive kid-
A apparent on the
ped in the ichthy-

TIIR DRVRLOPMKNT OP THB EMBUYO ITSELF. 118

opeida (fliheii and amphibians). A vascular process from the
|ierit(meum (glomerulus) projects into a dilated section of the
bcxiy cavity, which is in part separated from the rest of this
cavity (ccelom). ThiN process, together with the segmental duct,
now coilral, and certain short tubes developed from the original
duct, make up tho pronephros. The segmental duct opens at
length into tho cloiioii.

The metonephroa (Wolflian body), though largely developed
in all vertebrates during foittal life, is not a persistent excretory
organ of adult life.

In the fowl recent investigation has shown that the Wolffian
(segmental) tubes originate from outgrowths ef the Wolffian

I In the fowl (Uaddon).
lit (flattened) layer; Ay,
^, notochord; p. t., pro-

rio. 1«1.

i- lu. ISO,— Rndlmentarr prlmltlre kidnejr of embrjronte dof. The poaterlor portion of
the hoij uf the embryo t« leen from the ventral side, covered by the Inteetinal
layer or the yelk-*ac, which hae been torn away, and thrown biick In front in
Older to ihow the primitive kidney dncta with the primitive kidney tubet (a). A,
primitive vertebne; e, donal medulla; d, paaiage into the pelvic Inteetinal cavity.
(Haeekel, after Blicboff.)

Pio. ISI.— Primitive kidney of a hnman embryo, u, the urine-tnbes of tho primitive
kidney; w, Wolfllan dnct; to', npper end of the latter dforMgnl'i hydatid); m,
Mailerlan ductim', npper end of the latter (Faitoplan hydatid); ff, hermaphrwdita
gland. (After Kobelt")

duct and also from an intermediate cell-mass, from which latter
the Malpighian bodies take rise. The tubes, at first not con*
8

K: j ^t/.ij. ' feSMiJtfa J Vf-y.t'JiKit '!' - '

114

COMPARATIVE PHYSIOLOGY.

nected with the duct, finaUy join it. This organ is oontinuous
with the pronephros ; in fact, all three (pronephros, mt»one-
phros, and metanephros) may be regarded as largely oontinuar
tions one of another. ,1 *. *

The metanephros, or kidney proper, arises from mesoblast at
the posterior part of the Wolffian body. The ureter originates

Fia M8-8ecH«m of the tatennedlate cell-mM* of fourth d«y (^^Mjo'JSiLPtJfTi
atSi wSdewrt 1 X 180 m. metentery; L, ■omatoplenre; a', wwtlon ™ the
SJiSJinll enlSeiinm from the d^of Mtlller U formeS by tavoluiton; a, thlA-
SS ^rtlSi^SfgiSrepltheHu^^^^^ primitive ovj, Cwd o «»

Mm; iETmodifledmesoblMt which wlU form the etrama of the ovwy, WK,
WoOBan body; y, WoMBan duct.

first from the hinder portion of the Wolffian duci In the fowl
the kidney tubules bud out from the ureter as rounded eleva-
tions. The ureter loses its connection with the Wolffian duct
and opens independently into the cloaca.

The following account will apply espedally to the higher
vertebrates:

The segmental (arohinephric) duct is divided horaontally
into a dorsal or Wolffian (mesonephric) duct and a ventral or
MtUlerian duct. The Wolffian duct, as we have seen, develops
into both ureter and kidney proper.

To carry the subject somewhat further back, the epithelium

THE DEVELOPMENT OP THE EMBRYO ITSELF. 116

[an is oontinaouiii
aephros, meaone-
iargely oontinuar

rom mecoblast at
ureter originates

•y (Foster and Balfoor,
enre; a', pwtton ^ the
by iBvoiuuon; a, tnwk-
ImltWeova, Cando.we
ima of the ovary; WK,

duct In the fowl

as rounded eleva-

i the Wolffian duct

ally to the higher

vided horizontally
ot and a ventral or
lave seen, develops

aok, the epithelium

lining the ooelom at one region becomes differentiated into col-
umnar cells (germinal epitheUum) which by involution into
the underlying mesoblast forms a tubule extending from before
backward and in close relation with the Wolffian duct, thus
forming the Miillerian duct by the process of cleavage and
separation referred to previously.

Fig. 1».— Diacrammatic repreaentatlon of the genital oima of a human em^o m-
▼iomi to anual dirtinctfon (Allen Thontton}. W, Wolfflan body ; ae, ff »»»• e«2
m.M«leTlan duct; w, Wolfflan duct; wy, urogenital alnns: en. c"^ »' R™".'
i, intestine; el, cloaca; to, part from which the acrotnm or ]»W» matow we derel-
oped; ot, origin of the orary or teaticle reapectiveW; x, part of the wolfflan body
derelived ItSer Into the eonl vaiculaei: ^ ureter; 4, bladder; 5, nrachua.

The future of the Mfillerian and Wolfflan ducts varies ac-
cording to the sex of the embryo.

In the male the Wolffian duct persists as the vas deferens ;
in the female it remains as a rudiment in the region near the
ovary (hydatid of Morgagni). In the female the MWerian duct
becomes the oviduct and related parts (uterus and vagina) ; in
the male it atrophies. One, usually the right, also atrophies in
female birds. The smus pocularis of the prostate is the remnant
in the male of the fused tubes.

The various forms of the generative apparatus derived from
the Mfillerian ducts, as determined by diflierent degrees of fu-

116

COMPARATIVE PHT8I0L0 Y.

„ „-jnoftlieiiiaimn8ltontypeofiii^eBeMalo«Mui(«tt«5^

Fio. 194.-pUe«n<

vm\», cat ihort; «, caput epididymis; a, mi
Morncnl. the penlatent anterior end <rf toe
ends^ whichTonn the nteroi "•"••""nf

ibemacnlam; 1, recinin; m, hydaUd of

corpus

ididymla; a, saMinacniam; t, reciAm, m, ujru»jiu «.
mim end df tSe MUlerian dnct, the conjoint poaterlor
_ erai nuMculinnR; or, pioetate gland; #, icrotum; ip,
rtponirfomm wethne; t, teaUe (tertlclei In Jtte pUee of Its «['P2*' [J™f;
tlim -rte dotted line Indicates the d rectlon in which the testU and epidldymia
iCgeplS^Tthel" descent from the abdomen hito the scrotum: rd. ;]»**"•
enS^ ws aberrans; w, vasicuta semlnalto; W, remnants ofWoIfltan body (the
SSin oi oMdisw parahldywls of Waldeyer); h, 4. 6. as in Fig. 1».

sion, etc., of parts, may be learned 'rom the acoompanying
fliniree.

Fia U6-Diagi«m of the mammalian type of female •«»«».«5W2»i*'^5SS%
"^•JSz-AJHStu^ I. «n« flrniH) indioste fnnetional orsans in the other. 0, gland m

-•lSSdoti3irnl.fnrSS»«S^nM^^

Mrffeft^o^rantnbe; fl.J.irnd >«««SSi<2If15K^iSt «^m^
/Hiymen; I, rectum; /, labium; •».«?* '*»<»P'" *"~ <?SJ?f*iP^*^^

THE DBVKLOPMBNT OF THE EMBRYO ITSELF. 117

u (after (^lulii). Com-
ep, corpon caTernoM
racism; m, hydatid of
, the conjoint poeterior
gland; «, icnitnm; ip,
) of itR orioinal fonna-
i teetia ana epididrmia
Krotam: vd, raa defer-
I of WonBan body (the
in Fig. l«t.

le aooompanying

al onana (after Qnaln).
ntheotfaar. C.glandof
ridia; dO, remains of the
; /, abdominal r —

Iff to Qie nibetnacnlnm>;
flnet. orlCttleriandnet)
nm; $e, vaacnlar bnib or
satteiea lemaina of Wol-
oUBandoct; 8. meter; 4,
■ant of (talk of allantoia.

In both sezM the mort poBterior portiun of the WolfBaa duct
gives rim to the metanephrot, or what becomes the permaoent
kidn«y and ureter ; in the male also to the vaa deferens, testicle,
vas aberrans, and seminal vesicle.

The ovary has a similar origin to the testicle ; the germinal
epithelium furnishing the cells, which are tnmsformed into
Qraaflan follides, ova, etc., and the mesoblast the stroma in
which those structures are imbedded.

In the female the parovarium remains as the representative
of the atrophied Wolffian body and duct

The bladder and urachus are both remnants of the formerly
extensive allantois. The final forms of the genito-urinary or-
gans arise by differentiation, fusion, and atrophy : thus, the
cloaca or common cavity of the genito-urinary ducts is divided

Fia.UB.

Via.tB,

^^'

Fio. IM.

Fia.U0.

Fiei. U6 to !».— Diagiama iUnatnting the evdntion of the poateilar pasaagea (aflw

i^M^m and stiriug).
Fig. Ill— Allantoia eonttnnooa with reetom.
Fio. 117.— Oloaea formed.
Flo. UB.— Early eonditioa in male, befon the cloenre of the folda of. the groove on

the poeterior aide of the penia.
Fio. ]».— Bariy female oondltion.
A, commencemaBt of pnetodMim; A IL, allantoia; B, btaddor: C, penia; Ct, elonea;

M, Xttlerlan dnet; J{j«etam; r, urethra; 8, veatibole; aU, nrogenital anma; F,

vaa def erena in Fig. US, vagina in Fig. M9.

by a septum (the perineum externally) into a genito-urinary
and an intestinal (anal) part ; the penis in the male and the
ooneqKmding clitoris in the female appear in the region of the
cloaca, as outgrowths which are followed by extension of folds
of integument that become the scrotum in the one sex fnd the
labia in the other.

The urethra arises as a groove in the under suif aoe of fbo

^■Mtfi i wiMw.UHlWKiwii'iiuiiMh i B u i < m < ii» ^m. ji m i"mMmxm ■

118

COMPARATIVE PHYSIOLOGY.

peniB, which beoomeB a canal. The original opening of the
urethra was at the base of the penis.

In certain cases development of these parts is arrested at
various stages, from which result abnormalities frequently re-
quiring interference by the surgeon.

The accounts of the previous chapters do not complete the
history of development Certain of the renuuning subjects
that are of special interest, from a physiological point of view,
will be referred to again ; and in the mean time we shall con-
sider rather briefly some of the phjrsiological problems of this
subject to which scant reference has as yet been made. Though
the physiology of reproduction is introduced here, so that ties
of natural connection may not be severed, it may very well be
omitted by the student who is dealing with embryology for the

Fio. lao.— Varioni forms of ■ummaUan at«ri. A. Omlthochyiichiu. B. Did«lpliy»
doniaera. C. Phalangtstavnlpiiuk. D. Double atenu and TMriiim;hniiiMi uooift-
hr. B. Lepua cnnl'mlDa (mbblt). ntema dnplaz. F. Vtenis blconto. O. Utenu
blpartitas. H.- Utenu liinplex (bmnu). a, una; el, cloaca; o.<l. ovidoet: o. t,
OS tlncn (oa uteri); m, ovary; r. Tectum; «, Taginal aeptom; n. ft, nrinaiT bladder;
' «r, meter; ur.o, orUlce of same; u. t, uroK«nttal alnna; ut, utema; «, vagina; «. e,
vaginal cacum (Haddon).

first time, and in any case should be read again after the other
functions of the body have been studied.

TBB PBraOIiOOIOAXi ASPBOTB OF SBVaLOmBHT.

According to that law of rhythm which, as we have seen,
prevails throughout the world of animated nature, there are
periods of growth and progress, of quietude and arrest of devel-

^_.-

THE DEVELOPMENT OF THE EMBRYO ITSELF. 119

opening of the

is arrested at
B frequently re*

ot complete the
uning subjects
1 point of view,
le we shall con-
problems of this
made. Though
lere, so that ties
laj yery well be
>ryolog7 for the

mchm. B. Dldelphj*

<ngfam:
• bicor

• blcorato. O. Uteru
ca; o. <f, oviduct; o. t,
; N. b, vttoatj bladder;
Btenw; », vagina; «. e.

i after the other

IS we have seen,
lature, there are
1 arrest of devel-

opment ; and in vertebrates one of the most pronounced epochs
—in fact, the most marked of all— is that by which the young
organism, through a series of rapid stages, attains to sexual ma-
turity.

While the growth and development of the generative organs
share to the greatest degree in this progress, other parts of the
body and the entire being participate.

So great is the change that it is common to indicate, in the
case of the human subject, the developed organism by a new
name— the " boy " becomes the " man," the " girl " the " woman."
Relatively this is by far the most rapid and general of all the
transformations the organism undergoes during its extra-uter-
ine life. In this the entire body takes part, but very unequally.
The increase in stature is not proportionate to the increase in
weight, and the latter is not so great as the change in form.
The modifications of the organism are localized and yet a£Feot
the whole being. The outlines become more rounded ; the pel-
vis in females alters in diape ; not only do the generative organs
themselYes rapidly imdeigo increased development, but certain
related glands (mamnue) participate ; hair appears in certain
regions of the body ; the larynx, especially in the male, under-
goes enlargement and changes in the relative size of parts^ re-
sulting in an alteration of voice (breaking of the voice), etc.—
all in conformity with that excess of nutritive energy which
marks this biological epoch.

Correlated with these physical changes are others belonging
to the intellectual and mond (psychic) nature equally impor-
tant, and, accordingly, the future being depends largely on the
full and unwarped developments of these few years.

Sexual maturity, or the capacity to furnish ripe sexual ele-
ments (cells), is ftom the biological standpoint the most impor-
tant result of the onset of that period termed, as r^iards the
human species, puberty.

The age at which this epoch is reached varies with race,
sex, climate, and the moral influences which envelop the indi-
vidual. In temperate regions and with European races pubefty
is reached at from about the thirteenth to the eighteenth year
in the female, and rather later in the male, in whom develop-
ment generally is somewhat slower. Changes analogous to the
above occur in all vertebrat(». It is at this period that differ-
ences of form, voice, disposition, and other physical and psychic
chaxaoteristios first become pronounced.

aaeisESOTirassis

120

COMPARATIVE PHYSIOLOGY.

I-

As a matter of fact, the pig, sheep, goat, cat, dog, and certain
other animals may conceive when less than one year old ; and the
oow and the mare when under two years.

At such periods these animals are not of course mature and
should not be bred.

OVUXiATIOM.

In all vertebrates, at periods recurring with great regularity,
the generative organs of the female manifest unusual activity.
This is oharaoterised by increased vascularity of the ovary and
adjacent parts ; with other changes dependent on this, and that
heightened nerve influence which, in the vertebrate, seems to be
inseparable from all important functional changes. Ovulation
is the maturation and discharge of ova from the Graafian f olli-
oles. The latter, reaching the exterior aone of the ovary, be-
coming distended and thinned, burst externally and thiis free
the ovum. The follicles being very vascular at this period,
blood escapes, owing to this rupture, into the emptied capsule
and clots ; and as a result of organization and
subsequent degeneration undergoes a certain
series of changes dependent on the condition
of the ovary and related organs, which varies
according as the ovum has been fertilized or
not When fertilisation occiun the Graafian
follicle undergoes changes of a more marked
and lasting character, becoming a true corpus
luteum of pregnancy.

The number of Graafian follicles that ma-
ture and the number of ripe ova that escape at
about the same period varies, of course, with
the species and the individual, and is not al-
ways the same in the latter.

In species that usually bear several young
at a birth a corresponding number of ova must
^^^ be ripened and fertilized at about the same
FicF. in.-OTar7 of ^^^ > while the reverse holds for those that
Wtrn«.?ho;;^ usually give birth to but one.
tw TMiom (Ugea The ovum in the fowl is fertilized in the
of estmaion or _i. « i«_ .a ^ . .» .

ova. (Cbwiveu.) upper part of tne oviduct; m the mammal

mostly in this region also, as is shown hy the
site of the embryos in those groups of animals with a two-
homed uterus, and the occasional occurrence of tubal pregnao*

, .,^..,-.^. . . M|| i|i|

THE DEVELOPMENT OP THE EMBRYO ITSELF. 131

dog, and certain
^ear old ; and the

tune mature and

great regularity,
unusual activity,
of the ovary and
on this, and that
brate, seems to be
nges. Ovulation
\ie Graafian folli-
of the ovary, be-
lly and thus free
tr at this period,
) emptied capsule
organization and
lergoes a certain
on the condition
ans, which varies
been fertilized or
sun the Graafian
f a more marked
ling a true eorpua

follicles that ma-
ova that escape at
s, of course, with
lal, and is not al-

ear several young
imber of ova must
k about the same
Ids for those that
I.

i fertilized in the
; in the mammal
us is shown by the
bnals with a two-
I of tubal pregnao-

cy in woman. But this is not, in the human subject at least,
invariably the site of impregnation. After the ovum has been
set free, as above describcNl, it is conveyed into the oviduct
(Fallopian tube), though exactly how is still a matter of dis-
pute : some holding that the current produced by the action
of the ciliated cells of the Fallopian tube suffices; others that
the ovum is grasped by the fimbriated extremity of the tube as
part of a coH>rdinated act. It is likely, as in so many other
instances, that both views are correct but partial; that is to
say, both these methods are employ ed. The columnar ciliated
cells, lining the oviduct, act so as to produce a current in the
direction of the uterus, thus assisting the ovum in its passage
toward its final resting place.

(BttmilL— As a part of the general activity occurring at this
time, the uterus manifests certain changes, ohiefiy in its inter-
nal mucous lining, in which thickening and increased vascular-

Fie. US.— Diagram of the hniium ntema
jMt before meiMtnution. Tbe eluded
pottion lepreeeate the macoaa mem-
brMie'(HMt and Oarbonr, afUir J.
Williams).

Vio. in.~Utenw after menetmatioii haa
Jnat eeaaed. The easlty of the bodjr
of the uteroi is rappoeed to have
been deprived of mocona membiaae
(J. Wllllama).

ity ai« prominent Aflowof blood from the uterus in the form
of a gentle oonng follows; and as the superficial parts of the
mucous lining of the uterus undergo softening and fatly d^;en-

122

COMPARATIVE PHYSIOLOGY.

eration, they are thrown off and renewed at these periods {eata-
taenia, menses, etc.), provided pregnancy does not take place.
In mammals below man, in their natural state, pregnancy does
almost invariably take place at such times, hence this exalted
activity of the mucous coat of the uterus. In preparation for the
reception and nutrition of the ovum, is not often in vain. In
the human subject the menses appear monthly; pregnancy may
or may not occur, and consequently there may be waste of na-
ture's forces; though there is a certain amount of evidence that
menstruation does not wholly represent a loss; but that it is
largely of that character among a certain class of women is
only too evident. As can be readily understood, the catamenial
flow may take place prior to, during, or after the rupture of the
egg-capsule.

As the uterus is well supplied with glands, during this
period of increased functional activity of its lining membrane,
mucus in considerable excess over the usual quantify is dis-
charged ; and this phase of activity is continued for a time should
pregnancy occur.

All the parts of the generative organs are supplied with
muscular tissue, and with nerves as well as blood-vossels, so
that it is possible to understand how, by the influence of nerve-
oenters, the various events of ovulation, menstruation, and
those that follow when pregnancy takes place, form a related
series, very regular in their succession, though little prominent
la the consciousness of the individual animal when normal.

In all animals, without exception, the disturbance of the
generative organs during the rutting season (oestrum) is accom-
panied by unusual excitement and special alterations in the
temper and disposition, while ,it may perhaps be said that the
whole organism is correspondingly affected.

The frequency of the season of heat or rutting is variable, as
also its duration. In most of the domestic animaki it lasts but a
few days; though in the bitch it may be prolonged for a
month.

It is not common for conception to occur in the human sub-
ject while the young one is being suckled, and the same remark
applies to the domestic animals, though leas so, and with con-
siderable variation for different species.

Naturally, the periods of oestrum will depend considerably
on the occurrence of impregnation and the duration of gesta-
tion. It is usual for the mare to be in season in spring and fall,

THE DEVKLOPMENT OF THE EMBRYO ITSELF. 128

ese periods (eata-
m not take plaoe.
i, pregnancy does
enoe this exalted
eparation for the
ften in vain. In
pregnancy may
y be waste of na-
of evidence that
m; but that it in
n of women is

d, the oatamenial
he rupture of the

nds, during this

ining meml»mne,

quantity is dis-

I for a time should

re supplied with

blood-TOBsels, so

fluence of nenre-

lenstruation, and

e, form a related
I little prominent
nrhen normal,
sturbanoe of the
Bstrum) is acoom-
ilterations in the

be said that the

ing is variable, as
malsitlastsbuta
prolonged for a

I the human sub-
the same remark
BO, and with con-
end considerably
duration of gesta-
a spring and fall,

but, of course, if impregnated in the spring, there will be no au-
tumn oestrum on account of the prolonged period of gestation
in this instance; and, similarly, in the case of the cow and other
animals.

It is important to recognize that rutting is only the evidence
of the maturation of the Graafian follicle withiit the ovary and
of correlated changes.

In a state of nature— i. e., in the case of wild animals— the
male experiences a period of sexual excitement corresponding
with an increased activity of the sexual organs and at periods
answering to the rutting season of the female. In some species
the testes descend into the scrotum only at this season. This
may be observed in the rabbit But in our domestic animals, as
a class, the male, though capable of copulation at all times, is ex-
cited only by the presence of a female in season. It is only at
such periods that the approach of the male is permitted by the
opposite sex.

THB MUTHi ' i ' iO lf OF TBB OTUM (OdOnUI).

This will be best understood if it be remembered that the
ovum is a cell, undifferentiated in most directions, and thus a
sort of amceboid organism. In the fowl it is known that the
cells of the primitive germ devour, amoeba-like, the yelk-cells,
while in the w^ftmmAlian oviduct the ovum is surrounded by
abundance of proteid, which is doubtless utilized in a somewhat
similar fashion, as also in the uterus itself, until the embryonic
membranes have formed. To speak of the ovum being nour-
ished by diffusion, and especially by osmosis, is an unnecessary
assumption, and, as we believe, at variance with fundamental
principles; for we doubt much whether any vital prooeeti is
one of pure osmosis. As soon as the yelk-sac and allantois
have been formed, nutriment is derived in great part through
the vessel-walls, which, it will be remembered, are differenti-
ated from the cells of the mesoblast, and, it may well be as-
sumed, have not at this early stage entirely lost their amoeboid
character. The blood-vessels certainly have a respiiratory func-
tion, and BuflBce till the more complicated villi are formed.
The latter are in the main similar in structure to the villi of the
alimentary tract, and are adapted to being surrounded by sim-
ilar structures of maternal origin. Both the maternal crypts
and the foetal villi are, though complementary in shape, all but

■ '.MSHWWK'W^'.'

124

(X)MPARAT1VB PHYSIOLOOY.

identicid in minuto ntruoture in moit inntanoM. In Moh oaM
the blood-veaelB are covered miperfloially by oelii which we
can not help thinking are eeeential in nutrition. The villi are
both nutritive and respiratory. It in no more diffloult to under-
stand their function than that of the celli of the endoderm of a
polyp, or the epithelial coverings of lungs or gills.

Experiment proves thnt iLure is a respiratory interchange
of gases between the maternal and foetal blood which nowhere
mingle physically. The same law holds in the respiration of
the foetus as in the mammals. Oxygen passes to the region
where there is least of it, and likewise carbonic anhydride. If
the mother be asphyxiated so is the foetus, and indeed more
rapidly than if its own umbilical vessels be tied, for the mater-
nal blood in the first instance abstracts the oxygen from that
of the foetus when the tension of this gas becomes lower in the
maternal than in the foetal blood; the usual course of affairs
is reversed, and the mother satisfies the oxygen hunger of her
own blood and tissues by withdrawing that which she recently
supplied to the foetus. It will be seen, then, that the embryo is
from the first a panudte. This explains that exhaustion which
pregnancy, and especially a series of gestations, entails. True,
nature usually for the tinra meets the demand by an excess of
nutritive energy : hence many animals are never so vigorous in
appearance as when in this condition; often, however, to be fol-
lowed by corresponding emaciation and senescence. The full
and frequent respirations, the bounding pulse, are succeeded by
reverse conditions ; action and reaction are alike present in the
animate and inaninuito worlds. Moreover, it falls to the parent
to eliminate not only the waste of its own organism but that of
the foBtus; and not infrequently in the human subject the over-
wrought excretory organs, especially the kidneys, fail, entailing
disastrous consequences.

The digestive functions of the embryo are naturally inact-
ive, the blood being supplied with all its needful constituents
through the placenta by a much shorter process ; indeed, the
placental nutritive functions, so far as the foetus is concerned,
may be compared with the removal of already digested mar
terial from the alimentary canal, though of course only in a
general way. During foetal life the digestive glands are
developing, and at the time of birth all the digestive juices
axe secreted in an efficient condition, though only relatively
so, necessitating a special liquid food (milk) in a form in which

i»iaii 'iw> ii < * .' i jHj ii»'i'i

> " iWHwW i| l t» | ||» » i l'

THE DEVBIiOPMBNT OF THK EMBRYO IT8BLF. J^S

ea. In each oa«e
ircelli which w«
o. The villi are
iiffloitlt to under-
le «ndodenn of a
Uk.

lory interchange
~ which nowhere
he respiration of
w« to the region
io anhydride. If
uid indeed more
)d, for the mater-
izygen from that
mee low«r in the
course of affair*
en hunger of her
hioh she recently
ut the embryo is
izhaustion which
s, entails. True,
by an excess of
rer so vigorous in
lowever, to be fol-
icenoe. The full
, are succeeded by
ike present in the
falls to the parent
'anism but that of
I subject the over-
eys, fail, entailing

9 naturally inact-
idful constituents
loess ; indeed, the
itus is concerned,
ady digested mar
coarse only in a
istive glands are
B digestive juices
\i only relatively
a form in which

all the constituents of a normal diet are provided, easy of diges-
tion, i

Bile, inspissated and mixed with the dead and oastoiT epi-
thelium of the alimentary tract, is abundant in the intestine at
birth ; but bile is to be regarded perhaps rather in the light of
an excretion than as a digestive fluid. The sldn and kidneyti,
though not funotionless, are rendered unnecessary in great part
by the fact that waste can be and is withdrawn by the placenta,
which proves to be a nutritive, respiratory, and excretory organ ;
it is in itself a sort of abstract and brief chronicle of the whole
physiological story of foetal life.

All the foetal organs, especially the muscles, abound in an
animal starch (glycogen), which in some way, not well under-
stood, forms a reserve fimd of nutritive energy which is pretty
well used up in the earlier months of pregnancy. We may sup-
pose that the amoeboid cells— all the undifferentiated cells of
the body— feed ou it in primitive fashion; and it will not be
forgotten that the older the cells become, the more do they de-
part from the simpler habits of their earlier, cruder existence;
htmce the disappearance of this substance in the later months of
foetal Ufe.

In one respect the foetus closely resembles the adult : it draws
the pabulum for all its various tissues from blood which it-
self may, perhaps, be regarded as the first completed tissue. We
are, accordingly, led to inquire how this river of life is distrib-
uted; in a word, into the nature of the foetal circulation.

PMal OiMllktiOB.— The blood leaves the placenta by the
umbilical vein, reaches the inferior vena cava, either directly
(by theduohM venomtg), or, after first passing to the liver (by
the veme advehentea, and returning by the vetue r«vehentea\
and proceeds, mingled with the blood returning from the lower
extremities, to the right auride. This blood, though far from
being as arterial in character as the blood after birth, is the best
that reaches the heart or any part of the organism. After arriv-
ing at the right auricle,being dammed back by the Eustachian
valve, it avoids the right ventricle, and shoots on into the left
auricle, passing thence into the left ventricle, from which it is
sent into the aorta, anid is then carried by the great trunks of this
arch to the head and upper extremities. The blood returning
from these porta passes into the right auricle, then to the corre-
sponding ventricle, and thence into the pulmonary artery; but,
finding the branches of this vessel unopened, it takes the line of

irvrvKgO^vt?--*^': tW" ■w'sr®™

v-rrt f wvRjirtJaifipsBW ■'"

iWiMNary Art. ^

Formmm (halt.

lAutMAUm Valrt.
JUfht Awtie. - VmU. CJpmn^n^.

N^xMe Vtim.

Brtmehm of Uu
UmbHieal Vtin,
(othtLimr.

-^■^•i^umonarg Art.
•• Ltfi AurMt.
..Lfft Auri».-Vmt.
Ojmting.

THE DBVKLOPMENT OP THE KMUHYO ITSELF. 137

IfMwt rMiiUinoe through the duetu» arterioauit into thn aortio
uroh beyond Uie point where ita great bnuichea emerge. It will
be leen that the blood going to the head and upper part* of the
body ii greatly more yaluableaa nutritive pabulum thait the reet,
eapecially in the quantity of oxygen it contains ; that the blood
of the foBtut, at beat, is relatively ill-vupplied with its vital even-
tial; and ai a reault we And the upper (anterior in quadrupedn)
parta of the fcetua beat developed, and a decided reaemblance be-
tween the mammalian fcetua functionally and the adult forma uf
reptilea and kindred groupa of lower vertebratea. But thia con-
dition ia well enough adapted to the general enda to be attained
at thia period— the nouriahment of atructurea on the way to a
higher path of progreaa.

Aa embryonic maturity ia being reached, preparation ia made
for a new form of eziatenoe ; ao it is found that the Euatacbian
valve ia leaa prominent and the foramen ovale amaller.

€ht$ FtfMOtMa

PBRIOIM OP OHMPATION.

Aa a rule, the ahorter the period of geatation the more nu>
meroua the offapring at a aingle birth and the greater the num-
ber produced within the lifetime of the animal relatively to it«
duration. Thua, on account of the number of young produced
by the rabbit at one birth, the ahort period ot geatation, and the
frequency with which impregnation octrura, there ia a much
larger number of progeny, ahort as ia the animal's life uaually,
than in the case of the cow, for example, that may bear young
for a much longer period.

The following table givea approximately the duration of the
period of geatation of aome of our domestic animals and their
wild allies :

Ouinea-pig (cavy) 8 weeks.

Babbit, squirrel, rat. 4 "

Ferret 6 "

Oat 8 "

Dofi, fox

lion ■*

Sow 4

Sheep, goat 5

Bear 7

Reindeer 8

Cow, buffalo 10

monihti.

[Flint).

f!('IS?W!W09HWS''<™W™fiSII'lftf''

128

COMPARATIVE PHYSIOLOGY.

Mare, ass, zebra 11 months.

Camel 12 "

Giraffe U "

Elephant 22 to 25"

The period of gestation in the human subject is nine months;
in the monkeys and apes somewhat less. The incubation pe-
riod of certain of our domestic birds and related species is about
as follows :

Canary 14 days.

Pigeon 18 "

Hen 21 "

Duck, goose, pea-hen 28 "

Guinea-hen 26 "

Turkey 28 '•

It is interesting to note that the smaller varieties of fowls,
hatch out sooner than the larger ; and that the period of incu-
bation of all of the above varies with the weather, the steadi-
ness of the incubating bird, the date on which the eggs selected
were laid, etc. With very recent eggs, an attentive sitter, and
warm weather, the incubation period is shortened.

PARTUBinON.

All the efforts that have hitherto been made to determine
the exact cause of the result of that series of events which make
up parturition have failed. This has probably been owing to
an attempt at too simple a solution. The foetus lies surroimded
(protected) by fluid contained in the amniotic sac. For its ex-
pulsion there is required, on the one hand, a dilatation of the
uterine opening {oa uteri), and, on the other, an expulsive force.
The latter is furnished by the contractions of the uterus itself,
aided by the simultaneous action of the abdominal muscles.
Throughout the greater part of gestation the uterus experiences
somewhat rhythmical contractions, feeble as compared with the
final ones which lead to expulsion of the foetus, but to be re-
garded as of the same character. With the growth and func-
tional development of other organs, the placenta becomes of
less consequence, and a fatty degeneration sets iii, most marked
at the periphery, usually where it is thinnest and of least use.
It does not seem rational to believe that the onset of labor is
referable to any one cause, as has been so often taught ; but
rather that it is the final issue to a series of processes long ex-

irtill«.teHllkiJn.!y^m>.^i«Mt^].t

THE DEVELOPMENT OP THE EMBRYO ITSELF. 129

. . 11 months.
..12 "
..14 "
22 to 25 "
ct is nine months;
he incubation pe-
ed species is about

14 days.

....18 "

...21 "

... 28 "
...26 "

28 '•

r varieties of fowls.
;he period of incu-
reather, the steadi-
h the eggs selected
ttentive sitter, and
xjned.

made to determine
events which make
ibly been owing to
stus lies surrounded
ic sac. For its ex-
, a dilatation of the
an expulsive force,
of the uterus itself,
ibdominal muscles.
i uterus experiences
I compared with the
foetus, but to be re-
e growth andfunc-
ilacenta becomes of
ets in, most mark^
est and of least use.
he onset of labor is
> often taught ; but
f processes long ex-

isting and gradually, though at last rapidly, reaching that
climax which seems like a vital storm. The law of rhythm
affects the nervous system as others, and upon this depends
the direction and co-ordination of those many activities which
make up parturition. Wo have seen that throughout the whole
of foetal life changes in one part are accompanied by correspond-
ing changes in others ; and in the final chapter of this history
it is not to be expected that this connection should be severed,
though it is not at present possible to give the evolution of this
process with any more than a general approach to probable
correctness.

OBANCHBS nr TBE OIRODLA^ON AFTER BIRTB.

When the new-bom mammal takes the first breath, effected
by the harmonious action of the respiratory muscles, excited to
action by stimuli reaching them from the nerve-center (or
centers) which preside over respiration, owing to its being
roused into action by the lack of its accustomed supply of
oxygen, the hitherto solid lungs are expanded ; the pulmonary
vessels are rendered permeable, hence the blood now takes the
path of least resistance along them, as it formerly did through
the ductus arterioaua. The latter, from lack of use, atrophies
in most instances. The blood, returning to the left auricle of
the heart from the lungs in increased volume, so raises the
pressure in this chamber that the stream that formerly fiowed
through the foramen ovale from the right auricle is opposed
by a force equal to its own, if not greater, and hence passes by
on easier route into the right ventricle. The fold that tends to
close the foramen ovale grows gradually over the latter, so thai
it usually ceases to exist in a few days after birth.

At birth, ligature of the umbilicsJ cord cuts off the placental
circulation ; hence the duetu8 venosua atrophies and becomes a
mere ligament

The placenta, being now a foreign body in the uterus, is ex-
pelled, and this organ, by the contractions of its walls, closes
the ruptured and gaping vessels, thus providing against heemor-
rhage.

ooinra.

In all the higher vertebrates congress of the sexes is essential
to bring the male sexual product into contact with the ovum.
«

130

COMPARATIVE PHYSIOLOGY.

t i

}

Erection of the penis results from the conveyanoe of an ex-
cess of blood to the organ, owing to dilatation of its arteries,
and the retention of this blood within its caverns.

Fio. 185.— Section of eraetUe titcue (Cadlat). <i, trabeenl* of eonneettTe tlMne. with
elMtic flben, and bandle* of plain mnwular tlMne (e); b. venoas qwce* (Sduuer).

The str:'.c< ' - * the penis is peculiar, and, for the detailB of
the anatom; < il'> the male and female generative organs,
the student ik "•' ' .i-ad to works on this subject ; suffice it to
say that it consists of erectile tissue, the chief characteristic of
which is the opening of the capillaries into cavernous venous
spaces (gintiaes) from which the veinlets arise ; with such an
arrangement the circulation must be very slow— the inflow
being greatly in excess of the outflow — apart altogether from
the compressive action of certain muacles connected with the
organ. The manner and duration of the act of copulation in
the domestic animals varies witH the structure of the penis, the
animal's nervous excitability, etc. In the stallion the act is of
moderate duration, the penis long, and the glans penis highly
sensitive.

In the bull the penis is of a different shape. During erec-
tion it is believed that the S-shaped curve disappears, and that
the extremity of the organ enters the mouth of the utwus-itself.
Copulation is of very brief duration.

In the dog the penis is of very peculiar formation. Its an-

C--T-. aiiMMtlMMM

THB DEVELOPMENT OF THE EMBRYO ITSELF. 181

eyanoe of an ez-
ti of its arteries,

tenor part contaiiu a bone, while there are two erectile portions
independent of each other. During copulation the largest (pos-

ns.

■^<i«. .. tf

■ connective ttotne,wHh
iioiuqMM!ea(8cUUer).

for the details of
l^nerative organs,
>ject; sufBceitto
)f characteristic of
cavernous venous
ise ; with such an
slow— the inflow
rt altogether from
onnected with the
ct of copulation in
« of the penis, the
dlion the act is of
|rlans penis highly

pe. During erec-
aappears, and that
>fiheuterusitBelf.

brmation. Its an-

Fia. 186.— Section of parta of three Mminiferone tnbolea of the rat (Schifer). a, with
the ■pcrmatosoa leaet advanoed in development; h, more •dvaoced; t, containing
f ally developed apermatosoa. Between the tnbalea are aeen etmnda of interetitiai
cella, with blood-veaiela and iTmph-epacea.

tenor) erectile region is spasmodically (reflexly) grasped by the
sphincter cunni of the female, which is the analogu e of the
bulbo-cavemosus, isohio-cavemosus, and deep transverse mus-
cle of the perineeum, so that the penis can not be withdrawn
till the erection subsides, an advantage, considering that the
seminal vesicles are wanting in the dog, as well as Cowper's
glands. In the cat tribe there is also an incomplete penial
bone. The free portion of the organ is provided with rigid
papillffi capable of erection during copulation.

As previously expUuned, the spermatosoa originate in the
seminal tubes, from which they find their way to the seminal
vesicles or reoefrtacles for semen till required to be discharged.
The spermatocoa as they mature are forced on by fresh addi-
tions from behind and by the action of the ciliated cells of the
epididymis, together with the wave-like (peristaltic) action of
the vas deferens. Discharge of semen during coitus is effected
by more vigorous peristaltic action of the vas deferens and the
seminal <vericle8, followed by a similar rhjrthmical action of the
bulbo;cavemosus and ischio-cavemosus muscles, by which the
fluid is forcibly ejaculated.

•HiMiiUliiMMtsf

/-"

182

COMPARATIVE PHYSIOLOGY.

Via iir— OMienttvemvMia of the mate, iaolated and partly amned(C1i«nT^ 1,1,
JSri«^^l^la^tS>^^'f^^ •* tabe, exttnua face; 4. the wim. In-

SSfSe/ShiwuKSiS «« *«°!a*>«i V'«'''»«!Sj!f f^ 1;i2lfitaSSn^

ntMSsrV, a horn throW«iopeni 8. bodj of ntentf, nW» *««: .TlJlSSf J«5SS«
inTnMVix. with lu mncouYolaa; 11. cnl-de-tac of vagina with lU foWaof mncous

i of vnlva. '

h^v«n.mi«#>M<aMMisi'iii<" laJiH

■MMMiaMMiMa

THE DEVELOPMENT OP THE EMBRYO ITSELF. 188

a face; 4. the Mine, to;
vnni <• Intact born or
tace; 9, brotMl llgtment;
wlthlUfoWnrfmncoue
ia»fold,»Yert««eof lur-
1t»; IB, inferior commto-

Semen itself, though oompoMd essentially of spermatoMMt,
is mixed with the secretions of the vas deferens, of the seminal
vesicles, of Cowper's glands, and of the prostate. Chemically it
is neutral or alkaline in reaction, highly albuminous, and con-
tains nuclein, lecithin, cholesterin, fats, and salts.

The movements of the male cell, owing to the action of the
tail (cilium), sufBoe of themselves to convey them to the ovi*
ducts ; but there is little doubt that during or after sexual eon*
gress there is in the female, even in the human subject, at least

Fio. 1S8 — Uteiiu and ovarlea of the torn, aemi-dlMmmniatlc (after Dalton). o, ovary;
M, Fallopian tnbe; h, hem of Hifc oteruv; A, Dody of the ntenu; «, vagina.

in many oases, a r e t rograde peristalsis of the uterus and ovi-
ducts which would tend to overcome the results of the activity
of the dilated cells lining the oviduct. It is known that the
male cell can survive in the female organs of generation for
several days, a fact not diffleult to understand, from the method
of nutrition of the female cell (ovum) ; for we may suppose that
both elements ar« not a little alike, as th^ axe both slightly
modified amoeboid organisms.

Varvmu MMliaainii —Incidental reference has been made to
ihe directing influence of the nervous system over the events
of reproduction; especially their subordination one to another
to bring about the. general result These may now be consid-
ered in greater detail.

Most of the processes in which the uervous-«y8tem takes
part are of the nature of reflexes, or the result of the automa-
ticity (independent action) of the nerve-centers, increased by
some afferent (ingoing) impressions along a nerve-path. It is
not always possible to estimate the exact share each factor
takes, which must be highly variable. Certain experiments
have assisted in making the matter clear. It has been found

tmtim

184

COMPARATIVE PHYSIOLOGY.

that if, in a female dog, the spinal cord be divided when the
animal is still a puppy, menstruation and impregnation may
occur. If the same experiment be performed on a male dog,
erection of the penis and ejaculation of semen may be caused
by stimulation of the penis. As the section of the cord has left
the hinder part of the animal's body severed from the brain,
the creature is, of course, unconscious of anything happening
in all the parts below the section, of whatever nature. If the
nervi erigentes (from the lower part of the spinal cord) be
stimulated, the penis is erected; and if they be cut this act be-
comes impossible, either reflexly by experiment or otherwise.
Seminal emissions, it is well known, may occur during sleep,
and may be associated, either as mult or cause, with voluptu-
ous dreams. Putting all these facts together, it seems reaso,-
able to conclude that the lower part of the spinal cord contains
the nervous machinery requisite to initiate thone influences
(impulses) which, passing along the nerves to the generative
organs, exdte and regulate the processes which take place in
them. In these, vascular changes, as we have seen, always
play a prominent part.

Usually we can reoog^nize some afferent influence, either
from the brain (psychical), from the surface— at all events
from without that part of the nervous system (center) which
functions directly in the various sexual processes. It is com-
mon to speak of a number of sexual centers— as the erection
center, the ejaculatory center, etc — ^but we much doubt whether
there is such sharp division of physiological labor as these
terms imply, and they are liable to lead to misconception; ac-
cordingly, in the present state of our knowledge, we prefer to
speak of the sexual center, using even that term in a somewhat
broad sense.

The effects of stimulation of the sexual organs are not con-
fined to the parts themselves, but the ingoing impulses set up
radiating outgoing ones, which affect widely remote areas of
the body, as is evident, especially in the vascular changes; the
central current of nerve influence breaks up into many streams
as a result of the rapid and extensive rise of the outflowing
current, which b reaks over ordinary barriers, and takes paths
which are not properly its own. Bearing this fact in mind,
the chranical composition of semen, so rich in proteid and other
material yaluable from a nutritive point of view, and consid-
ering how the sexual appetites may engross the mind, it is not

iivided when the
npregnation may
1 on a male dog,
>n may be caused
the oord has left
1 from the brain,
thini; happening
tr nature. If the
9 spinal cord) be
le out this act be-
ent or otherwise,
cur during sleep,
ise, with voluptu-
r, it seems reasc.-
inal cord contains
thone influences
to the generative
hich take place in
iiave seen, always

influence, either
ice— at all events
)m (center) which
cesses. It is corn-
's—as the erection
iich doubt whether
oal labor aa these
misconception; ac-
edge, we prefer to
)nn in a somewhat

>igan8 are not oon-
ig impulses set up
ly remote areas of
cular changes; the
into many streams
of the outflowing
n, and takes paths
this fact in mind,
a proteid and other
f view, and consid-
I the mind, it is not

THE DEVELOPMENT OP THE EMBRYO ITSELF. 186

difHcult to understand that nothing so quicKly disorganizes the
whole man, physical, mental, and morai, as sexual excesses,
whether by the use of the organs in a natural way, or from
n^asturbation.

Nature has protected the lower animals by the strong bar-
rier of instinct, so that habitual sexual excess is with them an
impossibility, since the females do not permit of the approaches
of the male except during the rutting period, which occurs
only at stated, comparatively distant periods in most of the
higher m a mm als. When man keeps his sexual functions in
subjection to his higher nature, they likewise tend to advance
his whole development

Sviniliaiy.— Certain changes, commencing with the ripening
of ova, followed by their discharge and conveyance into the
uterus, accompanied by simultaneous and subsequent modifica-
tions of the uterine mucous membrane, constitute, when preg-
nancy occurs, an unbroken chain of biological events, though
usually described separately for the sake of convenience.
When impregnation does not result, there is a rotrogression in
the utems (menstruation) and a return to general quiescence
in all the reproductive organs.

Parturition is to be regarded as the climax of a variety of
rhythmic occurrences which have been gradually gathering
head for a long period. The changes which take place in the
placenta of a degenerative character fit it for being cast oB, and
may render this structure to some extent a foreign body before
it and the foetus are finally expelled, so that these changes may
constitute one of a number of exciting causes of the increased
uterine action of parturition. But it is important to regard the
whole of the occurrences of pr^^ancy as a connected series of
processes co-ordinated by the central nervous system so as to
accomplish one great end. the development of a new individual.

The nutrition of the ovum in its earliest stages is effected by
means in. harmony with its nature as an amoeboid organism ;
nutrition by the cells of blood-vessels is similar, while that by
villi may be compared to what takes place through.the agency of
similar structures in the alimentary canal of the adult mammal.

The circulation of the foetus puts it on a par physiologically
with the lower vertebrates. Before birth there is a gradual
though somewhat rapid preparation, resulting in changes which
speedily culminate after birth on the establishment of the per-
manent condition of the circulation of extra-uterine life.

186

COMPARATIVE PHYSIOLOGY.

The blood of the foetus (u in the adult) is the great store-
house of nutriment and the common receptacle of all waste
products ; these latter are in the main transferred to the moth-
er's blood indirectly in the placenta; in a similar way nutri-
ment is imported from the mother's blood to that of the foetus.
The placenta takes the place of digestivo, respiratory, and excre-
tory organs.

Coitus is essential to bring the male and female elements
together in the higher vertebrates. The erection of the penis is
owing to vascular changes taking place in an organ composed
of erectile tissue ; ejaculation of semen is the result of the
peristaltic action of the various parts of the sexual tract, aided
by rhythmical action of certain striped muscles. The sperma-
toEoa, which are unicellular, flagellated (ciliated) cells, make up
the essential part of semen ; though the latter is complicated
by the addition of the secretions of several glands in connection
with the seminal tract. Though competent by their own move-
ments of reaching the ovum in the oviduct, it is probable that
the uterus and oviduct experience peristaltic actions in a direc-
tion toward the ovary, at least in a number of mammals.

The lower part of the spinal cord is the seat in the higher
mammals of a sexual center or collection of cells that receives
afferent impulses and sends out efferent impulses to the sexual
organs. This, like all the lower centers, is under the control of
the higher centers in the brain, so that its action may be either
initiated or inhibited by the cerebrum.

••»*.,* - «?,isf,--;rta •-».TOiDCTan»«*( 2SHi4*ai«<KSi«^»i.-.«»JWieaSiin»!M»-jimati««f!S«Si^^

I the great store-
icle of all waste
Ted to the moth-
milar way nutri-
hat of the foetus,
ratory, and excre-

female elements
ion of the penis is
L organ composed
he result of the
exual tract, aided
ies. The sperma-
ed) cells, make up
ter is complicated
nds in connection
f their own move-
it is probable that
actions in a direc-
t mammals,
seat in the higher
cells that receives
ilses to the sexual
ider the control of
tion may be either

ORGANIC EVOLUTION RECONSIDERED.

ADMirrrao that the theories of the leading writers on the
subject have advanced us on the way to more complete views of
the mode of origin of the forms of the organic world, it must
still be felt that all theories yet propounded fall short of being
entirely satisfactory. It seems to us unfortunate that the sub-
ject has not received more attention from physiologists, as
without doubt, the Anal solution must come through that sci-
ence which deals with the properties rather than the forms of
protoplasm ; or, in other words, the fundamental principles
underl3ring organic evolution are physiological. But, in the
unmveling of a subject of such extreme complexity, all sciences
must probably contribute their quota to make up the truth, as
many rays of different colors compounded form white light.
As with other theories of the inductive sciences, none can be
more t^ft" temporary; there must be constant modification to
meet increasing knowledge. Conscious that any views we our*
selves advance must sooner or later be modified as all others,
even if acceptable now, we venture to lay before the reader the
opinions we have formed upon this subject as the result of con-
siderable thought.

AlU vital phenomena may be regarded as the resultant of
the action of external conditions and internal tendencies. Amid
the constant change which like involves we recognize two
things : the tendency to retain old modes of behavior, and the
tendency to modification or variation. Since those impulses
originally bestowed on matter when it became living, must, in
order to prevail against the forces from without, which tend to
destroy it, have considerable potency, the tendency to modifica-
tion is naturally and necessarily less than to permanence of
form and function.

From these principles it follows that when an Amoeba or
kindred organism divides after a longer ur shorter period, it is

mmMKiiMilMin

188

COMPARATIVE PHYSIOLOGY.

not in reality the same in all respects as when its existence be-
gan, though we may be quite unable to detect the changmi ; and
when two infuiorians conjugate, the one brings to the other
protoplaam different in molecular behavior, of necessity, from
having had different experiences. We attach great importance
to these principles, as they seem to us to lie at the root of the
whole matter. What has been said of these lower but inde-
pendent forms of life applies to the higher. All organisms are
made up of cells or aggregations of cells and their products.
For the present we may disregard the latter. When a muscle-
cell by division gives rise to a new cell, the latter is not identi-
cally the same in every particular as the parent cell was origi-
nally. It is what its parent has become by virtue of those ex-
periences it has had as a muscle-cell per m, and as a membm* of
a populous biological community, of the complexities of which
we can scarcely conceive.

Now, as a body at rest noay remain so, or may move in a
certain direction according to the forces acting upon it exactly
counterbalance one another, or produce a resultant effect in the
direction in which the body moves, so in the case of heredity,
whether a certain quality in the parent appears in the offspring,
depends on whether this quality is neutralised, augmented, or
otherwise modified by any corresponding quality in the other
parent, or by some opposite quality, taken in connection with
the direct influence of the environment during development.

This assumption explains among other things why acquired
peculiarities (the results of accident, habit, etc.) may or may
not be inherited.

These are not usually inherited because, as is to be expected,
those forces of the organism which have been gathering head
for ages are naturally not easily turned aside. Again, we urge,
heredity must be more pronounced than variation.

The ovum and sperm-cell, like all other cells of the body,
are microcosms representing the whole to a certain extent in
themselves — that is to say, cell A is what it is by reason of what
all the other millions of its fellows in the biological republic
are; so that it is possible to understand why seziial cells repre-
sent, embody, and repeat the whole biological story, though it
is not yet possible to indicate exactly how they more than others
have this power. This falls under the laws of specialization
and the physiological division of labor ; but along what paths
they have reached this we can not determine.

■;i*>-^!^WTB5TS«V#n«'3KI3WW.«W«»4**»

ORGANIC EVOLUTION RKtONSIDERED.

189

1 its existpnoe be-
the changm ; and
ings to the other
>f necemity, from
great importance
X the root of the
3 lower but inde-
All organiams are
id their product*.
When a muaole-
itter is not identi-
mt cell was origi-
rirtue of those ex-
ad as a membei* of
plexities of which

>r may mov« in a
ng upon it exactly
ultant effect in the
e case of heredity,
m in the offspring,
ted, augmented, or
ludity in the other
n connection with
ng development,
lings why acquired
etc.) may or may

ts is to be expected,
ten gathering head
i. Again, we urge,
iation.

cells of the body.
a certain extent in
I by reason of what
I biological republic
T sexual cells repre-
cal story, though it
By more than others
«rsof specialization
it along what paths
e.

Strong evidence is furnished for the above views by the his-
tory of disease. Scar-tissue, for example, continues to repro-
duce itself as such ; like produces like, though in this instance
the like is in the first instance a departure from the normal.
Gout is will known to be a hereditary disease ; noi only so, but
it arises in the offspring at about the same age as in the parent,
which iH equivalent to saying that in the rhythmical life of
certain cells a period is reached when they display the behavior,
physiologically, of their parents. Yet gout is a disease that can
be traced to peculiar habits of living and may be eventually
escaped by radical changes in this respect— that is to say, the
behavior of the cells leading to gout can be induced and can be
altered ; gout is hereditary, yet eradicable.

Just as gout may be set up by the formation of certain modes
of action of the cells of the body, so may a mode of behavior,
in the nervous system, for example, become organized or fixed,
become a habit, and so be transmitted to offspring. It will pass
to the descendants or not according to the principles already
noticed. If so Axed in the individual in which it arises as to
predominate over more ancient methods of cell behavior, and
not neutralized by the strength of the normal physiological ac-
tion of the corresponding parts in the other parent, it will reap-
pear. We can never determine whether this is so or not before-
hand ; hence the fact that it is impossible, especially in the case
of man, whose vital processes are so modified by his psychic
life, to predict whether acquired variations shall become heredi-
tary ; hence also the irr^larity which characterizes heredity
in such cases ; they may reappear in offspring or they may not.
In viewing heredity and modification it is impossible to get a
true insight into the matter without taking into the account
both the original natural tendencies of living matter and the
influence of environment. We only know of vital manifes-
tations in 8ome environment ; and, so far as our experience
goes, life is impossible apart from the reaction of surroimd-
ings. With these general principles to guide us, we shall at-
tempt a brief examination of the leading theories of organic
evolution.

First of all, Spencer seems to be correct in regarding evolu-
tion as universal, and organic evolution but one part of a
whole. No one who looks at the facts presented in every field
of nature can doubt that struggle (opposition, action and reac-
tion) is universal, and that in the organic world the fittest to a

140

COMPARATIVE PIlYSIOIiOOT.

given environment lurvivM. But Darwin hu pn>)>ably flxed
hii attention ton fllt>iiely on this principle and altentpttnl t«> ex-
plain t(M> much by it, oa well on foiled to see that there ore
other deeper facta underlying it. Variation, which thia autlmr
•oaroely attempted to explain, Heoms to ui to bo the natural re-
sult of the very condition! under which living things have an
existence. Stable equilibrium is an idea incompatible with our
fundamental conceptions of life. Altered function implies al-
tered molecular action, which sometimes leads to apprecinble
structural change. From our conceptions of the nature of liv-
ing matter, it naturally follows that variation nhould Ims great-
est, as has been obterrvd, under the greatest alteration in thu
surroundings.

We are but very imperfootly acquainted as yet with the
conditions under which life existed in the earlier epochs of the
earth's history. Of late, deep-sea soundings and arctic explo-
rations have brought surprising facts to light, showing that
living matter can exist under a greater variety of conditions
than was previously supposed. Thus it turns out that light is
not an essential for life everywhere. We think these recent
revelations of unexpected facts should moke us cautious in
assuming that life tdways manifested itself under conditions
closely similar to those we know. Variation may at one period
have been more sudden and marked than Darwin suppooei;
and there does seem to be room for such a conception as the
"extraordinary births" of Mivart implies; though we would
not have it understood that we think Darwin's view of slow
modification inadequate to produce a new species, we simply
venture to think that he was not justified in insisting so strongly
that this was the only method of Nature; or, to put it more
justly for the great author of the Origin of Species, with the
facts that have accumulated since his time he would scarcely
be warranted in maintaining so rigidly his conviction that
new forms arose almost exclusively by the slow process he has
so ably described.

We must allow a great deal to use and effort, doubtless, and
they explain the origin of variations up to a certain point, but
the solution is only partial. Variations must ailse as we have
attempted to explain, and use and disuse are only two of the
facton amid many. Correlated growth, or the changes in >«
part induced by changes in another, is a principle wL'- Vi
though recognised hy Darwin, Cope, and others, has not, we

ORGANIC EVOLUTION RECONSIDRRED.

141

iw protHibly fixed
attempted to ex-
)e that there are
which this author
n the natural re-
g things have an
upatible with our
motion iuipliea ai-
ds to apprecinble
the nature of llv-
Hhould be great-
alteration in thu

OH yet with the
rlier epochs of the

and arctic explo-
fht, showing that
iety of conditions
■ out that light is
think these recent
ke us cautious in

under conditions
may »t one period
Darwin suppose*;
, conception as the
though we would
Tin's view of slow
ipecies, we simply
udsting so strongly
[)r, to put it more
f Species, with the

he would scarcely
is conviction that
ilow process he has

Fort, doubtless, and
, certain point, but
Lst ailse as we have
re only two of the
the changes in «
I principle wLi.ii
>therB, has not, we

think, receivetl the attention it deserves. To the mind of the
phyNiologist, all changes must be correlated with othcns.

In what sense has the line that evolution has takiii been
prcdeterminetl » In the sense that all things in the universe
are unstable, are undergoing change, leading to now forms and
qualities of such a character tlu»t they result in a gradual prog-
ress toward what our minds can not but consider higher niani-
fostatiouN of being. *

The secondary methods according to which thiH takes place
lonstituto the Uws of nature, and as we learn from the prog-
ress of science are very numerous. The unity of nature is a
rt«lity toward which our conceptions are constantly leading
lis. Evolution is a necessity of living matter (indeed, all matter)
as we view it.

THE CHEMICAL CONSTITUTION OF THE
ANIMAL BODY.

One visiting the ruins of a vast and elaborate building,
which had been entirely pulled to pieces, would get an amount
of information relative to the original structure and uses of
the various parts of the edifice largely in proportion to his fa-
miliarity with architecture and the varioiis trades which make
that art a practical success. The study of the chemistry of
the animal body is illustrated by such a case. Any attempt
to determine the exact chemical composition of living matter
must result in its destruction ; and the amount of inf oi-mation
conveyed by the examination of the chemical ruins, so to speak,
will depend a great deal on the knowledge already possessed of
chemical and vital processes.

It is in all probability true that the nature of any vital pro-
cess is at all events closely bound up vrith the chemical changes
involved ; but we must not go too far in this direction. We are
not yet prepared to say that life is only the manifestation of
certain chemical and physical processes, meaning thereby such
chemistry and physics as are known to us ; nor are we prepared
to go the length of those who regard life as but the equivalent
of some other force or forces ; as electricity may be considered
as the transformed representative of so much heat and vice versa.
It may be so, but we do not consider that this view is warranted
in the present state of our knowledge.

On the other hand, vital phenomena, when our investiga-
tions are pushed far enough, always seem to be closely asso-
ciated with chemical action : hence the importance to the stu-
dent of physiology of a soimd knowledge of dhemical princi-
ples. We think the most satisfactory method of studying the
functions of an organ will be found to be that which takes into
consideration the totality of thw operations of which it is the
seat, together with its structure and chemical composition ;

— stswjjasB^uaii

■i.^«a»p*a)«!wa'«!»«sstiie8im'>iisK!»BB^^

CHEMICAL CONSTITUTION OP THE ANIMAL BODY. 148

N OF THE

»laborate buUdini^,
uld get an amount
icture and uses of
roportion to his fa-
trades which make
the chemistry of
Any attempt
of living matter

of infoi-mation

_ ruins, so to speak,
Jready possessed of

lase.
n

lUUti

re of any vital pro-
le chemical changes
i direction. We are
the manifestation of
aning thereby such
nor are we prepared
I but the equivalent
y may be considered
i heat and vice vena.
lis view is warranted

when our investiga-
i to be closely asso-
iportance to the stu-
I of 6hemical princi-
Ihod of studying the
that which takes into
OS of which it is the
emical composition ;

hence we shall treat chemical details in the chapters devoted to
special physiology, and here g^ve only such an outline as will
bring before the view the chemical composition of the body in
its main outlines ; and even many of these will gather a signifi-
cance, as the study of physiology progresses, that they can not
possibly have at the present.

Fewer than one third of the chemical elements enter into
the composition of the mammalian body ; in fact, the great
bulk of the organism is composed of carbon, hydrogen, nitro-
gen, and oxygen ; sodium, potassium, magnesium, calcium,
sulphur, phosphorus, chlorine, iron, fluorine, silicon, though
occurring in very small quantity, seem to be indispensable to
the living body ; while certain others are evidently only pres-
ent as foreign bodies or impurities to be thrown out sooner
or later. It need scarcely be said that the elements do not
occur as such in the living body, but in combination form-
ing salte, which latter are usually united with albuminous
compounds. As previously mentioned, the various parts which
make up the entire body of an animal are composed of living
matter in very different degrees ; hence we find in such parts
as the bones abundance of salts, relative to the proportion of
proteid matter; a condition demanded by that rigidity without
which an internal skeleton would be useless, a defect well illus-
trated by that disease of the bones known as rickets, in which
the limenudta are insufficient It is manifest that there may bo
a very great variety of classiflcations of the compounds found
in the animal body according as we regard it from a chemical,
physical, or physiological point of view, or combine many
aspects in one whole. The latter is, of course, the most correct
and profitable method, and as such is impossible at this stage
of the student's progress ; we shall simply present him with the
following outline, which will be found both simple and com-
prehensive.*

OHBlflOAIi OUMtfriTUTlON OF THB BODY.

Such food as supplies energy directly must contain carbon
compounds.

Living matter or protoplasm always contains nitrogenous
carbon compounds.

* Taken from the author's Outlines of Lectures on Physiology, W. Drys-
dale k Co., Montreal

144

COMPARATIVE PHYSIOLOGY.

In consequence, C, H, O, N, are the elements found in greatr
est abundance in the body.

The elements 8 and Pare i-saoci ted with the nitrogenous
carbon compounds ; they also for... metaUic sulphates and phos-

^ CI and F form salts with the alkaline metals Na, K, and the
earthy metals Ca and Mg.

Fe is found in hoemoglobin and its derivatives.

Protoplasm, when submitted to chemical exammation, is
kiUed. It is then found to consist of proteids, fats, carbohy-
drates, salines, and extractives.

It is probable that when Uving it has a very complex mole-
cule consisting of C, H, O, N, S, and P chieEy.

Proximate Pbinoipiss.

( (a) Nitrogenous. j Certun cryBUlline bodies.

1. Organic. \ (Carbohydrate*.

( (b) Non-nitrogenous. \ Ji^ta.

^ _ . S Mineral salts.

2. Inorgamc. | yfaier.

Salts —In general, the salts of sodium are more characteris-
tic of animal tissues and thoje ot potassium of vegetable tosues.

Na CI is more abundant in the fluids of animals ; K and
phosphates more abundant in tiie tissues.

Earthy salts are most abundant in Uie harder tissues.

The salts are probably not much, if at all, changed in their
vassage through the body.

tosome cLs tiiere is a change from acid to neutral or

alkaline. . ,, i_iii

The salts are essential <» preserve the balance of the nutntive
processes. Their absence leads to disease, e. g., scurvy.

OBNERAL CHABAOTERISnCM OF PKOTEIDB.

They are the dhief constituents of most living tissues, inclad-

coftstitution), and is formed of the elements C, H, N, O, B, and f.

All proteids are amorphous.

All are non-diffusible, the peptone* excepted.

They are soluble m strong acids and alkalies, with change of

nropertios or constitution. ,-, s.-

£ general, tiiey are coagulated by alcohol, etiier, and heating.

res.

examination, is
ds, fats, carbohy-

I more characteris-
r vegetable tissues.

' atiimn.la ; K and

rder tissues.

, changed in their

icid to neutral or

toe of the nutritive
f,, scurvy.

OTEIDS.

ing tissues, inclad-

of atoms (complex
,H,N,0,8,andP.

ted.

lies, with change of

ether, and heating.

■ CHEMICAL CONSTITUTION OP THE ANIMAL BODY. 145

Coagulated proteids are soluble only in strong acids and
alkalies.

Classification and Distinguishiitg Characters of Proteids.

1. Native albumins : Serum albumin ; egg albumin ; solu-
ble in water.

2. Derived albumins {albuminates) : Acid and alkali albu-
min ; casein ; soluble in dilute acids and alkalies, insoluble in
water. Not precipitated by boiling.

3. Globulins : Globulin (globin) ; paraglobulin ; myosin ;
fibrinogen. Soluble in dilute saline solutions, and precipitated
by stronger saline solutions.

4. Peptones: Soluble in water; diffusible through anima
membranes; not precipitated by acids, alkalies, or heat. De-
rived from the digestion (peptic, pancreatic) of all proteids.

6. Fibrin : Insoluble in water and dilute saline solutions.
Soluble, but not readily, in strong saline solutions and in dilute
acids and alkalies.

OBATAIN NON-ORTSTALLUne BODIES.

The following bodies are allied to proteids, but are not the
equivalents of the latter in the food.

They are all composed of C, H, N, O. Clhondrin, gelatin,
keratin have, in addition, S.

Chondrin : The oi^ganic basis of cartilage. Its solutions set
into a firm jelly on cooling.

Chlatin : The organic basis of bone, teeth, tendon, etc. Its
solutions set (glue) on cooling.

Elastin : The basis of elastic tissue. Its solutions do not
set jelly-like (gelatinize).

Mtusin : From the secretion of mucous membranes ; precipi-
tated by acetic acid, and insoluble in excess.

Keratin : Derived from hair, nails, epidermis, horn, feathers.
Highly insoluble.

Nuclein: Derived from the nuclei of cells. Not digested
by pepsin ; contains P but no S.

THE FATB. -

The fats are hydrocarbons ; are less oxidised than the carbo-
hydrates ; are inflammable ; possess latent energy in a high
degree.

Cihemically, the neutral fats are glyoerides or ethers of the
10

146 COMPARATIVE PHYSIOLOGY.

fatty addB, i. e., the acid radicles of the fatty acids of the oleic
and acetic series replace the exchangeable atoms of H in the
triatomic alcohol glycerine, e. g.

Glycerine,

(OH

Palmitic Mid,

HO.OO.CitH.

Glycerine triprimltate or palmltln.

O.CO.CiiHii

(OH HO.OO.C.H.. i RSS n'w 4. 1H.0

C5.H. } OH + HO.OC.C..H.. = C.H. ] O.OO.CuH.. + 3H.O
( OH HO.OC.C..H.. ( O.CO.CH..

Auoopisfonnedby the action of caustic alkaUeeon fats, e. g. :

TrlptUmltm. Pota«lamp.lmltate.

The soap may be decomposed by a strong acid into a fatty
aoid and a salt, e. g. :

C..H...CO.K + HCa = O..H...CO.H + KOI.

PotaMlumi«amltate. P«lmlUc acid.

The fata are insoluble in water, but soluble in hot alcohol,
ether, chloroform, etc.

The dUealine soaps are soluble in water.

Most animal fata are mixtures of several kmds m varying
proportions ; hence the melting-point for the fat of each species
of animal is different.

PBOUUAB FATS.

Lecithin, Protagon, Cerdmn:

They consist of O, H, N, O, and the first two of P m addi-
tion.

They occur in the nervous tissues.

OABBOHTDBATES.

General formula, C. (H,0).. « „ /^ jm

1 The Suoabs : Dextrose, or grape«igar, C,H.dO, reatttly
undergoes alcoholic fermentation ; 'ess readily hwticfermen

^^'IblLstoee, milk-sugar, 0„H„0,. ; susceptible of the lactic acid

fermentation. , .. 1 _*• *^__

Inowt, or muscle^raga^, C.H,.0. ; capable of the lactic fer-

mentation. . ,. « ± a^

Maltoee, O.AdO„, capable of the alcohohc fermentation.

The chief sugar of the digestive process.

All the above are much lesa sweet and soluble than ordinary

caneHnigar.

lids of the oleic
ns of H in the

tate or palmitin.

[!i.H.>

CuH.. + 3H.0

0..H..

lies on fats, e.g.

acid into a fatty

+ K01.

) in hot alcohol,

kinds in varying
at of each species

;wo of P in addi-

*, C,H,A readily
lily lactic fennen-

5 of the lactic acid

5 of .the lactic fer-

olic fermentation.

able than ordinary

CHEMICAL CONSTITUTION OP THE ANIMAL BODY. 147

2. The Stabohes : Glycogen, CVHraO„ convertible into dex-
trose. Occurs abundantly in many foetal tissues and in the
liver, especially of the adult animal.

Dextrin, C«H„0(, convertible into dextrose. Soluble in
water : intermediate between starch and dextrose ; a product
of digestion.

Pathological : Grape-sug^.: occurs in the urine in diabetes
mellittu.

Certain substances formed within the body may be regarded
as chiefly waste-products, the result of metabolism or tissue-
changes.

They are divisible into mtrogenoxis metabolites and non-
nitrogenous metabolites.

Nitrogenous Metabolitea.

1. Urea, luric acid and compounds, kreutinin, xanthin, hypo-
xanthin (sarkin), hippuric acid, all occuring in urine.

2. Leuoin, tyrosin, tau.. •. aholic, and glycocholic acids, which
occur in the digestive tract.

3. Ereatin, constantly found in muscle, and a few ot!iers of
less constar ' occurrence.

The above consists of C, H, N, O. Taurocholic acid contains
alsoS.

The molecule in most instances is complex.

Non-Nitrogei/ume Metabolites.

These occur in small quantity, and some of them are secreted
in an altered form.

They included lactic and sarcolaotic acid, oxalic acid, succinic
add, etc.

S^W^'^li'V^*^"^'-----^''^

PHYSIOLOGICAL RESEARCH AND
PHYSIOLOGICAL REASONING.

We propose in this chapter to examine into the methods
employed in physiologcial investigation and teaching, and the
character of conclusions arrived at hj physiologists as depend-
ent on a certain method of reasoning.

The first step toward a legitimate conclusion in any one of
the indtictive sciences to which physiology helongs is the col-
lection of facts which are to constitute the foundation on
which the inference is to be based. , If there be any error in
these, a correct conclusion can not be drawn by any reliable
logical process. On the other hand, facts may abound in thou-
sands and yet the correct conclusion never be reached, because
the method of interpretation is faulty, which is equivalent to
saying that the process of inference is either incomplete or in-
correct. The conclusions of the ancients in regard to nature
were usually faulty from errors in both these directions ; they
neither had the requisite Tacts, nor did they correctly interpret
those with which they were conversant.

Let us first exanune into the methods employed by modem
physiologists, and determine in how far they are reliable. First,
there is Uie method of direct observation, in which no appara-
tus whatever or only the simplest kind is employed ; thus, the
student may count his own respirations, feel his own heart-
beats, count his pulse, and do a very great deal more that will
be pointed out hereafter; or he may examine in like manner an-
other fellow-being or one of the lower animals. This method
is simple, easy of application, and is that usually employed by
the physician even at the present day, especially in private
practice. The value of the results obviously depends on the
reliability of the observer in two respects : First, as to the ac-
curacy, extent, and delicacy of his perceptions ; and, secondly,
on the inferences based on these sense-observations. Much

a.i«rti«W M MHwi'ii i r»iiii i iiM >ii iiiiiwi:i<ii^

amimtititmmit

PHTSIOLOOIOAL RESBARGH AND REASONING. 149

AND

NG.

nto the methods
teaching, and the
logists as depend-

lion in any one of
lelongs is the col-
foundation on
be any error in
by any reliable
J abound in thou-
e reached, because
_ is equivalent to
p incomplete or in-
a regard to nature
le directions ; they
correctly interpret

iployed by modem
are reliable. First,
1 which no appara-
nployed ; thus, the
eel his own heart-
leal more that will
in like manner an-
nals. This method
iiially employed by
pecially in private
sly depends on the
First, as to the ae-
ons ; and, secondly,
baervations. Much

must depend on praetioe — that is to say, the education of the
senses. The hand may become a most delicate instrument of
observation ; the eye may learn to see what it once could not ;
the ear to detect and discriminate what is quite beyond the
uncultured hearing of the many. But it is one of the most
convincing evidences of man's superiority that in every field of
observation he has risen above the lower animals, some of which
by their unaided senses naturally excel him. So in this science,
instruments have opened up mines of facts that must have other-
wise remained hidden ; they have, as it were, provided man
with additional senses, so much have the natural powers of
those he already possessed been sharpened.

But the chief value of the results reached by instruments *
consists in the fact that the movements of the living tissues can
be registered; i. e., the great characteristic of modern physiol-
€tgy is the extensive employment of the graphic method, which
has been most largely developed by the distinguished French
experimenter Marey. Usually the movements of the point of
lever are impressed on a smoked surface, either of glazed
paper or gla», and rendered permanent by a coating of some
material applied in solution and drying quickly, as shellac in
alcohoL The surface on which the tracing is written may be
stationary, though this^ is rarely the case, as the object is to get
a succession of records lor comparison ; hence the most used
form of writing surface is a cylinder which may be raised or
lowered, and which is moved around regularly by some sort of
clock-work. It follows that the lever point, which is moved Iqr
the physiological efifeot, describes curves of varying complexity.
That tracings of this or any other character ^ould be of any
'value for the purposes of physiology, they miist be susceptible
of relative measurement both for time and space. T is can be
accomplished only when there is a known base-line or abscissa
from which the lever begins its rise, and a time record which is
usually in seconds or portions of a second. The first is easily
obtained by simply allowing the lever to write a straight line
before the physiological e£fect proper is recorded. Time inter-
vals are usually indicated by the interruptions of an electric
current, or by the vibrations of a tuning-fork, s pen or writer
of some kind being in each instance attached to the apparatus
so as to record its movements.

* ninBtnted in the sections on musoie ptiysiology and others.

a!Ki«lWS!tt.W-fi

160

COMPARATIVE PHYSIOLOGY.

As levers, in proportion to their length, exaggerate all the
moyements impfurted to them, a constant process of cdrrectioii
must be carried on in the mind in reading the records of the
graphic method, as in interpreting the field of view presented
by the microscope.

The student is epeoially warned to carry on this process,
otherwise highly distorted views of the reality will become
fixed in his own mind ; and certainly a condition of ignorance
is to be preferred to such false knowledge as this may become.
But it is likewise apparent that movements that would without
such mechanism be quite unrecognised may be rendered visible
and utilised for inference. There is another source of possible
misconception in the use of the graphic method. The lever is
sometimes used to record the movements of a column of fluid
(manometer, Fig. 197), as water or mercury, the inertia of which
is considerable, so that the record is not that of the lever as
affected by the physiological (tissue) movement, but that move-
ment conveyed through a fluid of the kind indicated. Again,
all points, however delicate, write with some friction, and the
question always arises. In how far is that friction sufficient to
be a source of inaccuracy in the record ? When organs are di-
rectly connected with levers or apparatus in mechanical rela-
tion with them, one must be sure that the natural action of the
organ under investigation is in no way modified by this con-
nection.

From these remarks it will be obvious that in the graphic
method physiologists possess a means of investigation at once
valuable and liable to mislead. Already electricity has been
extensively used in the researches of physiologists, and it is to
this and the employment of photography that we look in the
near future for methods that are less open to the objections we
have noticed.

However important the methods of physiology, the results
are vastly more so. We next notice, then, the progress from
methods and observations to inferences, which we shall en-
deavor to make clear by certain cases of a hypothetical charac-
ter. Proceeding from the brain and entering the substance of
the heart, there is in vertebrates a nerve known as the vagu».
Suppose Uiat, on stimulating this nerve by electricity in a rab-
bit, the heart ceases to beat, what is the legitimate inference ?
Apparently that the effect has been due to the action of the
nerve on the heart, an action excited by the use of electricity.

'-mtm

HiMiiiliiliiM

PHYSIOLOGICAL RBSEARCIl AND HEASONINO. 161

aggerato all the
I of cdrrectioii
reoordfl of the

' view preMuted

on this prooeu,
ity will become
ion of ignorance
hii may become,
it woiild without
» rendered Tirible
ouroe of poerible
od. The lever is

column of fluid

inertia of which
X of the lever aa
it, but that move-
ndioated. Again,

friction, and the
ition sufficient to
ten organs are di-

mechanical rela-
fcural action of the
lifled by this con-
hat in the graphic
^estigation at once
ectrioity has been
ogists, and it is to
lat we look in the
I the objections we

Biology, the resulto
the progress from
hich we shall en-
ypothetical charac-
ng the substance of
lown as the vagus.
electricity in a rab-
[itimate inference }
> the action of the
3 use of electricity.

This does not, however, according to the principles of a rigid
logic, follow. The heart may have ceased beating from some
cause wholly unconnected with this experiment, or fr'^m the
electric current escaping along the nerve and affecting some
nervous mechanism within the heart, which is not a part of the
vagus nerve ; or it may have been due to the action of the cur-
rent on the muscular tissue of the heart directly, or in some other
way. But suppose that invariably, whenever this experiment
is repeated, the one result (arrest of the beat) follows, then it is
clear that the vagus nerve is in some way a factor in the causa-
tion. No-ff . if it could be ascertained that certain branches of
the nerve were distributed to the heart-muscle directly, and that
stimulation of these gave rise to arrest of the cardiac pulsation,
then would it be highly probable, though not certain, that there
was in the first instance no intermediate mechanism ; while
this inference would become still more probable if in hearts
totally without any such nervous apparatus whatever, such a
result followed on stimulation of the vagus. Suppose, further,
that the application of some drug or poison to the heart pro-
vided with special nervous elements besides the vagus termi-
nals prevented the effect before noticed on stimulating the
vagus, while a like result followed under similar circumstances
in those forms of heart unprovided with such nervous struct-
ures, there would be additional evidence in favor of the view
that the result we are considering was due solely to some action
of the vagus nerve; while, if arrest of the heart followed in the
first case but not in the second, and this result were invariable,
there would be roused the suspicion that the action of the
vagus was not direct, but through the nervous structures with-
in the iieart other than vagus endings. And if, again, there were
a portion of the rabbit's heart to which there were distributed
this intrinskfs nervous supply, which on stimulation directly
was arrested in its pulsation, it would be still more probable
that the effect in the first instance we have consiclered was due
to these structures, and only indirectly to the vagus. But be it
observed, in all these cases there ia only probability." The con-
clusions of physiology never rise above probability, though this
may be so strong as to be practically equal in value to absolute
certainty. Would it be correct, ^m any or all the experi-
ments we have supposed to have been made, to assert that the
vagus was the arresting (inhibitory) nerve of the heart ? All
hearts thus far examined have much in common in structure

ir*^

lfi2

COMPARATIVK PnVSIOLOOY.

and function, and in lo far ia the above ^nernlixntion probable.
Such a itatement would, however, be far fn»ni thut degree of
probability which ia poaaible, and should therefore not be ac-
cepted till more evidence has been gathered. The mere reaem-
blanoe in form and general function dnea not mince to meet the
demands of a critical logic. Such a aUitement an the above would
not neoeaaarily apply to the hearts of all vertebrates or even all
rabbits, if the experiments had been conducted on one animal
alone, for the result might be owing to a mere idioHyncrasy of
the rabbit under observation. The further we depart from the
group of animals to which the creature under experiment be-
longs, the leas is the probability that our generalisations for
the one class will apply to another. It will, therefore, be seen
that wide generalisations can not be made with that amount of
certainty which is attainable until experiments shall have be-
come very numerous and widely extended. A really broad and
■ound physiology can only be constructed when this science
has become much more comparative — ^that \h, extended to many
more groups and mib-groupa of animals than ut present.

We have incidently alluded throughout the work to tho
teaching of disease. " Disease " is but a name for disordered
function. One viewing a piece of machinery for the first time
in improper action might draw conclusions with comparative
safety, provided he had a knowledge of the correct action of
aifnilar machines. Our experience gives us a certain knowl-
edge of the functions of our own bodies. By ordinary observa-
tion and by experiment on other animals we get additional
data, which, taken with the disordered action resulting from
gross or molecular injury (disease), gives a basis for certain
conclusions as to the normal functions of the human body or
those of lower animals. This information is especially valu-
able in the case of man, since he can report with a fair de-
gree of reliability, in moat diseased conditions, his own sensa-
tions.

It is hoped that this brief treatment of the methods and
logic of physiology will suffice for the presei^t. Throughout
the work they will be illustrated in every chapter, though not
always with distinct references to the nature of the intellectual
process followed.

Sammary. — ^There are two methods of physiological observa-
tion, the direct and the indirect. The first is the simplest, and
is valuable in proportion to the aoeuraoy and delicacy and

;:iatmmimmsimmmmmmtm»B

m^mmgmm

Ration probftble.
1 that deiirrae of
ifore not be ac-
rhe mere reeem-
itllce to meet the
the above would
rates or even all
d on one animal
3 idioHyncmiy of

depart from the
< experiment be-
noralizations for
tierefore, be Men
h that amount of
to shall havebo-
really broad and
rhen this aoienco
ixtended to many
kt present.
the work to the
DO for disordered

for the first timo
vith comparative

correct action of
a certain knowl-
Drdinary observar
re get additional
n resulting from

basis for certain
B human body or
is especially valu-
•t with a fair de-
ls, his own sensa-

the methods and
evt. Throughout
lapter, though not
of the intellectual

siological obeerva-
B the simplest, and
and delicacy and

PHYSIOLOOIOAT, RESRARCn AND RRASONINn. 188

range of the nbiwrver ; the latter implies the use of apparatus,
und is more romplex, more extended, more doUcate. and precise.
It is UHUully employed with the graphic method, which has the
advantage of recording and thus preserving movemenU which
correspond with more or less exactnemt to the niovementa of
tiMues or organs. It is valuable, but liable to errors iu record-
ing and in interpretation.

The logic of phjrsiology is that of the inductive sciences. It
proceeds from the special to the general. Tlie conclusions of
physiology never pass beyond extreme probability, which, in
some cases, is practically equal to certainty. It is especially
important not to maice generalisations that are too wide.

sm^

THE BLOOD.

It ii • matter of oommon ob«enraUon that the Low of the
whole, or a very largo part, of the blood of the body entailii
death ; while an abundant hseniorrhage, or blood-dkeaii e in any
of it« forms, causes great general weakneas.

The student of embryology is led to inquire as to the neces-
sity for the very early appearance and the rapid development
of the blood-vascular system so prominent in all vertebrates.

An examination of the means of transit of the blood, as
already intimated, reveals a complicated system of tubes dis-
tributed to every organ and tissue of the body. These facts
would lead one to suppose that the blood must have a tran-
scendent importance in the economy, and such, upon the most
minute investigation, proves to be the case. The blood has
been aptly compared to an internal world for the tissues, an-
swering to the external world for the organism as a whole.
This fluid is the great storehouse containing all that the most
exacting cell can demand ; and, further, is the temporary re-
ceptacle of all the waste that the most busy cell requires to dis-
charge. Should such a life-stream cease to flow, the whole vital
machinery must stop — death must ensue.

OompMNitiTS,— It will prove more scientific and generally
satisfactory to regard the blood as a tissue having a fluid and
flowing matrix, in which flow cellular elements or corpuscles—
a view of the subject that is less startling when it is remem-
bered that the greater part of the protoplasm which makes up
the other tissues of the body is of a semifluid consistence. In
all animals possessing blood, the matrix is a cleae, usually more
or less colored fluid. Among invertebrates the color may be
pronounced : thus, in cephalopoda and some crustaceans it is
blue, but in most groups of animals and all vertebrates the
matrix is either colorless or more commonly of some slight
tinge of yellow. Invertebrates with few exceptions possess

^*j?'T/s:r^-itf-7)r«i!^;:r.T"»',-:r'r»ss'?^HSSK18S';S^

5iKSBiSSB'w««fK

THK BliOOn.

166

kt the 1mm of the
the body entailn
od-duewe in any

re as to the neoee-
ipid development
all vertebrate*,
of the blood, m
tem of tubee dis-
Ddy. These facts
lUst have a tran-
ch, upon the most
Tlie blood has
or the tissues, an-
aism as a whole.
r all that the most
the temporary re-
ell requires to dis-
>w, the whole vital

Iflo and generally
having a fluid and
ats or corpuscles—
irhen it is remem-
n which makes up
d consistence. In
clear, usually more
I the color may be
le crustaceans it is
all vertebrates the
ily of some slight
exceptions possess

only colorless corpuscles, but all vertebrates have colored cells
which invariably outnumber the other variety, and display
forms and sises
which are sufficient-
ly constant to be
characteristic. In all
groups below mam-
mals the colored cor-
puscles are oval,
mostly biconvex,
and nucleated dur-
ing all periods of the
animal's existence;
in mammals they are
circular biconcave
disks (except iu the
camel tribe, the cor-
puscles of which are
oval), and in post-
embryonic life vrith-
out a nucleus ; nor
do they possess a cue,
cell-wall. The red

cells vary in sise in different groups and sub-groups of animals,
being smaller the higher the place the animal occupies, as a

general rule; thus, they
are very large in verte-
brates below mammalu,
in some cases being al-
most visible to the un-
aided eye, while in the
whole class of mam-
mals they are very mi-
nute ; their numbers
also in this group are
vastly greater than in
others lower in the
scale.

The average size in
man is ^/nr inch (•0077

mm.) and the nnmber

Pio.lW.— Photograph of colored corpMCI** of frog. . _ ,u:_ ^iMi^^^,^

iitm. (After Flint.). ^ m a cubic millimetre

Via. tW.— Leneocytet of human blood, ihowlng •mo-
bold movement* (Landoli), These movement* are
not normJtlly In the blood-veeaele so marked a* pic-
tured hero, so that the figure repreaenta an extreme

y^^^S -< ''^^^^'■'^^^

156

COMPARATIVE PHYSIOLOGY.

of the blood about 6,000,000 for the male and 600,000 less for
the female, which would furnish about 860,000,000,000 m a
pound of blood. It will be understood that averages only are
spoken of, as all kinds of variations occur, some of wWch wUI
be referred to later, and their significance explained. The nze
of the corpuscles in the domestic animals is variable-a matter
of importance when transfusion of blood is under consideration.
Under the microscope the blood of vertebrates is seen to owe
ite color to the cells chiefly, and, so far as the red goes, almort '

wholly. Corpuscles
when seen singly are
never of the deep red,
however, of the blood
as a whole, but rather
a yellowidi red, the
tinge varying some-
what with the class of
animals from which
the specimen has been
taken.

Certain other mor-
phological elements
found in mammalian
blood deserve brief
menti >n, though their
— significance is as yet

Ml.-CorpoBclts from haman subject (JJnke). -^-tA-- of mUch dis-
A few coloSeM cotpnicles we teen among the col- a mailer oi mucii uis-
oted dinks, which ate many of them arranged In <^

'*^''*- 1. Theblood-plates

(plaques, lutmatobkuts, third element), very smaU, colorless,
Wconcave disks, which are deposited in great numbers on any
thread or similar foreign body introduced mtx> the circuhition,
and rapidly break up when blood is shed.

2 On a slide of blood that has been prepared for some Uttle
time, aggregations of very minu'^ granules (elementary »mn-
«fc») ^y^ seen. These are supposed to represent the dism-
tesrrating protoplasm of the corpuscles. .

The pakor colorless corpuscle are very few in number m
mammals compared with the red, thew being on the average
only about 1 in 400 to 600, though they become much more
numerous after a meal. They are granular in appearance, and
possess one or more nuclei, which are not, however, readily

Flo.

00,000 less for
),000,000 in a
•ages only are
of which will
led. The size
ble — a matter
consideration,
is seen to owe
d goes, almost
Corpuscles
een singly are
f the deep red,
ir, of the blood
lole, but rather
(widi red, the
rarying some-
ith the class of
B from which
cimen has been

tain other wior-
lical elements
in mammalian
deserve brief
ax, though their
sance is as yet
er of much dis-

rhe blood-plates
imallf colorless,
lumbers on any
the circulation,

1 for some little
ementary gran-
eaent the disin-

ir in number in
on the average
me much more

appearance,

and

lowever, readily

THE BLOOD.

167

seen in all cases without the use of reagents. They are charac-
terized by greater size, a globular form, the lack of pigmei t,

*'V

Fin. 148.— Blood-plaqneii and their derivatives (Landolt, after Blzzozero and Laker).
1, red blood-corpuacles on the flat; S, from the tide; 8, unchanged blood-plaques;
4, lymph-corpuscle surrounded with blood-plaques; 6, blood-plaques variously
altered; 8, lymph-corpuscle with two masses of fused blood-plaques and threads
of flbrin; 7, group of blood-plaques "fused or nm together; 8, similar small mass
of partially dissolved blood-plaques with fibrils of flbrin.

and the tendency to amoeboid movements, which latter may be
exaggerated in disordered conditions of the blood, or when the
blood is withdrawn and observed under artificial conditions.
It will be understood that these cells (leucocytes) are not con-
fined to the blood, but abound in lymph and other fluids.
They are the representatives of the primitive cells of the em-
bryo, as is shown by their tendency (like ova) to throw out
processes, develop into higher forms, etc. In behavior they
strongly suggest Amoeba and kindred forms.

We may, then, say that in all invertebrates the blood, when
it exists, consists of a plasma (liquor sanguinis), in which float
the cellular elements which are colorless ; and that in verte-
brates in addition there are colored cells which are always nu-
cleated at some period of their existence. The colorless celki
are globular masses of protoplasm, containing one or more
nuclei, and with the general character of amoeboid organisms.

168

COMPARATIVE PHYSIOLOGY.

The History of the Blood-Cellb.

We have already seen that the bl« od and the vessels in
which it flows have a common origin in the mesoblastic cells of
the embryo chick ; the same applies to mammals and lower
groups. The main facts may be grouped under two head-
ings : 1. Development of the blood-corpuscles during embry-
onic Kfe. 2. Development of the corpuscles in post-embryonic
life. The origin and fate of the corpuscles, especially of the
colored variety, have been the subject of much discussion.

* The best established
facts are stated in the
summary below, while
they are illustrated by
the accompanying fig-
ures.

The colorless cells
of the blood first arise
as migrated undifPeren-
tiated remnants of the
early embryonic cell
colonies. That they re-
main such is seen by
their physiological be-
havior, to be cqpsidered
a little later. Afterward
they are chiefly pro-
duced from a peculiar

Fig. l«.-8nTf«ce view from below of a «niallppr- f^j.^ ^f connective tis-

tion of potterior end of pellucid area of a chicV *"* "* "^ w.i**oi,i» ,^ „

of thirty-«ixhourB,l x 400 (Foster and Balfour), gue knOWn aS leucocy-
6. c, blood-corpuaclea ; o, nuclei, wlilch iubee- . , u- v. •

qnently become nuclei of cells forming walls of tenic, and wnicn 18

^^STnuiie'l^^tkfCS'u^l^H.Sr*'""' gathered into organs

(lymphatic glands), the
chief function of which is to produce these cells, though this
tisF.ue is rather widely distributed in the ma mm al ian body in
other forms than these.

Snnuiuury. — ^The student may, with considerable certainty,
consider tlid colorless corpuscle of the blood as the most primi-
tive; the red, derived either from the white or some form of
more specialized cell ; the nucleated, as the earlier and more
youthful form of the colored corpuscle, which may in some
groups of vei<tebrates be replaced by a more specialized (or de-

tie vessels in
tlastic cells of
Is and lower
jr two head-
irin^ embry-
«t-embryonic
scially of the
h discussion,
established
stated in the
below, while
illustrated by
ipanying &g-

olorless cells
K)d first arise
id undifPeren-
inants of the
ibryonic cell
That they re-
li is seen by
siological be-
be cqpsidered
sr. Afterward

chiefly pro-
tm a peculiar
onnective tis-
n as leucocy-
d which is

into organs
ic glands), the
8, though this
lalian body in

Me certainty,
le most primi-
some form of
lier and more
may in some
sializied (or de-

THE BLOOD.

159

graded ?) non-nucleated form mostly derived directly from the
former ; that in the first instance ^e blood-vessels and blood

c I

Fio. 144.

Via. 146.

Pia. 147.

Fie.l4&

Fio. 144.— Cell elements of red marrow, a, large grannlar marrow cells; b, smaller,
more vesicniar cells; e. free nuclei, or small lymphoid cells, some of which may
be even snrronnded with a delicate rim of protoplasm; d, nucleated red corpuccles
of the bone marrow.

?io. 146.— Nucleated red cells of marrow, illustrating mode of development into the
ordinary non-nucleated red corpuscles, a, common forms of the colored nucleated
cells of red marrow; A, 1, 8, S, gradual diHappearance of the nadens: e, large non-
nucleated red corpuscle resembling 8 and 8 of A in all respects save in the absence
of any trace of nucleus.

Fig. 146.— Nucleated red corpuscles, illustrating the migration of thenncleus from the
cell, a process not nnfreqnently seen in the red marrow.

Fiu. 147.— Blood of human embryo of four months, a, 1, 8, 8, 4r, nucleated red corpus-
cles. In 4 the same grannlar disintegrated appearance or the nucleus as is noted
in marrow cells, b, f, microcyte; 8, megalocyte; 8, ordinary red corpuscle.

Fio. 148.— From spleen. 1, blood-plsiques, colorless and varjrinK a little in size; 8, two
microcytes of a deep-red color; 8, two ordinair red corpuscles; 4,- a solid, translu-
cent, lymphoid cell or free nucleus. (Figs. 144-148 after Osier.)

arise simultaneously in the meeoblastic embryonic tissue ; that
such an organ may exist after birth, either normally in some
mammals or under unusual functional need ; that the red mar-
row is the chief birthplace of colored cells in adult life ; that

160

COMPARATIVE PHYSIOLOGY.

the spleen, liver, lymphatic glands, and other tissues of similar
structure contribute in a less degree to the development of the
red corpuscles ; and that the last mentioned organs are the chief
producers of the colorless amoeboid blood-cells.

Finally, it is well to remember that Nature's resources in
this, as in many other cases, are numerous, and that her mode
of procedure is not invariable ; and that, if one road to an end
is blocked, another is taken.

The Dedine and Death of the Blood*Celli.— The blood cor-
puscles, like other cells, have a limited duration, with the usual
chai>ters in a biological history of rise, maturity, and decay.
There is reason to believe that the red cells do not live longer
than a few weeks at most. The red cells, in various degrees of
disorganization, have been seen within the white cells (phagocy-
tes), and the related cells of the spleen, liver, bone-marrow, etc.
In fact, these cells, by virtue of retained ancestral (amoeboid)
qualities, have devoured the weakened, dying red cells. It seems
to be a case of survival of the fittest. It is further known that
abundance of pigment containing iron is found in both spleen
and liver ; and there seems to be no good reason for doubting
that the various pigments of the secretions of the body (urine,
bile, etc.) are derived from the universal pigment of the blood.
These coloring matters, then, are to be regarded as the excreta
in the first instance of cells behaving like amoeboids, and later
as the elaborations of certain others in the kidney and else-
where, the special function of which is to get rid of waste prod-
ucts. The birth-rate and the death-rate of the blood-cells must
be in close relation to each other iu health ; and some of the
gravest disturbances arise from decided changes in the normal
proportions of the cells (ancBmia, leucocythemia).

Both the red and white corpuscles show, like all other cells
of the organism, alterations corresponding to changes in the
surrounding conditions. The blood may be withdrawn and its
cells more readily observed than thone of most tissued ; so that
the study of the influence of tempeiBture, feeding of the leuco-
cytes, and the action of reagents in both classes of cells is both
of practical importaroe and theoretic interest, and wiil well re-
l)ay the student fc ' ae outlay in time and labor, if Attortion is
directed chiefly to the results and the lessons they convey, and
not, as too commonly happens, principally to the methods of
maniptilation.

The Ohemioal Cmnposition of the Blood.— Blood has a decide \

lues of similar
opment of the
8 are the chief

s resources in
hat her mode
road to an end

rhe blood cor-
with the usual
ty, and decay,
lot live lonjgfer
ious degrees of
jells (phagocy-
e-marrow, etc.
:ral (amoeboid)
sells. It seems
er known that
in both spleen
n for doubting
le body {urine,
i of the blood,
as the excreta
x)ids, and later
iney and else-
of waste prod-
[ood-cells must
ad some of the
in the normal

3 all other cells
changes in the
bdrawn and its
issuciii ; so that
ig of the leuco-
of cells is both
ad will well re-
•, if Attortion is

ey convey,

and

■h» methods of

)d has a decide \

THE BLOOD. iqi

but faint alkaline reaction, owing chiefly to the presence of
sodium salts, a saline taste, and a faint odor characteristic of
the animal group to which it belongs, owing probably to volatile
fatty acids. The specific gravity of human blood varies between
1045 and 1075, with a mean of 1066 ; the specific gravity of the
corpuscles being about 1105 and of the plasma 1027. This dif-
ference explains the sinking of the corpuscles in blood with-
drawn from the vessels and kept quiet. Much the same diffi-
culties are encountered in attempts at rhe exact determination
of the chemical composition of the blood, as in the case of other
living tissues. Plasma alters its physical and its chemical com-
position, to what extent is not exactly known, when removed
from the body.

Comporition of Senun.— The fluid remaining after coagula-
tion of the blood can, of course, be examined chemically with
considerable thoroughness and confidence.

By far the greater part of serum consists of water; thus, it
has been estimated that of 100 parts the following statement will
represent fairly well the proportional composition:

Water go parts;

Proteids 8 to 9 "

Salines, fats, and extractives (small in
quantity and not readily obtained
free) ito2 parts.

The proteids are made up * two substances which can be
distinguished by solubility, temperature at which coagulation
occurs, etc., known as paraglobulin and aerum-albumen, and
which may exist in equal amoimt.

It is not possible, of course, to say whether these substances
exist as such in the living blood-plasma or not.

The fata are very variable in quantity in serum, depend-
ing on a corresponding variability in the plasma, in which
they would be naturally found in graatest abundance after a
meal. They exist as neutral stearin^ palmitiu, olein, and as
soaps.

The principal extractives lound are urea, creatin and allied
bodies, sugar, and lactic acid. Serum in most animals contains
more of sodium salts than the corpuscles, while the laiter in
man and some other mammals contain a preponderating quan-
tity of potasnum compounds.

The principal salts of serum are sodium chloride, sodium bi-
carbonate, sodium sulphate and phosphate; in smaller quantity,

iteMtmMMi

169

COMPARATIVE PHYSIOLOGY.

also phosphate of calcium and xna^esium, with rather more
of potassium chloride.

It is highly probable that this proportion also represents
moderately well the composition of plasma, which is, of course,
from a physiological point of view, the important matter.

The Oompoiiti<m of the Cerpmolei.— Taken together, the dif
ferent forms of blood-cells make up from one third to nearly
one half the weight of the blood, and of this the red corpuscles
may be considered as constituting nearly the whole.

The colorless cells are known to contain fats and glycogen,
which, with salts, we may believe exist in the living cells, and,
in addition to the proteids, into which protoplasm resolves it-
self upon the disorganization that constitutes its dying, lecithin,
protagon, and other extractives.

The prominent chemical fact connected with the red corpus-
cles is their being composed in great part of a peculiar colored
proteid compound containing iron.

This will be fully considered later: but, in the mean time
we may state that the hemoglobin is itself infiltrated into the
meshes or framework (atroma) of the corpuucle, which latter
seems to be composed of a member of the globulin class, so well
characterized by solubility in weak saline solutions.

The following tabular statement represents the relative pro-
portions in 100 parts of the dried organic matter of the red cor-
puscles:

Haemoglobin 90*64

Proteids 8*67

Lecithin 0*54

Cholesterin 0*26

10000
The quantity of salts is very small, less than one per cent
(inorganic).

So much for the results of our analyses ; but when we con-
sider the part the blood plays in the economy of the body, it
must appear that, since the life-work of every cell expresses it-
self through this fluid, both as to what it removes and what it
adds, the blood can not for any two successive moments be of
precisely the same composition ; yet the departures from a nor-
mal standard must be kept within very narrow limits, other-
wise derangement or possibly death results. We think that,
before we have concluded the study of the various oiyans of

^^■'i'&ii^

t rather more

Iso represents
b is, of course,
\ matter.
Ifether, the dif
iird to nearly
red corpuscles
)le.

and glycogen,
ring cells, and,
im resolves it-
lying, lecithin,

the red corpus-
eculiar colored

^e mean time
trated into the
B, which latter
in class, so well
ms.

be relative pro-
of the red cor-

... 90-54
8-67
0-54
0-25

10000
m one per cent

it when we con-
of the body, it
jell expresses it-
ives and what it
moments be of
ires from a nor-
)w limits, other-
We think that,
rious organs of

THE BLOOD. les

the body, it will appear to the student, as it does to the writer,
that it is highly probable that there are great numbers of com-
pounds in the blood, either of a character unknown as yet to
our chemistry, or in such small quantity that they elude detec-
tion by our methods; and we may add that we believe the same
holds for all the fluids of the boay. The complexity of vital
processes is great beyond our comprehension.

It must be especially borne in mind that all the pabulum
for every cell, however varied its needs, can be derived from
the blood alone; or, as we shall show presently, strictly speak-
ing from the lymph, a sort of middle-man between the blood
and the tissues.

Th« Quantity and the Diitribation of the Blood.— The rela-
tive quantities of blood in different parts of the body have been
estimated to be as follows :

Liver one fourth.

Skeletal muscles " "

Heart, lungs, large arteries, and veins. " "

Other stioictures " "

The significance of this distribution will appear later.
The Goagolation of the Blood.— When blood is removed
from its accustomed channels, it undergoes a marked chemical
and physical change, termed clotting or coagulation. In the
case of most vertebrates, almost as soon as the blood leaves the
vessels it begins to thicken, and gradually acquires a consistence
that may be compared to that of jelly, so that it can no longer
be poured from the containing vessel. Though some have rec«
ognized different stages as distinct, and named them, we think
that an unprejudiced observer might fail to see that there were
any well-marked appearances occurring invariably at the same
moment, or with resting stages in the process, as with the devel-
opment of ova.

After coagulation has reduced the blood to a condition in
which it is no longer diffluent, minute drops of a thin fluid
gradually show themselves, exuding from the main mass, faintly
colored, but never red, if the vessel in which 4he clot has
formed has been kept quiet so that the red corpuscles have not
been disturbed; and later it may be noticed tt»at, tho main mass
is beginning to sink in the center {cupping) ; and in the blood
of certain animals, as the horse, which clots slowly, the upper
part of the coagulum {crasaamentum) appears of a lighter
color, owing, as microscopic examination shows, to the relative

104

COMPARATIVE PHYSIOLOGY.

?■

fewnesH of red corpuKcles. ThiH \n the butfy-coat, 6r, aa it oc-
curs ill intlammatory conditiuiiH of the blood, wan termed by
older writers, tlie oruata phlogiatica. It is to be distinguished
from the lighter red of certain iiartA of a clot, often the I'esult of
greater exposure to the air and more complete oxidation in con-
sequence. The white blood-cells, being lighter than the red, are
also more abundant in the upper part of the clot (buffy-coat).
If the coagulation of a drop of blood withdrawn from one's
own finger be watched under the microscope, the red corpuscles
may be seen to run into heaps, like rows of coins lying against
each other (rouleatix, Fig. 141), and threads of the greatest
fineness are observed to radiate throughout the mass, gradually
increasing in number, and, at last, including the whole in a
meshwork which slowly contracts. It is the formation of this
fibrin which is the essential factor in clotting; the inclusion of
the blofxl-cells and the extrusion of the serum naturally result-
ing from its formation and contraction.

Tlie great mass of every clot consists, however, of corpuscles;
the quantity of fibrin, though variable, not amounting to more
usually than about '2 per cent in mammials. The formation of
the clot does not occupy more than a few minutes (two to seven)
in most mammals, including man, but its contraction lasts a
very considerable time, so that serum may continue to exude
from the clot for hours. It is thus seen that, instead of the
plasma and corpuscles of the blood as it exists within the living
body, coagulation has resulted in the formation of two new
products— serum and fibrin — ditTering both physically and
chemically. These facts may be put in tabular form thus:

Blood as it flows \ Liquor sanguinis (plasma),
in the vessels. } Corpuscles.

Blood after co-
agulation.

{ Coagulum * ^""■■"'

I Serum.

) Corpuflolwk

As fibrin may be seen to arise in the form of threads, under
the microscope, in coagulating blood, and since no trace of it in
any form has been detected in the plasma, and the process can
be accounted for otherwise, it seems unjustifiable to assume that
fibrin exists preformed in the blood, or arises in axtf way prior
to actual coagulation.

Fibrin belongs to the class of bodies known as proteids, and
can be distinguished from the other subdivisions of this group
of substances by certain chemical as well as physical character-

THE DL(K)D.

166

, 6r, as It oc-
» termed by
listinguished
the rasult of
iation iu cou-
n the red, are
ihuffy-coat).
I from one's
ed corpuscles
lying against
the greatest
IBS, gradually
} whole in a
nation of this
B inclusion of
urally resu^t-

of corpuscles;
nting to more
) formation of
[two to seven)
action lasts a
inue to exude
instead of the
hin the living
tt of two new
hysically and
}rm thus:

na).

threads, under
lo trace of it in
,he process can
I to assume that
any way prior

IS proteids, and
IS of this group
sical character-

istics. It is insoluble in water and in solutionH of sodium chlo-
ride; insoluble in hydrochloric acid, though it swells in this
menstruum.

It may be whipped out from the freshly shed blood by a
bundle of twigs, wires, or otiior similar arrangement presenting
a considerable extent of 'surface ; and when washed free from
red blood-cells presents itself us a white, stringy, tough sub-
stance, admirably adapted to retain anything entangled in its
meshes. If fibrin does not exist in the plasma, or does not arise
directly as such in the clot, it must have some antecedents al-
ready existing as its inmiediate factors in the plasma, either
before rr after it is shed.

The principal theories of coagulation are these : 1. Coagu-
lation results from the action of a fibrin-ferment on flbrinogen
and paraglobulin. 2. Coagulation results from the action of
a fibrin-ferment on flbrinogen alone. Fibrinogen and para-
globulin (see sections on " The Chemistry of the Animal Body ")
are proteids originating from the plasma, during clotting in all
probability. Fibrin-ferment loses its properties on boiling, and
a very small quantity suffices in most cases to induce the i-esult.
For these and other reasons' this agent has been classed among
bodies known as unorganized ferments, which are distinguished
by the following properties :

They exert their influence only under well-deflned circum-
stances, among which is a certain narrow range of tempera-
ture, about blood-heat being most favorable for their action.
They do not seem to enter themselves into thti resulting prod
uct, but act from without, as it were (catalytic action), her.oe a
very small quantity suffices to effect the result. In all cases
they are destroyed by boiling, though they bear exposure for
a limited period to a freezing temperature.

From observations, microscopic and other, it has been con-
cluded that the corpuscles play an important part in coagula-
tion by furnishing the fib* ':: -ferment ; but the greatest diver-
sity of opinion prevaiL as to which one of the morphological
elements of the blood furnishes the ferment, for each one of
them has been advocated as the exclusive source of this fer-
ment by different observers.

We do not favor the current theories of the coagulation of
the blood. We would explain the whole matter somewhat thus :
What the blood is in chemical composition and other properties
from moment to moment is the result of the complicated inter-

166

COMPARATIVE PHYSIOLOGY.

aotion of all the various cells uud tiuuea of the body. Any one
of these, departing from its normal behavior, at onco affects the
blood ; but health implies a constant effort toward a certain
equilibrium, never actually reached but always being striven
after by the whole organism. The blood can no more maintain
its vital equilibrium, or exist an a living tissue out of its usiul
environment, than any other tissue. But the exact circum-
stances under which it may be<;<>iiie disorganized, or die, are
legion ; hence, it is not likely that the blood always clots in
the same way in all groups of animals, or even in the same
):!7«up. The normal disorganization or death of tlie tissue re-
sults in clotting ; but there may be death without clotting, as
when the blood is frozen, in various diseases, etc.

To say that fibrin is formed during coagulation expresses in
a crude way a certain fact, or rather the resultant of many
facts. To explain ; When gunpowder and certain other ex-
plosives are decomposed, the result is the production of cer-
tain gases. If we knew these gases and their mode of cor'
position but in the vaguest way, we should be in much i
same position as we are in regard to the cogulatiou of the
blood.

There is no difficulty in understanding why the blood does
not clot in the vessels after death so long as they live, nor why
it does coagulate upon foreign bodies introduced into the blood-
stream. So long as it exists under the very conditions under
which it began its being, there is no reason why the blood
should become disorganized (clot). It would be marvelous if
it did clot, for then we could not understand how it could ever
have been developed as a tissue at all. It is just as reasonable
to ask. Why does not a muscle-cell become rigid (clot) in the
body during lifef

Probably in no field in physiology has so much work been
done with so little profit as in the one we are now discussing ;
and, as we venture to think, owing to a misconception of the real
nature of the problem. We can understand the practical im-
portance of determining what circumstances favor coagulation
or retard it, both within the vessels and without them ; but
from a theoretical point of view the subject has been exalted
out of all proportion to its importance.

Coagulation is favored by gentle movement, contact with
foreign bodies, a temperature of about 38° to 40° C, addi-
tion of a small quantity of water, free access of oxygen, etc.

■"mm

TIIR BLOOD.

167

ly. Any one
CO affeots the
urd a certain
jeing striven
ore maintain
t of it« usual
xact circum-
I, or die, are
rays clots in
in the same
the tissue re-
it clotting, as

1 expresses in
ant of many
tin other ex-
iction of cer-
node of con'
in much
latiou of the

le hlood does
live, nor why
nto the blood-
iditions under
hy the blood
marvelous if
it could ever
as reasonable
i (clot) in the

ich work been
iw discussing ;
ion of the real
practical im-
[>r coagulation
>ut them ; but
I been exalted

,, contact with

40° C, addi-

>f oxygen, etc.

The pmoem is retarded by u low temperature, addition of
abuiKlunco of neutral Baits, extract of the mouth of the leech
|)eptone, much water, alkalies, and many other 8ubstauce>.
The excess of carbonic anhydride and diminution of ouyaen
seem to be the cause of the slower cootj^lation of venous i li}od, ^
hence the blood long remains Huid in animals asphyxiated. A
little refl)H;tion suffices to explain the action of most of the fac-
tors enumerated. Any cause which hastens the disintegration
of the blood-cells must accelerate coagulation ; chemical changes
underlie the changes in this as in all other cases of vital action.
Slowing of the blood-stream to any appreciable extent likewise
favors clotting, hence the explanation of the success of the
treatment of aneurisms by pressure. It is plain that in all
such cases the normal re'utions botween the blood and the tis-
sues are disturbed, and, whtiU this reaches a certain point,
death (coagulation) ei>, - s, as with any other tissue.

Clinioal and PathologioaL— The changes in the blood that
characterize certain abnormal states are highly instructive. If
blood from an animal be injected into the veins of one of an-
other species, the death of the latter often results, owing to non-
adaptation of the blood already in the vessels, and to the tissues
of the creature generally. The corpuscles break up — the change
of conditions has been too great. Deficiency in the quantity of
the blood as a whole {oligcemia) causes serious change in the
functions of the body ; but that a haemorrhage of considerable
extent can be so quickly recovered from speaks much for the
recuperative power of the blood-forming tissues. Various kinds
of disturbances in these blood-forming organs result in either
deficiency or excess of the blood-cells, and in some cases the
appearance of unxisual forms of corpuscles.

Ancemia may arise from a deficiency either in the numbers
or the qxiality of the red cells ; they may be too few, deficient
in size, or lacking in the normal quantity of hsempglobin. In
one form {pemicioua ancetnta), which often proves fatal in
man a variety of forms in the red blood-cells may appear in the
blood-stream; some may be very small, some larger than usual,
others nucleated, etc. Again, the white cells may be so multi-
plied that the blood may bear in extreme cases a resemblance
to milk.

In these cases there has been found associated an uniisual
condition of the bone-marrow, the lymphatic glands, the spleen,
and, some have thought, of oUier parts.

w<si*^^

mmum

108

COMPARATIVE PnYSlOLOOY.

The excPMivo uotion nf UieM) orfrana roMiltii in the pmtluction
and diHcliarKo into Uio hloocl-current of cellii timt »ro ininiaturt*
(uid onibryunic in character. This Menu to uh an oxantple of

««>

<S>^

^^-^ g^<a) *^ ^

riu. lao.

Viu. 14U,

Kiu. isa.

Fill, 140.— OutllnM of red conniMlo* In a cmc of profound nnremla. t, 1, normal cor-
puuclci: 8, large red corimKcle— megalocyte; 8,8, very Irregular fohna— polkllo-
cytea; 4, very itmall, dci'iirwl corpuicloa— ralcrocytoi. .^,„ ^. ,

Flo. ISO.— Origin of mlcrocytea from red corpuaclea by procMsof budding and flMlon.
HiKJclincn from red marrow. , ,

Fm. 161.— Nucleated rod hlood-corpnaclea from blood In caao of leoksmin.

Fio. IBtl.— C'orpnicle* containing red blood-corpiiaclea. 1, from blood of child at term;
si, from liltxHl of a loaksmlc patk<nt.

Fiu. lS8.—n. 1.8,8, apleen-cclli containing rod blood-corpuacleo. A, from marrow; 1,
cell c'jiilaUiing nine rod corpuKle«; iT cell with reddish granular pigment; 8, fimi-
form cell cnnUiining a alngfo red cori)urele. e, connectlve-tlMue corpuscle from
subcutaneous tisane of young rat, shuwlng the Intracellular development of red
blood-corpuscles. (Figs. 149-163, after Usiur.)

a reversion to an earlier condition. It is instructive also in that
the facts point to a possible seat of origin of the cells in the
adult, and, taken in connection with other facts, we may say, to
their normal source. Tliese blood-producing organs, having
too much to do in disease, do their work badly — it is incom-
plete.

Although the evidence, from experiment, to show that the

n profluclion

tv initiiaturt*

oxainple of

From marrow; 1,
pigment; 8, fiml-
I corpuicle from
elopDiuntof rud

I also in that
cells in the
) may say, to
;ans, having
-it ia incom-

ow that the

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THE BLOOD.

169

nervous system in mammals, and especially in man, has an in-
fluence over the formation and fate of the blood generally, is
scanty, there can be little doubt that such is the case, when we
take into ttccount instances that frequently fall under the notice
of physicians. Certain forms of anaemia have followed so di-
rectly upon emotional shocks, excessive mental work and worry,
as to leave no uncertainty of a connection between these and
the changes in the blood ; and the former must, of course, have
acted chiefly if not solely through the nervous system.

It will thus be apparent that the facts of disease are in har-
mony with the views we have been enforcing in regard to the
blood, which we may now briefly recapitulate.

Bmnmary. — Blood may be regarded as a tissue, with a fluid
matrix, in which float cell-contents. Like other tissues, it has
its phases of development, including origin, maturity, and
death. The colorless cells of the blood may be considered as
original undifferentiated embryo cells, which retain their primi-
tive character ; the non-nucleated red cells of the adult are the
mature form of nucleated cells that in the first instance are
colorless, and arise from a variety of tissues, and which in
certain diseases do not matyre, but remain, as they originally
were at first, nucleated. When the red cells are no longer
fitted to discharge their functions, they are in some instances
taken up by amoeboid organisms (cells) of the spleen, liver,
etc.

The chief function of the red corpuscles is to convey oxy-
gen ; of the white, to develop as requii«d into some more differ-
entiated form of tissue, act as porters of food-material, and
probably to take up the work of many other kinds of cells
when the needs of the economy demand it. The fluid matrix
or plasma furnishes the lymph by which the tissues are directly
nourished, and serves as a means of transport for the cells of the
blood.

The chemical composition of the blood is highly complex,
in accordance with the function it discharges as the reservoir
whence the varied needs of the tissues are supplied ; and the
immediate receptacle (together with the lymph) of the entire
waste of the body ; but the greater number of substances exist
in very minute quantities. The blood must be maintained of
a certain composition, varying only within narrow limits, in
order that neither the other tissues nor itself may suffer.

The normal disorganization of the blood results in coagula-

170

COMPARATIVE PHYSIOLOGY.

tion, by which a substance, proteid in nature, known as fibrin,
is formed, the antecedents of which are probably very variable
throughout the animal kingdom, and are likely so even in the
same group of animals, under different circumstances ; and a
substance abounding in proteids (as does also plasma), known
as serum, squeezed from the clot by the contracting fibrin. It
represents the altered plasma.

Certain well-known inorganic salts enter into the composi-
tion of the blood— both plasma and corpuscles— but the princi-
pal constituent of the red corpuscles is a pigmented, ferrugi-
nous proteid capable of crystallization, termed haemoglobin. It
is respiratory in function.

lown as fibrin,
y very variable
so even in the
stances ; and a
ilasma), known
sting fibrin. It

bo the composi-
-but the princi-
aented, ferrugi-
aemoglobin. It

THE CONTRACTILE TISSUES.

That contractility, which is a fundamental property in some
d^iree of all protoplasm, becoming pronounced and definite,
giving rise to movements the character of which can be pre-
dicted with certainty once the form of the tissue is known, finds
its highest manifestation in muscular tissue.

Very briefly, this tissue is made up of cells which may be
either elongated, fusiform, nucleated, finally striated lengthwise,

Fio. 154. Fio. ISB.

Fib. IM.— MuBcntar flben ttom the arinarr bladder of the hnman labjeet. 1 x SOO
(Sappoy.) 1, 1, 1, naclei; 8.2,8, boiden of lome of the flben; S,8, iMlated flben;
4,4, two flben Joined together at B.

Fw. 156.— Mnaenlar flben from the aorta of the calf. 1 » 800. (Sappey.) 1,1, flben
Joined with each other; 8, 8, 8, isolated flben.

but non-striped transversely, united by a homogeneous cement
substance, the whole constituting non-striped or involuntary

MlaMKKRWHitsi^^ins^fMrr:''

172

COMPARATIVE PHYSIOLOGY.

muscle ; or, long nucleate<l fibers transversely striped, covered
with an elastic sheath of extreme thinness, bound together
into small bundles by a delicate connective tissue, these again
into larger ones, till what is commonly known as a "muscle "
is formed. This, in the higher vertebrates, ends in tough, ine-
lastic extremities suitable for attachment to the levers it may be
required to move (bones). CJertain of the tissues will Iks found
briefly described in the sections preceding "Locomotion."

Comparative.— The lowest animal forms possess the power
of movement, which, as we have seen in Amoeba, is a result
rather of a groping after food ; and takes place in a direction
it is impossible to predict, though no doubt regulated by laws
definite enough, if our knowledge were equal to the task of de-
fining them.

Those ciliary movements among the infusorians, connected
with locomotion and the capture of food, are examples of a
protoplasmic rhythm of wonderful beauty and simplicity.

Muscular tissue proper first appears in the Coelenterata, but
not as a wholly independent tissue in all cases. In many
coelenterates cells exist, the lower part of which alone forms a
delicate muscular fiber, while the superficial portion (myoblaat),
composing the body of the cell, may be ciliated and is not con-
tractile in any special sense. The non-striped muscle-cells are

most abundant among the in-
vertebrates, though found in
the viscera and a few other
parts of vertebrates. This
form is plainly the simpler
and more primitive. The
^ voliratary muscles are of the

Fiu. is6.-MyobiMto of ajeiiyfl«h,thejft- gtviped variety in articulates
data Aunlia (Claus). /^ ,, . _i v *

and some other mvertebrate

groups and in all vertebrates ; and there seems to be some re-
lation between the size of the muscle-fiber and the functional
power of the tissue— the finer they are and the better supplied
with blood, two constant relations, the greater the contrac-
tility.

Whether a single smooth muscle-cell, a striped, fiber (celt),
or a collection of the latter {muscle) be observed the invariable
result of contraction is a change of shape which is perfectly
definite, the long diameter of the cell or muscle becoming
shorter, and the short diameter longer.

THE CONTRACTILB TISSUES.

173

striped, covere<1
30uiid together
lue, these again
as a " muscle "
8 in tough, ine-
even it may be
s will l>e found
omotion."

388 the power
oeba, is a result
e in a direction
fulated by laws
3 the task of de-

rians, connected
I examples of a
limplicity.
'celenterata, but
ises. In many
h alone forms a
tion (myoblast),
and is not con-
muscle-cells are
nt among the in-
hough foimd in
ind a few other
rtebrates. This
uly the simpler
primitive. The
uscles are of the
sty in articulates
her invertebrate
i to be some re-
id the functional
« better supplied
ter the contrac-

riped. fiber (oelZ),
ed the invariable
hich is perfectly
auscle becoming

Oiliary Morrauntl. — This subject has been already con-
sidered briefly in connection with some of the lower forms of
life presented for study.

It is to be noted that there is a gradual replacement of this
form of action by tliat of muscle as we ascend the animal
scale ; it is, however, retained even in the highest animals in
the discharge of functions analogous to those it fulfills in the
invertebrates.

Thus, ia Vorticella, we saw that the ciliary movements of
the peristome CAUsed currents that carried in all sorts of parti-
cles, including food. In a creature so high in the scale as the
frog we find the alimentary tract ciliated ; and in man himself
a portion of the respiratory tract is provided with ciliated cells
concerned with assisting gaseous interahange, a matter of the
highest importance to the well-being of the mammal. As be-
fore indicated, ciliated cells are found in the female generative
organs, where they play a part already explained.

It is a matter of no little significance from au evolutionary
point of view, that cil-
iated cells are more
widely distributed in
the foetus than in the
fully developed ani-
mal.

As would be ex-
pected the movements
of cilia are affected by
a variety of circum-
stances and reagents ;
thus, they are quick-
ened by bile, iicids,
alkalies, alcohol, ele-
vation of temperature
up to about 40° C,
etc. ; retarded by cold,
carbonic anhydride,
ether, chloroform, etc.

In some cases their
action may be arrested
and re-established by
treatment with rea-
gents, or it may recommence without such assistance. All this

Fiu. 1&7.— Nodes of Ranvler and llnca of Fromann
(Kanvier). A. Intercostal nerve of the mouse,
treated with silver nitrate. B. McrvtvUber from
the sciatic nerve of a full-grown rahbit. A, node
of Ranvicr ; if, medullary substance rendtaed
transparent by the action of gWeerin; CY, axis-
cylinder presenting the lines of Fromann, which

erv distinct near the node. The lines are less

edat ac"

nuirke

i distance from the node.

174

COMPARATIVE PUYSIOLOUV.

«_:

fioctns to point to oiliary aetion •■ tellinir under the law* gov-
erning the movementB of protoplasm m general. It is impor-
tant to bear in mind that ciliary action may go on in the cella
of a tiMsue completely isolated from the animal to which it be-
longs, and though inUuenced, as just explained, by the sur-
roundings, that the movement is essentially automatic, that is,
independent of any special stimulus, in which respect it differs
a good deal from voluntary muscle, which usually, if not al-
ways, contracts only when stimulated.

The lines along which the evolution of the contractile tissues
has proceeded from the indefinite outflow ings and withdrawals

of the substance of
Amoeba up to the
highly specialized
movements of a
striped muscle-cell
are not all clearly
marked out ; but
even the few facts
mentioned above
suffice to show gra-
dation, intermedi-
ate forms. A sim-
ilar law is involved

Flu. 168.— Modeof tormInHUonorUieuiou>r-nervv»(Fllut, in the musCular
after Rouget). A. Primitive fMcleuliu of the tbyro- ...

byoid mniele of the human lulijuct, and it* nerve- contractility mani-

tnbe : 1, J, primltlvu miiDCuiar raaclcuius ; >, nerve- *^i-j u„ --ii„ „:»u

tnbo ; 8, m^ullary inlMtanco of tlie tube, whicli U fested by CeilS With

■cen extending to the terminal plate, where it diiap- othAp f iin<>(inn«

pean ; 4, terminal plate iltnaterf beneath the aarco^ ""'®'' luncuons.

lemma— tliat la to lajr, between it and the elementary Xhe automatic (self-
flbrillm; 6, i, larcolemma. B. Primitive faaciculns of . . . i • j

the InteiGostal muMle of the llaaid. In which a nerve- originated, inde-

tubo terminate*: 1,1, iheath of the nerve-tnbe: S, _-„j„^* i..— ..^i^ -»#

nucleui of the sheath ; S. 3, larcolemnw becoming pendent largely OI

continuous with the sheath ; 4, medullary snbatauce - Btimiilna'k vhtriVim

of the nerve-tube, coaning abruptly at the site of the * BWmuiUS; rnyinm

terminal phite; 5, fi, terminal plate: e. 0, nnclci of the suinrestive of cUia-
< plate: 7, 7. granular substance which forms the princi- ^^

pal element of the terminal plate and which b con- ry movement, more

tinuous with the axis cylinder : 8, 8, niulnlation* of . - . .^ .•• _

the sarcolemma reproducing those of the flbrilhe; manitest m tne

»,»,nucieiofthesarcoiemma. earlier developed

smooth muscle than in the voluntary striped muscle of higher
vertebrates, indicating further by the regularity .with which
certain organs act in which this smooth muscular tissue is pre-
dominant, a relationship to ciliary movement something in
common as to orig^ — in a word, an evolution. And if this be
borne in mind, we believe many facts will appear in a new

vt the laws gov-
1. It is impor-
on in the cells
to which it he-
ed, hy the sur-
itomatic, that is,
espect it differs
uidly, if not al-

mtractile tissues
ind withdrawals
the substance of
loeba up to the
;hly specialised
vements of a
iped muscleKwll
I not all clearly
krked out ; but
m the few facts
mtioned above
ilce to show gra-
bion, intermedi-
> forms. A sim-
r law is involved
the muscular
ntractility mani-
ited by cells with
ler functions.
le automatic (self -
iginated, inde-
ndent largely of
itimulus) rhythm
ggestive of cilia-
movement, more
anifest in the
rlier developed
muscle of highei^
wity .with which
sulcur tissue is pre-
nt something in
1. And if this be
appear in a nnw

HiMipiWii; i|iiriMr

THE CONTRACTILE TISSUES.

176

light, and be invested with a breadth of meaning they would
not otherwise possess.

The Irritability of Maide tad Herye.— An animal, as a frog,
deprived of its brain, will remain motionless till its tissues have
died, unless the animal be in some way stimulated. If a mus-
cle be isolated from the body with the nerve to which it be-
longs, it will also remain passive ; but, if an electric current be
passed into it, if it be pricked, pinched, touched with a hot body
or with certain chemical reagents, contraction ensues ; the same
happening if the nerve be thus treated instead of the muscle.
The changes in the muscle and the nerve will be seen later to
have much in common ; the muscle alone, however, contraeta,
undergoes a visible change of form.

Fio. 180.— IntraflbrtiUr tcnnlnatioM of tbe motor nerve in itriated miucle, etalned
with Ko)d chloride (Landoiv).

Now, the agent causing this is a stimul'ttt, and as we have
seen, may be mechanical, chemical, thermal, electrical, or nerv-
ous. As both nerve and muscle are capable of being function-
ally affected by a stimulus, they are said to be irritable ; and
since muscle does not contract without a stimulus, it is said to
be non-automatic.

Now, since muscle is supplied with nerves, as well as blood-
vessels, which end in a peculiar way (endplatea) beneath the
muscle-covering (sarcolemma) in the very substance of the pro-
toplasm, it might be that when muscle seemed to be stimu-
lated, as above indicated, the responsive contraction was really
due to the excited nerve terminals ; and thus has arisen the
question, Is muscle of itself really irritable ?

What has been said as to the origin of muscular tissue points
very strongly to an aflBrmative answer, though it does not fol-
low that a property once possessed in the lower forms of a tissue
may not be lost in the higher. From various facts it may he
concluded that muscle possesses independent irritability.

THE GRAPIIIO METHOD AND THE STUDY OP
MUSCLE PHYSIOLOGY.

It is ImpoRfiiblo to study the physioloiyy of muscle to the best
advantage without the employment of the grraphio method ;

and, on the other hand, no
tissue is so well adapted for
investigation by the isolated
method— i. e., aipart from the
animal to which it actually
belongs — as muscle ; hence
the convenience of introduo'
ing at an early period our
study of the physiology of
contractile tissue and illus>
trations of the graphic meth-
od, the general principles of
which have already been
considered.

The descriptions in the
text will be brief, and the
student is recommended to
examine the figures and ac-
companying explanations
with some care.

Ohnmogntphi, SefolTiiig
Oylind«r% eto.— Fig. 160 rep-
■— B^— resents one of the earliest

'^"■'Z^^^m^'^TS^^T^'^mi forms of apparatus for the
^S°«voW' ^'^eS «V.-i ?: measurement of brief inter-

t weiditactlng M motive power; c,d,imaJl yals of time, consisting of a
balb for renulatlng the velocity of the *«"" , i • * ° „_^

cylinder ; <, marker recording a line on gunple mechanism lOr pro-

'y"°**'- ducing the movement of a

cylmder, which may be covered with smoked paper, or other-

3TUDY OP

Bcle to the best
tphio method ;
»ther hand, no
)U adapted for
by the isolated
flipait from the
ich it actually
lusole ; hence
ice of introduo-
rly period our
physiology of
»ue and iUus-
) graphic meth-
yl principles of
already been

iptions in the
brief, and the
commended to
figures and ac-
explanations
le.

tphi, SerolTiiig
>.— Fig. 160 rep-
of the earliest
paratus for the
; of brief inter-
consisting of a
lanism for pro-
novement of a
paper, or other-

THB STUDY OF MUMCLK PHYSr<)Ii(XJY.

177

wise prepared to receive improssions made upon it by a point
and capable of being raised or lowered, and \U movements re^-

Flu

• •"'•-MyoKraphlo trBclng, luch m i« obtained wliun the cyllndrr on which It In
written doei not rarolve during the contraction of the miucle (after lIcKendrIck).

ulated. The cylinder is ruled vertically into a certain number
of spaces, so that, if its rate of revolution is known and is con-
stant (very important), the length of time of any event recorded
on the sensitive surface may be accurately known. This whole
apparatus may be considered a chronograph in a rough form.

But a tuning-fork is the most reliable form of chronograph,
provided it can be kept in constant action so long as required ;

PiB. 10S.-llMvy'»chrpBogt«phM applied to revoWinR ejllnder (after McKendriek).
a, galvanic element; 6, wooden (land bearing (nning-tbrk (two hundred vibmtlona
per accond); e. electro-magnet between llmbi of tnnlng-fork; a.t, position* for
tunlng-fprku of one handred and Sfty vibration* per aecond; /, tDntng-fork lyinB
loose which imy be applied to rf; o, revolving cylinder; A, electric chronognph
kept in vibration synchronoui with the tuning-fork Interrupter. The current
working the electto-nmenet from a, is iutermpted at i. Foucanlt's regulator is
seen over the clock-work of the cylinder, a little to the right of g.

178

COMPARATIVE PUY81UL00Y.

<-•'

and is proTidecl with a recording •|>p«nitus that doM not eauM
enough friction to interfere with its vibrations.

Fig. 168 illuatratee one arrangement that answers these con-
ditions fairly well.

The marker, or chronograph, in the more limited sense, is
kept in automatic action by the fork interrupting the current
from a battery at a certain definite rate answering to its own
proper note.

Marey's chronograph, which is represented at h above, and
in more detail below, in Fig. 163, consists of two electro-mag-
nets armed with keepers, between which is the writer, which

Fro

168.— side view of Uutj't chTonogimph (after McKcmlrlck). a, o, colli of win;
b, b, keeper* of electro-mtgneU; e, vtbreting ttyle Used to the iteel pl«t« «; <t,
binding icrewi for etUchment of wire*; -f from Intermpting tnnlng-fork; - to
the battery.

has a little mass of steel attached to it, the whole working in
unison with the tuning-fork, so that an interruption of the cur-
rent implies a like change of position of the writing-style, which
is always kept in contact with the recording surface.

Fig. 178 shows the arrangements for recording a single

muscle contracUon, and
^ m Fig. 174 the character of

' ihii tracing obtained.

A muscle-nerve prepa-
ration, which usually con-
sists of the gastrocnemius
of the frog with the sciatic
nerve attached, clamped by

Via. ]64.-Mn*clenerve preparation, abowing a portion of the femur CUt

gastrocnemln* muecio, tclatlc nenre, and ^ ... ., ,

portion of femnr of frog, for attachment Oil Wltb tbe muscle, IS

i;..y|«> (after Roeenthal). ^^^^ ^^ stimulation, tO

■n"**"

iM not cauM

n theM con-

ited lenRo, is
( the current
IP to its own

h above, and
I eleotro-mag^
(rrlter, which

mmmmm.

immm

a, a, colli of wire;

« itcel pl«t« «; d,

tnnlng-forki - to

lie working in
ion of the our-
ig-style, which
tee.

ding a single
traction, and
) character of
ibtained.
}-nerve prepa-
1 usually con-
gastrocnemius
tvith the sciatic
ed, clamped by
the femur cut
he muscle, is
itimulation, to

THE HTUDY OF MU8CLE PHYSIOLOGY.

179

raise a weighted lever which is attached to a point writing on a
cylinder moved by some sort of clock-worlc. In this cam the
cylindur is kept stationary during the contraction of tlie mus-
cle ; hunoe the records appear as straight vertical linos.

For recording movements of great rapidity, so that the in-
tervals between them may be apparent, such an apparatus m is

Fio. 186.— Spring myogmph of On Bol»-Iio]nnoiid (after Roeenthtl). The amnge-
menta for reglaterlng varioua detalla are almllar to thoee for pendulam myottraub
(Fig. 178).

figured here (Fig. 165) answers well, the vibrations of a tuning-
fork being written on a blackened glass plate, shot before a chro-
nograph by releasing a spring.

Several records may be made successively by more compli-
cated arrangements, as will be explained by another figure later.

TBB JLPPABATUB USBD FOB THB STmuXiATION OF

MnSOLB.

It is not only important that there should be accurate and
delicate methods of recording muscular contractions, but that
there be equally exact methods of applying, regulating, and
measuring the stimulus that induces the contraction.

Fig. 166 gives a representation of the inductorium of Du
Bois-Beymond, by which either a single brief stimulation or
a series of such repeated with great regularity and frequency

':-*•-

180

COMPARATIVE PHYSIOLOGY.

1, secondary coll; e,

primary coU; ^ electro-magnet, «;WiMtnreoin«Muw^ hammer, and by

5-hTSiUt 'from •|«tt?7' "ren. f J^n/cSmKTalsSSa!^^ By con'-
icrew geU Into primary «;}}• "S>* .•™'J2Smd aJrft Iron of b. Iron become* a maa-
nectlon between primrjrcoHandwh«.«^^ ^^^^^ but when tl&

nectlon between primary ««•»»«««• ^"J^iSSnt thnrbrokeJivbut when

net. hammer l» attracted '»g» •«^/' •SJliirii!?. and. hammer ajkringlng t

occnrs, Bof t Iron wm*** «» b« » "^t "tST ""• "™

the who e conrw of eventt to ««pe"*^i * "K,

• urnnd The aboTe may be clearer from dlL„-_, -

l^Ap ind dSSii. .tfingth of liidnc«l current can

let nS5Wiirirf,'aJS7h«iinw J^"^ng »|«^

~il§ may occnr several bundred umMm

dii«P«n, Flg,ier.,„Bjr5llding .««nd.

igndnati

^u»y be elTected. The appamtus oonrists e««itially of a pri-
Zh coil, secondary coil, magnetic interrupter, and a scale

Ro. IW.-Dlagrammatlc represenUtlon of the working of Wg. IM (after Hoawithal).

aeeondary coll; 0,
ill movable ncrew.
[ hammer, and by
iarycoil. Bycon-
DD oecome* a mag-
etK but when thw
er tikringlDg back,
I hundrM umei in
Br alidiDg Mcmd-

fllly of a pri-
, and a scale

M (after BoMnthal).

THE STUDY OP MUSCLE PHYSIOLOGY.

181

to determine the relative strength of the current employed.
The instrument is put into action by one or more of the various
well-known galvanic cells, of which Daniell's are suitable for
most experiments.

Fio. 160.

Fis. IflS.

Via. 108.— Pflflger'a myognph. The mnacle may be flzed to the viae C In the moist
chamber, the viae coDiiecting with the lever EE, the point of which touches the
plate of amolced glasa O. The lever is held in equipoise by H. When weiehto are
placed in scale-pan f, the lever writes the degree of extension effected (after Bo-
senthal).

Fn». 168.— Tetanislng key of Du Bois-Reymond (after Rosenthal). Wires may be
attached at ft ande. When d is down the current is " short-circnited." 1. e., does
not pass through the wires, but direct from e through d to A, or the reverse, since
6. e, <f are of metal, and. on account of their greater croesMMCtlon, conduct eo
much more readily than the wirea. a Is an insulating plate of ebonite. This form
of key is adapted for attachment to a table, etc.

The access to, or exclusion of the current from, the induc-
torium is effected by some of the forms of keys, a specimen of
which is illustrated in Fig. 160.

The moist chamber, or some other means of preventing the
drying of the preparation, which would soon result in impaired

182

COMPARATIVE PHYSIOLOGY.

action, followed by death, is essential. A moist chamber con-
sists essentially of an inclosed cavity, in which is placed some
wet blotting-paper, etc., and is usually made with glass sides.
The air in such a chamber must remain saturated with moisture.

A good knowledge of the subject of electricity is especially
valuable to the student of physiology. But there are a few ele-
mentary facts it is absolutely necessary to bear in mind : 1. An
induced current exists only at the moment of making or break-
ing a primary (battery) current 2. At the moment of making,
the induced current is in the opposite direction to that of the
primary current, and the reverse at breaking. 3. The strength
of the induced current varies with the strength. of the primary
current. 4. The more removed the secondary coil from the
primary the weaker the current (induced) becomes.

The clock-work mechanism and its associated parts, as seen
in Fig. 170, on the right, is usually termed a myograph.

Fis. 170.— ArrMunment of appantiu for tcannniMion of mueolar movemeut by Um-
boura (after MeKendrick). a, galvanic elemsnt; 6, urimary coll; «, aecondaiy coil
of Indnctoriam; d, metronome for Intermpting pnmair circuit when indnetlon
cnrrent i» sent to electrodes k; h, forceps for femur: the mnacle, which la not
here represented, is attached to the recemng tamboar a, by which movement Is
transmitted to recording tambonr e, which writes on cylbider/.

Instead of muscular or other movements being communi-
cated directly to levers, the contact may be through -columns
of air, which, it will be apparent, must be capable of communi-
cating very slight changes if the apparatus responds readily to
the alterations in volume of the inclosed air.

Fig. 171 repreaento a Marey's tambour, which consists essen-

amber con-
>laced some
glass sides.
;h moisture,
s especially
re a few ele-
lind : 1. An
Qg or break-
of making,
> that of the
rhe strength
the primary
>il from the

larts, as seen
nph.

movemeut b; tain-
1; «, MComUry coU
It when induction
iKle, which is not
rhioh moveoMnt is

ng communi-
nigh columns
) of oommuni-
nds readily to

consists easen-

THB STUDY OP MUSCLE PHYSIOLOGY,

188

Flo. 171.— Tambour of Maiey (after McKendrick). a, metallic case; b, thin India-rob-
ber membrane; «, ttiin oiiK of alumininm supporting lever d, a small portion of
which only is represented; «, screw for placing support of lever verticallr over e;
f. metallic tube communicating with cavity or tambour for attachment to an In-
aia-mhber tube.

tially of a rigid metallic case provided with an elastic top, to
which a lever is attached, the whole being brought into com-
munication with a column of air in an elastic tube. The work-
ing of such a mechanism will be evident from Figs 170 and 172.

Fi«. ITS.— Tamboon of Karw amniaed for tcanamiasion of movement (after McKen-
drick). a, receiving tambour; 6, India-mbber tube; e, registering tambour; if.
spinu of wire, owing to ehwtioity of which, when tension is removed from a, the
lever ascends.

The greatest danger in the use of such apparatus is not fric-
tion but osciUation, so that it is possible that the original move-
ment may not be expressed alone or simply exaggerated, but
also complicated by additions, for which the apparatus itself is
responaible.

■ ^**vmtrtirv*rxM

l» NJ-^ T ^ ^■ l ^^' y^l Wl' ■- ' ^^' ^ i' i r»r-

184

COMPARATIVE PHYSIOLOGY.

Via. 173.

THE STUDY OP MUSCLE PHYSIOLOGY.

185

Fio. 173.— DiogrammHtic representation of the uendiilam myograph. The imoked-
^oao plate. A, swings with a pendulum, B. Before an experiment Is commenced
the pendulum is raiced up to the right and kept in |>o8ition by the tooth, a, catch-
ing on the spring-catch, b. On depressing the catch, b, the glass plate being set
free swings Into the new position indicated by the dotted lines, and is held there
by the tooth, a', meeting the catch, b'. In the course of its swing the tooth, a,
coming into contact with the projecting steel rod, e, knocks it to one side, into
the position indicated by the dotted line, c'. The rod, c, is in electric continuity
with the wire, x. of the primary coil of an induction machine. In like manner
the screw, d. Is in electric continnlty with the wire, y, of the same primary coil.
The screw, (/, and the ro<l, c, are provldt^ with platinum points, and both are in-
sulated by means of the ebonite block, e. The circuit of the primary coil to which
X and V l)elong is closed as long as e and U are in contact. When In its swing
the tooth, a', knocks c away from d, the circuit la immediately broken, and a
"breaking" shock is sent through the electrodes connected witli the secondary
coil of the machine, and so through the nerve. A lever Is brought to bear on the

ftlaas plate, and when at rest descnbcs an arc of a circle of large radius. The tun-
ng-fork,/(cnds only seen), serves to mark the time (after Foster).

Apparatus of this kind is not usually employed much for
experiments with muscle ; such an arrangement is, however,
shown in Fig. 170, in which also will be seen a metronome, the
pendulum of which, by dipping into cups containing mercury,
makes the circuit. Such or a simple clock may be utilized for
indicating the longer intervals of time, as seconds.

A SmOLB 8IBIPZ.B BCUSOnUkR OONTRAOTXON.

Sl^nimental Fkott.— The phases in a single twitch or mus-
cular contraction may be studied by means of the pendulum
myograph (Fig. 173). It consists of a heavy pendulum, which
swings from a position on the right to a corresponding one on
the left, where it is secured by a catch. During the swing of
the pendulum, which carries a smoked-glass plate (by means
of arrangements more minutely described below the flgure), a
tuning-fork writes its vibrations on the plate, on which is in-
scribed the marking indicating the exact moment of the break-
ing of an electric current, which gives rise to a muscle contrac-
tion that is also recorded on the plate.

The tracing on analysis presents : 1. The record of a tuning-
fork making one hundred and eighty vibrations in a second.
2. The parallel marking of the lever attached to the muscle
before it began to rise. 3. A curve, at first rising slowly, and
then rapidly to a maximum. 4. A curve of descent similar in
character, but somewhat more lengthened.

We may interpret this record somewhat thus : 1. A rise of
the lever answering to the shortening of the muscle to which it
is attached following upon the momentary induction shock,
as the entrance of the current into the nerve, the stimulation of
which causes the contraction, may be called. 2. A period before

186

COMPARATIVE PHYSIOLOGY.

the contraction be^ns, which, as shown by the time marking,

occupies in this case ^ , or about ^ of a second. In the tracing

the upward curve indicates that the contraction is at first rela-
tively slow, then more rapid, and again slower, till a brief sta-

a h

Sl.*Jk 'J?-i.irh jS mlSnred b? the w«^3 a tuning-Krii. nwkiiut one hundred
Wghty'd^le' vTbmt"^. InVSScSd^fnd In UiSfnuuiner theXratlon of the
other phMee of the contracUon may be estimated.

tionary period is reached, when the miiscle gradually but rap-
idly returns to its previous condition, passing through the same
phases as during contraction proper. In other words, there is
a period of rising and of falling energy, or of contraction and
relaxation. 4. A period during which invisible changes, as
inn be explained later, are going on, answering to those in the
nerve that cause the molecular commotion in muscle which
precedes the visible contraction— the latent period, or the period
of latent stimulation. „. . , x-

The facts may be briefly stated as follows : The stimulation
of a muscle either directly or through its nerve causes contrac-
tion, followed by relaxation, both of which are preceded by a
latent period, during which no visible but highly important
molecularchanges aretakingplace. The whole change of events
is of the briefest duration, and is termed a muscle contraction.
The tracing shows that the latent period occupied rather more
than Tk second, the period of contraction proper about ,fr, and
of relaxation rk second, so that the whole is usually begun and
ended within ^ second ; yet, as will be learned later, many
chemical and electrical phenomena, the concomitants of vital
change, are to be observed.

In the case just considered it was assumed that the muscle

ime marking,

In the tracing

is at first rela-
bill a brief sta-

roater). Bead from
lotween a and b, the
ukiiut one hnndred
' the dnratlon of the

lually but rap-
rough the same
words, there is
ontractiou and
ile changes, as
to those in the
muscle which
d, or the period

rhe stimulation
causes contrac-
> preceded by a
gblj important
change of events
cle contraction,
led rather more
r about tIt, and
lallyJbegun and
led later, many
mitants of vital

that the muscle

THE STUDY OF MUSCLE PHYSIOLOGY. 187

was stimulated through its nerve. Precisely the same results
would have followed had the muscle been caused to contract by
the momentary application of a chemical, thermal, or mechanical
stimulus.

If the length of nerve between the point of stimulation and
the muscle was considerable, some difference would be observed

Fio, 175.— DlaBTammntic representation of the mewnroment of yeloclty of nerrona
Impulse (Foeter). Tracing taken bjr iiendnlum myofpvph (Fig. 178). The nerve
of same ninscle-ncrve preparation i« sttmulntod in one caae as far aa possible from
muscle, in the other a* near to it as possible. Latent period ia <ri>, ar>\ respect-
ively. Difference between ab and av indicates, of conrse, length of time occu-
pied by nervous impulse in traveling along nerve from distant to near point.

in the latent period if in a second case the nerve were stimu-
lated, say, cloae to the muscle. This is represented in Fig. 176,
in which it is seen that the. latent period in the latter case is
shortened by the distance from V to 6, which mtist be owing
to the time required for those molecular changes which, occur-
ring in a nerve, give rise to a contraction in the muscle to which
it belongs ; in fact, we have in this method the means of estimat-
ing the rate at which these changes pass along the nerve— in
other words we have a means of measuring the speed of the
propagation of a nervous impulse. The estimated rate is for the
fw^ twenty-eight metres per second, and for man about thirty-
three metres. As the latter has bMn estimated for the nerve,
with its muscle in position in the living body, it must be re-
garded rather as a close approximation tlian as exact as the
other measurements referred to in this chapter.

It will be borne in mind that the numbers given as repre-
senting the relative duration of the events vary with the ani-
mal, the kind of muscle, and a variety of conditions infecting
the same animal.

TBTAXnO OOMTRAOnOir

It is well known that a weight may be held by the out-
stretohed arm with apparently perfect steadiness for a few

188

COMPARATIVE PHYSIOLOOY.

seconds, but that presently the arm begins to tremble or vi-
brate, and soon tlie weight must be dropped. The arm wax
maintained in its position by the joint contraction of several mus-
cles, the action of which might be describeil (traced) by a writer
attached to the hand and recording on a moving surface. Such
a record would indicate roughly what had happened; but the
exact nature of a muscular contraction in such a case can best be
learned by laying bare a single muscle, say in the thigh of a
frog, and arranging the experiment so that a graphic record
shall be made.

Using the apparatus previously described (Fig. 178), a series
of induction shocks may be sent into the muscle with the result
indicated in Figs. 176 and 177, according to the rate of interrup-
tion of the current.

1 1 II 11 II 1 1 1 1 II 1 1

rn 6

Fis. m.-Cnrvf of Imperfect tetanic contraction (Focter). Upuermoat tncins Indi-
cates contractions of muscle; intermediate, when the ahocks were given; lower,
time-marlcinKS of Intervals of one second. Carve to be read, like others, from left
to right, andlilnstrates at the end a " contraction remainder."

If the stimuli follow each other with a certain rapidity, such
a tracing as that represented in Fig. 176 is obtained; and if the
rapidity of the stimulation exceeds a fixed rate, the result is that
seen in ^ig. 177.

Pio. m.— Cunw of complete tetanic contractfcm (Foater).

--«Tv.. ■■»^■)^lww^l.^«>l«l

iw>i iW ) ie' tM» i' .Mwtm i w i' ^ tT » r* i.-»t

tremble or vi-
The arm was

of several mus-
led) by a writer
> surface. Sucb
ipeued; but the
case can best be

the thigh of a

graphic record

ig. 173), a series
I with the result
rate of iuterrup-

permost tracins Indl-
M were given; lower,
like othen, from left

in rapidity, such
ined; and if the
the result is that

:Fo«ter).

THE STUDY OP MUSCLE PHYSIOLOGY.

180

It is possible to see in those tracings a genetic relation, the
second figure being evidently derivable from the flrat, and the
third from the second, by the fusion of all the curves into one
straight line.

The Xmole Tone.— There are a number of experimental facts
from which the conclusion has been drawn that tetanic contrac-
tion i)> occomiKinied by a muscle tone which is in itself evidence
of the nature of the contraction.

We may safely conclude that, at all events, most of the mus-
cular contractions occurring within the living body are tetanic
— i. e., the muscle is in a condition of shortening, with only very
brief and slight phases of relaxation ; and that a comparatively
small number of individual contractions sufflce for tetanus
when caused by the action of the central nervous system;
though, as proved by experiments on muscle removed from the
hotly, they may be enormously increased. While a few stimu-
lations per second suffice to cause tetanus, it will also persist
though thoiisands be employed.

TBB OHAMOB8 ZN A HUBOLB SURINO OONTRAOTION.

Though the change in form is veiy great during the con-
traction of a muscle, the change in bulk is almost inappreci-
able, amounting to a diminution of not more than about itAn
of the volume. In fact, according to the latest investigator,
there is no diminution whatever.

Since the fibers of striped muscle are of very limited length
(30 to 40 mm.), it would seem that a contraction originating in
one fiber must be capable of initiating a similar action in its
neighbor; and, as the ends of the fibers lie in contact, it is easy
to understand how the wave of contraction spreads. Normally,
the contraction must pass from about the center of the muscle-
cell where the nerve terminates in the end-plate.

THIS ELASTIOITT OF MUSOLB.

In proportion as bodies tend to resume their original form
when altered by mechanical force are they elastic, and the ex-
tent to which they do this marks the limit of their elasticity.

If a muscle (best one with bundles of fibers of about equal
length and parallel arrangement) be stretched by a weight
attached to one end, it will, on removal of the extending force,

190

COMPARATIVE PHYSIOLOGY.

return to Iti original length; and if a aeries of weights which
differ by a oomnion increment be applied in auooeesion and the
degrees of extensions compared, as may be
done by the graphic method, it will be ap-
parent that the increase in the extension
does not exactly correspond with incre-
ment in the weight, but is proportionally
less. With an inorganic body, as a watch-
spring, this is not the case. ,

Further, the recoil of the muscle after
the removal of the weight is not perfect
for all weights; but within certain narrow
limits this is the case, i. e., the elasticity
of muscle, though slight (for it is easily
over-extended), is perfect. When once a
muscle is over-extended, so weighted that
it can not reach its original length almost
at once, it is veiy slow to recover, which
explains the well-known duration of the
effects of sprains, no doubt owing to some
profound molecular change associated with
the stretching.

The tracings below show at a glance
the difference between the elasticity of
muscle and of ordinary bodies.

It is a curious fact that a^muscle during
the act of contraction is more extensible
than when passive ; a disadvantage from
a purely physical point of view, but prob-
^i^^j. ably » real advantage as tending to obviate

i-o CpoBoit-iUv- "P"*™ ^y preventing too sudden an appli-
m>nd^~appMta* for cation of the extending foroe.
lSS.tt m«ttte It will be borne in mind that the limbs
22d "'.Sd" •tuihSr'S; are held together as by ehistic bands slightr
moKieistobeoiMervod jy ^^ ^^ stretohj owing to the elasticity
with* ten.. ^^ ^^^ muscles. Now, as seen in many

tracings of muscular contraction, there is a tendency to imper-
fect relaxation after contraction— the contraction .remainder
or elaatie aftereffect, which can be overcome by gentle trac-
tion. In the living body, the weight of the limbs and the action
of the stretched muscles on the side of the limb opposite to that
on which the muscles in actual contraction are situated, com-

.iiJumi ir iMWW iff ^ V" ! - I " "■"■■""■""I "■ 'i"^^— *''^

Wiiji > i i i i ifa .is^<<isiii«^^

■■

•mim'mmmm'''iimt

THR STUDY OP MUHCLR PIIYSIOIiOOr.

101

vreighta which
Msion and the
red, M may be
I, it will be ap-
the extension
id with inore-
proportionally
dy, ai a watoh-

te muacle after
; is not perfect
certain narrow
, the elasticity
for it is easily
When once a
I weighted that
1 length almost
recover, which
luration of the
, owing to some
associated with

ow ai a glance
le elasticity of
lies.

ft^muscle during
more extensible
idvautage from
view, but prob-
iding to obviate
ludden anappli-
«e.

i that the limbs
itic bands slight-
to the elasticity
i seen in many
tdency to imper-
iion .remainder
I by gentle trac-
bs and the action
> opposite to that
re situated, com-

bine to make the action of the muscle more perfect by over-
coming this tendency to imperfect relaxation, which is proba-

Fra. 170.— IllMtntlOM of the difference In eluftlcity of lnaiiim«te and living mttter
(•TtorYeo). ]. Hhowi graphically behavior of a iteel uprlnic under equal Inen-
menu of weight. II. A ■Inillar tracing obuhied from an India-rubber band, 8.
The aame from a frog'* mniele. Note that the oxtenilon decreaaei with eqnal In-
crement* of weight, and that the muKle fall* to return to Um odctnal uoalUon
(abwlaat) after removal of the weight.

bly less marked, independent of these considerations, in the
living body. This elasticity of living muscles, which is com-
pletely lost on death, is a fair measiire of their state of health
or organic perfection. Hence that hard (elastic recoil) feeling
of the muscles in young and vigorous persons, especially ath-
letes, in whom muscle is brought to the highest degree of per-
fection.

This property is then essentially the outcome of vitality,
which is in a word the foimdation of the differences noted be-
tween the elasticity of inorganic and organic bodies. A mus-
cle, the nutrition of which is suffering from whatever cause,
whether deficient blood-supply, fatigue, or actual disease, is
deficient in elasticity. We wish to emphasize these relations,
for we consider it very important to avoid regarding vital phe-
nomena in the light of physics merely, which the employment
of the graphic method (and indeed all methods by which we re-
move living things out of their normal relations) fosters.

Baetriml Pheaoimia of Miuel*.— The contraction and
probably the. resting stage of muscle are attended by the gen-
eration of electrical currents, the direction of which is indicated
in Fig. 180.

It will be observed that the diagram indicates that between
no current and the strongest obtainable there are all shades of

i9i

COMPAHATIVR PIIY8I0LtKJY.

Fiu. 180.— Reprf«eui«tlon of electrical carronU In a mtuctorhombiu (after Roaentlwl).

Strength, aooording to the parts of the muscle connected by the
electrodes. The strongest is tliat resulting when the superfi-
cial equator and the transverse center are connected ; and it is
found that the nearer these points are approached the stronger
the current becomes.

It is important to note that the electric current of muscle,
however viewed, is associated with the chemical aud all the
other molecular changes of which the actual contraction is
but the outward and visible sign ; and since the currenU have
an appreciable duration, wane with the vitality of the tissue,
and wholly disappear at death, they must be associated with the
fundamental facta of organic life ; for it is to be remembered
that electrical currents are not confined to muscle, but have
been detected in the developing embryo, and even in vegetable
protoplasm. Though the evidence ia not yet complete, it seems
likely that electrical phenomena may prove to be associated
with (we designedly avoid any more definite expression) ail
vital phenomena.

^}]ifm|i< ^l OhangM in MvioIa.— At a variable period after
death the muscles become rigid, producing that stiffness {rigor
mortis) ao oharaoteristio of a recent cadaver.

-o«iwMiwii^wii'iiiiwiiiiitai>M**"niiii<iiii

Mii.tfaieWfcw<it«-aJywi^'Hl >i'i i HilM <> tt l kjli ii gWft»ft'

TUB STUDY OF MU8CLB FHYSIOLUOY.

198

tnected by the
n the niperfl-
ited ; and it in
1 the stronger

»nt of muHole,
aud all the
sontraction ia ,
currents have
of the tiamie,
iated with the
remembered
uKle, but have
n in vegetable
iplete, it seems
be associated
sxpression) all

e period after
stiffness {rigor

The subject can be studied in som* of its aspects to great ad-
vantage in an JHolated individual muscle.

Three changes in a muscle that has passed into death rigor
are constant and pronounced. The living muscle, either alka-
line or neutral in reaction, has become decidedly acid ; an
nbundanoe of carbonic anhydride is suddenly given off ; and
inyoain, a specific proteid, has been formed. That tliese phe-
nomena have some indissoluble connection with each otlier so
far as the first two at least are concerned, while not ab«dutely
certain, seems probable, as will be learned shortly.

It will be borne in mind that muacle-flbers are tubes con-
taining semifluid protoplasm, and that a coagulation of the ImI-
ter must give rise to general rigor. This protoplasmic substance
can be extracted at a low temperature from the muscles of the
frog, and, as the temperature rises, coagulates like blood, giving
rise to a clot (myosin) and muscle-serum, a fluid not very unlike
the serum of blood.

This myosin can also be extracted from dead rigid muscles
by ammonium chloride, etc. It resembles the globulins gen-
erally, but is less soluble in saline solutions than the globulin
of blood (paraglobulin) ; is less tough than fibrin ; has a very
low coagulating point (56° to 60° 0.) ; and is somewhat jelly-
like in appearance. Tlie clotting of blood and of muscle is thus
analogous, myosin answering to fibrin, and there being a serum
in each case, both processes marldng the permanent disorgani-
sation of the tissue. The reaction seems to be due to the forma-
tion of a kind of lactic acid, probably saroolactic ; though
whether due to excessive production of this acid, on the death
of the muscle, which for some reason does not remain free in
the living muscle, or whether sarcolactio add arises as a new
product, is uncertain. It is certain that the acid reaction of
dead muscle is not owing to carbonic acid, for the reddened
litmus does not change color on drying.

That a muscle in action does use up oxygen and give' off
carbonic anhydride can be definitely proved ; though it is
equally clear that the life of a muscle is not dependent on a
oofMfant supply of oxygen as is that of the individual, for a
muscle can live, even contract long and vigorously, in an atmos-
phere free from this gas, as in nitrogen.

From the suddenness of the increase of carbonic anhydride,
the onset of death and rigor mortia has been compared to an
explosion.

194

COMPARATIVB PHYSIOLOGY.

After this the miucle becomes greatly changed physically ;
its elasticity and translucency are lost ; there is alMenoe of
muscle-currents ; it is wholly unirritable, is less extensible — it
is, as before stated, firmer— it is dead.

But these fundamental phenomena, the increase of carbonic
anhydride and the acid reaction, are observable after prolonged
tetanus. It was, therefore— putting all the facts together that
we now refer to and others, not forgetting that a muscle is
always respiring, inhaling oxygen, and exhaling carbonic an-
hydride — not unreasonable to conclude that normal tetanus
and rigor mortia were but exaggerated conditions of a natural
state. The coagulation of the muscle protoplasm (pHaama),
givini? rise to myosin, was, however, a serious obstacle to the
adoption of this view. But it has very recently been urged
with great plausibility that an old view is correct, viz., that
rigor mortis (contracture) is the last act of muscle-life ; it is, in
fact, a prolonged tetanus or contracture, ending in most cases,
though not all, in coagulation of the myosin. This state can
be induced and recovered from in favorable cases by cutting
o£ the blood tit>m a part by ligature, and later readmitting it
to the starving region. It has been suggested that the prod-
ucts of the muscle-waste, usually washed away by the blood-
stream, in such an experiment and after death, collect and act
as a stimulant to the musde, oansing it to remain in permanent
contraction.

The other constituents of dead muscle and their relative
properties may be learned from the following table (Von Bibra) :

Water. 744'6

Solid.?: Myosin, elastic substance, etc., in-

iBoluble in water 155*4

Soluble proteids .- 19*3

Gelatin 207

• Extractives and salts 37*1

^ats 230

265-tl^265'6

Total 1,000

' Among the extraetivea of muscle very important is creatin
('2 to '3 per cent), a nitrogenous crystalline body. Certain
allied forms, as xanthin, hypoxanthin (sarkin), camin, taurin,
and uric acid, are also found.

Glycogen (animal starch), very abundant in all the tissues,

II I . u ' L wtmj.kt<J i' >. « <^ r vi, i im;B ^

— w 'i »». i »ii« i «M l »« ft« »»j«vls'» i l«mWWiiW i <l i W iil l »

«d physically;

is absence of

I extensible — it

ise of carbonic
^fter prolonged
B together tliat
lat a muscle is
ig carbonic an-
lormal tetanus
18 of a natural
asm (plasma),
obstacle to the
tly been urged
Tect, viz., that
le-lif e ; it is, in
1^ in most cases,

This state can
ases by cutting
r readmitting it

that the prod-
Y by the blood-
, collect and act
,n in permanent

i their relative
jle{VonBibra):
.... 744-6

L55-4
19-3
207
371
230

256^-266-6

.... 1,000
ortant is creatin
body. Certain
), camin, taurin,

n all the tissues,

THE STUDY OP MUSCLE PHYSIOLOGY.

196

including the muscles of the embryo, is found in small quantity
in the muscles of the adult; and in the heart-muscle a peculiar
sugar (ino»it) is present.

It is, of course, very difficult to say to what extent the bodies
known as extractives exist in living muscle, though that glyco-
gen, fats, and certain salts are normally present admits of little
doubt

There is a coloring matter in muscle, more abundant in the
red muscles of certain animals than the pale, allied to htemo-
globin, if not identical with that body.

It may be stated as a fact, the exact significance of which
is imknown, that during contraction the extractives soluble in
water decrease, while those soluble in alcohol increase.

It will, however, Iw very plain, from what has been stated
in this section, that life processes and chemical changes are
closely associated, and«to realize this is worth much to the
student of Nature.

TBBBMAZi OBAMOBS IN TBB OOmRAOmVO MUSOLB.

Since very marked chemical changes accompany muscular
contraction, it might be expected that there would be some
modification in temperature, and probably in the direction of
elevation. Experiment proves this to be the case.

But why diould a muscle when at rest, as may be shown,
maintain a certain temperature, unless chemical changes are
oonstantiy taking place 1 As already stated, such is the case,
and the rise on passing into tetanus is simply an expression of
increased chemical action.

No machine known ^j us resembles muscle except super-
ficially. The steam-engine changes fuel into heat and mechani-
cal motion, but there the resemblance ends. Muscle changes
its food, or fuel, not direotiy either into heat or motion, but into
itself ; yet as a machine it is more effective than the steam-
engine, for more work and less heat are the outcome of its
activity than is the case with the steam-engine. ^

TH8 PHTBIOIiOOT OP MBRVB.

Muscle and nerve are ccnstantiy associated functionally,
and have so much in common thi^t it becomes dedrable to study
them together. Much that has been established for muscle

t«M

196

COMPARATIVE PHTSIOLOOY.

holds equally well for nerve; and the latter, though apparently
wholly different in structure at first sight, is really not so.
Nerve has its protoplasmic part (axis-cylinder), which is the
essential structure, its protective sheaths, and its nuclei (nerve-
corpuscles).

As already indicated, a nerve pomeeses irritahility.

It is foiind that when the constan t (polarising) current is
passing from above dow&ward — tStt is, when the cathode
(negative-pole) is on the side toward the muscle— the irritability
of the nerve is increased, and the reverse when the opposite
conditions prevail.

This altered condition is known as electrotonus.

It has been found as the result of many experiments that
profound modifications of the irritability of a nerve do take
place during the passage of a constant current These are
diagrammatioally represented m Fig. 181.

-'^ «

Fio. 181.— DbwraiiuiMtie MpntentatloB <rf wtatioiM la electratonai aeeofdlog to

■tnngth oTciureiit employed (r* — """ — ~~* "— * ''

{■*■ pole); k, cathode (— pole),

orcanent employed (after PflSser). n n', a McUon of nerve; a, aaoda
; k, cathode (— pole). Curvea above the horiaontal denote catelectroto-
nna; below, the oppoalte.

Briefly stated, they are these : 1. The nature of the change
depends on the direction of the polarising (ooostunt) current ;
hence, if the current is descending, there is an increase of irri-
tability (eatdectrotontu) in the portion of the nerve nearest the
muscle^' and vice versa. 2. The extent at the change of irrita-
bility is dependent on the strength of the polarising current.
3. This change is most marked close to the electrodes, spreads <
to a considerable extent beyond this point without the elec-
trodes (extra-polar rogions), and also exists within 'the region
of contact of the electrodes (intra-polar regions). 4. It follows
that there must be a point at which it is not experienced (indif-
ferent point or neutral point).

Now, it is possible to understand wl^ a sadden change in

' umawi tmu t ammuu^Km i LniViim ^ j t ^wn w a*!* ' ; '

vAi^iiiiiiwisiNffef;

|rh apparently

really not w>.

which is the

nuclei (nerve-

iUty,

og) current is
a the cathode
the irritability
a the opposite

perimentB that
nerve do take
it These are

Dtonu Mcording to
I of nerve; a, anode
denote cUelectroto-

I of the change
fltidit) current ;
increase of irri-
BTve nearest the
hange of irrita-
uicing current
Kstrodes, spreads
ithout the elec-
thin the region
). 4. It follows
lerienced (indif-

dden change in

THE STUDY OF MUSCLE PHTSIOLOOY.

197

the current should cause a muscular contraction. An equally
sudden alteration, a profound molecular effect, has been caused,
and this we must believe essential to the causation of a muscu-
lar contraction through the influence of a nerve.

To use an illustration which may serve a good purpose if
not taken too literally, it is a well-known experience that one
sitting in a room in which a clock is ticking soon fails to no-,
tice this r^^lar sound : but should the clock stop suddenly or
as suddenly commence to tick very rapidly, the attention is
aroused, while a very gradual slowing to cessation or the re-
verse would have escaped notice. The explanation of such
facts takes us dovm to the very foundations of biology ; but
just now we wish only to elucidate by our own experience
how it is possible to conceive of a muscle being stimulated
by the molecular movements of nerve, or rather a change in
these.

There are important practical aspects to this question. One
may understand why it is that electricity proves so ready a
stimulus, and is so valuable a therapeutic agent. It seems, in '
fact, as will be learned later, to be capable! of taking the place
to some extent of that constant nerve influence which we be-
lieve is being exerted in the higher animals toward the mainte-
nance of the regularity of their cell-life (metabolism).

Ptthologioal Ukd OUililMd.— It is believed that in the nerves
of a living animal body, the electrotonio condition can be in-
duced as in an isolated piece of nerve. Hence, the value of
the constant current in diminishing nerve irritability in neu-
ralgia and allied conditions. Apparatus of great nioety of con-
struction and capable of generating, accurately measuring, and
conveniently applying electrical currents of di£Feront kinds, now
adds to the resources of the practitioner. But we are probably
as yet only on the threshold of electro-therapeutics.

ElaetliMl OlfUlt.— Electrical properties can be manifested
by a large number of fishes; and the subject is of special theo-
retical interest It is now established that the development of
electrical organs points to their being spedally^ modified mus-
clea— tissues, in fact, in whieh the contractile substance has disap-
peared and the nervous elements become predominant and
peculiar. No work is done, but the whole of the chemical
energy is represented by electricity. Functionally an electric
organ (which usudly is some form of cell, on the walls of
which nerves are distributed, inclosing a gelatinous substance.

-■^.^^m'-'^r,-^^^-^^

198

COMPAEATIVE PHYSIOLOGY.

the whole being very miggeative of a galvanic battery) oloaely
resembles a mtuole-nerre preparation or its equivalent in the

normal body. The electric
<wgans experience fatigue ;
have a latent period ; their dis-
charge is tetanic (interrupted) ;
is excited by mechanical, ther-
mal, or electrical stimuli ; and
the effectiveness of the organs
is heightened by elevation of
temperature, and the reverse
by cooling, etc.

ainSOUIiAB WORK.

If during a given period
one of two persons raises a
weight through the same
height but twice as frequent-
ly as the other, it is plain that
he does twice the work ; from
such a case we may deduce the
rule for calculating work, viz.,
to multiply the weight and
height together.

The effectiveness of a given
muscle must, of course, depend
on the degree to which it shortens, which is from one half to
three fifths of its iMigth; and tlie number of fibers it contains
— i. e., upon its length and the area of its cross-section, taking
into account in connection with the first factor the arrangement
of the fibers ; those muscles in which the fibers run longitudinal-
ly being capable of the greatest total shortening.

There is, as shown by actual experimental trial, a relation
between the w<h^ done and the load to be lifted. With double
the weight the contraction may be as great as at first, or even ,
greater ; but a limit is soon reached beyond whidb contraction
is impossible. This principle may be stated thus: Tile controo-
iixm i» a function of the ttimulua, and is illustrated by the
diagram below (Fig. 183).

It has been shown experimentally that the chemical inter-
changes in a muscle, acting against a considerable res i sta nc e.

Via. 188.— The •Iwtrlc-flth tomdo, di«Mct-
ed to show electric appantnt (Huxley).
6,bmichia; «, bntln; «,eleetiie organ;

g, enuiiniii; m*, epinsl cord; m, nerve*
> pectoral Sna ; nl, nervl lateralea :
np, branolieB of imenmagaatric nerrea
to electric oigana; o, eye.

I JW i iijiJj i t]iM f a i i i lWJi i M« e W»»jtaka«8iJj* i »<4' ' Ww< ii h»tfwtuift ft w» «a<W^^^

attery) closely
ivalent in the
The electric
mce fatigue ;
riod; their dis-
! (interrupted);
ichanioal, ther-
1 stimuli ; and
B of the organs
ty elevation of
id the reyerse

k& WORK.

\ given period
irsons raises a
fh the same
ce as frequent-
it is plain that
lie work ; from
onay deduce the
ting work, viz.,
le weight and

sneosof a given
f course, depend
om one half to
bers it contains
-section, taking
tie arrangement
m longitudinal-

•

trial, a relation
L {W^ithdouUe
at first, or even
uch contraction
s: Tkeeontrac-
lustratedbythe

chemical inter-
rable resistance,

THE «TUDY OP MUSCLE PHYSIOLOGY.

199

are increased— i. e., the metabolism and the working tension
are related.

These experimental facts harmonize with our experience of
a sense of satisfaction and efPectiveness in the use of the muscles

<xn

10 ao 30

40 46 so » 00

TTT-T-T-r-T-.-

70 76 80 80 100

Flo. 188.— Dlasram of muMular contractlona with same stimnliu and Increaaing
welgbU. The nnmben repreaent gnuomea (McKendrick).

when weights are held in the hands ; and it must be a nutlter
of practical importance that each person should, in taking sys-
tematic exercise, keep to that kind which does not either over-
weight or underweight the muscles.

omouMerrAMOzis imfxiIjiinoino tbb oharao tbr
OF MUBOUXJUi AND NBRVous Aonvirr.

The Inflnenee of Blood-Snpply. Vatigne.— Fig. 184 shows at
a glance differences in the curves made by a contracting muscle
suffering from increasing fatigue.

180 DV.

Fie. 181— Cnnrea of a mnicle contnustion in dlfferant atagea of fatlgM (af ter Teo).
A, cnnre when muaclo waa fceah; J>, C, D, K, each Juat after mnecle bad alieady
contracted two hnndred tlmea. Tb« alteration in length of latent period la not
well brought ont in these tracinga.

Suppose that in such a case the blood had been witiiheld
from the muscle, and that it is now admitted, an almost im-
madiate effect is seen in the nature of the contractions ; but
even if only saline solution had been sent through the vessels of
the muscle, a similar change would have been noticeable. We
may fiurly conclude that the blood and saline removed some-
thing which had been exercising a depressing^ effect on the
vitality of the muscle. In a working muscle, like all living
tissues, thaw are products of vital action (metabolism) that are
poisonous. We have already learned that a working muscle
generates an excess of carbonic anhydride, and something which
gives it an acid reaction ; and that it uses up oxygen as well as
other matters derivable from the blood.

mmimrtmam^mi

200

COMPARATIVE PHYSIOLOGY.

Fatigue will occur, it is well known, if the muBcles are uBed
for an indefinitely long period, no matter how favorable the
blood-aupply— another evidence that there is, in all probability,
some chemical product, the result of their own activity, depress-
ing them; and this is remdered all the more likely when it is
learned that the injection of lactic acid, to take one example,
produces effects like ordinary fatigue.

It is also a matter of common experience that exercise, while
beneficial to the whole body, the muscles included, as shown by
their enlargement under it, becomes injurious when carried to
the point of fatigue.

Why the use of the muscles is conducive to their welfare is
but a part of a larger question, Why does the use of any tissue
improve it ?

When the nerve which supplies a muscle is stimvilated its
blood-vessels dilate, and it has been assumed that the same
happens when a muscle contracts normally in the body; and
when muscular action is increased there is a corresponding
augmentation in the quantity of blood driven through the
muscles in a given period, even if there be no actual increase
in the caliber of the blood-vessels, for the heart-beat is greatly
accelerated.

But repose is as necessary as exercise for the greatest effect-
iveness of the muscles, as the experience of all, and especially

athletes, proves.

That the nervous system plays a great part in the nutrition
of muscles is evident from the fact, among countless others,
that it is not possible to use the brain to its greatest capacity
and the muscles to their fullest at the same time ; the individual
engaged in physical " training " must forego severe mental ap-
plication. Nervous energy is required for the miisclee, and all
questions of blood-supply are, though important, subordinate.
But it would be t>remature to enter into a full discussion of this
interesting topic now.

The sense of fatigue experienced after prolonged muscular
action is complex, though there can be no doubt that the nerve-
centers must be taken into account, since any muscular work
that, fcom being unusual, requires closer attention and a more
direct influence of the will, is well known to be more fatigu-
ing. On the other hand, the accumulation of products of
fatigue doubtless reports itself through the local nervous mech-
anism.

BMSMlBsassas**!^"

THE STUDY OP MUSCLE PHYSIOLOGY.

201

iBcles are used
favorable the
,U probabiUty,
tivity, depress-
ely when it is
one example,

exercise, while
1, as shown by
len carried to

heir welfare is
a of any tissue

stim\ilated its
that the same
the body; and
corresponding
I through the
ictual increase
beat is greatly

greatest eifect-
and especially

1 the nutrition
untless others,
eatest capacity
the individual
ere mental ap-
lusclee, and all
it, subordinate,
icussion of this

aged muscular
that the nerve-
nuHOular work
on and a more
e more fatigu>
>f products of
nervous mech-

Bepantbrn of Muels fron tlw Ctontnl Vervooi Sjntom.—
When the nerve belonging to a muscle is divided, certain his-
tological changes ensue, which may be briefly described as
fatty degeneration, followed by absorption; and when rogenet^
ation of the nerve-fibers takes place on apposition of the cut
ends, a more or less complete restoration of the functions of
the nerve follows, but the exact nature of the process of repair
is not yet fully agreed upon; it seems, in fact, to vary in differ-
ent cases as to details, though it is likely that, in instances in
which there is a complete return to the normal fimctionally,
the axis-cylinders, at all events, are reproduced^

The degeneration downward is complete ; upward, only to
the first node of Banvier.

Immediately after the section the irritability of the nerve is
increased, but rapidly disappears, from the center toward the
periphery (Bittor-Valli law).

In the mean time the muscle has been suffering. Its irrita-
bility at first d iminis hes, then becomes greater than usual to
shocks from the make or break of the constant current ; but
finally all irritability is lost, and fatty degeneration and disap-
pearance of true muscular structure complete the history. It
is theoretically interesting, as well as of practical importance,
that degeneration may be delayed by the use of the constant
current, the significance of which we have already endeavored
to explain.

Th* Inflnenoe of T«mp«nitim.— If a decapiteted frog be
placed in water of the ordinary temperature, and heat be
gradually applied, the animal does not move (proving that the
spinal cord alone is not conscious), but the muscles, when 43°
to 60° C. is reached, contract and become rigid, a condition
known as " heat-rigor."

There are some advantages in investigating chai^ces in tem-
perature by the graphic method. Curves from a muscle-nerve
preparation show that elevation of temperature shortens the
latent period and the curve of contraction. Lowering the tem-
perature has an exactly opposite effect, as might be supposed,
and these changes take place in the muscles of both cold-
blooded and warm-blooded animals, though more marked in
the latter.

The modificationB evident to the ejre are accompanied by
others, chemical in nature, and a comparison of these shows
that the rapidity and force of th<^ muscular, contraction

Il l ^wjftl

mtimiulttmtmtmmm'^^*»*i<<>»i^ik

ao9

CUMPARATIVB PHTSIULOOY.

run pamllel with the rapidity and extent of the chemical
change*.

Certain drags also modify the form of the muiole<nirre very
greatly, to that it appears that the molecular action which un-
derlies all the phenomena of muscle and nerve (for what hai
been said of muscle applies also to nerve, if we substitute nerv-
ous impulse for contraction) can go on only within tho83 nar^
row bounds which, one realises more and more in the study of
physiology, are set to the activities of living things.

This form of muscular tissue is characteriied hy it> long
latent period, its slow wave of contraction, and the prog-
ress of the contraction being in either a transverse or longi*
tudinal direction, a wave of contraction in one cell being oap*
able of setting up a corresponding wave in adjoining cells
even when no nerve-flbers are distributed to them. It is ex-
cited, though less readily, by all the kinds of stimuli that act
upon striped muscle. In the higher groups of animals this
tissue is chiefly confined to the viscera of the chest and abdo-
men, constituting in the case of some of them the greater part
of the whole organ.

The slow but powerful and rhythmical contraction of this
form of muscle adapts it well to the part such organs play in
the economy. There are variations, however, in the rapidity,
force, r^fularity, and other qualities of the contraction in dif-
ferent parts; thus, it is comparatively rapid in the iris, and ex-
tremely powerful and regular in the uterus, serving to produce
that prolonged yet intennittent pressure essential under the
circumstances (expulsion of the foetus).

ChnnpantiTS.— Muscular contraction is relatively sluggish
and prolonged among the invertebrates, to which, however, the
movement of the wings of insects' is a marked exception, some
of them having been shown by the graphic method to vibrate
some hundreds of times in a second.

The slow movements of the snail are proverbial. As a rule^
the strength of the muscles of -the invertebrates is inbompaxaUy
greater than that of vertebrates, as witness the powerful grasp
of a crab's claw or a beetle's jaws.

These fads are in harmony with the generally slow metab-
(dism of most invertebrates and the lower vertebrates.

the chemical

BleHsurre very
Ion which un-
(for what has
ibttitute nerr-
[un thoR3 nar-
a the atudy of

k1 by iti long
and the prog-
verse or longi- .
cell being oap*
adjoining cella
lem. It ia ex-
timuli that act
»f animala this
best and abdo-
tie greater part

Taction of this
organs play in
in the rapidity,
itraetion in dif-
the iris, and es-
ving to produce
atial un^ the

itively duggish
ih, however, the
exception, some
itbod to vibrate

ibial. As a rule,
is inbompacaUy
powerful grasp

ally slow metab-
ibrates.

THB STUDY OF MUSOLB PHT8I0L0OT.

908

The mufloles of the tortoise contract tardily but with great
power, resist fatigue well, retain their vitality under unfavor-
able conditions, and after death for a very long period (days).

Without resorting to elaborate experiments, Uie student may
convince himself of the truth of most of the above statements
by observing the movements of a waternmail attached to a glass
vessel ; the note made by the bussing of an insect, and compar-
ing it with one approaching it in pitch sounded by some instru-
ment of music; the force necessary to withdraw the foot or tail
of a tortoise ; the peristaltic movements of the intestine and
other organs in a freshly killed animal ; or the action of a bee,
wasp, or wood-boring beetle on the cork of a bottle in which
one of them may be inclosed.

BPBOIAZ. aOir8mBRATION&

In the case of weakly tuberculous animals a sharp tap on
the chest will often produce a contraction of the muscles thus
stimulated; but, in addition, a local contraction lasting some
little time, known as a wheal or idio-muscular contraction, fol-
lows. This phenomenon seems to be the result of a special
irritability in such muscles.

Cramp may arise under a great variety of circumstances,
but it seems to be in all cases either a complete prolonged teta-
nus, in which there is unusual muscular shortening in severe
cases, at least, or the persistence of a contraction remainder.

The great differences known to exist between individuals of
the same species in rtrength, endurance, fleetness, and other
particulars in which the muscles are concerned, raise numer-
ous interesting inquiries. The build of the greyhound or raoe-
horse suggests in itself part of the explanation on mechanical
principles, lung capacity, etc. But when it is found that one
dog, horse, deer, or man excels another of the same raoe in
swiftness or endurance, and there is nothing in the form to
furnish a solution, we are prompted to ask whether the muscles
may not contract more energetically, experience a shortening
of the latent period or other phase of contraction; or whether
they produce less of waste-products or get rid of them mora
rapidly. The whole subject is extremely complicated, and we
may say here that there is some evidence to show that in races
of d(^ and other animals which surpass titeir fellows the
nerve regulating the heart and lungs (vagus) has greater power :

904

COMPARATIVE PHT8I0L0QY.

but, leaving this and much more out of the nocount, it is lilcely
there are individual differenoea in the functionul nature of the
muscle. Of equal or more importance ii the energiiing influ-
ence of the nenroui system, which probably under great excite-
ment (public boat-raoes, etc.) acts to produce in man those
Mupermaximal contractions which seem to leave the muscle
long the worse of its unusual action. The nerve-oenters, it is
likely, suffer still more from excessive discharge of nerve-force
(as we may speak of it for the present) necessary to originate
the muscular work. Hence the importance of training in all
animals to minimise the non-effective expenditure, ascertain
the capacity possessed, learn the direction in which wealaiesses
liu; and equally important the much neglected-period of reat
before actual contests— if such are to be undertaken at ail-
so that all the activities of the body may gather head, and thus
be prepared to meet the unusiial demand upon them.

The law of rhythm in organic nature is beautifully illus-
trated by the behavior of nerve and especially muscle; at least
it is more obvious in the case of muscle, at this stage of our
progiWH.

The regularity with which one phase succeeds another in a
single contraction; the essentially rhythmic (vibratory) char-
actor of tetanus, fatigue and recovery ; the recurrence of in-
crease and decrease in the muscle and nerve currents — ^in fact,
the whole history of muscle is an admirable commentary on
the truth of the law of rhythm, into which in further detail
space will not permit us to enter.

It is a remarkable fact that the endurance of man, especially
civilised man, seems to be greater than that of any other mam-
maL It may be hasardous to express a dogmatic opinion aa to
the reason of this, but the influence of the mind over the body
is unquestionably greater in man than in any other animal ;
and, if we are correct in assigning so much importance to the
influence of the nervotu system in maintaining the proper
molecular balance which is at the foundation of the highest
good of an organism, we certainly think that it is in this direc-
tion we must look for the explanation of the above-mentioned
fact, and much more that would otherwise be obactire in man*a
functional life.

PunetieMl VMriatJani.- We have endeavored, in treating
this subject of muscle, to point out how the phenomena vary
with the animal, the kind of muacle, and the oircumsttaices

- 'If ■ - ■'■■ ' j"fW!.'-^ gaa MMl

■■MMiKMMM

TUB STUD*' of MI'^CLK PUYSIOLOOY.

905

lunt, it [n likely
«I future of the
mergizing influ-
iler great excite-
I in nurn thoee
ove the muMle
nre-^senters, it i*
« of nerve-force
ary to originate '

training in all
diture, ascertain
hich weokneaiies
id-period of rest
ertaken at all—
e head, and thus
them,
beautifully illus-

muacle; at least
this stage of our

seds another in a
[vibratory) char-
'eourrenoe of in-
■urrents— -in fact,-
commentary on
in further detail

f man, especially
any other mam-
itic opinion as to
ad over the body
ly other animal ;
nportanoe to the
ining the proper
»n of the highest
it is in this direc-
above-mentioned
I obecUre in man's

ored, in treating
phenomena vaiy
he oircumsttmcea

ti ihey an <«nifMit«(l It may lie shown that every
one of qualitieD jjeh a mUHcId possesses varies with the
tsmpMk -e, the b] ««i-Mipply, the duration of its action, the
ehanwilf >f the 8tiii4>uiuti^ and other modifying agents. Not only
are theri grmt varM^ons for different groups of animals, but
lesser ones for individuals ; though the latter are made more
evident indirectly than when tested by the usual laboratory
methods ; but they must be taken account of if we would un-
derstand animals as they are. Some of thest will be referred
to later.

If a muscle-cell be regarded in the aspect that we are now
emphasising, its study will tend to impress those fundamental
biological laws, the comprehension of which is of more impor-
tance than the Requisition of any number of facts, which, bow-
ever interesting, can, when isolated, profit little.

luuBMrjr of tht Phjdology of MiuoU ud Vtrr*.— The
movements of a muscle are distinguished from those of other
forms of protoplasm by their marked deflniteness and limit-
ation.

The contraction of a muscle-flber (cell) results in an increase
in its short transverse diameter, and a diminution of its long
diameter, without appreciable change in its total bulk.

Muscle and nerve are not automatic, but are irritable.
Though muscle normally receives its stimulus through a nerve,
it possesses independent irritability.

Stimuli may be mechanical, chemical, thermal, electrical, and
in the case of muscle, nervous ; and to be effective they must
be applied suddenly and last for a brief but appreciable time.

Eleotical stimulation, espedally, is only effective when
there is a sudden change in the force or direction of the cur-
rents. This applies to both musde and nerve.

A muscular contraction consists of three phases : the latent
period, the period of rising, and the period of falling energy, or
of contraction and relaxation.

When the phase of relaxation is lAinimal and that of con-
traction approaches continuity, a tetanus results. The contrac-
tions of the muscles in aitu are tetanic, and are accompanied
by a low sound, evidence in itself of their vibratory character.

The prolonged contraction of a muscle leads to fatigue ;
owing in part, at least, to the accumulation of waste-products
within the muscle which depress its energies.

This is a necessary consequence of the fact that all proto-

•f

COMPARATIVB PnYSIOLOGT.

plwnnio activity in accompanied by chemical change, and that
■onie of those prooenea reeult in the formation of products
which are huri«i'l and are usually rapidly expelled.

Muscular contraction is accompanied by chemical changea,
in which the formation of carbon dfbxide, and some lubatance
that oauaea an acid rvaotion to tak<t the place of an alkaline or
neutral one. Bince free oxygen in not required for the act of
contraction, but is »■ till used up by a contracting muscle, it may
he assumed that the oxygen that plays a part in actual oontrao*
tion is intra-molecular.

Chemical changes are inseparable from the vital processes
of all protoplasm, and the phenrmena of muscle show that
they are constantly in operation, but exalted during ordinary
contraction and Uiat tetanic condition which precedes and
may end in coagulation of muscle plasma and the formation of
myosin. The latter is a result of the disorganisation of muscle,
and has points of reaemUanoe to the coagulation of the blood.

The contraction of a muscle and the passage of a nenrous
impulse are accompanied by electrical changes. Whether cur-
rents Axist in uninjured muscle and nerve is a matter of contro-
versy. SlU physiologists agree that they exist in muscle (and
nerve) duHng functional activity.

During the passage of a constant (polarising) current from
a battery through a nerve, it undergoes a change in its irrita-
bility and shows a variation in the electro-motive force of the
ordinary nerv»«urrent (electrotonus). This fact is of thera*
peutic importance. The electrical phenomena of nerve are
altogether more iwominent than the chemical, the reverse of
which is true of muscle. The activity of a muscle (and nerve
probably) is accompanied by the generation of heat, an exalta-
tion of which takes place dmring muscular contraction.

Rigor tnortia causes an increase in temperature and the
chemical interoluuiges which accompany the other phenomena.
A muscle may also become rigid by passing into rigor eaUoria.
Living muscle is translucent, alkaline or neutral in reaction,
and elastic ; dead muscle, opaque, acid in reaction, and devoid
of elasticity, but firmer than living muscle, owing to coagular
tion of the musole-plasma. Dead nerve undergoes similar
changes.

The elasticity of muade is restricted but perfect within its
own limits. It differs from that of inorganic bodies in that the
increments of extension are not directly proportioniU to the

-Wt e.1. ^ .*-

ftnge, and that
m of produotK
ed.

tnioal ohangaii
ome lubitanoe
an alkaline or
I for the aot of
muMle, it may
ftotual oontrao-

vital proo M wei
•cle ihoiw that
uring ordinary
, preoedea and
tie formation of
iticm of moacle,
1 of the Mood,
ge of a nerrous
Whether our-
Mktterof oontro-
in muflole (and

f) ourrent from
nge in ita irrita-
iye force of the
'act ia of thera-
la of nenre are
1, the rerene of
lacle (and nerve
heat, an exalta-
raotion.

ertiture and the
her phenomena.
io rigor oaloris.
tral in reaction,
tion, and devoid
ring to ooagola-
idergpes similar

lerfect within its
)odies in that the
portional to the

THB STUDY OF MUSCLE PHYSIOLOGY.

907

increments of the weight When overstretched, muscle does
not return to ita original length (loss of elasticity), hence the
serious nature of sprains.

It is important to regard muscular elasticity as an expression
of vital properties.

The work done by a muscle is ascertained by multiplying
the load lifted by the height; and the capacity of an individual
muscle will vary with ita length, the arrangement of ita fibers,
and the area of ita oross-seotion (i. e., the number of Bbers). .
The work done may be regarded as a function of the resist-
ance (load), as the contraction is also a function of the stimulus.
The separation of a muscle from ita nerve by section of the lat-
ter leads to certain changes, most rapid in the nerve, which
show that the two are so related that prolonged independent
vitality of the muscle is impossible, and make it highly proba-
ble that muscle is eon$tanUy receiving some beneficial stimulus
from nerve, which is exalted and manifest when contraction
takes place.

The study of the development of the electrical cells of cer-
tain fishes shows that they are greatly modified muscles in
which contractility, etc., has been exchanged for a very decided
exaltation of electrical properties. It is likely, though not
demonstrated, that all forms of protoplasm undergo electrical
ohangea— that these, in fact, like chemical phenomena, are vital
oonstanta.

The phases of the contraction of smooth muscular tissue are
all of longer duration ; the oontraotion-wave passes in different
directions, and may spread into cells devoid of nerves, which
we think not unlikely also to be the case, though less so, for all
forms of musde.

The smooth musde-oell must be regarded as a more primi-
tive, less speeialixed, form of tissue. Variations in all the phe-
nomena of muscle with the animal and the circumstances are
clear and impressive. Finally, muscle illustrates an evolutiaii
of structure and function, and the law of rhjrthm.

MiM;'■^ta»AVfaHSl'a^a!i^u<^|| | ■ ' '^■jl^^|j^

I.
I

THE NERVOUS SYSTEM.— GENERAL CONSIDER-
ATIONS. I

Swob in the higher vertebrate the nervous system is domi-
nant, regulating apparently every prooeas in the organism, it
will be well before proceeding further to treat of some of ite
functions in a general way to a greater extent than we have yet

done.

Manifestly, it must be highly important that an animal shall
be able to place itself so in relation to its surroundings that it
may adapt itself to them. Prominent among these adaptations
aie certain movements by which food is secured and dangers
avoided. The movements haying a central origin, a peripheral
mechanism of some kind must exist so as to place the centers
in connection with the outer world. Passing by the evolution
of the nervous system for the present, it is found that in verte-
brates generally there is externally a modification of the epi-
thelial covering of the body (end-crgan) in which a nerve te^
minates, which latter may be traced to a cell or cells removed
from the surface (center), and from which in most cases other
nerves proceed.

The nervous system, we may remind the student., consists in
vertebrates of centers in which nerveKjells abound, united by
nerve-fibers and by the most delicate form of connective tissue
known, in connection with which there are incased strands
of protoplasm or nerves as outgrowths. The main centers are,
of course, aggregated in the brain and spinal cord.

It is possible to conceive of the work of a nervous system
carried on by a single cell and an afferent and efferent nerve;
but inasmuch as such an arrangement would imply that the
central cell should act the pai-t of both receiving and origi-
nating impulses (except it were a mere conductor, in which case
there would be no advantage whatever in the existence of a cell
at all), according to the principle of the physiological division

w^^f^^^^

CONSIDER.

lystem is domi-
le organism, it
of some of ite
an we have yet

ua animal shall
undings that it
lese adaptations
ad and dangers
[in, a peripheral
lace the oentars
ly the evolution
id that in verte-
tion of the epi-
ich a nerve ter-
•r cells removed
nost cases other

lent., consists in
Dund, united by
lonnective tissue
incased strands
nain centers are,
trd.

nervous system
1 efferent nerve;

imply that the
iving and origi-
or, in which case
cistence of a cell
>logical division

NERVOUS SrSTEM.-OENERAL CONSIDERATIONS. 209

of labor, we might expect that there would be at least two cen-
tral cells— one to receive and the other to transmit impulses—
or at least that there should be some speoialiiation among the
central cells ; and we shall have good reason later to believe
that this has reaehed a surprising degree in the highest ani-
mals.

Moreover, it would be a great advantage if thf termination
of the ingoing (afferent) nerve should not lie exposed on the
surface, but be protected by some form of ce)! that had also the
power to transmit to it the impressions received from without,
in a form suitable to the nature of the nerve and the needs of
the organism. *

So that a complete mechanism in its simplest form would
furnish: 1. A peripheral cell or nerve end-organ. 8. Anaffer-
,ent or sensory nerve. 3. Two or more central cells. 4. An
efferent nerve, usually connected with— 6. A muscle or other
form of cell, the action of which may be modified by the out-
going nerve, or, as we should prefer to say, l^ the central
nervous ceUs through the efferent nerve. The advantages of
the principa]*oells being within and protected are obvious.

When, then, an impression made on the peripheral cell is
carried inward, there modified, and results in an outgoing nerv-
ous impulse answering to the afferent one, giving rise to a mus-
cular contraction or other effect not confined to the recipient
cells, the process is termed reflex (urfton.

The great size, the multiplicity of forms, the distinct out- \
line and large nuclei of nerve-cells, suggest the probability that
they play a very important part, and such is found to be the
case. Indeed, in some sense the rest of the nervous system may
be said to exist for them.

Probably nerve-cells do sometimes act as mere conductors
of nervous impulses originating elsewhere, but such is their
lowest function. Accordingly, it is found that the nature of any
refiex action depends most of all on the behavior of the central
cella.

It can not be too vrell borne in mind that, nerves are con-
ductors and such only. They never originate impulses.

The properties considered in the last chapter are common to
all kinds of nerves Imown; and though we must conceive that
there are some differences in the form of impulses, these are to
be traced, not to the nerve primarily, but to tiie organ in which
it ends peripherally or to the central cells.
U

itm

210

COMPARATIVE PH\SIOLOQY.

To ret>jm to reflex action, it is found that the muacula/ re-
sponse to a peripheral irritation varies with the point stimu-
lated, the intensity of the stimulus, etc., but is, above all, deter-
mined by the central cells.

Nerve influence may be considered as following lines of
least resistance, and there is much evidence to show that an im-
pulse having once taken a certain path, it is easier for it to pass
in this direction a second time, so that we have the foundation
of the laws of halnt and a host of interesting phenomena in
this simpk principle.

It is found that, in a frog deprived of its brain and sus-
pended by the under jaw, there is no movement unless some
stimulus be applied ; but if this be done under suitable condi-
tions, instructive results follow, which we now proceed to indi-
cate briefly. The experiments are of a simple character, which,
any student may carry out for himself.

Bjqys rimwitt J , —Preparing a frog by cutting off the whole
of the upper jaw and brain-case after momentary anaesthesia,
suspend the animal by the lower jaw and wait till it is perfectly
quiet. Add to water in a beaker sulphuric acid till it tastes
distinctly but not strongly sour, to be used as a stimulus. 1.
Apply a small piece of bibulous paper, moistened with the acid,
to the inner part of the thigh of the animal. The leg will be
drawn up and the paper probably removed. Remove the paper
and cleanse the spot 2. Apply a similar piece of paper to the
f middle of the abdomen ; one or both legs will probably be
drawn up, and wipe off the offending body. 3. Let the foot of
the frog hang in the liquid ; after a few moments it will be
withdrawn. 4. Repeat, holding the leg ; probubly the other
leg will be drawn up. 5. Apply stronger acid to the inside of
the right thigh ; the whole frog may be oonvulsed, or the left
leg may be put in action after the right. Even if the stimulat-
ing paper be applied near the anus, it will be removed by the
hind-legs. 6. Beneath the skin !>f the back (posterior lymph-
sac) inject a few drops of liquor strychnise of the pharama-
oopoeia; after a few minutes apply the same sort of stimulus to
the thigh as before. The effects follow more quickly and are
much more marked-^the animal, it may be, passing into a gen-
eral tetanic spasm.

These exiwriments may be varied, but suffice to establish the
following conclusions : 1. The stimulus is not immediately
effective, but requires to act for a certain variable period, de-

muscular re-
I point atimu-
love all, deter-

wing lined of
>w that an im-
r for it to pass
he foundation
phenomena in

tnrain and sua-
kt unless some
suitable oondi-
>rooeed to indi-
laracter, which,

o£F the whole
try anaesthesia,
1 it is perfectly
id till it tastes
a stimulus. 1.

I with the acid,
The leg will be
tnove the papw
of paper to the

II probably be
Let the foot of

lents it will be
bubly the other
o the inside of
Ised, or the left
if the stimulat-
removed by the
losterior lymph-
f the pharama-
t of stimuluK to
luickly and are
iiing into a gen-

» to establish the
Lot immediately
iable period, do*

NERVOUS 8Y8TBM.-GENBBAL CONSIDERATIONS. 211

UNMMV CtLL AND
AfnWMT NIKVt

''MOTCW CIU MW

immNTNmvt

MOTOM CIU WITH

immNTNnNi

*^"J«!:r°If'*" '5f4«* t" HlMtnrte nervona mechmbm oT-l. aatainulMii; 8.
wfiex action; ami S. how nervona impnlaea In the latter caae maj paaa Into tbS
bigher parte of brain and become part of conaolouaneaa, or be whAly inhibited.
^^^M 2Sm^°t£"^ '°*^' '•* "*'*''• o' •topUclty, be rwlnced to a ain-

pending diiefly on the condition of the central nervous sys-
tem. 2. The movements of the muscles harmonise (are oo-oi-di-
nated), and tend to accomplish some end— are purposive. If
the nerve alone and not the skin be stimulated, there may be a
spasm only and not adaptive movement 8. Nervous impulses,
when very abundant, may pass along unaccustomed or less ac-
customed patiu (experiments 4 and 5). This is sometimes spoken
of as the radiation of nervous impulses.

The sixth experiment is very important, for it shows that
the result varies far more with the condition of the nervous
centers (cells) than the stimulus, the pai. jxcited, or any other
factor.

AvtoaufcinL— But, seeing that these central cells have such
ind^endence and controlling power, the question arises, Are

312

COMPARATIVE PHYSIOLOGY.

these, or are there any such cells, capable of originating im-
pulses in nerves wholly, independent of any stimulus from
without? In other words, haye the nerveHwnters any true
autrmadsm ? Apparently this quality is manifested by uni-
cellular organisms of the rank of Amoeba. Has it been lost, or
has it become a special characteristic developed to a high degree
in nerve-cells ?

We shall present the facts and the opinions based on them
as held by the majority of pliysioiogists, reserving our own
criticisms for another occasion : 1. The medulla oblongata is
supposed to be the seat of numerous small groups of cells, to a
large extent independent of each other, that are constantly
sending out nervous impulses which, proceeding to certain sets
of muscles, maintain them in rhythmical action. One of the
best known of these centers is the respiratory. 8. The poste-
rior lymph hearts of the frog are supplied by nerves (tenth
(lair), which are connected, of course, with ^e spinal cord.
When these nerves are cut, the hearts for a time cease to beat,
but later resume their action. 3. The heart beats after all its
nerves are cut, and it is removed from the body, for many hours,
in cold-blooded animals. 4. The contractions of the intestine
take place in the absence of food, and in an isolated piece of
the gut The intestine, it will be remembered, is abundantly
supplied with nerve-elements. 5. In a portion of the ureters,
from which it is believed nerve-cells are absent, rhythmical ac-
tion takes place.

Conoliirioiii.— 1. Whether the action of the respiratory and
similar centers could continue in the absence of all stimuli can
not be considered as determined. 8. That there are regular
rhythmical discharges from the spinal nerve^iells along the
nerves to the lymph hearts seems also doubtfbl. 3. Later in-
vestigations render the automatidty of the heart more uncer-
tain than ever, so that the result stated above (3) must not be
interpreted too rigidly.

Similar doubts hang about the other oases of apparent au-
tomatism.

As regards the various comparatively isolated collections of
cells known as ganglia, the evidence, so far as it goes, is against
their possessing either automatic or reflex action ; and new
views of their nature will be presented in due course.

HoTfOU LlhiUtiBB.— If the pneumogastrio nerve passing
from the medulla to the heart of vertebrates be divided and the

V4i«i.

riginating im-
stimulus from
Lters any trae
fested by unl-
it been loet, or
> a high degree

based on them
>ving our own
a oblongata is
ps of cells, to a
are constantly
', to certain sets
m. One of the
, 2. The poste-
f nerves (tenth
lie spinal cord,
te cease to beat,
tats after all its
for many hours,
of the intestine
solated piece of
i, is abundantly
1 of the ureters,
rhythmical ao-

respiratory and
f all stimuli can
tiere are xegaHar
i-cells along the
bl. 3. Later in-
art more uncer-
) (3) must not be

I of apparent au-

»d collections of

it goes, is against

wstion ; and new

Bourse.

io nerve passing

B divided and the

NERVOUy SYSTEM.— GENERAL CX)NSIDERATIONS. 213

lower (peripheral) end stimulated, a decided change in the ac-
tion of the heart follows, which may be in the direction of
weakening or slowing, or positive arrest of its action.

Assuming, for the present, that the cells (center) of the me-
dulla have the power to bring about the same result, it is seen
that such nervous influence is preventive or inhibitory of the
normal cardiac beat, so that the vagus is termed an iidiibitory
nerve. Such inhibition plays a very important part in the
economy of the higher animals, as will become more and more
evident as we proceed. The nature of the influences that pro-
duce such remarkable results will be discussed when we treat
of the heart.

An illustration will probably serve in the mean time to make
the meaning of what has been presented in this chapter more
clear and readily grasped.

In the management of railroads a very great variety of com-
plicated results are brought about, owing to system and orderly
arrangement, by which the wishes of the chief manager ai«
carried out.

Tel^H^pIung is of necessity extensively employed. Sup-
pose a message to be conveyed from one office to another, this
may (1) simply pass through an intermediate office, without
special cognisance from the operator in charge ; (2) the operator
may receive and transmit it unaltered ; (3) he may be required
to send a message that shall vary from the one he receives in a
greater or less degree ; or (4) he may arrest the command alto-
gether, owing to the facts which he alone Imows and upon
which he is empowered always to act according to his best dis-
cretion.

In the first instance, we have an analogy with the passage
of a nervous impulse through central fibers, or, at all events,
unaffected by cells ; in the second, the resemblance is to cells
acting as conductors merely ; in the third, to the usual behavior
of the cells in reflex action; and, in the fourth, we have an in-
stance of inhibition. The latter may also be rendered clear by
the case of a horse and its rider. The horse is controlled by the
rider, who may be compared to the center, through the reins
answering to the nerves, though it is not possible for either rider
or reins to originate the movements of the animal, except as
they may be stimuli, which latter are only effective when there
are suitable conditions— when, in fact, the subject is irritable in
the physiological sense.

te^

Ifi.'

THE CIRCULATION OF THE BLOOD.

EvKRT tiaaue, eyery cell, requiring constant nourishment,
some means must necessarily have been provided for the con-
veyance of the blood to all parts of the orgasasm. We now
enter upon the consideration of the meohanisma by which this
is accomplished and the method of their regulation.

Let us consider possible mechanisms, and then inquire into
their defects and the extent to which they are found embodied
in nature.

That there must be a central pump of some kind is evident .
Assume that it is one-chambered, and with an outflow-pipe
which is continued to form an inflow-pipe. This might be pro-
vided with valves at the openings, by which energy would be
saved by the prevention of regurgitation. In such a system
things must go from bad to worse, as the tissues, by constantly
tising up the prepared material of the blood, and adding to it
their waste products, would effect their own gradual starvation
and poisoning.

It might be conceived, however, that waste at all events was
got rid of by the blood being conducted through some elimi-
nating organs ; and assume that one such at least is set aside
for respiratory work. If the blood in its course anywhere
passed through such organs, the end would be attained in some
degree ; but if the division of labor were considerable, we
should suppose that, gaseous interchange being so very impor-
tant as we have been led to see from the study of the chapters
on general biology, and on muscle, organs to accomplish this
work might receive the blood in due course and return it to the
central pump in a condition eminently fit from a respiratory
point of view.

Such, however, would necessarily be associated with a more
complicated pump ; and, if this were so constructed as to pre-
vent the mixture of blood of different degrees of functional
value, higher ends would be attained.

LOOD.

t nourishment,
ed for the con-
ism. We now
I by which this
ion.

len inquire into
ound embodied

tdnd is evident.
m outflow-pipe
is might be pro-
nergy would be
L such a sytiem.
8, by constantly
md adding to it
adual starvation

ii all events was
ugh someelimi-
least is set aside
Durse anywhere
attained in some
M>nsiderable, we
f so very impor-
r of the chapters
accomplish this
1 return it to thd
om & respiratory

ited with a more
bructed as to pre-
tm of functional

THE CIRCULATION OP THE BLOOD.

916

Turning to the channels themselves in which the blood
flows, a little consideration will convince one that rigid tubes
are wholly unflt for the purpose. Somewhere in the course of
the circulation the blood must flow sufficiently slowly, and
through vessels thin enough to permit of that interchange be-
tween the blood and the tissues, through the medium of the
lymph, which is essential from every point of view. The main
vessels must have a strength sufficient to resist the force with
which the blood is driven into them.

Now, it is possible to conceive of this being accomplished
with an intermittent flow ; but manifestly it would be a great
advantage, from a nutritive aspect, that the flow and therefore
the supply of tissue pabulum be constant With a pump regu-
larly intermittent in action, provided with valves, elastic tubes
having a resistance in them somewhere sufficient to keep them
oonstantiy ovecdistended, and a collection of small vessels with
walls of extreme thinness, in which the blood-ourr mt is greatiy
slackened, a steady blood-flow would be maintained, as the
student may readily convince himself, by a few experiments of
a very simple kind :

1. To show the difference between rigid tubes and ekstic
ones, let a piece of glass-rod, drawn out at one end to a small
diameter, have attached to the other end a Higginson's (two-
bulb) syringe, communicating with a vessel containing wator.
Every time the bulb is squeeaed, water flows from the end of
the glass rod, but the outflow is pmfeotiy intermittent.

8. On the other hand, with a long elastic tube of India-rub-
ber, ending in a piece of glass rod drawn out to a point as be-
fore, if the action of the pump (bulb) be rapid the outflow will
be continuous. An apparatus that every practitioner of medi-
chie requires to use answers perhaps still better to illustrate
these and other principles of the circulation, such as the pulse,
the influence of the force and frequency of the heart-beat on the
blood-pressure, etc. We refer to a two-bulb atomizer, the bulb
nearer the outflow serving to maintain a constant air-pressure.

We may now examine the most perfect form of heart
known, that of the mammal, in order to ascertain how far it
and its adjunct tubes answer to a priori expectations.

Th* Mammriltii EMurt.— In order that the student may gain
a correct and thorougfa knowledge of the anatomy of the heart
and the workings of its various parts, we recommend him to
pursue some ffuch course as the following :

'Bmmsmise^^iSimm

216

COMPARATIVE PHYSIOLOGY.

1. To consult a number of platM, roch as are usually fui^
nished in works on anatomy, in order to ascertain in a general
way the relations of the heart to other organs, and to the chest
wall, as well as to become familiar with its own structure.

8. To supplement
this with reading the
anatomical descrip-
tions, without too great
attention to details at
flrst, but with the ob-
ject of getting his ideas
clear so fkr is they go.
8. Then, with plates
and desariptions before
him, to examine sever-
al dead specimens of
the heart of the sheep,
ox, pig, or other mam-
mal, first somewhat
generally, then qrste-
matioally, with the
purpose of getting a
more exact knowledge
of the various struct-
ures and their anatom-
ical as well as physi-
ological relations.

We would not have
the student confine his
attention to any single
form of heart, for each
shows some one struofe-
uie better than the

Fiu

l»v.-The Mt mrid* Mid vmMcie owned rad

iSi;Sfci?i«?l7j||i^^P^ oomp.rii|on «e very

m»KlM:«.oi»<Nirnent «rfiU» »^^ T, ^^^ f^^ heart of

the ox, from its sue,
is excellent for the study of valvular action, and the framework
with which the muscles, valves, and mmOB are connected ;
while the heart of the pig (and dog) resemble the human organ
more closely than most othras that can be obtained.

i uiually fur>
in a general
1 to the cheit
ruoture.
supplement
reading the
al deeorip-
bout too great
to details at
with the ob-
tting his ideas
liar M they go.
m, with plates
?iptions before
xamine sever-
specimens of
t of the sheep,
>r other mam-
st somewhat
r, then vyste-
r, with the
of getting a
act knowledge
rariotts stmet-
. their anatom-
well as physi-
relations.
irould not have
ent confine his
n to any single
heart, for each
omeonestructr
Iter than the
and the addi-
advantages of
ison are very
Thq heart of
, from its sise,
the framework
ire oonneeted ;
B human organ
led.

THE CIRCULATION OP THE BLOOD.

217

It will be found very helpful to perform some of the dissec-
tions under water, and by the use of this or some other ^uid
the action of the valves may be learned as it can in no other
way. By a little manipulation the heart may be so held that
water may be poured into the orifices, prepared by a removal
of a portion of the blood-vessels or the auricles, when the valves
may be seen closing together, and thus revealing tiieir action in
a way which no verbal or pictorial representation can do at all
adequately.

A heart thoroughly boiled and allowed to get cold shows, on
being pulled somewhat apart, the course, attachment, and Other

m.9.t

LAT

V\a.im.—yUm or Ow otlflCM of tlie bwit fhn below, th* whole of the ventrlctee
having been cut awajr (after Hnzley). RAV, right anrlenk^Tentriealar oriflce.
•nmmiided hj the three Smm, /. r. 1. 1. 1. S, (. ». S, of the trienepM valve, whieh an
Mretehed bv weighta attaetcd to the «hcrttm Itmttime. LA V, left anrlcBlo-ven-
tncnlar oriloe. etc. PA, oriSce of the piiliiioiiai7 arteiy, the •emllanar valvea
ro|if aaaulad aa having met and eloaed together. ^ O, oriOee of the aorta.

features of the fibers very well, as also the skeleton of the organ,
which may be readily separated.

When this has all been done, the half is not yet accom-
plished. A visit to an abattoir will now repay amply for the
time spent Animals are there killed and eviscerated so rapidly
that an observer may not only gain a good practical acquaint-
ance with the relations of the heart to other parts, but may
often see the oi^^an still living and exemplifying that action

simtm

«UMb

218

COMPARATIVE PHYSIOLOUY.

;

p«ouUar to it ai it g^ndually approaoliM quiometice and death
—A matter of the uttnoat importance.

If the atudent wili then compare what he hai learned of the
mammalian heart in thia way with the beharior of the heart
of a frog, anake, flab, turtle, or other animal that may be killed
after brief ether narooaia, without ceaaation of the heart'a ac-
tion, he will have a broader baaia for hia cardiac phyiiology
than ia uaual; and wa think we may promiae the medical atu-
dent, who will in thia and other way* that may occur to him
aupplement the usual work on the human cadaver, a pleaaure
and profit in the study of heart-diaeaae which come in no
other way.

With the yiew of assiating the obaenration of the student
aa regards the heart of the mammal, we would call special attan
tion to the following points among others: Ita method of sus-
pension, chiefly by its great vesaela ; the atrong fibrous frame-
work for the attachment of valrea, veasels, and muaele-fibeis;
the great complexity of the arrangement of the latter; the
various lengths, mode of attachment, and the strength of the

Xrt

Fie. IflB.— OrMteM of the hMrt wm fram thtm, aftar the mrlelM and jnat i
had bementawv (after Hnxler). Pit.MlmomiryartcrTwIthlUaenidiwwTalnN.
Ao, aorta m a aimihur condition. KAV, ri(H>t aarlculo>veiitriealar oriflee, with

m. V. 1 and 9 flapa of mittal Talve; i, atjle p aa ii id Into eoranary ireiB. On the left
futotLAV the leetion of the aarlcle b eanied through ihe auricular appendage,
hence the toothed appearance due to the portiona in relief cut aeraaa.

inekstic chordae tendinese; the papillary muscles, which doubt-
leas act at the moment the valvea fiap bock, thus preventing

BQce and death

I learned of the
or of the heart
ti mmy be killed
r the heart's ac-
diao physiology
he medical itu-
ly occur to him
aver, a pleasure
ioh come in uo

I of the student
sail special atten
I method of sus-
f tLhfOvm frame-
id musole-flbers;
the latter; the
strength of the

rlolM nd rMt
IthlUMiniliuwTmlTW.
rantricalKr orWce. with
waiTveltt. Ontbelen
lie •orienlw •ppendafte,
eat aeroM.

sles, which doubtr
, thus prerenting

THE CIRCULATION OF THE BLOOD.

219

the latter being carried too far toward the auricles, the pocket-
ing action of the semilunar Talres with their strong margin
and meeting nodules (eorpora AranM) ; the relative thickness
of auricles and ventricles, and the much greater thickness of
the walls of the left than of the right ventricle -differences
which are related to the work these parts perform.

The latter may be well seen by making transverse sections
of the heart of an animal, especiidly one that has been bled to
death, which specimen also shows how the contraction of the
heart obliterates the ventricular cavity.

It will also be well worth while to follow up the course
of the coronary arteries, noting especially their point of
origin.

The examination of the valves of the smaller hearts of cold-
blooded animals is a matter of greater difficulty and is facili-
tated by dissection under water with the help of a lens or dis-
secting microscope; but even without these instruments much
may be learned, and certainly that the valves are relatively to
those of the mammalian hewt imperfectly developed, will be-
come very clear.

amaauLTsom of nn blood nr ram ««a««wAT.

It is highly important and quite possible in studying the
circulation to form a series of mental pictures of what is trans-
piring. It will be borne in mind that there is a set of elastic
tubes of relatively thick walls, standing open when cut across,
dividing into smaller and smaller branches, and finally ending
in vessels of more than cobweb fineness, and opening out into
others, that become larger and larger and fewer and fewer, till
they are gathered up into two of great sue which form the right
auricle. The larger pipes consist everywhere of elastic tissue
proper, muscular tissue (itself elastic), fibrous tissue, and a flat
epithelial lining, so smooth that the friction therefrom must be
minimal as the blood flows over it.

The return tubes or veins are like the arteries, but so thin
that their walls fall together when out across. They are differ-
ent from all the other blood-tubes in that th«y poss e ss valves
opening toward the heart throughout their course. The veins
aro at least twice as numerous as the arteries, and their capacity
many times greater. The small vessels or capillaries are so
abundant and wide-spread that, as is well known, the smallest

■MM

220

COMPARATIVE PHY8I0L00V.

out anywhere f^vea rite to A
flow of blood, owinff to wec-
tlou of wnne of these tubes,
which, it will be remembered,
are not yitible to the unaided
eye. It i« estimated that their
united area i« sereral hun-
dred (500 to 800) time* that of
the arteries.

If we suppose the epithe-
lial Ibaing pushed out of a
small artery we have, so far
as structure alone goes, a
good idea of a capiUary— i. e.,
its walls are but one cell
thick, and these cells though
long are extremely thin, so
that it is quite easy to under-
stand how it is that the amoe-
boid corpuscles can, under
certain circumstances, push
their way through its proba-
bly semi-fluid walls.

From what has been said,
it will be seen that the whole
collection of vascular tubes
may be compared to two inverted funnels or cones with the

Km. 18B.-V»rloui lav«n of tke wallt ofs
•mall ■rtenr (Undoii). t, •ndothellnm ;
i. «, intermt elMtle lamtM; e.m, dicii-

•■• moKoUur flb«n of the middle CMt;
«. (, coniMetlve Umm of the ontor eoM,
or T. ikdvaiititia.

Fio. 190.

Fts. in.

Pio. 190.— Vein with Ttlvee lying open (DaHoD). ^ , . , v •. v i _

Flu. 191.- Vein with valvet clowd, the blood pMtlng on by « latMid btWMsh below
(Didton).

fivea riM to •

swing to HM-

theM tubei,
remembered,

the unaided
ited that their
•ereral hun-
) timet that of

le the epithe-
lied out of a
) have, eo far
lone goes, a
ipillary— i. e.,
but one cell
i cells though
mely thin, lo
BMy to under-
that the amoe-

1 can, iinder
urtances, push
jgh ita proba-
nrallB.

has been Mid,
that the whole
raacular tubea
onea with the

THK OIRCITLATION OP TUB BLOOD.

8S1

''•%?ft"n^l*'J'»7 blood-T*i»U (Undolii. The CMnmt fulMUiic* between the en-
dolhellaiii hM bMit imdtnd daik by •Uver nilmte, and the nuolei made prominent

smaller end toward fbe heart and the widest portions repre-
senting the capillaries.

''••JftrBiSSi !?i!'"!?!i!» *•* ietaUrt proportloiH of thtt AgsreaMe MetloiwI area

flfttadUr&wtpaiitaorthevaaeiiIarij8tem(aftarY«o). A. aucta; O, capiUariaa; <

V, vaina*

222

COMPARATIVE PHYSIOLOOY.

THB AOnON OF THta

What takes place raay be thus very briefly stated : The
right auricle oontraoting squeeaes the blood through the au-
rioular-ventricular opening into the right ventricle, never quite

Inperior Vena
Cava.

Inferior Vena
Cava.

Capillariof of
Liver.

Portal Vein.

CapUlarieaof the
lead, etc.

Pnlmonaiy Ca-
pUlariea.

Main Arterial
Trunk.

Caplllariea of
. flplanehiilc
Area.

Caplllariea ot
Trankand
Loivvr Kc*
tnmltlM.

Fid IIM — Diaoram of Uw elRulation. Tbc arrowa indicate the eeWMOf tiie bteod.

aie rapnaented aoaa to ahowthe diatlnetMaa ofMd^ •» «J''^ 'iS»^!?2**fJ
Uiey m not IndMMndmt. BelaUte bI« of dl««iwit parte of the ayalam la only

very gwwnUly in d i cated.

emptying itsdf probably; immediately after the rij^t ventricle
contracts, by which its valves are brought into sudden tension
and opposition, thus preventing reflux into the auride ; while
the blood within it takes the path of least resistance, and the

i - t t i nL i m i< B — ■

' stated : The
ough the au-
le, never quite

CdPlllMiMofUie
~ Bowl, etc.

Pnlmonarjr Ca-
" pillaries.

Main ArtertatI
Trunk.

CapUlariMof
. BplHMhiile

ATM.

CapilltriM oT

, TtiuikMid

— liOwarBs-
tNmitict.

eottw of the blood.
•vitMric eiieataUon
be alio amrait that
A tlw umm to only

) right Tentriole
sudden tension
) auride ; while
istance, and the

THB OIBOULATION OF THB BLOOD.

298

only one open to it into the pulmonary artery, and by its
branches is conveyed to the capillaries of the lungs, from which
it is returned freed bom mudi of its carbonic anhydride and
replenished with oxygen, to the left auricle, whence it proceeds
in a similar manner into the great arterial main, the aorta, for
general distribution throughout the smaller arteries and the
capillaries to the mosi. remote as well as the nearest parts, from
which it is gathered up and returned laden with many impuri-
ties, and robbed of a large proportion of its useful matters, to
the right side of the heart

It will be remembered that corresponding subdivisions of
each side ot the heart act simultaneously, and that any decided
departure from this luamony of rhythm would lead to serious
disturbance.

THB VB10aiT7 OF THB BLOOD AMD BZiOOD^PBBSSDRBi

If the relative capacity and arrangement of the various parts
of the circulatory Byalbem be as has been represented, it follows
that we may predict with some confidence, apart from ezperi-*
ment, what the speed of the flow and the vascular tension must
be in different parts of the course of the circulation.

We should suppose that, in the nature of the cas«, the veloc-
ity would be greatest in Oie large arteries, gradually diminish
to the capillaries, in which it would be much the slowest and,
getting by degr ees faster, would reach a speed in the largest
veins approaching that of the corresponding arteries.

The methods of detennining the velocity of the bIood*fltream
have not entirely surmounted the difficulties, but they do give
results in harmony with the above-noted anticipations.

The area of the great aortic trunk being so much less than
thai of the capillaries, the flow in that vessel we should expect
to be very much swifter than in the arterioles or the capillaries.
Moreover there must be a great difference in the velocity during
cardiac systole and diastole, and according as the beat of the
heart is fordbie or otherwisa But apart from these more ob-
vious differences, there are variations depending on complex
changes in the peripheral circulation, owing to the frequent
variations in the diameter of the arterioles in different parts,
as well as differenoes in the resistance offered by the capillaries,
the causes of which are but ill undontood, though less obscure,
we think, than they are often represented to be. Since for the

•■■M^4»^"

224

COMPARATIVE PHYSIOLOGY.

^■'

i:.
at ■

maintenance of the circulation, the quantity of blood entering
and leaving the heart must be equal, in consequence of the sec-
tional area of the great veins that enter the heart being greater
than that of the aorta, it follows that the venous flow even at its
quickest is necessarily slower than the arterial.

GompafatiTe. — ^Therie must be great variations in velocity in
different animals, as such measurement* as have been made
demonstrate. Thus, in the carotid of the horse, the speed of
the blood-cunent is calculated as about 806 mm., in the dog at
from 205 to 357 mm. These results can not be considered as
more than fair approximations.

Highly important is it to note that the rate of flow in the
capillaries of idl animals is very slow indeed, not being as much
as 1 mm. in a second in the larger mammals. The time occupied
by the circulation is also, of course, variable, being as a rule
shorter the smaller the animals. As the result of a number of
calculations, though by methods that are more or less faulty,
the following law may be laid down as meeting approximately
the facts so far as warm-blooded animals are conoemed.

The circulation is effected by 27 heart-beats ; thus for a man
with a pulse of 81, the time occupied in the completion of the
course of the blood from and to the heart would be 14- = 3 ; i. e.,
ti.e <M ulation is completed three times in one minute, or its
pel. <' Ivrmty seconds; and it is to be well borne in mind
thai y ^' '■ he greater part of this time is occupied in traversing
the Cttpalaries.

TBB OIRODXJLnON lyMSBR ^BB lOiOROSOOPIi.

There are few pictures more instructive and impressive than
a view of the circulation of the blood under the mioroBoope.
It is well to have similar preparations, one under a low power
and another under a magnifioation of 800 to 500 diameters.
With the former a view of arterioles, veins, and capillaries may
be obtained at once. Many difltoent parts of animals may be
used, as the web of the frog's foot, its tongue, lung, or mesen-
tery ; the gill or tail of a small fish, tadpole, etc.

The relative sise of the vessels ; the speed of the'blood flow;
the greater velocity of the central part of the stream ; the aggre-
gation of colorless corpuscles at the sides of the vessels, and the
occasional passage of one through a capillary wall, when the
exposure has lasted some time; the crowding of the red cells;

I wM B Hp ijt . ' JMifW ri ft HMa *! * ' " " ? 1 ' 1 ^ 1 " "

wT'it yw iMB w www*-'

blood entering
snoe of the aec-
t being greater
flow even at its

B in velocity in
ave been made
e, the speed of
., in the dog at
B considered as

e of flow in the
; being as much
le time occupied
being as a rule

of a number of
9 or less faulty,

approximately
noemed.

thtu for a man
mpletion of the

be If = 8; i.e.,
e minute, or its

borne in mind
ied in traversing

cnosooPB.

impressiTe than
the mioKMOope.
der a low power
a 600 diameters.
1 capillaries may
animals maybe
lung, or xaxmesa-
c.

f thebloodflow;
ream; theaggre-
B vessels, and the
f wall, when the
of the red cells;

THE CIRCULATION OP THE BLOOD.

225

their plasticity; the small size of some of the capillaries, barely
allowing the corpuscles to be squeezed through; the changes in
the velocity ot the current, especially in the capillaries; its pos-
sible arrest or retrocession ; the velocity in one so much greater
than in its neighbor, without very obvious cause- -all this and

•howiiig Om Mood-TCMda, ud fai one cofBar the ptonrnt-Moto
TI» coBwe of U» blood i todlMtod by •nowfc ^^ ^^^

much more forms, as we have said, a remarkable lesson for the
thinldng student This, like all mioro«x>pic views, espeoiaUy
if motion is represented, has U« fallaoies.: It is to be ranem-
beredthat the movements are all magnified, <» else <nie is apt
to suppose the capillary drenlation, extremely rapid, whenas
it is like that of the most aloggish part of a straam, and very
irregular.

umiaiiiaimiM

226

GOMPi^TIVB PHYSIOLOGY.

•etoT The whole U dotted over with plgmciit niMHe.

THB OBARAOTBB8 OF TBB BLOOD-VXAW.

If an artery be opened, the blood is seen to flow from it in
a conrtant stream, with periodic exaggerations, which, it is
found, answer to the heart-beats ; in the case of veins and
capillaries the flow is also constant, but shows none of the
spurting of the arterial stream, nor hw the cardiac beat appar-
ently an equal modifying effect upon it.

We have already explained why the flow should be constant,
though it would be well to be clearer as to the peripheral re-
sistance. The amount of friction from linings so smooth as
thoae of the blood-vessels can not be considerable. Whence,
then, arises that friction which keeps the arterial vessels always
distended by its backward influence ? The microscopic study
of the circulation helps to answer this question. The plas-
ticity of the corpuscles and of the vessel walls themsdves must
be taken into account, in consequence of which a draggmg
influence is exerted whenever the corpuscles touch the wall,
which must constantly happen with vast numbers of them m
the smalltrt veMels and especially in the capillaries. The
arrangement of capillaries into a mesh-work, must als., in

HH«M ii >"i W'iii Wt i J iK

▼enoM tninlc com-
enaof BDwllerve*.

-FLOW.

low from it in
B, which, it is
I of veins and
8 none of the
iao beat appar-

ilA be constant,
I peripheral re-
I BO smooth as
ible. Whence,
I veasels always
croaoopic study
ion. The plas-
bemselves must
ich a dragging
touch the wall,
lers of them in
ipillaries. The
, must aUk, in

THE CIBCULATION OP THE BLOOD.

227

consequence of so many angles, be a source of much fric-
tion.

The action of the corpuscles on one another may be com-
pared to a crowd of people hurrying along a narrow passage —
the obstruction, comes from interaction of a yariety of forces,
owing to the crowd itself rather than the nature of the thor-
oughfare. We must set down a great deal to the influence of
the corpuscles on one another, as they are carried along accord-
ing to mechanical principles ; but, as we shall see later, other
and more subtle factors play a part in the capillary circulation.
Owing to the peripheral resistance and the pumping force of
the heart, the arteries become distended, so that, during cardiac
diastole, their recoil, owing to the closure of the semilunar
valyes, forces on the blood in a steady stream. It follows, then,
that the main force of the heart is spent in distending the
arteries, and that the immediate propelling force of the circu-
lation is the elasticity of the arteries in which the heart stores
up the energy of its systole for the moment.

Keeping in mind our 'schematic representation of the circu-
lation, we should expect that the blood must exercise a certain
pressure everywhere throughout the vascular system; that this
blood-pressure would be highest in the heart itself; considera-
ble in the whole arterial sjrstem, though gradually diminishing
toward the capillaries, in which it would be feeble; lower still
in the smaller veins; and at its minimum where the great veins
enter the heart. Actual experiments confirm the truth of these
views; and, as the subject is one of considerable importance, we
shall direct attention to the methods of estimating and record-
ing an animal's blood-pressure.

First of all, the well-known fact that, when an artery is cut,
the issuing stream spuria a certain distance, as when a water-
main, fed from an elevated reservoir, bursts, or a hydrant is
opened, is itself a proof of the existence of blood-pressure, and
is a crude measure of the amount of the pressure.

One of the simplest and most impressive ways of demon-
strating blood-pressure is to connect the carotid, femoral, or
other large artery at an animal by means of a small glass tube
(drawn out in a peculiar manner to favor insertion and reten-
tion by ligature in the vessel), known as a cannula, by rubber

■«i.-CT»t,« a» i i-«i ' ' n g-wii*'

COMPARATIVE PHYSIOLOGY.

Fltt. 107.

..iLji-ajL— a^ i !.uui . ' I ■ ' ' ' " ' ' I . i mmim

■in

THE CIRCULATION OP THE BLOOD.

Fill. 187.— Appantn* Died In nuUcIng « blood-praMaie uqwrliiwnt (afUir Kontcr). p. b,
prwiurc-boUle, elevated fo m to nlie the pr«<*«are wvenil Incnen of mercnry, ae
wen In the manometer (m) belr.w. It containe a naturated Milntlon of lodlum car-
bonate; r. t, rubber tube cop-jcctlng the jtb with the leaden tube: /. (, tube madv
of lead, M) ai to lie pliable, yet have rigid walli; «. c, a stop-cook, the top of which
li removable, to allow eecape of bubble* of air; p, the pen, writing on the roll of
laper, r. The former lloiiu on the mercury; m, the manometer, the (haded por-
tion of the bent lube denoting the mercury, the reet la fliled with a fluid unfavor-
able to the coagniation of tbel>lood, and derived from the preeeure-bottle; ea, the
carotid. In whieb la phMed the cannula, and below the latter a forcepa, which may
be removed when the blood-preMure ia to be actually meaanred. The rvgiatration
of the height, variation, etc., of blood-prwaure. It beat made on a continnoua roll
of paper, aa leen in Fig. 1118.

tubing, with a long glass rod of bora approaching that of the
artery opened, into which the blood is allowed to flow through
the above-mentioned connections, while it is maintained in a
vertical position.

To pravent the rapid coagulation of the blood in such ex-
periments, it is customary to fill the cannula and other tubes
to a certain extent, at least, with a solution of some salt that
tends to retard coagulation, such as sodium carbonate or bicar-
bonate, magnesium sulphate, etc. If other connections are
made in a similar way with smaller arteries and veins, it may
be seen that the height of the respective columns representing
the blood-pressure, varies in each and in accordance with ex-
pectations.

While all the essential facts of blood-prespure and many
others may be illustrated by the above simple methods, it is inad-
equate when exact measurements ara to be made <»• the results
to be recorded for permanent preservation ; hence apparatus of
a somewhat elaborate kind has been devised to accomplish these
purposes.

The graphic methods are substantially those already ex-
plained in connection with the physiology of muscle; but, since
it is often desirable to maintain blood-pressure experiments
for a considerable time, instead of a single cylinder, a series so
connected as to provide a practically endless roll of paper (Fig.
198) is employed.

When, in the sort of experiments raferred to above, the
height of the fluid used in the glass tube to pravent coagula-
tion just suffices to prevent outflow from the artery into the
connections, we have, of course, in this a measure of the blood-
pressure; however, it is convenient in most instances to use
mereury, contained in a glass tube bent in the form of a U, for
a measure, as shown in the subjoined illustration. It is also
desirable, in order to pravent outflow of the blood into the
apparatus, to get up a pressure in the U-tube or manometer as

S80

COMPARATIVE PIIYBIOLOOT.

near aa may be equal to that of the animal to be employed in
the experiment. This may be effected in a rariety of ways, one
of the most convenient of which is by means of a vessel con-
taining some saturated sodium carbonate or similar solution in
connection with the manometer.

It is important that the pressure should express itself as
directly and truthfully on the mercury of the manometer as
possible, hence the employment of a tube with ri«rid walls, yet
capable of being bent readily in different directions for the sake
of convenience.

Mercury, on account of its inertia, is not free from objec-
tion; and when very delicate variations in the blood-pressure—

. I

196.— LwsekyiiMcnplitWitkcoiiUniiou toll of paper (IVMtOT). Tkeeloek-work
nadiliimniuolinbepuMr fram the roil C, eutSi it raiootUy ovw tlM cyliodw
B, and tlim winds it apmto tiM roll A. Two eleetroHnumtie mark*'* an wn

Vis. 196.
maohliMiT

B. md tlw*- 1- — — —

In pMitionrccordins interval* of time on tiiamovliig roil of p^^. A anometer

may h» flsed in any oon««ni«nt poaition.

e. g., feeble pulse-beats— are to be indicated, it fails to express
them, in which case other fluids may be employed. ,

It will be noted that when an ordinary cannula is used,
inserted as it is lengthwise into the blood-vessel, the pressure
recorded is not that on the ride of the vessel into which it is
inserted as when a H* piece is used, but of the vessel, of which
the one in question is a branch. The blood-pressure, in the
main arterial trunk, for example, must depend largely on the

i employed in
y of ways, one
)t a veMel con-
lar solution in

press itself as
manometer as
rigid walls, yet
ns for the sake

w from objec-
ood-pressure—

ar). TlMCloek-work
klr over ihe cylinder
tie mMrken ueieen
A Mometer

fails to express
ed.

innula is used,
lel, the pressure
into which it is
vessel, of which
pressure, in the
i largely on the

THE CIRCULATION OF THE BLOOD.

S81

foroe of the heart-beat; consequently it would be expected, and
it is actually found, that the pressure varies for different ani-
mals, siie having, of course, in most instances a relation to
the result It has been estimated that in the carotid of the horse
the arterial pressure is 150 to 800 mm. of mercury, of the dog
100 to 175, of the rabbit 50 to 9^" Man's blood-pressure is not
Icnown, but is probably high, we may suppose not less than
150 to 200 mm.

After the fact that there is a certain ccusiderable blood-
pressure, the other most important one to notice is that this
blood-pressure is constantly varying during the experiment,
and, as we shall give reason to believe, in the normal animal;
and to these variations and their oauaea we shall presently turn
our attention.

THE HEART.

The heart, being one of the great centers of life, to speak
figuratively, it demands an unusually close study.

There is no special difSoulty in ascertaining the outlines of
the heart by means of percussion on either the dead or the
living subject. Quite otherwise is it with the changes in form
which accompany cardiac action. Attempts have been made
to ascertain the alterations in position of the heart with respect
to other parts, and especially its own alterations in shape dur-
ing a systole, the chest being unopened, by the use of needles
thrust into its substance through the thoracic walls; but the re-
sults have proved fallacious. Again, caste have been made of
the heart after death, in a condition of moderate extension, prior
to rigor tncrttB ; and also when contracted by a hardening fluid.
These methods, like all others as yet employed, are open to seri-
ous objections.

Following the rapidly beating heart of the mammal with
the eye produces uncertainty and confusion of mind.

It may be very confidently said that the mode of contrac-
tion of the hearts of different groups of vertebrates is variable,
though it seems highly probable that the divergences in mam-
mals are slight The most that can be certainly affirmed of the
mammalian heart is, that during contraction of the ventricles

88a

COMPARATIVE PI1Y8IOL.0OT.

they become more conical ; that the long diameter i« not appre-
ciably altered ; that the antero-podterior diameter is lengthened;
and that the left ventricle at leait turns on its own axis from
left to right. This latter may be distinctly made out by the eye
in watching the heart in the opened cheat.

THB mcvnitm of nn hsart.

When one places his hand over the region of the heart in i
man and other mammals, he experiences a sense of pressure
varying with the part touched, and from moment to moment.
Instruments constructed to convey this movement to recording

riB

rio. 109.— Manr't eudlM toand. which may b« need to explore the chamber* of the
heart 'after Foaler). a !• made of rahlMtr (tretehed orer a wire framework, with
metallic innMNrta above and helow; 6 le a long tab*.

levers also teach that certain movementH of the chest wall cor-
respond with the propagation of the pulse, and therefore to the
systole of the heart It can be recognised, whether the hand
or an instrument be used, that all parts of the chest wall over
the heart are not equally raised at the one instant If the beat-
ing heart be held in the hand, it will he noticed that during
systole there is a sudden hardening. The relation of the apex
to the chest wall is variable for different mammals, and with
difiFerent positions of the body in man.

As a result of the investigation which this subject has re-
ceived, it may be inferred that the sudden tension of the heart
owing to the ventricle contracting over its iluid contents,
causes in those cases in which during diastole the ventricle
lies against the chest wall, a sense of pressure beneath the
hand, which is usually accompanied by a visible movement'
upward in some part of the thoracic wall, and downward in ,
adjacent parts.

It will not be forgotten that the heart lies in a "poricardial
sac, moistened with a small quantity of albuminous fluid ; and
that by this sac the organ is tethered to the walls of the chest
by its mediastinal fastenings ; so that in receding from the
chest wall the latter may be drawn after it ; though this might

■■amneMM

;r is not appra-
iii lengthened;
own axis from
out by the eye

IT.

of the heart in
i8e of prewnire
Bnt to moment,
nt to recording

the chamben of the
Ira framework, with

cheat wall cor-
therefore to the
tether the hand
chest wall over
it If the beat-
ted that during
ion of the apex
tmals, and with

subject has re-
on of the heart,
fluid contents,
ie the ventricle
re beneath the
ibte movement'
d downward in

in a ^)ericardial
lous fluid ; and
Us of the chest
eding from the
>ugh this might

THE cmrULATlON OP THK BLOOD.

888

Right
aurlola.

Kight
ventricle.

Cardiac
Impolaa.

Fig. mo.— Blmnltaneoaa tracing* from the Interior of the right anrlcle, from the Inte-
rior of the right ventricle, and of the cardiac impniio In the horae (after Chanveau

and ilarev).

In the order from top to bottom,

Traolnga to be read from left to r^t. and the refeiencea above are
rom top to bottom. A complete cardiac eycla la Included between
the thick vertical llnea I and II. The thin vertical llnea Indicate tenthe of a aee-
ond. The gradual riae of nreeeure within the ventricle (middle tracing) during
diaetole, the sudden rise witn-the rystole, Its maintenance with oeclllatlons for an
appreciable time, Its sadden fall, etc., are all well shown. There la dlsi^nemiint
as to the exact meaning of the minor cnrree In the larger onea.

also follow from the intercostal muscles being simply unsup-
ported when the heart recedes.

nrmnOATioir op thb

T-BBAT FROM

By the use of apparatus, introduced within the heart of the
mamtnal and reporting those changes susceptible of graphic
record, certain tracings have been obtained about the details of
which there are uncertainty and disagreement, though they
seem to establish the nature of the main features of the cardiac
beat clearly enough. An interpretation of such tracings in the
light of our general and special knowledge warrants the follow-
ing statement.

1. Both auricular and ventricular systole are sudden, but the
latter is of very much greater duration.

2. While the chest wall feels the ventricular systole, the
auriculo-ventricular valves shield the auricle from its shook.

8. During diastole in both chambers the pressure rises gradu-

COMPARATIVE PHYSIOLOGY.

ally from the inflow of blood; and tbe auriouUr (Miutiootlon
pmducen a brief, decided, though but slight rise of preMure in
the ventricle!.

4. The onMt of the ventricular lystole ia rapid, ita maximum
preMure luddenly reached, and ita duration coniiderable.

The relations of theae varioua eveuta, their duration and
the oorreapondinff movementa of the ohent wall, may Iw luamed
by a study of the above tracing which the student will And
worthy of his close attention. i

ram oabxhulo somoMi.

Two sounds, differing iu pitch, duration, and intensity, may
be heard over the heart when the cheat is opened and the heart
listened to by means of a stethoscope. These sounds may also
be heard, and present the same characters when the h««art is
auscultated through the chest wall; hence the cardiac in oulae
can take no essential part in their production.

The sounds are thought to be fairly well represented, ko far
as the human heart is concerned, by the syllables lub, dup ; the
first sound being longer, louder, lower-pitched, and '' booming "
in quality; the second short, sharp, and high-pitched.

In the exposed heart, the flivt sound is heard most distinctly
over the base of the organ or a littla below it ; while the sec-
ond is communicated most distinctly over the roots of the great
ve ss e ls— that is to say, both sounds are heard best over the
aurioulo-ventricular and semilunar valves respectively. When
the chest wall intervenes between the heart and the ear, it is
found that the second sound is usually heard most distinctly
over the second costal cartilage on the right; and the first in
the fifth costal interspace where the heart's impulse is also often
most distinct In these situations the arch of the aorta in the
one case, and the ventricular walls in the other, are dose to the
situations referred to during the cardiac systole ; hence it is
inferred that, though the sounds do not originate directly be-
neath these spots, they are best propagated to the chest -wtJl at
theae points. Prior to the study of the heart, in our domestic
animals the student is recommended to investigate' the subject
on himself by means of a double stethoscope or on '•nother per-
son with or without any instruments.

There are, however, individual differences, owiu^ to a va-
riety of causes, which it is not always possible to explain fully

■' — ■■W " ^ -.. mi yr!

liar (Hiutrootlon
e of preuure in

id, ita maximum
■iderable.
r duration and
may be luamed
udeut wUl And

1 intensity, may
id and the heart
lounda may also
en the heart is
cardiao in ^ulse

^«Mmted, un far
mlubfdup; the
uid '• boomin; "
tohed.

1 most distinctly
; while the soo-
oota of the great
d best over the
jctively. When
nd the ear, it is
[ most distinctly
; and the first in
ulse is also often
the aorta in the
, are close to the
x>le ; hence it is
nate directly be-
;he chest will at
in our domestie
igate' the subject
• on "nother per-

owiuii^ to a va-
to explain fully

THE CIRCULATION OP THK BI/)OD.

986

in each case, but owing doubtless in great part to variations in
anatomical relations.

Tkt 0*«Mt of tht Soiiads of tho HMurt.— There is general
agreement in the view that the seoond sound is owing to ttie
closure of the semilunar valves of the aortic and pulmonary
vessels ; the former, owing to their greater tension in conse-
quence of the higher blood-pressure in the aorta, taking much
the. larger share in the production of the sound, as may be
ascertained by listening over these vessels in the exposed heart
When these valves are hooked back, the second sound disap-
pears, so that there can be no doubt that they bear some impor-
tant relation to the causation of the sound.

In regard to tixtflr§t sound of the heart the greatest diversity
of opinion baa prevailed and still continues to exist. Tho fol-
lowing among other views have been advocated by physiolo-
i^ts:

1. The first sound is caused by the tension and vibration of
the auriculo-ventricular valves.

S. The first sound is owing to the contractions of the large
mass of muscle composing the ventricles.

8. The sound is directly traceable to eddies in the Uood.

»io. XM. ifn. SOS.

Pie. aH.-rMienMcopic •ppeannce of Ab«n tram thehaart The oioM-ttrUi, dlvUtona

A*Miehlnr). and Joncture* are vtalblj (Laadols). „ _. , ^ w .

Fia. m.-MwcDlM' flbcr-celli from the hnrt. (t m 486.) a, Um of ionetar* between

two clUe; b. e, bnuwhlnf cells.

But, tfxjkmg at the whole question broadly, is it not unrea-
sonable to explain the sound resulting from such a complex act

286

COMPARATIVE PHYSIOLOGY.

as the contraction of the heart and what it implies in the light
of any single factor ? That such narrow and exclusive views
should have been propagated, even by eminent physiologists,
should admonish the student to receive with great caution ex-
planations of the working of complex organs, based on a single
experiment, observation, or argument of any kind.

The view we recommend the student to aidopt in the light of
our present knowledge is, that the first sound is the result of
sevcotd causative factors, prominent among which are the sud-
den tension of the auriculo-ventricular valves, and the contrac-
tion of the cardiac muscle, not leaving out of the account the
possible and probable influence of the blood itself through
eddies or otherwise; nor would we ridicule the idea that in
some cases, at all events, the sound may be modified in quality
and intensity by the shock given to the chest wall during sys-
tole.

mnDO-OABDZAO PBB8SaitEI&

Bearing in mind the relative extent of the pulmonary and
sjrstemic portions of the circulation, we should suppose that the
resistance to be overcome in opening the aortic valves and lift-
ing the column of blood that keeps them pressed together,
would be much greater in the left ventricle than in the right;
or, in other words, that the intra-ventricular pressure of the
left side of the heart would greatly exceed thai of the right, and
this is confirmed by actual experiment.

That there should be a negative pressure in, say, the left
ventricle, follows naturally enough fifom the fact that not only
are the contents of the ventricle expelled with great sudden-
ness, but that its walh remain (see Figs. 200 and 204) pressed
together for a considerable portion of the time occupied by the
whole systole; so that m relaxation it follows that there must
be an €»npty cavity to fill, or that there must be an aspiratory
effect toward the ventricle; hence also one factor in the closure
of the semilunar valves.

It thus appears that the heart is not only a force-pump but
also to some extent a suction-pump; and, if so, the aspirating
eflbct must express itself on the great veuw, lacking valves as
they do, at their entrance into the heart ; hence, with each
diastole the blood would be sucked on into the auricles, a
result that is inteniifled Dy the respiratory movements of the
thorax.

B ?<^ ."t. w ? . ii y . m^ i ju w^

MmMa^imtaijgggggiggM

{■

ies in the light
xclusive views
; physiologists,
eat caution ez-
sed on a single
d.

in the light of
I the result of
ch are the sud-
ad the contrao-
he account the
itself through
le idea that in
fled in quality
all during sys-

;>ulniona(y and
appose that the
ridves and lif t-
essed together,
in in the right;
pressure of the
if the right, and

n, say, the left
Bt that not only
1 great sudden-
nd 804) pressed
occupied hy the
that there must
le an aspiratory
ir in the closure

force-pump but
», the aspirating
eking ralves as
snoe, with each
the auricles, a
)vements of the

THE CIBCULATIOM OP TUB BLOOD.

287

■ \

Fio. SOS.— DtaRnn ahmriag the ralctiTe helsfat of the btoad<iii«Mai« in dUtomt parte
of tb« vwcnter sjitcm (after Too). A, heart; a, arteriolee ; o, email veine; A,
arteriee ; C, capiUarlea : V. laroe Tctna; B, V, r e p w eenthMr the aero-Ilne, I.e., fc^
moapherle p t eee n re : the Moaa-imMure la Indicated by ui« height of the canre.
The nambere on the left give the pranetire approximately. In mm. of mercnry.

Bdatifv Time oorafiad lij the VMrisnt Pluuwt of fhe OurdiM
Oyde.— The old and valuable diagram reproduced below is
meant to convey through the eye the relations of the main
events in a complete
beat of the heart or
cardiac cycle. The
relative length of the
sounds; the long peri-
od occupied by the
pause; the duration of
the ventricular sys-
tole, which it is to be
observed is in ezcew
of that of the first
soimd, are among the
chief facts to be noted.

The tracings of
Ohauveau and Ibrey,
obtained from the

heart of the horse, Tut. km.— Diagram repnaentlng tlie movementa and
V 1. V 1 eoandi of the heart daring a cardiac cycle (ftttmt

which has a very slow sharpey). ' >^

j^iygiraBkartMrt.,' \*H*f^^ir^

U-'

COMPABATIVE PHYSIOLOGY.

rhythm, show that of the whole period, the aurionlar systole
occupies t or A of a ser./^'l ; the yentricolar systole, f or -^ of
a second; and the dias'ole, ^ or ^ of a second.

With the more rapid beat in man (70 to 80 per minute), the
duration of the cardiac cycle may be estimated at about -Ar of
a second, uid the probable proportions for each event are about
these: The auricular systole, i>v of a second; the ventricular
systole, ^^otsk second; and the pause, -^ of a second.

It will be noted that the pause of the heart is equal in dura-
tion to the other events put together; and even aaniming that
there is some expenditure of energy in the return (relaxation)
of the heart to its passive form, there still remains a oonsider-
eble interval for rest, so that this organ, the very type of cease-
less activity, has its periods of complete repose.

IBB WOBS OF

Since the pressure against which the heart works must, as
we shall see, vary from moment to moment, and sometimes
very considerably, the work of the heart must also vary within
wide limits, even making allowance for large adaptability to
the burden to be lifted ; for it will be borne in mind that the de-
gree to which the heart empties its chambers is also variable.

If one knew'the quantity of blood ejected by the left ven.
tricle, and the rate of the beat, the calculation of the work done
would be an easy matter, since the former multiplied by the
latter would represent, as in the case of a skeletal muscle, the
work of the muscles of the left ventricle; from which the work
of the other chambers might be approximately calculated.

The work of the auricles must be slight . The right ven-
tricle, it is estimated, does from one fourth to one third the
work of the left

When we calculate the work done by the heart for certain in-
tervals, as the day, the week, month, year, and especially for a
moderate lifetime, and compare this with that of a»y machine it
is within the highest modem skill to construct, the great superi-
ority of the Vital pump in endurance and working mpacity will
be very apparent ; not to take into the account ai all its wonder-
ful adaptations to the countless vicissitudes of life, without which
it would be absolutely useless, even destructive to the organism.

Some of these variations in the working of the heart we may
now to advantage consider.

THE CIRCULATION OF THE BLOOD.

289

rlonlar t^rstole
itole, I or ^ of

Br minute), ihe
at about ^ of
svent are about
the ventricular
nncL

\ equal in dnra-
. aaroming that
im (relaxation)
una a oonsider-
r type of cease-

works must, as
and sometimes
Ibo Taiy within
adaptability to
md that the de-
also variable.
by the left veu.
r the work done
iiltiplied by the
etal muscle, the
which the work
calculated.
The right ven-
a one third the

rt for certain in-
especially for a
f any machine it
the great superi-
ng<»pacitywill
italiitswonder-
e, without which
to the organism,
he heart we may

▼ABZATIOMB IN TBB OABStAO FUIJIATION.

These may be ascertained either by the investigation of the
arteries or of the heart, for every considerable alteration in the
working of the heart expresses itself also through the arterial
system. In speaking of the pulse, the reference is principally
to the arteries, but in each case we may equally well think-of
the heart primarily as acting upon the arteries.

1. The frequeney of the heart-beat varies, as might be sup-
posed, with a great multitude of conditions, the principal of
which are: cige, being most frequent at birth, gradually slow-
ing to old age, while in feeble old age the heart-beat may, like
many other of the functions of the body, approximate the con-
dition at birth, being very frequent, small, feeble, and easily
disturbed in its rhythm; aex, the cardiac beat being more fre-
quent in females; poature, most rapid in the standing position,
slower when sitting, and slowest in the recumbent attitude;
aeaeon, more frequent in summer ; period of the day, more
frequent in the afternoon and evening. Elevation of tetn-
perature, the inspiratory act, emotions, and mental activity,
eating, musctUar exercise, etc., render the heart-beats more
frequent.

i. The length of the systole, though variable, is more con-
stant than that of the diastole.

S. The force of the pulsation varies very greatiy and exer-
cises an important influence on the blood-pressure and the
velocity of the blood-strean^ As a rule, when the heart beats
rapidly, especially for any considerable length of time, the
force of the individual pulsations is diminished.

4. The heart-beat may vary much and in ways it is quite
possible to estimate, either direotiy by the hand placed over the
organ on the chest, by the modifications of the cardiac sounds,
or by the use of instrmneuts. It is wonderful how much in-
formation may be conveyed, without tiie employment of any
instruments, tiuough palpation and auscultation, to one who
has long investigated the heart and the arteries with an intelli-
gent, inquiring mind; and we strongly recommend the student
to cfHnmenoe personal observations early and to maintain them
persistently.

Practitioners recognise the pulse (and heart) as " slow " as dis-
tinguished from " infrequent," " shipping," " heaving," " thrill-
ing," " bounding," etc.

■;■

:;!

240

COMPARATIVE PHYSIOLOGY.

Now, if with these terms there arise in the mind correspond*
ingf mental pictures of the action of the heart under the cir-
cumstances, well ; if not, there is a very undesirable blank.
How the student may be helped to a jmowledge of the actual
behavior of the heart under a variety of conditions we shall
endeavor to explain later.

Apart from all the above peculiarities, the heart may cease
its action at regular intervals, or at intervals which seem to
possess no definite relations to each other^-that is, the heart
may be irregular in its action, which may be made evident
either to the hand or the ear..

There are certain deviations from the quicker rhythm which
occur with such regularity and are so dependent on events that
take place in other parts of the body that they may be con-
sidered normal.

Comparatiye.— We strongly recommend the student to verify
all the statements made in these sections by direct observation
for himself. Such is invaluable to the practitioner. The fol-
lowing table gives the mean number of cardiac pulsations per
minute (after Qamgee):

SPECIES.

Adult

Youth.

Old age.

Hors6

86-40
46-50
46-60
70-80
70-80
90-100
130^140

60-73

66-75

60-70

86-96

100-110

110-120

iafr-140

82-88

Ass and mule. . .

65- 60

40-45

Sheen And soat

66- 60

oneep ana goal......... ...

65- 60

Dojr

60- 70

Cat..

100-120

The variations with age, for the horse and the ox, are as fol-
lows, according to Ereutser :

Horte,

At birth 100-120

When 14 days old 80 96

When 8 months old 6U- 76

When 6 months old 64-72

When 1 year old 48-66

When 2 years old 40-48

When 8 years old 88-48

When 4 years old 88- 60

Whenagisd 82-40

Ox.

Atbirth 92-182

When 4r-6 days old 100-120

When 14 days old 68

When 4-6 weekt) old 64

When 6-12 months old . . 66-68

For the young cow 46

For the toar-year«ld ox . 40

warn

nd oorreBpond'
under the cir-
esirable blank,
(e of the actual
itions we shall

leart may cease

which seem to

at is, the heart

made evident

rhythm which
: on events that
y may be con-

tudent to verify
vet observation
oner. The f ol-
I pulsations per

Old Age.

82-88

5&-60

40- 4S

05-60

06-60

60-70

100-120

le oz, are as fol-

Id.

old

hs old . .

^old ox .

•2-182

100-120

56-68
46
40

TUB CIRCULATION OP THE BLOOD.

TBB PDLSB.

241

Naturally the intermittent action of the heart gives rise to
corresponding phenomena in the elastic tubes into which it
may be said to be continued, for it is very desirable to keep in
mind the complete continuity of the vascular system.

The following phenomena are easy of observation : When
a finger-tip is laid on any artery, an interrupted pressure is felt;
if the vessel be laid bare (or observed in an old man), it may
be seen to be moved in its bed forward and upward ; the press-
ure is less the farther the artery from the heart ; if the vessel
be opened, blood flows from it continuously, but in spurts ; if
one finger be laid on the carotid and another on a distant ves-
sel, as one of the arteries of the foot, it may be observed (though
it is not easy from difiiculty in attending to two events hap-
pening so very close together) that the beat in the nearer ves-
sel precedes by a slight interval that in the more distant

Inv^ K igating the latter phenomenon with instnmients, it is
found tuat an appreciable iuter\-al, d'^'^f^nding on the distance
apart of the points observed, interven a.

What is the explanation of these facts ?

The student may get at this by a few additional observa-
tions that can be easily made.

Pio. S0&— Marev'g apMratna for ahowing the mode in which the polae is proDaoated
m the arteries. B, a robber pomp, with valves to provont rvgnqritationr^The
wortcing of the apparatns will be apparent from the inspection of tlie flgnre.

If water be sent through a long elastic tube (so coiled that
points near and remote may be felt at the same time) by a bulb
16

^M. i «WKnU!W I|

242

COMPARATIVE PHYSIOLOGY.

syringe, imitating the heart, and against a resistance made by
drawing out a glass tube to a fine point and inserting it into
the terminal end of the rubber tube, an intermittent pressure
like that occurring in the artery may be observed; and further
that it does not occur at precisely the same moment at the two
points tested.

Information more exact, though possibly open to error, may
be obtained by the use of more elaborate apparatus and the
graphic method.

By measvirement it has been ascertained that in man the
pulse-wave travels at the rate of from five to ten metres per sec-
ond, being of course very variable in velocity. It would seem
that the more rigid the arteries the more rapid the rate, for in
children with their more elastic arteries the speed is slower;
and the same principle is supposed to explain the higher veloci-
ty noticed in the arteries of the lower extremities. But with
such a speed as even five metres a second it is evident that with
a systole of moderate duration (say '8 second) the most distant
arteriole will have been reached by the pulse-wave before that
systole is completed.

It is known that the blood-current at its swiftest has no
such speed as this, never perhaps exceeding in man half a metre
per second, so that the pulse and the blood-current must be two
totally distinct things.

When the left ventricle throws its blood into vessels already
full to distention, there must be considerable concussion in con-
sequence of the rapid and forcible nature of the cardiac systole,
and this gives rise to a wave in the blood which, as it passes
along its surface, causes each part of every artery in succession
to respond by an elevation above the general level, and it is this
which the finger feels when laid upon an artery.

That there is considerable distention of the arterial system
with each pulse may be realized in various ways, as by watch-
ing and feeling an artery laid bare in its course, or in very thin
or very old people, and by noticing the jerking of one leg
crossed over the other, by which method in fact the pulse-rate
may be ascertained. And that not only the whole body but
the entire room in which a person sits is thrown- into vibra-
tion by the heart's beat, may be learned by the use of a tele-
scope to observe objects in the room, which may thus be seen to
be in motion.

Featoni of an Arterial FalM-TrMiiig.— In order to judge of

mama

tanoe made by
serting it into
ittent pressure
1; and further
ent at the two

1 to error, may
aratus and the

at in man the
metres per sec-
It would seem
the rate, for in
leed is slower;
J higher veloci-
ties. But with
ident that with
he most distant
ave before that

swiftest has no
an half a metre
int must be two

I vessels already
icussion in con-
cardiac systole,
ich, as it passes
ry in succession
rel, and it is this
r.

arterial system
^ as by watch-
, or in very thin
dng of one leg
ct the pulse-rate
whole body but
own- into vibra-
te use of a tele-
y thus be seen to

order to judge of

KsxnsrssssTKTr:

"Jli.r.;

THE CIRCULATION OP THE BLOOD.

243

the nature of arterial tracings, it is important that the circum-
stances under which they are obtained should be known.

■.S?n^*'2'*2 •.'?'"***^''P''ffi'™^P'' •"»««** 'or Uklng a tncing. A, steel
•prlniy; B.int lever; C, writing lever; C, iti free writing end; D. aettwtot
bringing B In conUct with V; 0, elide with nnoked papef; « ilMk-wSk; X
for Increasing the preMoro; AT, dial indicating the amount of preiaW

na for iiTiniv thn ■"■^'unient to th'^ "*~ -«•« *i*- i.a. ^- Ai^r^. m^. *

Bramwell).

^-iK2i"*f* '*" "*•"* 5^£ initmment to the annrand The latter" to"ueAMl^^
inclined plane or support (Byrom " "> >»»»■»••>-

The movements of the vessel wall in most wiAmmft la suitable
for experiment and in man is so slight that it becomes necessary
to ex&^fgerate them in the tracing, hence long levers are used to
accomplish this.

The sphygmograph is the usual form of instrument em-
ployed for the purpose. It consists, essentially, of a clock-work
for moving a smoked surface

(mica plate commonly) on
which the movements of a
lever^tip, answering to those
of a button placed on the
artery, are recorded.

We shall do well to in-
quire whether there are any
features in common in trac-
ings obtained in various
ways, and which have there-
fore in all probability a real foundation in nature.

An inspection of a large number of pulse-tracings, taken un-
der diverse conditions, seems to show that in all of them thei«
occurs, more or less marked, the following : 1. An upward

Fis. S07.— Diagrammatic schema showing the
essential part of the Instrument when In
working order. The knife-edge S" of
the short lever Is in contact with the
writing-lever C. Every movement of the
steel spring at ^'T communicated by the
arteriea. will be Imparted to the writtng-
lever (Byrom Bramwell).

944

COMPARATIVE PHYSIOLOGY.

curve. 2. A downward curve, rendered irrejfulor by the occur-
rence of peaks or cretU and notches. The flrst of these are

/V\A/VM/\MAAiWV

Fio,

man (after Mneni). x, cnm*

nt riso; C, dicrotic McondMr

wave; fl, protllcrotlc Becondnry wave; n, notch prccedinu thl»: D, iucceeding lec-

ravo. Curve above i» tUat made by a tunlng-furk with ten doable vibn*

, 908.— Pnlie tracing from carotid artery of healthv
mencemont of expannlon of artery; A, inramit of llr

tiona

•y wi
In a

second.

termed the prodicrotic notch and crest, and the succeeding ones
the dicrotic notch and crest The latter seem to be the more
constant.

Venont PuIm.— Apart from the variations in the caliber of
the great veins near the heart, constituting a sort of pulse,
though due to variationB in intra-cardiac pressure, a venous
pulse proper is rare as a normal feature. One of the best-known
examples of such occurs in the salivary gland. When, during
secretion, the arterioles are greatly dilated, a pulse may be wit-
nessed in the veins into which the capillaries open out, owing
to diminution in the resistance which usually is sufficiently
great to obliterate the pulse-wave.

^thdogioaL— In severe cases of heart-disease, owing to
cardiac dilatation or other conditionB, giving rise to incompe-
tency of the tricuspid valves, there may be with each ventricu-
lar systole a back-flow, visible in the veins of the neck.

A venous pulse is a phenomenon, it will be evident, that
always demands special investigation. It means that the usual
bounds of nature are for some good reason being overstepped.

CSompMntiye. — ^Before entering on the consideration of phe-
nomena that all are agreed are purely vital, we call attention to
the circulation in forms lower than the mammal, in order to
give breadth to the student's views and prepare- him for the
special investigations, which must be referred to in subsequent
chapters; and which, owing to the previous narrow limits (re-
searches upon the frog and a few well-known mammals) having
at last been overleaped, have opened up entirely new aspects of

lar by the occur-
irot of them are

ifter Moens). x, com*
; C, dicrotic locondary
lii»; 0, •uccecdina sec-
wlth ten doable vlbn*

I Bucoeeding ones
a to be the more

in the caliber of
a sort of pulse,
■essure, a venous
>f the best-known
. When, during
sulse may be wit-
open out, owing
ly is sufficiently

iisease, owing to
rise to incompe-
h. each ventriou-
the neck,
be evident, that
ins that the usual
ng overstepped,
ideration of phe-
e call attention to
umal, in order to
pare- him for the
I to in subsequent
tarrow limits (re-
mammals) having
)ly new aspects of

THE CIRCULATION OP THE BLOOD.

245

cardiac physiology— one might almost say revolutionized the
subject.

Owing to the limitations of our space, the references to lower
forms must be brief.

We recommend the student, however, to push the subject
further, and especially to carry out some of the experiments to
which attention will be directed very shortly.

In the lowest organisms {Infuaoriana) represented by Amoe-
ba, Vorticella, eto., there are, of course, no circulatory organs,
unless the pulsating vacuoles of some forms mark tiie crude
beginnings of a heart. It will be borne in mind, however, that
there is a constant streaming of the protoplasm itself within
the organism.

The heart is first represented, as in worms, by a pulsatile
tube, which may, as in the earth-worm, extend throughout the
greater part of the length of the animal, and has usually dorsal
and ventral and transverse connections

The dilatations of the transverse portions in one division
{metamere) of the animal seem to foreshadow the appearance of
auricles.

The pulsation of the dorsal vessel in a large earth-worm is
easy of observation.

In amphioxus, which is often instanced as the lowest verte-
brate, the blood-vessels, including the portal vein, are pulsatile,
while there is no distinct and separate heart.

Although the respiratory system will be treated from the

comparative point of view, the student will do well to note now

Ab Ao *■

Fio. 800.— Diagram of the cticnlatlon of a Teleoatean flah (Chraa). V, ventricle; Ba,
bnlbna arterioena, with the arterial arcbea which cany the blood to the gills; Ab,
arterial archei; Ao, aorta deecendena, into which the epibranchial arteriea paising
ont from the gliis unite; K, kidneya; /, intestine; Fio. portal circulation.

(in the figures) the close relation between the organs for dis-
tributing and aSrating the blood.

Passing on to the vertebrates, in the lowest group, the fishes,

i MH».IM<M W» l«MM I M I Wi».M

246

COMPAttATlVB PHYSIOLOGY.

the heart conaiit* of two chumbcw, an auricle and a ventricle,
the latter being Bupplemontetl by an extonHion {hulbtu nrterio-
urn) pulntUe in certain species ; and an examination of the

meit.

Fio. SIO.

Fig, 911.

Fio. 810.— The arterial trnnki and their main branches in the frog (Rana *teultnta).
1 K II. (Howei.) t, lingcal veMeh c. e, common carotid artenr; p.eu, pnlmo-
caUneoui artery; c. gl. carotid gland: au', right auricle; om", left auricle: v, Ten-
tricle; tr.a, tmncua arterioena; put', pulmonarv: Ig. left lung: ao, left aortic
arch; br, brachial; cu, cutaneooi; d. ao, doraal aorta; em, ci«llaco.<neaenterlc;
««' ciBllac; hp, hepatic vefteb; a, gaatric; /m!'. pancrww; m, metentnic; tp,
•pinilc; rfu', duodenal; A. hmndfAordal; W, Ileal; Ay, bTpogattric; c. U, com-
mon Iliac; «, renal; t, kiduajr; to, enennatic. , , V , ,.

Fiu.811.— Venouatrunk«andthelrmBlnbranchetlnthefrog(i»oiia««itoito). t « If
(Howea.) /, lingual vein; e.J. external jugular; In, Innominate; i.J, internal Jugu-
lar: t.sc, inbacapular; pr. f. rena cava anperior; i. ». ainua venoaua; hp, hepafic;
In', right lobe of liver; h". left lobe of liver; pi. e, venacaw Inferior; ov, ovarian;

(I. t. dorao-lumbar; od, oviducal; — ' — •♦"'• *- ♦-«—'• *• «'i«tl«' <•

femoro-aciatic anaatomoaia; pv', .^
domlnal; a', abdominal-portal anaati
/. M, lleno-inteitinal: g. gaatric; ~ '
museulo-cutaneoni; or, brachial.

course of the circulation will show that the heart u throughout
venous, the blood being oxidized in the gilla aftpr leaving the
former.

Among the amphibians, represented by the frog, there are
two auricles separated by an almost complete septum, and one

'■WW I IUHW

nnd a ventricle,
{h»lbtM nrterio-
mination of the

m0n.

Via. 111.

frog (Rana tteuUnU),
I artenr; p.eu, pnlmo-
u", left auricle: v, Ten-
't lanB: ao, len aortto
«, ciMiae<MneMiiterlc;
la; m, metenterio; «p,
lypogattric; c. U, com-

rana«M!(iteKe). 1 x U.
Date; i.^, internal Jngu-
I venoauv; hp, hepafle;
ra inferior; ov, ovarian;
femoral; «c, sciatic; a,
]; (M(. at. anterior ab-
iphrnic; <Ih', duodenal:
pii{, pulmonary; m.eu,

lart ia throughout
aft<^r leaving the

le frog, there are
I septum, and one

wm^mm^fm^m

TUB CIRCULATION OK THE BLOOD.

247

ventricle oharaoteriaed by a apongy arrangement of the muMsle-
flbera of ita walls.

In the reptiles the division between the auricles is complete,
and there is one ventricle which shows imperfect subdivisions.

A^f

rm*

rtona.

Fio. nt.

9w. «18.-Tlie frog'» heart, i««n from the front, the aortic arche* of the left •Ide hay-
ing been removed, (1 k 4.) . ea, carotid; e. gl, carotid gland; ao, loru; w'. right
auricle; au", left aoricle; pr.c. vena cava iuperlor; pt.e, vena cava inferior;

t>. CM, pulmtMUtaneous tmnk; tr, truncne arterliwiw; v. ventricle (Howea).
Pio. 818.— Tlie «ame, aeen from behind, the elnw venoaui having bMo opened

(1 K 4.) p.v, pulmonary vein- - - -' —

up to
•how the linn-auricnlar valve*. (J x 4.) p. », pulmonary vein; #.»,ainua veno-
•oa; «a", •Inn-anricnUr valve. Other lettering as in Fig. «» (Howea),

In the crocodile, however, the heart consists of four per-
fectly divided chambers. Of the two aortic arches, one arises
together with the pulmonary artery from the right ventricle,
and, as it crosses over, the left communicates with it by a small
opening, so that, although the arterial and the venous blood
are completely separated in the heart, they intermingle outside
of this organ.

In birds the circulatory system is substantially the same as
in mammals ; but in all vertebrate forms below birds the blood
distributed to the tissues is imperfectly oxidized oi* is partially
venous.

As a result of the entire vascular arrangements in the frog,
etc., the least oxidized blood passes to the lungs, and the most
aSrated to the head and anterior pai-ts of the animal.

Whatever ground for differences of opinion there may be
as to the extent to which the phenomena we have as yet been
describing are mechanical in their native, all are agreed that

248

COMPARATIVK PIIVHIOLOOY.

auch cxplaiiutioDH arc innutflcient wlieii applied tu the fttcti
with which wu liuve ynt to dcul. Thvy, at all events, can >)o
regarded only hh tlie rcHult of vitality.

Wh«m one reHectn ii|Ntn the vioimitudea through which an
animal must pam daily and hourly, necewitating either that
they be mot by modified action of the organH of the b«Mly or
that the deNtruction of the organiiim ensue, it becomes clear that
the varying nutritive needs of each {lart nmst be answered by
changes in the circulatory system. These changes may affect
any part of the entire arrangement, and it rarely happens, as
will appear, that one part is modified without a corresiionding
one, very frequently of a different kind, taking place in some
other. What these various correlated modifications are, and
how they are brought alM)ut, we sliall now attempt to describe,
and it will greatly assist in the comprehension of the whole if
the student will endeavor to keep a clear mental picture of the
parts before his mind throughout, using the figures and verbal
descriptions only to assist in the construction of such a mental
image. We shall begin with the vital pump— the heart.

TRB BBAT OF THB HBART AND ITt MOSIFIOATIOH8.

As has been already noted, the cardiac muscle has features
peculiar to itself, and occupies histolofrioally an intermediate
place between the plain and the striped musole-cells, and that
the contraction of the heart is also intermediate in character,
and is best seen in those forms of the organ which are somewhat
tubular and beat slowly. But the contraction, though peristal-
tic, is more rapid than is usually the case in organs with the
smooth form of muscle-fiber.

The heart behaves under a stimulus in a peculiar manner.
The effect of a single indtvttion shock depends on the phase of
contraction in which the heart happens to be at the moment of
its application. Thus at the commencement of a systole there
is no visible effect, while beats of unusual character result at
other times. But tetanus can not be induced by any form op
method of stimulation. The latent period of cardiac muscle is
long.

In a heart at rest a single stimulus (as the prick of a needle)
usually calls forth but one contraction.

'?r'3!j(rtj7»5pi<-:iB?i','?»7'c;'iwciMiW? ."'

;-:wf?^^ i'^'^n*'

r r:;)f¥{S?:3SHa«3i«TO»':»;ai

u the facta
nts, can tie

I which an

either that

the btxly or

M clear Uiat

answered by

may affect

happeiiH, OS

rreH|ionding

ace in some

ms are, and

to dencribe,

the whole if

icture of the

IB and verbal

tch R mental

heart.

nOATIONS.

I haa features
intermediate
bUb, and that
in character,
ure Bomewhat
>ugh peristal-
(ons with the

ilior manner.
I the phase of
lie moment of
systole there
ictor result at
r any form or
liao muscle is

ik of a needle)

TUB CIBCULATION OF THE ULUOD.

240

THB NIIBVOUS BTBTBM Of RBZJkTION TO TBB BIUIRT.

The atteiitptH to determine just wliy the heart beats at all,
and especially the share taken by the nervous system, if any
direct one, are beset with great difficulty ; thougli, as we shall
attempt to show later, this subject hIm) has been cramiMxl within
Uw narrow limits, and hence regarded in a false light.

Till comparatively recently the frog's heart alone received
much attention, if we except those of certain well-known mam-
mals. In the heart of the frog there are ganglion-cells in vari-
ous parts, especially numerous in the sinus venosus (or expan-
sion of the great veins where they meet the auricles) ; also in the
auricles, more especially in the septum (ganglia of Remak), while
they are absent from the greater part of the ventricle, though
found in the atiriculo-ventricular groove (ganglia of Bidder).

Recently it has been found that ganglion-cells occur in the
ventricles of warm-blooded animals. In the hearts of the dog,
calf, sheep, and pig, which are those lately subjected to investi-
gation, it is found that the nerve-cells do not occur near the
a\)ex of the ventricles, but mainly in the middle and basal por-
tions, being most abundant in the anterior and posterior inter-
ventricular furrows and in the left ventricle. But there are
differences for each group of animals ; thus, these ganglion-
cells are most abundant, so far as the mammals as yet inves-
tigated are concerned, in the ventricles of the pig, and least so
in those of the dog. In the cat they are also scanty. Qauglion-
cells occur in the auricles, and are especially abundant near the
terminations of the great veins.

It has long been known that the heai't ut' a frog removed
from the body will pulsate for hours, especially if fed with
serum, blood, or similar fluids ; and that it may be divided in
almost any conceivable way, even when teased up into minute
particles, and still continue to beat. The apex, however, when
separated does not beat. Tet even this quiescent apex may be
set pulsating if tied upon the end of a tube, through which it
may be fed under pressure.

We may here point'out that the whole he&rt or a part of it
may be made to describe its action by the graphic method in
various ways, the principles underlying which are nither that
the heart pulls upon a recording lever (lifts it) ; acts against the
fluid of a manometer ; or, inclosed in a vessel containing oil or
similar fluid, moves a piston in a cylinder.

260

COMPARATIVE PHYSIOLOGY,

It has also long beeu known that a ligature drawn around
the sinus venosus (in the frog) at its junction with the auricles
stopped the heart for a certain period, and this experiment (of
Stannius) was thought to demonstrate that the heart was ar-
rested because the nervous impulses proceeding to the ganglion-
cells along the cardiac nerves or ganglia of this region were
cut off by the ligature ; in other words, the heart ceased to beat
becaiise the outside machinery on which the action of the inner
depended was suddenly disconnected. Other explanations have
been offered of this fact.

Within the last few years great light has been thrown upon
the whole subject of cardiac physiology in oousequeuce of in-
vestigators having studied the hearts of various cold-blooded
animals and of several invertebrates. The hearts of the Che-
loniana (tortoises, turtles) have received special attention, and
their investigation has been fruitful of results, to the general
outeome of which, am well as those accruing from recent com-
parative studies as a whole, we can alone refer. Since in other
parts of the work the limits of space will not always allow us
to give the evidence on which conclusions rest, attention is
especially called to what here follows, as an example of the
methods of physiological research, and the nature of the reason-
ing employed.

Very briefly the following are sonu^ of the main facts :

1. In all cold-blooded animals the order in which the sub-
divisions of the heart ceases to pulsate when kept under the
same conditions is invariable, viz., ventricle, auricles, sinus.

2. The sinus and auricles, when separated by section, liga-
ture, or otherwise, either together or singly, continue to beat,
whether amply provided with or surrounded by blood.

3. The ventricle thus separated displays less tendency to
beat independent of some stimulus (as feeding under pressure),
though a very weak one usually suffices— i. e., its tendency to
spontaneous rhythm is less marked than is the case with the
other parts of the heart. These remarks apply to the hearte
of Chelonians — fishes, snakes, and some other cold-blooded
animals.

4. In certain fishes (okate, ray, shark) the beat may be re-
versed by stimulation, as a prick of thei ventrcle. This is
accomplished with more difficulty in other cold-blooded ani-
mals, and still more so in the mammal.

6. In certain invertebrates, notably the Poulpe (Octopus), a

thrown upon
quence of in-
cold-blooded
ts of the CAe-
ittention, and
to the general
a recent com-
Unce in other
rays allow us
;, attention is
ample of the
of the reason-
in facts :
rhich the sub-
ept under the
:les, sinus.
Y section, liga-
itinue to beat,
tlood.

i tendency to
ider pressure).
i tendency to
case with the
to the hearts
cold-blooded

at may be re-
-'cle. This is
1-hlooded ani-

e (Octopus), a

THE CIRCULATION OP THE BLOOD.

251

careful search has revealed no nerve-cells, yet their hearts con-
tinue to beat when their nerves are severed, on section of parts
of the organ, etc.

6. A strip of the muscle from the ventricle of the tortoise,
when placed iu a moist chamber and a current of electricity
passed through it for some hours, will commence to pulsate and
continue to do so after the current has been withdrawn ; and
this holds when the strip is whoU. free from nerve-cells.

From the above facts certain inferences have been drawn :
1. It has been concluded that the sinus is the originator and
director of the movements of the rest of the heart. 2. That this
is owing to the ganglia in its walls. While all recognize the
importance of the sinus, some physiologists hold to the gangli-
onic influence as essentictl to the heart-beat still ; while others,
influenced by the facts mentioned above, are disposed to regard
them as of very doubtful importance — at all events, as origina-
tors of the movements of the heart.

The tendency now seems to be to attach undue importance
to the spontaneous contractility of the heart-muscle ; for it by
no means follows logically that, because a muscle treated by
electricity, when cut off from the usual nerve influence that we
believe is being constantly exerted on the heart like other or-
gans, will contract and continue to do so in the absence of the
stimulus, it does so normally ; or, because some hearts beat in
the absence of nerve-cells, that therefore nerve-cells are of no
account in any case. Such views, when pressed to the extreme,
lead to as narrow conceptions as those they are intended to re-
place.

Taking into account the facts mentioned and othei-s we have
nof. space to enumerate, we submit the following as a safe view
to entertain of the beat of the heart in the light of our present
knowledge :

Becent investigations show clearly that there are great dif-
ferences in the hearts of animals of diverse groups, so that it
is not possible to speak of " the heart" as though our remarks
applied equally to ttiis organ in all groups of animals.

It must be admitted that our understanding of the hearts of
the cold-blooded animals is greater than of the mammalian
heart; while, so ffur as exact or experimental knowledge is con-
cerned, the human heart is the least un(' ^rstood of all, though
there is evidence of a pathological and clinical kind and subject-
ive experience on which to base conclusions possessing a certain

252

COMPARATIVE PHYSIOLOGY.

value ; but it is clear to those who have devoted attention to
comparative physiology that +he more this subject is extended
the better prepared wo shall be for taking a broad and sound
view of the physiology of the human heart and man's other
organs.

Whatever may be said of the invertebrates, among which
greater simplicity of mechanism doubtless prevails, there can
be no doubt that the execution of a cardiac cycle of the heart
in all vertebrates, and especially in the higher, is a very com-
plex process from the number of the factors involved, their in-
teraction, and their normal variation with circumstances ; and
we must therefore be suspicious of any theory of excessive sim-
plicity in tliis as well as other parts of physiology.

We submit, then, the following as a safe provisional view of
the causation of the heart-beat :

1. The factore entering into the causation of the heart-beat
of all vertebrates as yet examined are : (a) A tendency to spon-
taneous contraction of the muscle-cells composing the organ :
(6) intra-cardiac blood-pressure ; (c) condition of nutrition as
determined directly by the nervous supply of the organ and in-
directly by the blood.

2. The tendency to spontaneous contraction of muscle-cells
is most marked in the oldest parts of the heart (e.g., sinus),
ancestrally (phylogenetically) considered.

3. Intra-cardiac pressure exercises an influence in determin-
ing the origin of pulsation in probably all hearts, though like
other factors its influence varies with the animal group. In
the mollusk (and allied forms) and in the fish it seems to be the
controlling factor.

4. We must recognize the power one coll has to excite, when
in action, neighboring heart-cells to contraction. The ability
that one protoplasmic cell-mass has to initiate in others, under
certain circumstances, like conditions with its own, is worthy
of more serious consideiation in health and disease than it has
yet received.

6. The influence of the cardiac nerves becomes more pro-
nounced as we ascend the animal scale. Their share in the
heart's beat will be considered later.

6. Apparently in all hearts there is a functional connection
leading to a regular sequence of beat in the di£Ferent parts, in
which the sinus or its representatives (the terminations of great
veiiis in the heart) always takes the initiative. One part having

p—

attention to
t is extended
d and sound

man's other

jinong which
ils, there can
I of the heart
i a very com-
Ived, their in-
istances ; and
excessive sim-

iional view of

THE CIRCULATION OP THE BLOOD.

268

contracted, the others must necessarily follow; hence the rapid
onset of the ventricular after the auricular contraction in the
mammal, and the long wave of contraction that seems to pass
evenly over the whole organ in cold-blooded animals.

The basis of all these factors is to be sought finally in the
natural contractility of protoplasm. A heart in its most de-
veloped form still retains, so to speak, the inherited but modified
Amoeba in its every cell.

Whether the intrinsic nerve-cells of the heart take any share
directly in the cardiac beat must be considered as yet undeter-
mined. Possibly they do modify motor impulses from nerves,
while again it may be that they have an influence over nutri-
tive processes only. The subject requires further study, both
anatomical and physiological.

he heart-beat
lency to spon-
Lg the organ:
: nutrition as
organ and in-

f muscle-cells
b (e.g., sinus),

e in determin-
s, though like
al group. In
eems to be the

» excite, when
I. The ability
L others, under
)wn, is worthy
\se than it has

nes more pro-
• share in the

lal connection
lerent parts, in
lations of great
ne part having

XNFXiUBNOB OP THE VAGUS NERVE UPON THE HEART.

The principal facts in this connection may be stated as fol-
lows, and apply to all the animals thus far examined :

1. In all cases the action of the heart is modified by stimu-
lation of the medulla oblongata or the vagus nerve.

2. The modification may consist in prompt arrest of the
heart, in slowing, in enfeeblement of the beat, or a combination
of the two latter effects.

3. After the application of the stimulation there is a latent

JjUAil/lMilMaftA^

fiimm

Pig. 814.— Inhibition of froe'a heart by stimnlation of thS vagiis nerve. To be renrt
from right to left. The contractions of the ventricle are rcgiBtered by ft simple
lerer resting on it. The interrnptcd current was thrown in iit a. Note that one
beat occurred before arrest (1; tent period), and that when standstill of the heart
did take place it lasted for a considerable period (Foster).

period before the effect is manifest, and the latter may outlast
the stimulation by a considerable period.

254

COMPARATIVE PHYSIOLOGY.

4. In most animals the sinus venosus and auricles are af-
fected before the ventricles, and the vagus may influence these
parts when it is powerless over the ventricle.

5. After vagus inhibition, the action of the heart is (almost
unexceptionally) different, the precise result being variable, but
generally the beat is both accelerated and increased in force.
We may say that the werking capacity of the heart is tem-
porarily increased.

6. The improvement in the efficiency of the heart is in pro
portion to its previous working power, and in cases when the

SUmutatinn Vagm.

Fio. 815.— Effects of vagns Btimalation, illnstrated by a form of sphygmographlc curve
derived from the carotid of a rabbit (Foster).

action is feeble and irreg-.'lar (abnormal) it might be said to be
in proportion to its needs. This is a very important law that
deserves to receive a general recognition.

7. Section of both vagi nerves results in histological altera-
tions in the heart's structure, chiefly fatty degeneration, which
must, of course, impair its working capacity and exiKise it
to rupture or other accidents under the frequently recurring
strains of life.

8. In the cold-blooded animals the heart rnay be kept at a
standstill by vagus stimulation till it dies, a perit^d of hours
(one case ■:>( 3ix hours reported for the sea- turtle).

9. Certain drugs (as atropine), applied directly to the heart,
or injected into the blood, prevent the usual action of the vagus.

10. During vagus ari-est the heart substance undergoes a
change, resulting in an unusual dilatation of the or^an. This
may be witnessed whether the heart contains blood or not.

hWpmwp

■ ..jj i u i iiii i

iricles are af-
ifluence these

iart is (almost
r variable, but
ised in force,
heart is tem-

eart is in pro
ises when the

ijrgmographic carve

it be said to be
rtant law that

>logical altera-
Bration, which
and expose it
atly recurring

ty be kept at a
sriui of hours

y to the heart,
1 of the vagus.
) undergoes a
I or^an. This
od oi not.

THE CIRCULATION OF THE BLOOD.

as5

11. The heart may be arrested by direct stimulation, espe-
cially of the sinus, and at the points at which the electrodes are
applied there is apparently a temporary paralysis. The same
alteration in the beat may be noticed as when the main trunk
of the vagus is stimulated.

12. The heart may be inhibited through stimulation of vari-
ous parts of the body, both of the surface and internal organs
(reflex inhibition).

18. One vagus being divided, stimulation of its upper end
may cause arrest of the heart.

14. Stimulation of n small part of the medulla oblongata
will produce the same result, provided one or both vagi be
intaxst.

15. Section of both vagi in some animals (the dog notably)
increases the rate of the cardiac beat. The result of section of
one pneumogastric nerve is variable. The heart's rhythm is
usually to some extent quickened.

16. During vagus inhibition from any cause in mammals
and many other animals, the heart responds to a single stimu-
lus, as the prick of a needle, by at least one beat. An observer
studying for himself the behavior of the heart in several groups
of animals with an open mind, for the purpose of observing all
he can rather than proving or disproving some one point, be-
comes strongly impressed with the variety in unity that runs
through cardiac physiology, including the influence of nerve-
cells (centers) through nerves ; for it will not be forgotten that
normally nerves originate nothing, being conductors only, so
that when the vagus is stimulated by us we are at the most but
imitating in a rough way the work of central nerve-cells. We
can only mention a few jmints to illustrate this.

In the frog a succession of light taps, or a single sharp one
(" Elopfversuch " of Gtoltz), will usually arrest the heart reflexly ;
though sometimes it is very difficult to accomplish. But in the
fish the ease with which the heart may be reflexly inhibited by
gentlo stimulation of almost any portion of the animal is won-
derful. Again, in some animals the vagus arrests the heart for
only a brief period, when it breaks away into its usual (but in-
creased) action.

In the fish, menobranchus, and probably other animals, the
irritability of some subdivision of the heart is lost during the
vagus inhibition — i. e., it does not respond to a mechanical
stimulus.

256

COMPARATIVE PHYSIOLOGY.

There is usually a certain order in which the heart recom-
mences after inhibition (viz., sinus, auricles, ventricles); but
there are variations in this, also, for different animals. It is
also a fact that in most of the cold-blooded animals the right

R. Vagne.

Hearu

Brain above Mednlla.

Cardlo-lnhibltoryC't'u- ■ '
ter In Medulla Ob-
longata.

Afferent Nerve.

Ontlying Area with ItB

Nerves.

Fio. 810.— Blagram of the inhibitory mechanism of the heart. The arrows indicate
in all cases the path the nervous impu!"eB take. I. Path of afferent impulses
froih the heart itself. II. Path from parts of the brain above (or anterior to) the
vaso-motor center. A similar one might, of course, be mapped out along the
spinal cord. III. Path from some ptTipheral region. The downward arrows In-
dicate the course of efferent impulses, which probably usually pass- by both vagi.

vagus is more efficient than the left, owing, we think, not to
the nerves themselves ao much as to their inanuei" of distribu-
tion in the heart— the greater portion of the di-iving part of tho

heart reconi-
eutricles); but
ftnimals. It in
imals the right

rain above Hednlla.

irdlo-lnhlbltoryCt'ii-
ter In Medulla Ob-
longata.

fferent Nerve,

•ntlying Area with its

Nerveg.

Tho arrows Indicate
of afferent ImpulscB
e (or anterior to) the
ipped out aloni; the
lowuward arrown in-
ly pass- by both vagi.

e think, not to
mer of distribu-
s^iiig part of the

THE CIRCULATION OF THE BLOOD.

257

organ,so to speak, being supplied by the right nerve ; for, when
even a small part of the heart is arrested, it may be oyeroome by
the action of a hirger portion of the same, or a more dominant
region (tho sinus mostly).

Conclailoat.— The inferences from the facts stated in the
above paragraphs •-re these : 1. There is in the medulla a col-
lection of cells (center) which can generate impulses that reach
tho heart by the vagi nerves and influence its muscular tissue,
though whether directly or through the intermediation of
nerve-cells in its substance is uncertain. It may possibly be in
both ways. 2. This center (cardio-inhibitory) may be influ-
enced reflexly by influences ascending by a variety of nerves
from the periphery, including paths in the brain itself, as
shown by the influence of emotions or the behavior of the
heart. 8. The cardio-inhibitory center is the agent, in part,
through which the rhythm of the heart is adapted to the needs
of the body. 4. The arrest, on direct stimulation of the heart,
is owing to the effect produced on the terminal fibers of the
vagi, as shown by the dilatation, etc., corresponding to what
takes place when ttie trunk of the nerve or the center is stimu-
lated. 6. The quickening of the heart, following section of the
vagi, seems to show that in some animals the inhibitory center
exercises a constant regulative influence over the rhythm of
the heart. 6. The irritability and dilatability of the cardiac
tissue may be greatly modified during vagus inhibition. Some-
times this is evident before the rhythm itself is appreciably
altered. 7. The heart-muscle has a latent period, like other
kinds of muscle; and cardiac effects, when initiated, last a vari-
able period.

There are many other obvious conclusions, which the stu-
dent will draw for himself.

But a question arises in regard to the significance of the
cardiac arrest under these circumstances, and the altered action
that follows. The fact that, when the heart is severed from the
central nervous system by section of its nerves, profound
changes in the minute structure of its cells ensue, points un-
mistakably to some nutritive influence thatmust have operated
through the vagi nerves. That stimulation of the vagus re-
stores regularity of rhythm and strengthens the beat of the
failing heart, is also very suggestive. That many disorders of
the heart are coincident with periods of mental anguish or
worry, and that in certain cases of severe mental application
11

■■;*

358

COMI'ARATIVK PHYSIOLOGY.

the heart's rhythm hon become very slow, also point to influ-
ences of a central origin as greatly affecting the life-processes
oi this organ.

It has been shown that the vagus nerve in some cold-blooded
animals, as is probable also in the higher vertebrates, constats
of two sets of fibers— those which are inhibitory proper and
those which are not, but belong to the sympathetic system.

Separate stimulation of the former favors nutritive processes,
is preservative ; of the latter, destructive. This has been ex-
pressed by saying that the former favors constructive (anabolic)
metabolism ; the latter destructive (katabolic) metabolism. It
is assumed that all the metabolism of the body may be repre-
sented as made up of katabolic following anabolic processes.

Whether such a view of metabolism expresses any more
than a sort of general tendency of the chemistry of the body
is doubtful. It is a very simple representation of what in all
probability is extremely complex ; and if it be implied that
throughout the body certain steps are always taken upward in
construction to be always afterward followed by certain down-
ward destructive changes, we must reject it as too rigid and
artificial a representation of natural processes.

We think, however, that, upon all the evidence, pathological
aVid clinical as well as physiological, the student may believe
that the vagus nerve, like the other nerves of the body, accord-
ing to our own theory, exercises a constant beneficial, guiding
—let us say determining^influenoe over the metabolism of the
organ it supplies; and we here suggest that, if this view were
applied to the origin and course of cardiac disease, it would
result in a gain to the science and art of medicine.

THB AOOSUSRATOR (AUOMBHTOR)

HBART.

NBRynS OF THB

It has been known for many years that in the dog, cat,
rabbit, and some other mammals, there are nerves proceeding
from certain of the ganglia of the sympathetic chain high up,
stimulation of which lead to an acceleration of the heart-beat.
Very recently these nerves have been traced in a 'number of
cold-blooded animals, and the whole subject placed on a broader
and sounder basis.

There are variations in the distribution of these nerves for
.different groups of animals, but it will suffice if we indicate

nWHjtfi faWii'i'i'-

point to influ-
e life-proceflsefi

ne cold-blooded
ibrates, conaista
rry proper and
tic ayatem.
ritive procesBes,
is has been ex-
ctive (anabolic)
letabolism. It
IT may be repre-
ic processes.
»se8 any more
itry of the body
of what in all
le implied that
iken upward in
y certain down-
B too rigid and

ice, pathological
ent may believe
ne body, accord-
leflcial, guiding
itabolism of the
f this view were
iaeaae, it would
ae.

lyilS OF THB

in the dog, cat,
rves proceeding
3 chain high up,
' the heart-beat.
in a 'number of
sed on a broader

these nerves for
» if we indicate

THE CIRCULATION OP THB BLOOD.

359

their course in a general way. without special reference to the
variations for each animal group: 1. These nerves emerge from
the spinal cord (upper dorsal region), and proceed upward

gpinal r<wdl.

Accdientor Center in Me-
dull*.

Superior Cervical Oangllon.

Middle Cervical Oangllon.

Inferior Cervical Ganglion.

^1 OancHon In kegiirj

of Fint Rib.

Accelerator Nerve*.

Haart.

will be nnaeratooo inai "'V];; „„1 MTimiil Thue whUe the accelerator nerven
SlSlU« fn'?hlf JSy'Tt uKS£.tto^lm|llSd' that the heart iaacturiWaug.
^lihrtlS^^^ot'^o^^i^ «y ««^- The wrow.. a. before. ImUcab
the par- >' the impulaea.

before being distributed to the heart. 2. They may leave for
their cardiac destination either at (a) the first thoracic (or basal
cardiac ganglion, as it might be named in this case), (6) the in-
ferior cervical ganglion, (c) the annulus of Vieussens, or «f) the
middle oer/ioal ganglion. , ^ . j _i.

It follows that the heart may be made to do increased work
in three ways: Pirrt,the reh«ation of a normal inhibitory

■

.i<i;A.';?'«'-'fa'.^'i' ' ''M8(»'.'tt"

960

COMPARATIVE PHYSIOLOGY.

oontml through the va^« nerve by the oardio-lnhlWtory cen-
ter ; second, througrh the aympAthetio (motor) flbem in the
vagus itself ; and, flnully, through flbem with similar action
in the sympnthetic system, usually so called.

The share taken by them factors is certainly variable in dif-
ferent species of animals, and it is likely that this is true of the
same animals on different occasions. It is also conceivable,
and indeed probable, that they act together at times, the inhibi-
tory action being diminished and the augmentor influence in-
crmaed.

i-.

THB BBART Uf KBXsATtOfl TO BXiOOD-nUMtURB.

It is plain that all the other conditions throughout the cir-
culatory system remaining the same, an increase in either the
force or the frequency of the heart-beat must raise the blood-
pressure. But, if the pressure were generally ra' 'I when the
heart beats rapidly, it would fare ill with the ar » elasticity

of their arteries being usually greatly impaired, vs a matter of
fact any marked riie of preMure that would thus occur is pre-

^Kl^'^

Fin. 918

-Tracinit from • mbblt, showing Uie Inflncnce of CKdlac Inhibition on blood'
ireMore The fall In thU owe WMven- rapid, owlnR to "Jden coMjtlon of the
DMrt-beat. The retatWe empUneM of the veweto accoanU for the pecnitar char-
acter of the carve of rising bfood-preMoie (Foster).

vented as a rule, and in difTerent ways, as will be" sfeen ; but, so
far as the heart is concerned, its beat is usually the weaker the
more rapid it is, so that the cardiac rhythm and the blood-press-
ura are in inverse proportion to each other.

By what method is the heart's action tempered to the condi-

THE CIRCULATION OP THR BLOOD.

961

^-inhibitory oeii«
r) flbent in the
similar action

variable in dif<

■ is true of the

so conceivable,

mes, the inhibi-

or influence in- <

IfDRB.

)ughout the ciiv

Be in either the

raise the blood-

lm' "'1 when the

.! elasticity

^vs a matter of

lus occur is pre-

'N<t<^

ic inhibltton on blood'
dden eewatlon of the
for the pecnllar char-

be' ston ; but, so
the weaker the
the blood-press-

«d to the condi-

tions prevailing at the time in the other parts of the vascular
system ?

The matter is complex. The effect ofvci^ » •' "Simulation on
the blood-pressure is always very mark*><1, is would > < supposed.

As seen in the tracing, the beats, wh- n .he heart commences
its action again tell on the compcutitivoly nlack walls of the
arteries, distending them greatly, and this may be made evident
by the sphymograph as well as the manometer; indeed, may be
evident to the finger, the pulse resembling in some features that
following excessive loss of blood,

If the heart has been merely slowed, or its pulsation weak-
ened, the effects will of course be lees marked. •

The ftntatity of Blood.— The blood-pressure may also be
augmer.ted, the ?«rdiac frequency remaining the same, by the
quantt'ty of hlood ejected from the ventricles, which again
dep.j^'is on the quantity entering them, a factor determined
by the condition of the vessels, and to this we shall presently
turn.

In consequence of changes in different parts of the system by
way of compensation, results follow in an animal which might
not have been anticipated.

Thus, bleeding, unless to a dangerous extreme, does not lower
the blood-pressure except temporarily. It is estimated that the
body can adapt itself to a loss of as much as 3 per cent of the
body-weight.

The adaptation is probably not through absorption chiefly,
but through constriction of the vessels by the vaeo- motor
nerves.

Again, an injection of fluid into the blood does not cause an
appreciable rise of blood-pressure, 8o long as the nervoiis sys^
tem is intact ; but, if by section of U.\-j sp'ti ..1 cord the vaso-
motor influences are out off, then a rise may take place to the
extent of 8 to 8 per cent of the body-weight, the extra quan-
tity of fluid seeming to be accommodated in the capillaries and
smaller veins. These facts are highly signiflcant in illustrat-
ing the adaptive power of the circulatory sjrste^ (protective in
its nature), and are of practical importance in the treatment of
disease.

We think the benefit that sometimes follows bleeding has
not as yet received an adequate explanation, but we shall not
attempt to tackle the problem now. Changes in the circulation
depend on variations in the size of the blood-vessels.

•^.':?r!-i»^nm! Uftyiitw:>^ .i".i'aiwv.. ' . I ' .ij'iHaaH i '.j.aw.'."... ' A^M«i.!i ' iiniiiMn>jj.Lj. .. ' . i n i .n ' ,

COMPARATIVK i'HYHIOLOUY.

It in important in ooniiidAring this lubjeot to h«ve olMr no-
tiouH of the Ntructitra of tho blood-vomola. It will be borne in
mind that, while muMular elements are perhapa not wholly
lacking in any of the arteriea, they are moiit abundant in the
•mallent, the arteriole*, which by their variatiomi in Hiie are bent
fitted to determine the quantity of blood reaching any organ.
It in well known that nervea derived chiefly from the ayniiNi-
thfltic system pass to blood-vessels, though their exact m«>de of
termination in obscure. Ah the result of the section and stimu-
lation of certain nerves the following inferences liave been
dmtvrn. !n ren^nl to the nerves supplying blood-vessels.

1. f I* rr tire t iPo-motor nerves of two kindn—oaathcorutrict'
orit and i i,vHiilai o 'M—vrhieh may exist in nerve-trunks either
separately or n>ingl«)d. Examples of the former are found in
the cervical h> inpatlietio, splanchnic, etc., of the latter in the
chorda tympani, nerves of the muscles and nervi engente»
(from the first, second, and third sacral nerves), while the sci-
atic seems to contain both.

8. Impulses are constantly passing fron" the medullary vaso-
motor center along the nerves to the blood-vessels, hence their
dilatation after section of the nerves. The nerves are traceable
to I'ao tpinal cord, and in some part of their course run, as a
rule, ill ihe sympathetic system.

3. fiapulses pass at intervals to the areati of distribution of
yaso-dUators along these nerves, the effect of which is to dilate
the vessels through their influence, as in other cases, on the
muscular coat.

It is inferred that there are vaso- motor centers in the
spinal cord which are usually subordinated to the main center
in the medulla, but which in the absence of the control of the
chief center in the medulla assume an independent regulating
influence.

There is a nerw with variable origin, course, ete., in differ-
ent mammals, but in the rabbit given off from either the vagus,
the superior laryngeal, or by a branch from each, which, run-
ning near the sympathetic nerve and the carotid artery, reaches
the heart, to which it is distributed. This is known as the de-
prtnor nerve.

From stimulation of the central end of this nerve results
fbllow which warrant the conclusion that impulses can by it
reach the vaso-motor center in the medulla, and interfere with
(inhibit) the outflow of efferent, constrictive, or tonic impulses,

hHve olMir no-
rill bo lH>ni« in
ijfit not wholly
bundant in the
I in Hiie are bent
ling any organ,
oni the lynipu-
r exact mode of
tion and atiniu-
ices liave been
remeU.

-eaatHxnutrict-
re-truuka either
»rare found in
16 latter in the
nervi erigenteH
, while the Dei-

medullary vaso-
els, hence their
en are traceable
iourse run, as a

diatribution of
liich la to dilate
ir cases, on the

centers in the
he main center
I control of the
lent regulating

^ etc., in differ-
ither the vagua,
oh, which, run-
artery, reaches
lown as the de-

a nerve results

ulses can by it

interfere with

tonic impulses,

IMAGE EVALUATION
TEST TARGET (MT-S)

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Canadian Instituta for Historical IMicroraproductions / inttitut Canadian da microraproductions hiatoriquaa

THE CIRCULATION OP THE BLOOD.

263

whidi start from the vaso-motor center, deeoend the cord, and
find their way to the (wgana of a definite region, in oonaequence
of whioh the muaouUr coat* of the arterioles relax, more blood
flows to this area which is very large, and the general blood-
pressure is lowered.

Again, if the central end of one of the mam nerves— e. g.,
sciatic— be stimulated, a marked change in the blood-pressure

gpinalCord.

VMO-motor Center
InMednlla.

DeptvMor Menre.

Efferent YMO-mo
tor Ncrre*

AOeiant Menre
from PBripherr.

Fn».«I».— WtHitmoffierroMttio-niotormeetantom. 'iC«!S"?*tff2!!!?llH?^
ftSi tglSrtlt»elf»loB>tlieifap«e«w»rnem.. S:^«'SS£?iSS\SSSm&
orthetmin. IIL f'«miie from eonie peHphwnl f«mii •tegg • "wwu"^

iMmedfM the tdw or eim^UeiFto • eingle arteriole.

ramUi,1ratwhethM>in the direction of rise m fall seems to de-
pend upon the ccndition (Mt the central nervous qrstem, for, with
the animal uuder the influence of chloral, there is a fall; if
under urari, a rise.

M^timimi.ift4iiii>mmimii.0 l^

■I

264

COMPARATIVE PHYSIOLOGY.

It is not to be supposed that the change in any of these
cases is confined to any one vascular area invariably, but that
it is this or that, according to the nerve stimulated, the oondi-

JUlAAJUULAjUlAAAJUL AJLfi-JtJL/L ^

Pio. 2».-Curveof blood^pieMiire rewiUIng from itlmnliitlmi of *" fS^.^hilS
tSd™ie.«or nerve, fo be read from rrfrtit to left. ^ Indicate, the mte at wWch
the recording aurfaco moved, the Interyflg denoting •~°nd»- *» ^,*« •'i^^Sl
was thrown Into the nerve, and ahut off at 0. The reault appears after a period
of latency, and outlaots the stlmulua (Foater)

tion of the centei-s, and a number of other circumstances.
Moreover, it is important to bear in mind that with a fall of
blood-pressure in one region there may be a corresponding rise
in another. With these oonsiderationB in mind, it will be ap-
parent that the changes in the vascular system during the
course of a single hour are of the most complex and variable

character.

The question of the distribution of vaso-motor nerves to
veins is one to which a definite answer can not be given.

TBB OAPIXJUABIB8.

The cells of which the capillaries are composed have a con-
tractility of their own, and hence the caliber of the capillaries
is not determined merely by the arterial pressure or any similar
mechanical effect.

Certain abnormal conditions, induced in these vessels by
the application of irritants, cause changes in the blood-flow,
which can not be explained apart from the vitality of the ves-
sels themselves.

Waiched through the microscope under such circumstances,

\.,

ny of these
ly, but that
the oondi-

JULAJUL.

le central end of
thente at which
U C the current
trs after a period

rcumstances.
irith a fall of
iponding rise
it will be ap-
I during the
and Tariable

or nerves to
given.

1 have a con-
tie capillaries
r any similar

)e vessels by
9 blood-flow,
ky of the ves-

rcuuistances,

THE CIRCULATION OP THE BLOOD.

266

the blood-corpuscles no longer pursue their usual course in the
midnstream, but seem to be generally distributed and to hug the
walls, one result of which is a slowing of the stream, wholly
independent of events taking place in other vessels. It is thus
seen that in this condition (tiaaia) the capillaries have an in-
dependent influence essentially vitid. We say independent, for
it is still an open question whether nerves are distributed to
capillaries or not That inflammation, in which also the walls
undergo 'such serious changes that white and even red blood-
cells may pass through them {diapedeaia), is not uninfluenced
by the nervous system, possibly induced through it in certain
cases, if not all, seems more than probable.

But when we consider the lymphatic system new light will,
it is hoped, be thrown upon the subject of the nature and the
influences which modify the capillaries. One thing will be
clear from what has been said, that even normally the capil-
laries must exert an influence of the nature of a resistance,
owing to their peculiar vital properties ; and, as we have already
intimated such considerations should not be excluded from any
conclusions we may draw in regard to tubes that are made up
of living cells, whether arteries, veins, or capillaries, though
manifestly the applicability to capillaries, with their less modi-
fled or more primitive structure, is stronger.

It has now become clear that the circulation may be modi-
fled either centrally or peripherally; that a change is never
purely local, but is correlated with other changes ; that the
whole is, in the higher animals, directly under the dominion of
the central nervous sjrstem ; and that it is through this part
chiefly that harmony in the vascular as in other systems and
with other systems is established. To have adequately grasped
this oonoepHon is worth more than a knowledge of countless
details.

BPBOIAIt OONSCDBRAnOMS.

FathologiMd— Changes may take place either in the sub-
stance' of the cardiac muscle, in the valves, or in the blood-ves-
sels, of a nature unfavorable to the welfarejof the body. Some
of these have been incidentally referred to already.

Hypertrophy, or an increase in the tissue of the heart, is
generally dependent on increased resistance, either within or
without the heart, in the region of the arterioles or capillaries.
Imperfections of the aortic valves may permit of regurgitation

MMMfH

■MMli

266

COMPARATIVE PHYSIOLOGY.

of blosd, entailing an extra effort if it is to be expelled in addi-
tion to the usual quantity, which again leads to hypertrophy ;
but this is often suoeeded by dilatation of the chambers of the
heart one after the other, and a host of evils growing out of
this, largely dependent on imperfect yenoua circulation, and
increased venous pressure. And it may be here noticed that
arterial and venous pressures are, as a general rule, in inverse
proportion to each other.

If the quantity of blood in the ventricle, in consequence of
regurgitation, should prove to be greater than it can lift (eject),
the heart ceases to beat in diastole; hence some of the sudden
deaths from disease of the aortic valves.

As a result of fatty, or other forms of degeneration, the
heart may suddenly rupture under strains.

Actual experiment on the arteries of animals recently dead,
including men, shows that the elasticity of the arteries of even
adult mammals is as perfect as that of the vessels of the child,
so that man ranks lower than other animals in this respect

After a certain period of life the loss of arterial elasticity is
considerable and progressive. The arteries may undergo a de-
generation from fatty changes or deposit of lime ; such vessels
are, of course, liable to rupture ; hence one of the modes of
death among old animals is from paralysis traceable to rupture
of vessels in the brain.

These and other changes also cause the heart more work,
and may lead to hypertrophy. Even in young animals the
strain of a prolonged racing career may entaU hypertrophy or
some other form of heartrdiseaae.

We mention such ftwsts as these to show the more clearly
how important is balance and the power of ready adaptation
in all parts of the ciicuUtion to the maintenance of a healthy
condition of body.

The heart is itself nourished through the coronary arteries ;
so that morlnd alterations in these vesseU cause, if not sudden
. and painful death, at least nutritive changes in the heartrsub-
: stance, which nmy lead to a dnunatio end or to a slow impair-
ment of cardiac power, etc.

Penoiial ObMmtUm.— The circulation is one of those de-
partments of physiology in which the student may verify much
upon his own person. The cardiac impulse, the heart's sounds
(with a double stethoscope), the pulse— its nature and changes
with circumstances, the venous circulation, and many other

led in addi-
pertropby ;
ibera of the
ring out of
lation, and
lotioed that
i, in invene

sequence of

1 lift (eject),

the sudden

eration, the

cently dead,
riee of even
of the child,
respect
elasticity is
dergo a de-
suoh vessels
le modes of
i to rupture

more work,
animals the
terlxophy or

more dearly
y adaptation
>f a healthy

U7 arteries ;

not sudden

e heartHiub-

ilowimpair-

of thoM de-
rerify much
art's sounds
ind ohangw
many other

THE CIRCULATION OF THE BLOOD.

subjects, are all easy of observation, and after a little practice
without liability of causing those aberrations due to the atten-
tion being drawn to one's self.

The observations need not, of course, be confined to the stu-
dent's own person ; it is, however, very important that the nor-
mal should be known before the observer is introduced to cases
of disease. Frequent comparison of the natural and the dis-
eased condition renders physiology, pathology, and clinical
medicine much good service. We again urge upon the student
to try to form increasingly vivid and correct n.\ental pictures of
the circulation under its many changes.

Oompanltva^'— An interesting arrangement of blood'Yessels,
known as a r$U mirtMIe, oocurs in every main group of verte-

rie. m.— JMtmiraMiartlMep,MMiinpiaU«(«ftorOliuTMW). TkeluMrrtl* to

brates. An artery breaks up into a great number of vessels of
nearly the same size, which terminate, abruptly and without
capillaries, in another arterial trunk.

They are found in a variety of situations, as on the carotid
and vertebrate arteries of animals that naturally feed from the
ground for long periods together, as Ihe ruminants ; in the
sloth, that hangs from trees ; in the legs of swans, geese, ete. ;
in the horse's loot, in which the arteries break up into many
small divisions. It has been suggested that these arrangements

»tit»mmtiitautamKn»mmaiifBiimgmM»t/i^^

....

968

COMPARATIVE PHYSIOLOGY.

permit of a supply of arterwl blood being maintained without
oongeston of the parti. Very marked tortuosity of Tessels, as
in the seal, the carotid of which is said to be forty times as long

Fia. ■S.-deetkm of • lympiiatie rtU nUrtMU, turn thepopUlMl tpaoe (after OIuhh
t«M). 0, 0, aflefMit TatMl*. >, b, ttmat rewalt. 'mtwtuAtwtfnnagijtug-
■wto • erad* form of lymphatte ipaad.

as the space it traverses, in all probability serves the same puN
pose.

BvototiOlL — ^The comparative sketch we have given of the
vascular system will doubtless suggest a gradual evolution. We
observe throughout a dependence and resemblance which we
think can not be otherwise explained. The similarity of the
foetal circulation in the mammal to the permanent circula-
tion of lower groups has much meaning. Even in the highest
form of heart the original pulsatile tube is not lost. The great
veins still contract in the mammal ; the sinus venosus is proba-
bly the result of blending and expansion. The later differentia-
tions of the parts of the heart are clearly related to the adapta-
tion to altered surroundings. Such is seen in the foetal heart
and circulation, and has probably been the determining cause
of the forms which the circulatory organs have assumed.

It is a fact that the part of the heart that survives the long-
est under adverse conditions is that which bears the stamp of
greatest ancestral antiquity. It (the sinus venosus) may not

ed without

ace (•rtcr Chan.
*7*troagl]r*iig-

leaunepur-

[iyen of the
•lution. We
B which we
irity of the
ent oiretda-
the highest
The great
nu is ptoba-
'differentiar
the adapta-
foetal heart
ining cause
imed.

8 the long-
le stamp of
s) may not

THE CIRCULATION OF THE BLOOD.

be leas under nervous control, but it certainly is least dependent
on the nervous system, and has the greatest automaticity.

The law of rhythm in organic nature flnds some of its most
evident exemplifications in the circulation. Most of the
rhythms are com-
pound, one being
blended with or su-
perimposed on an-
other. Even the ap-
parent irregularities
of the normal heart
are rhythmical, such
as the very marked
sloMring and other
changes accompany-
ing expiration, espe-
cially in some ani-

j i

We trust we have
made it evident that
the greatest allow-
ance must be made
for the animal group,
and some even for
the individual, in esk
timating any one of

the factors of the cir- Fia. ■>.— V«liw of the foot of the hone (after Clin-

oulation. We know * '

a good deal at present of cardiac physiology, but we do not

know a physiology of " the heart " in the sense in which we

understand that term to have been used till recently — i. e., we

are not in a position to state the laws that apply to all forms of

heart.

ganuMrj of fhe Fhyilologj of the Oinnktion.— In the
mammal the ci "culatory apparatus forms a closed system con-
sisting of a -' 'Mral pump or heart, arteries, capillaries, and
veins. All the v^arts of the vascular system are elastic, but this
property is most developed in the arteries.

Since the tissue-lymph is prepared from the blood in the
capillaries, it may be said that the whole circulatory system
exists for these vessels.

As a result of the action of an intermittent pump on elastic

S70

COMPARATIVE PHYSIOIXKiY.

veawli againat peripheral resistance, in consequence of which
the arteries are always kept more than full (distended), the
flow througfh the capillaries and veins is constant— a very great
advantage, enabling the capillaries to accomplish their work of
feeding the ever-hungry tissues. While physical forces play a
very prominent part in the circulation of the blood, vital ones
must not be ignored. They lie at the foundation of the whole,
here as elsewhere, and must be taken into the account in every
explanation.

As a consequence of the anatomical, physical, and vital char-
acters of the circulatory system, it follows that the velocity of
the blood is greatest in the arteries, least in the capillaries, and
intermediate in the veins.

The veins with their valves, their superflcial position and
thinner walls, make up a set of conditions favoring the onflow
of the blood, especially under musctilar exercise.

In the mammal the circulatory system, by reason of its con<
neotions with the digestive, respiratory, and lymphatic systems,
and in a lesser degree with all parts of the body, especially the
glandular organs, maintains at once the usefulness and the fit-
ness of the blood.

The arterioles, by virtue of their highly developed muscular
coat, are enabled to regitktte the blood-supply to every i>art, in
obedience to the nervous system.

The blood exercises a certain pressure on the walls of all
parts of Che vascular system, which is greatest in the heart it-
self, high in the arterioi, lower in the capillaries, and lowest in
the veins, in the largest of which it may be less Uian the atmos-
pheric pressure, or negative. The heart, in the mammal consists
of four perfectly separated chambers, each upper and each
lower pair working synchronously, intermixture of arterial
and venous blood being prevented by septa and interference in
working by valves. The heart is a force-pump chiefly, but, to
some extent, a suction-pump also, though its power as such
purely from its own action and independent of the respiratory
movements of the chest is slight under ordinary circumstances.
In consequence of the lesser resistance in the pulmonary divis-
ion of the circulation, the blood-pressure within the hjMurt is
much less in the right than in the left ventricle— a fact in har-
mony with and causative of the .greater tiiicknees of the walls
of the latter; for in the foetus, in which the conditions are dif-
ferent, this distinction does not hold.

of which
nded). the
▼eiy great
ir work of
roM play a
vital ones
the whole,
it in every

vital char-
velooity of
llaries, and

Mition and
the onflow

of its oon-
iosystemi,
lecially the
and the flt-

d muacular
Bry jiart, in

rails of aU
he heart it-
i lowest in
the atmos-
oal consists
' and each
of arterial
rferenoe in
)fly, but, to
er as such
respiratory
imstances.
nary divis-
le hjsart is
'act in har-
P the walls
•ns are dif-

THE CIRCULATION OP THK BLOOD.

271

The ventricles usually completely empty themselves of
blood and maintain their systolic contraction even after this
has been effected. The contraction of the heart, which really
begins in the great veins near their junction with the auri-
cles (that do not fully empty themselves), is at once fol-
lowed up by the auricular and ventricular contraction, the
whole constituting one long peristaltic wave. Then follows
the cardiac pause, which is of longer duration than the entire
systole.

When the heart contracts it hardens, owing to closing on a
non-compremible fluid dammed back within its walls by resist-
ance a fronte. At the same time ihe hand placed on the chest-
walls over the heart is sensible of the cardiac impulse, owing
to what ban just been mentioned. The systole of Uie chambers
of the heart gives rise to a first and a second sound, so called,
caused by several events combined, in which, however, the ten-
sion of Uie valves must take a prbminent share. The work of
the heart is dependent on the quantity of blood it ejects and
the pressure against which it acts. The pulse is an elevation
of the arterial wall, occurring with each heart-beat, in conse-
quence of the passage of a wave over the general blood-stream.
There is a distention of the entire arterial system in every direc-
tion. The pulse travels with extreme velocity as compared with
the blood-current. The heart-beat varies in force, frequency,
duration, etc., and with age, sex, posture, and numerous other
circumstances.

The whole of the circulatory system is regulated by the cen-
tral nervous system through nerves. There is in the medulla
oblongata a small collection of nerve-cells making up the
oardio-inhibitory center. This center, with varying degrees of
constancy, depending on the group of animals and the needs
of the organism, sends forth impulses (which modify the beat
of the heart in force and frequency) through the vagi nerves.
There are nerves of the sympathetic system with a center in
the cervical spinal cord, and possibly another in the medulla,
which are capable of originating either an acceleration of the
heart rhythm or an increase of the force of the beat, or both
together, known as accelerators or augmentors. In the verte-
brates thus far examined the vagus is in reality a vago-sympar
thetic nerve, containing inhibitory fibers proper, and sympa-
thetic, accelerator, or motor fibers.

The inhibitory fibers can arrest, slow, or weaken the cardiac

MMMtMNNM*

973

COMPARATIVR PI1Y8I0L00Y.

best ; the lympathetio aooelerate it or augmmit ita force. When
both are Btiinulated together, the inhibitory prevail.

Them nervea, aa aim -the aooeleratora, exerciM a profounit
influence upon the autrition of the heart, and affect its electri-
cal condition when etimulated, and we may believe when influ- ,
enced by their own centers.

The inhibitory flbem tend to preeerve and restore cardiac
energy ; the aympathetin, whether in the vagua or aa tlie aug-
mentors, the reverse. The vagus nerve (and probably the de-
pressor) acta as an afferent, cardiac sensory nerve reporting on
the intra-cardiao pressure, etc., and so enabling the vaso-
motor and cardio-inhibitory centers, which are, it would seem,
capable of related and harmonious action to act for the general
good.

The arterioles must be conceived as undergoing very fre-
quent changes of caliber. They are governed by the vaso- motor
center, situated in the medulla, and possibly certain subordi-
nate centers in the spinal cord, through vaso-motor nerves.
These are (a) yaso-oonstrictors, which maintain a constant but
▼ariable degree of contraction of the muscle-cells of the vessels;
(b) Taso-dilators, which are not in constant functional activity ;
and (0) mixed nerves, with both kinds. An inherited tendency
to rhythmical contraction throughout the entire vascular sys-
tem, including the vessels, must be taken into account.

The depressor nerve acta by lessening the tonic contraction
of (dilating) the vessels of the splanchnic area especially.

It is important to remember that all the changes of the
vascular sjrstem, so long as the nervous system is intact— i. e.,
so long as an animal is normal — are correlated ; and that the
action of such nerves as the depressor is to be taken rather as
an example of how some of these changes are brought about,
mere chapters in an inoomidete but voluminous history, if we
could but write it all. The changes in blood-pressure, by the
addition or removal of a considerable quantity of blood, are
slight, owing to the sort of adaptation referred to above, effected
through the nervous system. Finally, the capillary circulation,
when studied microscopically, and especially in disordered con-
ditions, shows clearly that the vital properties of these vessels
have an important share in determining the character of the
circulation in themselves directly and elsewhere indirectly.

The study of the circulation in other groups shows that
below birds the arterial and venous blood undergoes mixture

timmm

mtmm

>rce. When

a profounil
3t itn electH-
when influ- ,

itore oardlao
f M tlie aug-
Mbly the de-
wporting on
g the vaso-
would seem,
r the general

ag very fre-
e vaso- motor
ain Bubordi-
otor nerves,
constant but
rthe vemels;
»nal activity ;
ted tendency
vascular ays-
unt.

a contraction
icially.
ftnges of the

intact— i. e.,
and that the
:en rather as
'ought about,
listory, if we
MMure, by the
of blood, are
bove. effected
y circulation,
iordered con-

theae vessels
iracterof the
idirectly.
B shows that
goes mixture

THE CIRCULATION OP THE BLOOR

278

Boinewhere, usually in the neatl, but that in all the vertebrates
the best blood is invariably that which paaseH to the heud and
upper i«gions of the body. The deficiencies in the heart, owing
to the imperfections of valves, hcpta, etc., are in part counter-
acted in some groups by pressure ittlations, the blood always
Howing in the direction of least resistance, so that the above-
mentioned result is achieved.

Oapillaries are wanting in most of the invertebrates, the
blood flowing from the arteries into spaces (sinuses) in the tis-
sues. It is to be noted that a modified blood (lymph) is also
found in the interspaces of the celUi of organs. Indeed, the
cirouUitory system of lower forms is in many respects analogous
to the lymphatic system of higher ones.

DIGESTION OF FOOD.

The processes of digestion may be considered as having for
their end the preparation of food for entrance into the blood.

This is in part attained when the insoluble parts have been
rendered soluble. At this stage it becomes necessary to inquire
as to what constitutes /ood or a food.

Inasmuch as mlmals, unlike plants, derive none of their
food from the atmosphere, it is manifest that what they take in
by the mouth roust contain every chemical element, in some
form, that enters into the composition of the body.

But actual experience demonstrates that the food of animals
must, if we except certain salts and water, be in organized
form— i. e., it must approximate to the condition of the tissues
of the body in a large degree. Plants, in fact, are necessary to
animals in \Torking up the elements of the earth and air into
form suitable for them.

Foodstuffs are divisible into :

I. Organic.

1. Nitrogenous, (o) Albumins; (6) Albuminoids (as gelatm).

2. Non-nitrogenous, (o) Carbohydrates (sugars, starches) ;

(6) Fats.

II. Inorganic.

1. Water.

2. Salts.

Animals may derive the whole of their food from the bodies
of otheranimals (camivora) ; from vegetable matter exclusively
(herbivora) ; or from a mixture of the animal and vegetable, as
in the case of the pig, bear, and man himself {omnivora).

It has been found by feeding experiments, carried opt mostly
on dogs, that animals die when they lack any one of the con-
stituents of food, though they live longev on the nitrogenous
than any other kind. In some instances, as when fed on gela-
tin and water, or sugar and water, the animals died ahnost as

having for
the blood.
8 have been
ry to inquire

one of their
they take in
lent, in some

>dof animalH
in organized
of the tissues
) necessary to
I and air into

Is (as gelatin),
us, starches) ;

>m the bodies
Br exclusively
T^^table, as
dvora).
edojut mostly
16 of the con-
) nitrogenous
n fed on gela-
ied almost as

DIGESTION OP FOOD.

275

soon as if they had been wholly deprived of food. But it has
also been observed that some animals will all but starve rather
than eat certain kinds of food, though chemically sufficient
We must thus recognize something more in an animal than
merely the mechanical and chemical processes which suffice to
accomplish digestion in the laboratory. A food must be not
only sufficient from the chemical and physical point of view,
but be capable of being acted on by the digestive juices, and of
such a nature as to suit the particular animal that eats it.

To illustrate, bones may be masticated and readily digested
by a hy6na, but not by an ox or by man, though they meet the
conditions of a food in containing all the requisite constituents.
Further, the food that one man digests readily is scarcely di-
gestible at all by another ; and it is within the experience of
every one that a frequent change of diet is absolutely necessary.

Since all mammals, for a considerable period of their exist-
ence, feed upon milk exclusively, this must represent a perfect
or typical food. It will be wortii while to examine the compo-
sition of milk. The various substances composing it, and their
relative proportions for different animals, may be seen from the
following table, which is based on a total of 1,000 parts :

Hunuui.

Oow.

Goat.

Aas.

Water

889-06

867-06

868-68

910-24

Casein

I 89-24

26-66

48-64

1-88

j 48-28

} 5-76

48-05

40-87

5-48

88-60
12-99
48-57
40-04
622

I 20-18
12-66

Albumin

Butter

Milk-sugar

Salts.

[ 57-02

Total solids....

110-93

14296

186-42

80 76

The following table, giving the percentage composition of
the milk of different animals, may prove instructive.

Woman.

Oow.

Mm«.

Biteh.

Casein

Pats

2H)0 .
2-75
0-25
5-00

4-00
4-00
0-60
4-40

2-50
2-00
0-60
5-00

lOOO
lOHX)

Salts

0-50

Sttffar

8-50

Total solids

10<K)
OOHX)

18-00
87-00

vyao

24-00

Water

76-00

276

COMPARATIVE PHYSIOLOGY.

1. The proteida of milk are :

(a.) An albumin very like senmwJbumin.

Q).) Casein, normally in suspension, in the form of eartremely
minute particles, which contributes to the opacity, of milk.

It can be removed by filtration through pcroelain ; and pre-
cipitated or coagulated by acids and by rennet, an extract of
' the mucus membrane of the calf s stomach. ' After this coagu-
hition, whey, a fluid more or leas clear, separates, which con-
tains the salts and sugar of milk and most of the water. Much
of the fat is entangled with the casein.

Casein, with some fat makes up the greater part of cheese.

2. Fote.— Milk is an emulsion— i. e., contains fat suspended
in a fine state of division. The globules, which vary greatly m
size, are surrounded by an envelope of proteid matter. This
covering is broken up by churning, aUowing the fatty globules
to run together and form butter.

Butter consists chiefly of olein, palmitin, and stearin, but
contains in smaller quantity a variety of other fats. The ran-
cidity of butter is due to the presence of free fatty acids, espe-
cially butyric.

The fat of milk usually rises to the surface as cream when

milk is allowed to stand.

3. Milk-sugar, which is converted into lactic acid, probably
by the agency of some form of micro-organism, thus furnish-
ing acid sufficient to cause the precipitation or coagulation of

the casein.

Milk, when fresh, should be neutral or faintly alkalme.

4. SalU (and other extractives), consisting of phosphates of
calcium, potassium, and magnesium, potassium cihloride, with
traces of iron and other substances.

It can be readily understood wlqr animals fed on milk
rarely suffer from that defl<nen<qr of calcium salts m the bones
leading to rickets, so common in the ill-fed. It thus appears
that milk contains all the constituents requisite for the building
up of the healthy mftminaliim body; and experiments prove
that these exist in proper proportions and in a readily digestible
form. The author has found that a large number of animals,
into the usual food of which, in the adult form, mil^ does not
enter, like most of our wild mammals, as well as most birds,
will not only take milk but soon learn to like it, and thrive well
upon it Since the embryo chick lives upon the egg, it might
have been supposed that eggs would form excellent food for

1 of extremely
of milk,
un ; and pre-
an extract of
ir this coagu-
8, which oon-
t<rater. Much

irt of cheese,
fat suspended
ary greatly in
matter. This
fatty globules

id stearin, but
ate. The ran-
ty acids, espe-

B cream when

acid, probably

thus furnish-

coagulation of

' alkaline,
phosphates of
chloride, with

fed on milk
te m the bones
t thus appears
or the building
)rimente prove
adily digestible
ber of animals,
, mil% does not
as most birds,
and thrive well
e egg, it might
ellent food for

DIGESTION OF POOD.

277

adult animals, and common experience proves this to be the
case ; while chemical analysis shows that they, like milk, con-
tain all the necessary food constituente. Meat (muscle, with
fat chiefly) is also, of course, a valuable food, abounding in

Animal Toods..

Bzplantftlon of the alfiit.

Water. JtoMda. AlbumtnoUU. JT-flrte org-bOdU*. Sa»«.

Beef.
Pork.

Coto's milk.
Human milk.

Vegetable Toodi.

'Explanation of the signs.

Water. PntteU* DliiettnU SotUUgettMe Satte.

If-free orgam hodUe.

Fl«.n«<Uiidois).

proteids. Cereals contain starch in large proportion, but also »
mixture of pioteids. Oreen vegetables contain little actual nu-

ill

278

COMPARATIVE PHYSIOLOGY.

tritive material, but are umful in furnishing salts and special
substances, as certain compounds of sulphur which, in some ill-
understood way, act beneficially on the metabolism of the body.
They also seem to stimulate the flow of healthy digestive fluids.
• CondimentB act chiefly, perhaps, in the latter way. Tea, coffee,
etc., contain alkaloids, which it is likely have a conservatiTe
effect on tissue waste, but we really know very little as to how
it is that they prove so beneficial. Though they are recognized
to have a powerful effect on the nervous system aS stimulants,
nevertheless it would be erroneous to suppose that their action
was confined to this alone.

The accompanying diagrams will serve to represent to the
eye the relative proportions of the food-eosentials in various
articles of diet.

Pw. an.— Alimentarv caiud of 'embiro while the radimentaUT mld-gat i« still in con-
tlnnlty with velk-«u! (KOIIlker, after Blachoff). A. View from before, o. phuTii-
ml pUtes; h, pharynx: e, e, dlvertlcnla forming the luiwe; d, atpmach; /, direr-
ticnla of IWer; g, membrane torn from yelk-eac; A, hind gat. B. Longltndinal
eectkm. a, dirertteuinm of a long; 6, atlNnaoh; «, liver; a, yelk-aac.

It is plain that if, in the digestive tract, foods are changed
in solubUity and actual ohemi<»l constitution, this must have
been brought about by chemical agencies. That food is broken
up at the very commencement of the alimentary tract is a
matter of common observation; and that there should be a
gradual movement of the food from one part of the canal to
another, where a different fluid is secreted, would be expected.
As a matter of fact, mechanical and chemical forces play a

8 and special
\x, in some ill-
1 of the body,
^festive fluids.
. Tea, coCFee,
conservative
tUe as to how
d?e recognized
iS stimulants,
A their action

tresent to the
Is in various

giat i« still in con-
lefore. a, piuurn-
itomach; /, direr-
B. LongitodiuU

k-MMS.

are changed
is must have
ood is broken
,ry tiact is a

should be a
t the canal to
I be expected,
forces play a

DIGESTION OF POOD.

279

large part in the actual preparation of the food for absorption.
Pehind these lie, of course, the vital properties of the glands,
which prepare the active fluids from
the blood, so that a study of diges-
tion naturally divides itself into the
consideration of— 1. The digestive
juices; 2. The secretory processes;
and, 8. The muscular and nervous
mechanism by which the food is
carried from one part of the digest-
ive tract to another, and the waste
matter finally expelled.

BmbryologioaL— The alimentary
tract, as we have seen, is formed by
an infolding of the splanchnopleure,
and, according as the growth is
more or less marked, does the canal
become tortuous or renuun some-
what straight. The alimentary tract
of a Tnfttnmftl passes through stages
of development which conrespond with the permanent form of
oflier groups of vertebrates, according to a general law of evo-
lution. Inasmuch as the embryonic gut is formed of mesoblaat.

Fia

906— Diaonun of alimentary
canal of chick at fourth day
(Foater and Balfour, after GOt-
te). la, diverticulum of one
lung; St, atomach; /, liver; p,
pancreaa.

Ida or — Poaltlon at varlona parta of alimentary canal at differoit ■tiaM. A. *n.
iSS;TfSKB week/ Bi OfelBht weeka. C. Of ten weeka (Allen TkomMm). I,
5S?^WSHinS;?«SS!ih^T«nall intortJne; *'. large tat«attne; ff.g^
ffi^lSi «, bliSiwjS; do«!»; e, cwnm; ni, dnctoa vitello-TateatiBalla; d, nio-
gnital unoa; «, yrik'Mc.

280

COMPARATIVE PHYSIOLOGY.

and hypoblast, it ia easy to understand why the developed tract
should so invariaably consist of glandular struoturea and mus-
cular tissue disposed in a certain regular arrangement. The
fact that all the organs that pour digestive juices into the ali-
mentary tract are outgrowths from it serves to explain why
there should remain a physiological connection with an ana-
tomical isolation. The general resemblance of the epithelium
throughout, even in parte widely separated, also becomra clear,
as well as many other pointe we can not now refer to in detail,
to one who realiies the significance of the laws of descent (evo-
lution).

OompuntiT*. — Amoeba ingeste and digeste apparently by
every part of ito body ; though exact studies have shown that
it neither accepte nor retains without considerable power of
disorimioation ; and it is also possible that some sort of digest-
ive fluid may be secreted from the part of the body with which
the food-particles come in contact It has been shown, too^
that there are differences in the digestive capacity of closely
allied forms among Infusorians.

The ciliated Infusorians have a permanent mouth, which
tagkj also serve as an anus ; or, there may be an anus, though
usually less distinct from the rest of the body than the mouth.

Among the Ocelenterates intrcHielluJar digestion is found.
Certain cells of the endoderm (as in Hydra) take up food-parti-
cles Amoeba-like, digest them, and thus provide material for
other cells as well as themselves, in a form suitable for assimi-
lation. This is a beginning of that differentiation of function
which is carried so far among tiie higher vertebrates. But, as
recent investigations have shown, such intra-cellular digestion
existo to some extent in the alimentary canal of the highest
members of the vertebrate group (see page 345).

The means for grasping and triturating food among in-
vertebrates are very complicated and varied, as are also those
adapted for sucking the juices of prey. Examples to hand are
to be found in the crab, crayfish, spider, grasshopper, beetie,
etc., on the one hand, and the butterfly, housefly, leech, etc., on
the other.

Before passing on to higher groups, it will be well to bear
in mind that the digestive organs are to be regarded as the out-
come both of heredity and adaptation to circumstances. We
find parts of the intestine, e. g., retained in some animals in
whose economy they seem to serve littie if any good purpose, as

veloped tract
rmalndmuB-
cement The
into the ali-
explain why
with anana-
le epithelium
eoomes dear,
r to in detail,
deaoent (evo-

ppArently by
e shown that
lie power of
iort of digest-
Y with which
L shown, too,
ty of closely

louth, which
anus, though
I the mouth.
Ion is found,
ip food-parti-
material for
lie for assimi-
n of function
ites. But, as
liar digestion
f the highest

id among in-
uce also those
IS to hand are
lopper, beetle,
leech, etc., on

e well to bear
ed as the out-
stances. We
le animals in
Dd purpose, as

DIGESTION OF POOD.

281

the vermiform appendix of man. Adaptation has been illus-
trated in the lifetime of a single individual in a remarkable

side* of body;

gated roond gdllet

manner ; thus, a seagull, by being fed on grijm^ has had ite
stomach, naturally thin and soft-walled, converted mto a mus-

*"ffince digiwtion is a process in which the mecham^ and
chemical are both involved, and the food of anmials differs so
widely, great variety in the alimentary teact, both anatomical
and ph^ological, must be expected. V^t»>^//^r*$
usuaUy be Sen in much htfger bulk to furnish the needed
elements, hence the great length of intestine habitually found
in herbivorous animals, associated often with a capacious
and chambered stomach, furnishing a larger labof^tory m
which Nature may carry on her processes. To illustrate, the
stomach of the ruminants consists of four parte (rumen, retwu-
lutn, omasum or psalterium, abomamm). The food when
cropped is immediately swallowed; so that the Pa«n«M"*"!^>
is a merfl storehouse in which it is softened, though but Uttte
changed otherwise ; and it would seem that real gastnc digestion
is almost confined to the last division, which may be compared

98S

COMPARATIVE PHYSIOLOGY.

to the simple stomaoh of the Camivora or of man ; and, before
the food reaches this region, it has been thoroughly masticated
and mixed with saliva.

The stomach of the honw is small, though the intestine,

■t25i;% 1m" "' tS^^^* — ■•« "P<» ■•mPly opening the cavities of the
^SS\ ^i*!*^- "u5 '^'Sr' S^l ftwthw d«iseSfenTUrc«TJty of the thonS,
cS^i^SSL^JL^^lL^^i^' *'«*"*»«»: <?.»witricleeof the heart: AaSS
SSt'.rf'JK.?^ W ^Sr^lii ""^i 0,amm coltaDsed, and occnpTf ng only back
5fft^S2f?i\iJvIS?*'lJf**"5^»^ P(«»"" nienifiranee; /, cartHage at the end
id^2IS^"i'T} **?'?f"}i ^portion of the wall of iMdy left between thona
Mt ?hS??f"*L"'J2f.*^.? ttie riS7 i the Hw. In this caw lying more to the
•wtttan to the right of the body; M, the stomach, a large part of the gnater
S2^S^'^»?°'H: ^' <>»«"«">»; 0. small lnte«^;Tthe SMnSTw
^iSy^ '"'^ '"•• ■*• ""^ herilTorons animals; C. the large tataS)n~

and, before
masticated

e inteatine,

DIGESTION OP POOD.

283

eqiecially the large gut is capacious. The stomach is divisible
into a cardiac region, of a light color internally, and lined
with epithelium, like that of the oesophagiis. and a redder

•TitiM of the
>f the tbomx,
leart: D, Miri-
ring only back
ige at the Mtd
•tween thonz
ig more to the
of the greater
he caeam, eo
ffge inteatino.

Fia.SSOii

Fia.an.

iho 9m— General and lateral view of dog'i teeth (after ChsoTean).

SS: S:l5SSfor^ STnclaoi. and wnine teeth in a yea^old dog (Ohanvean).

Tfw. m-Dentition of inferior Jaw of hone (after Chaitvean).

pyloric area, in which the greater part of the digestive process
goes on (Fig. 866).

284

COMPARATIVB PHYSIOLOOY.

The mouth parts, even in dome of the higher vertebratee, as
the Camivora, serve a prehensile rather than a digestive pur-
pose. This is well seen in the dog, that bolts his food ; but
in this and allied groups of mammals gastric digestion is very
active.

The teeth as triturating organs find their highest develop-
ment in ruminants, the combined side-tondde and forward-and>
backward motion of the jawa rendering them very effective.

In Camivora the teeth serve for grasping and tearing, while
in the Insectivora the tongue, as also in certain birds (wood-
peckers), is an important organ for securing food.

Fie. an.— n«flle of nmMr toath of the banc, man cnMclally Intcndad to fhow the
melan, the fangi haTtng been exposed (Chmnvean). a, molar teeth; 6, rapple-
mentwy molar; e, tnek; a. inelson. *^*^

It is to be noted, too, that, while the horse crops grass by
biting it off, the ox uses the tongue, as well as the teeth and
lips, to secure the mouthful.

Man's teeth are somewhat intermediate in form between the
carnivorous and the herbivorous type. Birds lack teeth, but
the strong miiscular gizsard imfflces to grind the food against
the small pebbles that are habitually swallowed.

The crop, well developed in granivorous birds, is a dilatation
of the oesophagus, serving to store and soften the food.

In the pigeon a glandular epithelium in the crop secretes a

Fie. SM.— General view of dlgettWe apparatna of fowl (after ChanTean). 1, tongue;
8. pharynx; 8, flrat portion of gMophans: 4, crop; 6, eecond portion of OMopha-
Boa; 6, mocentric Tentrlele (piovenMcahu); 7, giward; 8, origin of dnodennm: 0,
mt blanch of dnodenal flexure; 10, ■eeond branen of lame; 11, origin of floating
portion of •mall intestine; IS, email Intestine; ir, terminal portion of thia intee-
tbw, flanked on each side by the two eaca (regarded as the analogue of colon of
mammals); 18. 18. free extremities of cacnms; 14. Insertion of these two tmlt-dt-
$ae Into Intestinal tube; 16, rectum; 16, cloaca; 17, mns; 18, mesentny; 10. left
lobe of liver; SO, right lobe; 81, gall-bhidder: 81, insertion of pancreatic and biliary
ducts: the two pancreatic duets are the most anterior, the choledie or heptttie is In
the middle, and the cystic duet is posterior; 88, pancreaa; 94, diq>hnigmule aspect
of lung; a6,ovary(lnsst8te«f anophy); 98, oviduct

rtebraU*, m
gMtive pur-
I food ; but
ition is very

Mt deyelop-
orward-ond-
Bflfeotive.
taing, while
>irds (wood-

lad to *how th*
Nth; b, lapple-

pa gnuM by
e teeth and

Iwtween the
k teeth, but
iood against

a dilatation
od.
pHecretes a

M). LUmgue;
tlonof oaaopha-
f daodwram: 0,
riglii of flMtlng
in of thia IntM-
gne of colon of
■M twoenb^-
Mntcry; 19. left
attic and biliary
or hepaUe ia in
NRmKlo aapcct

SOTPWi

S86

COMPAKATIVH PIIYHIOLOOY.

milky-lookinir lulMtenm that ia ra^rgitated into the mouth of
the youiiff one, which ia inierted within that of the parent binl.

The proventriouliu— an enlargement juat above the ginaid
— ia relatively to the latter very thin-walled, but providea the
true gaatrio juicen.

Certain planta digeat proteid matter, like animala ; thua the
■un-dew (Droaero), by the oloaure of ita leavea, oapturea inaeota,
whioh are digeated and the produota abaorbed. The digeative
fluid conaiaU of a pepain-oonUining aeoretion, together with
formic acid.

•TRUOTORB, AMUWOMM aWT, AW P nONIFIOAIfOII
OF THB TMfFM.

In a tooth we reoogniie a portion imbedded in the jaw (fang,
root), a free portion (crown), and a oonatricted ragion (neck).

Fi«, an.

Fio. M7.

litnetare;

Fill. MS.— Mapitfled Mcttoii of • cuIm tooth, thowing Ita Intimate ■traotuM. ].

crowni a, M, neck; 8, fang, or root; 4, eavltM palM; 6, opening br wblcit tlie ^

■ele and nenrea cominnnleate with the palp; t, 8, ivorjr, aiiowing wioaa atmeti

7J; enamel; 8, 8. cement.
Flo. W.— A, tran*vetM Motion of enamel, abowlng ita hezagowd priima; B, aeiw-

rated priama iChaavean). "^

''"•J'Tir^'!?"."!'*!^ 'f^ ?* molar tooth (OhaaveMi). a, a. dentine traveraed

by Ita tabnil; b, b, Intatglooalar or aodolar hijar; e, «, oementam.

le mouth of
Muvnt bird,
theiriiiard
rovidM the

■ ; thuf the
irm inMotR,
le digestive
[ether with

) jaw (fang,
a (neck).

DI0B8TI0N OK FOOD.

98T

•tiactuM. 1,
irhlch the tw-
tMU itraeture;

Ifnw; B, MP*-

llM tnmiMd

Fio. M8.-liicUor tMlh o» the haim. DHalli of itmeturB (Ownvetii). J, » tof* •"
which >■ iodteatod gmml ihaiM of • permHiMit Inolior Mid the iMrticolw lanue
nu^iveW M^ani^^enuruble IneoiMeqaMioe of frIcUon and theeontlnued
nuhhur onlwwd of theee teeth; 8, • rlriin tooth, anterior and poeterior facee: 8.
Imottudlnal Motion of a vlrsln tooth, Intended to ihow the Internal conformation
and etractare. Not to eonpllcata the flrare, the external cement and that amazed
In the Infnndlbulnm have notbeea emhlblted; 4, tranaveiM eectlon for the taoie
pnrpaee; a, encircling enamel; ft. central enamel; «, dental itar; d, dentine; 6,de-
clduone tooth.

A tooth is made up of enamel, dentine or " ivory," and ce-
ment ieruata petrota). The relative distribution of theee is
shown in Fig. 285.

Fi«. MB.— Traneveree aectlon of a hone'e upper motar tooth (Olwuveau). A, estemai
«wwnit; BTesteiiial enamel; 0. denttoeTb. Internal enamel; B. Internal cement.

288

COMPARATIVE PHYSIOLOGY.

Enamel is made up of elongated hexagonal prisms aet almost
ertically in the dentine (Fig. 886).

It is the hardest substance known in the animal body, con-
sisting almost entirely of inorganic material ; and when lost is
but indifferently if at all replaced.

Fia. MO.— Tooth of cat in aita (Walderw). - 1, anamel; 9, dentine; 8, cement; 4, peri-
oeteam of alveolarcaTlty; 5* bone o? ]aw; 0, pnlp cavity.

Dentine is traversed by the dentine tubules (Fig. 237),
which radiate outward from the pulp cavity.

)i^pWjpWI»<lli|i i| ip TWMM P WUJ ' * ' ' « W** l '''''"J W

908 aet almost

al body, oon-
when lost is

, cement; 4, p«ci-
I (Fig. 287),

DIGBSTION 0^ FOOD.

289

The latter is filled by the tooth-pulp, which consists of a
delicate connective tissue supporting blood-vessels and nerves
which ramify in it after entering by the openings in the fang
of Uie tooth. From the pulp protoplasmic fibers extend into
the dentine tubules.

The crusta petroea is very similar to bone, but is usually
without Haversian canals, and, like bone, is covered with peri-
osteum.

Fio. 941.— The teeth of the rat (Ohanveu). 1. upper Jaw, wlOi a. MeUon iiurface, and
b, extenwreurfaee; S, lower Jaw, with a, dental tables, and b, external face.

Teeth are simple and compound. In the former (camivora)
the entire crown is covered with enamel ; in the latter, owing
19

p^imm0m m > m mMmmi> i mmimim 'i i ■ i

-.Jii-Aof*

290

COMPARATIVE PHYSIOLOGY.

to wear, the other constituents appear on the upper surface of
the crown (Figs. 888, 239, 240).

It follows that the former are better adapted for tearing,
the latter for grinding, as the different components wear un-
equally and leave the top of the crown rough, so that the upper
and lower jaws of a ruminant are like two millstones, (Fig.
241).

It also follows that in the horse and in ruminants the age
may be learned with considerable accuracy from the condition
of wear of the teeth and as the inci^rs are most readily ex-
amined they are taken as the chief indicators of the age of
the animal.

In nearly all animals are found the deciduous or milk teeth
succeeded by the permanent teeth. This arises as a necessity
from the growth of the jaw and the need of stronger teeth, either
as weapons of defense and attack or in order the more, effectu-
ally to secure and prepare food. The permanent teeth are also
more numerous than the milk teeth.

The dentition of our domestic animals may be expressed
thus r

8-8

Dog. Incison, 2^ ; canines, j^ ; premolars, j-j

Cat.

Man.

Pig.

Ox.

Horse.

8-8

8-8'

2-2

8-8

8-8'

0-0

8-«'

8-8

8-«'

8-8'

1-
1-:
0-0
0-0

4-4

2-2
molftrs, g^ = 42.

8-8

a-3'

2-2'

8-8

8-8'

8-3

8-8'

8-^

8-8'

0-0

0-0'

= 80.

1-1
1-1

8-a

^ = 92.

j5 = 44.

8-8

8^ = «^-

8-f

8-8

8-3

8-8-^-

= 40.

The

The latter is the representation of the milk dentition,
mare is without canines ("tushes**).

It will be noticed that in the ox incison and canines do not
appear in the upper jaw, though they are represented by embry-
onic rudiments.

The table above and that on page 296 (after Leyh) give a
large amount of mformation in a small space, and are illus-
trated by the accompanying figures :

per surface of

1 for tearing,
ents wearun-
that the upper
llstonea, (Fig.

Hants the age
the condition
fit readily ex-
ot the age of

or milk teeth
IS a necessity
iv teeth, either
more.effectu-
teeth are also

r be expressed

2-2
lolan, g^ = 42.

= 80.

1-1
1-1
8-8 ^

^-44
8-8

8-8

= 40.

8-«
8-8 ».

mlition. The

anines do not
ited by embry-

Leyh) give a
and are illus-

DIGBSTION OF FOOD.

291

s X

no. ML-The tMlli of the pig (ChmvMD). 1, vpfn teetk. table earfMe; », kuwer
teetk, tobleaqieet; S, latemk view of Jawt.

(8 bRMOiDdwn.)

4 yean.

(BbraadinciMM.)

Over 7 yean.
(Sbraadlneiaon.)

2 montlM.
(MUk-teetb.)

Hyean.
(abroad'

llyean.
(4 broad inclao

Ra. att.— Chantaa

inciiata.) (4 broad liici«>«a.)

in ineiMir teetb of tbe aheap (WiickenslL

suMm^-v^mm.wJMkmy'MUMti ii l t i k

292

COMPARATIVB PHYSIOLOGY.

New-born,

SmoBtlu.

;,JL^

6 monthii.

lyaw.

ayaHt.

aijrean.

tjtm.

y .

SjTMn.

7 7a«n.
of hone with age (WUekHW).

I month*.

St yean.

Sywn.

(rUekMM).

(ftmi ii m w i ii iii lili

DIGESTION OP POOD.

298

.-V"^

8 yean,

9 yean.

"WS^-

9 yean (t).

10 yean (f).

tlyean(n.

13 jean.

Ujreaia.

CJ^M^

18 yean. 84 yean.

Flo, 9M W. Cl»i«ea in inciaor teeth of bone with age (Wilckena).

u6if

294

COMPABATIVE PHYSIOLOGY.

NMf*boni«

Sdv*.

4melBi.

»jtm.

Hymn.

SyMH-

Hjmn.

;>»%

4ytu».

tn. MB (l).-CliHiKM in UkHmt

'A^y,*^;^

SyMis.
of ox with age (WUekmw).

UekeM).

DIOESTIOM OP POOD.

295

tjf V> i^r- tVi_

87«an.

^ ':=«;»

ia7«ui<

^ 'iV

IOtmuw.

Utmh.

uJJi*'^

16 jean. 18 years. »jeaw.

Fio. MB (>).— ChangM in inolaor teeth of ox witb age (WUckens).

ao6

COMPARATIVE PHTSIOLOOT.

'if

I'd 2s

Si;

_=i«i_»j

5f «r

ill

^ •• s

-s

s
©

I
I

a
j&

2 a

11^

S S

« «

III

? ares'

..I

a {us

a*^a

I.I

^1 iit^

BttSaSx

99 99

«8

'll%IJlMWMItf.lJJWB»gl ll i l lW>lM NI» i l * i) w

fiQ

55!

DIGESTION OP POOD.

THB DMHBmVll JUICJBS.

297

BftliTa.— The aaliva t mnd in the mouth ia a mixture of
the secretion of three pan 4 of glands, alkaline in reaction, of a
low speciflo gravity (variable in different groups of animals),
with a small percentage of solids consisting of salts and organic
bodies (mucin, proteids). ^

Saliva serves mechanical functions in articulation, in moist-
ening the food, and dissolving out some of its salts. But its
principal use in digestion is in reducing starchy matters to a
soluble form, as sugar. So far as known, the other constituents
of the food are not changed chemically in the mouth.

TIm Amylolytlo Aetion of the Baliya.— Starch exists in grains
surroimded by a oeUuioae covering, which qaliva does not digest :
hence its action on raw starch is slow.

It in found that if a specimen of boUed starch not too thick
be exposed to a small quantity of saliva at the temperature of
the body or thereabout (87° to 40° C), it will speedily undergo
certain changes :

1. After a very short time sugar may be detected by Feh-
ling's solution (copper sulphate in an excess of sodium hydrate,
the sugar reducing the «upric hydrate to cuprous oxide on
boiling).

2. At ibis early stage starch may still be detected by the
blue color it gives with iodine ; but later, instead of a blue, a
purple or red may appear, indicating the presence of dextrin,
which may be regarded as a product intermediate between
starch and sugar.

8. The longer the process continues, the more sugar and the
less starch or dextrin to be detected ; but, inasmuch as the
quantity of sugar at the end of the process does not exactly
correspond with the original quantity of starch, even when no
starch or dextrin is to be found, it is believed that other bodies
are formed. One of these is achroodextrin, which does not
give a color reaction with iodine.

The sugars formed are : (a) Dextrose. (6) Maltose, which
has less reducing power over solutions of copper salts, a more
pronounced rotatory action on light, etc.

It is found that the digestive action of saliva, as in the
above-described experiment, will be retarded or arrested if the
sugar is allowed to aooumulato in large quantity. That diges-
tion in the mouth is substantially the same as that just de-

.-.ji*

298

COMPARATIVE PIIY8I0L00V.

■cribed can be easily shown by holding a solution of starch in
the mouth fur a few seconds, and then testing it for sugar,
when it will be invariably found.

While salivary digestion is not impossible in a neutral me-
dium, it is arrested in an acid one even of no great strength
(less than one per cent), and goes on best in a feebly alkaline
medium, which is the condition normally in the mouth. Though
a temporature about equal to that of the body is best adapted
for salivary digestion, it will proceed, we have ourselves found
at a higher temperature thui digestion by any other of the
juices, so far as man is concerned— a fact to be connected, in all
probability, with his habit for agea of taking very warm fluids
into the mouth.

The active principle of saliva is ptyalin, a nitrogenous body
which is assumed to exist, for it has never been perfectly iso-
lated. It belongs to the class of unorganised ferments, the
properties of which have been already referred to before (page

les).

GhaxMt«riit«j of flw BeeNtka of th« Diftrail Okndi,—
Parotid saliva in in man not a viscid fluid, but clear and limpid,
containing very little mucin. Submaxillary saliva in mofit
ftnitngl" and iu man is viscid, while the secretion of the sub-
lingual gland is still more viscid.

OompantiTe.— 8aliva differs greatly in activity in different
animals ; thus saliva in the dog is almost inert, that of the
parotid gland quite so; in the oat it is but little more effective;
and in the horse, ox, and sheep, it is linown to be of very feeble
iigestive power.

In man, the Ghiinea-pig, the rat, the hog, both parotid and
submaxillary saliva are active ; while hi the rabbit the sub-
maxillary saliva, the reverse of the preceding, is almost in-
active, and the parotid secretion very powerful.

An aqueous or glycerin extract of the salivary glands has
digestive properties. The secretion of the different gkmds may
be collected by passing tubes or cannulas into their ducts.

The saliva, normally neutral or only faintly add, may be-
come very much so in the intervals of digestion. The rapid
decay of the teeth occurring during and after certain: diseases
seems in certain cases to be referable in part to an abnormal
condition of the saliva.

The tartar which collects on the teeth consists largely of
earthy phosphates.

of starch in
I it for sagnr,

neutnil tne-

it atrength

ibly ailcaline

iuth. Though

bwt adapted

ilvw found

other of the

ineoted, in all

warm fluids

Dgenousbody

perfectly iso-

ferments, the

before (page

at CQuuU—
r and limpid,
Hva in mopt
of the sttb-

y in different
;, that of the
toreeffectiTe;
9t very feeble

parotid and
bbit the sub-
• almost in-

y glands has
t glands may
r duets,
tcid, may be-
The rapid
■tainr diseases
m abnormal

ts laigely of

8T10N o poon.

OMtriO JliM.— Oastrio juioe may tie olx ^ from i>
lous opening into the stomach. Such niii.v aiHile tuii .oally
by an incision orer the organ in the middh i«, o«t«!hia^ it up
and stitching it to the edges of the wound, ^^•inmtc uud lumrt-
ing a special form of cannula, which may be oluoed oi .opened
atvrill.

Digestion in a few cases of accidental gastric flstulsB has
been made the subject of careful study. The most instructive
case is that of Alexis St. Martin, a French Canadian, into
whose stomach a considerable opening was made by a gunshot-
wound.

GhMrtric juice, in his case and in the lower animals with
artificial openings in the stomach, has been obtained by irri-
tating the mucous lining mechanically with a foreign body, as
a feather.

The great difficulty in all such c as e s arises from the impos-
sibility of being certain that such fiuid is normal ; for the con-
ditions which call forth secretion are certainly such as the
stomach never experiences in the ordinary course of events,
and we Iwve seen how saliva varies, according as the animal is
fasting or feeding, etc.

Bearing in mind, then, that our knowledge is possibly only
approximately correct, we may state what is known of the se-
cretions of the stomach.

The gastric secretion is clear, colorless, of low specific grav-
ity (1001 to 1010), the solids being in gnat part made up of
pepsin with a Hinall quantify of mucus, which may become ex-
cessive in disordered conditions. There has been a good deal
of dispute as to the add found in the stomach during digestion.
It is now genurally agreed that during the g reater part of the
digestive process there is free hydrochloric add to the extent
of about '3 per cent It is maintained that lactic acid exists
normally in the early stages of digestion, and it is conceded that
lactic, butyric, acetic, and other adds may be present in certain
forms of disordered digestion.

It is also generally acknowledged that in nuMnmulM the woric
of the stomach is limited, so far as actual chemical changes go,
to the conversion of the proteid constituents of food into pep-
tone. Fats may be released from their protdd coverings (cells),
but ndther they nor starches are in the least altered chemically.
Some have thought that in the dog there is a slight digestion of
fatii in the stomach. The solvent power of the gastric juice is

800

("OMPARATIVR PIIVBIOLOOY.

greater than can be aocounted for hy the preeenoe of the acid it
oontaina merely, and it ha« a marked antueptic action.

Digestive pmcei«ea may be conducted out of the body in a
very simple manner, which the student may carry out for him-
self. To illustrate by the case of gastric digestion: The mucous
membrane is to be removed from a pig's stomach after its nur-
faoe has been washed clean, but not too thoroughly, chopiHMl
up fine, and divided into two parts. On one half pour witter
that shall contain '8 per cent hydrochloric acid (made by add-
ing 4 to 6 cc. commercial acid to 1,000 co. water). This will
extract the pepsin, and may be used as the menstruum in which
the substance to be digested is placed. The best is fresh fibrin
whipped from blood recently shed.

Since the fluid thus prepared will contain traces of peptone
from the digestion of the mucous membrane, it is in some
respects better to use a glycerin extract of the same. This is
made by adding some of the best glycerin to the chopped up
mucous membrane of the stomach of a pig, etc., well dried with
bibulous paper, letting the whole stand for eight to ten days,
filtering through cotton, and then through coarse filter-paper.
It will be nearly colorless, dear, and powerful, a few drops
sufficing for the work of digesting a little fibrin when added to
some two per cent of hydrochloric acid.

Digestion goes on best at about 40* C, but will proceed in
the cold if the tube in which the materials have been placed is
frequently shaken. It is best to place the test-tube containing
them in a beaker of water kept at about blood-heat. Soon the
fibrin begins to swell and also to melt away.

After fifteen to twenty minutes, if a little of the fluid in the
tube be removed and filtered, and to the filtrate added carefully
to neutralisation dilute alkali, a precipitate, insoluble in water
but soluble in excess of alkali (or acid), is thrown down. This
is in most respects like acid-albumen, but has been called para-
peptone. The longer digestion proceeds, the less is there of
this and the more of another substance, peptone, so that the
former is to be regarded as an intermediate product. Peptone
is distinguished from albuminous bodies or proteids by— 1.
Not being coagulable from its aqueous solutions on boiling.
8. Diffusing more readily through animal membranes. 8. Not
being precipitated by a number of reagents that usually act
on proteids.

In artificial digestion it is noticeable that much more fibrin

iiS»u-_i-_

pour

N the arid it
ion.

le budy in «
lout for liim-
I The niucuuH
(after its sur-
ily, chopiHHl
wuler
le by add-
Thin will
itn in which
freah fibrin

I of peptone
is in eome

|ne. This is
chopped up

II dried with
to ten days,
filter-paper.

a few drope
len added to

II proceed in
Mn placed is
B containing
t. Soon the

I fluid in the
ed carefully
ble in water
lown. This
called para-
is there of
BO that the
t- Peptone
Bids 1^—1.
on boiling.
les. 8. Not
usually act

nore fibrin

DIGESTION OP FOOD.

801

or other proteid matter will be dissolved If It be finely divided
and frequently shaken up, so that a greater surface is ex|MMe<l
to the digestive fluid.

The exact nature of the pniceas by which proteid is changed
to peptone is not certainly known.

Since starch un the addition of water becomes sugar (CJiw
Ot -f HiO )■ 0JIiiO(), and since peptones have been formed
through the action of dilute acid at a high temperature or by
superheated water alone, it is possible that the digestion of both
starch and proteids may be a hydration ; but we do not know
that it is such.

As already explained, milk is curdled by an extract of the
stomach (rennet) ; and this can take place in the absence of all
acids or anything else that might be suspected except the real
cause; there seems to be no doubt that there is a distinct fer-
ment which produces the coagulation of mUk which results
from the precipitation of its oasein.

The activity of the gastric juice, and all extracts of the mu-
cous membrane of the stomach, on proteids, is due to pepain, a
nitrogenous body, but not a proteid.

like other ferments, the conditions under which it is effect-
ive are well defined. It will not act in an alkaline medium at
all, and if kept long in such it is destroyed. In a neutral me-
dium its power is suspended but not destroyed. Digestion will
go on, though less perfectly, in the presence if certain other
acids than hydrochloric. As with all dige^uve ferments, the
activity of pepsin is wholly destroyed by boiling.

IN 100 PABTB.

Mm.

Ox.

P««.

DOO.

rresb.

rromKAll-
UmMw.

Water

86-8

18-7

7-4

8-0
2-2
1-1

00-4
0-6

8-0

0-8
1-8

88-8

11-2

i 7-8

) 2-2
0-6
11

95-8
4-7
8*4

0*5
0r2
(HI

80-2

Solids

14-8

Bilemlto

12-6

Leoethin, oholesterin

Fata, soaps

1-8

Mucin and coloring matter . .
Inomnio salts

0-8
0-6

The color of the bile of man is a rick golden yellow. When
it contains much mucus, as is the case when it remains long in
the gall-bladder, it is ropy, though usually dear. Bile may
contain small quantities of iron, manganeee, and copper, the

802

COMPARATIVE PHYSIOLOGY.

latter two especially being absent from all other fluids' of the
body. Sodium chloride is the most abundant salt Bile must
be regarded as an excretion as well as a secretion ; the pig-
ments, copper, manganese, and perhaps the iron and the cho-
lesterin being of little or no use in the digestive processes, so
far as known.

The hUe-^alts are the essential constituents of bile as a
digestive fluid. In man and many other animals, they consist
of taurocholate and glyoooholate of sodium, and may be ob-
tained in bundles of needlenshaped crystals radiating from a
common center. These salts ar6 soluble in water and alcohol,^
with an alkaline reaction, but insoluble in ether.

Glycocholic acid may be resolved mto cholalic (cholic) acid
and glycin (glycocol) ; and taurocholic acid into cholalic acid
and taurin. Thus : ^

QljrcochoUc acid. ChoUdio add. Glycin.

Ct«H4iN0. + H.0 = C.4H«.0t + OiH.NO..

Thurochollc aoid ChcdaUc add. Taurin.

Ct.H«.N80t -f- Hm = C«H«.0. + OtHtNSO..
Glycocol (glycin) is amido-aoetic acid—

, and

Taorin, amido-isethionic acid,

C«H4<^^, and may be made artifi-
cially from isethionic acid.

It is to be noted that both the bile acids contain nitrogen,
but that cholalic acid does not The decomposition of the bile
acids takes place in the alimentary canal, and the glycin and
taurin are restored to the blood, and are possibly used afresh in
the construction of the bile acids, though this is not definitely
known.

Bile>Piglll0iltt.— The yellowish-red color of the bile is owing
to Bilirubin (CuHuNtOt), which may be separated either as
an amorphous yellow powder or in tablets and prisms. It is
soluble in chloroform, insoluble in water, and but partially
soluble in alcohol and ether. It makes up a large, part of
gall-stones, which contain, besides cholesterin, earthy salts in
abundance.

It maybe oxidised to BUiverdin (CnHuNtOi), the natural
green pigment of the bile of the herbivorsf. When a drop of

luids' of the
Bile must
|>n ; the pig-
Jrnd the cho-
I prooeases, ao

>f bile as a

they ooiuist

may be ob-

jtting from a

I and aloohol,t

(cholio) acid
cholalio acid

In.

made artifl-

un nitrogen,
n of the bile
9 glycin and
Bed afresh in
lot definitely

bile is owing
»d either as
>ri8ms. It is
l>ut partially
Eirge. part of
rthy salts in

the natural
en a drop of

DIGESTION OP POOD.

sro8

nitric acid, oontainiug nitrous acid, is added to bile, it under-
goes a series of color changes in' a certain tolerably constant
order, becoming green, greenish-Uue, blue, violet, a brick red,
and finally yellow ; thou^^'h the green is the most characteristic
and permanent Bach one oi these represents a distinct stage
of the oxidation of bilinibin, the green answering to biliverdin.
Such is Gmelin's test for bile-pigments, by which they may be
detected in' urine or other fluids. The absence of proteids in
bile is to be noted.

The DigcitiT* Aotion of Bile.— l. So far as known, its action
' on proteids is nil. When bile is added to the products of an
artificial gastric digestion, bile-salts, peptone, pepsin, and para-
peptone are precipitated and redissolved by excess. 8. It is
slightly solyent of fats, though an emulsion made with bile is
▼ery feeble. Bht it is likely helpful to pancreatic juice, or
more efficient itself when the latter is present With free fatty
acids it forms soaps, which themselves help in emulsifying fat
3. Membranes wet with bile allow fats to pass mere readily;*
hence it is inferred that bile assists in absorption. 4. When
bile is not poured out into the alimentary canal the foces
become clay-odlored and ill-smelling, foul gases being secreted
in abundance, so that it would seem that bile exercises an anti-
septic influence. It may limit the quantity of indol formed.
It is to be understood that these various properties of bile are
to be traced almost entirely to its salts ; though its alkaline
reaction is favorable to digestion in the intestines, apart ftmm
its helpfulness in soap-forming, etc. 5. It is thought by some
that the bile acts as a stimulant to the intestinal tract giving
rise to peristaltic movements, and also, mechanically, as a lubri-
cant of the fsBoes. In the opinion of many, an excess of bile
naturally poured out causes diarrhoea, and it is well known
that bile given by the month acts as a purgative. However,
we must distinguish between the action of an excess and that
of the quantity secreted by a healfliy individual. The acid of
the stomach has probably no effect allied to that produced by
giving acids medicinally, which warns us that too much must
not be made out of the argument Atom biliolu diarrhgea. 6. As
before intimated, a great part of the bile must be regarded as
excrementitious. It looks as though much of the effete haemo-
globin of the blood and of the oholesterin, which represents
possibly some of the waste of nervous metabolism, weire expelled
from the body by the bile. The cholalio acid of the faaoes is

804

COMPARATIVE PHYSIOLOGY.

derived from the decomposition of the bile acids. Part of their
mucus must also be referred to the bile, the quantity originally
present in this fluid depending much on the length of its stay
in the gall-bladder, which secretes this substance. 7. There is
throughojit the entire alimentary tract a secretion of mucus
which must altogether amount to a large quantity, and it has
been suggested that this has other than lubricating or such like
functions. It appears that mucus may be resolved into a pro-
teid and an animal gum, which latter, it is maintained, like
vegetable gums, assists emulsiflcation of fats. If this be true,
and the bile is, as has been assarted, possessed of the power to
break up this mucus (mucin), its emulsifying effect in the in-
testine may indirectly be considerable. Bile certainly seems to
intensify the emulsif jring power of the pancreatic juice.

There does not seem to be any ferment itf bile, unless the
power to change starch into sugar, peculiar to this secretion in
some animals, is owing to such.

Comparatiye.— The bile of the camivora and omnivora is
yellowish-red in color; that of herbivora green. The former
contains taurocholate salts almost exclusively; in herbivorous
animals and man there is a mixture of the salts of both acids,
though the glycocholate predominates.

Fio. 948.— Gallbladder, dactas chotedochaa and pancieaa in man (after Ui Bon), a,
gall-bladder: b, hepatic dnct: «, opening of aecond dnct of pancfeM: d, opening
of main pancreatic dnct and bUe-anot; «, «, daodenom; /, dnctne cboledoclina; p,
pancreaa.

Pturt of their
ty oripnally
th of its stay

7. There is
on of mucus
y, and it has
f or such like
id into a pro-
ntained, like

this be true,
the power to
ect in the in-
inly seems to
juice,
le, unless the

secretion in

omnivora is

The former

I herbivorous

of both acids,

(after Le Bon), a,
Miew: <f , opening
u cttoiedoGhna; p.

DIGESTION OF POOD.

806

PuuSMtie JviM.— This fluid is found to vary a good deal
quantitatively, according as it is obtained from a temporary
(freshly made) or permanent fistula— a fact which emphasizes
the necessity for caution in drawing conclusions about the
digestive juices as obtained by our present methods.

The freshest juice obtainable through a recent fistulous
opening in the pancreatic duct is clear, colorless, viscid, alka-
line in reaction, and with a very variable quantity of solids
(two to ten per cent), less than one per cent being inorganic
matter. ,

Among the organic constituents the principal are albumm,
alkali-albumin, peptone, leucin, tyroan, fata, and soaps in small
amount The alkalinity of the juice is owing chiefly to sodium

Fw. M7.— dTitals of lenein (nmke).

Vto. MB.— Ckjitdf of tyitwin {VmHn).

carbonates, which seem to be associated with some proteid
body. There is little doubt that leucin, tyrosin, and peptone
arise from digestion of the proteids of the juice by its own
action.

Xspwiawntal.— If the pancreatic gland be mostly freed from
adhering fat^ out up, and washed so as to get rid of blood;
then minced as fine as possible, and allowed to stand in one-per-
cent sodium-carbonate solution at a temperature of 40° C, the
following ranilts maybe noted: 1. After a variable time the
reaction may change to acid, owing to free fatty acid from
the decomposition (digestion) of neutral fata. 2. Alkali-albu-
min, or a body closely resembling it, may be detected and sep-
arated by neutralication. 3. P^tone may be detected by the
SO

siSiitKa»P«a#«6;/3; -siaxir^cnii^m:

806

COMPARATIVE PHYSIOLOflV.

tue of a trace of copper milpliate added to a few drops of caustic
alkali, which becomes red if this body be present. 4. After a
few hours the smell becomes fsecal, owing in part to indol,
which gives a violet color with chlorine-<vator; while under
the microscope the digesting mass may be seen to be swarming
with bacteria. 5. When digestion has proceeded for some time,
leuein and tyrorin may be shown to be present, though their
satisfactory separation 'in crystalline form involves somewhat
elaborate details. These changes are owing to self-digestion
of the gland.

All the properties of this secretion may he demonstrated
mora satisfactorily by making an aqueous or, bettor, glycerin
extract of the pancreas of an ox, pig, ete., dnd carrying on arti-
ficial digestion, as in the case of a peptic digestion, with fibrin.
In the case of the digestion of fat, the emulsifying power of a
watery extract of the gland may be shown by shaking up a
little melted hog's lard, olive-oil (each quite fredi, so as to show
no acid reaction), or soap. Kept under proper conditions, free
acid, the result of decomposition of the neutral fats or soap
into free acid, eto., ma,y be easily shovm. The emulsion, though
allowed to stand long, persists, a fact which is availed of to
produce mora palatable and easily assimilated praparations of
cod-liver oil, eibo., for medicinal use.

Starch is also converted into sugar with great ease. In
short, the digestive juice of the pancreas is the most complex
and complete in ite action of the whole series. It is amylolytic,
proteolytic, and steaptic, and these powers have been attributed
to three distinct ferments— omytopwn, triptin, and ateapsin.

Proteid digestion is carried further than by the gastric juice,
and the quantity of Crystalline nitrogenous producte formed is
in inverse proportion to the amount of peptone, from which it
seems just to infer that part of the original peptone has been
converted into these bodies, which ara found to be abundant or
not in an artificial digestion, according to the length of time
it has lasted—the longer it has been under vraj the mora leudu
and tyronn present. Leuein is another compound into which
the amido (NHt) group enters to make amido-caproic acid— one
of the fatty series— while tyrosin is a very complex member of
the aromatic series of compounds. Thus complicated ara the
chemical effects of the digestive juices ; and it seems highly
probable that these ara only some of the compounds into which
the inoteid is broken up. Though putrafsctive changes with

ops of caustic
t. 4. After a
[lart to indol,
; while under
I be swarming
For some time,
, though their
vea somewhat
self-digestion

demonstrated
etter, glycerin
Tying on arti-
n, with fibrin.
Dig power of a
shaldng up a
, so as to show
onditions, free
1 fats or soap
ulsion, though
availed of to
(reparations of

reat ease. In
most complex
; is amylolytic,
teen attributed
md ^eapain.
e gastric juice,
lucts formed is
from which it
itonehas been
Be abundant or
length of time
he more leudu
ind into which
jroic acid— one
lex member of
licated are the
; seems highly
nds into which
B changes with

DIGESTION OP POOD.

807

formation of tndol, etc., occur in pancreatic digestion, both
within and without the body, they are to be regarded as acci-
dental, for by proper precautions digestion may be carried on

■y

=S:

\l)(^ '^l

V... a<o iiipnvorMiiiniu Of lam intestine (after Uudoit). 1, bRCteriam coll com-
"^^ .iStr aMSSm KtU .ftSenM? 8. 4, iMge bMiUi oi Blen.t«sk, trtth |Mutl«l

^ISi^,m>Sl^^^^^tt^tyuiM^ itMV* ot development of bMillas which

caniee fennenution of albamen.

in the laboratory without their occurraioe, and they vary in
degree with the animal, the individual, the food, and other con-
ditions. It is not, however, to be inferred that micro-organisms
serve no useful purpose in the alimentary canal ; the subject,
in fact, requires further investigation.

Snoeot Ettterioni.— The difficulties of collecting the secre-
tions of Ueberkahn's, Brttnner's, and other intestinal gh»nds will
be at once apparent. But by dividing the intestine m two
places, so as to isolate a loop of the gut, joiningthe sundered

Pi«. am.— Portion of one of Brttanert glanda (Chtnv»«n),

ends hy ligatures, tiras making the continuity of the main gut
as complete as before, closing one end of flie isolated loop, and

:®KfS^SS»B'J^i«S«;'A«Sii.&S»*!5?SS»K-'"

808

COMPARATIVE PHYSIOLOGY.

bringing the other to the exterior, as a flrtulous opening, the
aeoretions could be collected, food introduced, etc.

But it aeenu highly improbable that information approxi-
mately correct at beet, and powibly highly miBleading, could

I I

Fio 851.-Inte«tln«l tabaiea (folllcJ!* of Ueberkttm) 1 k J 9 (Sappey). A, from dog;
B, ox; C, slwep; D, pig: E. Mhblt.

be obtained in mich manner. Moreover, the greoteit diversiiy
of opinion prevaiU as to the facts themselves, so that it seems
scarcely worth whUe to state the contMMlictory conclusions ar-

rived ttt.

It is, however, on the face of it, probable that the intestine-
even the large intestine-does secrete juices that in herbivora,
at all event*, play no unimportant part in the digestion of their

Fi«. m-Goaewl tJow of howeVjntertliiei; •"l""^'* P'«*2 i?.iS^&hSS 'iSJSIt

"^r-^

^./tp^KEl^

opening, the

>^^^^^^^k

ion approxi-

tding, oould

wy). A,fMnda|;

■teat diverrity
> that it aeenis
onoliurionB ar-

the intestine—
, in herbivora,
lestion of their

its back, ■adintw-
MfMM behind gnat
wcMcal portton; D,

•wo; fi ?< P**"'
ylinginatle flMnuw.

Fia.aa.

■S3IBIiilSSStiWiAl^i'>im't 'Mt

810

CX)MPARATIVB PHYSIOIiOOY.

bulky food ; and it is alau probable, as in m many other in>
stances, that, when the other parts of the digestive tract fail
when the usual secretions are not prepared or do not act on the
food, glands that normally play a possibly insignificant part
may function excessively— we may almost say vicariously—
and that such glands must be sought in the email intestine.
There are facts in clinical medicine that seem to point strongly
in this direction, though the subject has not yet been reduced to
scientific form.

OoaptntiTe.— Within the last few years the study of vege-
table assimilation from the comparative aspect has been fruit-
f ul in results which, together with many other facts of vegeta-
ble metabolism, show that even plants ranking high in the
organic plane are not in many of their functions so different
from animals as has been supposed. It has been known for a
longer period that certain plants are carnivorous ; but it was
somewhat of a surprise to find, as has been done within the
past few years, that digestive ferments are widely distributed
in the vegetable kingdom and are found in many different parts
of plants. What purpose they may serve in the vegetable
economy is as yet not well known. At present it would seem
as though, from their presence in so many cases in the seed,
they might have something to do with changing the cruder
forms of nutriment into such as are better adapted for the nour-
ishment of the embryo.

Thus far, then, not only diastase but pepsin, a body with
action similar to trypsin, and a rennet ferment, rank among the
vegetable fermenti best known.

A ferment has been extracted from the stem, leaves, and un-
ripe fruit of Cariea papaya, found in the Bast and West Indies
and elsewhere, which has a marked proteolytk) action.

It is effective in a neutral, most so in an alkaline medium ;
and, though its action is suspended in a feeble acid menstruum,
it does not appear to be destroyed under such circumstances, as
is trypnn. This body is attracting a good deal of attention,
and its use has been recently introduced into medical prac-
tice.

Veiy lately also a vegetable rennet has been found in sev-
eral species of plants. The subject is highly i^mnising and
suggestive.

ly other in-
re tract fail
9t act on the
liflcant part
ioariouBly—
dl intestine,
tint strongly
n reduced to

ndy of vege-

beenf mit-
ts of yegeta-
high in the

BO different
mown for a

but it was
b within the
y distributed
ifferent parts
He Tcgetable
would seem
in the seed,

the cruder
'or the nour-

a body with
ik among the

Bves, and uh-
1 West Indies
ion.

ne medium ;
1 menstruum,
umstanoes,as
of attention,
nedical prac-

'ound in ser-
romising and

DIGESTION OF FOOD.

811

SaORBnOlf At A PBTBIOIiOOHOAZ. PROOBBt.

SMNtion of tfts ftallTary OUuidi.— We shall treat this subject
at more length because of the light it throws on the nervous
pheuomenaof vital process ; and, since the salivary glands have
been studied more thoroughly and successfully than any other,
they will receive greater attention.

FM. Mi Fwi. SB4.

n*. «.-liO»«ta of pM«tid glMd. mjected wtth mutm, "« «•«»««*» W dlMM-
Fio.'Sl4.-0J»Ul«T "etwork uooBd the follicle of th« paroUd gtand.

The main facts, ascertained experimentally and otherwise,

are the following : , , , , ^

Assuming that the student is familiar with the general ana-
tomical reUtions of the saUvary glands in some mammal, we
would further remind him that the submaxillary gland has a
double nervous supply : 1. From the cervical -y^P***^* J^
branches passing to the ghmd along its arteries. 2. From the
chorda tympani nerve, which after leaving the facial makes
connection with the lingual, whence it proceeds to its destl-

m following facts are of importance as a basis for conclu-
sions: 1. It is a matter of common observation that a flow of
saliva may be excited by the smell, taste, sight, or even thought
of food. 2. It is also a matter of experience that emotionj As

fear, anxiety, etc., may pareh the ""»»*;-»•.?• r*»*,**'*J;^
of saliva. The excited speaker thus suffers m his early ^rfforts.
3 If a glass tube be placed in the duct of the gland and any
substance that naturaUy causes a flow of saliva be placed on
the tongue, saUva may be seen to nse rapidly m the tube. 4.
The same may be observed if the lingual nerve, the glossophar

rt i iiiiiM>ttiiiM i i«Min

aifl

COMPARATIVR PHT»IOU)OY.

ryngoal, and many other uenrM be ■timulated ; aim if food be
introduced into the itonuMsh through a flatula. 5. If the pe-

Fia. 958.— HuiUary and Mbllnaul gtand (OhuvMw).
ton 'a dnct; T, inblinBnal gutnd.

B, mulUary gtand; 8, Whai^

ripheral end of the chorda tympani be stimulated, two remlta
follow : (a) There is an abundant flow of saliva, and (ft) the
arteriolef of the gland become dilated : the blood may pass
through with such rapidity that the venous blood may be
bright red in color and there may be a venous pulse. 7. Stimu-
lation of the medulla oblongata gives rise to a flow of saliva,
which is not possible when the nerves of the gland, especially
the chorda tympani, are divided ; nor can a flow be then excited
by any sort of nervous stimulation, excepting that of the ter-
minal branches of the nerves of the {^and itself. 8. If the sym-
pathetic nerves of the gland be divided, there is no immediate
flow of saliva, though there may be some dilatation of its vea-

.v,iiiliil > M;

-^■mmmm

tesxm^

DioBsnoN OP poon.

818

also if food be
, S. If the pe-

larjr gland; 8, Wtaar-

ted, two remits
ra, and (b) the
lood may paaa
blood may be
ulae. 7. Stimu-
i flow of galiva,
land, especially
be then excited
that of the ter-
8. If thesym-
B no immediate
ation of its vea-

RelN U Stimulation of the terminal endii of the nympathetic
and ohf^fda nerves causes a flow of saliva, differing as to total
quantity and the amount of contained solids; but the nerve
that produces the more abundant watery secretion, or the re-
verse, varies with the animal, e. g., in the cat chorda saliva w

Itirt of brain cibovt medulla '

AffentU nervM

iffentU

mgue

lallvary (fiand

lilumi vtucl
of (fland

"StJmiMthctCc n«rte

Fi«. es. -DtagTMn tntoided to tndieato the Mrrou BMohMilHn of ••Hvwy iwireUoii.

more viscid, in the dog lees so; though in all animals as yet
examined it seems that the secretion as a result of stmiulatiwi
of the chorda tympani nerve is the most abundant; and m the

mmtiL-i.i!m!>ftifmt«~i

■ ■.■mmr&t-i^- t?e,«r(S-.r!!a,i»s

814

COMPARATIVE PHYSIOLOGY.

oMe of stimuUtion of the chorda the veMwU of the gUnd are
dihited, while in the caie of the eympathetio they are con-
■trioted. 10. If atrupin be injected into the blood, it ii impoe-
■ibla to induoe lalivary aeoretiou by any form of itimuhition,
though excitation of the chorda norvo still oauaee arterial dila-
tation.

Ooadutou.— 1. There ii a center in the medulU predding
over Nalivary Moretion. 8. The influence of this center i« ren-
dered effective through the chorda tympani nerve at all events,
if not also by the sympathetic. 8. The chorda tympani nerve
contains both secretory and vaso-dilator fibers; the sympathetic
secretory and vasooonstriotor fibers. 4. Arterial change is nut
essential to secretion, though doubtless it usually accompanies
it. Secretion may be induced in the glands of an animal after
decapitation by stimiilatioD of its chorda tympani nerve, analo-
gous to the secretion of sweat in the foot of a recently dead
animal, under stimulation of the sciatic nerve. S. The char-
acter of the saliva secreted varies with the nerve stimulated, so
that it seems likely that the nervous centers normally in the
intact animal regulate the quality of the saliva through the
degree to which one or the other kind of nerves is called into
action. 6. Secretion of saliva nugr be induced refiexly by ex-
periment, and such is probably the normal course of events.
7. The action of the medullary center may be inhibited by the
cerebrum (emotions).

Some have located a center in the cerebral cortex (taste cen-
ter), to which it is assumed impulses first travel from the
tongue and which then rouses the proper seoretingr centers in
the medulla into activity. It seems more likely that the corti-
cal center, if there be one, completes the physiological processes
by which taste sensations are elaborated.

From the influence of drugs (atropin and its antagonist
pilocarpin) it is plain that the gland can be effected through
the blood, though whether wholly by direct action on the cen-
ter, on any local nervous mechanism or directly, on the cells, is
as yet undetermined. It is found that pilocarpin can act long
after section of the nerves. This does not, however, prove that
in the intact animal such is the usual modus operandi of this
or other drugs, any more than the so-called paralytic secretion
after the section of nerves proves that the latter are not con-
cerned in secretion.

We look upon paralytic secretion as the work of the cells

*':W*^f?

the gland on
Ouy are oon-
d, it is impod-
>f ■timulAtion,

arterial dila-

ulla predding

center i« ren-
At all erenti,
jrmpani nerve
teqrmpathelio

change ii not
r acoompaniea
I animal after

nerve, analo-
reoently dead

5. The ohar-
■timulated, en
rmallirin the
k through the
ii called into
«flexl7 by ex-
ne of eventfk
libited by the

»z (taite oen-
vel from the
lug centers in
that the oorti-
fical iwooeeBes

ite antagonist
cted through
I on the oen-
n the cells, is
can act long
)r, prove that
rand* of this
rHo secretion
are not con-

of the cells

DiaBSnON OP FOOft.

816

when gone wrong— passed from under the dominion of the
nerveKjenters. Secretion ia a part of the natural life-provesses
of gland-cells— we may say a series in the long chain of pro-
oesseii which are indispensable for the health of these cells.
They must be either Necreting cells, or have no place in the nat-
ural order of things. It is to be especially noted that the secre-
tion of saliva continues when the pressure in the ducts of the
gUnd is greater than that of the blood in its vessels or even
of the carotid; so that it seems possible that over-importance
has been attached to blood-pressure in secretory processes gen*
erally.

It nwy, then, be safely assumed that formation of saliva re-
sults in consequence of the natural activity of certain cells, the
processes of which are correlated and harmonised by the nerv-
ous system; their activity being accompanied by an abundant
supply of blood. The actual outpouring of saliva depends usu-
ally on the establishment of a nervous reflex arc. The other
glands have been less carefully studied, but the parotid is
known to have a double nervous supply from the cerebro-
spinal and the sjrmpathetic systems.

It would appear that, as the vaso-motor changes run paral-
lel with the secretory ones, the vaso-motnr and the proper
secretory centers act ia concert, as we have seen holds of the
former and the respiratory center. But it is to our own mind
very doubtful whether the doctrine of so sharp a demarkation
of independent centers, prominently recognised in the physi-
ology of the day, will be that ultimi^y accepted.

ttoerttlOB bf tlM MomadL— The mucous membrane of St
Martin's stomach was observed (through an accidental fistulous
opening) to be pale in the intervals of digestion, but flushed
when secreting, which resembled sweating, so far as the flow
of the fluid is concerned. When the man was irritated, the
gastric membrane became pale, and secretion was lessened or
arrested, and it is. a common experience that emotions may
help, hinder, or even render aberrant the digestive proc e ss es .

While the evidence is thus clear that gastric secretion is
regulated by the nervous system, the way in^whioh this is ac-
complished is very obscure. We know little of either the cen-
ters or nerves concerned, and what we do know helps but
doubtfully to aa understanding of the matter, if, indeed, it does
not actually confuse and puzsle.

Digestion can proceed in a fttfhion after section of the nerves

i iai mMMiftB K.!- i !ii MW [a ii»w« i fiat tawag ^w a wMawfewl-t- r

316

COMPARATIVE PHYSIOLOGY.

going to the stomach, though this has little force as an argu-
ment against nerve influence. We may conclude the subject
by stating that, while the influence of the nervous system over
gastric secretion is undoubted as a fact, the method is not un-
derstood; and the same remark applies to the secreting activity
of the liver and pancreas.

The Seoietion of Bile and Paaoreatio Jnioe.— When the con-
tents of the stomach have reached the orifice of the discharging
bile-duct, a large flow of the biliary secretion takes place, prob-
ably as the result of the emptying of the gall-bladder by the
contraction of its walls and those of its ducts. This is probably
a reflex act, and the augmented flow of bile when digestion is
proceeding is also to be traced chiefly to nervous influences
reaching the gland, though by what nerves or imder the gov-
ernment of what part of the nervoiis centers is unknown.
Very similar statements apply to the secretion of the pancre-

Fio. 367.— Diagmn to show Inflnence of food in Mcretioii of pwierMtic juice (after
N. O. Berniteln). The •bactoMe repneent honn after tuiog food ; ordinates
araonnt in cabic eentigramme* of aebretton in ten minatee. Food waa taken at
B and O. This diagram very nearly alio repreaeuta the aeeretion of bile.

atic glands, though this is not conctant, as in the case of bile—
at all events in most animals.

It is known that after food has been taken there is a sudden

I as an arga-
ide the subject
system over
tiod is not un-
crating activity

len the con-
le discharging
:e8 place, prob-
[bladder by the
is probably
en digestion is
ous influences
mder the gov-
is unknown,
of the pancre-

SI«I7I8 | 0| 10

icrMtlcjnlce (after
w food ; ordlmtM
rood WM taken at
on of bile.

case of bile—
re is a sudden

DIGESTION OP FOOD.

817

increase in the quantity of bile secreted, followed by a sudden
diminution, then a more gradual risu, with a subsequent fall.
Almost the dame holds for the pancreas.

It seems impossible to explain these facts, especially the
flrst rapid discharge of fluid apart from the direct influence of
the nervous sjrstem.

Upon the whole, the evidence seems to show that the press-
ure in tiie bile-ductu is greater than in the veins that unite to
make up the portal system; but there are difficulties in the
investigation of such and kindred subjects as regards the liver,
owing to its peculiar vascular supply. It will be borne in mind
that the liver in mammals consists of a mass of blood-vessels,
between the meshes of which are packed innumerable cells, and
that around the latter meander the bile capillaries; that the
portal vein breaks up into the intralobular, from which capil-
laries arise, that terminate in the central interlobular veins,
which make up the hepatic veinlets or terminate in these vessels.
But the structure is complicated by the branches of the hepatic
artery, which, as arterioles and capillaries, enters to some extent
into the formation of the lobular vessels.

A question of interest, though difficult to answer, is the
extent to which the various constituents of bile are manufact-
ured in the liver. Taurin, for example, is present in some of

PiA. xe.— Lobnlea at Uver, interlobular reiiela, and intralobnlar reins (Sappey). 1, 1,
1, 1. 8, 4, lobnlea; t, B, S, S. intraiobolar rOaa injected with white; ^1i, 5, 5, 5, in-
trdobalar veaaela fllled with a dark injection.

liUmiiimtm

10'

818

COMPARATIVE PHYSIOLOGY.

K**-

the tissues, but whether this is used in the manufacture of
taurocholic acid or whether the latter is made entirely auew,
and possibly by a method in which taurin never appears as
such, is an open question. It is highly probable that a portion
of the bile potired into the intestine is absorbed either as such
or after partial decomposition, the products to be used in

some way in the econo-
my and presumably in
the construction of bile
by the liver. There are
many facts, including
some pathological phe-
nomena, that point
clearly to the formation
of the pigments of bile
from hsBmoglobin in
some of its stages of de-
generation.

?stludogloaL— When
the liver foils to act,
either from derange-
ment of its cells prima-
rVyni wing to obstruc-
tioii. ^. (' outflow of
bile 1 <t> ■" ■ reabsorp-
tion by the liver, bile acids and bile pigme^ib appear in the
urine or may stain the tissues, indicating their presence in ex-
cess in the blood.

This action of one gland (kidneys) for another is highly
suggestive, and especially important to bear in mind in medical
practice, both in treatment and prognosis. The chances of re-
covery when only one excreting gland is diseased are much
greater evidently than when several are involved. Such facts
as we hvve cited show, moreover, that there are certain common
fundamental principles underlying secretion everywhere— a
statffluent which will be soon more fully illustrated.

Fie. a59. -Portion of tnurene laetion of hepatic
(KOIIl-

lobDle of nbbit magniaed 400 diameter* (I

"" ■ — Mood-Tecaelr

, liTercell*.

ker). bA,b, cuillarr blood-Tecaele; g, g, g, c»t^

THB WATOBB OP TBB AOT OF nBOBBTION.

We are now about to consider some investigations, more
particularly their results, which are of extraordinary interest
The secreting cells of the salivary, the pancreatic glands,

v^htM^mkMttiKiimiilitdiMtm^Mmm

laniifacture of

entirely auew,

ver appears as

that a portion

either as such

to he used in

y in the econo-

presumably in

ruction of bile

ret. There are

lets, including

thological phe-

that point

> the formation

igments of hile

emoglobin in

its stages of de-

tn.

ogimL— When
r fails to act,
'rom derange-
its cells prima-
ring to obstruc-
I c outflow of
. '• reabsorp-
> cppear in the
presence in ex-

>ther is highly
lind in medicid
chances of re-
ised are much
id. Such facts
ertain common
everywhere— a
bed.

BBTIOir.

igations, more
lary interest
sreatic ghinds,

DIGESTION OP POOD.

810

and the stomach have been studied by a combination of histo-
logical and, more strictly, phjrsiological methods, to which we
shall now refer. Specimens of these glands, both before and
after prolonged secretion, under stimulation of these nerves,

Fie. MO.— Poition of pcnereM of rabbit (after Ktthne and Lea), a repreeeiits gland
at reet; B, during accretion.

were hardened, stained, and sections prepared. As was to be
expected, the results were not entirely satisfactory under these
methods ; however, the pancreas of a living rabbit has been
viewed with the microscope in its natural condition ; and by
this plan, especially when supplemented by the more involved
and artificial method first referred to, results have been reached
which may be ranked among the greatest triumphs of mod^n
physiology.

Some of these we now proceed to state briefly. To begin
with the pancreas, it has ^H«n shown that, when the gland is
not secreting— i. e., not discharging its prepared fluid—or dur-
ing the so-called resting stage, the appearances are strikingly
diflFerent from what they are during activity. The cell pre-
sents during rest an inner granular zone and an outer clearer
zone, which stains more readily, and is relatively small in size.
The lumen of the alveolus is almost obliterated, and the in-
dividual cells very indistinct. After a period of secreting
activity, the lumen is easily perceived, the granules have dis-
appeared in great part, the cells as a whole, are smaller, and
have a clear appearance throughout Ck>incident with the
changes in the gland's cells it is to be noticed that more blood
pasMM through it, omng to dilatation of the arterioles.

Again, the course of the changes in the salivary glands,
whether of the mucous or serous variety, is very similar. In

820

COMPARATIVE PHYSIOLOGY.

the mucous glaad in the resting stage the cells are large, and
hold much clear matter in the interspaces of the cell network;

Piu. asi.— Section of mncoua gland (after Lavdowaky).
after secreting for lome time.

In A, slM>d at feet; in B,

and, as this does not stain readily, it can not be ordinary
protoplasm. This, when the gland is stimulated through its
nerves, disappears, Iraving the containing cells smaller. It
haft become mucin, and may itself be called mwsinogen.

It is to be noted that, as the cells become more protoplasmic,
less burdened with the products of their activity, the nucleus
becomes more prominent, suggestive of ita having a probable
directive influence over these manufacturing processes.

Substantially the same chain of events has been established
for the serous salivary glands and the stomach, so that we
may safely generalize upon these well-established facts.

It seems clear that a series of changes conshractive and, from
one point of view, destructive, following the former are con-

Fio. a(B.-C»i»ngei in parotid ((erona) gland dnrlmc aecietlon (after tangley). A, dnr-
ing^St: BVafter mSderate, C, after prolongea stimnlatlon. Fignree partly dia-
grammatic.

stantly going on in ttie glands of the digestive organs. Proto-
plasm under nerve influence constructs a certain substance.

,. iidy i m Biif t M i t M m Ni t i*' * iiiiJ if vm i m m*i ' »

Eure large, and
cell network;

[land at nst; in B,

t be ordinary

sd through its

Is smaller. It

Inogen.

9 protoplasmic,

y, the nucleus

ing a probable

icesses.

sen established

ih, BO that we

1 facts.

ctive and, from

>rmer are con-

wLangley). A.dnr-
Fignras partly dia-

irgans. Proto-
tain substance.

DIGESTION OP FOOD.

821

which is an antecedent of the final pixiduct, which we term a
ferment It is now customary to speak of these changes as
constructive (anabolic) and destructive (katabolic), though we
have already pointed out (page 268) that this view is, at best,
only one way of looking at the matter, and we doubt if it may
not be cramping and misleading.

We must also urge caution in regard to the conception to
be associated with the use of the terms " resting " and " active
staee It is not to be forgotten that strictly m livmg cells
there' is no absolute rest^-such means death ; but, if these terms
be understood as denoting but degrees of activity, they need
not mislead. It is ahw more than probable that in certam of
the glands, or in some animals, the processes go on simultane-
ously : the protoplasm being renewed, the zymogen, or mother-
fennent, being formed, and the latter converted into actual fer-
ment, all at the same time.

The nature of secretion is now tolerably clear as a whole;
though it is to be remembered that this account is but general,
and Suit there are many mi:ior differences Tor each gland and
variations that can scarcely be denominated mmor for different
animals. Evidently no theory of fUtration, no pro<»s8 depend-
ing solely on blood-pressure, wUl apply here. And if m this,
the best-studied case, mechanical theories of vital proojsses
utterly fail, why attempt to fasten them upon other ghmds, as
the kidneys and the lungs, or, indeed, apply such crude concep-
tions to the subtle processes of living protophism anywhere or

in any form ? . _« n

It is somewhat remarkable that an extract of a perfecUy
fresh pancreas is not proteolytic; yet the gland yields such an
extract when it has stood some hours or been treated with a
weak acid. Those facta together with the microscopic appear-
ances, suggested that there is formed a forerunner to the actual
f erment-a zymogen, or mothei^f erment, which at the moment
of discharge of the completed secretion is converted into the
actual ferment. We might, therefore, speak of a pepsinogen,
trypsinogen, etc., and, though there may be a cessation in the
series of processes, and no doubt there is in some animals, this

may not be the case in all, or in all glands.

Beeretioil by th« StOHUUdl.— The glands of the stomach differ

in most animals in the cardiac and pyloric regions. In those
of the former zone, both central (columnar) and parietal (ovoid)
cells are U be recognized. It was thought that possibly the Ut-

FM.agi.

Fra. atS.

Fie. 9(8.— Pits in moe> lembnne of •toowch in which are openlnn of tabular

giMMU, 1 >cao<8ap. ^^ "

Flo. M4.— Olanda of ttoh. ch with both centnl and parietal (oTOid) cells (Heidenhaiii).
Vi«. aSk— Pyloric giaodi iBbetein).

issfsmassisissnmm

DIGESTION OF FOOD.

338

■ingt of tabular
'lb (Heideiilwiii).

ter were concerned in the secretion of the acid of the atomuch,
but this is by no means certain. PoMubly these, like the demi-
lune cells of the pancreas, may be the progenitors of the centhil
(chief) cells. The latter certainly secrete pepsin, and probably
also rennet. Mucus is secreted by the cells lining the neck of
glands and covering the mucous membrane intervening be-
tween their mouths. The production of hydrochloric acid by
any act of secretion is not believed in by all writers, some hold-
ing that it is derived from decomposition of sodium chloride,
possibly by lactic acid. So simple an origin is not probable, not
being in keeping with what we know of chemical processes
within '- animal body.

C nt-t igMkUm of the DigMtiYe OlgUll.— It has been found,
both in man and other mammals, that when death follows in a
healthy anibjeot while gastric digestion is in active progress
and the body is kept warm, a part of the stomach itself and
often adjacent organs are digested, and the question is con-
stantly being raised. Why does not the stomach digest itself
during life ? To this it has been answered that the gastric
juice is constantly being neutralized by the alkaline blood ;
and, again, that the very vitality of a tissue gives it the neces-
sary resisting powers, a view contradicted by an experiment
which is conclusive. If the legs of a living frog be allowed
to hang against the inner walls of the stomach of a mammal
when gastric digestion is going on, they will be digested.

The first view (the alkalinity of the blood) would not suffice
to explain why the pancreas, the secretion of which acts best in
an alkaline medium, should not be digested.

It seems to us there is a good deal of misconception about
the facts of the case. Observation on St. Martin shows that
the secretion of gastric juice runs parallel with the need of it,
as dependent on the introduction of food, its quantity, quality,
etc. Now, there can be little doubt that, if the stomach were
abundantly bathed when empty with a large quantity of its
own acid secretion, it would suffer to some extent at least. But
this is never the case ; the juice is carried off and mixed with
the food. This food is in constant motion and doubtless the
inner portions of the cells, which may be regarded as the dis-
charging region (the outer, next the blood capillaries, being
the chief manufacturing region of the digestive ferment), are
frequently renewed.

Such considerations, though they seem to have been some-

"eawwffliwiKawww.l*'

.^■- 'ii u»*a i »m »i L ! ..

884

COMPABATIVB PHYSIOLOOY.

what left out of the oaM, do not go to the bottom of the matter.
Amoeba oiid kindred organiums do not digest themaelvee.
Home believe that the little pulsatile vacuoles of the Infusorians
are a sort of temporary digestive cavities.

But, to one who sees in the light of evolution, it must be
clear that a structure could not have been evolved that would
be self-destructive.

The difficulty here is that which lies at the very basis of all
life. We might ask, Why do living things live, since they are
constantly threatened with destruction from within as from
without i Why do not the liver, kidney, and other glands that
secrete noxious substances, poison themselves ? We can not
in detail explain these things ; but we wish to make it clear
tliat the difficulty as regaros the stomach is not peculiar to that
gland, and that even from the ordinary point of view it haa
been exaggerated.

GompMrntife. — More careful examination of the stomachs of
some mammals has revealed the fact that in several animals,

in which the stomach appears to
be simple, it is in reality com-
pound. There are different
grades, however, which may be
regarded as transition forms be-
tween the true simple stomach
and that highly compound form
of the organ met with in the
ruminants.

It has been shown recently
that the stomach of the hog has
an oeaophageal dilatation ; and
that the entire orgm may be
divided into several sones with
different kinds of glandular epi-
thelium, etc. These portions
differ in digestive power, in the characteristics of the fluid se-
creted, and other details beyond those which a superficial exam-
ination of this organ would lead one to suspect.

The stomach of the horse represents a more advanced form
of compound stomach than that of the hog, which is not evi-
dent, however, until its glandular structure is examined closely. '
The entire left portion of the stomach represents an oesophageal
dilatation lined with an epithelium that closely resembles that

Pia. MS.— Intwtor of hotae't itonMeh
(aftmr OlwuTMn). A. left mc; B,
right Mc; C, dnodeiial dlUrtatkM.

mmmmmidmitimmimitmMkiiiit

f the matter.
thenuelvM.
e InfuDoriana

n, it must be
that would

y basis of all

nee they are

thin as from

r glands that

We can not

nake it clear

culiar to that

' view it has

e stomachs of
eral animals,
loh appears to

reality com-
ire different
'hich may be
ion forms be-
nple stomach
mpound form

with in the

lown recently
if the hog has
atation ; and
ngan may be
al aonee with
Bflandular epi-
leee portions
f the fluid se-
erfloial exam-

dvanoed form
ch is notevi-
mined closely. '
n oesophageal
esembles that

DIGRSTION OP FOOD.

325

of the oesophagus, and with little if any digestive function. It
thus appears that the stomach of the horse is in reality smaller,
as a true digestive gland, than it seems, so that a great part of
the work of digestion must be done in the intestine ; though in
this animal, if the food be retained as long as it is in the hog,
which is not, however, the general opinion as regards the
stomach of the horse, salivary digestion may continue for n
considerable period after the food has left the mouth. The
secretion of mucus by the stomach in herbivora is abundant.

As has been already explained, the stomach of ruminants
consists of several compartments which are supplementary to
one another, though genuine gastric digestion does not take
place except in the fourth stomach.

The first and second stomachs being destitute of other than
mucous glands, and lined with a homy epithelium, are to be con-
sidered rather as dilatations of the oesophagus. They answer
admirably the purpose of storehouses for the bulky food in
which the softening process preparatory to mastication goes on.

Fia. 887.— Stomach of the ox Men an it* right upper face, the abomarom being de-
prcMcd (Chaiiveau). A, ramen. left hemlapheK; B, ramen, right lieniiephcre; C,
iennlnation of the iMophagna; D, retlcnlnm; E, omaram; F, abomasom.

836

COMPARATIVK PHYSIOLOGY.

Fia

968.-Intwlar of ■toOMh In ramlMiitis the uppw ptene of the romen »iid retteo-

1^ with the OMDlMfe.) ttuTcmJphtnrMm^ *• '•.'J IK SL iSSJS'SSVi.Slw"^
rior extremity orthMMe tunwd bMk oo riRht «w; C. Its potterlor extremity, or
lift conlcai cy.t; O, McUon of .ntenor pfllw of rumen: a,g \tM two •"P«ri,<»
bmncheB; H, posterior pillar of tame; *. ft. A. lU iivm Inferior branohe.; I. cella
of wtlculum y, cHophagMl farrow; K, ««topha«ni; L. abomaeum.

Fio 900.-Stomach of llama (ColJn). A. lower estiemlnr of pUet; B. aingto pillar of
mSthMMlMmal; C, •nperior opening of the jaalfer; B, reticnlnmjnB. H^J "»
StefKrwate?"ll.; P, fitelor watercella; O. KJhy column aepMattng the two
cell groapa.

■Umim

I rumen And reticn-
le rumen; B, ante-
»r1or extremity, or
U Ita two wiperior
■ bmnchef ; I, cell*

DIOI-aTION OP FOOD.

t; B, lintde pillw ot
ticalnm; B, right or
•epamttng the two

The wUculuni, m> called from the peculiar arrangenKjnt of
tho nmcu. membrane, \h usually regarded a. a '«fP»«''«j";
water mon, especially; however, thi. sU,mach .. U. be regarded
Lth anatomically and phy.iol.«ically a. a «,bdlvi«o« of the
flrtt or at all t vent* a« equivalent to that.

The quantity of food that it can hold in the ox » ei^ortnouH.
(150 to m pound!), a condition of things advantageous m an

•t C, fourth atomach.

animal feeding upon «,hstances so pH>r in n^tntive material in
proportion to their bulk and requirii.g so much i™»t>«^» ^
St them to be acted on by the digestive juices. The reaction
of the first two stomachs is alkaUne.

In the camel tribe, water cells are a»«.ged m PT^^^I^I;!
in the rumen. The edges of these are provided with muscular

898

COMI'AHATIVK PHYHIOLOOY.

Hbem ctiniititutinR iiphinctora by which th«ir oponiuKi Inward
limy be (;Iomn1. 'Diera cells number Heveral hundred, and are
(wpabln f)f containing Mime quarto of water.

Fio 871 -A HtonuMih of iheep. B. StoHweh of mu»k-de«r. m, aiophainM; /fn. ni-
men'; ffi* reMcnlum: ft, pn^Hwlumj A. Ab, •bomwnm; Du, duod«num; Py.
pylorus (Huxley).

The manyplies is so named from the arrangement of its
mucus membrane in folds, a condition, however, not equally
well marked in all ruminants.

A structure known as the oesophageal canal, (furrow, groove)
communicates with the flrst three stomachs. During swallow-
ing, its lower portion is raised above the level of the third
stomach, so that it is likely that this is a barrier against the
entrance of all except liquids or soft foods into the manyplies.

It is diffloult to make any podtive statement as to what other
part it may take in determining the direction of food when en-
tering or leaviiig the various stomachs. It does not seem to be
essential to return of the cud.

jmummmm u imtumm i ii* « m! » Mm i » » w»— i Wnw

LIUIlll, H|i|| l l l>IIMl ''»l ll l 'llll* »' l' l 'l ""* 'l * 'l

immfm

xwiifn

i wi l B WI

i\uga inward
Irad, And are

)

■ophagiM; Kn, ni*
(, dnodennm; /V<

g^ement of ite
r, not equally

irrow, groove)
ring swallow-
of the third
r against the
3 manyplies.
to what other
rood when en-
lot seem to be

DKIKHTION (»F PiM)D. tM

The abomanuni or rennet re«jnibleii other formi of true
dittentive itomachii in all imitential partirulMW.

While the opening between the ftrtt and Becoml «tomachH \n
large enough to ullow of free Intercommunication, the revenw
applies to the entrance into the third .toinach

The rumen \h nearly alway. tolerably well filled with f.KKl, a
oondiUon of thing- favorable to its return for remaBUoation.

F.O aT«.-8tomach of hor- (.ff r Cl»nv«»..). .4. cardie oxtremlty of oB.ophignt;
B, prioric ring,

We may conclude that only food in a proper form for the
action of the fouHh stomach passes to any extent beyond the

*"After the food has been duly softened and has undergone
son». ( >;. nentativechanges in the rumen, lewling to the evolution
of i^.^ (C50^ H.8) and certain otganic acids ^acetic, butyric),
it is^igurgitoted by a process tkM closely resen..,Ies vom.tmg
In this the diaphragm and ttie abdommal musoles, as well

i j inm ii i ii imiM i

830

COMPARATIVE PHYSIOLOGY.

as the stomach itself and the gaWet, take part Probably as a
result of the descent of the diaphragm and consequent diminu-
tion of the intrathoracic pressure, the ascent of the cud is as-
sisted by an aspiratory process. The returning food is pre-
vented from passing into the nasal chambers by co-ordinated
movements analogous to those of swallowing. The whole pro-
cess is reflex in the same sense as is deglutition.

Normally the rumen always contains considerable liquid, a
portion of which passes up with the cud, but is in great part
returned it once. A ruminant given dry food without water
can not return the cud.

In the second mastication the process is in most ruminants
unilateral ; and as hundreds of cuds are to be chewed, a cbn-
piderable proportion of the whole day is occupied with rumina-
tion. When a single cud is sufficiently masticated it is swallowed,

Fio. 878.— Stonuwh of dog {after Ctiav«i>n). A, aeaophagni; B, pylorus.

and being finely comminuted passes at once through the small
opening between the reticulum and manyplies into the third
stomach, and thence into the abomasum, though possibly on
the way a little may pass into the first two stomachs.

PathologiflaL— While moderate fullness of the paunch is

DIGESTION OP FOOD.

331

Probably as a
luent diminu-
cud is as-
|g food is pre-
oo-ordinated
36 whole pro-
arable liquid, a

in great part i
[without water

lost ruminants
ihewed, a cbn-
i with rumina-
t is swallowed,

B, prlonu.

mgU the small

into the third

h possibly on

shs.

the paunoh is

favorable to rumination, extreme distention tends to paralysis
of the muscular ooat of the organ, allowing of the accumulation
of the gases of fermentation which may lead, if not artiUcially
relieved, to rupture of the organ.

THB AltlBCBNTARY OANAIt OF TUJB VSRTBBRATB.

Amid all variations in this great group, the alimentary canal
has common features, both of structure and function. Through-
out the entire tract muscle cells of the unstriped (involuntary)
kind, arranged in two layers, constitute the motor mechanism
for the transportation of food from one part to another. Out-
side of these is the serous coat, consisting of fibrous and elastic
tissue, and admirably adapted to preserve organs from undue
distention, at the same time providing a smooth external cover-
ing which lessens the friction of one organ against another in
the abdominal cavity ; while folds of such tissue constitute the
omentum for supporting the various organs.

Between the muscular and mucous coats of the organs that
constitute the alimentary canal there is a submucous coat of
loose connective tissue in which ramify blood-vessels, nerves, etc.

It is the mucous coat, however, that is of paramount impor-
tance, and for which all other parts may in some sense be con-
sidered to exist ; for it is from the glands with which it is sup-
plied that the digestive juices are derived, as well as that mucus
which keeps the tract moist and its delicate structures shielded
imder all circumstances. The amount of surface provided by
the mucous membrane is increased by its various foldings
(rttgee, vaJvuhe conniventes, etc.), so generally present, and
which also allow of distention ; and if the. secreting glands
are regarded as minute induplications of this coat, it will
be evident that its total area is much greater than at first ap-
p6ftrs*

While each part has glands with structure peculiar to them-
selves, it may be noticed that all the essential epithelium has a
tendency to assume a somewhat cubical form.

The secreting glands of the stomach and intestines are tubu-
lar ; while the salivary glands, the pancreas, and the liver are
masses of cells so pcusked together as to form great colonies of
cells with lesser subdivisions (lobules), the whole being boimd
together by some form of connective tissue, and well supplied
with blood-vessels and nerves, thus constituting organs with a

882

COMPARATIVE PHYSIOLOGY.

covering (capsule) in structure allied to the serous covering of
the stomach and intestines.

Details will be referred to in various parts of the sections
devoted to this subject as far as may be necessary to render
function clear, but we think these few generalizations may tend
to widen the student's field of view, and at the same time lessen
his labor and render it more effective.

THB MOVBMBMTB OF THB DiaBSVIVB OROAM8.

As with other parts of the body, so in the alimentary tract,
the slower kind of movement is carried out by plain muscular
fibers ; and the movements, as a whole, belong to the class
known as peristaltic ; in fact, it is only at the beginning of the
digestive tract that voluntary (striped) muscle is to be found
and to a limited extent in the part next to ^is— i. e., in the
oesophagus.

Teeth in the highly organized mammal are remarkable in
being to the least degree living structures of any in the entire
animal, thus being in marked contrast to other organs. The
enamel covering their exposed surfaces is the hardest of all the
tissues, and is necessarily of low vitality. We have already
alluded to the difference in the teeth of different animals, and
their relation to customary food and digestive functions. In
fact, it is clear that the teeth and all the parts of the digestive
system are correlated to one another. The compound stomach
of the ruminants, with its slow digestion uf a bulky mass of
food which must be softened and thoroughly masticated be-
fore the digestive juices can attack it successfully, harmonizes
with the powerful jaws, strong muscles of mastication, and
grinding teeth : and all these in marked contrast with the teeth
of a carnivorous animal with its simple but highly effective
stomach. Compare figures in earlier pages.

Mastication in man is of that intermediate character befits
ting an omnivorous animal. The jaws have a lateral and for-
ward-and-backward movement, as well as a vertical one, though
the latter is predominant. The upper jaw is like a fixed mill-
stone, against which the lower jaw works as a nether millstone.
The elevation of the jaw is effected by the masseter, temporal,
and internal pterygoid muscles ; depressed by the mylohyoid
and geniohyoid, though principally by the digastric. The jaw
is advanced by the extenwl pterygoids; unilateral contraction

unSm

mDt\nM*

I ooTerinif of

the sections
ary to render
I may tend
ae time lessen

OBOANS.

entary tract,
ain muscular

to the class
inning of the

to be found

— i. e., in the

emarkable in

in the entire

organs. The

lest of all the

have already

animals, and

functions. In

the digestive

ound stomach

bulky mass of

masticated be-

[y, harmonizes

tstication, and

with the teeth

ighly effective

laracter befit-
kteral and for-
il one, though
) a fixed mill-
ber millstone.
>ter, temporal,
be mylohyoid
tie. The jaw
d contraction

DIGESTION OF POOD,

888

iiiiiiiiimii'iHii

of these muscles also produces lateral movement of the inferior
maxilla, which is retracted by the more horizontal fibers of the
temporal. The movements of mastication are, of course, very
pronoiinced in ruminants.

The cheeks and tongue likewise take part in preparing the
food for the work of the stomach, nor must the lips be over-
looked even in man. The importance of these parts is well
illustrated by the imperfect mastication, etc., when there is
paralysis of the muscles of which they are formed. Even when
there is loss of sensation only, the work of the mouth is done
in a clumsy way, showing the importance of common sensation,
as well as the muscular sense.

Hervons Supply. — ^The muscles of the tongue are governed by
the hypoglossal nerve; the other muscles of mastication chiefly
by the fifth. The afferent nerves are branches of the fifth and
glosso-pharyngeal. It i&, of course, important that the food
should be rolled about and thoroughly mixed with saliva (in-
salivation).

DeglatitiOIL— The transportation of the food firom the mouth
to the stomach involves a series of co-ordinated muscular acts,
of a complicated character, by which difflculties are overcome
with marvelous success.

It will be remembered that the respiratory and digestive
tracts are both developed from a common simple tube— a fact
which makes the close anatomical relation between these two
phjnriologically distinct systems intelligible ; but it also involves
difficulties and dangers. It is well known that a small quantity
of food or drink entering the windpipe produces a perfect
storm of excitement in the respiratoiy system. The food, there-
fore, when it reaches the oesophagus, must be kept, on the one
hand, from entering the nasal, and on the other, the laryngeal
openings. This is accomplished as follows : When the food has
been gathered into a bolus on the back of the tongue, the tip of
this organ is pressed against the hard palate, by which the
mess is prevented from passing forward, and, at the same time,
forced back into the pharynx, the soft palate being raised and
the edges of the pillars of the fauces made Jo approach the
uvula, which fills up the gap remaining, so that the posterior
nares are dosed and an inclined plane provided, over which
the morsel glides. The after-result is sud to depend on the
sise of the bolus. When considerable, the constrictors of the
pharynx seize it and press it on into the gullet; when the mor-

884

COMPARATIVE PHYSlOLOttY.

sel is small or liquid is swallowed, it is rapidly propelled on-
ward by the tongue, the cesophagus and pharynx being largely
passive at the time, though contracting slowly afterward; at

Tm. 874.— CSiTitlM of mooth and phwrnz, ete., in man (after B«pii«7). Bectton, in
median line, of face and Rupenor portion of neck, deaifgned to thow the month in
itfi relations to the nasal fowK, pharynx, and tarjmz: 1, aphenoldal linasea: S, in-
ternal oriflce of Enatachian tube; 8, palatine arch; 4, veiam peDdolam patatt; 5.
anterior pUIar of aoft palate; 6, poeterlor pillar of soft palate; 7, tonsil; 8, lingoal
portion of cavity of 0iai7nz; 9, epislottb; 10. aecUon of hjoid bone; 11, laryn-
geal portion of cavity of pharynx; 1!^ cavity of larynx.

the same time the larynx as a whole is raised, the epiglottis
pressed down, chiefly by the meeting of the tongue and itself,
while its cushion lies over the rima glottidigj which -is closed
or all but dosed by the action of the sphincter muscles of the
larynx, so that the food passes over and by this avenue of life,
not. only closed but covered by the glottic lid. The latter is
not so essential as might be supposed, for persons in whom it

VJ?! y -iv ' :;,»y%;»wi^ ' w^«MM.tte'Mfe-''iM'-^^lwwa^^ .' jM^ -.< 'j^i ,'.'.ir.' W * M 8 '.Wi '

tmj). Section, In
•now the month in
iul •InoMe; 8, in-
mdnlnm paiati; S,
r.tonaU; klhigiua
id bone; II, Iwyn-

the et>iglotti8
ue and itself,
tioh-is closed
lusoles of the
venue of life,
The latter is
is in whom it

DIOBSTION OF FOOD.

886

was absent have been known to swallow fairly well. The
ascent of the larynx any one may feel for himself ; and the be-
havior of the pharynx and larynx, especially the latter, may
be viewed by the laryngoscope. The grip of the pharyngeal
muscles and the oesophagus may be made clear by attadiing a
piece of food (ceat) to a string and allowing it to be partially
swallowed.

The upward movement of food under the action of the
constrictors of the pharynx is anticipated by the closure of
the passage by the palato-glossi of the anterior pillors of the
fauces.

The circular muscular fibers of the gullet are probably the
most important in squeezing on the food by a peristaltic move-
ment, passing progressively over the whole tube, though the
longitudinal also take part in swallowing, perhaps, by steady-
ing the organ.

Deglutition can take place in an animal so long as the
medulla oblongata remains intact ; and the cec" r^ seems to lie
higher than that for respiration, as the latter . ct is possible
when, from slicing away the medulla, the former is not. An-
encephalous monsters lacking thr cerebrum can swallow, suck,
and breathe.

Food placed in the pharjmx of animals when unconscious
is swallowed, proving that volition is not essential to the act;
but our own consciousness declares that the first stage, or the
removal of the food from the mouth to the pharynx, is volun-
tary.

When we seem to swallow voluntarily there is in reality a
stimulus applied to the fouces, in the absence of food and drink,
either by the back of the tongue or by a little saliva.

It thus appears that deglutition is an act in the main reflex,
though initialed by volition. The afferent nerves concerned
are usually the glosso-pharyngeal, some branches of the fifth,
and of the vagus. The efFerent nerves are those of the numer-
ous muscles concerned.

When food has reached the gullet it is, of course, no longer
\mder the control of the will.

Section of the vagus or stimulation of this nerve modifies
the action of the oesopliagus, though it is known that contrac-
tions nay be excited in the excised organ ; but no doubt nor-
mally the movements of the gullet arise in response to natural
nerve stimulation.

886

OOMPARATIVK PHYSIOLOGY.

OompantiT*.— That swallowing is independent of gravity is
evident from the fact that long-necked animals (horse, giraffe)
can and do usually swallow with the head and neck down, so
that the fluid is rolled up an inclined plane. The peristaltic
nature of the contractions of the gullet can also be well seen in
such animals. In the frog the gullet, as well as the mouth, is
lined with ciliated epithelium, so that in a recently killed ani-
mal one may watch a slice of moistened cork disappear from the
mouth, to be found shortly afterward in the stomach. The rate
of the descent is surpriring^in fact, the movement is plainly
visible to the unaided eye.

The MoTtmanU of th* BtomML— The stomach of mammals,
including man, is provided with three layers of muscular fibers;
1. External longitudinal, a continuation of those of the oesopha-
gus. 2. Middle circular. 8. Internal oblique. The latter are
the least perfect, viewed as an investing coat. The pyloric end
of the stomach is best supplied with muscles; where also there
ia a thick muscular ring or sphincter, as compared with which
the cardiac sphincter is weak and ill-developed.

Fio. m.

Ti«. tni.

Fio. 87S.— lilaieaUir flbb.d of the itamach of hone: eztemal and middle lavm (Chan-
veM). A, flben of extenwl layer enTeloping left eac; B, flben of middle plane
In right aac; C, flbera of <ctophain». ^ ^

Fia. >ra.— Deep and mnaeular layers expoeed by removing mncooa membrane from an
everted atomach (Cbanveaa). A, deep layer of flbera enveloping left sac; B, fiber*
of middle plane which aione fonn the mnacnlar layer of right aac; C, fibers of
ceaophagna.

The movements of the stomach begin shortly after a meal
has been taken, and, as shown by observations on St. Martin,
continue for hours, not constantly, but periodically. The effect

■y ji ll 6» )iliw a «M( W W« te

'HSjgaaiw aiMii i wiiii i wtf mmim t m

of gravity is
lorae, giraffe)
eck down, so
le peristaltic
well seen in
the mouth, is
tly killed ani-
pear from the
ich. The rate
lent is plainly

of mammals,
iiscular fibers;
f the oesopha-
The latter are
le pyloric end
ere also there
)d with which

I. tn.

liddle layers (Chaa-
m of middle plane

membrane from an

f left sac; B, ttberi
aac; C, flbcT* of

rafter a meal
m St. Martin,
y. The effect

iii

OlOE^TION OP POOD.

887

of the conjoint action of the different seto of muscular fibers is
to move the food from the cardiac toward the pyloric end of
the stomach, along the greater curvature and back by the lesser
curvature, while there is also, probably, a series of in-and-out
currents to and from the center of the food-mass. The quantity
of food is constantly being lessened by the removal of digested
portions, either by the blood-vessels of the organ or by its
passing through the pyloric sphincter. The empty stomach is
quiescent and contracted, its mucous membrane being thrown
into folds.

The movements of the stomach may be regarded as reflex,
the presence of food being an exciting cause, though probably
not the only one ; and so largely automatic is the central mech-
anisms concerned that but a feeble stimulus suffices to arouse
them, especially et the accustomed time.

Of the paths of the impulses, either afferent or efferent,
little is known. Certain effects follow section or stimulation of
the vagi or splanohnics, but these can not be predicted with
certainty, or the exact relation of events indicated.

It is said that the movements of the stomach cease, even,
when it is full, during sleep, from which it is argued that gas-
tric movements do normally depend on the influence of the
nervous system. However, the subject is too obscure at present
for further discussion.

CompUBtiT0. — Recent investigations on the stomach of the
pig indicate that in this animal the contents of the two ends of
the stomach may long remain but little mingled ; and such is
certainly the case in this organ among ruminants.

P t t hiOlflgiwL— Distention of the stomach, either from excess
of food or gas arising from fermentative changes, or by secre-
tion from the blood, may cause, by upward pressure on the
diaphragm, etc., uneasiness from hampered respiration and
irregularity of the heart, possibly, also, in part traceable to the
physical interference with its movements. After great and
prolonged distention there may be weakened digestion for a
considerable interval. It seems not improbable that this is to
be explained, not alone by the impaired elasticity (vitality) of
the muscular tissue, but also by defective secreting power. It
is not necessary to impress the lesson such facts convey.

The Liteftliial Momunti.— The circular flbeM play a much
more important part than the l<nigitudinal, being, in fact, much
more developed. It is also to be remembered Chat nerves in
23

i i iaw'uiiu

888

COMPARATIVK PHJTSIOLOGy.

the form of plexuses (of Auerbach and Meiasner) abound in ita
walla.

Normally the movement, slowly progrenive, with occasional
halting is from above downward, stopping at the ileo-csecal
valve ; the movements of the large gut being apparently mostly
independent.

Movements may be excited by external or internal stimula-
tion, and may be regarded as reflex ; in which, however, the
tendency for the central cells to discharge themselves is so great
(automatic) that only a feeble stimulus is required, the normal
one being the presence of food.

It is noticeable in a recently killed animal, or in one in the
last stages of asphyxia, that the intestines contract vigorously.
Whether this is due to the action of blood overcharged with
carbonic anhydride and deficient in oxygen on the centers pre-
siding over tiie movements, on the nerves in the intestinal
walls, or on the muscle-cells directly, is not wholly clear, but it
is probable that all of these may enter into the result. The
vagus nerve, when stimulated, gives rise to movement* of the
intestines, while the splanchnic seems to have the reverse effect ;
but the cerebrum itself has an influence over the movements of
the gut, as is plain from the diarrhoea traceable to unusual fear
or anxiety. There is little to add in regard to the movements
of the large intestine. They are, no doubt, of considerable im-
portance in animals in which it is extensive. Normally they
begin at the ileo-ciBcal valve.

Defeoatioin.— The removal of the waste matter from the ali-
mentary tract is a complicated process, in which both smooth
and striped muscle, the spinal cord, and the brain take part.

Defecation may take place during the unconsciousness of
sleep or of disease, and so be wholly independent of the will ;
but, as we all know, this is not usually the case. Against ac-
cidental discharge of fsaces there is a provision in the sphinc-
ter ani, the tone of which is lost when the lower part of the
spinal cord is destroyed. We are conscious of being able, by an
effort of will, to prevent the relaxation of the sphincter or to
increase its holding power, though the latter is pijpbably almost
wholly due to the action of extrinsic muscles ; at all events any
one may convince himself that the latter may be made to take
a great part in preventing faecal discharge, though whether the
tone of the sphincter can be increased or not by volition it is
diflScult to say.

ibound in it«

th oocarional
le iIeo-c8Boal
«ntly mostly

mal stimula-
however, the
'es is so great
the normal

in one in the

!t vigorously.

charged with

e centers pre-

he intestinal

y clear, but it

result The

emento of the

everse effect ;

movements of

» unusual fear

le movements

isiderable im-

f ormally they

• from the ali-
both smooth
take part,
isciousness of
t of the will ;
. Against ac-
n the sphinc-
)r part of the
ag able, by an
phincteror to
pbably almost
all events any
made to take
1 whether the
f volition it is

DIGESTION OF FOOD.

389

What happens during an ordinary act of defecation is about
as follows : After a long inspiration the glottis is closed ; the
diaphragm, which has descended, remains low, atfording, with
tLe obstructed laryngeal outlet, a firm basis of support for the
action of the abdominal muscles, wliich, bearing on the intes-
tine, forces on their contents, which, bdore the act hus been
oalle^ for, have been lodged mostly in the large intestine ; at
the same time the sphincter ani is relaxed and peristaltic move-
ments accompany and in some instances precede the action of
the abdominal muscles. The latter may contract vigorously on
a full gut without success in the a'>»«nce of the intestinal peri-
stalsis, as too many oases of obstinate constipation bear witness.

Like deglutition, and unlike vomiting, there is usually both
a voluntary and involuntary part to the act

Though the will, through the cerebrum, can inhibit defeca-
tion, it is likely that it does so through the influence of the
cerebrum on some center in the cord ; for in a dog, the lumbar
cord of which has been divided from the dorsal, the act is, like
micturition, erection of the penis, and others which are under
the control of the will, still possible, though, of course, per?
formed entirely xmoonsoiously.

Vomitiilg. — ^If we consult our own consciousness and observe
to the best of our ability, supplementing information thus
gained by observations on others and on the lower animals, it
will become apparent that vomiting implies a series of co-ordi-
nated movements into which volition does not enter either
necessarily or habitually. There is usually a preceding tiausea,
with a temporary flow of saliva to excess. The act is initiated
by a deep inspiration, followed by closure of the glottis.
Whether the glottis is closet! during or' prior to the enUrance
of air is a matter of disagreeti;ent At all events, the dia-
phragm descends and remains fired, the lower ribs being re-
tracted. The abdominal muscles then acting against this sup-
port, force out the contents of the stomach, in which they are
assiirted by the essential relaxation of the cardiac sphincter, the
shortening of the oesophagus by its longitudinal fibers, and the
extension and straightening of the neck, togetljer with the open-
ing of the mouth.

As the expulsive effort takes place, it is accompanied by an
expiratory act which tends to keep the egtista out of the la^nx
and carry them onward, though it may also contribute to over-
come the resistance of the elevated soft palate, which serves to

840

COMPARATIVE PHYSIOLOGY.

protect the dmaI pMngee. The atoiiMoh and ooaophagui are
not wholly paMive, though the part they take actively in vom-
iting ia variable in different auimali.

Betohing may be very violent and yet ineffectual when the
cardiac iphincter ia not fully relaxed. The pyloric outlet in
umuUly doied, though in aevere and long-continued vomiting
bile ii often ejected, which muit have reached the etomach
through the pylonu.

OoapantlT*.— The eaw with which lome animab vomit in
oompariaon with other* is extraordinary, as in camivora like
our doge and cati ; a matter of importance to an animal accus-
tomed in the wild state to eat entire oaroaHea of animala— hair,
bones, etc., included.

The readiness with which an animal vomits depends in great
part on the conformation and relations of the parts of its digest-
ive tract.

The stomaoh of the human being during infantile life is leas
pouched than in the adult, which in part explains the ease with
which very young children vomit

It is well known that the hone vomits rarely and with great
difficulty. This has been attributed by different writers to va-
rious conditions of a struotnisl kind, surh as the length of the
gullet ; the manner in which it enters the stomach (centrally) ;
the pressure of a tightly closing sphincter at this point ; the
valve-like foldings of the mucous membrane at the cardiac
opening ; the small size of the stomach and its sheltered posi-
tion, so that the abdominal muscles can not readily act on it ;
the existence of a considerable length of the oesophagus be-
tween the stomach and diaphragm which is against dilatation
of the orifice by the Idngitudinal fibers of the gullet ; the open
pylorus, permitting of the gastric contents being driven into the
intestines rather than upward.

But in the ox these peculiarities do not exist; in fact, from a
mechanical point of view, the stmoture and relation of parts is
favorable, yet this animal seldom vomits, and never with ease.
Why does the horse vomit after rupture of the stomach when
conditions are less favorable from a mechanical point of view ?
There is the greatest difference as to the readiness with which
different human beings vomit ; moreover, persons that vomit
usually with difficulty may do so very perfectly when suffi-
ciently prepared, as by sea-sickness.

These and many other considerations have led us to conclude

;,IMiiiii

mtUitiblmiM^^^

iphaf^ are
|rely in voin-

w)ien the
Irio outlet M
led Tomitinf
the stomach

mdi in great
of ita digeat-

ile life it leaa
the ease with

id with great
writers to va-
length of the
1 (centrally) ;
is point ; the
b the cardiao
heltered posi-
ily act on it ;
aophagus be-
nst dilatation
let ; the open
riven into the

a fact, from a
on of parte is
er with ease,
tomach when
oint of view f
B wiUi which
s that Tomit
f when suffl-

is to conclude

D10K8TI0N OF POOD.

341

that, while there is a certain amount of force in the TariouH
views stated briefly above, they do not go to the n;ot of the
matter.

Vomiting is a very complex act, implying numerous muscu-
lar and nervous coK)rdinations. In the natural wild state the
horse can have but rare necessity to vomit (unlike the cami vora>,
hence these co-ordinations have not been organised by habit
and use ; they are foreign to the nature of the animal. After
rupture of the stomach in the horse, and in sea-sickness in man,
the nervous system is profoundly affected and the unusual hap-
pens ; in other words, the necessary muscular and nervous
co-ordinations take place. At all events, we are satisfied that it
lies witli the nervous system chiefly.

Similarly, the habit of regurgitating the food is intelligible
in the light of evolution. The fact that mammals are descended
from lower forms in which unstriped muscle-cells go to form
organs that have a rhythmically contractile function, renders
it clear why this function may become, as in ruminants, spe-
cialized in certain parts of the digestive tract; whyoamivora
should vomit readily, and why human subjecta should learn to
regurgitate food. There is, so to speak, a latent inherited ca-
pacity which may be developed into actual function. Apart
from this it is difficult to understand such cases at all.

The vomiting center is usually located in the medulla, and
is represented as working in concert with the respiratory center.
But when we consider that there is usually an increased flow
of saliva and other phenomena involving additional central
nervous influence, we see reason to believe in coordinated
action implying the use of parte of the central nervoiis system
not HO closely connected anatomically as the respiratory and
vomiting centers are assumed to be.

TUB RBM OTAIt OP SKUMTBD F&OOUOTS IHOM IHB
AZJIfllMTART OAMAL.

The glands of the stomach are simply secretive, and all ab-
sorption from this (Mrgan is either by blood-jressels directly or
by IjrmphatiGS; at least, such is the onlinary view of the subject
—whether it is not too narrow a one remains to be seen.

It is important to remember that the intestinal mucous
membrane is supplied not only with secreting glands but lym-
phatic tissue, 17^ the form of the solitary and agminated glands

;.'3r,vr;it'55si?!pjK

mJI

842

COMrARATlVn PHYSIOLOWV.

^n, and Uiickly studded with tIUI, irlvioR the
liuit velvety uppoanuice appreciable even by the

(Peyer'B p.
■mall tgnt
naked eye.

It will not be forgotten that the capillaries of the digertive
organa terminate in the veina of the portal ■yitmn, and that the
blood from thtm parta is conducted through the liver before it
Maohea the general circulation.

Main vetum trm»

BMihi aurteU

Vtna t(ua

Lymph, viand

n»w-l «i«m -Ks. M \ ^i^ «««' «**''• ^•■^ •*"••

I ^llm«n(ary(rMt

v.« on niMMm Intandad to IHiMtnt* the msenl leUtkM* of blood and lympb to
''°«*JubiWra«tlS»W S^^ lympl»Uc. •»! ««n.

enl venooi tiritMiw «• wtatwl to the •IliMiitMy met

The lymphatics of these organs form a part of the general
lymphatic system of the body 5 but the peculiar way in which
absorption is effected by villi, and the fact that the lymphatics
of the intestine, etc., at one time (fasting) contain ordinary
lymph and at another (after meals) the products of digeation,
imparts to them a physiological character of their own.

AbMwption wiU be the better understood if we treat now of
lymph and chyle and the lymph vascular system, which were
purposely postponed tUl the present; though its connection
with the vascular system is as close and important as with the
digestive organs.

The lymphatic system, as a whole, more closely reaembles
the venous than the arterial vessels. We may speak of lym-
phatic capillaries, which are, in essential points of structure,
like the arterial capillaries-, while the larger vessels may be
compared to veins, though thinner, being provided with valves
and having very numerous anastomoses. These lymphatic

mem

, ifivintr the
rren by the

the digestive
and that tlie
rer before it

ind

I vtmtl, timu mR«,

sod tnil lympb to
nptetlc, Mid inn-

( the general
irayin whioh
le lymphatios
«in ordinary
I of digestion,
own.

) treat novr of
t, whioh were
te connection
nt as with the

ely resembles
■peak of lym-
of structure,
sBsels may be
d with valves
3Be lymphatic

DIOKHUHN OP FCH)D.

oapillaries bejrin in spttces between the tls«»-
ceiu, from which they uJie up the effete
lymph. It !• interesting to note that there
Me also periva«Jular lymphaUc^ the exist-
ence of which again shows how close is the
relation between the blood vascular and lym-
phatic systems, and as we would suppose, and
as is actually found to be the case, between
the contents of each.

Lymph aiid ChyU.-If one compares the
mwentcry in a kitten when fasting with the
wme part in an animal that was killed some
hours after a full meal of milk, it may be seen
that the formerly clear lines indicating the
course of the lymphatics and ending in glands
have in the hitter case become whitish (hence
their name, lacteaU), owing to the absorp-
tion of the emulsified fat of the milk.

Microscopic examination shows the chyle
to contain (when coaguUted) fibrin, many

848

Fw. tm.-v»ivM

of lymphatic*
(8app«7).

Unm. U. FerivMCulw canal.

igm

_ lym-

endotlie-

344

COMPARATIVE PHYSIOLOGY.

leucocytes, a few developing red corpuscles, an abundance of
fat in the form both of very minute oil-globules and particles
smaller still.

Fio. no.— Epithelium from dnodennm of
rabbit, two honra after having been fed
with melted batter (Fanke).

Fio. asi.— Villi fllM with fat. from
■mall intestine of an execnted crim-
inal, one hour after death (Fanke).

There are also present fatty acids, soaps small in quantity
as compared vrith the neutral fats, also a little oholesterin and
lecithin. But chyle varies very widely even in the same animal
at di€Ferent times. To the above must be added proteids (fibrin,
serum-albumin, and globulin) ; extractives (sugar, urea, leucin) ;

and salts in which sodium
chloride is abundant.

The composition of
lymph is so cnmilar to that
of chyle, and both to blood,
that lymph might, though
only roughly, be re^rded
as blood without its red cor-
puscles, and chyle as lymph
with much neutral fat in a
very flne state of division.

TIm Mofvments of fhe
Lymph— oompanttve. —In
some fishes, some birds, and

.Fio.MS.— Ch;
thoracic

iTie taken from Ow lacteal* and amphibians, there are lymiA
dnct of a crtmlnal execnted dur- , *_.

ins diMtion (Fnnke). Shows leneocy tes
vM excessiTely line granules of fatty
emnlslon.

hearts.

In the frag there are two

■fm^ sH m

(bundance of
id particles

t wfth fat. from
tn ezccated crtin-
ir death (Ponke).

in quantity
olesterin and
s same animal
■oteids (fibrin,
urea,leucin);
rhich sodium
udant

position of
imilar to that
both to blood,
light, though
be regarded
at its red ooiv
jle as lymph
iitral fat in a
of division,
nenti of th*
•nthrs. — In
me birds, and
)re are lymph

there are two

DIGESTION OP FOOD.

345

axillary and two sacral lymph hearts. The latter are, espe-
cially, easily seen, and there is no doubt that they are under
the control of the nervous system.

In the mammals no such special helps for the propulsion of
lymph exist.

There is little doubt that the blood-pressure is always higher
than the lymph-pressure, and when the blood-vessels are dilated
the fluid within the perivascular lymph-channels is likely com-
pressed; muscular exercise must act on the lymph-channels as
on veins, both being provided with valves, though themselves
readily compressible; the inspiratory efforts, especially when
forcible, assist in two ways: by the compressing effect of the
respiratory muscles, and by the aspirating effect of the negative
pressure within the thorax, producing a similar aspirating
effect within the great veins, into which the largo lymphatic
trunks empty. The latter are provided at this point with
valves, so that there is no back-flow; and, with the positive
pressure within the laige lymphatic trunks (thoracic duct, etc.),
the physical conditions are favorable to the outflow of lymph
or chyle.

Our knowledge of the nature of the passage of the chyle
from the intestines into the blood is now clearer than it was till
recently, though still incomplete.

The exact structure of a villus is to be carefully considered.
If we assume that the muscular cells in its structure have a
rhjrthmically contractile function, the blind terminal portion
of the lacteal inclosed within the villus must, after being
emptied, act as a suction-pump to some extent; at all events,
the conditions as to pressure would be favorable to inflow of
any material, especially fluid without the lacteal. The great
di£Qculty hither^ was to understand how the fat found its way
through the villus into the blood, for, that most of it passes in
this direction there is little doubt.

It is now known that leucocytes (amceboids, phagocytes)
migrate from within the villus outward, and may even reach
its surface, that they take up (eat) fat-partidles from the epi-
thelium of the villus, and, independently themselves, carry
them inward, reach the central lacteal and break up, thus re-
leasing the fat. How the fat gets into the covering epithelium
is not yet so fully known— possibly by a similar inceptive pro-
cess; nor is it ascertained what constructive or other chemical
processes it may perform; though it in not at all likely that

Fia. 883

^'^an '^.s^itmtn^i-sasaamte^SK i'Htsw H i

DIGBSTIUN OP POOD.

847

Fio. S88.— Lympluitlc syitem of hone (Chanveaii). A, facial and naaal plexu* whom)
branches paa* to robgloual glandi; B, C, iwrotid lymphatic gland, aendlne vea-
«els to pharyngeal guind; D, E, larse tmnki pauing toward thorax: F, Q, H,
glanda receiving Huperflcial hrmphatica of nock, a portion of those of iimba, and
tnoie of pectoral parietea: 1, Junction of Jagulara; J, axillary veina; K, ■tuunlt
of anterior vena cava; L, thoracic dnct; M, lymphatics of apleen; N, of atomach;
O, of large colon; S, of amall colon; R, lacteala of small Intesuiw, all going to
form two trunks, P, Q, which open directlv into recuptaculom chyli; T, trunk
\Vhich receives branches of sublumbar glands, U, to which vessels of Internal iliac
glands, V, the receptacles of lymphatics of abdominal parietes, pass: W, precrural
glands receiving lymphatica of posterior limb, and which arrive inoependently in
the abdomen; X, superficial inguinal glands into which lymphatics of the mam-
nue, external generative organs, some superficial trunks of posterior limb, etc.,
pass; Z, deep inguinal glands receiving the superficial lymphatics, Z, of posterior
limbs.

the Mvork of the amoeboid cells is confined to the transport of fat
alone, but that other matters are also thus removed inward to
the lacteal.

When a multitude of &ots are taken into account, there

Fio. m.- Perpendicular seetion thronsh one of IVyMr*s patohe* in the lower part of
the ileum of the sheep (Chatveau). a, a, lact««l vessels In villi; 6, i, superficial
larar of lacteal vessels; e, e, deep larer of lacteals; if. tf, efferent vessels provided
with valves: /, Payer's glands; g, circular muscular layer of wall of Intestine; h,
longitudinal layer.

seems little reason to doubt that so important a process as ab-
sorption can not fail to be regulated by the nervous centers.

iMiaiiiiiii

848

COMPARATIVE PHYSIOLOttY.

There are two points that are very far from being deter^
mined: the one the fate of the products of digestion; the other
the exact limit to which digestion is carried. How much— e. g.,
of proteid matter — does actually undergo
conversion into peptone; how much is
converted into leucin and tyrosin; or,
again, what proportion of the albuminous
matters are dealt with as such by the in-
testine without conversion into peptone
at all, eithtr as soluble proteid or in the
form of solid particles ?

1. It is generally believed that solu-
ble sugars are absorbed, usually after
conversion into maltose or glucose, by
the capillaries of the stomach and intes-
tine.

2. There is some positive evidence of
the presence of fats, soaps, and sugars in
unusual amount after a meal in the por-
tal vein, which implies removal from the
intestinal contents by the capillaries,
though, so far as experiment goes, the
fat is chiefly in the form of soaps,

Certain experiments have been made

Fiu, 88B.— Intettiual vUlu
(after Lcydig). a, a, a

Hpitiwiiaicoveriiw; b,b,

jongitodinai rauMuW Uv litrating the pyloric end of the stom-

flben; d, lacteal. •'. ? T^. , . . i_ :_i„ ♦!...

taplllarr networl

ongitodlnal ma _ ^

ach, by introducing a cannula into the
thoracic duct, so as to continually remove its contents, etc.
But we are surprised that serious conclusions should have been
drawn under such circumstances, seeing that the natural condi-
tions are so altered. What we wish to get at in physiology is
the normal function of parts, and not the possible results after
our interference. Under such circumstances the phenomena
may have a suggestive but certainly can not have a conclusive

value. ,.

It is a very striking fact that little peptone (none, according
to some observers) can be detected even in tV^ ;iortal blot>d.
True it is, the circulation is rapid and consbuiv, and a small
quantity might escape detection, yet a considerable amount be
removed from the intestine in the spRce of a few hours by the
capillaries alone. Peptone is not found in the contents of the

thoracic duct ,

For a considerable period it has been customary to use the

Kmm

laiiMiiiiniii

being deter-
t>n; the other

much — e.g.,

lly undergo
much is

tyrosin; or,

I albuminous

wh by the in-

into peptone

|>teid or in the

red that solu-
ustially after
r glucose, by
ach and intes-

re evidence of
and sugars in
eal in the por-
koval from the
le capillaries,
lent goes, the
F soaps,

kve been made
i of the stom-
mula into the
contents, etc.
mid have been
natural condi-
1 physiology is
le results after
le phenomena
'e a conclusive

one, according
;»ortal blood.

k, and a small

ble amount be
hours by the

>ntents of the

ary to use the

DIGESTION OP POOD.

840

terms osmosis and diffusion in connection with the functions
of the alimentary canal, and especially the intestinal tract,
as if Ibia thm-walled but complicated organ, or rather coUec-

Fio. nt.— A. VUIi of num. ihowliig blood-VMMto and ImImI*; B. VUlu of ibeep
(•f tw Chanveaa).

tion of organs, we>« little more, so far as absorpticm is con-
cerned, than a moist membrane, leaving the process of the re-
moval of digested food products to be explained almost wholly
on physical principles.

From such views we dissent. We believe they are opposed
to what we know of living tissue everywhere, and are not sup-
ported by the special facts of digestion. When certain foreign
bodies (as purgatives) are introduced into the blood or the ali-
mentary ranal, that diffusiion takes place, according to physical
laws, may indicate the manner in which the intestine can act;
but even admitting that under such circumstances physical
principles actually do explain the whole, which we do not grant,
it would by no means follow that such was the natural behav-
ior of this organ in the disoharge of its ordinary functions.

850

COMPARATIVE PHYSIOLOGY.

When we consider that tJie blood tend* to maintain an equi-
librium, it must be evident that the removal of substances from
the alimentary canal, unless tliero is to be excessive activity of

Pie.

epi-
., een-
rrog'i

. ma.— A. 8eeti<m of tIIIiu of tat MIM dnriiiR fat •bMrption (Sehlfer). «p<
tMUom; itr, atriatad bolder; e, lymph-eclla; «*, lymph-cella in epithdinm: I,
tral lacMkl contahitaig dlaintegratlnfr coipoKle* . B. Macon* membnute of f i „ _
Intcattne dnrinc fat abaorption (Schifer). tp, epithellnm; itr, (trtated border; C,
lympb-corpiiaclea; /, lactMl.

the excretory organs and waHe of energy both by them and
the iligestive tract, must in some degree depend on the demand
for the products of digestion by the tissues. That there is to
some extent a corrective action of the excretory organs always
going on is no doubt true, and that it may in o<utes of emergency
be great is also true ; but that this is minimized in ways too
complex for us to follow in every detail is equally true. Diges-
tion wuts on appetite, and the latter is an expression of the
needs of the tissues. We believe it is literally true that in a
healthy organism the rate and character of digestion and of
the removal of prepared producto are largely dependent on the
condition of the tissues of the body.

Why is digestion more perfect in overfed animals after
a short fast ? The whole matter is very complex, but we tkink

ttain an equi-
wtancea from
ve activity of

str

(Sehirer). <tp,ept-
epHhaUom: /, ten-
lembnuie of fros'a
itrlkted border; C,

bj them and
n the demand
lat there is to
•rgans always
of emergency
d in ways too
true. Diipea-
'«8sion of the
rue that in a
BRtion and of
indent on the

inimals after
but we think

DIGESTION OF POOD.

861

it is infinitely better to admit ignorance than attempt to «•
plain by principles that du violence to our fundamental con-
ceptions of life processes. 'To introduce " ferments '* to explain
so many obscure points in physiology, as the conversion of
peptone in the blood, for example, is taking refuge in a way
that does no credit to science.

Without denying that endosmosis, etc., may play a part in
the vital processes we are considering, we believe a truer view .
of the whole matter will be ultimately reached. In the mean
time we think it best to express our belief that we are ignorant
of the real nature of absorption in great part ; but we think
that, if the alimentary tract were regarded as doing for the
digested food (chyle, etc.) some such work as certain other
glands do for the blood, we would be on the way to a truer con-
ception of the real nature of the processes.

It would then be possible to understand that proteids, either
in the form of soluble or insoluble substances, including pop-
tone, might be taken in hand and converted by a true vital
process into the constituents of the blood.

If we were to regard the kidney as manufacturing useful'
instead of harmful products, the resemblance in behavior would
in many points be parallel. We have seen that physical expla-
nations of the functions of the kidney have failed, and that it
must be regarded even in those parts that eliminate most water
as a genuine secreting mechanism.

We wish to present a somewhat truer conception of the
lymph that is separated from the capillaries and bathes the
tissues.

We would regard its separation as a true secretion, and not
a mere diffusion dependent wholly on blood-pressure. The
mere ligature of a vein does not st^ce to cause an excess of
diffusion, but the vaso-motor nerves have been shown to be
concerned. The effusions that result from pathological pro-
cesses do nut correspond with the lymph — that is, the nutrient
material — provided by the capillaries for the tissues. These
vessels are more than mere carriers ; they are secretors — in a
sense they are glands. We have seen that io the foetus they
function both as respiratory and nutrient organs in the allan-
tois and yelk-snc, and, in our opinion, they never wholly lose
this function.

Tile kind of lymph that bathes a tissue, we believe, depends
on its nature and its condition at the time, so that, as we view

COMPARATIVE PHY810LOOV.

^■:

tiasue-lymph, it is not a mere effusion with which the tiamies,
for which it ii provided, have nothing to do. The differences
may be beyond our chemistry to determine, but to assume that
all lymph poured out is alike is too crude a conception to meet
the facts of the case. Glands, too, it will be remembered, derive
their materials, like all other tissues, not directly from the
blood, but from the lymph. We believe that the cells of the
capillaries, like all others, are influenced by the nervous system,
notwithstanding that nerves have not been traced terminating
in them.

It is to be borne in mind that the lymph, like the blood,
receives tissue waste-products — in fact, it is very important to
realise that the lymph is, in the first instance, a sort of better
blood— an improved, selected material, so far as any tissue is
concerned, which becomes gradually deteriorated.

We have not the space to give all the reasons on which the
opinions expressed above are founded; but, if the student has
become imbued with the principles that pervade this work thus
far, he will be prepared for the attitude we have taken, and
sympathise with our departures from the mechanical (physieal)
physiology.

We think it would be a great gain for physiology if the use
of the term " absorption." as applied to the alimentary tract,
were given up altogether, as it is sure to lead to the substitu-
tion of the gross conceptions of physical processes instead of
the subtle though at present rather indefinite ideas of vital
processes. We prefer ignorance to narrow, artificial, and er-
roneous views.

FlthologioaL— Under certain circumstances, of which one is
obstruction to the venous circulation or the lymphatics, fluid
may be potired out or effused into the neighboring titnues or the
serous cavities. This is of very variable composition, but always
contains enough salts and proteids to remind one of the blood.

Such fluids are often spoken of as '* lymph,*' though the
resemblance to normal tissue-lymph is but of the crudest kind;
and the condition of the vessels when it is secreted, if such a
term a here appropriate, is not to be compared to the natural
separation of the normal lymph— in fact, were thirf not so, it
would be identical with the latter, which it is not When such
effusions take place they are in themselves evidence of altered
(and not merely increased) function.
. The Ibom— The faeces may be regarded in at least a three-

the tinues,

le differenoea

aaaume that

[ption to meet

ibered, derive

ly from the

|e cells of the

[rvoiu system,

terminating

ke the blood,
important to
sort of better
any tissue is

on which the
e student has
his work thus
re taken, and
ioal (physieal)

ogy if the use
mentary tract,
o the substitu-
Ms instead of
ideas of rital
iflcial, and er-

f which one is
nphatics, fluid
f tissues or the
on. but always
of the blood.
," though the
crudest kind;
)ted, if such a
to the natural
thief not so, it
When such
ince of altered

least a three-

DIOESTION OF FOOD.

fold aspect. They contain undigested and indigestible rem<
nauts, the ferments and certain decomposition products of the
digestive fluids, and true excretory matters.

In carnivorous and omnivorous animals, including man,
the undigested materials are those that have escaped the action
of the secretions— such as starch and fats— together with thoHe
substances that the digestive juices are powerless to attack,
as homy matter, hairs, elastic tissue, etc.

In vegetable feeders a larger prs-jportion of ohlorophyl, cel-
lulose, and starch will, of course, be found.

These, naturally, are variable with the individiial, the spe-
cies, and the vigor of the digestive organs at the time.

Besides the above, certain products are to be detected in the
faeces plainly traceable to the digestive fluids, and showing
'that they have undergone chemiceJ decomposition in the ali-
mentary tract, such as cholalic acid, altered ooloring-matiei'i!>
like urobilin, derivable probably from bilirubin v also oholes-
terin, fatty acids, insoluble soaps (calcium, magnesium), to-
gether with ferments, having the properties of pepsin and
amylopsin. Mucus is also abundant in the fteoes.

We know little of the excretory products proper, as they
probably normally exist in'small quantity, and it is not impos-
sible that some of the products of the decomposition of the
digestive juices may be reabsorbed and worked over or excreted
by the kidneys, etc.

There is, however, a recognized non-nitrogenous crystalline
body known as exeretin, which contains sulphur, salts, and
pigments, and that may rank perhaps as a true excretion of
the intestine.

It is well known that bacteria aboimd in the alimentary
tratst, though their number is dependent on a variety of circum-
stances, including the kind of food and the condition in which
it is eaten. These minute organisms feed, of course, vnd to get
their food produce chemical decompositions. iSw*^ tta\\ indol
are possibly thus produced, and give the faecal odOr to the con-
tents of the intestine. But as yet our ignorance of these
matters is greater than our knowledge — a remark which ap-
plies to the excretory functions of the alimentary tract gen-
erally.

Pttih0logil»l. — ^The facts revealed by clinical and pathologi-
cal study leave no doubt in the mind that the intestine at all
events may, when other glands, like the kidney, are at fault,

w wi" i' <n»wfim i n»n ' MWW t .i w .i^

8ft4

OOMPARATIVB PHYSIOLOGY.

undertake an unumial share of excretory work, probably eren
to the length of diwharging urea.

Obooure as the Bubjeot is, and long as it may be before we
know exactly what and how matter is thus excreted, we think
that it will greatly advance us toward a true conception of the
vital proT' .xMS of the mammalian body if we regard the ali-
mentary tract as a collection of organs with both a secreting
and excreting function : that what we have been terming ab-
sorption is in the maiii, at least, essentially secretion or an
allied process; and that the parts of this long train of organs
are mutually dependent and work in concert, so that when one
is lacking in vigor or resting to a greater or less degree, the
others make up for its diminished activity ; and that the whole
must work in harmony with the various excretory organs, as
an excretor itself, and in unison with the general state of the
economy. We are convinced that even as an excretory mech-
anism one part may act (vicariously) for another.

Of course, in disease the condition of the faeces is an indica-
tion of the state of the digestive organs ; thus color, consistence,
the presence of food in lumps, the odor, and many other points
tell a plain story of work left undone, ill-done, or disordered
by influences operating from within or from without the tract.
Ilie intelligent physician acts the part of a qualified inspector,
surveying the output of a great factory, and drawing oonolu-
sions in regard to the kind of work which the operatives have
performed.

THB ORAMOBS PRODUOBD IN TBB FOOD Df THB
AUmiMTART OAlTAZa.

We have Aow considered the method of secretion, the secre-
tions themselves, and the movements of the various parts of
the digestive tract, so that a brief statement of the results of
all this mechanism, as represented by changes in the food, will
be appropriate. We shall assume for the present that the effects
of the digestive juices are substantially the same in the body as
in artificial digestion.

\mong mammals food is, in the mouth, comminuted (except
in the case of the camivora, that bolt it almost whole, and the
ruminants, that simply swallow it to be regurgitated for freah
and complete mastication), innalivaled, and, in most species,
chemically changed, but only in so far as starch is oonoemed.

>robably eren

\)e before we
ated, wu think
seption of the
egard the ali-
>th a Moreting
)n terming ab-
cretion or an
ttin of organs
that when one
BU degree, the
that the whole
lory organs, as
«! state of the
ccretory meoh-

m is an indica^
Dr, consistence,
ly other points
, or disordered
bout the tract,
ifled inspector,
rawing condu-
>peratives have

OD nr TBB

etion. the secre-
'arious parts of
f the results of
in the food, will
t that the effects
e in the body as

minuted (except
t whole, and the
(itated for fresh
in most species,
h. is oonoemed.

D10B8T10N OP FOOD.

866

Deglutition is the result of the ooK)rdlnat«d action of many
muscular mechanisms, and is reflex in nature. The oesophagus
secretes mucus, which lubricates its walls, and aids mechan-
ically in the transport of the food from the mouth to the stom-
ach. In the stomach, by the action of the gastric juice, food
is further broken up, the proteid covering of fat^lls is digested,
and the structure of muscle, etc., disappears. Proteid matters
become peptone, and in some animals fat is split up into free
fatty add and glycerin ; but the digestion of fat in the stom-
ach is very limited at best and probably does not go on to
emulsiflcation or saponification. The digestion of starch con-
• 9

■ ns.— MnUMi takM fiom pylorie portion of itoouich of dog djwl"* ''f**^!" 'l'

SiSS; M. wM«»«Sl>b«"' In whlchTfri.. tore pwUy dlMppewed; rf. drS. g«ob-
alwor fU; «,«, ■Uu«li; g. molcealw gnnalM.

tinues in the stomach until the reaction of the food-mass be-
comes add. This in the hog may not be far from one to two
hours, and the amylolytic ferment acts with great rapidity even
without the body. The food is moved about to a certain ex-
tent, so as to expose every part fredy to the mucous mem-
brane and iti seoretionsi It is likely that the sugar resulting
from the digertion of starch, the peptones, and, to some ex-
tent, the fat formed (if any), is received into the blood from
thestnmach.

tF.vip'.^'^'^'S!-"V-r-v' t^rtcr-.i"*'

l^-i.;!'- t.7T-;-]n3^;,

S56

COMPARATIVB PHYSIOIiOOY.

Aa the partially digested maM (chyme) it pamed on into the
iiiteitine aa a reault of the action of the alkaline bile, the para-
lieptone, pepain, and bileHuUta are depoaited. Certain of the
conatitiienta of digeation are thua delayed, a portion of the pep-
ain ia probably abaorbed, either altered or unaltered, and pep-
ain ia thua got rid of, making the way dear, mi to apeak, for the
action of trypain. At all eventa, digeation in one part of the
tract ia antagonised by digeation in another, but we muat aiao
add aupplemented.

The fat, which had been but little altereti i > '>ir.'iUi}lt>d by
the joint action of the bile and pancreatic aecx >u a p< i-tion
ia aaponifled, which again helpa in emulaiflration, whi In an {-Addi-
tional part, in form but little changed, ia probably dealt with by
the abaorbenta.

Proteid digeation ia continued, and, beaidea peptonea, nitro-
genoua oryatalline bodiea are formed (leuoin and tyroain), but
under what oonditlona or to what exl/r-nt ia not known; though
the quantity ia likely very variablo, lioth with the apeoiea of
animal and the oiroumatancea, auoh as <]uantity and quality of
food; and it ia likely alao dependent not i>. 'nlilo on the rate of
alMorption. It aeema altogetiier probable that In thoae that uae
an exceaa of nitrogenotu food more of theae bo«Ii>:a are formed,
and thua give an additional wurk to the vxeivting organa, in-
cluding the liver. But the abaenoe of albumin from healthy
fsBcee pointa to the complete digeation of proteMs in the ali-
mentary canal. Plainly the chief work of inteatinal digeation
ia begun and carried on in the upper part of the tract, where
the ducta of the main glanda are to be found.

The contenta of the intestine awarm with bacteria, though
these are probably kept imder control, to some extent, by the
bile, the functions of which as an antiseptic we have already
considered.

The removal of fats by the villi will be shortly considered.
The other products of digestion probably find their way into
the general circulation by the portal blood, passing through
the liver, which organ modifies some of them in ways to be
examined later.

The voIvuUb eonniventes greatly increase the surface of the
intestine, and retard the movements of the partially digested
mass, both of which are favorable. The peristaltic movements
of the small gut serve the obvious purpose of moving on the
digesting mass, thiu making way for fresh additions of chyme

id on into th«
>lle, the pam-
ertain of the
m of the pep-
ired, and pep*
•peak, for the
A part of the
we must alio

o»iiilii}lt>d by
loir, ap«»''i<>n
wliili)ftnj-,H'<U-
' deait with by

eptonet, nitro-
I tyrosin), but
town; though
the Bpeoiea of
smd quality of
on the rate of
those that use
[>:b are formed,
i.<g organs, in-
from healthy
lida in the ali-
tinal digestion
ke tract, where

uteria, though

extent, by the

I have already

ily considered.

their way into

Basing through

in ways to be

i surface of the
rtially digested
Itio movements
moving on the
tionsof chyme

- I ■■■ l i ' ■ !■

ir~::l-(>''<:?^y--fMl^'-W-^.-¥\.\

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^^4^ij^0i'' r ,^^ig)«?p,^■1t.4,V^^>iwr^^!y*^^■i«'*^

DIOBSTION OF FOOD.

8S7

from the stomaoh, and carrying on the more elaborated con-
tents to points where they can receive fresh attention, both
digestive and absorptive.

CkmpantifBi — In man, the camivora, and some other groups,
it is likely that digestion in the large intestine is slight, the work
being mostly completed— at all events, so far as the action of
the secretions is concerned— before this division of the tract is
.leached, though doubtless absorption goes on there also. The
muscular strength of this gut is important in the act of defe-
cation.

But the great sise of the large intestine in ruminants— in
the horse, etc.— together with the bulky character of the food
of sudi animals, points to the existence of possibly extensive
^oceeses of which we are ignorant It is generally believed
that food remains but a short time in the stomach of the horse,
and that the osacum is a sort of reservoir in which digestive
processes are in progress, and also for water.

Fermentationa go on in the intestine, and probably among
ruminants tb«y are numerous and essential, though our actual
knowledge of the subject is very limited.

The gases found in the stomaoh are atmospheric air (swal-
lowed) and carbon dioxide, derived from the blood. Those of
the intestine are nitrogen, hydrogen, carbonic anhydride, sul*
phnretted hydrogen, and marsh'gaa, tiie quantity varying con-
siderably with the diet In hertnvora the quantity of COt and
CHBUislarge.

Although our knowledge of the actual processes 1^ which
food is digested in the domestic animals is meager, there are
certain considerations to which it may be well to give promi-
nence at this imint

The whole subject becomes clearer and Uie way is paved for
more exact and comprehenrive knowledge^ it be borne in
mind tiiat the entire alimentary tract has a common embryo-
logical origin from the splanchnopleure (Fig. SS5, etc.), coiuristr
ing of outer mesoblast and lining hypoblast the former giving
rise to the muscular and other less essential structures, the latr
ter to the all-important glandular ^thelium. - But of all re-
gjcms the alimentary tract has been modified in relation to
the development and habits of the animal group. It can not
be too wdl romembered that digestion is h^^y complex, with
one organ and one process snp^ementary to another.

U maatioation is imperfect, as in the camivora, gastric dige»>

fummmm mmimB ii iiJ ii' 'i^ii ' i>iiKi > ^

- ■ /*M»MW'fJ~ ' >MijJ l ^. i ^^" * # W HH^LJ<ftJw l

858

COMPARATIVE PHYSIOLOGY.

tion is unusually active, as is well seen in the dog; if the stom-
ach is capacious the intestine is shorter, also exemplified in
this group. The stomach may be small and the small inte»-
tines not lengthy, but the large intestine of enormous sise, as in
the horse.

When the quantity of starchy matters found in the food of
the animal is large, provision is made for its digestion in sev-
eral parte of the alimentary tract. This is seen in the horse
and other herbivora. Mastication is fairly complete in these
animals, yet a part of the small stomach of the horse is a sort
of oesophageal dilatation (Fig. 266) in which amylolytic diges-
tion goes on by the action of the swallowed saliva and possibly
by a ferment provided in this region of the organ.

The gastric juice of the horse has been proved capable of
digesting starch, possibly because mixed with the swallowed
saliva. The stomach of the pig is large, and both proteid and
starchy digestion exceedingly active. In the intestines tiie pro-
cesses are of brief duration, but very effective.

Digestion in the upper part of the small intestines is, in
some ftpiniRlH, as the horse, really a continuation of that in the
stomach; or, at all events, the contente of the duodenum and
jejunum are usiially acid in reaction, so that the digestion
peculiar to one region of the tract does not always abruptly
end when food has left that part The readiness with which
food passes horn the stomach into the intestines is very vari-
able in different animals, and even in the same animal under
different circumstances. In the horse the pyloric orifice seems
never to be very tightly dosed, though in most of our domestic
animals the reverse is the case; and with them the quantity of
undigested material, as fat, that passes into the small intestine
depends on the rate of digestion and absorption in the latter.

In the horse, if water, or even hay, be given alter oate a por-
tion of the latter is soon carried on into the intestines, so that
the obvious rule for feeding such an animal is to give the water
and hay before the aaia, or, at least, the water and no hay im-
mediately after the oats.

Digeation in the large intestine is of great importance in the
monogastric herbivora, as the horse. The caecum is of enor-
mous siie— about twice that of the stomach— and has dommuni-
oation with the colon by a small opening, so that it furnishes a
sort of supplementaiy reservoir for digestion as well as for
watw. As ttie resulte of experiments, it has been concluded

; if theslom-
ixemplifled in
e small inte»-
lous rise, aa in

in the food of
estion in ser-
in the horse
plete in these
hone is a sort
frlolytio diges-
k and possibly

red capable of
ha swallowed
h proteid and
fitines tiie pro-

itestines is, in
of that in the
uodenum and
the digestion
ways abruptly
88 with which
» is very vari-
animal under
ic orifice seems
f our domestic
;he quantity of
imall intestine
a the latter,
f ter oats a por-
Mitines, so that
giye the water
nd no hay im-

wrtance in the
im is of enor-
has dommuni-
; it furnishes a
as well as for
een concluded

HP*

DIOBSTION OF FOOD.

that food is found in the stomach twelve hours after feeding;
in the caecum after twenty-four hours, with a residue in the
jejunum; after forty-eight hours, in the ventral colon, with re-
mains in the caecum; after seventy-two hours, in the dorsal
colon; and after ninety hours in the dorsal colon and rectum.

The caecum appears to digest large quantities of cellulose,
which does not seem to be affected by either the saliva, gastric,
or pancreatic juices. The process is ill understood. In her-
trivcra the large intestine takes some very important part— in
digestion and absorption— and we would again remind the stu-
dent that the latter term has been used in a very vague if not
unwarrantable sense. It is important for the practitioner to
bear in mind that nutrient enemata can be utilized for the gen-
eral good of the economy when passed into either the large or
small intestine.

During the suckling {teriod digestion in all the various
groups of animals is probably closely analogous. At this time,
in ruminants, the first three divisions of the stomach are but
slightly developed.

PtttlialogioaL — In subjects of a highly neurotic temperament
and unstable nervous system it sometimes happens that im-
mense quantities of gas are belched from an empty stomach or
distend the intestines.

It is known that the oxygen swallowed is absorbed into the
blood, and the carbonic anhydride found in the stomach de-
rived from that fluid.

It will thus be seen that the alimentary tract has not lost its
respiratory functions even in man, and that these may in cer-
tain instances be inordinately developed (revenion).

spsoiAz. oomnmRATiomk

It is a matter well recognised by those of much experience
in breeding and keeping animals with restricted freedom and
undw oflier conditions differing widely from the natural ones
— i. e., ihoae tmder which the animals exist in a wild state— that
the nature of the food must vary from that which the untamed
ancestors of our dimiestic animals used. Food may often with
advantage be cooked for the tame and confined animal. The
digestive and the assimilative powers have varied wifii other
changes in the organism Iwought about by the new surround-
ings. So much is this the case, that it is necessary to resort to

^fif^lflgSf^^^

860

COMPARATIVE PHTSIOLOUT.

common experience and to more exact experiments to ascertain
the beat methods of feeding animals for fattening, for work,
or for breeding. Inferences drawn from the feeding habits of
wild animals allied to the tame to be valuable must always,
before being applied to the latter, he subjected to correction by
the results of experience.

It is now well established by experience that animals kept
in confinement miist have, in order to escape disease and attain
the best results on the whole, a diet which not only imitates
that of the corresponding wild forms generally, but even in
details, with, it may be, altered proportions or added constitu-
ents, in consequence of the difference in the environment To
illustrate: poultry can not be kept healthy confined in a shed
without sand, gravel, old mortar, or some similar preparation;
and for the best results they must have green food also, as
lettuce, cabbage, chopped green clover, grass, etc. They must
not be provided with as much food as if they had the exercise
afforded by running hither and thither over a large field. We "^
have chosen this case because it is not commonly recognised
that our domesticated birds have been so modified that special
study must be made of the environment in all cases if they are
not to degenerate. The facts in regard to homed cattle, horses,
and dogs are perhaps better known.

Cooking greatly alters the chemical composition, the mci-
chanical condition, and, in consequence, the flavor, the digesti*
bility, and the nutritive value of foods. To illustrate: meat in
its raw condition would present mechanical difficulties, the di-
gestive fluids permeating it less completely; an obstacle, how-
ever, of far greater magnitude in the case of most v^[etable
foods. By cooking certain chemical compounds are replaced
by others, while some may be wholly removed. As a rule,
boiling is not a good form of preparing meat, because it with-
draws not only salts of importance, but proteids and the ex-
tractivea— nitrogenous and other. Beef-tea is valuable chiefly
because of these extractives, though it also contains a little
gelatin, albumin, and fats.

Meat, according to the heat employed, may be so cooked as
to retain the greater part of its juices within it or the reverse.
With a high temperature (65° to 70° C.) the outride in KMurting
may be so quickly hardened as to retain the juices.

In feeding dogs it is both phyriological and economical to
give the animal the broth as well as the meat itself.

t,.

■ to ascertain
ng, for work,
ling habits of
must always,
correction by

animals kept
and attain

only imitates
but even in
dded oonstitu-
ironment To
ned in a shed
r preparation;
I food also, as
B. They must
ad the exercise
kTge field. We ^^
mly recognised
ed that special
lases if they are
d cattle, horses,

Nation, the me-
Yor, the digesti-
Lstrate: meat in
[Bculties, the di-
ti obstacle, how-
most v^ietable
ids are replaced
ed. As a rule,
because it with-
lids and the ex-
raluable diiefly
iontains a little

be so cooked as

i or the reverse.

ride in roasting

see.

i economical to

lelf.

DIOBSTION OF FOOD.

861

It is remarkable in the highest degree that man's appetite,
or the instinctive choice of food, has proved wiser than our
science. It would be impossible even yet to match, by calcula-
tions based on any data we can obtain, a diet for each man equal
upon the whole to what his instincts prompt With the lower
mammals we can prescribe with greater success. At the same
time chemical and physiological science can lay down general
principles based on actual experience, which may serve to cor-
rect some artificialities acquired by perseverance in habits that
were not based on the true instincts of a sound body and a
healthy mental and moral nature; for the influence of the
latter can not be safely ignored even in such discussions as the
pr e s e nt These remarks, however, are meant to be suggestive
rather than exhaustive.

We may with advantage inquire into the nature of hunger
and thirst. These, as we know, are safe guides usually in eat-
ing and drinking.

After a long walk on a warm day one feels thirsty, the
mouth is usually dry; at all events, moistening the mouth,
especially the back of it (pharynx), will of itself partially re-
lieve thirst But if we remain quiet for a little time the thirst
grows less, even if no fluid be taken. The dryness has been
relieved by the natural secretions. If, however, fluid be intro-
duced into the blood either directly or through the alimentary
canal, the thirst is also relieved speedily. The fact that we
know when to stop drinking water shows of itself that there
must be local sensations that guide vm, for it is not possible to
believe that the whole of the fluid taken can at once have en-
tered the blood,

Hunger, like thirst may be mitigated 1^ injections into the
intestines or the blood. It is, therefore, clear that, while in the .
case of hunger and thirst there is a local expression of a need,
a peculiar sensation, more pronounced in certain parts (the
fauces in the case of thirst the stomach in that of hunger),
yet these may be appefMcd from within tiirough the medium
of the blood, as well as from without by the contact of food or
water, as the ease may be.

Up to the fwesent we have assumed that the changes
wrought in the food in the alimentary tract wwe identical with
those jwoduoed by the digestive ferments as«btidned by extracts
of the orgaM J naturally producing them. But for many reasons
it seems probable that artificial digesticm can not be regarded as

•MMiii

-«

86S

COMPARATIVK PHYSIOLOGY.

parallel with the natural prooeeMa except in a Terjr general
way. When we take into account the abience of muaoular
movements, regulated according to no rigid principl«a,hutyary-
ing with innumemble circumstanoea in all probability; the ab-
sence of the influence of the nenroua ayetem determining the
yariationi in the quantity and composition of the outflow of the
■ecretiona; the changes in the rate of so^Mdled absorption,
which doubtless influences also the act of the seor^on of the
juices— by these and a host of other considerations we are led
to hesitate before we commit ourselves too unreservedly to the
belief that the processes of natural digestion can be exactly
imitated in the laboratory.

What is it which enables one animal to digest habitually
what may be almost a poison to another f How is it that each
one can dispose readily of a food at one time that at another is
quite indigestible t To reply that in the one case, the digestive
fluids are poured out and in the other not, is to go little below
the surface, for one asks the reason of this, if it be a fact, as it
no doubt is. When we look furthw into the peeuliaritiea of
digestion, etc., we recognize the influence ot race as such, and
in the race and the individual that obtrusive though ill-unda>>
stood fact— the force of AoMt— operative here as elsewhere.
And there can be little doubt that the habits of animals, as to
food eaten and digestive peculiarities established, become or-
ganiied, flxed, and transmitted to posterity.

It is probably in this way that, in the course of the evolu-
tion of the various groups of aninaals, they have come to vary
so much in their choice of diet and in their digestive proc e ss e s,
did we but know them thoroughly as they are; for to assume
that even the digestion of mammals can be summed up in the
.Bunple way now prevalent seems to us too broad an assump-
tion. The flfild is very wide, and as yet but little explored.

TTie ktw of rhythm is i/lustrated, both in health and disease,
in striking ways in the < v'^itive tract. An animal long accus-
tomed to eat at a certain iaz ' <r of the day will experience at that
time not only hunger, but other sensations, probably referable
to secretion of a certain quantity of fhe digestive juices and to
the movements that usually accompany the presence of food in
the alimentary tract Hence that '* colic " so common in horses
fedat irregular times and unwisely, after excessive work, etc

It is well known that defecation at periods fixed, even within
a few minutes, has become an established habit with hosts of

▼cry gmeral
of muaoular
>l«a,butTMry-
lility; thaab-
ermining the
ratflow of the
1 abiorptioti,
ir^ion of the
■ we are led
inredly to the
n be exactly

habitually
I it that each
at another ia
, the digeetive
[o UtUe below
M a fact, as it
eculiaritiea of
> aa such, and
ugh ill-under-
ai elsewhere,
animali, as to
id, become or-

of the eroln-
I come to vary
itive processes,
for to assume
ned up in the
td an assump-
ezplored.
th and disease,
lal long acous-
arience at that
lably referable
B juices and to
inoe of food in
imon in horsea
ive work, etc
id, even within
with hosts of

0I0E8T10N OF PUOD.

tas

people; and the same is to a deg r ee true of dogs, etc., kept in
confinement, that are taught cleanly habits, and encouraged
therein by regular attention to their needs.

This tendency (rhythm) is important in p r es er r i ng energy
for higher ends, for such is the result of the operation of thia
law everywhere.

Th» taw of eorrtlation, or mutual dependence, is well
illustrated in the aeries of organs composing the alimentary
tract.

The condition of the stomach has its counterpart in the
rest of the tract ; thus, when Bt. Martin ha ' a disordered
stomach, the epithelium of his tongue showed corresponding
changes.

We have already referred to the fact that one part may do
e^tra work to make up tor the defldenciea in another.

It ii confidently aaMrted of late that, in the case of persons
long unable to take food by the mouth, nutritive substancea
given by enemata find their way up to the duodenum l^ aati-
peristalsis. Here, then, is an example of an acquired adaptive
arrangement under the stress of dreumstanoea.

It can not be too much imp re ss e d on the mind that in Che
complicated body of the mammal the work of any one organ
is constantly varying with the changes else«'here. It is this
mutual dependence and adaptation— an old doctrine too much
left out of sight in modem physiology— which makes the at*
tempt to eompUfMy unravel vital processes well-nigh hopdess;
though each accumulating true observation gives a better in-
sight into this kaleidoacopio mechaninn.

We have not attempted to make any statements as to the
quantity of the various secretions discharged. This is large,
doubtless, but much is i»obably reabsorbed, either altered or
unaltered, and used over again. In the case otfittnke, Uie con-
ditions are so unnatural that any conolnsions as to the normal
quantity from the data they afford must be highly unsatisfac-
tory. Moreover, the quantity must be very variable, accord-
ing to the law we are now considering. It is well known that
dry food prondEee a mofe abundant discharge of saliva, and
this is doubtless but one example of many other relations be-
tween the character of the food and the quantity of secretion
provided.

Xvolntiaa. — We have from time to time either distinctly
pointed out or hinted at the evolutionary implications of the

laiJu Bi iMJ V"m. » f M Hmmx tllhn

wwnma iiwa u i j f i

H Hi J iti jnsj' ^iU M. 'f ea wyi n ' i'Wj ' Mim WH ' w w »

864

COMPARATIVE PHYSIOLOGY.

facta of thin department of phyriology. The Btructufe of the
digeetive organs, plainly indicating a riling icale of oontplexity
with greater and greater differentiation of function, ia, beyond
queation, an evidence of evolution.

The law of natural aelection and the law of adaptation,
giving riie to new forma, bnve both operated, we may believe,
from what can be observed going on around ua and in our-
aelvea. The occurrence of tramdtional forma, aa in the epi-
thelium of the digeative tract of the frog, ia alao in harmony
with the conception of a progreaaive evolution of atructure and
function. But the limito of apace will not permit of the enu-
meration of details.

luunary.— A very brief riswmii of the auhject of digestion

will probably aufflce.

Food is either organic or inorganic and comprises proteids,
fats, carbohydrates, salts, and water ; and each of these must
enter into the diet of all knowii animala. They must also be
in a form that is digestible. Digestion is the reduction of food
to such a form that it may be further dealt with by the aliment-
ary tract prior to being introduced into the blood (absorption).
This is efltoted in different parte of the tract, the various con-
stituento of food being differently modified, aooordmg to the
secretions there provided, etc. The digestive juices contain
essentially fermento which act only under definite conditions of
chemical reaction, temperature, etc.

The changes wrought in the food are the following : starches
are converted into sugars, proteids into peptones, and fate into
fatty acids, soaps, and emulsion; which alterations are effected
by ptyaUn and amylopain, pepsin and tiypsin, and bile and pun-
creatio steapsin, respectively.

Outside the mucous membnoie containing the glands are
muscular coate, serving to bring about tiie movemente of the
food along the digestive tract and to expel the fteoes, the oirou-
lar fibers being the moro important These movemente and the
prooenes of secretion and so-called absorption an under the
control of the nervous vystem.

The preparation of the digestive secretions involves a series
of changes in the epithelial cells concerned, which.can be dis-
tinctiy traced, and take place in response to nwvoos stimula-

These we regard as inseparably bound up with the healthy
life of the cell. To be natiual, it must secrete.

ructura of the
I of oomplexitjr
ion, ia, beyond

of adaptation,
re may believe,
us and in our-
ai in tiie epi-
lao in harmony
f structure and
mit of ihe enu-

Bot of digestion

priiea proteida,
. of theae muat
ey muat also be
duotion of food
by the aliment-
3d (absorption),
he varioua oon-
joording to the
juioea contain
ite conditions of

Dwing: starches
Bs, and fats into
ions are effected
nd bile and puo-

the glands are
Dvements of the
fteoes, the drou-
irements and the
n are under the

involves a series
rhieh.can be dis-
lervooB stimula-

irith the healthy

i mii pw

D10B8T10N OF FOOD.

165

The blood-vessols of the stomach and int«stln« and the villi
of the latter receive the digested food for furth*r,r elaboration
(absorption). The undigested remnant of food and the excre-
tions of the iut*«tine make up the fasces, th« latter being ex-
pelled by a series of ooKirdinated muscuUr movements essen
tially reflex in origin.

i taw>. » iwiw « f ' '

THE RESPIRATORY SYSTEM.

Ik th« nunkinud the Iwwthing orguui are lodged in s oloeed
oavity, Mpuwted by a muaoular partition from that in which
the digeatire and oertain other organs are contained. This
thoracic chamber may be said to be reaenred for circulatory
and respiratory organs which, we again point out, are so related
that they really form parts of one system.

The mammal's blood requires so much airation (ventilation)
that the lungs are very huge and the respiratory system has
become greatly spedaliied. We no longer find the sUn or ali-
mentary canal taking any large shivr in the process; and the
lungs and the meolumisms by which they are made to more the
gases with which the blood and tissues are concerned become
very complicated.

Our studies of muscle physiology should have made dear
the fact that tissue-life implies the constant consumption of
oxygen and discharge of carbonic anhydride, and that the pro-
ceases which give rise to this are going on at a nq>id rate; so
that the demands of the animal for oxygen constantly may be
nadily understood if one assumes, what can be shown, though
less raadUy than in the cmw of muscle, that all the tianies are
constantly cmring, as it were, for this essential oxygen— well
called "vital air."

Beq>iration may, then, be regarded from a phyrioal and
chemical pohit of view, though in this as in other instances we
must be on our guard against regarding physiologioal processes
as ever purely lAiysical or purely chemical. The respiratory
process in the mammal, unlike the frog, ooniiats of an active
and a (largely) paarive phase. The air is not pumped into the
lungs, but sucked in. So great is the complexity of the lungs
in the mammal, that the frog's lung (which may be readily
understood by blowing it up by inserting a small pipe in the
glottic opening of the animal and then ligaturing the distended

mmili-'.

Iged in s oIoMd
that in which
ntdiMd. This
for oirouUtory
t, are lo related

sn (ventilation)
ory ■ystem has
the ddn or ali-
rooeai; and the
ide to move the
loemed heoome

vn made dear
xnunimption of
id that the pro-
a rapid rate; eo
utantly may be
I ahown, though
1 the tiamee are
1 oxygen— well

a phyaioal and
Mr inatanoea we
logfaal prooeM W B
The respiratory
Ota of an active
^omped into the
ity of the lungs
may he readily
nail pipe in the
ag the distended

••mmm

mtmm''

BPflilP

,M|l. | llMll ii U i l.| l illU |

THK BJWnRATORY SYSTEM.

organ) may be compared to a single infundihulom of the mani>
malian lung.

Aaniming that the student Is somewhat oonveraant with the
onane and fine anatomy of the respiratory organs, we call at-

Vis. »».— Lnngi, antwior *tew (SqiiMy). 1, nrnwr loba of left Inng; S, lower lobe; 8.
flimre; 4, notch c onee p oiidiM to apei: of beart; S, pericarMnm; 6, np|wr tobe of
rlfiU laiw; 7. middle lobe: C lower lobe; 0, aMure: 10, flMore; 11, diaphrma;
iCmtertor medlMthium; a. thyroid gland; 14, middle cervical aponeaMele: 16.
pnweea of attachment of mediaallnnm to pericaidlam; 10, M, eerenth rUw; 17, 17,
tianavenalaa mnadae; IS, linea alba.

tention to the physiological ai^eets of some pinnts in their
structure. The lungs rep re se nt a membranous wcpansion of

368

COMPARATIVK PHYSIOLOGY.

(Treat extent, liiied with flattened cell* and supporting innu-
merable capillary blood-vessels. The air is admitted to the oom-

Fi«v«»-B«?^.«2*I'!2<?'i>2^SL::!Z

1, 1, iiimmlt at Inn; 9, %

plicated foldings of this memh«ane by tubo which remain,
tiiroughout the greater part of their ertent, open, being com-
posed of cartilaginous rings, completed l^ soft tisroes, of which
plain pmscleHsells form an important part, serving to main-
tain a tonic resistance against pulmonary and bronchial prese-
ure. as well as serving to aid in the act of «iaghing, etc.,
BO important in expelling foreign bodies or preventmg their

*°*Se bronchial tubes are lined with a mucous membrane,
kept moist by the secretions of it* ghmds, and covered wi^
cUiated epitheUum, as aie also the nasal passages, whwh, by
the outward current* they create, favw diffusion of gases and
removal of excess of mucus. The thoracic walls and the lungs

porting innu'
ed totheoom-

nmlt of Iny*; 9> >>
tper lobe a« fiuifi; «.
lobe; 9, dhriakm to
inch; IS, left mrlcle
polmoiMnr Tein; 16,
gil^; 17, inferior vena

which remain,
pen, being com-
iames, of which
rving to main-
Iwonohial prees-
oooghing, etc.,
reyenting their

ous membrane,
id covered with
ages, whids by
ion of gaaes and
is and tilie lungs

THE RESPIRATORY SYSTEM.

369

themselveB aw covered with a tough but thin membrane hned
with flattened oella, which aecrete a mnaU quantity of fluid
that serve* to maintain the aurrouading parta in a moiat con-

b7ta)wU<«. fram the hmiiMt inbleet (Bol&^

ditioB. thus knening friction. The importance of this ai^
rangemeht is well seen when, in otmsequence of inflammation
of this pleum, it becomes dry, giving rise during each reapira-
toiy movement to a frictionHwund and a painful sensation.
It will not be forgotten that this membrane extends over the
diaphragm, and that, in consequence of the lungs completely
filling all the space (not occupied by other organs) during every
position of the diest-waUs> the costal and puljnonary pleural
surfooes a«e in constant contact By far the greater part of
the luBifWibstance conaiste of elastic tissue, thus adapting the
principal xef^ratory organs to that amount of distention wid
recoil to which they are oeaseleasly subjected during the entire
lifetime of the anima}.

8T0

COMPARATIVE PHYSIOLOGY.

Fitt. WL-BMtfoB «C tt*,.—
mmuf mrtm (BAalM).
biiHieh.

amBAMcni Ain> wot or Mm,

Since the lung, an up » «»nipl«Wy ««» *«^*,°S^^
.mSl/anyXnge in the me of «h. ktter m«-k !«*.*»
^r^lrSLn in the q«mtity of «2^^-
SLetheairwitWn flie ««^«*«^ ««^ ^JJ^ SJiS«S
XdS it. oxygen, «id ««»•>«;* ^j^^^^-JJ^^,
oarbonie dioxide,the former murt he renewed and tte uwer

ooSlW^ thi. in the m«nmri, ^^^.P^f*^ J^Sthedie

the thoi«5ic e«Yity in the «nte.«MP«rt«w^^
chert, in confluence, geto wider from *°^ *2™ w 4?IJ^
th^vS«di«neter; which i.«o»ov«r«rtrtBd^eem^
^iSfLtower border, of the rib.; «ul, tftoeoonve^^

^phragm were dimini.hed by ita «^?«*^ S^^SSSTTn
S«wen?Uwould foUowthrt the chert would be increwed in

It; ft, •mall arterUU

Junacie osvity,
r mmfc ImwL to
ir <h«7 contain,
eing oonstanily
ihe additUm of
and «he latter
M> dowly to ao-
aadaled by the
to aitiir the dw
>1a^obiiqueiy,
) eiilarg*«n*Bt of
etar; uid,astiie
nmtravd, alao in
Btedbyiheevei^
oonvMcityotihA
and oonMMl«nt
be inereaaed in

III ' m i « i iW i i^^ %» iW ji mt',>,"_Wi,i i T

THE RRSPIRATOKY SYSTEM.

871

the vertical diameter also. All thew events, favorable to
the entrance of air, actually take place through agencies we
must now considpr. The student is recommended to look into
the insertion, etc., of the muscles concerned, to which we can
only briefly refer. We have made the deaoriptions and cuts
appUcable to man, so that it may be easy for the student to ver-
ify all essential points on his own person. Respiration in our
domestic animals is in the main as in man.

The act of insi»ration commences by the fixation of the
uppermost ribe, beginning with the first two, by means of the

wofent ma80les,thiB act being followed up by the contraction of
the external intcMoatals, leading to the elevation of the other
riba; at the same tima, the arch of the cUaphragm desoendsm
Qonaeqaenoe <rf the cimtraetioo of its various ^UKJular bundles.
Undw theae cinsunwhuioes, the air fwan without muat rush in,
or a vacaum be ftmffled in the thoracic cavity ; and, since there

872

CX)MPARATIVB PHT8I0L00T.

u free acrm for the air through the glottic opening, the lungs
are of neoeauty expanded. This ingoing air has haid to over-
come the elaatio renatanoe of the lungs, which amoonta to about

Fi«. viL-AppuatiM to UhHtnte Ntatkn* of tetM'ttwNide and •st(!!"^_P!!f*K!!
Ofter BeiwnSr^ A giMt bell-Jw 1; pwwMrf with • ^tttapprnj^trngi wJfch
liMM« a iMwAtag gW tabe fltud with • pair of elaMc bi«i rq»MBtiii|( iDBg^
fSebottom of iS ^ !• eloMd by niMMr nambiMM npnamtiiiK dUphncm. A
™,iajiMii MnT r^-"' "— the difltnww in h«moi« within ud withoat ttw
^H/. IaMt-hmlflciueltwinbeMenthat&MpnMiirMM««qoia:lnrigfat
(in«>ii«tloiit, the mctemal |H«Mni« U ooMiteably gnattr. At one part («> as
eiaMo meidmne flIU a bole in Jar, lepnaentlng an iBtereoatal i

flVe niilliiaeteea of mercury in man, as ascertained by ^ying m
manometer in the windpipe <rf a dead sal^ect, and then opening
the thorax to jagualiie the iniide and outside {ffeasurea, when

the lungs at once collapse and
^e mancnneter shows a rise of
the mercury to the extent indi-
cated above. To this we must
add the influence of the tonie
contraction of the bronchial
muscles before referred to,
though this is probably not vevf
greet

That there are varialaons of
intrapnlmonaty pressure may
be aseentained by connecting a
uianwn etw with on<$ nostrilr-
the other being closed— or with
the irindppe. The mercury
l^).'*LkSigmiY£«t^watSI?5i show* a nogative pressure with
«»u«»^ mtMcoatai; 8, inianai in- ^^^^ in.pi»tory, and a positive

Bto. aw.— Oonal view tH fonr vartebnt
and thiee attached riba, iiM>wfn|rat>
tacbmeni of elevator jnudea oTrlbe
and intereoatiUe (after Allen Tlior

ing, the lungB
I had to over-
onntB to about

iiwr, thioagli wUeh
npnMBtlng luiigi.
tugdUphnin. A

«M«aqiUkl:terigfat
Atone iNirt(«>aa:

aed by ^ring »
1 then opening
seoBures, when
se oollapeeand
ihows a riae of
he extent indi-
) thia we must
le of the tonio
the bronohkil
referred to,
>bablynotT«f

!ev«riBlioiiB of
preesuxe may
>y oonnecting a
I on<$ nostril —
sloeed— or with
The mercury
i preamuewith
,anda poritiTe

THE RESPIRATORY 8Y8TBBL

878

with each expiratory act This may amount to from 80 to 70
millimetreawith strong inspiration, and 60 to 100 in forcible ex-
piration.

When inspiration ceases, the elastic recoil of (he rib carti-
lages and the ribs themselvM, and of the sternum, the weight
of these parts and that of the attached muscles, etc., assists in
the return of the chest to its original position, entirely inde-
pendently of the action of muscles. Moreover, with the d«^
scent of the diaphragm the abdominal viscera have been thrust
down and compressed together with their included gases; when
this miucle relaxes, they naturally exert an upward pressure.
Putting these events together, it is not difficult to understand
why the air should be squeeaed out of the lungs, the elasticity
of which latter is. as we have shown, an important factor in

itself.

Tht MwdM of B«pintiOB.— The diaphragm may be con-
siderad the most important single respiratory muaole, and can
of itself maintain respiration. The
aeateni are important as fixators
of the ribs ; the levatorea eoata-
rum and exterTial intenxmtals, as
normal elevators. The quadra-
tua himborum assists the dia-
phiaiill by fixing the last rib.
These, iHth the terrahta poatieua
supertor, may be regarded as the
prindpal musdes called into w>-
tion in an ordinary inspiration.
The muscles used in an ordinary
expiratory act are the intemal in-
tercotlah, the MunguJaris stemt,
and sarratuB po$tieu9 inferior.
In forced inspiration the lower
ribs are drawn down and re-
tracted, giving support in their
fixed pocdtion to the diaphragm.
The aoaleni, pectOrales, serratus
magnus, latiasimus dond, and oth-
ers axe called into actio n ; hu t
when dyspnoea becomes extreme, , , .,

as in one with a fit of asthma, nearly all the musoks of the
body may be called into phiy, even the muscles of the face.

Vm. aw.— U rympweoplc view* ot

CMrmak). I. Lannx fa qaiet
btMthtag. n. I>Bufiac«dMpiii-
nlMtiaa. In this ewe Um Hnga
<aOte tndiMt and eonmieMe-
KMDt or-1m»elit ate viiible.
Bach a coMHtkm to penieteiit in
■nnrfonna of diaeaae ta wkt^
tig^atkiB to attended with dlf-

874

COMPARATIVE PHYSIOLOGY.

which are not normaily active at all or but very ulightty in natr

und breathing. . ^ s v •

Faeial and laryngeal retpiratim is be«t seen in «uch ani-
maJi as the rabbit, and it is this condition which is ap-
proximated in disordered states in^"*"-;™ '«»»' "J'^.w?
S^ToMiM inspiration is very labored (asthma, diphtheria,

''^ in man and most mammals, unlike the frog, ttie glottic
opening is never entirely closed during any part of the respira-
imy act, though it undergoes a rhythmical change of site.

FM.M6.

Fi«.tM.

(Star hSS^. T^Wcto; 0, •urietoi: r,ne^mxp, V*f»*^i ♦v™«*' ^
Fio. $».-^m oi Uh (peich), to Hln^Me i^la^ona 9t iittmmi Wooa-T«*«i, «c..

iewinaoMHMcUoii; V, bnncMal wlii; «, ». bfMicIwii of •rterjr and Ttfn n-
cpeetffdy.

widemng during ins^ration and narrowing during .expiration,
in aooordanoe with the action of the musclea attached to the
arytenoid cartilages, the action of which may be studied in man
by means of the laryngsoope. , . i ^

■Hie abdominal muscles have a powerful ihythmical aotMm
during fawsed respiration, though whether they function du«w

|j»j i VN wi ^ *»"t i i' . i j''»i»' ^ ' ii ' ^" * V ''*'' » "'''''i'* *^*" '' '"

»il Ot to«4 ttNlWM(»W»W H g . B H >F» ^

III III li i^irrii'ii^ilMi

Ightly in nai-

in nioh ani-
vhich is ap-
, when from
i, diphtheria,

g, (he glottic
if the reapira-
ange of size,

mftm) ttnmi^ heart
swdimn; i. niiMr, o,
L imntle lobes. ,
t bkMNl-T«eede, etc,
i B. tmnehlal aicli

•ing .expiration,

attached to the

studied in man

yihmical action
y function dur-

THB RBSPIRATORY 8TSTBM.

ing ordinary quiet breathing ia undetermined ; if at all, prob-
ably but lUghtly. Though the removal of the external inter-
coetalH in the dog and some other animahi rereali the fact
that the internal iniercoatals contract alternately with the dia-

Fis 100— Diunmof •eomlon.iiMMitvf the appandafea baving beennmoTed (after

poaltion of ventiml gwq^loiiated Mnl: ff, S**"!* .■?"*??L^uS5"* jST #5'
■S^JISSatotWentlrtrMntte. IV, V.VK ba«a Jotota o« pilpilpl and two fol-
lowing pain of limb*.

phragm, it must not be regarded as absolutely certain that such
is their action when their companion muadea aie present, for
Nature has more ways than one of aocompUshing the same
purpose— a foot that seems often to be forgotten in reasoning
from experiments. This result, however, carries scnne weight

withit

TypwafBM|lnitioiL— There are among m a mmals two pnn-
oipal types of bveathing recognujable— the costal (thoracic) and
abdominat-aooovding as the movements of the diest or the
abdomen (diaphragm) are the more pranounced.

Ftiminl ObiaititlaB.— The studmt would do well at Uiis
stage to test the statements we have made in regard to the respirar

tory movements on the human subject especially. This he can
very well do in his own person when stripped U> the waist be-
fore a minw. Many of the abnormalities of the forced rea^rsr
ation of disease may be imitated— in fact, this is one of the
departmenti of phydology is -^^lioh the human tapecto may be

'.Mf

876

COMPARATIVE PHYSIOLOGY.

examined into by a ipeoies of experiment on one'* lelf that is
aa simple aa it is valuable.

OMiptntiVt.— It is hoped that the yarious figures accompa-
nied by descriptions, introduced in this and other chapters, will

rM.ao>.

I'M. SOI.

Fia. aOl.-A. PnliDOiM»y vut. B. Rwplratoqr tadiato of «wrpto oeMmtu (tftw
]^, iwlSSairriSSSftoj hg, •tin-. Of opMiDg foformer.

make the relations of the circulation and respiration in the va-
rious classes of animals, whether terrestrial or aquatic, evident

tiuS ■ecmi to lie OB ilgfct iuteM or len mm.
Without extended treatment of the subject in «iet«rt. What
we are desiroos^f impressing is that throughout the entire
animal kingdom respiration is essentiaUy the same process; that

»H i irj."i i i i j i i iii rTM .«

Mfcl!M*fe#i^wiSl*m»i*«««>»«i

M a SMaM ii Maiki> l »'"'"'"'«L ' ' i * i ''' ' ' """ '1 '^"

m's aelf that is

^rMBOcompa-
' ohaptera, will

7)lo oceltantu (after
ipUar (•(tw Oogte).

ktion in the t»-
iquatio, evident

Irw

aj). n, nwMi mm; a,<
■Dcken: d, opeicatar
nt of hind-ltmb; k. »,
m nvelMd, this aper-

thetext. What
^hout the entire
me procen; that

THE RESPIRATORY SYSTEM.

877

finally it vmtlrtt itwM into tiwue-breathinfr-the appiopriaUon
of oxygen and the exoietion of carbon dioxide. Since the man-
ner in which oxy-
gen is Intro
into the lungs and
foul s^mn expelled
trom them in some
reptiles and amphib
ians is largely dif-
ferent from the
method of respirflr
tion in the mam«
mal, we call atten-
tion to this process
in an animal readily
watched— the com-
mon frog. This
creature, by depress-
ing the floor of the
mouth, enlarges his
airnq^aoe in this re-
gion and conse-
quently the air free-
ly enters through
the nostrils; where-
upon the latter are
closed by a sort of
valve, the glottis
opened and the «ir
forced into the lungs
by the elevation of
the floor of the
mouth. By a series
of flank movements
tha dastioity of tbe
lungs is aided in
expelling the air
through the now
open nostrils. The
reepirati6n of the
turtle and some oth-
er reptiles is somewhat similar.

Flo.

804.— Oensral view of ah;*Merroli» of d»ck,

of trank (after Bappey). 1, 1, anterior extremity or

dIapliragmattcreaerTotr: 4, PMtoriordltto; 8. i^tom-
indrawrToIr; a. memtaime fomaiiiK anterior dla-

.hraomatie leaervolr; b, membrane f wmtafpaaterior
iutoT^iSAIon of tlioii«KM*dMnlnal dli5l«««: d.
rabpecteal pMlongaUon of ttoracic w«w»olr; «,
^tGaSm\f, ll*w; g, ■iaaard: A. iDt«Ntin«Ni; m,
hMitMt Ml Mctton of smS pectoral maacle above ita

terior clavicle of right aide cut and turned outward.

In the case of aquatic a nimals ,

M«niM4rMMMtMi

878

COMPARATIVB PHYSIOLOOY.

both invcvtolmito and Tertobrnto, «soeptinf maminalis the blood
ia fraely exponed in the gills to oxygen diMolred in the water m
it is to the same gas mixed with nitrogen in terrestrial animals.
In the land-snail, land-orah, etc., we have a sort of intermediate
condition, the gills being kept mdst. It is not to be forgotten,
however, that normally the respiratory tract of m a mm als is
never other than slightly moist.

QOAKimW OP An

We distinguish between the quantity of air that usually is
moved by the thorax and that which may be respired under
special effort, which, of course, can never exceed the capacity
of the respiratory organs.

Aceovdingly, we recognise: 1. TidtU air, or that which
panes in and out of the res^ratory passages in ordinary quiet
braathing, amounting to about 600 cc., or thirty cubic inches.
8. Onplementol air, which may be voluntarily inhaled by a
forced inspiration in addition to the tidal air, amounting to
1,600 cc., or about 100 cubic inches. 8. SupplemmUal (reatrve)
air, which may be expelled at the end of a normal respiration
— i. e., after the escpol'don of the tidal air, and which represents
the quantity usually left in the lungs after a normal quiet ex-
piration, amounting to 1,600 cc. 4. Reriduai air, which can
not be voluntarily expdled at all, amounting to about 8,000 cc.,
or ISO ouMc inches. Although these quantities have been esti-
mated for man, proibaUy a similar relation (i»oportion) between
them holds for the domestic aainals.

The oitolcapaot'ty is estimated by the quantity of air that
may be eiq^ired after the most forcible insphwtion. This will,
of course, vary with the age, which determines largely the elas-
ticity of the thorax, together with sex, position, height, and a
variety of other circumstances. But, inasmuch as the result
may be greatly modified 1^ practice, like the power to expand
the chest, the vital capacity is not so valuable an indication as
might at first be supposed.

It is important to bear in mind that thetUalairis scarcely
more than sufBdent to fill the upper air-passages and larger
Iwonohi, so thai it requires from five to ten respiratioos to re-
move a quantity of air in^ired by an (Midinary act Very much
must, flierefore, depend on diffusion, the quantity of air remain-
ing in the lungs after each breath being the sum of the residual

»t iimu l )« ll ll i »' » iu«W< i>

lala, the blood
I the water M
trial animals,
intermediate
be forgotten,
mammala ia

lat oiually is

espired under

the oapaoity

ir that which
ordinary quiet

oubio inches.

inhaled by a
amounting to
mtal (reasTM)
tal reqtiration
ioh represente
mial quiet ex-
tlr, which can
ibout S,000 cc.,
lave been esti-
'rtion) between

ity of air that
n. This will,
irgely the das-
, height, and a
as the result
wer to expand
i indication as

air is scarcely
les and larger
Irations to re-
;. Very much
of airremain-
of the residual

THR RB8PIRAT0RY SYSTEM.

879

and reserve air, or about 8,S00 oo. (8S0 cubic inches). Consider-
ing the creeping slowness of the capillary circulation, it would
not be supposed that the respiratory process in ite essential
parts should be the rapid one that a greater movement of the
air would imply.

.TORT

In man, and most of our domestic mammals, a deRnito
though somewhat different relation between the cardiac and
res^ratory movements obtains, there being about three to Ave
heart-beats to one respiration, which would make the rate of
breathing in man about sixteen to eighteen per minute. Usual-
ly, of course, the largest animals have the slower pulse and res-
piration ; and this is an invariable rule for the varieties of a
spedes, as observable in the canine race, to mention a well-
known instance. The horse breathes 9 to 19 times in a minute ;
the ox 15 to SO ; the sheep 18 to 17 ; and the dog 16 to SO.

The rate of the respiratory movemento is to some extent a
measure of the rapidity of the oxidative pr oces se s in the body^
as wituesB the slow and intermittent breathing of cold-blooded
animals as compared wttb the more rapid respiration of birds
and mammals (Fig. 808).

PsthfllogiMd.— Any condition that lessens the amount of re-
spiratory surfooe, or diminishes the mobility of the chest-walla,
is usually accompanied by accelerated movements, but beneath
this is the demsod for oxygen, part of tiit avenues by which
this gas usually enters having been dosed or obstructed hy the
disease. So that it is not surprising that, in consequence of
the eflhision of fluid into the thorado cavity, leading to the
compression of the lung, the opposite one should be called into
more frequent use, and even enlarge to meet the demand.
These fiscto show how urgent is the need for constant ventila-
tion of the blood, and at the same time bow great is the power
of adaptation to meet the emergency.

The difllerence between the inspiratory and the expiratory
rhythm may be gathered by watching the ntovements of the
bared chest, or m<»« aoouratdy from a graphic record. It is
usually considered that ex^ration is only sightly Itmger than
ini^ifation, and that any marked deviation from this relation
should aioose snsjndon of disease. NormaUy the respiratory
pause is very slight, so that inspiniti<m seems to follow directiy

880

COMPARATIVE PnYSlOLOOY.

f'*

on expintion ; though the latter act ranindi vm of the pro-
longation 0^ the Tentriottlar qntole after the blood ia expelled.

. tAA^a -^AAt

VAiWVUVlA/lM

bMUs'i^alt dog; W. rabbit: 11, nuui: lk d(«: IS, bone. CompHW tbMe. aad
note that in n/ mplnition la aballow, and In MTdWip.

i | M|l| l U I IJH i * i MHi i>* <HW^— "l ii '" '*W*'^*— ^'* "* ' *' ''"

jimwiii iimi 1 1 ii'ii i ri «ii ii iV iii i' ii ' i t'' i "' '■'*•"'■

MmacMMMi^rii

u of the pr»
d is expelled.

—Vi

inHmmm

mmmffif'

rWYlAnAfW

iloaftnff to dUfctent
ina«|>ih,fiMMiieT.

ortolie; 8, Mder <in
7, Itaard; S. CMury-

Compare thMe, aiid

THE RIWP1RAT0RY RT8TKM.

If, in the tHMsing, the wauAl w»Tee on the upper purt of the
expimtory ourre reidly repreient the effect of the heart-be^
it makee it eaeier to uudentend how aooh might Miiit in ▼entl-
IsUng the blood when the reepimtions occur only once in •
eondderable intenral and rery Ibebly then, m in hibernating
anlnuOi or indiriduala that hare fainted ; though it must be
mnembwed that diffuilon ii a oeaMleM piooeM ui aU Uying
Tttiebratei.

Vie.

rnj wmui kuum iIiiMi ■ imnvvwrn

n«WMHMMMM||||

aMTot apwUMnt.

It ia Maioely neceewHry to point out that the renpiratory
movementi are inoteawwl by exerdw, emoUon*, podtiou, sear
■on, hour of the day, taking meals, etc.

SMpbatorj tkranda.— The entrance and exit of air are ac-
companied hy certain sounds, which vary with each part of the

882

COMPARATIVE PHYSIOLOf Y.

■wpiratory tract. To these aounda names have been given, but
in ihey are somewhat inconstant in their application, or at least
have several s3rnonym8, we pass them by, recommending the
student to actually learn the nature of the respiratory murmure
by listening to the normal chest in both man and the lower ani-
mals. With the use of a double stethoscope he may practice
upon hunself, though not so advantageously as in the case of
the heart

The sounds are caused in part by the friction of the ur,
though th«y are probably complex, several factors entering
into thohr causation. T •

OOMPABnOM OF THB IMSPIBBD AMD BZPIBBD AIR.

The changes that take place in the air respired may be brief-
ly stated as follows:

1. Whatever the condition of the inqrired air, that expired
is about saturated with aqueous vapo^-i. e., it contains all that
it is capable of holdmg at the existing temperature.

2. The temperature of the expired air is about that of the
blood itaelf , so that if the air is very cold when breathed, the
body loses a great deal of its heat in warming it The expired
air of the naud passages is slightiy wanner than that of the

mouth. , . . 11 j» •

3. Experiment shows that the expired air is really dunin-
ished in volume to the extent of from one fortieth to oiw fif-
tieth of the whole. Since two volumes of carbonic anhydi^e
reauire for their composition two volumes of oxygen, if the
amount of the former gas expired be not equal to the amount
of oxygen inspired, some of the latter must have been used to
form other combinations. ^, amounting to rather less than

1, is called the resi»ratory coeffldent ^

4. The difference between inspired and expired air in man
may be gathered from the fdlowing:

Oxjrgen.

Inspiredsir »mO

Expired air »«■«»_

Mttroften.

79-150

7»-»87

Owbonic diozlde.
(HMO
4-8B0

Fromwhicb the most important conclusions to be drawn
are, that the expired air is poorer in oxygen to the extent of 4
to B per cent and richer in carbonic anhydride to somewhat

tn given, but

I, or at least

unending the

ktory murmura

the lower ani-

may practice

■in the case of

|iou of the air,
;tors entering

d may be brief-

ir, that expired

mtainsall that

ire.

out that of the

pi breathed, the

k. The expired

um that of the

is really dimin-
tieth to oneflf-
<mic anhydride
oxygen, if the
to the amount
re been used to

Rather lenthan

red air in num

OHbonicdloKlde.
(HMO
«-8B0

IS to be drawn
the extent of 4
e to somewhat

THE RRSPIBATORY SYSTEM.

leas than this amount. A similar relationship may be considered
to hold for the domestic animals, ihe quantities varying, of course.

From experiment it has been ascertained that the amount
of carbonic dioxide is for the average man 800 grammes (406
litres, equivalent to 818*1 grammes carbon) daily, the oxygen
actually used for the Skone period being 700 grammes. But the
variations in such cases are very great, so that these numbers
must not be interpreted too rigidly. Experience proves that,
while chemists often work in laboratories in which the per-
centage of carbonic anhydride (from chemical decompositions)
reaches 6 per cent, an ordinary room in which the amount of
this gas reaches 1 per cent is entirely unfit for occupation. This
is not because of the amount of the carbon dioxide present^ but
of other impurities which seem |o be excreted in proportion to
the amount of this gas, so that the latter may be taken as a
measure of these poisons.

What than an is as yet almost entirely unknown, but tliat
they are poisons is beyond doubt Small efltete particles of
once living protoplasm are carried out with the bre a th , but
these other substances are got rid of from the Uood by a vital
process of secretion (excretion), we must believe; whidi shows
that the lungs to some degree play the part of glands, and that
their wh<de action is not to be explained as if they were merely
moistened bladders acting in ancordamie with ordinary physi-
cal laws.

An estimation of the amount of atmospheric air required
may be calculated tnm data already given.

Thus, assuming that a man gives up at each breaih 4 per
cent of carbon dioxide to the 800 cc. of tidal air he expires, and
bceathes, si^, seventeen times a minute, we get for the amount
of air thus charged in one hour to the extent of 1 per cent:
800 X 4 X 17 X 00 as 8,040,000 cc., or 8,040 Utres.

But if the air is to be contaminated to the extent of only -^
per oMit of earboDie anhydride, the amount should equal at
least 8,040 x 10 hourly. A very much largw quantity would,
of oonrae^ be required for a horse or an ox.

liiiaHitMtHMMHiiMitfiiHiMi^

mom VK

It may be noticed that arterial blood kept in a confined sprnx
grows gradually darkor in color, and that the original bright-
scarlet hue may be ijestored l^ shaking it up with air. When

L^i'^-is^iA*-' .^«^^ .,..!

-r-r '-"-af"

884

COMPARATIVE PHYSIOTiOGT.

the blood has vamtA through the capillariee and fCMshed the
veins, the color has changed to a sort of purple, chaxaeteristie
of venous blood. Patting these two f aoU together, we am led
to suspect that the diange has been caused in some way by
oxygen. Exact experimenti with an appropriate form of blood-
pump show Oiat from one hundred volumes of Wood, whether
arterial or venous, about sixty volumes <rf gas vaaj be obtained :
that this gas oonsists ohieay of oxygen and carbonic anhydride,
but that the proportions of each present depends upon whether
the blood is arlraial or venous.

The following taUe will main this dear:

Arterial blood »

Venonsblood *-18

OMlMialeMilqrdride.
40
46

mtroRM.

from 100 volumes of blood at 0" C. and 7«0 millimetre pressure.
Arterial blood, then, contains 8 to 13 per cent more oxygen
and about 6 per cent more carbonic dioxide than venous blood.
It is not, of course, true, as is sometimes supposed, that arterial
blood is "pure blood ''in the sense that it contains no carbonic
anhydride, as in reality it always carries a: large percentage of

this gas. ....«• J

. TIm (koidttioBi udar wkkb dM CtaMt cadit ill tlM Blood.--

If a fluid, as water, be exposed tosmixture of gases which it
can absorb under pMBSuie, it is found that the amount taken up
depends on the quantity of the pariieular gas present independ-
ent of the presence or quantify of the others; thus, if water be
exposed to a mixture of oxygen and nitrogen, the quantify of
oxygen absorbed will be the same as if no nitrogen were pws-
ent—i e., the absorption of a gas varies with the porWoI press-
ure of that gas in the atmosphere to whidi it isexposed . But
whether blood, deprived of its gases, be thus exposed to oxygpni
underpressure, or whethmihe attempt be made to remove this
gas from arterial blood, it is found that the above^itated law

does not apji^y.

When blood is placed under the exhanstioii-pump, at first
very little oxygen is given off; then, when the pressure is con-
siderably reduced, the gas is suddenly liberated in large quan-
tity, and after this comparatively Uttle. A precisely an alogous
course of events takes 0aoe when blood itoprived of its oxygen
is submitted to this gas under pre ss u re. On the other hand,
if these experimeuts be made wifli mrum, absoiption follows

»Jltl ll iU»UMiai l K'l'Jll i Wl*fW ' ««* >

« i i < i >ilj|iliiM)i> li >iili» l r

I reaehed the
ohaneteriatje
ter, we are led
some way by
form of blood-
ilood, whether
y be obtained:
nic anhydride,
upon whether

tde.

MltraRMi.
1-8
1-8

metre presmire.
I more oxygen
TenouB blood,
d, that arterial
ns no carbonic
) pwoentageof

In the Blood.—
gaaea which it
noont taken np
aaent independ-
lUB, if water be
the quantity of
igen wefO
i partial :,
lexpoaed. But
HJied to oxygen
r to remove this
liove^itated law

ii-pamp,at fint
prenore is con-
in large qnan-
iiaely analogous
id of its oxygen
Ihe other hand,
KHption follows

THE RB8P1RAT0RT SYSTEM.

885

Hfocording to the law of pressures. Evidently, then, if the oxy-
gen is merely dissolved in the blood, such solution is peculiar,
and we shall presently see that this supposition is neither ne-
cessary nor reasonable.

sBMOou^oanr amd m SHBiVAnvBfl.

HsemogloUn oonstitutes about A of the ooi^pusoles, and,
though amorphous in the living blood-cells, may be obtained
in crystals, the form of which variai with the animal; indeed,
in many animals this substance crystallises spontaneously on
the death of the red cells. It is unique among albuminous
compounds in being the only one found in the animal body
that is suaceptiUe of crystallisation. Its estimated composi-
tion is:

Ovbon 88-86

Hydrogen.. 788

Nitrogen 1«17

Oxygen 21-84

Iron '48

Sulphur "S*

together with 8 to 4 per cent of water of crystallisation.

The formula assigned is: CM*HM/>inNiMFeBi. The molecu-
lar constitution is not known, and the above formula is merely
an approxhnation, which will, however, serve to oonv^ an idea
of the great complexity of this compound. The presence of
iron seems to be of great importance. If not the essentiaL re-
spiratory constituent, certainly the administration of this mMal
in smne f «rm proves Yvy valuable when the blood is deficient

in haemoglobin.

This snbatanoe can be recognised moai certainly by the qpeo-

troBoope. The appearances vary with the rtvength of the solu-
tion, and, as this tert for blood (haemogld^n) is of much prao-
tioal importance, it will be necessary to dwell a littie upon the
subject; though, after a student has once recognised <^early the
differences of the qpeetmm i^pearanees, he has a soai of knowl-
edge that no verbal description can convey. This is easily ac-
quired. One <m]y needs a small, flsinridedbottie and 1i pocket-
spectroscope. FUUng the hotae half full of water, and getting
the spectroscope so foeosed that the Frannhofer lines appear
distinctiy, blood, blood-stamed serum, a solution of hnnoi^
Mn crystals, <m> the e^pwntisl substence in any form of dihifte

aiii i ii i iflli i iW jIi OM i wa *

886

COMPARATIVE PHYSIOLOGY.

solution, may be added drop by drop till changei in the apeo-
trum in the form of cUtfkbanda appear. By gradually morea*-

ing the qtiantity, ap>
pearanoes like those fig-
ured below may be ob-
served, though, of course,
much will depend on the
thiokneas of the layer of
fluid a« to the quantity
to be added before a par- '
tioular band comes into
view.
^^^ ^^ When wishing to be

^^^^ \^ ^W^ precise, we speak of the

^ jK a,^^^ most highly oxidised
^^^ ^W^ yMr^^ jo,^ of hsemc^lobin as
•4Q|^^^^^ ^^^ ozy-hsemoglobin (0-H),

^^K^^* ^ and the reduced form as

^^^^^^ ^^^ haemoglobin nmply, or

^^^^^ A ^^ reduoedhaemoglobinCH).

WStl^^ ^^ By a comparison of

the spectra it will be seen
that the bands of oxy-
hsBmoglobin lie between
the i> and £ lines; that
the left band near Z> is
always the moet definite
in outline and the most
/nSViteii: " " pronounced in every re-

spect except breadth; that it is in ^^;f''^Z^^J^Z.
W. and the last to disappear on reducta<m; that t»««^ JT
Stances in which then, may be a «ngle band from hi^^
bia-in the one «»e when the solution is v«T ^ffl^f^^
iVfaW concentrated. These need never be misbjerf for each
^h J^r^X band of reduced b«»ogU>Wn The latter i^
hwy bioad band with comparatively indisbnct ouflmes, and

"•'hfl ^•f:^"noticed that m an ^^^^^^J^

from the b«ids,the spectrum is «*»»«;!^i-S?"^;il2S
end, K» that the d«.ker the mow centndly ptaced du««^««^

Wnthe more is the light at the same time cut off a* each
end of the spectrum.

>▲*

Fie. 807.' -

lobinCOMtiM). a,».
' of man; «■ fvm

?KSm^ JrSTGohSrpIg; *. or'»«mot,

«a in thespeo-
dually inoreM-
qtiantity, ap-
) like thorn flg^
)w may be ob-
Loughjofooone,
11 depend on the
I of the layer of
to the quantity
ied before a par- <
and comes into

a wiiihing to be
ire speak of the
ighly oxidised
haemoglobin as
aoglobin (0-H),
reduced form as
obiu fdmply, or
hsBmoglobin(H).
t comparison of
trait will be seen
s bands of oxy-
lobin lie between
mdJii lines; that
; hand near Z> is
the most definite
ne and the most
need in every re-
ns the first to ap-
bat there are two
I from hsemoglo-
dilute and when
mistaked for each
1. The latter is a
net oufiines, and

« ini^ces, apart
modified at each
iced charactoristio
ne out off at eaob

iHB . ! . . 1 i iiiiii i iii n i p wiiwpwifii l i | -- ii -i iii iir ii rT-ni-

THB RBSPIBATOBT SYSTEM.

887

wjasssasssKBaasJsWBSsrassswBKssis

888

COMPARATIVE PHYSIOLOGY.

If, now, to a gpecimen ihowing the two bands of oxy-hsemo-
fflobin distinctly a few drops of ammonium rolphide or other
reducing agent be added, a change in the color of the solution
wiU result, and the single haiy band charactenitic of h»mo-
globin will appear.

It is not to be supposed, however, that venous blood gives
this spectrum. Even after asphyxia it will be difficult to see
this band, for usually some of the oxy-hsemoglobm lemams
reduced; but it is worthy of note, as showing that the appear ,
anoes are normal, that the blood, viewed through thin tissues
when actually circulating, whether arterial or venous, gives
the spectrum of oxy-hsemoglobin. At the same time there can j
be no doubt that the changes in color which the blood under-
soes in passing through the capaiaries is due chiefly to loss of
oxvaen, as evidenced by the experiment before referred to : and
the reason that the two bands are, always to be seen in venous
blood is simply that enough oxy-hamoglobin remains to give
the two-band spectrum which prevails over that of (reduced)
haemoglobin. We are thus led by many paths to the important
conclusion that the red corpuscles are oxygen-camers, and,
though this may not be and probably is not their only func-
tion, it is without doubt ttieir principal one. Of their oxygen
they aro being constontly roUeved by the tissues; hence tiie
ne«issity of a circulation of the blood from a respiratory pomt

°* niro are other g«MB that can leplaee oxygen and fonn
compounds witti hasmoglobln; hence we have 00-hasmoglobin
and NO-hiBmogloWn, which in turn are replaced »>yo»y8«° ™
no Utfle difflc«lty-a fact which exphiins why <»f»»; °»?«»
«, fWal^hen respired, and, as t is a ^-^-tj'f"* *»' *"r^
"g^the causTof the dealhof those i»l^"»K «»r^"^»
oftennotfartoseek. Blood may, in fact, be satumted with
carbonic oxide by aUowing illuminating gas to Pass through i^
whena change of color toacherrywd may be observed, and
which wiUrMnain in spite of prolonged shaking up with air or
attempte at reduction with the usual reagents. : ,H»mo^n
mavto «««>lved into a proteid Cflobin) not well understood,
Td iELSi This hapjTwhen the hlo^ » »»«»lf (P^'^
also in certain cases of lightninr-trolce), and whim "^^K «««»;
are added. Hamiatln is soluWa in dilute adds and alkalies, and

SiSenduSSS.ap«^ ^^^^ ^^'IS^^TL^
duoed; and, as the iron can be separated, resulting m a change

of oxy-hsemo-
phide or other
of the solution
iatic of hsemu-

ua blood given
difficult to aee
{flobin remainB
Out the appear-
igh thin tissues
r venous, gives
I time thM<e can
le blood under-
ihiefly to loss of
referred to; and
I seen in venous
remains to give
latof (reduced)
to the important
m-carriers, and,
their only func-
Of their oxygen
isues; hence the
■espiratory point

cygen and form
OOhsemoglobin
1 by oxygen with
carbonic oxide is
entof illnminat-
ling the lattor is
B saturated with
> pass through iti
be observed, and
Qg up with air or
a. Haemoglobin
well understood;
is hoSM. (perhaps
rhen strong aoidB
aBdalkaliea,and
Doatinmaybe re-
Iting in a change

THE RESPIRATORY S78TBM.

889

of color to brownish red, after which there are no longer any
reducing effects, it would seem that the oxygen-canying power
and iron are associated. This iron-free hflamatin is named
Juematorporphyrin or heematoin.

HcBtnin is hydroehlorate of hsematin (Teichmann's crystals),
and may be formed by adding glacial acetic add and common
salt to blood, dried blood-clot, etc., and heating to boiling. This
is one of the best tests for blood, valuable in medico-legal and
other oases.

When oxy-hsemoglobin stands exposed to the air, or when
diffused in urine, it changes color and becomes, in fact, another
substance— mettomogiloMn, irreducible by other gases (CX), etc.),
and not surrendering its oxygen in vacuo, though giving it up
to ammonium sulphide, becoming again ozy-haemoglobin, when
shaken up with atmospheric air. Its spectrum differs from
that of oxy-hsemoglobin in that it has a band in the red end of
the spectrum between the C and D lines. HcemaMdin is some-
times found in the body as a remnant of old blood-dots. It is
probably closely allied to if not identioal with the bUirtMn
of bile.

Oompantiv*.— While hsBmoglobin is the reai^ratory agent in
all the groups of vertebrates, this is not true of the inverte-
brates. Red blood-cells have as yet been found in but a few
spedes, though haemoglobin does exist in the Uood phunna of
several groups, to one of which the earth-worm and several
other annelids belong. It is interesting to note that the respir-
atory compound in certain fiunilies of crustaceans, as the com-
mon crab^ horseshoe-crab (limulus), etc, is Uue^ and that in
this substance copper seems to take the place of iron.

TIm VitragtA ud tlM Oarbon Dtoddt of ik» Hood. -The
little nitrogen which is found in about equal quantity in venous
and arterial blood seems to be simply dissolved. The relations
of carboni<; anhydride are much more complex' and obscure.
The main foots known are that— 1. The quantity of this gas is
as great in serum as in Uood, or, at all events, the quantity in
serum is very laige. 2. The greater part may be extracted Iqr
an exhansticm-pump; but a small percentage (S to 6 volumes
per cent) does not yield to this metiipd, but is given off when
an add is added to the serum. 8. If the entire Uood be sub-
jected to a vacuum, the whole of the 00« fs given off.

From these facts it has been concluded that the greater part
uf the OOt, exists in the plasma, associated probably with sodium

am -mmi»!iims i

890

00MPARAT1YB PHYSIOLOGY.

aam M Mdium biearbonate, but t^ ^,be oorpuaolM in aome way
determine its relatioiu of asMciatk. and diaa«ooiation. Some
think a good deal of this gas is actually united with the red cor-
puscles.

We may now inquire into the more intimate nature of respi-
ration in the blood. From tlie facts we have stated it is obvious
that respiration can not be wholly explained by the Henry-Dal-
ton law of pressures or any other physical law. It is also plain
that any explanation which leaves out the principle of jwessure
must be incomplete.

While there is in oxy-hsBmogloUn a certain quantity of
oxygen, which is intnknioleoular and inc^wble of removid by
reduction of pressure, there is also a- portion which is subject
to this Iaw, though in a peculiar way ; nor is the question' of
temperature to be excluded, for experiment shows that less
oxygen is taken up by Uood at a high than at a low tempera-
ture.

We have learned that in ordinary respiration, the propor-
tion of carbonic dioxide and oxygen in different parts of the
respiratory tract must vary greatly ; the air of necessity being
much leas pure in the alveoli than in the larger bronchi.

It is customary to speak of the oxygen of oxy-hsemoglobin
as being in a state of ^ looae chemical combination." The en-
tire truth seems to lie in neither view, though both are partially
correct. The view entertained by some physiologists, to the
effect that diffusion explains the whole matter, so far, at least,
as carbonic anhydride is concerned, and that the epithelial cells
of the lung have no share in the respiratory pnloess, does not
seem to be in harmony either with the facts of respiration or
with the laws of biology in general. Why not say at once that
the facts of respiration show that, here as in other parts of the
economy, while physical and chemical laws, as toe know them,
stand related to the vital processes, yet, by reason o( being vital
proc es s es , we can not explain them according to the theories of
either physics or chemistry Y Surely this very subject shows
that neither chemistry nor physics is at present adequate to
explain such proc e ss e s. It is, of course, of value to know the
dronmstanees of tension, temperature, etc., under which respi-
ratioa takes place. We, however, nudntain that these are con-
ditions only e s sen tial no doubt, but though important, that
they do not make up the process of respiration. But, because
we do not know the real explanation, let us not exalt a lew

I in some way
biation. Some
llth the red oor-

kture of rMpi-
itisobrioiui
|the Heniy-Dal-
It fai aLm plain
fiple of jnvHure ,

quantity of
B of remoTal by
rhioh ia subject
the quflition'of
ihows that leM
a lowtemper»-

ion, the propor-
rent parte of the
' neoenity being
r branohi.
oxy-heemoglobin
lation." The en-
)oth are partially
viologietR, to the
r, 80 far, at leaat,
he epithelial cells
pnhieai, does not
of respiration or
t say at once that
othor parts of the
w we know them,
■on o( being vital
to the theories of
»ry subject shows
esent adequate to
ralue to know the
nder which respi-
hat these are oom-
h important, that
on. But, because
IB not eultalew

THB RESPIRATORY SYSTEM.

891

fiots or theories of chemistry or physios into a solution of a
complex problem. Besides, some of the experiments on which
the conclusions have been based are questionable, inasmuch as
they seem to induce artificial conditions in the animals oper-
ated upon; and we hare already insisted on the Uood being
regarded as a living tissue, behaving differently in the body
and when isolated ttom it, so that even in so-called blood-gas
eoqieriments there may be sources of fallacy inherent in the
nature of the case.

lonigB Qmw Ud iMfintiiB.— These are divided into:

1. Indit^erewt gcuea, as N, H, OH4, which though not in
themselves injurious, are entirely useless to the economy.

9. Poimmoue gaaee, fatal, no matter how abundant the nor-
mal respiratory food may be. They are divisible into : (a) those
that kill hy disphusing oxygen, as NO, 00, HON; (h) nareotie
gaaea, as 00«, NiO, producing asphyxia when present in large
quantitiee; (0) reducing goMs, as Bfi, (NH«)A PH., AaH., 0^«
which rob the haemoglobin of its oxygen.

There are probably a number of poisonous products, some
of them possibly gases, produced by the tissues themselves and
eliminated normally by the respiratory tract ; and these are
doubtless greatly augmented, either in number or quantity, or
both, when other excreting orgaaoM are disordered.

1.T1011 nf nno hmdml

We first direct attention to certain striking facts:
1. An isolated (frog's) musde will continue to contract for
a considenihle period and to exhale carbon dioxide in the total
absence of oxygen, as in an atmosphere of hydrogen; though,
of course, there is a limit to this, and a muscle to which either
no blood fiows, or only venous blopd. soon shows signs of
fktigue. 9. In a frog, in which physiological saline solution
has hem substituted for Uood, the metabolism will continue,
carbonic anhydride being exhaled as usual. 8. Substances,
which are readily oxidised, when introduced into the blood of
a living animal or into that bkmd when withdrawn undofgo
but little oxidative diange. 4. An entire frog'will respire car-
bonic dioxide for hours in an atmosphere of nitrogen.

Such facts M these seem to teach certain lessons deariy. It
is evident, first of all, that tlw oxidative pr oc e ss e s that give rise
to carbon dioxide opour chiefly in the tietuea and not in the

WfcB» ! jta^^Si.^ ■ n^-«^;l^ ! W^ l M i VJ^ ■ ^lfVK^^M:-^KJ. '^^r^B^

nRMKI

•J-

892

OOMPABATIVB PHTSI0L06Y.

blood ; that in the one of miunle the oxygen that « » <i is flnt
Uid by, banked M it were againet • time of need, in r form of
intra-moleoular oxygen, which ia again Mt free in the foruk of
oarbon dioxide, but by what eeriea of ohangee we are quite un-
able to My. Though our knowledge of the respiratory proocMee
of muwle ie greater than for any other tianie, there wenie to
be no reaeon to believe that they are wentially different elae-
where. The advantagca of this banking of oxygen are, of
ooune, obrioua; were it otherwiae, the life of every cell muit
be at the nieroy of the slightest interruption of the flow of
blood, the entrance of air, etc. Even as it is, the need of a
oofutofU supply of oxygen in warm-blooded animals is much
greater than in cold-blooded creatures, which can long endure
almost entire cessation of both respiration and circulation,
owing to the comparatiTely slow rate of qwed of the vital
machinery.

If one were to rely on mere appearances he might suppose
that in the more aotiye condition of certain organs there was
less chemical interchange (respiration) between the Mood and
the tissues than in the resting stage, or, properly speaking,
more tranquil stage, for it must be borne in mind that a living
cell is never wholly at rest ; its molecular changes are cease-
less. It happens, e. g., that when certain glands (salivary) are
secreting actively, the blood flowing ttma. them is less venous
in appearance than when not functionally active. This is not
because less oxygen is used or less abstracted firom the blood,
but because of the greatly increased q^eed of the blood-flow, so
that the total supply to draw from is so much larger that,
though more oxygen is actually used, it is npt so much missed,
nor do the greater additions of Mrbon dioxide so rapidly pol-
lute this raind stream.

It is thus seen that throughout the animal kingdom respiror
tion is fundamentally the same process. It ia in every case
flnally a consumption of oxygen and production of carbonie
anhydride by the individual cell, whether that be an Amcsba
or an element of man's brain. These are, however, but the
beginning and end of avery eomplioated Uologinl history (rf
by far the greater part of which nothing is yet kniown ; and it
must be admitted that diffusifni or any physical explanation
carries us but a little way on toward the understanding of it

in t )'■ f(»rmof
in the form of
ire we quite un-
tntory proocMei
there twemito
y different elie-
oxygen are, of
every cell muit
of the flow of
the need of a
nimals it mueh
Ban long endure
and cirouhition,
ed of the vital

B might nippoee
irgana there was
a the hlood and
Dperly speaking,
ind that a living
langes are cease-
da (salivary) are
im is less venous
tive. This is not
1 from the blood,
the Uood-flow, so
uoh larger that,
; so mudh missed,
le so rapidly pol-

kingdom leapim-
ia in every <»se
:tk» of carbonie
it be an Amoeba
aowevar, but the
login], history of
t known ; and it
noal explanation
ntanding of it

898

THK UBBPIRATORY 8Y8TBM.

iToot nvrmM m bbultion to
noN.

We have oonsidered the muscular movements by which the
air is made to enter and leave the lungs in consequence of
changes in the diameters of the air-inclosing case, the thorax.
It rtkoaini to examine into the means by which these muscles
were set into harmonious action so as to accomplish the pur-
pose. The nerves supplying the muscles of respiration are de-
rived from the spinal cord, so that they must be under the do-
minion of central nerve-cells situated either in the cord or lUe
brain. Is the influence that proceeds outward generated within
the cells independently of any afferent impulses, or is it depend-
ent on such causes t

A host of facts, experimental and other, show that the cen-
tral impulses are modified by afferent impulses reaching the
center through appropriate nerves. Moreover, drugs seem to
act directly on the center through the blood.

The vagus is without doubt the afferent respiratory nerve,
though how it is affected, whether by the mechanical movemeiit
of the lungs, merely, by the condition of the blood as regards
its contained gases, or, as' seems most likely, by a combination
of circumstances into which these enter and are probably the
principal, is not demonstrably clear. When others function as
afferent nerves, capable of modifying the action of the respira-
tory center, th«y are probably influenced by the respbratory
condition of the blood, though not necessarily exclusively.

But when all the principal afferent impulses are cut off by
division of the nerves reaching the respiratory center directly
or indirectly, respiration will still continue, provided the nwtor
nerves and the medulla remain intact.

The center, then, is not mainly at least, a reflex but an auto-
matic one, though its action is modified by afferent impulses
reaching it from every quarter.

It has been ai>gued that there are both inspiratory and ex-
pirakny centen in the spinal cord, but this can not yet be re-
garded aa established. But, as we have pointed out, on more
than one occasion, we must always be on our guard in inter-
preting the behavior of one part when anpther is out of gear.

Thtt JnH/miM tijbtb (kaiitim of th> Blood ia BwgfartiaiL—
If lor any reason the tissues are not receiving a due supply of
og^gen, fh«y manifest their disapproval, to speak flguratively.

j5!«a>«t»»WWJa»*rf!aR!3»E«(-sW-«K(V,..ji<»^

OOMPARATIVK PHYSIOLOOY.

I Brain (Onm iMdMttafnmi^Uh
k-(m|NiiM modtftlbm rtvtralbM

ttfftma MifWiM* prwMd <«<
fMlly to train.

mfinUUM

mtm»r f at$fnm¥ihUlk
I Oipiihw prwMtf dk

imilrfltoi"|f ifXHc«

iwtth

B of im p l w UoB. Aifowt

THB RIMPIRATORT 8Y8TBM.

895

by raporto to the ratpouiible center in the medulla, end if the
nwdulle is • ehnrer in the leek, m it natomlly would be, it takes
action independently. One of the nMiet obTioue inatancee in
which there ia oxygen etarvation ie when there i« hindrance to
the entrance of air, owing to obetruotion in the reepiratory tract.

At flnt the b r ea th ing ia merely accelerated, with perhapa
aome incraaae in the depth of the inapiratlona (hyptrpnoea), a
utage which ia aoon auooeeded by labored breathing (dyapnoM),
which, after the medulla haa called all the muaolea uaually em-
ployed in reapiration into riulent action, paaaea into oonvul-
aiona, in which every muaole may take part.

In other worda, the reapiratt ^ry iropulaea not only paa along
their uaual patha aa energetically aa poaaible, but radiate into
unuaual oiiea and paaa by nenrea nof. commonly thua aet into
functional aotirity.

It would be more correct, perhapa, to aiaaume that the vari-
oua parte of the nerroua ayatem are ao linked together that ex-
oaaaiTC actirity of one aet of oonnectiona acta like a atimulua to
rouae another aet into action, the order in which thia happena
depending on the law of habit— habit peraonal and eapedally
aaoeatral. An oppoaite condition to that deacribed, known aa
apnaea, may be inducied by pumping air into an amimal'a cheat
Tery rapidly by a bellowa; or in one'a self by a auooeaaion of
rapid, deep reapirationa.

After ceaaing, the breathing may be entirely interrupted
for a brief interval, then oommenoe very quietly, gradually in-
creaaing to the normal.

J^pmmt haa been interpreted in two waya. Some think that
it iadoe to fatigue of the muaolcs of reapiration or the reepira-
tory center; othera that the blood haa under theae drcum-
atanoea an e xceaa of oxygen, which ao influencee the reepiratory
center that it ia quieted (inhibited) for a time.

The latter view ia that uaually adopted ; but otmaidering that
apiioa reaulta from the aobbing of children following a pro-
longed fli of crying, alao in Oheyne4}tokea and other abnormal
forma of breathing, and that the blood ia normally almoat aatu-
rated with oxygen, it will be agreed that theroJa a good deal to
be aaid for the flrat view, eapedally that part of it which repre-
aenta the enaaation of breathing as owing to exceasive aotivftgr
and exhanation of the reepiratory center. We find auoh a«a]m
in asphyxia after the oonvulaive atorm. Perhapa if we regard
the reepiratory center aa double, half being situated on each side

«««*»*< «. -'i'.'fiK^eiMu^vt'-KaiiK ;w >mmm^i"^ii:''t^,-;i,si,i!,

Hl»fli>?-«i*^^^'i<-^«f> .

8V6

COMI'ARATIVB PHYSIOLOGY.

of the middle line; also as made up of an inspiratory and ex-
piratory part; automatic essentially, but greatly modified by
afferent impulses, especially those ascending the vagi nerves;
while the latter may be considered as containing both inhib-
itory and augmenting fibers for the center, the whole process
will be cleaver. Respiration on this view would be self-regula-
tive; the deeper the inspiration, the stronger the inhibitory in-
fluence, so the greater the tendency to arrest of inspuration;
hence either expiration or apnoea.

Is it, then, the excessive accumulation of carbon dioxide or
the deficiency of oxygen that induces dysimcea I Considering
that the former gas acts as a narcotic, and does not induce con-
vulsions, even when it constitutes a large percentage of the
atmosphere breathed, ard that the need of oxygen for the tis-
sues is constant, it certainly seems most reasonable to conclude
that the phenomena of dyspnoea are owing to the lack of oxy-
gen, chiefly at least; though the presence of an excess of oar-
bonic anhydride may take some share in arousing that vigorous
effort on the part of the nervous system, to restore the func-
tional equilibrium, so evident under the circumstances.

IWFliUJ B MOl l OF RB8PmATK)H ON TBB
OSBOUSiATXOB.

An examination of tracings of the intra-thorado and blood-
pressure, taken simultaneously, shows (1) that during inspira-
tion the blood-pressure rises and the intara-thoracic pressure
falls ; (2) that during expiration the reverse is true ; and (3)
that the heart-beat is slowed, and has a decided effect on the
form of the pulse. But it also appears that the period of high-
est blood-pressure is just after expiration has begun.

We must now attempt to explain how these changes are
brought about By intra-thoracic pressure is meant the pren-
ui« the lungs exert on the costal pleura or any organ within
the chest, which must differ from intrarpulmonary pressure
and the pressure of the atmosphere, because of the resistance of
the lungs by virtue of their own elastioity.

It has been noted that even in death the lungs ijeraain par-
tially distended ; and that when the thorax is opened the pul-
monary collapse which follows demonstrates that their elas-
ticity amounts to about five millimetres of mercury, which
must, of course, repreeent bat a small portion of that elasticity

-J

■I Wiii4*<W l U'l»iWiiWW| i W.|p i W i -i>. , :

THE RESPIRATORY SYSTEM.

897

iratory and ex-
ly modified by
lie vagi nerves;
ing both inhib-
e whole pro^eRs
i be aelf-regula-
e inhibitory in-
of inspiration;

rbon dioxide or '
, ? Considering
not induce oon-
foentage of the
gen for the tis-
lUe to conclude
the lack of oxy-
in excess of car-
ag that vigorous
restore the f unc-
Btances.

ON TBB

radc and blood-
during inspira-
loracic pressure
is true ; and (3)
ted effect on the
) period of high-
igun.

leae changes are
neant the press-
ay organ within
nonary pressure
the resistance of

mgs ijenaain par-
I opened the pul-
I that their elas-
mercury, which
of that elasticity

which may be brought into play when these organs are greatly
distended, so that they never press on the costal walls, heart.

leiim of Mood-DNMnn and Intrathofaoic pKMiiia In the dog (after
a XXotSmwSSm ■howing irwgataritles due to reqilmUooMd

Fio. 810.— TnusI
Foster), a, _.

^ •iSJS "hSS M^ewwtatorj btaet conrfnnee, to bMome • f^tld fall ^
iiu|>bnttiim begliia.

etc., with a pressure equal to that of the atmosphere. It follows
that the deeper the inspiration the greater the difference he-,
tween the intra-thoracic and the atmospheric pressure. Bv«n
in expiration, except when forced, the intra-thoracic preamre
remains leas, for the same reason.

These conditions must have an influence on the heart and
blood-vessels. Bearing in mind that the pressure without is
practically constant and always greater than that within the
thorax, the conditions are favorable to the flow of blood toward
the heart As in in^iration, the pressure on the great veins
and the heart is diminished, and, as these organs are not rigid,
they tend to expand within the thorax, thus favwing an on-
waid flow. But the opposite effest would follow as regards the
large arteries. Thwr expanaitm must tend to withdraw blood.
Durii^ exiaration the conditions are reversed. The effects on
the great veins can be ohwrved by laying them bare in the
neck of an anfanal,when it may be seen that during hupiration
they become partially collapsed, and refilled during expiration.
In cOTsequenceof the marked thtokneas of the coato ofttie
great arteries, the effect of changea in intra-Qioracks pressure
must be aUght The oomparaUvely thin-walled auricles act
somewhat as the veins, and it is likely that the increne of
pressure during exi^ratkm must f aror, so far as it goea, the car-
diac ^stole.

^^gfjfj^^Jfl ig-.jf(glffgf^f O«r---i.^

niJk»-s*WK"i:

mMIC

898

COMPARATIVB PHTSIOLOOT.

More blood, then, entering the right side of the heart dur-
ing inspiration, more will be thrown into the Bystemic oiroula-
tion, unlen it be retained in the lungs, and, unless the effect be
counteracted, the arterial pressure will rise, and, as all the con-
ditions ai!« reyersed during expiration, we look for and Bnd
exactly opposite results. The lungs themselves, however, must
be taken into the account During inspiration room is pro-
vided for an increased quantity of blood, the resistance to its
flow is lessened, hence more blood reaches the left side of the
heart The immediate effect would be, notwithstanding, some
diminution in the quantity flowing to the left heart, in conse-
quence of the sudden widening of the pulmonary vessels, the
Inverse of which would follow during expiration ; hence the
period of highest intra-thoradc pressure is after the onset of
the expiratory act During inspiration the descent of the
diaphragm compressing the abdominal organs is thought to
force on blood from the abdominal veins into the thoracic vena
cava.

That the respfaratory movements do exort in mmo way a
pronounced effect on the circulation the student may demon-
strate to himself in the following wajrs : 1. After a full insinrB-
tion, close the glottis and attempt to expire forcibly, keeping
the fingers on the radial artery. It may be noticed that the
pulse is modified or possibly for a moment disappears. 2. Re-
verse the experiment by trjring to inspire forcibly with dosed
glottis after a strong expiration, when the pulse will again be
found to vary. In the first instance, the heart is comparatively
empty and hampered in its action, intra-thoradc pressure being
so great as to prevent the entrance of venous blood by com-
pression of the heart and veins, while that already within the
organ and returning to it from the lungs soon passes on into
the general qrstem, hence the pulseless ocmdition. The expla-
nation is to be reversed fmr the second case. The heart's beat is
modified, probably reflexly, throogh the oardio-inhibitory cen-
ter, for Ihe changes in the pulse-rate do not occur when the vagi
nerves are out, at least not to nearly the same extent

OoBpantiT*.— It may be stated that the cardiac phenomena
referred to in this section are much more marked ih some ani-
mals than in othen. Very little change may be obsorred in
the pulse-iftte in man, wMle in the dog it is so decided that one
observing it for the first time might sappose that sndi pro-
nounced inregularity of the heart was the result of disease ;

wmiitiiiaiiaiiii

the heart Jur-

jretemic oiroula*

esB the e£Feot be

OB all the con-

: for and Bnd

however, miut

room is pro-

reeiBtaace to its

left side of the

istanding, some

heart, in conae-

lary vessels, the

ion ; hence the

Ler the onset of

deaoent of the

s is thonsfht to

te thoracic vena

in sfwoe way a
mt may demon-
Br a full inspira-
'oroibly, keeping
noticed that the
appears. 2. Be-
libly with dosed
Ise will again be
is comparatively
o pressure being
% blood byoom-
«ady within the
•n passes on into
on. The ezpla-
lie heart's beat is
^inhibitory oen-
au> when the vagi
stent

diac phenomena
ked ih some ani-
be observed in
decided that one
» that soeh pro-
wultof

««MBa

THB RBSPIKATOBT 8T8TBM.

though even in this animal there are variations in 4ihis respeet
with the breed, age, etc.

The B«9ixstiOB ud Oinnlatim in A^plifzia.- A roost in-
structive experiment may be arranged thus:

Let an anaesthetiaed rabbit, cat, or such-like animal, have
the carotid of one side connected with a glass tube as before
described (pages 888, 389), by which the blood-pressure and its
changes may be indicated, and, when the normal respiratory
acts have been carefully observed, proceed to notice the effects
on the blood-pressure, etc., of pumping air into the chest by a
bellows, of hindering the ingress of air to a moderate degree,
and of struggling. With a small animal it will be diflteult to
observe the respiratory efltects on the blood-pressure by simply
watching the oscillations of the fluid in the glass tube, but this
is readily oiough made out if more elaborate arrangements be
made, so that a gn^hio tracing may be obtained.

But the main events oS asphyxia may be well (perhaps best)
studied in this manner:

Let the trachea be occluded 01g*tured). At once the blood-
pressure will be seen to rise saaA raamin elevated for some time*
then gradually fall to sero. "nieae changes are contemporane-
ous with a series of remarkable manifestations of disturbance
in the respiratoiy qrstem as it at first amiears, but in reality
due to widespread and profound nutritive disturbance. Bo far
as the breathing is concerned, it may be seen to beoiHne more
rapid, deeper, and lalMired, in which the expiratory phaae be-
comes more than proportionably marked (dyspnoea) ; this is fol-
lowed by the gradual action of other muaeles than those usually
emplxqred in reparation, until the whole body paaaes into a ter-
rible convulsion— a mindeHrtorm in consequence of a nerve-
storm. When this has lasted a variaMe time, but usually
about one minute, there follows a period of exhaustion, during
which the subject of the expniment is in a motionless condi-
tion, interrupted by an occasional respiration, in which inspi-
ration is more pronounced than expiration: and, finally, tiie
animal qnietfy stretches every limb^ the sphincters are relaxed,
there may be a discharge of urine or fnoea, from peristaltic
movements of the bladder or intestines, and death ends a stiik-
jig scene. These events may be claasifled in three stagea,
though the first and second eqiedally merge into one anoClier:
1. Stage of dyspnoea. 8. Stage of convulsions. 8. Stage of
exhaustion.

.WB«8lftt&eK>;iJafiv«^^i,afta-tet?«WI»Sfs-^(^/frrtRyW>*;» f^«tr*>:^J*F*«^V- :if^^i»fc."»W?^-.7-*?

400

COMPARATIVE PHTSIOLOOT.

It is daring the flnt two stagw that the blood-prMmre riaea,
and during the thud that it sinka, due in the flnt instance
chiefly to ezceniye activity of the vaao-motor center, and in
the second to its exhaustion and the weakening of the heart'
beat

These yi<^nt morements ara owing, we repeat, to the action
of blood defldent in oxygen on the respirator;^ center (or cen-
ters), leading to inordinate action followed by exhaustion.

The duration of the stages of asphyxia varies with the ani>
nud, but rarely exceeds flve minutes. In this connection it may
be noted that newly bom animalB (kittens, puppies) bear im-
mersion in water for as much as from thirty to fifty minutes,
while an adult dog dies within four or five minutes. This is
to be explained by the feeble metabolism of new-born mam-
mals, which BO slowly uses up the vital air (oxygen).

If the chest of an anl&wl be opened, though the respiratory
muscles contract as usual there is, of course, no ventilation of
the lungs which lie collapsed in the chest; and the animal dies
about as quickly as if its trachea were occluded. It passes
through all the phases of asphyxia as in the former case; but
additional infbrmatioa may be gained. The heart is seen to
beat at flrst more quickly and forcibly, later vigorously though
slower, and flnally both feebly and inegularly, till the ventri-
cles, then the left auricle, and flnally the right auricle cease to
beat at all or only at long intervals. The terminationB of the
great vdns (representing the ainug venomu) beat last of all.

At death the heart and great vems are much distended
with blood, the arteries comparatively empty. Even after
rigor mortis has set in, the rij^t heart is still much engorged.

These phenomena are the result of the operation of several
causes. The increasingly venouff blood at first stimulates the
heart probably directly, in part at least, but later has the con-
trary effect. The nutrition of the organ suffers from the de-
graded blood, firom which it must needs derive its suppliea.
The cardio-inliibitory cmter probably has a large share in the
slowing of the heart, if not also in quickening it Whether
the accelerator fibos of the vagus or sympathetic play any
part is tmcertain. The increase of periphmal resistailoe caused
by the action of the vaso-motor centw makes it more difficult
for the heart to empty its left side and thus receive the venous
blood as it'ponni on. At the same time the deep inspirations
(when the chest is unopened) favor the onflow of venous blood;

««h^MHrik«HMMMMAMMWM«^

■ l *»M i i! Ji wrii< iiiM rt i

preamreriaM,
|Ant instance
iter, and in
I of the heart-
to the action
iter (or oen-
kuation.
with theani-
teotion it may
•pie«) bear im-
flfty minutes,
rates. This is
w*bom mam-

he respiratory

ventilation of
le animal dies
ed. It passes
mer case; hut
Mrt is seen to
irously though
till the ventrt-
kuricle cease to
inalioos of the
Untofall.
luoh distended
Even after
MJh engorged,
tion of several
stimulates the
sr has the con-
's from the de-
e its supplies,
resharein flie

It Whether
tetic play any
dstanoe caused

moredifBcuIt
ive the venous
Bp inspirations
venous blood;

THE BBSPIRATOKT SYSTEM.

401

•ud in any case the whole venous sjrstem, including the right
heart, tends to become engorged from these several causes act-
ing together. The heart gives up the struggle, unable to main-
tain it, but not so long as it can beat in any part

Tbe share which the elasticity of the arteries takes in
forcing on the blood when the heart ce a ses , and the contraction
of the muscular coat of these vessds, eepeoially the smaller,
must not be left out of the account in explaining the phenom-
ena of asphyxia and the po»t-moriem appearances.

Patluilogk»L— The importance of being practically as well
as theoretically acquainted with the facts of asphyxia is very
great

The appearance of the heart and venous system gives une-
quivocal evidence as to the mode of death in any case of as-
phyxia; and the contrast between the heart of an animal bled
to death, or that has died of a lingeriug disease, and one
drowned, hanged, or otherwise asphyxiated, is extreme.

We strongly recommend the student to asphyxiate some
small maounal placed under the influence of an anaesthetic,
and to note the phenomena, preferably with the chest opened:
and to follow up these observations by others after the onset of
rigormorH$.

Though at flist sight these seem so different, and are so as
regards acts of e x p re s s ion, yet from the respiratory point of
view they resemble each other dosely ; th«y are all reflex, and,
of course, involuntary. Many of them have a common pur-
pose, either the better to ventilate the lungs^ to clear them of
foreign bodies, or to prevent their ingress.

Coughing, in which such a purpose is evident, is made up of
several exiMratrary effo;-ts preceded by an inspinrtory act The
afferent nerve is usually the vagus or laryngeal. Wt may be one
or more of several otheon^

The glottis presents oharaoteristio appearances, being closed
and then opened suddenly, the mouth being kept open.

Cknighing is often induced in attempting to examine the ear
with instruments. (Beflex act).

Laughing is very similar to the last, so Jar as -the bdiavior
of the glottis is concerned, though it usually acts more rapidly,
of conise. Several expirations follow a deep inspiration.
8«

402

COMPARATIVE PHY8I0L0QY.

Cfrying is eawntially the aame as laughing, but the facial
expnMion i« different, and the lachrymal gland funotioni ez-
oeMively, though with aoine perMU thia oocum during laughter

alio.

SMring is made up of a wries of inq^tions, in which the
glottis ia partially oloaed, followed by a deep expiration.

Yawning involvea a deep<lrawn, slow inipiration, followed
by a more midden expiration, with a well-known deprenion of
the lower jaw and uiually atretdiing movementa. ^

Sighing is much like the preceding, though the mouth is not
opened widely if at all, nor do the stretching movements com-
monly occur. - 1. u

Hieeough is produced by a sudden inspiratory effort, though
fhiitlflss, inasmuch as the glottis is suddenly dosed. It is
spoken of as spann of the diaphragm, and when Iwig continued
is very exhaustiYe.

Sneezing is the result of a powerful and suddm expiratory
act foUowing a deep inspimtion, the mouth being usually closed
by (he anterior pillars of the fauces against the outgoing cur-
rent of air, which then makes its exit through the nose, whUe
the glottis is forcibly opened after sudden closure. It will be
noticed that in most of these acts the glottis is momentarily
dosed, which is never the case in mammals during quiet res-
piration. . , __

This temporary ocdusion of the resplretory passages per-
mits of a higher intrapulmonary prewure, which is very effect-
ive in dearing the passages of excess of mucus, etc, when the
glottis is suddenly opened. Though the acts described are all
involuntary, they may most of them be imitated and thus
rtudied ddiberatdy by the student It will also appear, con-
sidering the many ways in which some if not all of them may
be brought about, that if the medullary center is responsible for
the initiation of them it must be accessible by numberlesr pafts.
Ooi^ptnttf*.— Vew of the tower animals cough with the
same fadlity as man, while laughing is aU but untaiown, cry-
ing andsobWng rare, though As wUmSag^Uolfi is aUied to
the crying of human beings. , '

Sneenng seems to be voluntary in some amm«)s,as squir-
rels, when enmged in toilet operatiMia, etc

Baf*ing is voluntary, and in medianism resembles oouj^-
ing, the vocal cords being, however, more deflnitdy empkjyed,
as also in growling.

:, but the facial
id funotioiui vx-

IS, in which the

pbration.

ration, followed

n deprearion of

he mouth is not

korements oom-

y effort, though
f dosed. It is
I long continued

dd«i expiratory
g usually closed
e outgoing our-
the nose, while
lure. It will he
I is momentarily
nring quiet res-

py passages per-
sh is very effect-
I, etc, when the
lescribed are all
litated and thus
Oso appear, oon-
ill of them may
B responsihle for
nmberleas paths,
cough with the
it oxiknown, cry-
is allied to

nimals, M squir-

fesembles oough-
outdy empWed,

THE RBSPIRATOBT SYSTEM.

BawUnQy neighing, braying, etc., are made up of long ex-
piratory acta, preceded by one or more inspirations. The vocal
cords are also rendered tense.

i m g ifn iii iiL i l wiiwi tf ii'i' 1 1 * 1 I ' ll " **

the amount of available pulmonary tissue, or hamper tho move- .
ments of the cheat, are many, and only the briefest reference

can be made to a few of them.

Jti/Ianiwation of the lungs may render a greater or lees por-
tion of one or both lungs solid; inflammation of the pleura
(pleuritis, pleurisy) by the dryness, pain, etc., may restrict Ihe
thoracic movements; phthisia may solidify or excavate the
lungs, or by pleuritic inflammation glue the costal and pulmo-
nary pleural surfacea together; hrondiiHa may dog the tubea
and other air-passages with altered secretions; emphymma (dis-
tention of air^sells) may destroy elastidty of parts of the lung;
pneumorthorax from rupture of the lung-tisnie and consequent
accumulation of gases in the pleural cavity, or pleurisy with
effurion render one lung all but useless from pressure. In all
such oases Nature attempts to make up what is lost hi amplitude
by hiorease hi rairidity of thf respi»tory movements. It is
interesting to note too how the other lung, in diseased condi-
tions, if it remain unaffected, enlarges to compensate for the
loss on the opposite side. When the musdea are weak, espe-
cially if there be hindrance to the dntvance of air while the
thoracic movements are nuurind, there may be bulging mward
of the intercostal spaces.

Normally, this would also occur, as the intrarthoraeio press-
ure is less than the atmospheric, were it not for the fact that the
intercostal modes when contracting have a certain iesirting

power.

The imperfect respiration of animals whrai dying, penmttmg
the accumulation of oarbcmio anhydride with its soporiflo
efltots, smooths the way leading to flie end; so thai there m^
betotihemihiUiated the appearance of a sufTering which does
not exist, consdoumess itsdf being dtiier wholly or partially
absent The j^Bpnoea of anasmio anfanals, whether from sud-
den loss oCUood «f from imperfect renewal of the haemo-
globin, shows that this substanoe has a leqpiratory funetion;
while m fonns of oardiae disease with regurgitation, etc, the

ff9Sl*#W*I

»9fe-W»ai<i>tt^J ' l* * > ' '' *■"'' - 'i ^'***' ''! ' '' '' '' '* ' '"'^ ' ' ' ^'**^ ' '^*^^

"Wi-

404

COMPARATIVB PHYSIOLOOT.

n'f

blood may be imperfectly oxidiied, giring riie to Ubored
piration.

PwimmI ObwrvatioB.— Ai hinted from time to time during
the treatment of this subject, there is a large number of facts
the student may verify for himself.

A simple way of proving that OOt is exhaled is to breathe
(blow) into a vessel containing some clear solution of quick-
lime (OaO). the turbidity showing that an insoluble salt of lime
(OaOOi) has been formed by the addition of this gas.

The functions of most of the respiratory muscles, the phe-
nomena of dyspnoea, apnoea (by a series of long breaths), par-
tial asphyxia hy holding the breath, and many other experi-
ments, simple but oonvinomg, will occur to the student who is
willing to learn in this way.

The obeervation of respiration in a dreaming animal (dog)
will diow how mental ooonrrenoes affect the respiratory center
in tiie absence of all the usual outward influences. Therespira-
tion of the domestic animals, and of the frog, turtle, snake, and
fish, is easily watched if these cold-blooded animals be placed
for observation beneath a glass vcsscL Their study will teach
how manifold are the ways by which the one end is attained.
Gompare the tracings of Fig. 808.

Ifolvtioii.— A study of embryology shows that the respirar
toiy and oironlatory systems develop together; that the vascu-
lar system functions laigely as a respiratory cystem also in cer.
tain stages, and remains such, from a physiological point of
view, throughout embryonic life.

The changes that take place in the vascular syvtom— the
hearty especially— of the mammal when the lungs have become
functionally active at birth, show how one set of organs modi-
fies the other.

When one considers. In addition to these Esols, that the
diigpestive as well as the vaaoalar and reqpiratory ovgans are
represented in one group of structures in a jelly-fish, and that
the hugs of the mammal are derived from the same mesoblast
as gives rise to the digestive and dreulatory organs, many Cjf
the relations of these systems in the highest groups of animals
become intelligible; but unless there be descent with modifiea-
timi, these fscts, clear enough from an evolutionary standpoint,
are isolated and out of joint, bound together by no common
prindide that satisfies a philoaophioal bi^ogy.

It has been found that in hnnting4ogs imd wild rabbits the

labored

J to time durinf
lumber of facta

is to breatbe

ion of quiok-

ItbleMJtoflime

iIm, the phe-
g breaths), par-
ly other esperi-
■tudent who ia

ig animal (dog)
■piratory center
ee. Therespira-
irtle, uiake, and
imals be placed
■tudy will teach
end ia attained.

that thoreepirar

that theTaacu-

ratem alao in cer.

(logical point of

liar ayatem— the

iga haTO become

of organa modi*

» Caota, that the
itory ovgana are
illy-flah, and that
I aame meeoblaat
organa, many a|f
roupa of animala
nt with modiftca-
nary atandpoint,
• by no common

wild labbita the

i««niMM«fa

t^tmm

:iS£6

^iiiMu

THE RBSPIRATORT 8TSTBM.

406

Tagoa ia more efficient than in other racea of doga and in rab-
bita kept in confinement; and poaaibly thia may in part account
for the g re at er apeed and eapedally the endurance of the
former. The Tary conformation of aome animala, aa the grey-
hound, with hia deep cheat and capaoioua lunga, indkmtea an
unuaual reapiratory cKptucHky.

The Into o/lMiMia well iUuatratedinthecaaeof diTera,who
can bear deprivation of air longer than thoae unaocuatomed to
aunh aubnumioa in water. Qreater toleration on the part of
the reapfaratory center haa probably much to do with the caae,
though donbtleaa many other departurea from the normal occur,
either independently or correlated to thti changea in the rcaidfa-
tory center. Some mammala, like the whale, can long remain
underwater.

tOMMffj flf tiM Pljiiologj of BMpfntin.— The purppae
of reapiration in all animala ia to fnmiah oxygen for the tiaaiiea
and remove the carbonic anhydride they produce, which in all
▼ertebtatea ia accomplished by the expoaure of the blood in
oapillariea to the atmospheric air, eitlMr free or diaaolvecl in
water. A membrane lined with cdla alwi^ intenrenea between
the oapillariea and the air.

The air may be pumped in and out, or aucked in and forced
out

SMflntim la tk* MunuL— The air enteit the lunga,
owing to the enlargement of the chest in three directiona by tlie
aotk>n of certain muscles. It leaves the lunga beoauae of their
own daatic recoil and that of the chest-wall chiefly. Inqdiation
is active, expiration chiefly passive.

The diaphragm ia the principal muade of respiration. In
srane animals there is a well-maikad tedal and laryngeal as
well as thoracic respiration. Respiration is rhythndcal, con-
sisting of inspiration, succeeded without appveeiahle pause by
expiration, the latter being in health of only slightly Icmger
duration. There is also a definite relation between the number
of reapirationa and of heart-beata. According aa reapiration ia
normal, hurried, labored, or interrupted, we deacribe it aa
enpnoB, hj/perpncBaf dytpnaa, and apima. The intra-thoradc
p re s su re is never equal to the atmospheric— L e.. it is always
negative— except in forced expiration ; and the lunga are nev^
collapaed so long aa the cheat is wuqwned. Tlie expired air
diffecB from that insinred in being of the tempecatnre of the
body, aatnrated with moiatnre, and oontaining about 4 to S per

•MUSMr

i ilili li<l iwi»*. W^WW>WHW>>MH

Mi^SHMlw

406

OOMPARATiyB PHT8I0L0OT.

flMit 1«M oxyfMn and 4 per cent more oarbonio anhydride, be-
lidM oertain indlffaNotij known bodiei, the reault of timie
metaboUun, eservled by the long*.

The quantity of air actually mored by a reeirffalory aot, as
compared with the total capacity of the req;>iratory organ*, ia
•mall ; hence a great part muit be played by diffusion. The
portion of air that can not be remored from the lunge by any
reepiratory effort is rdatlTcly large.

It is customary to distinguish tidal, complementary, supple*
mentary, and residual air.

The rital capacity is estimated by the quantity of air the
respiratory oigans can move, and is rery TariaUe.

The blood is the respiratory tissue, through the mediation
of its red cells, by the lusmoglobin they contain. This sub-
stance is a ferruginous proteid, eKgtblt of erystalliiation, and
assuming under chemical treatment many mncUAoationB. When
it oontains all the ozygan it can retain, it is said to be saturated
and is called ozy-haBmogloUn, in which form it exists (with
some reduced haemoglobin) in arterial jblood, and to a lesser
extent in venous blood, which differs from artorial in the rela-
tive proportions of haomoglobin (reduced) it contains, as viewed
from tlie respiratoiy standpoint

Oxy-baomoglobin does not assume or part with its oxygen,
according to the Henry-Dalton law of pressures, nor is this gas
in a state of ordinaiy chemical combination. It is found that
the oxygen tension of the blood is lower and that of carbonic
anhydride higher than in the air of the alveoli of the lungs,
while the same may be said of the tissues and the blood re-
spectively. This has been, however, recently again denied.

Bespiraition is a vital process, though certain physical con-
ditions (temperature and pressure) must be rigidly maintained
in order that the gaseous interohangea shall take place. Baa-
pi|»tion is always fundamentally bound up with the metabo-
lism of the tissues themselves. All animal cells, whether they
exist as unicellular animals (Amoeba) or as the components of
complex Mgans, use up oxygen and produce carbonic dioxide.
Bespiratory organs, usually so called, and the respiratory tissue
par exMOmiee (the blood) are only supplmnentary mechanisms
to fbeilitate tiaroe respiratkm. Oaibonio anhydride exists in
blood probably in combination with sodium salts, though the
whole matter is very obscure.

Beqriieilan, like all the other functions of the body, is con-

mtdm

<tmmmmmimmam»mitrmmmmmmmMmmmmaimii jM > vj f i ' '■' ggj a a w

THB BBSPISATORY SYSTEM.

407

lanhydrkla, be-
lt of tiMue

itary, nipple-

itity of air the
lie.

I the mediation
ain. This mib-
■talliiatioii, and
Boationi. When
I to be aaturated
I it exiita (with
and to a leawr
irial intherela-
itaina, ai viewed

irith its oxygen,
«, nor is this gas
It is found that
that of carbonio
>U of the lungs,
ad the blood re-
gain denied,
in physioal con-
{idly maintained
ake place. Bes-
rith the metabo-
lis, whether ihey
e oomponenti of
Wbonio dioadde.
vspiratory tissue
taiy meehanisms
lydride exists in
lalts, though the

the body, is oon-

troUed by the central nerTous system through nerroo. The
medulla oblongata is chiefly concerned, and especially one
small part of it known as the respiratory center. It is possible,
eren probable, that there are subordinate centers in tlie cord,
which, under peculiar circumstances, assume importance ; but
how far they act in concert with the medullary center, or
whether they act at all when normal conditions y.-wrail, is an
open question.

The vagus is the principal afferent respirr^ory n««Te. The
efferent nerves are the phrenics. interoostals, lUid others supply-
ing the various muscles used in moving the uliest-walls, etc.

The respiratory center is automatic, but its action is sus-
ceptible of modification through afferent influences taking a
variety of paths, the principal of which is along the vagi nervrs.
The respiraUwy, vaso-motor, and cardio-inhibitory centers seem
to act somewhat in concert.

Blood-pressuro is being constantly modified by the respira-
tory act, rising with inspiration and sinking with expiration..
In some animals the heart-beat also varies with these phases of
re«piratk>n, becoming slow and irregular during expiration;.
Into the causation of these changes both mechanical and nerv-
ous factors enter, and make a very complex mesh, which we
can at present but imperfectly unravel. When the access of
air to tile tissues is prevented, a series of stages of respiratory
activity and decline, acctnnpanied by pronounced changes in
the vascular syrtem, are passed through, known as asphyxia.

Three stages are distinguishable : one of dyspnoea, one of
convulsions, and one of exhanstion— while at the same time
there is a rise of blood-pressure during the first two, and a
decline during the third, aooompanied by mariEcd alterations in
the cardiac rhythm.

'tiiimit

w'>iiiliiiii'ir>iiiiii'iruu]'Mi'i«rtiiiMHiin' iafliiiii')rtWiiiiii wmmlimtammmm

mmmimimimt

PROTBOTIVB AND EXCRETORY FUNCTIONS
OF THE SKIN.

Am has been inUnwted from time to time, thue far, m a
ranilt of the metabolism of tl|e tiHoee, oertain products require
oonatant remoral from the blood to prevent poisonous effects.
These substanoes are in all probability much more numerous
than physiological chemistry has as yet distinctly recognised
or, at all events, isolated. QnantitatiTely considered, the moat
important are carbonic anhydride, water, urea, and, of less im<
portance, perhaps, certain salts.

In many inVeHebrates and in all vertebrates several organs
take part in this work of elimination of waste products or puri-
floation of the blood, one set of which— the respiratory— we
have just studied ; and we now continue the ooMideration of
the subject of excretion, this term being reserved for the pro-
cess of separating harmful products from the blood and di»
charging them fifom the body.

We strongly recommend the student to make the study of
excretion comparative in the sense of noting how one organ
engaged in the process supplements another. A dear under-
standing of this relation even to details makes the praotioe of
medicine more seientiflo and practically effective, and gives
physiology gre at er breadth.

Hie ddn has a triple function : it is protective, excretory,
sensory, and, we may add, nutritive (absorptive) and respira-
tory, especially in some groups of animals,

As a sensory organ, the skin will receive attention later.

PniMthra VuutiMi of Iki lkia.—Ooaqrantty«.— Among
many groups of invertebrates the principal use of the exterior
covering of the body is manifbsUy protection. Among these
forms, an internal skeleton bring absent, the exo^keleton is
developed externally, and serves not only for inoteotion, but
for the attachment of muscles, as seen in crustaceans and in-

l>IMll»l)lll

AtfUifm

JN0TI0N8

, thus far, m a
roducto require
rieonotu effecto.
nore numeroue
totljr reoogniiod
dered, the mort
and, of lew im-

WTeraloi^oa
roducte or puri-
reapirotory— we
soniideration of
red for the pro-
) blood and dia-

kke the study of
how one organ
▲ olear under-
I thepnotioe of
otive, and giyes

etive, excretory,
▼e) and reapira-

mtion later,
nttvt. — ^Among

of the exterior
. Among than

exoHricdeton is
> proteotion, hut
itaoeana and in-

PROTEOTIVI FUNCTION OP THR SKIN.

409

■eota. But thia part of the mibjeot is too large for detailed
treatment in sueh a work as this. Turning tn the vertebratea,
we see soales, bony plates, feathers, spinas, hair, etc., most of
them to be regarded as modiSoations of the epidermis, alwa.'«
useful, and frequently also ornamental.

PrimitiTe man waa piobab^ much more hirsute than Mj
modern f epreaentatJTe ; and, though the human subjeot is ut
present prorided with a skin in whkh proteotira funotions ara
at their loweat, still the epidermis does serve such a purpose, as

all have soma time realised when
it baa been aoeidenlally removed
I^^^^^^^^^^^^Hi by blistering, etc.

Taking the structure of the

skin of man as representing that

of mammals generally, certain

l^^^^^^^^^^^^^H points claim attention from the

4^^^^^^^^^^H^ physiologist. Iti elastkity, the

l^^^^^^^^^^^^Hi failure of whteh in old age ao-

oouuts for wrinkles; its epider-

^Mi

■^^■■■^■j

vw.nt.

Fi«.nt.

fn>.sn. ■■JoripiWMidawdfc IxW. {Attar Upptj) 1. 1, MMMnlt; 9, •, i

ta^; a, 9, pfMllto: 4. 4, denna; B, B, MbeataiiwiM araol* Omm; 6. S. 0, S, kodo-
ripaMMMUjU^ 7, adlpoM vMklw; 8, S, eserttory doeti In daraia; 9, 9, ascn-

Via. ail— ^sftiM of skta of palm of haad about one-half an Ineh (1t7 mm.) MinaTC.
}«4. (Aftar Sappay.) 1,1, 1, 1, openlncaof andorireroindnela;a.t,t,t, ■taorca
fca tw ea n papUto of aWn.

mal covering, made up of numarons layers of cells; its coiled
and spirally twisted sudoriferous glands, permitting of move-
ments of the skin without harm to these stmeturea; its hair-
follidea and associated sebaceous glands, the fatty secretion of
which keeps the hair and the skin generally soft and pliable.

410

COMPARATIVE PHYSIOLOGY.

The muacles of the skin, which either move it as a whole or
erect individual hairs, play an important part in modifying ex-
pression, well seen in the whole canine tribe and many others.

There are several
modifications of the
sebaoeousglandsthat
furnish highly odor-
iferous secretions as
in the civet cat, the
skunk, the musk-
deer, and many low-
er vertebrates. In
some, these are pro-
tective (skunk) ; in
others, though they
mi^ not be agreeable
to the senses of man,
th«y are doubtless atr
tractive to the fe-
males of the same
tribe, and are to be
regarded as impor-
tant in "sexual se-
lection," being often
cooflned to the males
alone.

Bar-wax and the
Meibomian secretion
are the work of
modified sebaoeoos
glands ; as also the
oU-glanidB so highly
developed in birds,
especially aquatic
forma, and of which
these cMaturea make
great use in pnaerv- '
ing iheir feathers
from wetting.

In our domestic
animals we may es-
pecially notioe a ou

of balr; t, bnlborbilr:

a, tetMoia MoMiMifb:

foUtote; 7, 7. moWBtar bM«J5*H^^ '^!S^
&8.extnBiHiw of Iwodt mmIiic tn ikia: •, cob*

apparfltira of foHIele:' 11, ainpi*
Vt, opnliig or tUilr-foUiele.

r Bi li ii i iri i i i n^' ^iii jij i ii i j>iLMuiji.' i «; ii iiMi i . nif.umaimWi

«*»

l lill l l HI] » M ii ' ii W»«X1l ii l>« li »

MgMiKM(9«B»WMII«MnWM

, as a whole or
modifying ex-
many others,
ere are several
Ications of the
tousglandsthat
ih highly odor-
B secretions as
i civet cat, the
:, the musk-
Bud many low-
irtehrates. In
these are pro-
B (skunk) ; in
I, though they
lot he agreeable
) senses of man,
ire doubtless at-
ve to the fe-
I of the same
and are to be
ded as impor-
in "sexual se-
o," being often
aed to the males
I.

ftr-wax and the
omian secretion
the work of
fled sebaoeous
Is ; as also the
lands so highly
loped in birds,
(ially aquatic
a, and of which
icreatureamake
iuaein pmerv-
thd* feathers
wetting.
1 our domostie
tail we may es-
tlly notice a cu

THE BXCRBTORY FUNCTION OF THE SKIN. 411

taneous ghmd hi the pig, placed at the posterior inner aq>ect of
the knee and of considerable siae.

In the sheep, the tnferungutote
gkmd is an inversion of the integu-
ment forming an elongated sao,
which is supplied with secretmg
structures analogous to the sebar
oeous glands. The importance of
protective struotures of this kind
in such rituations is obvious.

TBB BZOBBfOKT FUMOIIOH

or no 9Bm.

The quantity of matter dis- ^JSiil^^mStt^ ^
charged ti«ough ^e Am *■ l«8e Pff»?',.ruSS&'^fia! t
~-greaterm man than by the lungs orUMoritodiieL

(about as 7 to 11), though the

amount is very variable, depending on the degree of activ-
ity of other related excreting organs, as the lungs and kidneys
and largely upon the temperature as a physical condition ; and

so in otiiOT a nim a l s.

When tiie watery vapor ia carried off, before it can condense,
tiie perspiration is sud to be JnMiMt&Ie; when small droplets
become visible, mmble. As to wh«tiier tiie one or the other is
predominant wUl, of course, depend on tiie rapidity of renewal
of tiie air, its humidity, and its temperature. Apart from tiie
tempeitttiire, tiie amount of sweat is influenced by tbe quality
and quantity of food and, especially of drink taken, tiie amount

of exewise, and psychic conditions; not to speak of tiie effect of

drugs, poisons, or disease. „ , , .*i.

Ftespinition in man is a dear fluid, moetty colorless, witii
a oharwJteristic odor, devoid of morphological elements (ex-
cept epidermal scales), and alkaline in reaction. It may be
aiM from tiie admixture of tiie secretion of tiie sebaceous

glands. ,. ..

Iti solids 0am than 8 per cent) consist oi sodium satts,
niosfly cUorides, oholesterin, neutral IWs, and traces of ur«.
The adds of tiie sweat belong to tiM ftitiy series (acetic butyric
formic propionic oaprylic o^roic etc.)i ■

PatiMla|iaaL--Tbe sweat may contain Uood, proleida, abun-
dance of urea (in cholera), uric acid, oxalirtae, wgwf, l«ot«c ■«*

»l rti«^ NWI i U'W l fcl' W illi

mMmM \ im i 0mn

412

COMPABATIVB PHYSIOLOOT.

bile, indigo, and other pigmenti. Many medicinee are elimi-
nated in part tlirough tlie ddn.

Xaqpintiaa hj th* Udn.— Oomptntiv*.— In reptileii and
batrachians, witli smooth, moist ddn, the respiratory functions
of this <wgan are of great importance; hence tliese animals can
live long under water.

It is estimated that in the frog the greator part oi the car-
bonic anhydride of the body-waste is eliminated by the skin.
Certainly frogs can live for days immersed in a tank supplied
with running water ; and it is a significant fact that in this
animal the vessel that gives rise to the pulmonary artery sup-
plies also a cutaneous branch.

The respiratory capacity of the skin in man and most
mammals is comparatively small under ordinary circum-
stances. The amount of carbonic anhydride thus eliminated
in twenty-four hours in man is estimated at not more than 10
grammes. It varies greatly, however, with temperature, exer-
cise, etc.

The skin is highly vascular in mammals, and its importance
as a heat regulator is thus very great.

When an animal is varnished over, its temperature rapidly
falls, though heat i»oduction is in excera. From the hat that
life may be prolonged by diminishing loss of heat through
wrapping up the animal in cotton-wool, it is inferred that
depression of the temperature is, at all events, one of thfe causes
of death. Though the subject is obscure, it is likely that the
retention of poisonous products so w^'a as to derange metabo-
lism, as well as poison directly, which might thus lead to the
disorganization of the machinery of life to the point of disrup-
tion or death. It is also possible that the reduction of the tem-
perature from dilatation of the cutaneous vessels may be so
great that the animal is cooled bdow that point at which the
vital funotimis can continue.

.noH.

IBM WMJIUn'lOW OF

In secretion in tLe widw sense we find usually certain nmr-
ous and vascular effeets associated. The vessels su|4plying the
gland are dilated during the most active ^lase, and at the same
time nervous impulses are ccmvqyed to the secreting eells which
stimulate them to action. There is a certain proportion of
water given off hy tranqnration ; but the sweat, as a whole,

les are eUmi-

reptilea and

functions

lanimahi can

of the ear-
by the akin,
tank supplied
that in this
try artery sup-
nan and most
inary oircum-
hns eliminated
; more than 10
tperatnre, ezer-

its importanoe

Brature rapidly

the foot that

heat throu^^h

inferred that

le of thd causes

likely that the

sninge metabo-

lus lead to the

Dint of disrup-

ion of the tern-

■els may be so

It at which the

SON.

r certain nmr-
suplplyingr the
nd at the same
ingoells which
proportion of
it, ■> a whole,

THB BXCRBTION OF PBRSPIBATIUN.

418

even the nu^r part of the water, is a genuine secretion, the
result of the metabolism of the cells.

From experiments it is clear that nervous influences alone,
in the absence ol any vascular changes, or in the total depriva-
tion of blood, suflBce to induce the secretion of perspiration. If
the central stump of the divided sciatic be stimulated, sweating
of the other limbs follows, showing that perspiration may be a
reflex act It is found that stimulation of the peripheral end of
the divided cervical sympathetic leads to sweating on the cor-
responding side of the face.

Sweating during dyspnoea and from fear, when th.e cutane-
ous surfaces are pale, as well as in the dying animal, shows also
the independent influence over the sudorific glands of the nerv-
ous system. Heat induces sweating hj acting both reflexly and
directly on the sweat-centers we may suppose. Unilateral
sweating is known as a pathological as well as experimental
phenomenon. Perspiration may be either increased or dimin-
ished in paralysed limbs, according to circumstances. It is
possible that there is a paralytic secretion of sweat as of saliva.
The subject is very intricate, and wUl be referred to again qa
account of the light it throws on metabdio pro ce ss es generally.

Abaorption by thedEin in man and other mammals is, under
natural conditions probably very slight, as would be expected
when it is borne in mind that the true skin is covered by sev-
eral layers of cells, the outer of which are hardened.

Ointments may unquestionably be forced in 1^ rubbing ;
and perhaps absorption may taire place when an animal's tis-
sues are starving, and food can not be made available through
the usual channeb. It is certain that abraded surfaces are a
source of danger, from affording a means of entrance for dis-
ease-producing substances or for germs. •

Chnpantb*.— It is usually stated in Works on physiology
that the horse sweats profusdy, the ox less sO; the pig in the
snout: and the dog, cat, rabbit, rat, and moose, either not at all
or in the feet (beUvem the toes) only. That a closer observa-
tion of these animals will conviiioe any one that the latter
statements are not strictly crarrect, we havQ^no doubt. These
animals, it is true, do not p«pspire muMy to any great extent;
but to maintain that their skin has no excretory function is an

-The skin of the mammal has protective, sensory,
respiratory, and excretory functions. Hie respiratory are in-

HmHimUiMmt

'mmliMuiliimitjimiiii^

414

OOMPARATIVB PHYSIOLOOY.

sUmifloant under oidiiuury cireumitaiioM in thta gwmp, though
well mMked in reptile, and eq»ci«lly in hatrachian. (ft«g,
menobranohua). Sweating is probably dependent on ^e action
of oenten eltuated in the brain and apinal cord, through nenrea
that run genewOly in sympathetic tracts during some part of
their course. While the function of sweating may go on ind^
pendently of abundant blood-«ipply, it is usually assocated
with increased Tascularity. , « . . ,u it ;„

Sweat contains a very small quantity of soUds, w alkaline m
taction when pu«», but liable to be acid from the admixtare of
sebaceous matter that has undergone decomposition. Sebum
consists chiefly of olein^ palmitin, soaps, cholesterin, and «t-
tnaotives of Uttte known composition. The salty taste of the
perspiration is due chiefly to sodium cWorlde, and its smell to
volatile fatty acids; especially is this so of the sweat of certain
Dwts of the body of man and other mammals.

The functional activity of the ddn varies with the twnpem-
ture, moisture, etc., of the air and certain internal conditions;
flBpeoially is it important to remember that it is one of a series
Te^cretory orgmis which act in hwm^y to •1"""**«^;
waste of tiie body, so tiiat when one functions more the other

may and usually does function less.

The protective function of the skin and its mod Jed epithe-
lium (hir, horns, nails, featiiers. etc.) is in man .%ht, but very

hZS in^y other vertebrates, among whidi pr^s^n
^nst undue lo-i ^ tempenrture is one of the mort con^^^^^
oiTrativcand enables a vast number of groups of animals to
adapt sttcoessfnlly to their varying suiroundings.

m t mmm

-i ii iij nwmny i wiiti i ]

HJgjT I fffTP ' W, ' >ff "^J'i' * !"! '!' ! "»" » ^'^

I groap, though
braohiaiiB (firog,
at on the action
through nerves
ig aome pert of
may go on inde-
oally aaaociated

ds, i« alkaline in i
he afdmixture of
oaition. Sebum
leeterin, and ex-
nlty taste of the
and its smell to
sweat of certain

rith the tempera-
Brnal conditions;
is one of a series
to eliminate the
s more the other

modified epithe-
n slight, hut very

which provision
» most constantly
ipg of animals to
igs.

EXCRETION BY THE KIDNEY.

Tm kidney in man and other mammals may be described as

a very compli arrangement of tube, lined with ^^^^
ei^fLis of secreting cells, surwnmded by a great meA work ^

^piMM, boundl^ther by connective tissue, the quantity

varying with the animal, and the whole inclosed in a capwite.
The organ is wdl supplied with lymphatics and nerros.
Thongli the tuhea aw ao complex, Ihe kidney may be divided
into lones which contain moMj but one kind ^ tobBde.

Among vertebMiteB, till the reptiles are reached, the kidn«y
is a penristentWolfflan body, hence its more simple form.

In most fldMS the kidney is a very elongated organ, thoagb

.H. i MH i l , l |l l !'| il |, .1 . ' <"

BXCRBTION BY THJB KIDNBT. 41T

inthelowertitooMlrtiof Utile mow ttum tubulei, ooiling but
•lighUy, ending by one extremity in a glomeniluB and by the

#■

418

COMPARATIVE PHY8I0L00T.

oUier opming into m long oonunon efferent tube or duot. The
glomerulus ii, however, peeollar to the vertebrate kidn«7.
The giKled complexity in wramgement, e«o., of the tubei is
rapreientMlwell in the flgun below. It ii » rigniflouit faet

ito.su,-:

la«nl«M

that the kidney of the hunwn lubjaek is lobulated in the embryo,
whichoonditioniBpeniitent iniome nuonmali (ruminant^ etc.).
As the lungt are the orgain employed einpeeially «» fte
elimination of oaibonio anhydride, lo the Wdn«y» awe above
all ottwM the eMWtore of the nitrogenona warte produda otf the

body chiefly in the form of uric add or urea. Before tieatiiig of
lllewetion by the kidn^it win be well to eatamlne into the ^
i«aimd olMmieal fMpwtiea of urine with Bomedetail, fliped^
on aooount of ite great impprtanee in the dipgnoalB of («— —

B.ai||,'"'./f'

WPP^Iff"

BXORBTION BY THB KIDNEY.

41»

or duot. The
ibrate kidney.
>f the tubee is
igniflouit faet

ijlM of kUhMT Otflw
laigepartor H«

din the embryo,
runiinanti,eto.).
peeially tor fhe
ineys are dbore
B piodiUstB of the
ietott treating of
ae into fhe phye-
detidl,flipeei«l]y
lodeef <"

mimi cxmnoinuD FHiwcmuiT amd

OAZAT.

Urine is nattmlly a fluid of very yariable oomposition, espe-
ciaUy regarded quantitatively— a fact to be borne in inind in
considering all statoments of the constitution of this fluid.

tpaditt Qntttj.— Urine must needs be heavier than water,
on account of the large variety of solids it contains. The ave^
age speoiflo grarity of the urine for the twenty-four hours is in
m^ 1015 to 1080 ; in the horse, 1080 to 1060 ; in the ox, 1080
to 1080? in the sheep and goat, 1006 to 1016; in the pig, 1010 to
1018 ; in the dog, 1080 to 1060. It is lowest in the morning and
varies greatly with the quantity and kind of food eaten, the ac-
tivity of the lungs and espedaUy of the skin, etc

Ookr.— Some shade of yellow, which is also very variable,
being increased in depth either by the presence of an excess <rf
pigment or a diminution of water. In herWvora the unne is
turirid, and may darken on exposure to the air.

Hm iMfltlon of human urine is add, owing to acid salts,
especially acid sodium phosphate (NaHiPO«). In the camivora it
isst>onglyaoid;intheherbivora,alkaUne. The reaction of urine
depends largely though not wholly on the character of the food.

iluatity.— This is, of counn, like the speciflo gravity, highly
variable, and f lequenUy thqr run parallel with each other.

The following tabular statament will prove useful for refei^

AVI AA *

C&mpoaition oftht Urint (Souatingauify

Una

PotsMiam hippurste

AUttliM laotetsB. :

PotsHinm bioarboiuite

Magnasium osibonsta

Calcinm csrboiwt«

Potaaaium sulphate

Sodium chlorida

Sfltoa ;

Plioqiliataa

Water and sabstancaa undetermiMd.

Hofw.*

Total

Sl-O
4-7

90-1

16'5
4<S

10«
1-S

0-r
i-o

OK)
910O

Oow.t

10C0<»

18>6

l«-5

17-2

164

4-7

8-6

1*6

tiaoa.

-0«

881-8

H«*

lOOM)

10-7
0-9

trace.
8-0
1*8
0-1
1«

979-1

loowT

• Diet o( dover, graaa, and oata.
^ Diet of potatoes) oooked.

f Diet of hay and potatoah

490

OOMPABATIVB PHYMOliOOY.

VitnftB«M OryitalUM MUm.— Thew are the derivativM
of the meliAolliin of the body, and not in any apprBclable de-
gree drawn fiom the food lt«lf. Beddei urea, and of much le«
Importance, occurring in small quantltiea, are bodies *»»* may
be regaided as le* oxidiied forms of nitrogenous metoboliMn,
suchM creatinin, xanthin, hypoxanthin (sarkin), hippurio aoid,
ammonium oxaluiate, and urea, CO j gg. The latter was
first prepared arUttclaUy from ammonium oyw»^NH«( ^'
with which it is isomeric. The quantity of urea is generally
in inverse proportion to that of hippurio acid, ««» Taries much
with the diet in the herblvora. The richer in proteids the diet,
a. when oats are fed, the greater the V>»^^f "^ "^ y^J^
horse this proportion raries with the ordinary diet betwwm
S'S and 4*0 per cent

When air has f re* aocess to urine for some time in a warm
room, the urea beoomes ammonium carbonate by hydration,
probably owing to the influence of microK>rgani«ns. thus:
CO (NHO.+ « HdO - (NHO. 00, ; hence the strong ammoniacal
smell of old urine, urinals, etc.

Urie acid (OAN.O1) occurs sparingly (see table), comWnett
with sodium and ammonium chiefly as acid salts.

Vm'BitNgwrai Orgute BodiM.— A series of weU-known
aromatic bodies occurs in urine, especially in tiiat of the horse,
cow, etc. These are phenol, oresol, pyrocatoohin, etc., which
occur not free, but united with sulphuric acid.

Jnmaia Mta— These are mostiy in simple solution, in
urine, and not as in some other fluids of the body, united with
Dtoteid bodies. The salts are chlorides, phosphates, sulphates,
StMtes, and carbonates ; tiie bases being -°*»»vl«JfT;
cakdum, magnesium. The phosphates are to be traced to the
food, to the ph*«phorus of proteids, and to 1>»»**P^«^ /^^
(lUdtiiin). The sulphales are derived from those ^the food
and frimi the sulphur of the proteids of tiie body. TJe gi«rt«r
part of the cariwnates is suppUed directty by the food In tiie
hone the salts of potassium and calcium (OaOO.), are abundant;
while in the dog magnesium and oaldum salts abound as sul-
idiates and phosphates.

Doubtless many bodies appear either '^^^y. ?' °~"*°5;
ally in urine that have so ht escaped detectton, which w»» "•»
the poisonous exhalations of tiie lungs, not the iMs important
because unknown to science.

it>»ife<« w » « w>>lltJi i »i*M< i » ll»iiii

the derivatirM
Rpprwiable de-
id of much IcM
lodiM that awy
ui metabolkm,
hippurio acid.

"he

latter
ON i

was

NH,J °'
«a ii generally
nd Tariea much
roteids the diet,
f urea. In the
ry diet between

ime in a warm
I by hydration,
rganiami, thui:
>ngammoniaoal

table), combined

i of well-known
Lat of the hone,
hin, etc., which

iple eolation, in
ody, united with
thatisB, lulphatea,
lium, potaminm,
he tnioedto the
hoephoriaed fata
uMe of the food
ly. The gr eate r
he food. In the
i), are abundant;
I abound aa aul-

irly or oooasion-
, which are, like
le l«fli important

RXORBTION BT THX KIDNEY.

481

Ataonul XTrlM.— Tb#r« ia not a mbatanoe in the itrii^B that
doea not ^ary under diaeaae, wliile the poaaible additiona act-
ually known are Ingion. Theae may be derived either from
the blood or ftom the kidneya and other parte of the urinary
tract. The kidneya aeem to take upon themaelTta more readily
than any other organ the duty of eliminating foreign mattera
from the body. But thia aspect of the lubjeot ia too wide for
detailed oonsideration in this work.

The atudent of medicine should be thoroughly familiar with
the urine in its normal condition before he eutera upon the
examination of the yariationa produced by disease. This is not
dilBoult, and much of it may be carried out with but a meager
aupply of qn?*ratu8. For thia purpoae, however, we recom-
mend some work deroted to the chemical and mioroscopio study
of the urine.

It greatly assists to remember a few points in regard to solu-
bilities. From a physiological point of view, the urine and its
variations, as the result of changes in the organism, may be ob-
aerved witti advantage in one's own person— eg., the influence
of food and drink, temperature, emotions, etc.

OoapantiYt.— In fishes, nptUes, and birds, uric acid re-
plaoea urea, and is very abundan.. In these animals most of
tWs substance is white. The urine ia passed with the fsBcea.

In certain groupa of invertebratea uric acid seems to be a
normal exoretioa • t

nn nKnumoN op uums.

By meana of apparatus adapted to register the changes of
volume the kidney undergoes, it is found tiiat this organ not
only responds to every general change in blood-pressure, but
to each heart-beat— that is, its volume varies momentarily.
This shows how sensitive it is to variations in bloiDd-pressure.

Theories regarding the secretion of urine may be divided
into those that are almost wholly physical, partly physksal,
and purely secretory: 1. To the first class belongs that of
Ludwig, whkh teaohea that very dilute urine is separated from
the blood in the glomeruli, and by a process of osmosis and
absorption of water by the tulnilar capillaries is gradually
concentrated to the normal. 2. As an example of the second
class is that of Bowman, who maintained that the greater part
of the water and some of the more soluble and diffusible salts

i'""i r"^

■■■■^■■ii

4i9

COMPARATIVK PHYSIOLOGY.

tof wpumtod by the glomwuli but th« ohanMtoriatlo ooiutitu-
«nta of the urine by the epithelium of the mud tubulee. 8. Aa
•n exAoiple of the third ii the theory of Heidenhain, who attrilK
uted little to blood-pre«ure in iteelf, and much, if not the
whole, tu the eeoreting aotiTity of the epithelium of the tubulee
more partioulnrly. This phytloloffiik ihowed that while llg»-

ownrt, IntOTVi

ture of a r^ miaed the biood-pruNure within a crloinenilua, it
waanot followed by any ineraati .n fhequ'' tityo^' *heaaoretion,
but by ita actual arreat He alao ahowed . -yt injection of a ooK
oi«d aubatanoe (aodiun aulphindigodal' . ' >. lu the blood, after the
pveaaure had been gi**^ low«t«d hy auodon of tb* lyinal cord,
led to ita appeamnoe in the a .-!■« and mioroaoop^ < <aininatieo
■howed tlfat it had paaaod hrov "h the epMMiial cella uf tiM
tobulea, not of the glomeruli.

It ia found, howerer, that after the femoval of a ligtiivi ;
applied to the renal artery the urine ia albaninoua, ahowing
plainly that the cella hare been injured by (he operation ; henoe
Heidenhain'a experiment deacribed ihove ia not valid againat
the blood-preaaure themy. ;li>i«o>Ter, too mneh muai not be
inferred from the action of fcweiga anbataneaa imdar the ab-
normal conditiona of aooh an experiaaent While aome phyai-
ologiata claim that the glomemli are Altering meohaniama, they
explain that filtration ia not to ba uu da i - a l o o d m ila oacUnary
laboratory acceptation, bat that the glomeraU dtaorinainate aa
to what thay allow to paaa, yet they in no way Buglain how
ihia ia done. X" f make the whole proeeaa depend on blood-
preaaure, and M! .ibuie little apecial aotioB ta the flat'epMMium
of the Malpighian ciq^aalea.

Though «e can not admit ttie full fovae of H4danhain'« ec"
perimen.^ aa he inteipreta them, we atill beUere that hia riewa
mn r i«c!t in harmony with the general lawa of Ikiogjr and the

,vO'sa>afliBfasp(«t-«?s^,«fe : nv^Feaaiias^^MiKJsisBfWHa

oonstitu-
libulM. S. Aa
in, who •ttrib>
^h, if not tha
UMtubnlM
whUelig».

• kMui: T.

SKJC

flrlooMnilai, it

m' 'heMoretion,

MsUon of a ool-

[Uood, after the

k ' vaminatian
iiai cella uf tha

il of a Ug!<i.','v >
kinoua, ahowing
Miation; henoa
>t valid afainat
ih muai not be
under the ab-
ile aomephjil-
whanjama, they
ia ila oedioarjr

<y B jn ia in haw
pend on blood-
flatepWMliain

[«>id«nhain's «)►■
that hlaviewa
»iolog7 andtlie

BXOBVTION BT TBB KIDNET.

498

apeoial facta of renal aeoretion. Mora recently it haa been ran-
dared clear that phyaioal theoriea of the worli of the Iddney can
not hold, eren of Uie f lomeruU, which are ahown to be^ aa we
ahould have expected, true aeerating organa. Now, there can
be no doubt that blood-preaauie ia a nwat important determin-
ing condition here aa in f>thar accreting proeaaaea, in the mam-
nwl at all ereuta; but whether of itaelf or beoauae of the influ-
ence it liaa on the rapidity of blood-flow, it ia difficult to deter-
mine; or rather whether aolely to the latter, foir that the con-
atant aupply of fraah blood ia a regular condition of normal
aecretion there can be no doubt. Further, it aeema probable that
blood-prearare haa more to do with the accretion of water than
auy other conatituent of urine. But we maintain that it ahould
be called a genuine aeoretion, and that nothing ia gained by
uaing the term " filtration "—on the contrary, that it ia mialead-
ing, and tenda to dirert i|ttention from the real though often
hidden nature of vital p r oeeaaea. The facta of diaaaac and the
evidence of thcnpeutica, we think, all favor auoh a view of the
work of the Udneya.

Nervea having an influence over the accretion of urine aimi-
lar to thoae acting on the digeative glanda have not yet been
determined. Hie powerful influence of emotion, eapecially
well aeen in thd dog, over the aeoretion of urine ahowa that
there muat be nervoua chaanela through which the nerv»>
centera act on the kidneya; though whether the reaulta are not
wholly dependent upon vaao-motor effeota may be ooaaidered
aa an open queation by many. We iliink auch a view Im*
probable in the higheat degree. Hie moat recent in v eeti gati on a
would aeem to ahow that the vaao-motor fibera run in the dor-
aal nervaa, eqpeoiaUy the elevaiiih, twelfth, and thirteenth, in
the dog, and that of theae the vaaoHxmatriotorB are the beat de-
veloped.

Pltt w lt* — 1 —When the Iddnfya are exdaed, the uretera
ligatured, or when the former are ao diaeaaed aa to be inoa-
paUe of perfcMrming thdr funotiona, death ia the reault, bring
preeedad by nuuked deprcerion of the brain-centera, paaaing
into eoma. Fiwaetly which of the retained prodnota bringa
about thaae raanlti ia not known. They are likely due to aev-
ecal, and it impreaaaa im the mind the importance of thoae pro-
eeaaea by which the oonataBtly anwimnlating waate ia eUmi-

nated.

''mimt^

424

OOMPABATiyB PHTOIOLOOT.

nOB BMJnJUSBOM OF jnUMM.

We now prawnt in ooncise form certain fumbB on which to
bttw opinionB m to the nature of the proc eww l^ which the
bladder is emptied.

It will behome in mind that the aeoretion of urine ia oon-
■tant, though of ootune very variable, that the urine is con-
veyed i|i minute quantitiee by rhythmically contraotUe tubes
(nieten) which open into the bladder obliquely; and that the
Madder itMlf is highly mnaeular, the cells being arranged both
oiicnlarly and obliquely, with . a spedal aocumnlation of the
circular fibers around the neck of the organ to form the qiJktnc-
lereesjoo!.

1. It is found that the p res sure which the sphincter of the
bladder can withstand in the dead is much less (about one
third) than in the living subject 8. We axe conscious of being
able to empty the bladder, whether it contains much or little
fluid. 8. We are equally conscious of an urgency to evacuation
of the vesical contents, according to the fullness of the oigan,
the quality of the mine, and a variety of other conitionB.

4. Amotions may either retard or render micturition uigemi

5. In a dog in which the cord has been divided in the dorsal
regkm. some months previously, micturition may be induced
reflezly, as by sponging the anna. 6. In the panJyred there
may be retention or dribbling of urine. 7. In oa s e s of urethral
obstruction fh>m a calculus, stricture, etc., there nuqr be azoess-
ive activity of the mnaeular tissue of the bladder walls. 8.
Evacuation of the bladder may occur in the absence of coa-
aciousnw (sleep).

The most obvious condnaions from these fkots are that— 1.
The urine finds its way to the bladder partly through muscular
(peristaltic) oontraetions of the urrters, partly through gravity,
in man i^ all events, and partly from the p re ss u re within the
tubules of the kidneys themsdves. 2. The evacuation ni urine
may take place independently of the will (see 8), and ia a reflex
it!) act. 8. MictnriticKi mi^ be initiated by the will, which ia
uanally the ease, when by the aetion of the abdominal muades
a little urine is squeesed into the urethra, upon which afferent
impulses set up contractions t^ the bladder by acting on the
detmacMr center of the cord and at ithe same time inhibit the
center presiding over the sphincter (if such there be), pennitr
ting of its relaxation. 4. BmotionB seem to infetfeie with the

miKiftiam

iHMMtaiwiiii

' aaA MBenl vimr of the guMo-mtmrf mmmmIu in Um ttaUion

i the MMiM (OhaavcM). A, Wt kUimi B, right uaiiMr; a. 6, weteni; C. C,

■taa; D, Utddart >. B. tcMfelM; «, heed, of eptdUlmte; ^, m

Us: #, «Mta«nt OMWI; O, peWle dilatation of tfefttent canal; H, left

IvwieM; the ^iff»t hm been remand, alang with the deferent canal of

4S0

COMPARATIVE PUYSIOLOOT.

aide, to •how inMKion of nratan into blwld«r; I, DrMtato; J, Ooirper't
gUndi; K,_ inembtMoiujor Intai^lvfe poftiaBof uratlmrcaM]; l, iu bolboat

partian: H, eavernoo* body of pent*; m,mi^lt» toatt:
aominu aorta: t,S,art«riea '

f «» |#vHw, Iff*, w*. ■■■ svfuvv. N« head of pnila; 1. ab*

(nnial) gtviur oB principal eapnilar artMy; % tow-

matic artery; 4, common origin of ■mmilcal and artariea of Imlb; 6, nmblPeal
artery; 8, iia veaical biBMh; 7, internal ailery of bolb; 8^ it* vceieo-proetatlc
branch.

ordinary ooHfroI of the Itoain-oentera over thoM in the spinal
cord. 5. It may be amuned (hat the normal tone of the
sphincter of the bladder is maintained reflexly by the spinal
cord. The unwonted muscular contraction associated with an
obstruction to the outflow of urine may be in part of nervous
origin, but is also, in all probability, owing in some degree to
the muscle^jells resuming an independent contractility, due to
what we recognize as the principle of reversion. The same is
seen in the heart, ureters, and similar structures.

Pathdigiiml— There may be incontinence of urine from pa-
ralysis, the cerebral centers being unable to control those in
the spinal w>rd. Dribbling of urine may be due to retention in
the first instance, the tone of the sphincter being finally over-
come, owing to increase of preanm within the bladder. Over-
distention of the bladder may arise in consequence of lack of
tone in the muscular iiralls, thou^ this is rare. Strmtgury is
due to excessive action of the walls of the bladder and the
sfdiincter. brought about refiexly, when the organ is unduly
irritable, as in inflammation, after the abuse of certain drugs
(cantbarides), etc.

Oonpantira.— In man the last dnqis of urine are expelled
by the action of the bulbo-oavemofms muscle and perhaps some
others. In the dog and many other animals the regulated and
voluntary use of this muaole, marked in a high degree, produces
that interrupted flow so oharaoteristic of the micturition of
these animals.

lOflajMiy.— Urine is in mammals a fluid of variable specific
gravity and reaction, yellow in odor, and containing certain
salts, pigments, and aitrogenoos bodies. The chief of the latter
iitaea.

The kidneys and skin eqpeeiaUy supplement one another,
and normally great activity of the <me implies lessened ae-
activity of the other. Thisisavailedof in the treatment of die-

Both the Malpighian capsules and tibe rmal tubules have a
true seoretmy fnnotion, though the larger part of the water of
urine is secreted by the former. Mood- pr ea ror e is an important

Min

Li i niniijmi,j i | i ii j w i ,.i ii » ■

Me: J, Cowper'i

1 of pcnit; 1. mXh
u wienr; t, fgm-
bnib; 6, nmblPoil
* TMioo-ptattatic

iu the ttpinal
tone of the
by the spinal
uitedwith an
lit of nervous
>me degree to
otility, due to
The same is

irine from pa- ■
ntrol those in
to retention in
g finally over-
ladder. Over^
loe of lack of

(Strangury is
adder and the
pai is unduly

owtain drugs

le are expelled
1 perhaps some
regulated and
Bgree, produces
micturition of

rariable specific
taining certain
iet of the latter

it one another,
es lessened ao-
rottaaentof dis-

tuholeshave a
of the water of
is an imp(»tant

EXCRETION BY THE KIDNEY.

4S7

condition of secretion, though it is Ukely that ^is «» chiefly
3«» it favors a rapid renewal of the blood cifcuI-Ung
S^ugh the organ. Whether there are nerves timti^ce
Iec«>tion diiwtly, as in the case of the slan, is not determmed.
C^on '^ the renal fmictions lead. *« -y^P^ms m
whTch ttie nervous system is recogniwd " »»ff«"°» *°. ^^
Txtent often of coma, ending in death. Theunneof mostottier

:SZl^?more c^trated than that of man , ^^^^^_
iu camivopa being acid, and in herbivora alkaline m «>acfaon.

THE METABOLISM OF THE BODY.

Ih the widest sense the term miiahoMiin may he oonven-
iently applied to all the numerous changes of a chemical kind,
resulting from the activity of the protoplasm of any tissue or
organ. In a more restricted meaning it is confined to changes
undergone by the food from the time it enters till it leaves the
body, in so far as these are not the result of obvious mechi . 'lad
causes. The sense in which it is employed in the prbucnt
chapter will be plain from the context, though usually we shall
be concerned with those changes effected in ^he as yet compara-
tively unprepared products of digestion, by vsrhich they are ele-
vated to a higher ranic and brought some steps nearer to the
final goal toward which they have been tending from the first
As yet our attempts to trace out these steps have been little
better than the fhtitiess efforts of a lost traveler to find a road,
the general direction of which he knows, but the ways by which
it is reached only the subject of plausible ocmjecture. We
shaU therefore not discuss the subject at length from this point
of view.

VHB mRAaoum or na uvbr.

ISiis organ has two well-recognized functions : 1. The for-
mation of bile. i. The formation of glycogen. We have
already considered the first

Olyoogen may be obtained from the liver of mammals as a
whitish amorphous powder, having the chemical ctMnpoaition of
starch, and has in fact been termed animal starch.

By appropriate ti«atment it may be converted int6 sugar by
a process of hydration (C*Hi.Ot -I- HiO a CtHitO*).

The principal facts as to the storage of glycogen in the liver
may be briefly stated thus :

1. Glycogen has hem found in the liver of a large number

MOM

THE MBTAB0L18M OF THB BODY.

4S»

►DY.

ly be oonven-
shemical kind,

any tiflsae or
ed to changes
1 it leaves the
OS meebi . 'cal
D the prudent
lually we shall
I yet oompara-
1 they are ele-

nearer to the
from the first
are been little
bo find a road,
irays by which
ijectnre. We
^m this paint

: 1. The for-
n. We have

inft»nmit^» as a

cfMupoaition of

I int6 sugar by

pen in the liver

I large number

of Bwrnpa of animals including some invertebrates. J. Among
mammals it is most abundant when the animal feeds largely
on oarbohydiates. 8. It is found in the liver of the carmvora,
and in those of omnivom, when feeding exclusively on ilesh.
4 When an animal starves (does not feed), the glycogen grad-
uaUy disappears. 6. A f atdiet does not give rise to glycogen.
«. l>uring early foetri life glycogen is found in all the tissues,
but later it is restricted more and more to the liver, ttough
even in adults it is to be found in various tissues, espociaUy the

muscles, from which it is almost never absent

From tiie facts tiie inference is plain tiiat glycogen is formed
from carbohydrate materials ; or, to be rather more Mutious,
that tiie formation of this substaooe is dependent on the pres-
ence of such material in the food.

Th* 7(M of OlyoogML— No positive statement can be made on
thissubjeot Itisgenerallybelievedtobetransformedintosugar.

What is the fWe of the traaafcmned glycogen t What be-
comes of flie sugar ! We can answer, negatively, tiut it is not
rm up fai the blood, it is not oxidised flieie ; but by what
Uwuea it is used or how it is made available in the economy is
a suUect on which we are profoundly ignorant The presence
of so much glycogen in the partiaUy developed tissues of the
foetus points to ite importance, and suggests its being a crude
material which is laid up to be further eUboiated, as in vege-
tables, by tiio growing protoplasm.

The physiological signiflcanoe of the peenMar structure of
this organ, tiiough not yet fully understood, is much plainer
than it was till recently. The student is recommended to look
carefully into the histology of the spleen, espedaUy tiie to-
tribution of ite muscular tissue and the peculiarities of ite
blood-vascular system. It has afaready been pointed out that
tihere is little doubt that leuoocyteB are manufactured here even

in the adult, poeriUy also red cells; and that the latter an dis-
integrated, and the resulting substances worked over, possibly
by this organ itself. This view is rendered probable, not only
bymierasoopiostndyof tiie organ, but by a chemical examinar
tion of the splenic pulp; for a ferruginous proteid, and nnmer^
ons pigments, of a duvactw such as hannonises with this 0(m>

option, are found. .

■iui/l.jMiP

tss^steimmitmm

480

COMPARATIVB PHYSIOLOGY.

The fact that the «pleen-pulp doee not agree in compoeition
with either blood or •erum ; that it abound* in extractive* such

s.- oM v.>«4«ai aeetlon or • mall MiMTtetal portion nf Imiiuin tplc^i: Men with

pW.ffirSK«rrn ^-.^Srah M wterjr I. *~n cntt«n.v.«ely. in ti.e other.
nSiSdlmSly; d. Injected arteriiU twlgi; e. epleen-pulp.

as lactic, butyric, formic, and acetic acids, together wiOi inoeit,
xanthin, hypoxanthin, leucin and unc acid— points to its being

Fia.an.— Thin ■eetkmor •pleeB-milp. .
a nutll veiain the intenticee of pnl
dn^ which we In eontlnnitrwith otl
of pulp; H, w«U of TelB. "^- -'— '

■». ehowinit mode of origin of
'llto^iM hoSiee ammw ted corpoeelee are pde ea>>

1 compodtion
tractiTM such

n •plc^.'; Men with
rabecol*, ', e, Mai-
«iMl7, In Ute other.

ter with inosit,
nts to its being

IB mode of origin of
dwilhblood-corpas-
eeeotretifanitlMM
pneelee are pale eoc-

THE MBTTABOLISM OP THE BODY.

481

the seat of a complex metaboliwn, though neither the changea

thenuelves nor their purpoM are well understood.

Neverthelftw, it muat be admitted that to reoogniie thia was

a great advance upon the view that the ipleen had no impor-

tant function, and that thia was shown by the removal of

the organ without

change in the Ani-

mal'a economy.
But to believe

that there are no

such changes, and to

have clear jnoof of

it, are two difltoent

things. Asamatter

pf fact, closer study

does show that in

some animals there

are alterations in the

lymphatic glands

and bone -marrow,
which organs are
undoubtedly manu-
facturers of blood-
cells.

These changes ,

ara unquestionably compensatory, and that other similar ones
owresponding to comparatively unknown functions of the
qileen have not as yet been discovered is owing likely to our
fkdlures rather than their real sbsence. We dwell for a mo-
mv<fnt on this, because it illustrates the danger of the sort of rear
sonii^g that has been amdied in the case of this and other or-
gans; and it shows the hnportanoe of reedgniiing the force
o| the general principles of biology, md also the desiraMlity
of refraining fiwn drawing conclusions that are too wide
for the i^remises. In every department of physiology it must
be mfwe and mm recogniwd that what is true of (me group
of animals is not necessarily true of another, <sr even <rf other
individuals, though the differences in the latter case are of
oouxw usually leas marked. We have referred to this be-
fore, and shall do so again, for it is aa y«ft bui. ^ little con-

uTwphatle) eorpmcJcTftiter CadiatV ' "* —

ISSSTwiieriKSSSiirirpiisa^ a. muSS^

■ploen-polp, taJwst^C, aiterr of eorpoaele ramify-
Sgln TSNmphatte tHrae. The ciear apaoe aioand
eSpiMcie repreaeata a lymphatic einna.

m w i-wn'M ' .i i Wi' J8ii < immmmvax

mmm

4tS

OOMPABATIVB PHTSIOLOOT.

OP PAT.

It is A well-known fact that, speaking generally, a diet rich
in oarbohydratee fayon fat formation, both in man and other
animals; though it is not to be forgotten that many persons
seem to be unable to digest suoh food, or, at all events, to as-
similate it so as to fbrm fat to any great extent Pttrsonsgivem
to exoessiTe fkt production are as fkeqoently as not sparing
users of fat itself.

It is possible in man and probable in ruuiinants that fer-
mentations may occur in the intestines giving rise to fatty adds
which are possibly converted into fall by the cells of the villi
or elsewhere. Certain feeding experiments favor the view
tiiat carbohydrates may be converted into fat or in some way
give rise to an increase in this substance ; for it is to be borne
in mind that fat may arise fkom a certain diet in various
wajrs other than its direct transformation into this substance
itself.

There are certain facts that make it dear that Hi can be
formed from proteids: 1. A cow will produce more butter than
can be accounted for by the fat in her food alone. S. A bitch
which had been fed on meat produced m(»« fat in her milk
than could have been derived directly from her food, and this,
when the animal was gaining in wdi^t, which is usually to be
traced to the addition of fat; so that the fat of the milk was
not, in all probahility, derived from that of the dog's body;
and, as will be seen presently, can be accounted for without
such a suppodtion. 8. It has been dicwn by analysis that 478
parts of Alt were depodted in the body of « pig for every 100 in
itofood.

These facts of themselves suffice to diow that fat can be
formed from protdd, or at least that proteid food can of itsdf
give rise to a metabolism, resulting in UA formationt and the
latter is probably the better way to state the case in the pre s en t
condition of knowledge.

That fat is a real formation, dependent for its compodtion
<m the work of living tissues, is dear from the wdl-known fret
that the fat of one anunal differs from fliat of another, Imd that
it pr e s erv e s its identity, no matter what the food may be, or in
what form fat itsdf may be provided. Certain constituents of
the animal*s fat may be whdUy absent from the fat of its food,
jret they appear just the same in the fat produced under such

f, • diet rich
an And other
ittny penona
eyenti, toM*
Penona given
I not iparing

inte that fer^
itofattyacida
la of thevilU
ror fli0 Tiew
' in aome waj
ia to be borne
let in yarioaa
Ihia aubatanoe

lat fM can be
re butter than
e. S. A bitch
it in her milk
food, and thia,
auaoallytobe
r themUkwaa
le dog*a body;
id for without
ialyaiathat47S
or every 100 in

hat fat cam be
odoanof itaelf
latkm; and the
B in the prawnt

ita oompoaition
reU-known ftust
lother.imdthat
d mi^ be, or in
oonatitnenta of
I fat of ita food,
used under auoh

THK METABOLISM OP THB BODY.

488

diet. Even beea can conatruot their wax from protdd, or uae
unlike aubatanoea, aa aealinfrwax.

riSS^'^ ^IIHNW UUk-dMt IB Idp^.

But hiatologioal examination of farming adipoae iiaaue itaelf
ihrowB much light u^on the aubject Fafr«ella are thoee in
which the prot^laam haa been Uuigely leplMwd by fat. The

«ffilHill»utt^iNnMffri

HWWMKWwftfiii"'^

484

OOMPARATIVR PHYSIOLOOY.

totter it Men to ariw in the fonner m very ■mall globulei
which run tof(ether more and more till thqr may wholly n-
place the original protoplasm.

The history of the mammary gland i«, perhape, still more
instructive. In this case, the appearance oi the cells during
lactation and at other periods is entirely different. Fat may be
seen to arise within these cells and be extruded, perhaps in the
same way as an Amoeba gets rid of the waste (rf its food. So
far as the animal is concerned, milk is an excretion in a limited
sense.

It is, in the nature of the case, impo»ible to follow with
the qre the formation and separation of milk-sugar, casein, etc.

Vie. v.— L Aetam tnm nai
Darlnc MentlMi of Milk,
patecelto.

nw of ■ bitok wbMi taMctlv* (ttUt HaMenlukUi). IL
0, 6, mUk-gwbolM: «, 4, i, oolMtmrn-corpaicM; /,

But the whok prooess is plainly the work of the cells, and in
no mechanieal sense a msre deposition of fat, etc., from the
blood ; and the same view applies to the oonstruotion of fat by
connective (adipoee) tissue.

Whether hi, as such, or fatty acid, is dealt with without
being built up into the protoplasm of the cell, is not known ;
but, taking all the facts into the account, and considering the
behavior of oelb generally, it seems most natural to regard the
construction of fat as a sort of secretion or excretion. To sup-
pose that a living cell acts upon material in the blood as a
workman in a factory on his raw material, or even as a chemist
does in tho laboratmy, seems to be too crude a conception of
vital prooessee. Until it can be rendered very much dearer
than at present, it is not iutfe to assume that their chemistry is
our chemistry, or their uiethods our methods. It maj be so;
bat let us not, in our desire for simple explanatjons or undue
haste to get some so'.i of theory tliat apparently fits into our

All globules
kjr wholly re-
ps, still more
cells during
Fat may be
rhaps in the
itofood. Bo
n in a limited

follow with
kr, casein, etc.

map

iftnr HeMmlMln). IL
dMtmm-cotpaaclM; /,

the cells, and in
st, etc., from the
ruction of fat by

alt with without
1, is not known ;
I considering the
iral to regard the
cretion. To sup-
1 fhe blood as a
even as a chemist
I a conception of
ery much dearer
heir chemistry is
I. It maybe so;
nations or undue
ftttly fits into our

fUB MBTAB0LI8M OF TUK BUDY.

485

own knowledge, assume it gratuitously, in the absence of the
clearest proofs, especially when our failures on this supposition
are so numerous.

We may say, then, tliat fat is not merely selected from tlie
blood, but formed in the animal tissues ; that fat formation

ria. M — MkniMOiric •ppmmmm of-Ijnnk; II, eiMm; lU, batter; IV. colottrnm
o(iiiM«; V,«olMtniiii of oow (after TbaabaCw).

may take place when the food consists largely of carbohydrates,
when it is chiefly proteid, or when proteid and fatty. In other
words, fat results from the metabolism of certain cells, which
is facilitated by the consumption of carbohydrate and fatty
food, but is possible when the food is chiefly nitrogenous. We
must, however, recognise differences both of the species and the
individual in this respect, as to the extent to whidi one kind of
food or the other most favors fat formation (excretion). The
use of the adipose tissue as a packing to prevent undue escape
of heat is evident ; but more important p u rposes are probaUy
served, as will appear from later considerations.

IMiolafiML— Excessive fat fonnation, leading to the ham-
pering of respiration, the aoti«m of the muscles, and, to a certain
extent, many othe^r Auctions of the body, does not arise in man

I J

486

COMPARATIVB PHTSIOLOGY.

usiuillj till after middle life, when the organiim haa aeen Ha
beat dajB. It eee m e to indicate, if we Judge by the frequency
of fatty degeneration after diaeaae, that the {irotoplaBm atopa
abort of ita beat metaboUam, and baooniea degraded to a lower
rank ; for certainly adipoae tiaaue doea not occupy a high
place in the hiatological aoale. Such pathological facta throw
a good deal of light upon the general nature of hi excre-
tion, aa it would ba better to term it, parfaapa, and aaem to
warrant tha riew that we have praaented of the mataboUc pro-

Although the nerrea goyeming the wscretion of milk have
not been traced, there can be no doubt that the nenroua qratem
controla thii gluid alao. The influence of the amotiona on both
the quantity and quality of the milk in the human aubject and
in lower animals is well known.

CoapiunitiTa— While breeders reoogniae certain foods aa
tending to fait formation and othera to milk production, it ia
interesting to note that their experience shows that race and
individuality, even on the male side, tell. The same oonditionH
being in all leapecta obaerved, one breed of cows giTea more
and better milk than another, and the bull ia himself able to
transmit this peculiarity ; for, when c r oaaed with inferior Inveds,
he improrea the milking qualitiea of the latter. Individual
differenoea are also well known.

TBS n'UUI OF

It will be abundantly evident that our attempta to follow
the changea which the food undevgoea fkom the time of ita
introduction into the blood until it ia removed in altered form
from the body haa not been aa yet attended with great auccesa.
It ia possible to establiah relatione between the ingesta and the
egeata, or the income and output which have a certain value.
It is importauti however, to remember that, when qoantitive
estimations have to be made, a amall error in the data becomes
a large error in the final eatimate ; one untrue assumption
may vitiate completely all the conclusions.

In discussing the subject 'we rindl iBtreduce a Bimber of
tablea, but it will be remembered that the reaults obtained by
one investigator difder fhnn those obtained by another ; and
that in all of them there are some deviations from atrict ao-

— • -■-.iii.uiiir

II ni-iiiiimilala— teaU

MfMMMHP

hM Men Hi
M frequency
ofriann ttoiM
4 tt> • lower
jupy A high
J facts throw
of ftkt exor*-
•nd Mem to
MtaboUo pro*

of nuilk have
urroua eyitem
itiona on both
n Bubject and

tain foods as
>duotion, it is
that race and
me oonditionH
n givM more
ImMlf able to
nfbrior breeds,
Individual

opts to follow
le time of its
I altered form
k great suooess.
ngestaandthe
certain value,
ben qoantitive
e data becomes
ue assumption

e a number of
Its obtained by
r another ; and
from striet ao-

THB METABOLISM OP THE BODT. 487

cunwy, so that the iMults must be regarded as only approxi-
mately oorrwjt. It is, however, we think, better to examine
such Btattttioal tablM of analyses, etc., than to rely on the mere
verbal sUtement of certain rMults, as it leaves more room for
individual judgment and the assimilation of such ideas as they
may suggest outside of the subject in hand. ,„ . .

The subject of diet is a very large one -, but it will be evi-
dent on i^ecUon that, before an average diet can be prescribed
on any soientiao grounds, the composition of the body and the
nature of thoM process* on which nutrition generally depends
must be known. Not a little may be learned by an examina-
tion of the behavior of the body in the absence of all diet,
when it may be said to feed on itMlf, ono tissue supplying
another. AU starving animals are in the nature of the case

carnivorous. , „ .

For the oat an analysis bu yielded the following ;

Muscle and tendons. 460 per cent

Bones **'''

i^ "'0 ;;

Mesentery and adipoM tissue 88 ^

Liver J*J „

Blood (escaping at death) »« ^

Other organs and tissues , * . , „ i

The h»ge proportional weight of the muscles, the •imi>»riy
large .ZSt of bl.od they roceive, which i-/tfWng, »«.«;•
c-Tof the liver, also suggest that Je rcieU.^\i^^ot th«e
struci,ir.:«, is veiy «!tive, and. we '^^^Jd e«P«t t^ they
would loM groaUy during a starvation P«»«Alt taa natter of
Jlmon oSrin that -nimal. do loM wi^ «d g~w
thin under such ciroumstances, which means that ttey must

CiXmuMlM and the adipoM «««»•^^*S"Jf*^Ii^^;
made to determine exactly the. extent to wWJ t»«^«;
tissues do suffer during complete absUnenoe from food, and
this may be gathered from the table given below.

It wUl n<5 be forgotten that about three fomrths of the body

is made up of water, so th%t the Iom of a large amount of the

latter during utarvation is to be expected. ^ thi^^j.

In the caM of a oat during a starvation period of thirteen
davs 784 gramuMss of soUds were lost, of which 848 grammes
wSfat Sd?18m«Mle-i. e.. about one half of the total loss
was referable to thsM two tissues alone.

The other tissues lost as foUows, estimated as drf solids .

■wKwwewwsfttr-

--.^i .iM i n i J ui. i i .lU is' w ii

488

COMPARATIVE PHYSIOLOGY.

Adipose tissues. 97*0 per cent.

Spleen 6.31

liver 66-6 "

Mnsoles 30-2 "

Blood... 17-6 "

Brain and spinal cord U'O "

It will be observed (a) that the loss of the fatty tissue was
greatest, nearly all disappearing; (6) that the grandular struct-
ures were next in order the greatest sufferers ; (o) that after
them oome the skeletal muscles.

Now, it has been already seen that these tissues all engage
in an active metabolism with the exception of adipose tissue.

The small loss on the part of the heart, which is still less for
the nervous system, is especially noteworthy. The loss of adi-
pose tissue is so striking that we must regard it as an especially
valuble storehouse of energy, available »a required.

When we turn to the urine for information, it is found that
in the above case 27 grammes of nitrogen were excreted and
almost entirely, of course, in the form of urea; and since the
loss of nitrogen from the muscles amoimted to 16 grammes, it
will appear that more than one half of the nitrogenous excreta
is traceable to the metabolism of muscular tissue. It has been
customary to account for the urea in two ways: first, as derived
from the metabolism of the tissues as such, and continuously
throughout the whole starvation period; and, secondly, from a
stored sui^lus of proteid which was assumed to be used up
rapidly during the early days of the fitting, and was the luxus
consumption at certain investigators.

OomptntiTe. — Experiment has shown that the lenrrth of
time dur&ig which different groups of animals can endiiro com-
plete withdrawal of food is very variable, and this applies to
individuals as well as species. That such differences hold for
the^ human subject is well illustrated by the history of the sur-
vivors 6f wrecks. Making great allowances for such devia-
tions from any such results as can be established by a limited
number of exiteriments, it may be stated that the human being
succumbs in from twenty-one to twenty-four days; dogs in
good condition at the outset in from twonty-eighi to thirty
days; small mammals and birds in nine days, and frogs in
nine months. Very much depends on whether water is allowed
or not— life lasting much longer in the former case. The very
young and the very old yield sooner than persons of middle

THE METABOLISM OF THE BODY.

489

percent.
It

M
u

tty tissue was

idular struct-

o) that after

» all engage
pose tissue.
iS still less for
e loss of adi-
an especially
I.

is found that
excreted and
und since the
5 grammes, it
venous excreta
It has been
rst, as derived
I continuously
wndly, from a
k> be used up
was the luxus

the Jenrrth of
n endure com-
lihis applies to
enoes hold for
ory of the tur-
v such devia-
1 by a limited

human being
lays; dogs in
tight to thirty

and frogs in
»ter is allowed
ise. The very
aob of middle

age. It has been estimated that strong adults die when they
lose A of the body-weight. Well-fed animals lose weight more
rapicUy at first than afterward.

Dirt. — All experiments and observations tend to show that
an animal can not remain in health for any considerable period
without having in its food proteids, lata, carbohydrates, and
salts; indeed, sooner or later deprivation of any one of these
Mrill result in death.

Estimates based on many observations have been made of
the proportion in which these substances should enter into a
normal diet.

For the herbivora from 1 to 8-9 (stmie claim 1 to 5i) is the
estimated ratio of nifax>genous to non-nitrogenous foods; and 2
of the former to 1 of fat.

One conclusion that is obvious from analysis of foods is that,
in order to obtain the amount of proteids needed from certain
kinds, enormous quantities must be eaten and digested; and as
there would be in such cases an excess of carbohydrates, fats,
etc., unnecessary work is entailed upon the organism in order
to dispose of this; so that to feed a working horse entirely on
grass, a dog wholly on porridge, or a man on bread would be
very unwise.

rBBSXata SJOPSRIIOBSmi (lagMU and BgMU).

If all that enters the body in any form be known, and all
that leaves it be equally well known, conclusions may be drawn
in regard to tbe uoetabolisro the food has undergone. The pos-
sible sources of fallacy will appear as we proceed.

The ingesta, in t'ue widest sense, include the respired air as
well as the food ; though from the latter must be subtracted
the waste (undigested) matters that appear in the faeces. The
ingesta when analjrzed include carbon, hydrogen, oxygen, ni-
trogen, sulphur, phosphorus, water, and salts, their source being
the atmosphere and the food-stuffs.

The egesta, the same, and chiefly in the form of carbonic an-
hydride, of water from the lungs, skin, alimentary canal, and
kidx^eys, of salts and water from the ddn and kidneys, and of
nitrof vn, chiefly as urea almost wholly from the kidneys. Usu-
ally in experimental determinations the total ouantiity of the
nitrogen of the urine is estioaitted. If free nitrogen plays any
part in the metabolic prooessea it is unknown.

440

COMPARATIVE PHYSIOLOGY.

A large number of feeding experiments have been made by
different inyeetigatom, chiefly, though not exclusively, on the
lower animals. Some such method as the following has usu-
ally been pursued: 1. The food used is oar^lly weighed and a
sample of it analysed, so thai more exact data may be obtained.
2. The amount of oxygen used and carbonic anhydride exhaled,
as well as the amount of water given off in any form is esti-
mated. 8. The amount of the nitrogenous excreta is calculated,
chiefly from an analysis of the urine, though any loss by hair,
etc., is also to be taken into account.

It has been generally assumed that the nitrogen of the ex-
creta represents practically the whole of that element entering
the body. This has been denied by some investigators.

The respiratory products have been estimated in various
ways. One consists in measuring the quantity of oxygen sup-
plied to the chamber in which the animal under observation is
inclosed, and analjrdng from time to time samples of the air as
it is drawn through the chambsr; and on these results the total
estimates are based.

It will appear that even errors in calculating the composi-
tion of the food— and this is very variable in different samples,
e. g., of flesh; or any errors in the analysis of the urine, or in
the more difiicult task of estimating the respiratory products,
may, when multiplying to get the totals, amount to serious de-
partures from accuracy in the end; so tliat all conclusions in
such a complicate case must be drawn with the greatest cau
tion. But ii. can not be doubted that such investigations have
proved of much practical and some scientific value. The labor
they entail is enormous.

Vitrogenou IquQilxriinn.— It is possible to so feed an ani-
mal, say a dog, that the total nitrogen of the ingeeta and ^[esta
shall be equal; and this may be accomplished without the ani-
mal losing or gaining weight appreciably or again while he is
gaining. If there be a gain, it can usually be traced to the
formation of fat, so that the proteid, we may suppose, has been
split up into a part that is constructed into fat and a part which
is reinesented by the urea, the fat being either used up or stored
in the body. Moreover, an analysis of a pig that had been fed
on a fixed diet, and a comparison made with one of the same
litter killed at the commencement of the experiment, showed
that of the dry nitrogenous food only about seven per cent in
this uiimal, and four per cent in the dieep had been laid away

jbeen made by
Bively, on the
ring has usu-
reighed and a

be obtained,
le exhaled,

form is esti-
> is calculated,

loss by hair,

m of the ex-
inent entering
Wtors.

ed in various
»f oxygen sup-
obscnrvation is
» of the air as
esults the total

IT the cpmposi-
'erent samples,
he urine, or in
ktory products,
t to serious de-
conclusions in
.e greatest cau
itigations have
lue. The labor

so feed an ani-
estaand egeaiA
ithout the ani-
ain while he is
a traced to the
ppose, has been
id a part which
led up or stored
it had been fed
me of the same
riment, showed
ren per cent in
leen laid away

THB METABOLISM OF THE BOOT.

441

as dry proteid. It is perfectly plain, tiien, that proteid diet
does not involve only proteid construction within the body.

Cmpfntiv*.— The amount of flesh which a dog, being a
carnivorous animal, can digest and use for the maintenance of
his metabolic processes is enormous; though it has been learned
that ill-nourished dogs can not even at the outset of a feeding
experiment of this kind maintain the equilibrium of their body
weight on a purely flesh diet (fat being excluded). They atl
once commence to lose weight — i. e., they draw upon their own ;
limited store of fat.

The digestion of herbivora being essentially adapted to a
vegetable diet, they can not live at all upon flesh, while a dog
can consume for a time without manifest harm ^g io jf^ot its
body-weight of this food.

Man, when fed exclusively on meat soon shows failure, he
being unable to digest enough to supply the needed carbohy-
drates, etc. But the large amount of urea in the urine of car-
nivorous animals generally, and the excess found in the urine
of man when feeding largely on a flesh diet, show that the pro-
teid metabolism is under such circumstances very active.

It is also a well-known observation that carnivorous ani-
mals (dogs) are more active and display to a greater extent
their latent ferocity, evidence of their descent from wild car-
nivorous progenitors, when like them they feed very largely on
flesh. The evidence seems to point pretty clearly to the con-
clusion that a nitrogenous (flesh) diet increases the activity of
the vital processs of the body, and especially the proteid me-
tabolism.

But in all them considerations it must be borne in mind that
the metabolic processes go on in the tissues and not in the
blood, and probably not in the lymph. Not that these fluids
(tissues) aro without their own metabolic-processes for and by
themselves; but what is meant to be conveyed is that the met-
abolic processes of the body generally do not take place in the
blood.

Hw IfliMtt of 0«l«tiii in the Btet— Actual experiment shows
that this substance can not take the place of proteid, though it
also makes it evident that loss of the latterlsaffices when mixed
with a certain proportion of gelatin. It will be borne in mind
that ordinary flesh contains, as we flnd- it naturally in the car-
cass, not only some fat, but a good deal of fibrous tissue, whidi
can be converted by heating into gelatin.

443

OOMPARATIVB PHTSIOLOOY.

I \

-.1 t

\ \

Fata uid OHrbohydntM.— It is a matter of common obaenra-
tion and of inore exact experiment that even a oamivomnM ani-
mal thrives better on a diet of fat and lean meat than on lean
flesh alone. Thus, it has been found that nitrogenous equi-
librium was as readily established by a due mixture of fat and
lean as upon twice the quantity of lean flash alone. It is plain,
then, that the metabolii'm is actually slowed by a fatty diet
When an animal is nfiven but little fat, none whateyer is laid
up, but all the carbon of the fat can be aooouiited for in the
excreta, chiefly as carbonic anhydride. A({atn, the fatty por-
tion remaining constant, it has been found that increasing the
proteid leads not to a storage of the carbon of the proteid ex-
cess, but to an increased consumption of this element. It is
then possible to understand how excessive consumption of pro-
teids may lead, as seems to be the case, to the disappearance of
fat and loss of weight, so that a proteid diet increases not only
nitrogenous but non-nitrogenous metabolism. That carbohy*
drates mixed with a due proportion of the otiier constituents
of a diet do increase fat formation is well established; though
there is no equally well-grounded explanation of how this is
accomplished. Upon the whole, it seems most likely that fat
can be directly formed from carbohydrates, or, at all events,
that they directly give rise to fat if they are not converted
themselves into that substance.

Oompantive.— It is found that there are relations between
the food used and the quantity of carbonic dioxide expelled
which are instructive. The formula following show the amount
of oxygen neoeMniy to oon'v«rt a stansh and a fat into carbonic
anhydride and water:

1. C.H..O.-t-0..=e(CO,)-f5(H.O).

2. C.TH..40.-»-0...=67(COt)-«-68(H.O).

It will be observed that in the first case the oxygen used to
oxidi»i4 llio str^Tch has all reappeared as COs, while in the sec-
UD<?. only 114 parts out of 160 so reappear. As a matter of fact,
mot-e oi the oxygen uaed does in herUvora reappear as C0«,
and less as water, while the rev er se holds for the camivora, the
proportion being, it is estlwated, as ninety to sirty per cent
This is to ba explained by the idiaraeter of the food in eaA
instance, for tbis relation no longer holds during fasting, when
the herbivorous animal becomes oamivoioas m the sense that
it consumes its own tissues.

imon obaenra-
ivoroiM ani-
than on lean
10U8 equi-
<ure of fat and
le. It is plain,
a fatty diet
Whatever is laid
iited for in the
the fatty por-
increasing the
the proteid ez-
element. It is
imption of pro-
■appearanoe of
reawB not only
That carbdiy-
ler constituents
tlished; though
of how this is
likely that fat
r, at all events,
not converted

lations between
lioxide expelled
how the amount
it into carbonic

ItO).

oxygen used to
rhile in the sec-
\ matter of fact,
Mppear as CO«,
» eamivora, the
siirty per cent.
e food in eaeb
g fasting, whMi
i the sense that

THE METABOLISM OF THE BODY.

448

Th* UbeU of Batti, W«t«r, tie., In iho IMit.— When we
come to inquire as to the part salts play when introduced into
the blood, we soon find that our knowledge is very limited.

Sulphur, and especially phosphorus, seem to have some im-
portant use which quite eludes detection. It is important to
remember that certain salts are combined with proieids in the
body, possibly to a greater extent than we can leaf u from the
mere analysis of dead tissues.

^ttUudogioaL— The withdrawal of any of the important salts
of the body soon leads to di8ease,,clear evidence in itself of their
g^reat importance. This is notably the case in oourvy, in which
disease the blood seems to be so disordered and the nutrition
of the vessel'Walls so altered thai the former (even some of the
blood-cells) passes through the latter.

Watir.— The use of water certainly has a great influence
over the metabolic proceoes of the body. The temporary ad-
dition or withdrawal of even a few ounces of water from the
regular supply of a dog in the course of a feeding experiment
greatly modfles the results obtained for the time. It is well
known that increase of water in the diet leads to a correspond-
ing increase in the amount of urea excreted. It is likely that
even yet we fail to appreciate fully the great port which water
pilars in the animAl economy.

THB aMBROT OP VBB AMIIIAXi SOOT.

As already explained, we distinguish between potential or
latent and actual energy. All the energy of the body is to be
traced to the influence of the tissues upon the food. Energy
may be estimated as mechanical work or as. heat, and the one
may be converted hito the othbr. All the processes of the
organism involve chemical changes, and a- large proportion of
these are of the nature of oxidations : so that speaking broadly,
the oxidations of the animal body are the sources of its energy ;
and in estimating the quantity of energy, eith<^ as heat or work,
that a given food-stuff will produce, one must consider whether
the (nidative proocsweB are complete or partial ; thus, in the case
of proteid food, if we suppose that the urea excreted reiweaents
the form in whiish the oxidative processes end or are arrested,
we must, in estimating the actual eneisy of the proteid, sub-
tract the amount of energy that would be produced were the
urea itself completely oxidised (bmmed.)

444

COMPARATIVE PHYSIOLOGY.

If the amount of heat that a b' > will produce in its oom-
buation be known, then by the law of the oonvenion uid equiv-
alence of energy the mechanical equivalent can be estimated in
that particular caae.

The heat-producing power of different substances can be
diractly learned by ascertaining the extent to which, when fully
burned (to water and carbonic anhydride), they eleyate the
temperature to a given volume of water; and this can at once be
translated into its mechanical equivalent of work, so that we
may say that one gramme of dry proteid would give rise to a
certain number of gramme-degrees of heat or kilogramme-
metrea of work. A few Bgures will now show the relative
values of certain food-stuffs:

1 gramme proteid
1 gramme urea . . .

Available energy of the proteid

anuii.-<leK.

8,106
785

Kttomet

2,161
811

1,800

The reason of the subtraction has been explained above.

Taking another diet in regard to which the estimates differ
somewhat from those given previously, but convenient now as
showing how equal weights of substances produce very dif-
ferent amounts of energy, we find that—

Onun.'-dec.

Kflomet.

IflO cniimmeg nroteid vield

486,800
006,000
088,880

188,000

1(10 rTAfnmes lat vield

884,100

9in orn.Tntnes stiimh vield

807,680

Total

3,381,880

066,780

In other words nearly a million kilogramme-metres of en-
ergy are available from the above diet for one day, provided it
be all oxidized in the body.

Food-stuffs, thee, with the oxygen of the air, are the body's
sources of energy. What are the forms in which its expendi-
turo aiHiiearB ? We may answer at once heat and mechanical
•waA; for it is assumed that internal movements as Uiose of
the visoenk, and all the friction of the body, all its molcular
moticni, all secretive processes, are to be regarded as finally

WBW*«>««"

THE MKTABOLISM UP THE BODY.

446

Be in its oom-
on and equiv-
e estimated in

jinoes can be
;h, when fully
y elerate the
can at once be
irk, so that we
give rise to a
kilogramme-
V the relative

KUomet

2,161
811

1,850

led above,
•timates differ
renient now as
luce very dif-

Xflomet.

185,000
884,100
887,680

)

966,780

le-roetres of en-
ay, provided it

, are the body's
ich its expendi-
md mechanical
ints as Uiose of
II its molcolar
rded as finally

augmenting the heat of the body. Heat is lost by the skin,

*"X"<S;r;'oltl into hea^producer. .nd i^^^-^
is uniustiflable, a. will appear from what »»• i«f,»««" •^^:
M well a. f~n. such facte as the production of fat '~^ F«t«^
food thus showing that the totter is indirectly a P^-cef. «J
«;rtiSr.lhydride, assuming that fat is oxidised mto that

substance.

Though a large part of the heat genemted within the tody
is talkie locations taking place in «»« ^7^;' JJ^^
to speak of the beat as being the outcome of aU the c»»e«»i^
^rTllL of the organism; and thojMTh heat ma^^^^
latent in certain organs for a time, m ihe end it must appear.
While all tiie tissues are heat-producers (^"^"^^^^^J^^
tent to which tiiey are such would depend, we f <»'^d ™5^
upon tfie degree to which tiiey were tiie seat of ™etatolio pro-
^; andlitual teste ertablish this fact. J^^^^l^^f^
the li;er is the greatest heatrproducer ; hencethe blood f^m
this organ is tiie warmest of tiie whole body. The muscles also
are esoedally the thermogenic tissue.

SrSmiLture of tEwood in tiiehepatic vein is warmer
iharC inTe portal, a dear evidence thij IJe »e^boltam of
this organ has elevated tiie temperature of tiie blood flowing

•*^'^*'tLperatu«, of tiie blood (ite own metetolism being
slight) is a pretty fair indication of tiie resultant effect of tiie
nrodwstion and the loss of heat. .

For obvious reasons, tiie temperature of different parte of
the bodv of man and other animals varies.
* 'Se i^^te of observers in regard ^ thetemp«rata« of
various animals and of different p«te of ije ^y^^J^J"
a way that would be punUng, were it not known how diffloult
it is to pn>c«re perfectly accurate thermometens not to mentis
iSvidual differences. The axiUary temperature is m man
ZT^O. (98-6 F.): that of the mo«*h /^WJ* ^^Sff' ^^
of the redum or vagina slightiy «^ •^- T*** '»«"
temperature of the blood is placed at 89' C. (108 8 F.).

SSSttf..-Thetempe»tu«ofv.^groujjrf«^i^^

hasbeSrtated to be as foUows: Hen and pigera, 42 (IW « »;)j
J;X^4408-(inWF.); dolphin, 85-5- (95-9 F.); mouse, 411-

446

COMPARATiVK PHT8I0L00Y.

(lOe F.); uakM, 10* to 19° (50 to S8-6 F.); but higher in larg«
■pecimens (python). Cold-blooded animalii have m tenipen-
ture a little higher (lees than 1" 0. usually) than the ■urround-
ing air. During the ewarming of beet the hive temperature
may Hk from 8S* to 40° (898 to 104 F.). All cold-blooded
animala have probably a higher temperature in the breeding*
aeaaon. In our domestic mammals the normal temperature in
not widely different from that of man. In the horse the aver-
age is 37-5° to 38° (99*5 to 1004 F.) ; in the ass, 88° to 89-ft° (1004
to 108 F) ; in the ox, 88° to 88*5° (100*4 to 101 '8 F.) ; in the sheep
and pig, 89° to 40° (108'8 to 104 F.) ; in the oat, 88-5° to 89° (101-8
to lOS-2 F.); in the dog, 88S° (101 '3 F.).

Variations in the average temperature are dependent on
numerous causes which may affect either the heat production
or heat loss : 1. CThange of climate has a very slight but real
influence, the temperature being elevated a fraction of a degree
when an individual travels from the poles toward the equator,
and the same may be said of the effect of the temperature of a
warm summer day as compared with a cold winter one. The
wonder is that, considering the external temperature, the vari-
ation is 80 light 2. Starvation lower* the temperature, and
the ingestion uf food raises it slightly, the latterincreasing, the
former decreasing, the rate of the metabolic processes. 3. Age
has its influence, the very young and the very old, in whom
metabolism (oxidation) is feeble, having a lower temperature.
This especially applies to the newly bom, both among man-^
kind and the lower mammals; and, as might be supposed, the
temperature falls daring sleep, when all the vital activi-
ties are diminished. The same remark applies with greater
force to the hibernating state of animals. The temperature
of man does not vary more than about 1° C. during the twenty-
four hours.

It will be inferred, from the facts and figures already cit<r^,
that' different kinds of food have considerably different capacity
for heat produotion.

It is well known that an animal when working not only
feels warmer, but actually produces m<we heat

It appears from a multitude of considerations that the body
is like a steam-engine, iModueing heat and doing work ; but it
is found that while a very good steam-engine, as a result of the
chemical prticesMS giring on within it, otmverts ^ of the poten-
tial energy of its supplies into mechanical work, the other {

THE METABOLISM OF THE BODY.

447

jrher in largo
• tempera-
|the ■urround-
temperature
cold-blooded
breeding-
smperature in
>ne the aver-
Se-S" (100-4
the sheep
'• to as" (101-8

dependent on

it production

ight but real

>n of a degree

i the equator,

iperature of a

ter one. The

ture, the vari-

perature, and

Qcreasing, the

3. Age

old, In whom

temperature.

among man-,

supposed, the*

vital aotivi-

with greater

B temperature

ig the twenty-

alreadyci^'-.^.
Brent capacity

ing not only

that the body
work ; bat it
1 result of the
ol tbepoten-
;, the other {

appearing aa heat, the animal body produces | as work and | as
heat, from its income of food and oxygen.

While it is perfectly clear that it is in the metabolic pro-
cesses of the body that we must seek for the final cause of the
heat produced, it is incumbent on the physiologist to explain
the remarkable fact that the mammalian body maintains,
under a changing external temperature and other oliouti?
conditions, and with a varying diet, during rest and labor, a
temperature ■nryvag within, usually, no more than a fraction
of a degree centigrade. This we shall now endeavor to explain
in part.

Tkt Xtgnltliion of Ttmptnkare.— It is manifest from the
facts adduced that so long as life lasts heat is being of necessity
constantly produced. If there wera no provision for getting
rid of a portion of this heat, it is plain that the body would soon
be consumed as effectually as if it wera placed in a furnace.
We observe, however, that heat is being constantly lost by the
breath, by perspiration (insensible), by conduction and radia-
tion from the surface of the body, and periodically by the
nrine and fseces. We have seen that, while heat is being pro-
duced in all the tissues and organs of the body, some aro es-
■peoially thermogenic, as ibn glands and muscles. The skin
presents an extensive surifar o, abundantly supplied with blood-
vessels, which wh;>u dilated may receive a large quantity of
blood, and whdn contracted may necessitate a much larger in-
ternal su«rt«ly, in the splanchnic region especially. It is a mat-
ter of common observation that, when an individual exercises,
the skin becomes flushed, and so with the increased nroducUon
of heat, especially in the mtisoles (see page 19S), there is a pro-
viston for unusual escape of the surplus ; at the same time
sweat breaks out visibly, or if not, the insensible perspiration
is generally increased ; and this accounts for an additional in-
crement of loss ; while the lungs do extra work and exhale an
inoreaiwd quantity of aqueous vapor, so that in these various
wi^ the body is cooled. Manifestly there is some sort of rala-
tion between the p rocess e s of heat production and heat expendi-
ture. The vaso-molor, secretory, and respiratory functions are
modified. We may suppose that the varions co-ordinations
eflleeted, ohiefly at all events through the central nervons qrs-
*tem, and not by the direct action at the heat upon local nerv-
ons mechanisms, or the tissues themselves directly, ara re-
flexes.

448

COMPARATIVK PUTSIOLCKIY.

The production of heat, however, wemi to be equally under
the influence of the nervous ■yitem, though we know lew about
the detaila of the matter.

A oold-blooded animal diffen from i^ warm-blooded one in
that its temperature varies more with the lurrounding medium!
hence the terms poUrilothermer and homoiothermer for cold*
blooded and warm-blooded, would be appropriate.

Sueh an animal, as a frog or turtle, may have its chemical
processes slowed or quickened, almost like Uiose going on in a
test-tube or crucible, by altering the temperature. Very differ-
ent is it, as we have seen, in the normal state of the animal with
any mammal. Hence hibernation or an allied state has be-
come a necessary protection for poikilothermers, otherwise (he;
would perish outright, and the groups become extinct in nc.ibr*
em latitudes.

It is pill X vaso-motor changes alone can not explain

these effects , and, though possibly a part of the rise of tem-
perature, following exposure of the naked body in a cool air,
may be accounted for by the increased metabolism of internal
organs, accompanying the influx of blood caused by constric-
tion of the cutaneous capillaries, it is probable that in this as in
so many other instances the blood and circulation have been
credited with too much, and the direct influence of the nervous
systeqi on nutrition and heat production overlooked or under-
estimated. The thermogenic center has not yet been definitely
located, though some recent investigations seem to favor a spot
ta or near the corpus striatum for certain mammals. Some in-
vestigators also reoogniae a cortical heatoenter. It has been
suggested that we may to advantage speak of a thermotaxie
(rf>gulative of loss) and a thermogmtie mechanism (regulative
of production), and even a thermolyHe or discharging mechan-
ism. It has been further suggested that diflhrent nerve-fibers
may ba eoncemed in the actual work of conveying the different
impulses of these respective mechanisms to the tissues; and the
whole theory has been framed in accordance with the prevalent
conception of metabolism as consisting of anabolism and oa-
tabolism, or constructive and destructive processes. But these
theories have not yet been confirmed by experiments on ani-
mals, though th^ are, in the o|rfnion of their authors, in har-
mony with the facts of fever. Certainly, any theory that will
imply that vital processes are more under the control of the
nervous qrstem than haa hitherto been taught, will, we think,

ftlly under
Icwaboui

led one in
ig medium:
for cold*

tta ohemioAl
ingon in •
Very differ-
Janimal with
t»te hu be-
lerwiee (he;
lot in no.;iv

not explain
riie of tern- .

a cool air,
I of internal
byoonitric-
in thii aa in
b have been
the nervous
id or under>
•n definitely
favor a spot
le. Some in-
It has been
tkermoUtaeie
X (regulative
[ingmechan-
I nerve-flben
the different
luee; and the
the prevalent
Uam and oa-
I. But these
lents on ani-
horsiin har>
}ry that will
ntrol of the
ill, we think,

THR MKTAiMLIHM OF TUB BOOY.

449

advance pi \ >to.ii(' , as will shortly appear from our discussion
of the . rJl uauce of iae nervous system on the various metabolic
prucesii'M ^nerally.

The phenomena observable in an animal gradually freesing
to death point strongly to the direct influence of the nervoun
system on the production as well as the regulation of heat.
The circulation must of course be largely concerned, but it ap-
pears as though the nervous system refused to act when the
temperature falls below a certain point A low temperature
favors hibernation, in which we believe the nervous system
plays the chief port, though the temperature in itself is not the
determining cause, as we have ourselves proved. The fact that
the whole metabolism of a hibernating animal is lowered, that
with this there is loss of consciousnem much more profound
than in ordinary sleep, of itself seems to indicate that the nerv*
ous system is at the bottom of the whole matter.

FatholOfiMd.— It is found that many drugs and poisons
lower temperature, acting in a variety of ways. In certain dis-
as cholera, the temperature may sink to 83° O. in extreme
I before death supervenes. When the temperature of the
blood is raised 6° to 8° 0. (as in sunstroke, etc.), death occurs ;
and it is well kcown that prolonged high temperature leads to
fatty degeneration of the tissues generally. All the evidence
goes to show that in fever both the heat production and the
heat expenditure are interfered with ; or, at least, if not always,
that ihwe may be in certain cases such a double disturbance.
In fever excessive consumption of oxygen and production of
carbO') dioxMe occur, the metabolism is quickened, hence its
waslitig (c.>u^'jming) effects ; the rapid respiration tends to in-
crease the thirst, from the extra amount of aqueous vapor ex-
haled. The body is actually warmest during the " cold stage "
of fever, when the vessels of the skin are constricted and the
patient feds cold, because the internal metabolism is heightened ;
while the "sweating stage" is marirad by a natural fall of tem-
perature. The fact that the skin may be dry and pale in fever
shows that the thermotaxic nervous mechanism is at fault; but
the chemical fhcts cited above (excess of CX)t eta) indicate that
the thermogenic mechanism is also deranged;

460

COMPARATIVR PHYSIOLOGY.

If the student will now read afresh what hai been written
under the above hooding in relation to the mbjeot of digeition,
it will probably appear in a new light. We endeavored to show
that, according to that general principle of correlation which
holds throughout the entire organism, and in harmony with
certain facts, we were bound to believe that digestion and as-
similation, or, to speak in other terms, the metabolic prucoasea
of the yarioiu tissues, in a somewhat restricted sense, were
closely related. Beneath the common observation that " diges-
tion waits on appetite " lies the deeper truth that food is not
prepared in the alimentary canal (digested) without nome rela-
tion to the needs of the system generally. In otlier words, the
voice of the tissues elsewhere is heard in the councils of the
digestive tract, and is regarded ; and this is effected chiefly
through the nervous system. Excosh in eating may lead to
vomiting or diarrhoea — plain ways of getting rid of what can
not be digested.

Brolution,— Wo have already alluded to some of those modi-
fications in the form of the digestive organs that indicate an
unexpected plasticity, and impress the fact of the close rela-
tion of form and function. The conversion of a sea-gull into a
graminivorous bird, with a corresponding alteration in the na-
ture of the form of the stomach (it becoming a gizzard), with
doubtless modifications in the digestive processes, when re-
garded more closely, implies ooadaptations of a very varied
Icind. These are as yet but imperfectly known or understood,
and the subject is a wide and inviting field for the phjrriologist.
Darwin and othen have indicated, though but imperfectly,
some of the changes that are to bo regarded in animals as cor-
relations ; but in physiology the subject has received hut little
attention as yet. We have in several parts of this work called
attention to it ; but the limits of space prevent us doing little
more than attempting to widen the student's field of vision by
introdnoing such oonsideratiains. The influence of climate on
metabolism, an undoubted fact, has many implications.

Any one who keeps a few wild animals in confinement un-
der dose observation, and endeavors to ascertain how their
natural, self-chosen diet may be varied when confined, will
be astonished at the plasticity of their instincts, usually con-
sidered as so rigid in regard to feeding. These facts help one

been written
of digwtion,
rond to show
BlaUon whioh
artnony with
ifltion and a*-
mHo procoaaeit
i Mnse, were
1 that " digw-
it food is not
iut Home reUi-
ler word«, the
juncila of the
[feoted chiefly
• may lead io
I of what can

of those modi-
at indicate an
the close rela-
sea-guU into a
;lon in the na-
, gizzard), with
snes, when re-

a very varied
or undentood,
le physiologist,
it imperfectly,
tnimals as oor-
leived but little
his work called

us doing little.
Id of vision by
) of climate on
cations.

onflriement un-
tain how their
I confined, will
its, usualfyoon-
le facts help one

m;«ii<>ii>!»il>"

IMAGE EVALUATION
TEST TARGET (MT-3)

Photographic

Sciences

Corporation

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WIISTI«,N.Y. 14SM

(716)S72-4S03

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Microfiche

Series.

CIHM/ICMH
Collection de
mi

Canadian Instituta for Hiatorical Microraproductions / Inatitut Canadian da microraproductiont liiatoriqua«

THB METABOLISM OF TUB BODT.

451

to understand how by the law of habit and heredity each group
of animals has come to prefer and flourish best upon a oertain
diet. But habit itself implies an original deviation some time,
in which is involved, again, plasticity of nature and power to
adapt as well as to organize. Without this, evolution of func-
tion is incomprehensible ; but with this principle, and the
tendency for what has once been done to be easier of repetition,
and, finally, to become organized, a flood of light is thrown
upon the subject of diet, digestion, and metabolism generally.
On these principles it is possible to uudei-stand those race differ-
ences, even individual differences, which as facts must be patent
to all observers.

The principle of natural selection has clearly played a great
part in determining the diet of a species; the surviving immi-
grants to a new district must be those that can adapt to the local
environment best, including the food which the region supplies.
The greater capability of resisting hunger and thirst in some
individuals of a species implies great differences in the meta-
bolic processes, though these are mostly unknown to us; and
the same remark applies to heat and cold

It seems clear that hibernation is an acquired habit of the
whole metabolism, with -great changes in the functional condi-
tion of the nervous system recurring periodically, and, in fact,
dependent on these, by which oertain large divisions, as the
reptiles, amphibians, and certain mammals among vertebrates,
are enabled to escape individual death and extinction as groups.
We may suppose that, for example, among invertebrates, by a
process of natural selection, those survived that could thus adapt
themselves to the environment; while, among mammals, hiber-
nation may be considered as a process of reversion, perhaps, for
the homoiothermer becomes very much a poikilothermer during
hibernation, the latter reverting to a condition existing in lower
forms, and not wholly unlike that of plants In winter. This
iCan be understood on the principle of the origin of higher from
lower forms; otherwise it is difficult to understand why similar
states of the metabolism should prevail in groups widely sepa-
rated in form and function. If all higher tn^ups bear a derivar
tive relation to the lower, what is common in their nature, as
we uaoally find them, as well as tiie peonliar resemblances of
the metabolism of higher to lower forms in sleep, hibernation,
etc., can be understood in the light of physiological reversion.

The origin of a homoiothermic (warm-blooded) condition

ssss

ttmmm

mmmttrn

469

COMPARATIVE PHysiOLOGY.

itself is to be sought for in the principle of natural selection.
It was open to certain organisms, we may assume, either to
adapt to a temperature much below that of their blood, or to
hibernate; failing to make either adaptation would result in
death; and gradually, no doubt, inyolving the death of num-
berless individuals or species, the resisting power attained the
marvelous degree that we are constantly witnessing in all
homoiothermers.

The daily variations of the bodily temperature in homoio-
thermers is a beautiful example of the law of rhythm evident
in the metabolism. Hibernation is another such. While these
ore clear cases, it is without doubt true that, did we but know
more of the subject, a host of examples of the operation of this
law might be instanced.

We can but touch on these subjects enough to show that
they deserve an attention not as yet bestowed on them; and to
the thoughtful it will be evident that their influence on prac-
tical life might be made very great were they but rightly ap-
prehended.

THB XNFLUBNOB OF TBB MBRVOnB BT8TEM ON
BtBTABOLIBM ( MUTHITIO N).

This subject is of the utmost importance, and has not re-
ceived the attention hitherto, in works on physiology, to which
we believe it is entitled, so that we must discuss it at some
length.

We may first mention a number of facts on which to base
conclusions: 1. Section of the nerves of bones is said to be fol-
lowed by a diminution of their constituents, indicating an
alteration in their metabolism. 3. Section of the nerves sup-
plying a cock's comb interferes with the growth of that ap-
pendage. 3. Section of the spermatic nerves is followed by de-
generation of the testicle. 4. After injury to a nerve or its
center in the brain or spinal cord, oertun affections of the
skin may appear in regions corresponding to the distribution
of that nerve; thus, herpes zoster is an eruption that follows
frequently the distribution of the intercostal nerve. 6. When
the motor cells of the anterior horn of the spinal cord or cer-
tain cells in the pons, medulla, or cms cerebri are disordered,
there is a form of muscular atrophy which has been termed
" active," inasmuch as the muscle does not waste merely, but

selection,
^me, either to
blood, or to
>uld result in
ath of num-
attained tbe
[lessing in all

ire in homoio-
lythm evident
While these
we but know
leration of this

1 to show that

them; and to

lenoe on prao-

mt rightly ap-

TBTBII ON

nd has not re-
ology, to which
:u8s it at some

which to base
s said to be fol-

indioating an
he nerves sup-
rth of that ap-
oUowed by de-

a nerve or its
'ections of the
he distribution
>n that follows
pve. 8. When
al cord or oer-
lue disordered,
« been termed
ite merety, but

THE METABOLISM OV THE BODY.

468

the dwindling is accompanied by proliferation of the muscle
nuclei. 6. After neurotomy for navicular disease a form of de-
generation of the structures of the foot is not uncommon. 7.
After section of both vagi, death results after a period, varying
in time, as do also the symptoms with the animal. In some
animals pneumonia seems to account for death, since it is
found that, if this disease be prevented, life may, at all events,
be greatly prolonged. The pneumonia has been attributed to
paralyses of the muscles of the larynx, together with loss of
sensibility of the larynx, trachea, bronchi, and the lungs, so
that the glottis is not closed during deglutition, and the food,
finding its way into the lungs, has excited the disease by irrita-
tion. The possibility of vaso-motor changes is not to be over-
looked. In birds, death may be subsequent to pneumonia or
to inanition from paralysis of tbe oesophagus, food not being
swallowed. It is noticed that in these creatures there is fatty
(and sometimes other) degeneration of the heart, liver, stomach,
and muscles. 8. Section of the trigeminus nerve within the
skull has led to disease of the corresponding eye. This opera-
tion renders the whole eye insensible, so that the presence of
offending bodies is not recognized; and it has been both as-
serted and denied that protection of the eye from these pre-
vents the destructive inflammation. With the loss of sensi-
bility there is also vaso-motor paralysis, the intra-ooular ten-
sion is diminished, and the relations of the nutritive lymph to
the ocular tissues are altered. But all disturbances of the eye
in which there are vaso-motor alterations are not followed by
degenerative changes. 0. I>egeneration of the salivary glands
follows suture of their nerves. 10. After suture of long-di-
vided nerves, indolent ulcers have been known to heal with
great rapidity. This last fact especially calls for explanation.
It will be observed, when one comes to jxamine nearly all such
instances as those referred to above, that they are complex.
Undoubtedly, in such a case as the trigeminus or the vagi,
many factors contribute to the destructive issue; but the fact
that many symptoms and lesions are concomitants does not, of
itself, negative the view that there may be lesions directly
dependent on the absence of the functional influence of nerve-
flbeis. We prefer, however, to discuss the subject on a broader
basis, and to found opinions on a wider survey of the facts of
physiology.

After a little time (a few hours), when the nerves of the lub-

■^MWWPPM^waifMl

> /

45:1

COMPARATIVE PHYSIOLOGY.

maxillary gland have been divided, a flow of saliva begins and
is continuoiis till the secreting cells become altered in a way
visible by ihe microscope. Now, we have learned that proto-
pli^m can discharge all its functions in the lowest forms of
animals and in plants independently of nerves altogether.
What, then, is the explanation of this sow^tlled " paralytic se-
cretion " of saliva ? The evidence that the various functions
of the body as a whole are discharged as individual acts or
series of acts correlated to other functions has been abundantly
shown; and, looking at the matter closely, it must seem un-
reasonable to suppose that this would be the case if there was
not a close supervision by the nervous system over even the
details of the processes. We should ask that the contrary be
praved, rather than that the burden of proof should rest on the
other side. Let us assume that such is the case; that the entire
behavior of every cell of the body is directly or indirectly con-
trolled by the nervous system in the higher animals, especially
mammals, and ask. What facts, if any, are opposed to such a
view ? We must suppose that a secretory cell is one that has
been, in the course of evolution, specialized for this end. What-
ever may have been the case with protoplasm in its imspecialized
form, it has been shown that gland-cells can secrete independ-
ently of blood-supply (page 314, etc.) when the nerves going to
the gland are stimulated. Now, if these nerves have learned, in
the course of evolution, to secrete, then in order that they shall
remain natural (not degenerate) they must of necessity secrete;
which means that they must be the subject of a chain of meta-
bolic processes, of which the final link only is the expulsion of
formed products. Too much attention was at one time directed
to the latter. It was forgotten, or rather perhaps unknown,
that the so-called secretion was only the last of a long series of
acts of the cell. True, when the cells are left to themselves,
when no influences reach them from the stimulating nervous
centers, their metabolism does not at once cease. As we view
it, they revert to an original ancestral state, when th^y per^
formed their work, lived their peculiar individual life as less
specialized forms wholly or partially independent of a nervous
system. But such divorced cells fail; they do not produce
normal saliva, their molecular condition goes wrong at once,
and this is soon followed by departures visible by means of the
microscope. But just as secretion b tisually accompanied by
excess of blood, so most functional conditions, if not all, de-

THE METABOLISM OF THE BODY.

iSft

|a begfinsand
in a way
that proto-
it forms ol
altogether,
paralytic se-
»us function*
[dual acts or
abundantly
just seem un-
if there was
ver even the
) contrary be
d rest on the
hat the entire
idireotly con-
ils, especially
led to such a
one that has
I end. What-
imspecialized
ete independ-
rves going to
re learned, in
liat they shall
98sity secrete;
hain of meta-
! expulsion of
time directed
ps unknown,
long series of
> themselves,
ting nervous
As we view
en th^y per-
il life as less
of a nervous
not produce
ong at once,
means of the
tmpanied by
f not all, de-

mand an unusual supply of pabulum. This is, however, no
more a cause of the functional condition than food is a cause of
a man's working. It may hamper, if not digested aud assimi-
lated. It becomes, tlien, apparent that the essential for metab-
olism is a vital connection with the dominant nervous system.

It has been objected that the nervous system has a metab-
olism of its own independent of other regulative influences;
but in this objection it seems to be forgotten that the nervous
system is iteelf made up of parts which are related as higher
and lower, or at all events which intercommunicate and ener-
gize one another. We have learned that one muscle-cell has
power to rouse another to activity when an impulse has reached
it from a nervous center. Doubtless this phenomenon has
many parallels in the body, and explains how remotely a nerv-
ous center may exert its power. It enables one to understand to
some extent many of those wonderful co-ordinations (obscure
in detail) that are constantly taking place in the body. We
think the facts as they accumulate will more and more show,
as has been already urged, that the influence of blood-presstire
on the metabolic (nutritive) processes has been much over-
estimated. They are not essential but concomitant in the
highest animals. Turning fo the case of muscle we flnd that
when a skeletal muscle is tetanized the essential chemical and
electrical phenomena are to be regarded as changes differing in
degree only from those of the so-called resting state. There is
more oxygen used, more carbonic anhydride excreted, etc. The
change in form seems to be the least important from a physio-
logical point of view. Now, while all this can go on in the
absence of blood or even of oxygen, it can not take place with-
out nerve influence or something simulating it. Out the nerve
of a muscle, and it undergoes fatty degeneration, aud atrophies.
True, this may be deferred, but not indeflnitely, by the applica-
tion of electricity, acting somewhat like a nerve itself, and in-
ducing the approximately normal series of metabolic changes.
If, then, the condition when not in contraction (rest) differs
from the latter in all the essential metabolic changes in rate or
degree only ; and if the functional condition -or accelerated
metabolism is dependent on nerve influence, it seems reason-
able to believe that in the resting condition the latter is not
withheld.

The recent ir.vestigations on the heart make such views as
we are urging clearer still. It is known that section of the

■"tt-Mj!e4w i u) i' ..j i i ' -)i»AU 'g'*iW(i!W>ftW

466

COMPARATIVE PHYSIOLOGY.

yagi leads to degeneration of the cardiac atruoture. We now
know that this nerve containa flben which have a divene
action on the metabo]i«m of the heart, and that, according
aa the one or the other set is stimulated, so does the electri-
cal condition vary; and everywhere, so far as known, a differ-
ence in electrical conditions seems to be associated with a
difference in metabolism, which may be one of degree only,
perhaps, in many instances— still a difference. The facts as
brought to light by experimental stimulation harmonize with
the facts of degeneration of the cardiac tissue on section of the
vagi ; but this is only dear on the view we are now presenting,
that the action of the nervous system is not only universal,
but that it is constant; that function is not an isolated and
independent condition ol an organ or tissue, but a part of a
long series of metabolic changes. It is true that one or more
of such changes may be arrested, just as all of them may go
on at a less rate, if this actual outpouring of pancreatic secre-
tion is not constant; but secretion is not summed up in dis-
charge merely; and, on the other hand, it would seem that in
some animals the granules of the digestive glands are being
renewed while they are being used up, in secreting cells. The
processes may be simultaneous or successive. Nor do we wish
to imply that the nervous system merely holds in check or in
a very general sense co-ordinates processes that go on unorigi-
nated by it. We think the facts warrant the view that they are
in {he highest mammals either directly (mostly) or indirectly
originated by it, that they would not take place in the absence
of this constant nervous influence. The facts of common ob-
servation, as well as the facta of disease, point in the strongest
way to such a conclusion. ISvery one has observed the in-
fluence, on not one but many functions of the animal, we might
say the entire metabolism, of depressing or exalting emotions.
The failure of appetite and loss of flesh under the influence of
grief or worry, tell a plain story. Buoh broad facts are of infl-
nitely more value in settling r < .b a question as that how dis-
cussed than any single experimeut. The best test of any theory
is the extent to whidi it will explaia the whole round of facts.
Take another instance of the influence over metabolism' of the
nervous system.

Every trainer of race-horses knows that he may overwork
his beast— i. e., he may use his muscles so much as to disturb
the balance of his powers somewhere— very frequently his di-

MjmtW

THE METABOLISM OF THE BODY.

46t

We now
a diyene
according
the electri-
vn, a differ-
ted with a
egree only,
!he facts as
nonize with
iion of the
presenting,
y universal,
isolated and
a part of a
3ne or more
lem may go
reatio seore-
1 up indis-
leem that in
s are being
[cells. The
do we wish
check or in
on unorigi-
hat they are
r indirectly
the absence
common ob-
he strongest
'ved the in-
d, we might
g emotions,
influence of
> are of infl-
lat how dis-
' any theory
nd of facts.
Dlism of the

y overwork
IS to disturb
ntly his di-

gestion ; but often there seems to be a general break — the whole
metabolism of the body seems to be out of gear; and the same
applies to our domestic animals. If we assume a constant
nervous influence over the metabolic processes, this is compre-
hensible. The centers can produce only so much of what we
may call nervous force, using the term in the sense of directive
power; and if this be unduly diverted to the muscles, other
parts must suffer.

On this view also the value of rest or change of work
becomes clear. The nervous centers are not without some re-
semblance to a battery; at most, the latter can generate only a
deflnite quantity of electricity, and, if a portion of t in be di-
verted along one conductor, leas mtist remain to pass by any
other.

It is of practical importance to recognize that under great
excitement unusual discharges from a nervoKsenter may lead
to unwonted functional activity; thus, under the stimulus of
the occasion an animal may in a race originate muscular con-
tractions that he could not call forth imder other ciroumstanoes.
Such are always dangerous. We might speak of a reserve or
residual nerve force, the expenditure of which results in serious
disability.

It seems that the usually taught views of scxsretion and
nutrition have been partial rather than erroneous in themselves,
and it is a question whether it would not be well to substitute
some other terms for them, or at least to reoogtfize them more
clearly as phases of a universal metabolism. We appear to be
warranted in making a wider generalization. To regard pro-
cesses concerned in building up a tissue as apart from those that
are recognized as constituting its function, seems with the knowl-
edge we at present possess, to be illogical and unwise. Whether,
in the course of evolution, certain nerves, or, as seems more
likely, certain nerve-fibers in the body of nerve-trunks, have
become the medium of impulses that are restricted to regulat-
ing certain phases of metabolism— as e. g., expulsion of formed
products in gland-cells — is not, from a general point of view,
improbable, and is a fitting subject for further- investigation.
But it will be seen that we should regard all nerves as ^ tro-
phic " in the wider sense. What is most needed, apparently, is
a more just estimation of the relative parts played by blood
and blood- pressure, and the direct influence of the nervous
qrstem on the life-woric of the cell.

• ■ jiyw^g,'»*aiK<:jt!«w»An«j. ',')i».n-;.-.iJi '" ,['.j.

458

COMPARATIVE PHYSIO LOO Y.

Wo muMt regard the nervous oenten iis the source of cease-
letw impulHes that operate upon all iwrtti, originating and con-
tMlling the entire metaboliHin, of which what we terui funo-
tionfl are but certain phasos, parts of a whole, but essential for
the health or normal condition of the titssues. Against such a
vi')w we know no facts, either of the healthy or disordered or-
ganism.

Banuiiaiy of Mttabaliim.— Very briefly and somewhat in-
cc>mpletely, we may sum up the chief results of our present
kuowledge (and ignorance) as follows:

Glycogen is found in the livers of all vertebrate and some
invertebrate animals. The quantity varies with the diet, being
greatest with an excess of carbohydrates.

Glycogen may be regarded as stored material to be convert-
ed into sugar, as required by the organism ; though the exact
use of the sugar and the method of its disposal are unknown.

Fat is not stored up in the body as the result of being
merely picked out from the blood ready made; but is a genuine
product of the metabolism of the tissues, and may be formed
from fatty, carbohydrate, or proteid food. This becomes es-
pecially clear when the difference in the fat of animals from
that on which they feed is considered, as well as the direct re-
sults of feeding exr-^imenta, and the nature of the secretion of

milk.

Tlie liver seems to be engaged in a very varied round of meta-
bolic processed; the manufacture of bile, of glycogen, of urea,
and probobly of many other substances, some known and
others unknown, as chemical individuals. Urea is in great
part probably only appropriated by the kidney-oells (Amceba-
like) from the blood in which it is found ready mode; though
it may be that a part is formed in these cells, either from
bodies some steps on the way toward urea, or out of their pro-
toplasm, as fat seems to be by the cells of the mammary gland.

The leucin (and tyrosin ?) of the digestive canal sustains
some relation to the manufacture of urea by the liver, and pos-
sibly by the spleen and other organs ; for a proteid diet increases
these products, and also the urea excreted. Creatin, one of the
products of proteid metabolism, and possibly allied bodira, may
be considered as in a certain sense antecedents of urea ; uric-aoid,
however, does not seem to be such, nor is it to be regarded as a
body that has some of it escaped complete oxidation, but rather
as a result of a distinct departure of the metabolism ; and there

oeof oeaae-
ag and con-
terui funo-
BBseiitial for
ainst iuoh a
ordered or-

raewhat in-
our present

te and some
» diet, being

be convert-
h the exact
mknown.
It of being
is a genuine

be formed
becomes es-
limals from
be direct re-
secretion of

und of mota-
^n, of urea,
known and
is in great
Us (Amoeba-
ade; though
either from
)f their pro-
mary gland,
nal sustains
irer, and pos-
liet increases
1, one of the
bodies, may
sa; uric-acid,
igarded as a
n, but rather
I ; and there

THE MKTABOLISM OF THE liODY.

45»

•re facts which seem to indicate that the urio-acid mt>ttboliHm
is the older, from an evolutionary point of view, and that in
mammals, and especially in noan, aa the results of cortuin errors
theru may be a physiological (or pathological) revemion. Hip-
purio acid, as replacing urio add in the herbivora, may be re-
garded in a similar U(rht.

Our knowledge of the metabolism of the spleen, beyond its
relations to the formation of blood-cells and their disintegra-
tion, is in the suggestive rather than the positive stage. It
seems highly probable that this organ plays a very important
port, the exact nature of which is us yet unknown.

When an animal starves, it may be considered as feeding on
its own tissues, the more active and important utilizing the
others. Notwithstanding, organs with a very active metabo-
lism, as the muscles and glands, lose weight to a large extent.
The presence of urea to an amount not very greatly below the
average in health, shows that there is an active proteid metabo-
lism then as at all times in progrew.

General experience and exact experiments prove that, while
an animal's diet may be supplied with special regard to fatten-
ing, to increase working power, or simply to maintain it in
health, as evidenced by breeding capacity, form, etc., in, all
cases there must be at least a certain minimum quantity of each
of the food-stuffii. No one food can be said to be exclusively
fattening, heai-fonning, or muscle-forming.

A carbohydrate diet tends to production of fat ; proteid food
to supply muscular energy, but the latter also produces fat, and
a diet of proteid mixed with fat or gelatin will serve the pur-
poses of the economy better than one containing a very much
larger quantity of proteid alone. Muscular energy, as is to be
inferred from the excreta, is not the result of nitrogenous me-
tabolism alone; and in arranging any diet for man or beast the
race and the individual must be considered. Amnuds can not
be treated as machines, like engines using siipilar quantities of
fuel ; though this holds iar more of man than the lower ani-
mals— i.e., the results may be predicted from the diet with far
more certainty in their case than for man.

Food is related to excreta in a definite way, so that all that
enters as food mast sooner or later appear as urea, salts, car-
bonic anhydride, water, etc. These are individually to be re-
garded as the final links in a long chain of metabolic processes,
or rather a series of these. Fats and carbohydrate ore repre-

' H . f .... ^ [ ' ■ ' .', '< ;- ' -

460

COMPARATIVK PHYSIOLOOf.

■ented flnally m oarbonio anhydride and wator principally,
protelds ai urea.

Nitro|{enous foodi may be regarded a« accelerating the
metabolic prooeami generally and proteid metaboliam in par-
ticular, while fats have the reverM eifect ; hence fat in the diet
render* a lew quantity of proteid miffloient. Oelatin neema to
act when mixed with proteid food either like an additional
quantity of proteid, or pooribly like fat, at all events under mich
ciroumatanoea leaa proteid aufflcea.

These facta have a bearing not only on health but on econ-
omy, in the expenditure for food.

EMta hold a very important place in every diet, though
their exact influence ia in great part unknown. The heat of
the body ia the resultant of all the metabolic proceaaea of the
organiam, especially the oxidative onea. Certain food-atuffa
have graater potential capacity for heat formation than othera ;
but. Anally, the result depends on whether the organism can
best utilise one or the other.

A certain body temperature, varying only within narrow
limits, is maintained, partly by regiUation of the supply and
partly by the regulation of the loss.

^th these are, in health, under the direction of the nervous
aystem, and both are co-ordinated by the same. Loss is chiefly
through the skin and lungs ; gain chiefly through the organs
of most active metabolism, as tlie muscles and glands.

Vaso-motor effects play a gteat part in the escape of heat.
Animals may be divided into poikilothermers and homoio-
thermers, or cold-bloodud and warm-blooded animals, accord-
ing as their body heat varies with or is independent of the ex-
ternal changes of temperature. All the facts go to show that
in mammals the j^rooesses of the body (metabolism) can con-
tinue only within a slight range of variations in temperatui«,
though the upward limit is narrower than the downward.

Upon the whole, the evidence justifles the conclusion that
the nervous system is oonoemed in all the metabolic processes
of the body in mammals including man, and that, as we descend
the scale, the dominion of the nervous qrstem becomes leas till
we reach a point when protoplasm goes through the whole
cycle of its changes by virtue of its own properties uninfluenced
by any modifloation of itself in the form of a nervous system.

principally,

erating the
inn in par-
i in the diet
in Heema to
k additional
I under auch

ut on econ-

liet, though
rhe heat of
saaee of the
I food-etufifa
han others ;
'gauism can

,hin narrow
supply and

the nervous
iss is chiefly
I the organs
is.

le of heat
md homoio-
oals, aooord>
t of the ex-
bo show that
im) can oon-
temperature,
award,
lolusion that
»lio prooessee
8 we descend
mes lees till
h the whole
cininfluenoed
>us system.

THE SPINAL CORD.— GENERAL

Amowo the hii^er vertebrates the spinal cord is found to
consist of nerveKJolls, nerve-flbers, and a delicate connective tis-
sue binding tiiem together ; while these different structures are
arranged in definite forms, so that a cross-section anywhere pre-
sents a characteristic appearance, the more important gangli-
onic nerve-oells being internal and forming a large part of
the gray matter of the cord. All the various regions of this
organ or series of organs are connected with one another,
white with white and gray matter, as well as white with gray

substance.

While we do not attempt to furnish a complete and detailed
account of the anatomy of the cord or other parts of the nervous
system, for which the student is referred to works on'anatomy,
we would remind him that the spinal cord Is situated within a
bony case with joints permitting of a certain amount of move-
ment, variable In different regions. Inasmuch as the cord Itself
does not fill Its bony covering, but floats In fluid and teth-^red
to the walls by bands of connective tissue. It Is well protected
from laceration, bruising, or concussion. Like the brain, It has
a protective tough outer membrane (dura mater) with a doser-
fltting inner covering abounding in blood-vessels {pia mater).
The white matter of the cord invest* the horns of gray
matter and is made up of nerve-flbers wanting the outer sheath.
Here, as elsewhere, these fibers have only a conducting func-
tion ; they do not originate nervous impulses. The gray matter,
on the other hand, abounds in cells, some of them with many
prooesaes, that can originate, modify, and conduct impulses.
Certain weU-reoognlied groups of these cells are arranged In
columns throughout the cord, as shown in the accompjatty-
ing figiires. The supporting basis for these cells (neuroglia) is
the most delicate form of connective tissue known.

The cord may be regarded either as an Instrument for the

i:&

Wia.tK.

Pffs^

THE SPINAL CORD.— GENERAL.

468

Fio. 82r.-Gcnei«l view of iplnal cord (Chauveau). A, cervical bnlb; B, lumbar bnlb;

Fio^^^-ScXrat of spinal cord at the cervical bulb, or brachial plexuB, ghowlng itn
npwr face and the rooU of the apinal nervea (Chauveau). A, anperior roots; «,
"nYcrior roots; C, multiple ganglfa of superior roots; D, single ganglion on an
cxcepUonal pair; B, £, upper roots passing through the envelopee.

reception and generation of impulses independent of the brain;
OP as a conductor of afferent and efferent impulses destined for
the brain or originatihg in that organ. As a matter of fact,
however, it is better to bear in mind that the cord and brain
constitute one organ or chain of organs, which, as we have
learned from our studies in development, are dilferentiations
of one common track, originating from the epiblast.

While the brain and the cord may act independently to a

Pl«. 88B.-Transvcr«e section of spinal cord of child six months old, at middleof ln»
tar r«rion, showing ewMiclally the libers of gray subetanc«fc In 80. (After G«-
2»W* intoriorwluSw: 6, posterior colunns; e, lateral cotamns; f anterto
SSw; «%Stolo» rort.; / anlStor white commissure: v, wnh^ *!S^"?^h^
raliSel&fMlU; A, connMtlve-tlssne substance summndlnkjlt; i, t""^"* "JS"
dr Kray commissure to front, and t. the same behind cenlnri canal; '.^ '•"»•
rat acroes^ anterior comoa; », great lateral cell sronp of anterior cornoa: o,
teiSJ^tor w^l pi^icolumnfTft smalleat aeatan cell group: «. porterior
c^mulnMcendlng fasclMdi to pdsterlor comu; i, substantia geJalto.

COMPARATIVE PHYSIOLOGY.

iha sea -Oroao of celto to connection with Mterior roptj of ipjnd »«»;•• •••^J^
and with flben of anterior roots.

▼ery large extent, as may be shown by experiment, yet it can
not be too well borne in mind that in the actual normal life of
an animal such purely independent behavior must be exceed-
ingly rare. We are constantly in danger, in studying a sub-
ject, of making in our minds isolations which do not exist m
nature. When one accidentally site upon a sharp object, he

»i«jM

aervM, M aeen in
). A,emetgmae
I with eMhotiier

it, jet it can
ormal life of
it be ezceed-
ilying a sub-
not exist in
rp object, he

THE SPINAL CORD.— GENERAL.

465

F» an — WvWon of • •lender nerfa-tber, and eommanlMtloa ^* '•"^'f?, 'iSf
h^ynmi^ig proceed* «* *««> nenro^elli from ■piiul cold of ox. 1 * IM.
(iSterCNHdacbT

rises suddenly without a special effort of wUl power; he expe-
riences pain, and has certain thoughts about the object, etc.
SO

^^^

466

COMPARATIVE PHYSIOLOGY.

Now, in reality this ia
yery complex, though it
can be analyzed into its
facton. Thus, aflferent
nerves are concerned, the
spinal cord as a reflex
center, efferent nerves to
the musdes called into
action, the cord as a con-
ductor of impulses which
result in sensations, emo-
tions, and thoughts refer-
able to the brain; so that
if we would grasp the state
of affairs it is of impor-
tance to HO combine the
various processes in our
mental conception that it
shall in our minds form
that whole which corre-
sponds with nature, as we
have been insisting upon
in the last chapter. With
this admonition, and as-
suming a good knowledge

of the general and minute
Fia.aM.—MaltipoIarguigUoii cell from anterior -_„i,-__ _« xi,. <,^;__i
BnyiiMtterl^apiDidrcwd of oz(«fterDet. anatomy oi the spmal

W^txli cylinder t«oceM; 6, biuclied ^^ ^^ shall proceed tO

discuss its functions.

THB BBFLBX FDNOTIOMS OP TBB BPOfAXi OOBB.

The following experimental observations may readily be
made by the student himself: Let a decapitated frog be sus-
pended freely (from the lower jaw). It hangs motionless and
limp at first, but when it recovers from the shock (abolition of
function) to the spinal cord produced by the operation, it may
be shown that this organ is functional: 1. When a piece of
bibul o us pvperdipped in <^ttte acid is placed upon the thigh,
the leg is drawn up and wipes away the offending body. 2. If
the paper be placed on the anus, both legs may be drawn up,
either suooeHiyely or simultaneously. 3. If the leg of one

litythisis

though it
ed into its
a£Ferent
cemed, the
a reflex

nerves to
ailed into
I as a con-
tlses which
tions, emo-
ightB refer-
in; so that
«p the state

of impor-
»mbine the
ses in our
tion that it
linds form
lioh ooire-
iture,aswe
sting upon
Iter. With
»n, and as-
knowledge
ind minute
the spinal
proceed to
itions.

< OOBO.

readily be
rag be sus-
ionlesB and
ibolition of
ion, it may

a piece of
. the thigh,
Ddy. 8. If

drawn up,
eg of one

THE SPINAL GOBD.-^BNERAL.

4«7

tide be allowed to hang in the dilute add, it will be withdrawn.
4. If a small piece of blotting-paper dipped in the acid be
placed on the thigh, and the leg of that side gentl;^ held, the
other may be drawn up and remove the object

It may be noticed that in every case a certain interval of
time elapses before the result follows. Upon increasing the
strength of the acid very much this interval is shortened, and
the number of groups of muscles called into ncUon ia increased. -
Again, the result is not the same in all respects when the nerve
of the 1^ is directly stimulated, as when the skin first receives
the impression. Section of the nerves of the parts abolishes
these effects; so also does destruction of the spinal cord, or the
part of it with which the nerves of the looalitiea stimulated are
connected; and more exact experiments show that in the ab-
sence of the gray matter the section of the posterior or anterior
roots of the nerves also renders such manifestations as we have
been describing impossible.

These experiments and others seem to show that an afferent
nerve, an efferent nerve, and one or more central cells are
necessary for a reflex action; that the latter is only a perfectly '
co-ordinated one when the skin (end-organs) and not the nerve-
trunks are stimulated; that' there is a latent period of stimula-
tion, suggesting a central "summation" of impulses necessary
for the effect ; th|it the reflex is not due to the mere passage of
impulses from an afferent to an efferent nerve through the
ccnd, but implies important p r oc e s se s in the central cells them-
selves. The latter is made further evident from the fact that
(1) strychnia greatly alters reflex action 1^ shortening the
latent period and extending the range of muscular action, which,
it has been shown, is not due to changes in the nerves them-
selves. A very slight stimulus suffices in this instance to cause
the whole body of a decapitated frog to pass into a tetanic
spasm. We must suppose that the processes usually confined
to certain groups of central cells have in such a case involved
others, or that flie ** resistance** of the centen of the cord has
been diminished, so that many more cells are now involved;
hence many more muscles called into action. Normally there is
resistance to thepassageof an impulse to the opposite side of the
cord, as is shown by the fset that when a slight stimulus is ap-
plied to the leg of one side the reflex is confined to this member.

It is evident, then, that the reflex resulting is dependent on
(1) the location of the stimulus, (S) its intensity and duration,

i i

=-tr^-y*w\giA-

468

COMPARATIVE PHYSIOLOGY.

(3) its character, and (4) the condition of the spinal cord at the
time. Occasionally on irritating one fore-limb the opposite
hind one answers reflezly. Such is a *' crossed reflex," and is
the more readily induced in animals the natural gait of which
involves the use of one fore-leg and the opposite hind-limb
together. -^

iMtU

Fio. 8M.— Dittnnunktic lepreMntetion to Ulutnte the raflez mc (Brunwell whI Rmi-
ner). 1, S, Mnsory flbow; 8, motor-cdJ of Miterlpr horn; 4, motor-llber cpniieetM
with 8 and MMins oat by anterior root to muele: ,5, flber Joinlmt gangll<mie cell
(8) with croJSS pfraroldal tract, C. P. C; 8, nm^jon on root orpoaterior ipinal
nerve; 7, flber joining 8 with Tliek<a oolomnTT. Fiber » la repreaented aa paaa-
ing throogfa Bnidach'a column to reach the cell, 8.

Reflexes are often spoken of as purposive, and sug^iest at
first intelligence in the cord; but such phenomena are explained
readily enough without such a strained assumption.

Evoltaion, heredity, and the law of habit, apply here as else-
where. The relations of an animal to its environment must
necessarily call into play certain nervo-muscular mechanisms.

"mt

iord at the
e opposite
Bz," and is
t of which
hind-limb

iMUI

'(■•KK

■M«M

(IU11M7).

nwell vcA Ran*
BbercoDBeeted
guiglt<mle cell
^teiior ipinal
lented m psM-

suggest at
•e explained

nereaselae-
iment must
leohanisms.

THE SPINAL CORD.— GENERAL.

469

which from the law of habit come to act together when a
stimulus is applied. Naturally those that make for the welfare
of the animal are such as are most used under the influence of
the intelligence of the animal— i. e., of the domination of the
higher cerebral centers, so that when the latter are removed it
is but natural ^t the old mechanisms should be still employed.
Moreover, the reflex movements are not always beneficial, as
when a decapitated snake coils itself around a heated iron
under reflex influence, which is readily enough understood if
we remember the habit of coiling around objects, and what
this involves— vis., organized tendencies.

TwIiiMtitHi of B«fltXM.— It can be shown in the case of a frog
that still retains its optic lobes and the parts of the brain pos-
terior to them that, when these are stimulated at the same time
as the leg, the reflex, if it occurs at all, is greatly delayed.

On the other hand, in the caw of dogs, from which a part
of the cerebral cortex has been removed, the reflexes are much
more prominent than before. Experience teaches us that the
acts of defecation, micturition, erection of the penis, and many
others, are susceptible of arrest or may be prevented entirely
when the usual stimuli are still active, by emotions, etc.

These and numerous other facts tend to show that the higher
centers of the brain can control the lower; and it is not to be
doubted that pur© reflexes during the waking hours of the
higher animals, and especially of man, are much less numerous
than among the lower vertebrates. The cord is the servant of
the brain, and a faithful and obedient one, except in cases of
disease, to some forms of which we have already referred.

TBB nnDrAXi OORD as a OOMBUOTOR of mPDUHBS.

It is to be carefully borne in mind now, and when studying
the brain, that a conducting path in the nervous centers is not
synonymous with conducting fibers. The cells themselves
and the neuroglia probably are also conductors. We shall
now endeavor to map out, as established by the method of
Fleohsig, Waller, and others, the main fibw tracts of the spinal

cord.

1. ilntoftMiMduin Columns (columns of Turck). — These
probably decussate in the cervical region, where they are most
marked, constituting the direct or uncrossed pyramidal tract
and disappear in the lower d(»nal region.

Bf«t*f«ic&»IHWsr.-

470

COMPARATIVE PHYSIOLOGY.

Bedondary degeneration ensues in these tracts upon certain

brain lesions, in the motor regions.

2. Crvaaed Pyramidal IVrkrts.— They pass forward to form

part of the anterior pyramids of the medulla after decussation

in their lower part. Simi-
larly to the first, degenera-
tion follows in these tracts
when there are brain - le-
sions of the motor area.
Hence, both of these consti-
tute desoendingmotorpaths.
8. Anterior Fasciculi
(fundamental or ground
bundle). — They ponibly
connect the gray matter of
the cord with that of the
medulla.

4. Anterior Bcuiicttlar
Zoitea, in the anterior part
of the lateral column.

5. Miaeed Lateral Col-
umns.— Theae and the pre-
ceding are functionally sim-
ilar to 3. Neither 8, 4, nor
5 degenerate, on section of
the cord, from which it is
inferred that they have
trophic cells both above and
below.

6. Direct Cerebellar IVturfs.— These bundles, passing by the
funiculi graciles or posterior pyramids of the medulla, reach
the cerebellum by its inferior pcdundee.

These fescionli enlarge from their site at origin in the lum-
bar cord upward. After section of the cord they show ascend-
ing degeneration, so that it seems probable that their trophic
cells are to be referred to the posterior gray comua of the cord,
which they connect in all probability with the cerebellum.

7. Columns of Burdaeh (postero-lateral columns)'. —This
tract is connected with the restiform bodies and reaches the
cerebellum by the inferior peduncles. Secondary degenera-
tions do not occur in these fasciculi, so that it seems likely that
they connect nerve-cells at different levels in the cord; and

Fio. SK.— DIagnunmatio leprcwnUtion of col-
nmnt and condnctins path* In aplnal cord
in npper donal region (after Flint and
Landoia). AR. AILanterior rooto of ipl-
nal nervea: PR, Mt poeterior njote; A,
colnmna of Tflrck (antero- median .coi-
umni) ; B, anterior fandamental faaeien-
loi; C, colnmna of Goll; D. colnmna of
Bardacli: E, B, anterior ndlcniar aonea:
F, P, mixed lateral colamnr, O. O, crpiMd
pynunldal tracU; H, H, direct cereMlar
flDert.

ipon certain

ard to form

deciuaation

part. Simi-

d«geneni-

these tracts

e brain -le-

Qotor area.

these consti-

motor paths.

' Fcuciouli

ground

ty possibly

»y matter of

that of the

' Radicular
interior part
)lumn.
'jaUral Col-
and the pre*
itionallysim-
ther 8, 4, nor
in section of
I which it is
they have
th abore and

issing by the
edulla, reach

I in the lum-
ihow ascend-
their trophic
I of the cord,
ibellum.
nns). — This
reaches the
ry de^nera-
is likely that
le cord; and

THE SPINAL GOBD.-OENBRAL.

471

they may also connect the posterior gray comua with the cere-
bellum as 6.

Columns of OM (postero-median columns). —They do not
extend beyond the lower dorsal or upper lumber region ; and
their fibers pass to the funiculi graciles of the medulla. Ascend-
ing degeneration follows section of these columns.

The degenerations referred to above are visible by the micro-
scope, and of the character following section of nerves. It is
probable that they are the later stages of a primary molecular
derangement in consequence of interference with that continu-
ous functional connection between all parts on which what has
been called nutrition, but which we have shown is but a phase
of a complex metabolism, depends.

DxwilMltlail — Sections of the cord, when confined to one lat-
teral half, are followed by paralysis on the same side and loss of
sensation, confined chiefly to the opposRe half of the body be-
low the point of section. The results of experiment, patho-
logical investigation, etc., have rendered it clear that— 1. The
great majority of the fibers passing between the periphery and
the brain decussate somewhere in the centers. 2. Afferent fibers
cross almost directly but also to some extent along the whole
length of the cord from their point of entrance, the decussation
being, however, completed before the medulla is passed. 8.
Motor or efferent fibers decussate chiefly in the medulla, though
crossing is continued some distance down the cord, such latter
fibers being but a small portion of the whole. This fact is best
established, perhaps, by noting the results of brain-lesions.
With few exceptions, susceptible of explanation, a lesion of one
side of the cerebrum is followed by loss of motion of the oppo-
site side of the body. These are all central, well-established
truths. It ha also now pretty well determined that voluntary -^
motor impulses descend by the pyramidal tracts, both the direct
and the crossed. That the posterior columns of the cord are in
8ome way concerned with sensory impulses there is no doubt;
but when an attempt is made to decide details, great difficulties
are encountered. Experiments on animals are of necessity very
unsatisfactory in such a case, from the difficulty experienced in
ascertaining their sensations at any time, and especially when
disordered.

BMihioIoglflal. — A good deal of stress has been laid upon
the teachings of locomotor ataxia in the human subject The
symptoms of this disease are found associated with lesions of

47S

COMPARATIVE PHYSIOLOOY.

the posterior oolumiu of the eord. The eeaential feature it an
inability to oo-ordinate moTemente, though muMular power
may be unimpaired. But luoh inco-ordination is not usually
the only symptom; and, while the disease seems usually to
begin in Burdaoh's columns, the columns of Gk>ll, the posterior
nerve-roots, and even the cells of the posterior oomua, may be
involved, so that the subject becomes very complicated. Co-
ordination of muscular movements is normally dependent upon
certain afferent sensory impulses, themselves very complex. It
is to be remembered also that there are numberless connecting
links between the two sides of the cord and between its different
columns of an anatomical kind, not to mention the posdbly
numerous ph]rsiologioal< (functional) ones.

Via. SW.-'Dlagfm to UlMtmt« prolwble coutm taken by flben of nerve-raoto on ca-
tMlDf; ipliwl cold (Schtf er).

We have stated above that section of one lateral half of the
cord is followed by loss of sensation on the opposite side of the
body ; but directly the contrary has been maintained by other
obeervers; while still others contend that the effects are not
confined to one side, though most pronounced on the side of
the section. The same remark applies to motion.

While there is considerable agreement as to the pyramidal
tracts of the lateral column, the functions of the rest of these

BttSl

iture iaui
lar power
tot uauslly
usually to
le pmterior
ua, may be
sated. Oo-
ident upon
mplex. It
oonneoting
ta different
le poadbly

w-rooUon «&-

half of the
side of the
d by other
»ts are not
the aide of

pyramidal
It of theae

THE SPINAL CORU.-ORNBRAfi.

478

divitiont of the oord are by no meana well eatabliahed. It ia
poMible that vaso-motor, reapiratory, and probably other kinda
of impulaea, paM by portions of the latenl traota other than
the croMwd pyramidal. When a lateral half of the oord ia
divided, the Iom of function ia not permanent in all inatanoea,
but has been reoovernd from without any regeneration of the
divided flbera; and even when a section has been made higher
up on the opposite side, partial recovery haa again followed ;
80 that it would appear that impulaea had pursued a tigsag
course in such cases. We do not think that such experiments
show that impulses do not usually follow a definite course, but
that the reaouroes of nature are great, and that, when one tract
is not available, another is taken.

It is plain that impulses do not in any oaae travel by one and
the same nerve-flber throughout the cord, for the siie of this
organ does not permit of such a view being entertained; at the
same time there is a relation between the sise of a crossHwotion
of the oord at any one point and the number of nerves con-
nected with it at that region.

We may attempt to trace the patha of impulses in a oord
somewhat as follows: 1. Volitional impulses decussate chiefly

I TiTiuni V iriuu i muzavmraviTiTiuuivinvuviT ituiu i
SaenO. Xiumbor. ilorMl. Cirvtoal.

matter, (A

. 07.— Diagnm to ninttnt* ntottT* and nbwriat* ntant of Cl)jnv matt

white eoInmiM in raccaMlve arctional aieaa of epIiMi cord, and (STaeetioaal

of aereml nerreToota entering cord. IfS, nerve foott; A.C,LO,PC, anterior,
lateral, poaterior colnnina; Or, giaj natter (after Schlfer, Lndwig, and Woro-
aehihm).

in the medulla oblongata, but also, to some extant, throughout
the whole length of the spinal oord. They travel in the lateral
columns (orosaed pyramidal traota chiefly, if not exclusively),
and eventually reach the anterior roots of the nerves through
the anterior gray oomua, passing to them, possibly, hy the ante-
rior columns. From the cells of the anterior oomua, impulses

474

COMPARATIVE PHYSIOLOOT.

PI-

trare) by the anterior nerve-root* to the motor nerves, by
which connection ii made with the muiwlea. 8. Beneory im-
pul'iee enter the <*ord from the afferent nerve-flbem by the poe-

6 IMJ

Lowm

Wf». San.— Dlwnun ihowlnf eoane of aben In •pinal eoid (tftor RuuMr). 1, 1', dlMct
ptTMnkUrbniidlM: a, r, crotMd pynunldal iinndlet, daeniMtIng In OMdnlla: & 8',
ainct ocniMllar flbert: 4,4', flban nlated to "moacular MnM," dMOMMlnt^in
mednlte ; 5, 6*, Mid 0, 6*. Ahtn relating to the appieeUtlon of toneh, peln, and
tempemtnte. The motor bandiae have a dot upon them to npraaant the motor
cells of the cord (anterior horn). Note that the motor Iben eacape from the ante-
rior nerve-root (a. r.), and that the eenaory bnndlea enter at the poaterior nerve-
root (p. r.), which hai a gaagUoB {g) upon it.

terior nerv»-rootB, pairing probably by the poaterior oblumna to
the po«teri<»r comua, thenoe to the Uiteral columns, decunation
being largely immediate though not completed for some dia-
tence up the cord.

It would seem that the lateral oolumna are the great high-

or nervM, by
Benaory im-
en by the pos-

UUM7). l.l'.diNCt

ig In nMdalta: 8.8'.
le," dcooMMlii^lii
4 tooeb, pain, and
ipiMMt the motor
Mpe from the uto-
w poMarlor nwve-

ior oolumns to
B, deouaaation
for some dis-

le gTMt high-

TIIB SPIKAL CORD.-OBNEHAL.

475

waya of impulaea; though in all tnatuiooa it ia liitely that tb*
gray matter of the oord playa an important part in modify>
ing them before they reach their deatination. Borne obaervera
believe that aenaory impulaea giving riae to pain travel by the
gray matter of the cord almoat excluaively. It would be eoay
to lay out the patha of impulaea in a more deftnito and dog-
matic manner ; but the evidence doea not aeem to wan-ant it,
and it ia better to avoid making atatementa that may require
aerioua modification, to aay the leoat, in a few montha. The
prominent principle to bear in mind aeema to be that while
there are tracta in the oord of the animala that have been exam-
ined and probably of all that have well-formed apinal oordii,
along which impulaea travel more frequently and readily than
along othera, it Im equally true that theae paUia are not invaria-
ble, nor are they preoiaely the aame for all groupa of animala.
The oord can not be conaidered independently of the brain ; and
there can be no doubt that the paths of impulaea in the former
are related to the conatitution, anatomical and phyaiologioal, of
the latter. It ia atill a matter of diapute whether the oord ia
itaelf irritable to a atimulus. Aa a whole it ia without doubt ;
aa also the white matter by itaelf. The gray matter ia certainly
conducting, but whether irritable or not ia atill doubtful. Why
the aenaibiUty of the aide of the body on which one lateral half
of the cord haa been divided ahould be increaaed (hyperseethe-
aia), is alao undetermined. Poaaibly it ia due to a temporary
diaturbance of nutrition, or the removal of certain uaual inhibi-
tory infltenoea from above, either in the cord or brain.

ram automatio PONonomi op tbb spinal oord.

Reference haa been already made to the fact that when por-
tiona of a mammal'a cerebrum are removed the reflexea of the
cord become more pronounced, owing apparently to the removal
of influencea operating on the cord from higher centera.

When the oord itaelf ia completely divided acroaa, it often
happena (in the dog, for example) that there are rhythmic
movementa of the poaterior extremitiee— i.e., when the animal
haa recovered from the ahock of the operation— that part of the
oord now independ«it of the reat and of the brain leema to
manifeat an unuaual automatiam. The queation, however, may
be raiaed aa to whether thia ia a purely automatio effect, or the
reault of reflex action. But, whichever view be entertained,

^'.

476

COMPARATIVE PHYSIOLOGY.

theae phenomena certainly teach the dependence of one part
non another in the normal animal, and should make one oau-
ti 's in drawing conclusions from any kind of experiment, in
regard to the normal functions. As we have often ui^^ed in
the foregoing chapters, what a part may under certain circum-
stances manifest, and what its behavior may be as usually
placed in its proper relations in the body, are entirely different,
or at least may be. When one leg is laid over the other and a
sharp blow struck upon the patella tendon, the leg is jerked up
in obedience to muscular contraction. It is not a little difficult
to determine whether this result is due to direct stimulation of
the muscle or to reflex action, the first link in the chain of
events necessary to call it forth originating in the tendon ;
hence the term tendon-reflex. But at present it is safer to
speak of it as the "knee-jerk," or the "tendon-phenomenon."
It disappears, however, when the spinal cord is destroyed or is
diseased, as in locomotor ataxia, or when the nerves of the
muscles or the posterior nerve-roots are divided, showing that
the integrity of the center, the nerves, and the muscles are all
essential. There are normally many such phenomena (reflexes)
besides the "knee-jerk."

Another question very difficult to decide is that relating to
the usual condition of the muscles of the living animal. It is
generally admitted that the muscles of the body are all in a
somewhat stretched condition, but it is not so clear whether
the skeletal muscles are imder a constant tonic influence like
those of the blood-vessels. It is certain that, when the nerves
going to a set of muscles are cut, when even the posterior roote
of the nerves related to the part involved are divided or the
spinal cord destroyed, there is an unusual flaccidity of the
limb involved. But the natural condition may be, it has been
suggested, the result of reflex action. The subject is probably
more complex than it has hitherto been considered.

The facts of such a case— those of the tendon-phenomenon
and similar onee— would be better understood if the spinal
cord, til's nerrm, and the musdes associated with them, were
regarded as parts df a whole so connected in their functions
that severance of any one of them leads to disorder of the rest
That the cells of the cord are constantly exercising an influence
through the nerves on the muscles, while they in turn do not
lead an independent existence, but are as constantly influenced
by afferent impulses, and that one of the results is the oondi-

"«ac

ice of one port
make ooe oau-
ezperiment, in
often ui^ged in
certain circum-
be as usually
irely different,
he other and a
»g is jerked up
la little difficult
stimulation of
the chain of
n the tendon ;
it is safer to
phenomenon."
estroyed or is
nerves of the
, showing^ that
nusoles are all
nena (reflexes)

lat relating to
animal. It is
ly aie all in a
clear whether
influence like
lien the nerves
Msterior roots
iivided or the
eidity of the
>e, it has been
!t is probably
d.

i-phenomenon
if the spinal
h them, were
leir ftinctions
» of the rest
r an influence
1 turn do not
ly influenced
is the oondi-

THE SPINAL CORD.-OBNERAL.

477

tion of the muscles referred to, is, we are convinced, the case.
To say that it is either entirely automatic or purely reflex, or
that the whole of the facts would be covered even by any com-
bination of these two processes, would probably be unjustifiable.
The influence of the centers over the metabolism of parts is
both constant and essential to their well-being ; and in such a
case as that now considered it may be that a certain degree of
tonus is normal to a healthy muscle in its natural surround-
ings in the body.

There is now considerable evidence in favor of placing cer-
tain oeniers presiding over the lower functions, as micturition,
defecation, erection of penis, etc., in the spinal cord of mam-
mals, especially its lower part— which centers, if they be not
automatic, are not reflex in the usual sense ; but their considera-
tion is betier attempted in connection with the treatment of the
physiology of the parts over which they preside.

SPBOIAZi OOVntOBBATlOm.

Oompantive.— Among invertebrates there is, of course, no
spinal cord, but each segment of the animal is enervated hy a
special ganglion (or ganglia) with associated nerves. Nevertiie-
less, these are all so connected thai there is a co-ordination,
though not so pronounced as in the vertebrate, in which the
actual structural bonds are infinitely more numerous, and the
functional ones still more so. From this result possibilities to
the vertebrate unknown to lower forms ; at the fwme time, in-
dependent life and action of parts are necessarily much greater
among invertebrates, as evidenced especially by the renewal of
the whole animal tram a single segment in many groups, as in
certain divisions of worms, etc.

It also follows from the same focts that a vertebrated ani-
mal must suSer far more from injury, in consequence of this
greater dependence of one part on another ; a thousand things
may disturb that balance on which its well-being, indeed, its
very life hangs. It is noticeable, moreover, that, as animals
occupy a higher place in the organic scale, their nervous sys-
tem becomes more concentrated ; ganglia seem to have been
fused together, and that extreme massing -seen in the i^inal
oord and brain of vertebrates is foreshadowed. In the chapters
on the brain numerous illustrations of the nervous system in
lower forms will be found.

■5

'; i

478

COMPARATIVE PHYSIOLOGY.

The fact that the brain and cord arise from the same germ
layer, and up to a certain point are developed almost invoiaely
alike, is full of signifioanoe for phjrsiology as well as morphol-
ogy. That original deep-lying connection is never lost, though
functional differentiation keeps pace with later morphological
differentiatioii. But even among vertebrates the spinal cord
shows a complexity gradually increasing with ascent in the
organic series. In the lowest of the fishes or vertebrates (Am'
phioanu lanceolatua) the creature possesses a spinal cord only
and no brain, so that an opportunity is afforded of witness-
ing how an animal deports itself in the absence of those direct-
ive functions, dependent on the existence of higher cerebral
centers. The Laneelet spends a great part of its life buried in
mud or sand on the bottom of the ocean, and its existence is
very similar to that of an invertebrate, though, of course, the
dependence of parts on each other is somewhat greater.

Xvidlition. — According to the general law of habit and in-
heritance, we should suppose that at birth each group of ani-
mals would manifest those reflex and other functions of the
cord which were peculiar to its ancestors. Observation and
experiment; both show that reflexes, etc., are hereditary ; that
they tend to become more and more so vrith each generation ;
and at the same time that habit or exercise is essential for their
perfect development They stand, in fact, in the same relation
as instincts, which are dosdy connected with them. Like the
latter, they may be modified by way of increase or diminution
and otherwise. To illustrate, it can not be doubted that gallop-
ing is the natural gait of horses, as shown by the tendency of
even good trotters to "break " or pass into a gallop ; but it is
equally well known that famous trotters breed trottera. In
other words, an acquired gait becomes organised in the nervous
system (especially) of the animal, and is transmitted with more
and mora fixity and certainty with the lapse of time. But all
experienca goes to show that walking, running, or any of the
movements of animals are, when fully formed as habit-reflexes,
dependent for their initiation on the will in most but not all
instances, and require for their execution certain comlnnations
of sensory and other afferent impulses, and the integrity of a
vast comj^x of nervous connections in the spinal cord.

It is wdl knowm that (me in a period of absent-mindedness
will walk into a building to which he was accustomed to go
yean before, though not of late, showing plainly that volition

16 Bamegenn
lOBt predaAj

an morphol-
r lost, though
norphologioal
B spinal cord
ascent in the
tebrates (Am'
lal cord only
I of witnesB-
' those direct-
fher cerebral
life buried in
s existence is
>f course, the
aater.

labit and in-
proup of ani-
ictions of the
lervation and
Bditary ; that
1 generation ;
itial for their
lame relation
m. Like the
r diminution
ithatgallop-
i tendency of
op ; but it is

trotters. In
a the nerrous
ed with more
tme. But all
r any of the
tabli-reflexes.
it but not all
Bomlnnations
ategrity of a
cord.

t-mindedness
■tomed to go
that volition

THE SPINAL COBR— QBNBRAL.

479

was not momentarily required for Ihe act of w^Okmganda^
that is involved in the above behavior. it^W-t-*^,^^"
^ous and muscular connections have been formed, function-
ally at least. Plainly, then, we should not expect ea«h mdi-
^U man's spinal ird to be the same, but that the ^^^
mechanisms of which every spinal cord is "f^^^P/^J^lj JJ"

with experience ; and if this holds for i^J^^^^ua^ h?^r^
more must it be tme of different groupe of ammals, the habito

of which differ so widely.

All the fads go to show that the cord is made up of nervous

mechanisms-if we may so spedc-which are naturally a-oo-
ated, boOi structurally and functionally, with oeiiain nervea
^muscles; these, like the path, whioh impuljN- tiJce to^
from the brain, though usual, are not abwlutely toed, though
more so as reflex than conducting paths, while they aw con-

stanay liable to be modified in action by the condition of
nwEfaboring groups of mechanisms, etc.

We hai^ said less about the gray matter of the coid as a
conductor than its importance perhaps deserves. Itisbelieved
by many that impuLwi which give rise to ■en«tious of v^
^waysteavelbythe gmy matter; and there is not a httle ev^-
?^ tol^w U whS^none of th. white column. «« «^
aWe. owing to operative procedme, disease, or ottier dkabhng
*i^T|my .^will conduct impukes that umudiy pr^

''^IXjSS.^e spimd cord i. compo«^ of Ij^^
nei^Sto^fibers, and connecting neuroglia. FunoUonally it
TT^J^O^ seat of certain automatic e»t«. ^ o'
wflexmechani;ms. P~»«Wy in ev«T ca« the one ftmcton »
to a certain extent associated with the oUier-L e., when the
«^ ^«flexly it i. also a conductor, and tbe cell, con^

are so readUy excited tocertain discharge. of nwwu. en«rgy
Tat auJoSity i.«ig,p-ted, ~d y in ««-^«^ ^^J
in the case of automatidty, reflex influence or aflefent impnlM.
are with difficulty entirely excluded from oonridwa^

The neat majority of conducting fiber, seeinto cross wUier
intiiecSTitoelforinihemeduUaoblongate. J^J.^^'?^
Mth. that have been diown by pathological and cbniori inve^
ti«Son to be bert marked out in the «*n^ cord are thoj for

;^^ motor impul*.. So fto a. the function, of «to

CmT^ «e concerned, ^imoa^ •»*. Pj^^^TibSS^
have thrown the gwsatert amount of direct light on the robjeot,

■I

A ;

480

COMPARATIVB PHYSIOLOOT.

but the inferenoes thus drawn have been modified and supple<
mented by the results of experiments on certain other mam-
mals.

It is especially important to bear in mind that, while certain
conducting paths are usual, they are not invariaUe: in like
manner, reflex impulses may not be confined to usual groups of
ceUs, but' may extend widely, and so bring into action a large
number of muscles. The resulting reflex in any case is depend-
ent on the character, intensity, and location of the stimulus,
and especially on the condition of the central cells involved.
In the whole functional life of the cord the influence of higher
centers in the organ itself and especially in the brain is to be
considered. The cord is rather a group of organs than a
single one.

1 and nipple<
i other mam-

-i

while certain
aUe: in like
ual groups of
ction a large
aae is depend-
the stimulus,
ells involved,
ice of higher
train is to be
•gans than a

THE BRAIN.

At the outset we may renuurk that the whole subject will
be studied more profitably if it be borne in mind that— 1. The
bndn is rather a collection of organs, bound together by the
4slosest anatomical and phjrsiological ties than a single one; in
consequence of which it is quite impossible to understand the
normal function of one part without constantly bearing in
mind this relationship. This aspect of the subject has not re-
ceived the attention it deserves. No one r^iards the aliment-
ary tract as a single organ; but it is likely that the dependence
functionally of one part of the digestive canal upon another
is not mote intimate than that established in that great coUeo-
tion of organs crowded together and making up the twain. 2.
Since the ralative siie, position, and anatomical connections of
the parts that make up the brain are different in different
groups of ftni"(»<»l», not to speak of the fact that the functions
of any part of the brain of an animal, like that of its apinal
cord, already alluded to, must depend in great part upon its
own and its inherited ancestral experiences, it follows that the
greatest caution must be exercised in applying oondurions true
of one group of animals to another. 8. It follows fimm what
has been referred to in 1 above, that oondusions based upon the
behavior of an animal after section or removal of a part of the
brain must be, until at least corrected by other fsots, received
with some hesitation. 4. It also might be inferred firom 1 that
it is desirable to study the ampler forms of bndn found in the
lower vertebrates, in order to prepare tor the more elabor^
development of the encephalon in the hi^^ m a mmals and in
man. 5. The embryologioal development of the oxgan also
throws much light upon the whole subject

The student will see from these remarks that asonndknowl-
edge of the anatomy of the brain and its connections is india-
pcmaable for a just approciation of its physiology; nor must
81

-i

MMMtlMII

482

COMPARATIVE PHYSIOLOGY.

such knowledge be oonfl9ed to any single form of the organ.
There is only one way by which this oan be attained: dissection,
with the help of plates and descriptions. The latter alone fre-
quently impart ideas that are quite erroneous, though they
serve an especially good purpose in helping to fix the pictures
of the natural objects, and in reviving them when they have
become dim.

It is neither tUfflcult to obtain nor to dissect the brain of the
fish, frog, bird, etc. Valuable material may be saved and the
subject approached profitably, if, prior to the dissection of a
human brain, a few specimens from some group or groups of the
domestic animals be examined. However useful artificial brain
preparations may be, they are so far from nature in color, con-
sistence, and many other properties, that, taken alone, they cer>
tainly may serve greatly to mislead; and we hope the student
will allow us to urge upon him the methods above suggested
for getting real lasting knowledge. The figures given below
may prove helpful when supplemented as we advise.

The great difference in total sise, and in the relative propor-
tion, situation, etc., of parts, will, however, be obvious, from the
figures themselves; and as we have already pointed out more
ttn^n once, the preponderance of the cerebrum in man must
ever be borne in mind in the consideration of his entire organi-
sation, whether phj^cal, mental, or moral.

AMUIAIiB DUFHIVA I D OF THB dBBBBRUlC

The cerebrum may be readily removed from a frog, without
producing either severe prolonged shock or any considerable
haemorrhage. Such an animal remains motionless, unless
when stimulated, though in a somewhat different position from
that of a frog, having only its spinal cord. It can, however,
craiTl, leap, swim, balance itself on an inclined plane, and when
leaping avoid otatacles. One looking at such an animal per-
forming these various acts would scarcely suspect that any-
thing was the matter with it, so perfectly executed are its move-
ments. We are forced to conclude, from its re maining quiet,
except whmi aroused by a stimulus, that its volition is lest; but,
apart from that, and the fact that it evidently does not see as
well as before, it appears to be normal. It has no intelligent
directive power over its movements. It remains, therefore, to
explain how it is that they aro so much more complete, so

rMiMI

THE BRAIN.

488

I of the organ.
Bd: diaeotioD,
tier alone fre-
though they
be the piotoree
hen they have

le bndn of the
Bayed and the
liaeeotion of a
r groups of the
artificial brain
> in color, con*
tlone, they cer>
»pe the student
love suggested
is given below
rise.

elative propor-
rious, from the
inted out more
in man must
I entire organi-

IBRUIC

a frog, without
ly considerable
ionless, unless
t position from
i can, however,
lane, and when
au! animal per-
peot that any-
)d are its move-
imaining quiet,
ion is lest; bu^
does not see as
B no intelligent
IS, therefore, to
re complete, so

much better coordinated in the entire animal than when only
the spinal cord is left. It seems to be legitimate to infer that
the other parts of the brain contain the nervous machinery for
this work, which is usually aroused to action by the will, but
which an external stimulus may render active. All the connec-
tions, structural and functional, are present, except those on
which successful volition depends. The frog with the cord
only, sinks at once when thrown into water; when gently
placed on its back, it may and probably will remain in that
position, without an attempt at recovery. There is, in fact,
very limited power of coK>rdination.

Removal of the cerebral lobes in the bird is more likely to
be attended with difficulties, and conclusions must be drawn
with gn^eater caution.

But a pigeon may be kept alive after such an operation for
months. It can stand, balancing on one leg; recover its posi-
tion when placed on its side; fly when thrown into the air;
it will even preen its feathers, pick up food, and drink water.
Its movements are such as we might expect from a stupid, drow-
sy, or probably intoxicated bird; but it is plainly endowed with
vision, though not as good as before. But spontaneous move-
mento are absent, and the pecking at food, etc., must be consid-
ered as associate reflexes, and as such are very interesting, in
that they show how maehine-like, after all, many of the appar-
ently volitional acts of animals really are. In a m a mm a l so
great is the shock, etc.. resulting from the operative procedure,
thui the actual functions of the remaining parts of the brain,
when the cerebral convolutions are removed, are greatly ob-
scured ; nevertheless, littie doubt is left on the mind that homol-
ogous parts discharge analogous functions. It can walk, run,
leap, right itself when placed in an unnatural position, eat when
food is placed in its mouth, and avoid obstacles in its path,
though not perfectly. Tet it remains motionless unless sthnu-
lated; all objects beftm its eyes impress it alike if at all. The
animal evidentiy has neither volition nor intelligence. Now, if
any of the parts between the cerebrum and the medulla be
removed the creature shows lessened co-ordinating power; so
that the inference that these various parts are essential constittt-
ents of a complex mechanism, all tiie components of which
are necessary to the highest forms of muscular ooKwdination
>>nd probably other functions, is unavoidable.

Knee we are dealing with ooK>rdinated movements, we may

484

COMPARATIVE PHYSIOLOGY.

now triMit of the functions of a portiop
our pnaent oUuwifloation.

* the ear, according to

■ATB TBB MMCOIHO ULAH OAK AM A OO-ORXXm AT-

oro FONonoif 7

Phyiiologiita have a« yet been unable to aasign to the aemi-
circular canals a function in hearing, and upon certain results,
partly of disease but chiefly of experiment, it has been con-
doded, though somewhat dubiously, that they are concerned
with those sensations that conduce to or are essential to main-
tenance of the sense of equilibrium ; in a word, that they are
the organs of that sense in the same way that the eye is the
organ of vision.

Until further evidence is forthcoming, we are not inclined
to give assent to the existence of any mechanism in the semi-
circular canals, affording sensory data so etttirely different
from those furnished by other recognised (and unrecognised)
senseKnuans, that upon them alone, or in a manner entirely
their own, arises a consciousness of equililwium. We are in-
clined to regard the latter as depending upon the fusion in con-
sciousness of a vast complex of sensations ; and that upon the
whole being there represented, or a portion wanting, depends
either the p reser v a tion of equilibrium, or a partial or entire loss
of the same. Nevertheless, it is highly probable that sensory
impulses of a very important character, in addition to such as
are essential for hearing, may proceed from the semicircular
canals, and indeed other parts of the lahyrinth of the ear.

When certain portions of the brain of the tnamma.! have
■leen injured, movements of a spedal character result, and, inas-
much as they are not voluntaiy, in the ordinary sense at least,
have been spoken of as forced or compulsory. The movements
may be daasifled according as they are around the long, the
veiiicalorthetransverseaxisof the body of the animal. Henoe
tjiere are "circus" movements, when the creature simply turns
about in a.circle, " rolling '* movementa, etc. These and othera
may be toward or from the side of injury. While in some
oases there may be a certain amount of muscular weakness in
oonsequenee of the injury, which may, in party account for the

mmmimimmnimM

according to

>-ORBIMAT-

to the Mini-
ertain results,
las been con-
ire oonoemed
ntial to main-
, that they are
the eye is the

) not inclined
n in thesemi-
rely different
unreoogniied)
tnner entirely
, We are in-
fusion in con-
that upon the
nting, depends
1 or entire loss
ie that sensory
Ion to such as
le semicircular
f the ear.

mammal have
nnilt, and, inas-
T Mnse at least,
lie moTements
1 the long, the
nimal. Henoe
<e simply turns
lese and others
VHiile in some
vr weakness in
ftocount for the

THE BRAIN.

486

direction of the movements, this is not so in all oases; nor does
it, in itself, explain the fact of their being plainly not volun-
tary in the usual sense.

The parts of the brain, which, when injured, are most liable
to be followed by forced movements are the basal ganglia (oor-
pora striata and optic thalami), the crura cerebri, corpoita quad-
rigemina, pons Varolii, and medulla oblongata, and especially
if the section be unilateral. We have already seen that several
of these parts are concerned in muscular co-ordination ; hence
the disorderly character of any movements that might now re-
sult when any part of this relMed mechanism is thrown out of
gear, so to speak ; but, apart from that, we think that the view
presented in the previous sections is applicable in this case also,
while the forced movements themselves throw light upon the
symptoms following injury to the semicircular canals. When
that constant afflux of sensory impulses toward the nervous
centers is interfereid with, as must be the case in such sections
as are now referred to, it is plain that the balance in conscious-
ness must be disturbed ; confusion results, and it is not sur-.
prising that, instead of a passive condition, one marked by dis-
orderly movements should result in an animal, since movement
so largely enters into its life-habits. It is iqaportant to remem-
ber, in this connection, that the great h^hwayof impulses
between the cerebral cortex and other parts of the brain and
the spinal cord lies in the very parts of the encephalon we are
now considering.

pimotaoini OP. TBI OHHiiHH i H i cKUWoiiirnoim.

Oonpanlif*.— It will conduce to th^ oompvehension of this
subject if some reference be now made to the development of
the brain in the different groups of the animal kingdom.

Invertebrates not only have no cerebrum, but no brain in
the strict sense of the term as applied to the higher mammals.
In most forms of this great subdivision of the animal kingdom,
the first or head segment is provided with ganglia arranged in
the form of a collar around the oesophagus, by means of com-
missural nenre connections ; so that the nervous supply of the
head is not widely diflereni from that of the oilier segments
of the body. But as we ascend in the scale among the in-
vertebrates i^uBB ganglia become more crowded together, and
so resemble the vertebrate Inrain with its massed ganglia and

■s!

•'

MMMMP

«n

COMPARATIVB PHYSIOLOOV.

numerous oonneolioiu through n«iTe-flb«n, etc. But in
raipeot we find great differance unong vertebratea. W#
reoogniM, on paaiing upward from the Amphioxtu, deeti <tte
of a brain proper, to man, all gradationa in the form, relative
■iie, multiplicity of connecting tiet, etc.

Speaking generally, there is great difference in the weight
of the cerebrum, both relative and abaolute. In all animalii be-
low the primates (man and the apee) the cerebellum ie either
not at all or but imperfectly covered by the cerebrum ; while

ria. aw.— Nervow tyttan of aiedieiiud l««eli {»tU» Owm). a, doabl* inpnHMpDlui-
omI gMgllon conneoted with rndiiiMnUqr oc«IU (6, b) by nenret; e, double InfiS'
>iiagMl nngllonlc imm, which Is contlnnoiw with doable ventnl cord, hav-
wmponnd nnslfai at iwalMr Interval!.

Ing componnd ganglia at regular

in man, so great is the relative sise of the latter, that the
cerebellum is scarcely visible from above. If we except the
elephant, in which the brain may reach the weight of ten
poimds, and the whale with its brain of more than Ave pounds

Vm.

of vacna: L npper twig of tame: m, dorwa branch of trigMntnM, Joined bjr n, im-
ad bmaeh olvagns: a. f, y, t&iee branches of trigndnns; Ir. facial nerre; A.
branchial branches of vagna.

mmmm

But ill »
tM. Wo *a
KTIM, dMto 'ite

form, relative

n the weight
Jl animalit bo-
[lum is either
Bbrum ; while

ibl« inpnHMoplM-
•; 0, double Infra-
I rentnl cord, luiv-

tter, that the
we except the
weight of ten
in five pounds

tftor GMMibMir and
, optic lobe; C.ceie-
r; K, brtaral branch
M, Joined b]rii,dor-
<r, facial nerre; A,

TUB BRAIN.

in the largeet ■peoimens, the brain of man is eren absolutely
heavier than that ot any other animal, which is in gr«at part
due to the preponderating development of the cerebrum.

While the cerebral surface is smooth in all the lower verte-
brates, and but little convoluted until the higher mammals are
reached, the brain of the primates, and especially of man, has
its surfac- enormously increased, owing to its numerous As-
sures and convolutions, which, in fact, arise from the growth

Fi«. «41.-Braln and iplnal cord of frog (BaitlHi). i4. olfactojjr lobea: AMiebral
loble; A pineal body; ft X», opUc Tobea; g, cerebellum; H, iplnal cord. The
cerebellnin li notably anull.

of the organ being out of proportion to that of the bony case
in which it is contamed ; and since those cells which go to
make up the gray matter and are devoted to the highest func-
tions, are disposed over the surface, the importance of the fact
in accounting for the superior intelligence of the primates,

Vi«.a«i.

ria.S48.

■MMM

Fio. aiL-Biain of the pike, yiewed from abow ^ul«7)- iM'«S ^!S^ZSV!*,Z
Ubaa, and baMatti^Mm the optle nerrea; B, the eetebfal hamiqiberaa; C, the

the rhiBaneephaloa. or otfaetmr lobea, with /, the olfactonr nerrea; JK),ttie Mfe>
bial hemlKdiena; JPA.o^ the thalamenoephakm with the pineal gland, Ai; L.ep,
^Itte lobM^, oenbellun; 8. rh, tb» fowth Tcntrlcle; Jfe, medulla <A>loiicaU.

488

COM PA RATI VB PHYSIOLOGY.

ria. M4.-A. V, the brain of • llMrd ( P u m mot tm nis AMifnlfMb), and B, D, of a
" ■" ii — '

•tath twin of eaNbral imtymi iV. pitnllaij bo««y.

Via. S4B.— BralM of • HmfA (AwmiMwaMnw ButgiriguU} Mid of • ^MVMfagrti
gaUoiMMa) In longltiidiwil and vertical tMllon. Tlw nppw flgoN rapnMnta tha

:'l

THE BRAIN.

489

), •Bd B, p. of •
of equki l«iigUM
1*. d^r.olfMlonr
lobw of lb* mid-
cond fonrth, Mid

H«nl>i hnlB- llM W»w«f . tluit of th* Wid «»fl« lfu«l«y Md CfTU). I-jttwf •• III
•j?"" ' "Si -' iiVM>r.»..iir / } lamina l*rmiHaH*, or ktilcrlor w»U of th« Ihurd

Sr,W"«i «% .««"?;;• 'iSi Mr«n th. bnln WWch MI.W.,. to Ih.
valiM of VlaMMiM,

Md en»eciiaiy of m.n, baoom«i apparent. Depth of flouring
is, however, of moie importmoe than multiplicity of furrowi ;
Mid it nwy be obMrved that intelligence i« not alwayi in pro-
portion to the extent to which the cerebral murfaoe in broken
up into flaniree and oonvolutiona. The depth of the gray mat^
ter ii alao very variable, and aeenu to be«r an important reU-
Uon to peyohic development Man's brain, then, ii character-
iiad by ita great riie and complexity ; while thoee parta treated
elaewheiv, concerned in coKjrdinaUon, vision, etc., •'•well
developed, the cerebrum, eepecially it« convolutions as distin-
guished from its basal ganglia, is, out of all proportion, greater
than in any other animal.

The gray matter of the bruins of the higher vertebrates is
distributed as masses of ganglionic cells intemaUy, and as a
fairly uniform layer over its surface. The brahi of man weighs
•bout three pounds on the average, that of the male being
a few ounces (four to six) heavier than that of the female.

• bitdMIWMvrto

M NpnMBtt th*

VicSM.

VN.S«r.

9n.tm.

.— Bi/!ln Hid •plnal oofd of ebick

Vis. 8M.-BnlB ot

ecrcbcUom
n«.S47. ~ ■

Via

A, ewabnd hemlqthMM; », optie lob«; 0,
S'ibrtSrodsyi oM; optle lobM, », m 11111

'•^/S^mSSauA ombeUam, e, Iwgeir dmUqwd.

The individual and race differences, though considerable, are
not comparable fai degree to those that distinguish man from
even the highest apes, the brain of the latter weighing not
more than about one third as much as that of the human sub-
ject While it has been shown that individual men and women,
having bnins of avwrage or even sub-medium weight, may reach

490

COMPARATIVE PHYSIOLOGY.

even dvitinctioii in the intellectual world; and though idiots
have been known to poasesB brains abnormally heavy, it is

Fia. aw.

Fio. 840.— Ooter surface of brain of hone (after SoUr and Lenret). «, olftifitorjr lobe;

A, bippocampal lobe (procewoa jpyrifonnis); i.i,t, lobe* of cerebellnm; o, optic

nerve: m, motor ocnll: p, fonrtn nerve; t, fifth nerve; m, lixth nerve; /, facial;

(, anditorr; ff. gloaao-phar]mgeal; e, vagos; «, spinal accessory; n, hypoglossal;

X, pons varolir
Fio. aso.— Longitndiiial section throngh center of brain of hone, presenting view of

internal surface (after Solly and Lenret). e. e, corpns callosom; p, thalamiu; eo,

middle commissore; t.q, corpora qnadrigemina, in front of which is the pinsM

body. The cerebellnm nas been cat through.

nevertheless true that brain-weight and the higher powers of
man bear a close though not invariable relationship. The
apparent discrepancies are susceptible of explanation.

Besides the gray matter, with its uells of highest fohctional
value from the standpoint now taken, the brain consists, and
in large part, of neuroglia and nerve-fibers, wifli probably
chiefly, and in the case of the fibers solely, a conducting func-
tion.

'mm

though idiots
r heavy, it is

THE BRAIN.

491

The OoniMotioii of one Put of tlie Brain with another.—
Though it has long been known that the different parts of the

«, olftintorjr lobe;
Tebellnm; o, optic
I nerve; /, facial;
; n, hrpogloMal;

lireaeiiting view of
i; p, thaluniu; «pl
liieh is tlie pineal

her powers of
onship. The
ion.

est fuhctional

consists, and

ifli probably

ducting funo-

mmm

mim

Fia. 161.— lAteial riem of tke braint of a rabbit, a vig, and a eUmpancee, drawn of
nearly the Mune abaolnte eiae (Hnzley). The rabbit^a biain ia at the top; the pig'a.
in the middle; the chimpanaee'a, loweat Of. olfactoiy lobe; A, frontal lobe; B,
occipital lobe; C, temporal lobe; Sn, the aylvianSMun; /w, the inanla: a. Or,
•npra-orbital; S. f, H. F, 1. 1", inperior, middle, and inferior frontal nrrl; A. P,
antero-parietal; P. J^ poatero-parietal gjrri; S, aniens of Rolando; P. Ft, poatero-
parletal lobnle; 0, If, eztemal perpendicalar or oeeipito-tempoial aniens: An.
uumlmt gynui % *.«• annectent an; A. T, M. T, P. T, the three tempotal, and
aV Jfroe, /. Off, the three oecipBal gyrl.

492

COMPARATIVE PHYSIOLOGY.

brain were connected by bridges of fibers {commisgures, etc.),
the physiological significance of the fact seems to have been
largely ignored, and even at the present day is too little con-

Pie. 8S8.— Inner views of cerabcal hemisptaerM of the nbblt, pig, md ohlmpuaee,
dnwn u l>ef ore, and placed in tbe Mnne order (Hnxley I. 0^ otttetorjrlobei O.e,
coipne calloanm ; A. e, anterior eommlMWe; H, hlppocampal aiueiu; Vh, imel-
nate; JT, nuu|^nal; OctfloMl gjrri; I.P, intmMl perpendlcnlar; Oa, cakailiie;

Cbtf,'coli«teiu anlci; >, fornix.

Bidered. 1. Certbral flben pass between the convolutions of
this part of the brain and the oerebellnm; between the former

i \

MROa

miamtres, etc.),
I to have been
too little con-

i \.

nlar; Oa, caleailiM;

Kmvolutioiu of
een the former

MROa

494

COMPARATIVE PHYSIOLOGY.

Fio. 8M.— Diacrammatle horiWHital teetton of a vertobnte brtin (HnzleyV The f qllo«r-
Ins lettenMrvefw both tUallgare and the one foHowtng. JTft, mfd-bnin. What
Itea in front of thli ii the foie^iraln, and what Ilea behind, the hind-biain. X. (.
the lamina tennlnalla; W, olfactorr lobea; Onp, hemiiidieres; 7%. ^. thria-
mencephalon; Ai. pineal tfand; /V, pltoitatT body; jrjr,fommen ofMnnro; Ca,
corpna itriatnm: ''
brh Cb, cerebelin

opUcl; /ZI'. point o. «.....'.«_>.— -. ~. <--v^ -.. ^

of abdacenA; V-XII. origins of the other cerebral nerrea. 1, olfactorr Ten-
tride; S, lateral ▼entrlele; 8, third ventricle; 4. fourth Tentricle; ■•■. iUr a terOo
ad quamtm vtrUrtetOum.

and the main baaal ganglia; between the gray matter of the
oonvolutiona on the same nde, and between the latter and those

Fis. IBS.— A longitodinal and vertical nctlon of a vertebrate brain (Hozlev). Lrttere
aa above. Ae kmUrnt ttrmt$t4in$ la represented by the strong black Ime between
/VandS.

ey). The follow^
ifdi-bniii. Wlukt
liind-bmiii. L. t,
as; 7%. ;e',.Uialk-
m of Mnnro; CS,
,; CC, cnm ceie-
/.oltectoril; /A
of pathetici; F/.
1, olfactoi7 ven-
; +, Utr a UtHo

natter of the
ter and those

TrTir

Haxlev). Lrtters
ilack Ime between

TRB BRAIN.

496

on the oppomte halves: between the gnj matter of the cortex
and the internal oapmile, the corpora striata, optic thalami, pons
Varolii, the medulta oblongata, and so to the spinal cord. The
course of the latter t«cts of fibers have been, especially by the
help of pathology, definitely foUowed. Some of these connec-
tions are given in more detail below. . , ,, »
1. Cenibro-eereMlar ftben. (a.) From the cortical ceUs of
the anterior cerebral lobe to the pons Vaiolii, passmg through
the internal capsule and thence through the lower and outer
part of the orus cerebri (ortiirfa). (6.) Fibers from the occipital
and tempo«Mq»henoidal lobes, passing by the orusta, reach the
upper surface of the cMebellum. /^ ^ t»„
. T Fibem bridging the two Me$ of the eerOrum. (a.) By
means of the corpus oalloeum chiefly, pa«ing from the gny
matter in the first instance. (6.) From the tempoKxphenoidal
lobe on each side through the corpora striata and anterior com-
missure, (c.) Fibers from the upper part of the cruscerebn
(teamentHm) to the optic thalamus of each side and onward
tothe tempoiwiphenoidal lobes, forming the posterior com-

misBure. , ^.

8. Fiben connecting different parta of the eerOmaeonvoM-

tiona on the same tide. Theee are exceedingly numaroas and
belong to such tracte as tho " arcuate dbers," pesshig ftfwn one
gyrus to another; "collateral fibers," forming distant convo-
lutions; fibers of the fornix between the uncinate gyrus, hip-
pocampus major, and optic thalamus; longitudinal fibers of the
corpus callosum; fibers of the tsenia semicufcularis, uncinate

fasciculus, ete. , .

4. Fiben forming the oereftruw and the epiwa eord. Ac-
cording as they pass downward or upward do they converge or
diverge, and the most important seem to pass through the m-
temal capsule; and whUe the majority do perhaps form some
connection either with the corpora striata and optic th^i,
some seem to pass direcUy downward through the intem^<»p-
sule. It is held by many that the fibers passing through tte
posterior portion of the internal capmUe are derived from the
posterior lobe of the cerebrum, and are the paths of sensory un-
p^ upward; while the rest of the internal oapnile ismade
vm of fibers from the anterior, and especially the middle portion
of the cerebral cortex (motor ana), and theee fibers are the
paths of motor (eflteent) impulses.
' It now becomes dearer that the bwin is constituted a whole

496

COMPARATIVE PHYSIOLOGY.

by such connections; and that, apart fix,m ttie multiplicity of
cells with different functions to perforin, situated in different

9ia im.-I)ii«aTMnmatlc wprewntotUm of the conne of mum of Um «bew in tlw o«f«-
brnm ofiSn (»f ter Le Bon).

aMMM, the complexity and at the sanM time the unity of the
encephalbn becomes increasingly evident, imaiely upon aaaatomi-
Cid irrounds ; but we shaU find such a view still furtherslWengtt-
ened by study of the functions of the various parts. While toe
tracts enumerated are anatomical and have been clearly traoei^
there can be Uttle doubt that many ottiers yet rwriain to be
marked out; and that, apart from such collections of abers^ we
must recognise functional paths by the neuroglia, and possibly
others stUl. It is not to be forgotten that in the brain, win the
apinal cord, nerve-oells are themselves conductors, and while

THE BRAIN.

497

ultiplioity of
in Aiflereut

there may be certain aie»s within which the w»i«tance » such
that impulses are usuaUy confined to them, it is also true that,
as in the cord, thew may be a kind of overflow. Adjacent cells,
possibly widely separated cells, may become involved. We shall
return to this important subject again, however, as, without
recognising such reUtionships, it seems to us quite impossible
to understand the facts as we Bnd them in the working of the
body and the mind.

iMflbenintlwetn-

le unity of the
-uponanstomi-
irtherstrength-
rts. While the
L clearly traced,
t remaia to be
tns of fibers,- we
ia, and jmssibly
brain, as in the
itors.ani'i while

The eotlml (torttt— We may now proceed to inquire what
are the functions of the cells of the gray matter covering the
surface of the censbrum. Before the Wrth of physiology as a

B«»ri6s«;:

^.■ai Ma« i M# i<» iiiii i ii « MW ii« ii v;^^

498

COMPARATIVE PHYSIOLOGY.

■cienoe,Oall raoogniwd and Uuir^t that the enoephalon is a col-
lection of organs; that these have separate functions; that the
rolative liie of each determines the degree of its functional ac-
tivity; and that the cranium developing in proportion to the
growth of the brain, the former might give information as to
the probable sixe of what lay beneath it in different regions.
It will be seen that, as thus interpreted, phrenology is a very
differant thing from what usually passes under that name, and
is paraded before wondering audiences by ignorant charlatans.
In the main the doctrines of OaU are not without a certain
foundation in facto; and the modem theory of localization of
function bean some leeemblanoe to what GaU taught, though
with greater UmiUtions.

VSmotor area in BMn Md the monkey— 1. e., the aiea which moet ohjervere oe-
ItovrtoS aSoctated with certain Tolnntary mwremwitt of the limb., rtc.

In the mean time it has been found that in many oases it
was possible to locate the site of a brain-lesion (tumor, etc.) by
the symptoms, chiefly motor, of the patient; and brain-surgery

tlon isaool*
i«; that the
ictional ao-
rtion to the
lation as to
mt regions,
y is a very
name, and
charlatans,
it a oertain
salization of
ght, though

ovtioD npKMntft
MMt oltwrven be-
imbs, 4ftc.

aany oases it
mor, etc.) by
)rain-surgery

THE BRAIN.

499

has in consequence entered upon a new era of deTelopment
Tumors thus localised have been removed successfully, and the
patients restored to health. As a result of the Tarioua kinds of
obsenrations and discussions on this subject of late years, the
looalicationists are willing to admit that the areas of the cortex
can not be marked off mathematically— that, in fact, th«y
"overlap." This is in itself an important concession. Again,
there is less confidence in the location of the various seiuory
centers than of the motor centers. Most inveat^tors are be-
lievers in a ** motor area " par exctUenee (for the arm, leg, etc.)
around the fissure of Rolando (Fig. 868). This view is now, so
fkr as man is concerned, widely aoo^ted.

There is agreement in placing the sensory centers behind
the above-mentioned motor area, and especially in the occipital
lobes. The tendency to locate a visual center in this region is
growing stronger. There is much disagreement as to the other
sensory centers formerly placed in the angular gyms and tem-
poro-sphenoidal lobes. The intellectual faculties have not been
located in any such sense as Gkdl and his followers attempted
to establish. The first two frontal convolutions are those, per-
haps, to which localisation has as yet been least applied.
Chiefly on clinical and pathological grounds a center for
speech has long been located in the third (left) frontal convolu-
tion (Braca's) and parts immediately behind it It has been ob-
served that when disease attacks this area speech is interfered
writh in some way.

We may say then, generally, taat the tendency at the pres-
ent time, both on the part of physiologists and clinical ob-
servers, is to admit localisation to some degree and in some
sense. This has been the result in part of experiments on the
dog and especially on the monkey, combined with the discus-
sion of clinical cases which resulted in death (followed by an
autupsy), or of others marked by a successful diagnoids and re-
moval of lesions or other treatment In other words, the truth,
if it is to be reached at all, must be sought by the plan we
have advocated throughout this work— the discussion of the re-
sults of as many different methods as can be Inrought to bearon
this or any other subject Neither the experimental nor the
pathological method alone can settle such complex questions.
Although localization of function uas not be6n established tor
the cerebral cortex in theoase of those animals with which the
practitioner of veter inary medicine has to deal as it has for man

600

COMPAHATIVB PHYSIOLOOY.

and the monkey, we have thought it well to bring the mbjeot
before the atudent of oompamtiTe medicine, since it can not be
doubted that future research will put the physiology of the
brains of the domesticated animals in a new light, in doing which
guidance will naturally be sought from what has been already
done, more especially in the case of the human subject mai his
nearest allies. Some would maintain that in the case of the
dog, motor and sensory localisation baa been estabHshed; that
in this animal there is a motor area in the region of the crucial
sulcus corresponding to that around the fissure of Rolando in
man. The subject is, however, far from finally settled even in
the case of the dog, the brain of which has been more thoroughly
investigated than that of any other of our domestic animals.
Very little can as yet be said in regard to cortical localisation
in the horse, ox, etc. It seems highly probable that investiga-
tion will show that cortical localisation in the primates (man
and the monkey tribe) exists in a far higher degree than in
any other animals.

TIm CHieolation in tht Bnia.— The brain, being inclosed
Mrithin an air-tight bony case, its circulation is of necessity
peculiar. Since any undue compression of the encephalon may
lead to even a fatal stupor, it is clear that there must exist some
provision to permit of the excess of arterial blood that is re-
quired for uniURial activity of the brain. It is to be borne in
mind that the fluid within the ventricles is continuous, through
the foramen of Magendie in the roof of the fourth ventricle,
with that surrounding the spinal cord (spinal cavity) ; so that
an increase in the volume of the encephalon in consequence of
an afflux of blood might be in some degree compensated by an
efflux of the oerebro-spinal fluid. The part played by this ar-
rangement has, however, been probably overestimated. But
the peculiar venous sinuses do, it is likely, serve to regulate the
blood-supply; being very large, they may answer as temporary
overflow receptacles. An inspection of the fontanelles of an
infant reveals a beating corresponding with the pulse; and,
when a large part' of the cranium is removed in an animal, a
plethysmograph shows a rise in volume corresponding with
the pulse and the respiratory movements, as in the osse of the
fontanelles. But, beeidee these, periodic waves of contraction
are now known to pass over the cerebral arteries.

Whether the latter is part of a general vrave traversing the
whole arterial system is as yet uncertain. Though there is

themibjeot

can not be

logy of the

ting which

in already

It ani hie

caae of the

inahed; that

the crucial

Rolando in

ied even in

thoroughly

itic animals.

localiiation

lat inveatiga-

inwtflB (man

than in

ing incloaed
of neoeesity
ephalon may
ist exist some
)d that is re-
o be borne in
nous, through
irth ventricle,
dty); so that
insequenoe of
enaated by an
ed by this ar-
timated. But
> regulate the
as temporary
kanelles of an
e pulse; and,
an animal, a
ponding with
he oue of the
if contraction

raversing the
}ugh there is

t "■ ■ M" '>ff'

THE BRAIN.

501

considerable anastomosis of vessels in the enoephalon, it is not
equal to what takes place in many other organs. It is well
known that a clot or other plug within a cerebral vessel is more
serious than in many other regions, which is partly to be ex-
plained by the lack of sufficient anastomosis for the vascular
needs of the parts. It is also well known that, in organs which
constitute parts of a related series, as the different divisions of
the alimentary tract, all are not usually at the same tiro«> vas-
cular to the same extent. While they act functionally iu r«la-
tion to each other, they exemplify also a certain degr<v of indu*
pendence. Such a condition of things is now known to exist in
the brain— i. e., certa^ areas may be abundantly supplied with
blood as compared with others: and it seems highly probable
that a condition of equal arterial tension throughout is scarcely
a normal condition. Though the quantity of Uood contained
within the vessels of the whole brain at any one time is not so
large as in some other organs (glands), yet the foregoing facts
and the rapidity of the flow must be taken into account. The
capillaries are very close and abundant, in the gray matter es-
pecially; and it is to be borne in mind that it is chiefly these
vessels which are concerned in the actual metabolism (nutri-
tion) of partri. However, the chemical changes in the nervous
system being feeble, it would appear probable that it does its
work with less consumption of pabulum than other parts of
the body. We wish to lay stress on the local nature of vascular
dilatation in the brain, as it greatly assists in explaining certain
phenomma about to be considered.

SUcpii— Observations upon animals from which portions of
the cranium have been removed, so that the brain was visible,
show that during sleep the blood-vessels are much leas promi-
nent than usual ; and it is well known that means calculated to
diminish the circulation in the brain, as cold and pressure, favor
sleep. It ia also well established by general experience that
withdrawal of the usual afferent impulses through the various
senses favors sleep. A remarkable case is on record of a youth
whose avenues for aenaory impreasions were limited to one eye
and a single ear, and who could be sent to sleep by dosing
these against the outer world. Tet this subject after a long
sleep would awake of his own accord, showing that, while affer-
ent impulses have undoubtedly much to do with maintaining
the activity of the cerebral centers, yet their automaticity (in^
dependence) must also be recognized.

ut&jHAi rt* #<w.th i ^iwj ' i .t,M <iwity

5()S

COMPARATIVE PHY8I0L0UY.

It ia A nuittMr of oonunon experienoe that wtiurintm, or the
exhaiution following on pain, mental anxiety, etc., is farorable
to aleep.

A good deal of light ie thrown on this lubjeot by hiberna-
tion, partioularljr in niantmals.

From epedal study of the nibjeot we hare ounelvee learned
that, however temperattue, and certain other conditione may
influence this itata, it will appear at definite periods in defiance,
to a large extent, frf the ooodilions prerailing. Hibernation,
we are convinced, is marked by a general slowing of all of the
vital proceaMB in which the nervous system takes a prominent
part. Sleep and hibernation are closely related. In both there
is a diminution of the rate of the vital pr ocess e s, as shown by
the income and output, measured by chemical standards, with
of course obvious physical sign% as slowed respiration, circula-
tion, etc. While sleepy then, is primarily the result of a rhyth-
mical retardation of the vital processes, especially within the
nervous system, it is like hibernation in some degree (in the
lowest creatures, without a nerve system) the outcome of that
rhythm impress e d on every cell of the organism and the influ-
ence of wUoh is felt in a thousand wmyn, that no doubt we are
quite unable to recognise.

HypaotiML— By the help of the above principles the sub-
ject of hypnotism, now of absorbing interest, may be in great
part explained. This condition is characterised by loss of vo-
lition and judgment It may be induced in man and certain
other animals by prolonged staring at a bright object, assisted
by A concentration of the attention on that aknu^ as far as pos-
sible, combined with a condition of mental pasrivity in other
respects. The individual graduaUy becomes drowqr, and flnally
falls into a state in many respects strongly resembling sleep.

Hypnotism proper may be combined with ocrfa Jepsy, a con-
dition in which the limbs remain rigid in whatever condition
they may be placed. Modifications of the vascular and respira-
tory systems occur. Various animals have been hypnotised, as
the fowl, rabbit, Chiinea-pig, crayfish, frog, etc. This condi-
tion is readily induced in the common fowl, more especially
the wilder individuals, l^ holding the oreaturo with the bill
down on a table and the whole animal perfectly quiet for a
short time. Upon the removal of the pressure the bird re-
mains perfectly passive and apparently asleep for some little
time.

rincMhortlM
, is farorabto

I by hibemo'

elvM learned
aditiont majr
\» in dflflanoe,
Hibematioii,
of All of the
a prominent
In both there
aa shown by
indardt, with
ition, oiroula-
ilt of a rhyth-
ly within the
iegree (in the
»ome of that
and the influ-
doubt we ara

iplea the nib-
ky be in great
by Ion of to-
ui and certain
>bject, aaaiated
^ aa f ar aa poa-
ivity in other
qr, and finally
ilincr ileep.
talepty, a con-
iver condition
IT and reapira-
hypnotiaed, aa
. This oondi-
lore eapecially
with the bill
iy quiet for a
i the bird re-
For some little

TUK BHAIN.

508

Via aM -UtwiU iorf •«!• or bnta of menkwr, dUvteytng motor hms rtftw HowJey
md ScMfw).

Fio. m-MediM •arf.ee of bnUn of monkey («fter Honley •««» Schlfer).
rtee. SM aiMl m mv be lald to embody the view, of Honley and Schlfer more eipe-
cUUly In regard to motor loMllMtion.

"■ii ^ 1^ ;***/■ ■:-P**t<''

'■.XS,!''!"'"*''''*''''^"^'**'

504

COMPARATIVE PHYSIOLOGY.

FUNCTIONS OF OTBBR PORTIONS OF TBB BRAIN.

Certain parts of the encephalon are spoken of as the basal
ganglia, prominent among which are the corpus striatum and
the optic thalamus.

The Oorpoi Striatum and fhe Optio Thalamiu.— The corpus
striatum consists of several parts, the mam divisions being an
intra-ventricular portion or caudate nucleus, and an extra-ven-
tricular part or lenticular nucleus.

Fis. aBl.-TramverM MCtkm of ombnl hemispheiM of man M level of cerebral wn-
Rita (after Dalton). 1, great longitadinal Itararc; 8, part of aame between occipital
fobet; 8, anterior part of co^ calloanm; 4, flwure of 8ylvlu«i 5. conYOUtlons
of iSand "Bell (tniila); «, canSata nncleua of corpua atriatam; 7, lenUcntar nu-
clensS corpna aWatum; 8, optic thalamna; 9, Internal capanle; 10, external cap
aale; 11, Clanatmni.

3 BRAIN.

the basal
Iriatum and

•The corpus
IS being an
extra-ven-

"mm

\ of cerebral gan-
letween occipital
; 5, coDTolntlons
7, lenticnlar nu-
10, external cap-

THE BRAIN.

BOB

Between these lies the internal capsule, through which
pasH fibers that spread out toward the cortex, as the wrona
ntdiata.

Pathology, especially, has shown that a lesion of the intra-
ventricular portion of the corpus striatum, and, above all, of
the internal capsule, is foUowed by failure of voluntary move-
ment (akinesia). It would appear that a great part of the
fibers from the motor area around the fissure of Rolando, pass
through the intra-ventrioular parts of the corpus striatum, and
especially its internal capsule. But it is also to be borne in
mind that a large part of the fibers passing from the cortex
make connection with the cells of the corpus striatum before
reaching the cord. These facts render the occurrence of loss of
voluntary motor power comprehensible. '

The fibers of the peduncles of the brain may be divided into
an interior or lower division (ertuta), going mostly to the

Fio. 88*.— TnuMvene Mction of hninan bnia (after Dalton). Thia and thepNoeding
Sgnre are aomewliat diaaraminatie. 1, pmia Varolii; 8,8, cmra cerelirf; 8,8, in-
ternal capanle; 4, 4, corona radiata; 6, optic thaiamns; «, lenticular nucieaa; 7,
corpna calloaam. "

corpus striatum, and a posterior division {tegmentum), passing
principally to the optic thalami ; many, possibly most of them,
ultimately reach the cortex. Many clinical observers do not
hesitate to speak of the optic thalamus as sensory in function.

606

COMPARATIVE PHYSIOLOGY.

and the corpus striatum as motor; but the clinical and patho-
logical evidence is conflicting — all lesions of these parts not
being followed by loss of sensation and motion respectiyely;
though an injury to the internal capsule generally results in
paralysis. All are agreed that the symptoms are manifested on
the side of the body opposite to the side of the lesion, so that a
decussation must take place somewhere between the ganglion
and the periphery of the body.

There is no doubt that the optic thalamus, especially its
posterior part, is concerned with vision, for injury to it is fol-
lowed by a greater or less degree of disturbance of this func-
tion. As has been already pointed out, unilateral injury of
either of these ganglia leads to inco-ordination or to forced
movements. That these regions act some intermediate part in
the transmission of impulses to and from the 1n«in cortex, and
that the anterior one is concerned with motor, and the pos-
terior possibly with sensory (tactile, etc.), and certainly with
visual impulses, may be stated with some confidence, tiiough
further details are not yet a subject of general agreement

Corpora Qwidxigailillft. — ^The function of these parts in vis-
ion, as in the co-ordination of the movements of the ocular
muscles, and their relations to the movements of the pupil, will
be considered later. However, the actual centers for these func-
tions seem to lie in the anterior portion of the floor of the
aqueduct of Sylvius, and are indirectly affected by stimulation
of the corpora quadrigemina. Extirpation of these parts on
one side produces blindness of the opposite eye, and in birds,
etc., the same result follows when their homologues— the optic
lobes— are similarily treated. There can be no doubt, therefore,
that they are a part of the central nervous machinery of vision,
and it seems to be probable that the anterior parts of the cor-
pora quadrigemina alone have this visual function. But, since
it is Uie opposite eye that is affected, and in some animals
(rabbits) that alone, «ne are led to infer a decussation of the
optic fibers, or at least of impulses. In dogs, on the other hand,
the crossing seems to be but partial

It begins to appear that there are several parts of the brain
concerned with vision. After removal of almost any' part of
the cerebral cortex, if of sufficient extent, vision is impaired.
We may si^, then, that before an object is " seen " in the high-
est sense, processes beginning in the retina undergo further
elaboration in the corpora quadrigemina, optic thalami, and.

Vita

and patho-
le parts not
■espectively;
ly results in
anifestedon
on, so that a
le ganglion

specially its

to it is fol-

of this f unc-

il injury of

or to forced

diate part in

I cortex, and

md the pos-

rtainly with

mce, iliough

eement

parts in vis-

•f the ocular

le pupil, will

>r these func-

floor of the

r stimulation

lese parts on

ind in birds,

ee— the optic

bt, therefore,

)ry of vision,

ts of the cor-

. But, since

»me animals

ation of the

) other hand,

of the brain
any part of
is impaired,
in the high-
argo further
luJami, and.

THE BRAIN..

607

finally in the cerebral cortex. We may safely assume that the
part played by the latter is of very great importance, making
the perception assume that highest completeness which is of

Via.

,— DtaannuBatie npNMotetim of bnin on tw m w w w e tlon to Ulmtnte
conne oflben (after Undoto). C, C, cortex cerebri; Cj, coipiu ■trlatum; IT. I,
lenttcnlar noeleu; T.o, optic thalamne; P. pedancle; B. tMuantaiii; «, emeta;

, -_„-,-, , ^, -—- »t«|Biiento .

m, fnrtlier oonne of theie flbere; 8, 8, flbere from corpu ■Mstom and untteatar
nacleaa to craata ofpedaiicte of oeiebmni: if, farther ooone of theae; 8, 8, eooiae
of aeniorr flbera; B, taamrtne MttUm <A epbial cord; e. IT, aatwior, and A. ?r,
poaterior mote; a, a, lyatem of aaaoeiation Sbeia; o, «, commiaaoral floera.

m^liiit0

508

COMPABATIVE PHYSIOLOGY.

▼ery varying character, no doubt, with different groups of ani-
mals. In a Mnse, all mammals may see alike, and, in another
sense, they may see things very differently ; for, if we may judge
by the differences in this respect between educated and unedu-
cated men, the great dissimilarity lies in the interpretation of
what is seen ; in a word, the cortex has to do with the perfect-
ing of visual impulses. Nevertheless, a break anywhere in the
long and complicated chain of processes must lead to some
serious impairment of vision. Much of the same sort of reason-
ing applies to the other senses and also to speech.

To speak, therefore, of a visutd center or a speech center in
any very restricted sense is unjustifiable; at the same time, it
is becoming clearer that there is in the occipital lobe, rather
than in other parts of the cortex, an area which takes a pecul-
iar and special share in elaborating visual impulses into visual
sensations and perceptions ; and there can be little doubt
that the other senses are represented similiarly in the cerebral
cortex.

Th« Cerebelluin.— Both physiological and pathological re-
search point to the conclusion that the cerebellum has an im-
portant share in the co-ordination of muscular movements.
Ablation of parts of the organ leads to disordered movements ;
and, when the whole is removed in the bird, co-ordination is
all but impossible, and the same holds for mammals. Section
of the middle peduncle of one side is liable to give rise to roll-
ing forced movements. In fact, injury to the cerebellum causes
symptoms very similar to those following section of the semi-
circular canals, so that many have thought that in the latter
case the cerebellum had itself been injured.

PathologioaL— Tumors and other lesions frequently, though
not invariably, give rise to unsteadiness of gait, much like that
affecting an intoxicated person. It may safely be said that the
cerebellum takes a very prominent share in the work of the
muscular co-ordination of the body.

As has already been pointed out, several tracts of the spinal
cord make connection with the cerebellum, and it is not to be
forgotten that this part of the brain has, in general, most ex-
tensive connections with other regions. Insufficient study has
as yet been given to the cerebellum, and it is likely that the
part it takes in the functions of the enoephalon is greater than
has yet been rendered clear. The old notion that this organ
bears any direct relation to the sexual functions seems to be

9upB of ani-

in another

) may judge

and unedu-

pretation of

»perfeot-

rhere in the

id to some

; of reason-

:h center in
ame time, it

lohe, rather
Jces a pecul-

into visual
littlft doubt
the cerebral

lological .e-
a has an im-

movements,
movements ;
>rdination is
als. Section
I rise to roU-
ellum causes
of the semi-
in the latter

ntly, though
ich like that
said that the
work of the

>f the spinal
is not to be
ral, most ex-
it study has
elythat the
i^eaterthan
t this organ
seems to be

THE BRAIN.

009

without foundation. It has now been clearly demonstrated
that the lower region of the spinal cord is, in the dog and prob-
ably most mammals, the part of the nerve-centers essential for
the sexual processes.

Grant Cntlnri and Pons YuroUL— As has been already noted,
the peduncles (crura) are the paths of impulses from certain
parts of the cerebral cortex, the basal ganglia, and the spinal
cord. The functions of the gray matter of the crura are un-
known. But, since forced movements ensue on unilateral sec-
tion, it is plain that they also have to do with muscular co-
ordination.

The transverse fibers of the pons Farolt'i connect the two
halves of the cerebellum. Its longitudinal fibers have extensive
connections — the anterior pyramids and olivary bodies of the
meduUa, the lateral, and perhaps also a part of the posterior
columns of the cord, while upward these fibers connect with
the crura cerebri and so with the cortex.

PakhologiotL— Paraljrsis of the face usually occurs on the
same side as that of the rest of the body ; hence it must be
inferred that there is a decussation sohiewhere of the fibers of
the facial nerve ; but there is much still to be learned about
this subject.

Medulla OUongata,— In some animals (hogs) it is certainly
known that this r^on of the brain has a co-ordinating func-
tion, and it iti probable that it is concerned with such uses in
all animals that possess the organ, or rather collection of organs,
seeing that thk part of the brain must be regarded as especially
a mass of centers, the functions of which have been already
considered at length. So long as the medulla is intact, life may
continue ; but, except imder special circumstances, which do
not invalidate this general statement, its destruction is followed
by the death of the animal.

We may simply enumerate the centers that are usually
located in the medulla : The respiratory (and convulsive), car-
dio^nhiUtory, vaso-motor, center for deglutition, center for
the movements of the gullet, stomach, etc., and the vomiting
center ; center for the secretion of saliva and possibly other of
the digestive fluids. Some add a diabetic and other centers.

610

COMPARATIVE PHYSIOLOGY.

SPBOIAIi OOmmBRATIONS.

XmlnTOlogiML— The foiiher we progreM in the study of the
nenroua system, the greater the signifloanoe of the facta of its

Fie. IM.— Vertical longltndlv ' "iii n> of bnin of hmnan •mbryo of foartceii week*.
1 » 8. (iUter Sharpey and "■' d«rt.) e, eerabnUhemtaphere; e«,corpo«ealloaniii
beoinnliut to paa* back; /, lot^men of Mnnro; p, memnrane OT«r tblrd ventricle
and theMnealbody; (A, tbalamua; 8, third ventriole; I, olfactorrbalb; «?, oorpora
qnadrigemlna; er, cmra cerebri, and above them, aqnednct of Sjlvtoa, atiil wide;
e, cerabeliom, and below it the fourth ventricle; jw, pona VarolU; m, nednlla
oblongata.

early development becomes. It will be remembered that from
that uppermost epiblastio layer of cells, so early marked off in

Vitt.ass.

Fis. 885.— Ooter anrface of haman fcetal brain at alx month*, ahowing origin of prin-
cipal flienrea (after Sbarpey and R. Wagner), r, frontal lobe; P, parietal; O.
occipital; T, tempoml; a, a, a, faint appearance of aeveral frontal oonvolntiona;
#, ». Sylvan llHare: «', anterior division of aame: C, central lobe of ialand of Bell ;
r, flianie of Rolando; />, external jieipendtcnlar StMire.

Fio. 888.— Uppor anrface of brain rqweaented In Fig. 884 (after Bbarpey an4 R. Wag-
ner).

the blastoderm, is formed the entire nervous sjrstem, including
centers, nerves, and end organs. The brain maybe regarded
as a specially differentiated part of the anterior region of the

itudy of the
facts of its

roiutMnwwlM.
Borpnaeallotnm
' tblnl ventricle
nib: eq, eorpom
Tlaa, Tun wide;
dU; m, niednlU

d that from
irked off in

m otigia of prin-

If iilaadof Bell;
pey Mi4 B. Wag-

in, including
be regarded
Bgion of the

pJi>JiM l illlil> i|> « > ll

THE BRAIN.

611

medullary groove and iti subdivisions ; and the dose relation
of the eye, ear, etc., to the brain in their early ongin, is not
without special meaning, whUe the more diffused sensory de-
velopments in the skin connect the higher anunalsdosely w th
the lower-even the lowest, in which sensaUon isalmost whoUy
referable to the surface of the body. , ,j , , .

Without some knowledge of the mode of development of
the encephalon, it is scarcely possible to appreciate that n«ng
ffrade of complexity met with as we pass from lower to higher
L>up8 of anima^ especially noticeable in vertebrates ; nor is
it possible to recognise fully the evidence found in ^ nervous
aystmi for the doctrine that higher are derived from lower
forms by a process of evolution.

Ifoliition.— The same law applies to the nervous system as
to other parts of the organism, vis., that the individual devel-
opment (ontogeny) is a synoptical representation, m a general
way, of the development of the group (phylogeny). A com-
parison of the development of even man's brain reveals the fact
tha^ its earliest stage, it is scarcely, if at dl^durtinguishable
from that of any of the lower vertebmte^ ^T^«".» • P^°J
when even this, the most convoluted of all brains, u as smooth
and devoid of gyn as the brain of a frog. The extreme com-

ntei nlBO UlMtrate the lemuk made after thoee louowing.

piexity of the human brain is referable to excessive growth of
certain parts, crowding and alteration of shape, owmg to the
influence of ita bony case, ite membranes, etc.

613

COMPARATIVE PHYSIOLOGY.

It is evident, from an inspection of the cranial cavities of
those enormous fossil forms that preceded the higher verte-
brates, that their brains, in proportion to their bodies, were
very small, so that any variation in the direction of increase
in the encephalon— especially the cerebrum— must have given
the creuturea, the subject of such variation, a decided advan-
tage in the struggle for existence, and one which may partly
account, perhapn, for the extinction of those animals of vast
proportions but limited intelligence. That the siie of the brain

Fi«. 888.— A, bnin of • chelonlm; B, of • fotal calf: C, of a cat. (All after Oegm-
baur.) /, indicatea cerebral bemlipberea ; //, tbalamoa ; ///, corpora qnadri-
— ^ .. — _-^^^.... — . . .. — "xi *. hlppocam-

wlllbeobMnred

) developed brain In

a lower form, and (>) bow certain part* become crowded togetber and covered

over by more prominent re((lona, e. g., the oerebnun, aa we aacend the animal aeale.

baur.) /, inaicatea cereorai nemiipnerea ; //, inaiamiu ; iii, corpoi
gemina; IV, cerebellnm; F. medulla; «f, corpus etriatnm: /, fornix: A. I
ptie; «r, fonrth ventricle: g, aenfenlate body: et, olfactory lobe. It will b«
(I) how the ftetal brain in a nigher anhnal form leeemblee the develops

as well as its quality can be increased by use, seems to have
been established by the measurements, at different periods of
development, of the hi...ds of those engaged in intellectual pur-
suits, and comparing the results with those obtained by similar
measurement of the heads of those not thus specially employed.
Of course, it must be assumed that the head measurement is a
gauge of the site of the brain, which is approximately true, if
not entirely so.

Recent investigations seem to show that the development
of the ganglion cells of the brain takes place first in the me-
dulla, next in the cerebellum, after that in the mid-brain, and
finally in the cerebral cortex. Animals most helpless at birth
are those with the least development of such cells. The me-

^^L

oavitiM of

liigher verte-

mmUm, were

of inoreaae

have given

Bided advan-

^y partly

i\» of vast

I of the brain

(All after Oegen-
r, eorpara qnadrl-
viz: h, hippocMn-
It will be obeerved
leveloped brain In
ither and covered
1 the animal acale.

Benw to have
at periods of
ellectual par-
ed by similar
ily employed,
urement is a
lately true, if

development
tt in the me-
id-brain, and
tieas at birth
Is. The me-

mmftaimr *-**^^ —

THE DRAIN.

518

dulla may be regarded in some sense as the oldest (phylogenoti-
oally) part of the brain. In it '>,re lodged those cells (centers)
which are required for the maintenance of the functions essen-
tial to somatic life. This may serve to explain how it is that
so nany centers are there crowded together. It is remarkable
that so small a part of the brain should preside over many im-
portant functions ; but the principle of concentration with pro-
gressive development, and the law of habit making automatism
prominent, throw some light upon these facts, and especially
the one otherwise not easy to understand, that so much impor-
tant work should be done by relatively so few cells. Possibly,
however, if localization is established as fully as it may eventu-
ally be, this also will not bo sc astonishing.

The law of habit has, in connection with our psychic life
and that of other mammals, some of its most striking develop-
ments. This has long been recognised, though that the same
law is of universal application to the functions of the body has
as yet received but the scantiest acknowledgment.

We shall not dwell upon the subject beyond stating that in
our opinion the psychic life of animals can be but indifferently
understood unless this great factor is taken into the account ;
and when it is, much that is apparently quite inexplicable be-
comes plain. That anything that has happened once any-
where in the vital economy is liable to repetition under a

Fi«. SN.

Flo. aro.

Flo. am.— Brain of eat, eeen fram abore (after Ttedemann).
Flo. 870.— Brain of dog, aeen fiom above (after Tledemann).

slighter stimulus, is a law of the utmost importance in physiol-
ogy, psychology, and pathology. The practical importance of
this, especially to the young anhnal, is of the highest kind.
SjnoptioaL— There is as yet no ^ystematiied clear physiology
83

.']

K(*««^->«-M^teW--

S14

COMPARATIVE PHT8I0L00T.

of "thebndn.*' We wr* oonvenaiit with certain phenomena
referable to this organ in a number of animalH, chiefly the
higher mammali ; but our knowledge ia as yet inauflScient to
generalize, except in the broodeat way, regarding the functiona
of the brain — i.e., to determine what ia common to the broina of
all vertebrmtea and what ia peculiar to each group. Referring,
then, to the higher mammria, eapeoially to the dog, the cat, the
monkey, and man, we may make the following atatementa :

The medulla oblongata ia functionally the ruler of vegeta-
tive life — the lower functiona ; and ao may be regarded oa the
seat of a great number of ^ centers," or colleotiona of cella with
functiona to a large degree distinct, but like close neighbors,
with a mutual dependence.

Pl^logenetically (anceotrolly) the medulla ia a very ancient
region, hence the explanation apparently of ao many of its
functions being common to- the whole vertebrate group.

Ports of the mesencephalon, the pons Varolii, the optic lobes
or corpora quadrigemina, the crura cerebri, etc., are not only
connecting paths between the cord and cerebrum, but seem to
preside over the co-ordination of muscular movements, and to
take some share in the elaboration of visual and perhaps other
sensory impulses.

The cerebellum may have many functions unknown to us.
Its connections with other ports of the nerveH»uters ore numer-
ous, though their signiflconce ia in greot part unknown. Both
pothologicol ond physiologicol investigation point to its having
a large share in musoular co-ordination.

It is certain that the cerebrum is the part of the broin essen-
tial for all the higher psychic monifestotions in the most ad-
vanced mammals and in mon.

The preponderoting development of man's cerebrum ex-
plains at once his domination in the animal world, his power
over the inanimate forces of Nature, and his peculiar infirmities,
tendencies to a certain class of diseases, etc.,— in a word, man is
mon, lorgely by virtue of the size and peculiarities of this part
of his brain.

Modem research has made it cleor also that there ia a " pro-
jection " of sensory and motor phenomena in the cerebral cor-
tex ; in other words, that there ore sensory and motor centers
in the sense thot in the cortex there ore certain cells which hove
an importont shore in the initiation of mot6r impulses, ond
others employed in the final eloborotion of sensory ones.

\ phenomena
S chiefly the
laufflciemt to
^e functions
the braina of
I. Referring,
I, the cat, the
ktementa :
ier of vegeta-
garded em the
I of cells with
•e neighbors,

k very ancient
many of its
pnup.

he optic lobes
are not only
(1, but seem to
tments, and to
perhaps other

Jcnown to us.
ers are numer-
Iraown. Both
t to its having

le brahi eseen-
i the most ad-

oerebrum ex-
jrld, his power
liar infirmities,
ft word, man is
ties of this part

biere is a '' pro-
le cerebral cor-

motor centers
)11b which have

impulses, and
>ry ones.

THE BRAIN.

515

It is even yet premature to dogmatise in regard to the site
of these centers; esp* rially an v.. not ready for hirge generali-
lations. In man the convolutions around the fissure of RoUndo
constitute the motor area >" -at determined.

The whole subject of cortical localisation requires much ad-
ditional study, especially by the comparative method in tJie
widest sense-i. e., by a comparison of the results of operative
procedure in a variety of groups of animahs and the ««»W« o/
clinical, pathological, physiological, and psychological investi-
iration. Especially must allowance be made for differences to
be observed, both for the group and the individual ; and also
for the influence which one region exerts over another. Be-
tween the weight of the cerebrum, the extent of its cortical
surface, and psychic power, there is a general relationship.

GENERAL REMARKS ON THE SENSES.

OtJB Btudlw in embryology have taught u« that all the vari-
uua forms of end-organs are developed from the epiblait, and
so may be regarded as modified epithelial cells, with which are
associated a vascular and nervous supply. These end-organs
are at once protective to t.Me delicate nerves which terminate in

Via. m.-PapOto of lUn of palm of hand (after 8«pp«T) A va«!ular oflWfMrk in all
uwn, ani In MMM nerve* and lactUe conHWulan. enter the papilte.

them, and serve to convey to the latter peculiar impressious
which are widely different In most n stances from those result-
ing from the direct contact of the nerve with the foreign body
All are acquainted with the fact that, whan the epithelium is
removed, as by a blister, we no longer possess tactile sensibUity
of the usual kind, and experience pain on contact with objects;
in a word, the series of connections necessary to a sense-pereep-
tion is broken at the commencement.

Seeing that all i: <■ -ad-organs on the surface of the body
have a common ontl, luorphologioally, it would be reasonabk
to expect that the senses would have much ia eommon, espe-
cially when these organs are all alike connected with central
nervous cells I ; nerves. As a matter of fact, such is the case.

NSES.

fall thevari-
I epibUuit, and
ith which are

le end-organ*
, terminate in

lular iwtwotk in all

tr imprearious
a those reeuli-
foreign body
I epithelium ia
itUe mnsibility
t withobjeote;
k Mnae-per«ep-

oe of the body
i be reaaonabl*
aommon, espe-
i with oentrttl
«h is the case,

ORNERAL REMARKS ON THE 8EN8E8.

617

and In every instance we can dlirtinguish between woMory im-
pulaea generated in the end-organ, conveyed by a nerve inward,
and tho« in the oelU of the^ central nervoua ■ystemi, giving
Fine to certain molecular change*
which enable the mind or the
ego to have a perception proper;
which, when taken in connec-
tion with numerous past experi*
encea of this and other senses,
furnishes the material for a sen*
sory judgment.

The chief events are, after
all, internal, and hence it it

Fis. art.

FmSTS.

n..m--,^---^!rJ^,^^l^-

£i; i from coBjunoUv. of calt.U may be KotSs^" <*«'"•" »'»^ **^ *"*
iS^ IMM tta Don-eMentlal puts befoN entMrlng the corpiucle.

fount that Oie higher in the scale the animal ranks, the more de-
veloped its hervous oentew, especially its brain, and the more it
ai able to capitalise its sensory impulses; also the greater the de-
gttm of possible improvement by experience, a difference well
seen m blind men whose ability to succeed in life without vmon
is krgely in proportiou to their innate and acquired inental
powwik Inannuch as all cdls require reirt, one would expect

618

COMPARATIVE PHYSIOLOGY.

that under constant stimulation fatigue would soon result and
perceptions be imperfect Henoe it happens that all the senses

fail when exercised,
even for but a short
period, without changu
of stimulus leading to
alteration of condition
in the central cells.
The change need not
be one of entire rest,
but merely a new form
of exercise. Hence the
freshness experienced
by a change of view on
passing through beau-
tiful scenery.

Exhaustion may
not be confined wholly
to the central nerve-
cells, but there can be
little doubt that they
are the most affected.
Sinee also there must be a certain momentum, so to speak, to
molecular activity, it is not surprising that we find that the
sensation outlasts the stimulus for a brief period; and this ap-
plies to all the senses, and necessarily determines the rapidity
with which the successive stimuli may follow each other with-
out causing a blending of the sensations.

Thus, then, in every sense we must recognise (1) an end-
organ in viiich the chain of processes begins; (2) a conducting
nerve through which (3) the central nervensells are affected;
and we may speak, therefore, of (1) sensory impulses and (8)
sensations, when these gfive rise to affections of the central
nervous cells resulting in (1) perceptions and (2) judgments,
when we take into account the psychic processes; and, from the
nature of cell-life generally, we must recognise a certain inten-
sity of the stimulus neoeasary to arouse a sensation -and a limit
within which alone we have power to discriminate (range of
stimulation and perception); and also a limit to the rapidity
with which stimuli may succeed each other to any advantage,
so as to give rise to new sensations; and a limit to the endur-
ance of the apparatus in good working condition corresponding

Fio. 374.— NeiTW with gtkngUon cells (O) benMth •
tactile briitle (7%), noin akin of an Mtbropod
( CtmMra) larra.

iip mli( * w l i W W"f> l ijuiJ

. -> imif

GENBBAL REMARKS ON THE SENSES.

519

a result and
U the senses
L exercised,
but a short
houtchangi)
IS leading to
of condition
tutral cells,
ge need not
entire rest,
J a new form
!. Hence the
experienced
je of view on
irough beau-
nry.

Btion may
fined wholly
intral nerve-
there can be
bt that they
lost affected.
) to speak, to
Ind that the
and this ap-
I the rapidity
ti other with-

I (1) an end-
a conducting
are affected;
iilses and (8)
\ the central
I) judgments,
and, from the
seiiain inten-
n-and a limit
ite (fange of
the rapidity
ly advantage,
to the endur-
orresponding

to clear mental perceptions, together with the value of past ex-
perience in the interpretation of our sensations. A man can
necessarily have positive knowledge only of his own conscious-
ness; but he infers similarity of conscious states by likeness in
action and expression in his feUows. It is by an analogous
process and by such alone that we can draw any conclusions m
regard to the sensations of the lower animals. The presence of
structures, undoubtedly sensory, in them is fairly good evidence
that their sensations resemble ours.when similar organs are em-
ployed. However, this does not absolutely follow; and the-
whole subject of the senses of animals incapable of articulate
speech is beset with great difficulties. It only remains for us to
set forth what is known retarding man, assummg that at
least much of it applies to our domestic animals. Patient
thoughtful observation will in time place tiie subject m a better
position.

THE SKIN AS AN ORGAN OP SENSE.

Bearinq in mind that all the sensory organs originate in
the ectoderm, we find in the skin even of the highest animals
the power to give the central nervous system such sense-im-
pressions as bear a relation to the original undifferentiated
sensations of lower forms as derived from the general surface
of the body, but with less of specialization than is met with in
the sense of hearing and vision, so that it is possible to under-
stand how it is that the skin must be r^^arded not only as the
original source of sensory impulses for the animal kingdom,
but why it still remains perhaps the most important source of
information in regard to the external world, and the condition
of our own bodies; for it must be remembered that the data
afforded for sensory judgments by all the other senses must
be interpreted in the light of information supplied by the skin.
We really perceive by the eye only retinal images. The dis-
tance, position, shape, etc., of objects are largely determined by
feeling them, and thus associating with a certain visual sensa-
tion others derived from the skin and the muscles, which latter
are, however, generally also associated with tactile sensations.

It is recorded of those blind from birth that, when restored
to sight by surgical operations, they find themselves quite un-
able to interpret their visual sensations; or, in other words,
seeing they do not understand, but must learn by the other
senses, especially tactile sensibility, what is the real nature of
the objects that form images on their retinae. All objects seen
appear to be against the eyes, and any idea of distance is out of
the question.

Special forms of end-organs are found scattered over the
skin, mucous fmd serous surfaces of the body, such as Pacinian
corpuscles, touch-corpuscles, end-bulbs, etc.; while in lower
forms of vertebrates many others are found in parts where sen-
sibility io acute. There seems to be little doubt that these are

3NSB.

s originate in
;hest animals
uoh sense-im-
difFerentiated
neral surface
met with in
ible to under-
>t only as the
ual kingdom,
ant source of
the condition
that the data
' senses must
by the skin,
res. The dis-
letermined by
visual sensa-
I, which latter
le sensations,
rhen restored
vea quite un-
other words,
by the other
aal nature of
1 objects seen
mce is out of

«d over the
1 as Pacinian
ile in lower
bs where sen-
liat these are

THB SKIN AS AK ORGAN OF SENSE.

621

all concerned with the various sensory impulses that originate
in the parts where they are found, but it is not possible at pres-
ent to assign definitely to each form its specific function.

It has been contended that the various specific sensations
of taste, as bitter, sweet, etc., are the result of impulses con-
veyed to the central nervous system by fibers that have this
function, and no other; and a like view has been maintained
for those different sensations that originate from the skin.
For such a doctrine there is a certain amount of support from
experiment as well as analogy^ but the more closely tlie subject
is investigated the more it appears that the complexity of our
sensations is scarcely to be explained in so simple a way as
many of these theories would lead us to believe. Whether
there are nerve-fibers with functions so specific, must be re-
garded as at least not yet demonstrated.

Let us now examine into the facts. What are the different
sensations, the origin of which must be in the first instance,
sought in the skin, as the impulses aroused in some form of
end-organ or nerve-termination ?

Suppose that one blindfolded lays his left hand and arm
on a table, and a piece of iron be placed on the palm of his
hand, he may be said to be conscious of the nature of the sur-
face, whether rough or smooth, of the form, of the size, of the
weight, and of the temperature of the body ; in other words,
the subject of the experiment has sensations of pressure, of
tactile sensibility, and of temperature at least, if not also to
some extent of muscular sensibility. But if the right hand be
used to feel the object its form and surface characters can be
much better appreciated; while, if the body be poised in the
hand, a judgment as to its weight can be formed with much
greater accuracy. The reason of the former is to be sought in
the fact that the finger-tips are relatively very sensitive in
man, and that from experience the mind has the better learned
to interpret the sensory impulses originating in this quarter;
which again resolves itself into the particular condition of the
central nerve-cells associated with the nerve-fibers that convey
inward the impulses from those regions of the skin. Mani-
festly if there be a sense referable to the muscles (muscular
sense) at all, when they are contracted at will the impression
must be clearer than when they but feebly respond to the mere
pressure of some body.

62a

COMPARATIVE PHYSIOLOOT.

PRB88UIUB BUmUkTZONS.

1. Th'«re is a rel&tion between the intensity of the atimultu
and the sensation resulting, and this limit is narrow. The
greater the stimulus the more pronounced the sensation, though
ordinary sensibility soon passes Into pain. 2. The law of con-
trast may be illustrated by passing the finger up and down in a
vessel containing mercury, when the pressure will be felt most
distinctly at the point of contact of the fluid. 8. Pressure is
much better estimated by some parts than others ; hence the use
of the employment of those to so large an extent.

THBBMAZi nnraATioNt.

1. The law of contrast is well illustrated by this sense; in
fact, the temperature of a body exactly the same as that of the
part of the skin applied to it can scarcely be estimated at all.
The first plunge into a cold bath gives the impression that the
water is much colder than it seems in a few seconds after, when
the temperature has in reality changed but little; or, perhaps,
the subject may be better illustrated by dipping <^ne hand into
warmer and the other into colder water than tiiat to be ad-
judged. The sample feels colder than it really is to the hand
that has been in the warm water, and wanner than it is to the
other. 2. The limit within which we can discriminate is at most
small, and the nicest determinations are made within about 27"
and 33" O. — i. e., not far from the normal temperature of the
body. S. Variations for the different parts of the skin are
easily ascertained, though they do not always correspond to
those most sensitive to changes in pressure. The cheeks, lips,
and eyelids are very sensitive to pressure.

Beoent investigations have revealed the fact that there are in
the human skin " pressure-spots," and " cold-spots," and " heat-
spots "*-i. e., the skin may be mapped out into very minute
areas which give when touched a sentotion of pressure different
from that produced by the same stimulus in the intermediate
regions; and in like manner are there areas which are sensitive
to warm and to cold bodies respectively, but not to both; and
these do not correspond with the pressure-spotr, nor to those
that give rise when touched to the sensation of j: jin.

It has been shown, also, that the extent of the area of skin
stimulated determines to a large degn^ee the quality of the re-'

THE SKIN AS AN ORGAN OP SENSE.

628

the stimuliu

UTow. The

tion, though

law of oon-

d down in a

be felt moot

Pressure is

lence the use

tiis sense; in
I that of the
nated at all.
don that the
B after, when

or, perhaps,
le hand into
lat to he ad-
I to the hand
fi it >>> to the
lateisatmost
liin about 27"
rature of the
the skin are
onespond to
) cheeks, lips,

tt there are in

*'and"heat-

veiy minute

lure different

intermediate

aresensitiTe

to both; and

nor to those

I area of skin

ty of the re-'

suiting sensation. Thus, the temperature of a fluid does not
seem the same to a finger and the entire hand. This fact is not
irreconcilable with the existence of the yarious kinds of ther-
mal spots, referred to above, but it does re-enforce the view we
are urging of the complexity of those sensations which seem to
us to form simple wholes — as, indeed, they do— just as a piece
of cloth may be made up of an unlimited number of different
kinds of threads.

TAOTOJB HWEIBlZilTy.

As a matter of fact, one may learn, by using a pair of com-
passes, that the different parts of the surface of our bodies are
not equally sensitive in the discrimination between the contact
of objects — i. e., the judgment formed as to whether at a given
instant the skin is being touched by one or two points is de-
pendent on the part of the body with which the points are
brought into contact.

Certain it is that exercise of these and all the senses greatly
improves ^ .>«. />, though it is likely that such advance must be
referr^'' .ather to the central nerve-cells than to the peripheral
mechanism.

We practically distinguish between a great many sensations
that we can neither analyze nor describe, though the very
variety of names suffices to show how much our interpretation
of sense depends on past experience.

Mammals are always able to define the part of their bodies
touched, and with great accuracy, no doubt, owing to the simul-
taneous use in the early Jnonths and years of life of vision and
the senses resident in the skin.

An impression made on the trunk of a nerve is referred to
the peripheral distribution of that nerve in the skin; thus, if
the elbow be dipped in a freeanng mixture, the skin around the
joint will experience the sensation of cold, but a feeling of pain
will be referred to the distribution of the ulnar nerve in the
hand and arm. The same principle is illustrated by the com-
mon experience of the effects of a blow over the ulnar nerve,
the pain being referred to the peripheral distribution ; also Vy
the fact that pain in the stump of an amputated limb is thought
to arise in the missing toes, etc.

524

COMPARATIVE PHYSIOLOGY.

TBB MUSOnZJkR SSMm.

Every one muat be aware how difficult it is to regulate hig
movements when the limba are cold or otherwise deadened in
sensibility. We know too that, in judgin^r of the muscular
effort necessary to be put forth to accomplish a feat, as throw-
ing a ball or lifting a weight, we judge by our past experience.
It is ludicrous to witness the failure of an individual to pick up
a mass of metal which was mistaken for wood. In these facts
we recognize that in the successful use of the muscles we are
dependent, not alone on the sensations derived from the skin,
but also from the muscles themselves. True, the muscles are
not very sensitive to pain when cut; it does not, however, fol-
low that they may not be sensitive to that different effect, their
own contraction. Whether the numerous Pacinian bodies
around joints, or the end-organs of the nerves of muscles are
directly concerned, is not determined.

FathologioaL— The teaching of disease is plainly indicative
of the importance of sensations derived both from the skin and
the muscles for co-ordination of muscular movements.

In locomotor ataxy, in which the power of muscular co-
ordination is lost to a large extent, the lesions are in the pos-
terior columns of the spinal cord, or the posterior roots of )». >
nerves, or both, and these are the parts involved in the trans-
mission of afferent impulses.

ComparatiTe.— The more closely the higher vertebrates are
observed, the more convinced does one become that those sen-
sory judgments, based upon the information derived from the
skin and muscles, which they are constantly called upon to form
are in extent, variety, and perfection scarcely if at all surpassed
by those of man. Of course, sensory data in man, with his ex-
cessive cerebral development, may by associations iti his expe-
rience be worked up into elaborate judgments impossible to the
brutes, but we now refer to the judgments of sense in them-
selves.

The lips, the ears, the vibrisssa or stiff hairs, especially about
the lips, the nose, in some cases the paws, all affoi^ delicate and
extensive sensory data.

It is a remarkable fact that the most intelligent of the
groups of animals have these sensory surfaces well developed,
as witness the elephant with his wonderful trunk, the band of
the monkey, and the paws and vibrissae of the cat and dog tribei.

Jt li .^ g , | p.\ l|WI* W W

regulate his '
deadened in
be muBcular
at, as throw-
t experience,
lal to pick up
[n these facta
iiacles we are
om the skin,
I muscles are
however, fol-
it effect, their
linian hodies
muscles are

ily indioatiye
the skin and
ents.

muscular co-
ire in the pos-
r roots of w '^
in the trans-

eriebrates are
tat those sen-
ved from the
[upon to form
i all surpassed
1, with his ex-
8 ih. his expe-
possible to the
ense in fhem-

peeially about
'd delicate and

lligent of the
rell developed,
k, the hand of
and dog tribe.

THE SKIN AS AN ORGAN OP SENSE.

525

On the other hand, the groups with hoofs are notably inferior
in the mental scale. When we pass to the lower forms of n-
vertebrates the appreciation of vibrations of the air or water
m which they live, of its temperature, of its pressure, etc., must
be considerable to enable them to adapt themselves to a suitable

*"l!^"hive not spoken of sensations derived from the internal
orirans and surfaces. These are iUnlefined, and we know them
mostly either as a vague sense of comfort or discomfort, or as
actual pain. We are quite unable to refer them at present to
special forms of end-organs. They are valuable as reports and
warnings of the animal's own conditions.

Aft^impressions (" after-images") of all the senses referred
to exist, mosUy positive in nature-i. e., the sensation remams
when the stimulus is withdrawn. .

grnopticaL— The information derived from the skin in man
and the other higher vertebrates relates to ««^ti«"f°' P'T;
ure, temperature, touch, and pain. The muscle, also supply
TnT^rmatton of their condition. In hoV ftjr these are rrferable
to certain end-organs in the skin is uncertain. There are der-
mal areas that give rise to the sensations of heat, oold pressure
TdpSn Whether these are connected with nerve-flbers that
conv^o other forms of impulses than those thus ansmg is

"" ti*^uSes^ senses the laws of contrast, duration of the im-
pression, limit of discrimination, etc., hold.

The udgments based on sensations derived from the .^n
are syntiieses or the result of the blending of many component
sensations rimultaneous in origin. All our sensory judgments
are very largely dependent on,our past experience.

•ected bSckeo as to uncover the choroid coat; 6, co™«»i«"l'^f^Ji?*ff'?~5?a
^th «!lerottc coat; •, cnri of Schtommj J. external •»*•?• °'5*g5'^!*tato
by one of the long ciliary arteries and byclHwy """f i ,?i.«l"™'2f^' /P™
wWh theeoto v^Oeoea empty: «, 10. choroid aones 11, e">*fy °«2^ iVL iif
dllSy artery; 18, anterior eiUS^ •rteries; 14, Iris; 16, rascular circle ct Iria; 16,
pupil.

this subject either with the eyes of the physiologist or the phys-
icist, according as we regard the cause of the effects or the
latter and their relations to one another. It is, however, im-
possible to understand the physiology of vision without a
sound knowledge of the anatomy of the eye, apd an apprehen-

WiigiWiiiiiiiiJiflWN

VISION.

697

•ion of at IcMt some of the Uw. of the •oienoe of optic.. The
.tudent i^ therefore, recommended to loam practaoally the

SUPERIOR RECTUS

ivee of each
■isthevibra-
er, to a non-
may look at

; 8, 4, scleratio dlt-
id and folded back
choroid, trkvened
wDtnl veMel, into
rr nervM: 18, long
' ciRte M iito; IS,

it or the phys-
effects or tiie
, however, im-
cm without a
I an apprehen-

CHOROID

OPTIC NERVE

CHOROID

INFERIOR MOTUfl

Fi«. m-8«cUoB of houm ey«, •onwwhrt di«gr«iiin«Uc (•ftor Flint)

coarse and mioroecopio structure of the eye in detaiL The eyes
S^mal. are .uffldently alike to make tbe dis^on of ^y
of them profitable. BuUooks' eyes are readily obtamable. and
?n,mthe& large ri«e may be used to advantage. Wereoom-
mend one to be boUed hard, another to be froson, and secta^
in different meridians to be made, especially «»« »"»1^;S^«J
longitudinal section. Other specimens may be dusected with
and without the use of water. j*i..*4i,«

Assummg that some such work has been done, and that the
rtudent has become quite familiar with the gef^^J'^f'T
7te eye, we call attention specially to the stirength of the
msleroUc c^it; the great vamnilarity of «»« choroid ~jt and its
terminal ciliary processes, ite pigmented character adapting it
for the ab«,rpti\m of light, the complicated ^<^'^^ ^.
tooted position of the retinal-expansion. It may be said that

,^m «ie»!)mm*m mt mi:mii \ ^ i*'«M

628

COMPARATIVE PHYSIOLOaY.

the whole eye exiato for the retina, and that the entire meohaii<
iani beside* ia subordinated to the furmatiou of images on this

Fra. 87?.— Certain piu'ti
hytloid membnao; .
tbtn of cillarjr mnicle:

II of eye. 1 * 10. (AftM Sappey.) 1, 1,
; 8, cooDlo of ZInn; 4, lii»; 5, a cUianr |
Kle; 7, Motion of eironlar portion of cHIsi

1, 1, eiTftaUine lent; 8,
proesM; 0, radiating
irr mnsele: 8, venou*

canal of Bcblemm.

nervous expansion. The eye of the m a mm al may be regarded
as an arrangement of refracting media, protected by coverings,
with a window for the admission of light, a ourtoin regulating
the quantity admitted; a sensitive screen on which the images
are thrown; surfaces for the absorption of superfluous light;
apparatus for the protection of the eye as a whole, andfor pre-
serving exposed puts moist and clean.

SmlnryologioaL — We have already learned that the first indi-
cation of the eye is the formation of the optic vesicle, an out-
growth from the first cerebral vesicle. This optic vesicle be-

l l .l lil WHI-llll' i r-Tir i n llirinn -'"-"' ll- ' n,-i.Bt-jaa:jaaii.,y |-

ire meohan-
Agetonthii

fftalline leni; 8,
sbm; 6, radiating
ansele: 8, venom
epithelial layer of
Id; It, •pitbeUnin
ea; 18, lection of

' be regarded
by coverings,
n regulating
bthe images
luoua light ;
, aud'for pre-

the first indi-
ssicle, an out-
bic vesicle be-

VISION.

oomeH more contracted at the baw, and the optic stalk renmliw
as the optic nerve.

At an early stage of development (second or third day in the
chick) the outer portion of the optic vesicle is pushed inward«

Fio. 879.

Fio. S78.— Section through head of chick on third day, showing origin of eye (after
Tec), a, epiblait undergoing thickening to form lent; o, optic veeicle: V„ flrat
cerebral veeivie; V,, poatorior cerebral veeicle. It will be olxerved that the retina
ia already diithicUy Indicated.

Fio. S7V.— l«ter itagea in development of eye (after Cardial), a, cpiblaat; c, develop-
ing lene; o, optic veatele.

SO that the cavity is almost obliterated; the anterior portion,
becoming thickened, ultimately forma the retina proper, while
the posterior is represented by the tesselated pigment layer of
the choroid.

As this retinal portion breaks away from the superficial
epithelium, the latter forms an elliptical mass of cells, the future
lens, the changes of which in the formation of the cells peculiar
to Uie lens illustrate to how great lengths differentiation in
structue is carried in the development of a single oi^gan. It
will thus be seen that the most essential parts of the eye, the
optic nerve, the retina, and the crystalline lens, are, according
to a general law, the earliest marked out The cornea, the iris,
the choroid, the vascular supply, the sclerotic, etc, are all sec-
ondary in importance and in formation to these, and are derived
from the mesoblast, while the essential structures are traceable,
like the nervous system itself, to the epiblastic layer.

Any act of perfect vision in a mammal may be shown to
consist of the following: (1) The focusing of rays of light from
S4

.■iast)emxiamaiiiiMiM>ammifmts»mmm

waMa|IM«Mll|i

680

COMPARATIVE PIIVHIOLOOY.

an obj«ci on the retina, no •• to form a well defined Image; (%)
the conduction of the ■enaory impuliee thu« generated in the

Via SW) -Mor« •dvtncrf ittM of dwrrtopnwnt of eye rtfter Cjrdtot). «• •P"J*"'j!
to form conJonctlTt; d, t, two lann of opMc i?!iS^."2*inJ^liSi •tStllSw
ATdevelopIng optio nerre; i, Mtve-Ibcn entcnnK num.

i«tina by the optic nerve inward to certain centers; and (8) the
elaboration of theae data in oontciousnem.

We thus have the formation of an image— a physical pw^
cess; sensation, perception, and judgment-physiological and
psychical processes.

In the natural order of things we must discuss first those
arrangements which are concerned with the focusing of light—
i. e., the formation of the image on the retinal screen.

<A imase; (V)
BMtod in th«

rdUt). «.«pHh«lW
ineoiw llMue •bout
dad back and form-
reellular inbatMiM;

tn; and (8) the

k phyflioal pro-
riiological and

Muw Bnt thoM
uing of light—
oreen.

HaMwai««Wii»iwii«Baw*<MHM4NMi

mmmtsr—

VISION.

oiopnuot or tuion.

581

One of the mort ■atiBf»cU)r.v methotU of aMcrtaining that
the eye doea form images of the objecta in the Held of vision
i« to remove the eyo of a recently killed albino mbbit. On
holding up before such an eye any Bniall object, a« a pair of
fofceps, it may be readily obwjrved that an invert«Ml image of
the object ia formed on the buck t»f th« eye (Jundua). If,
however, the lens be removed from wch an eye, no image is
formed. If the lent be itaelf held behind the object, an in-
verted image will be thrown upon a piece of paper held at a
miitable (iU focal) distance. By aubatituting an ordinary bicon-
vex lens, the same effect follows. It thus appears, then, that
the leas iii the essential part of the refracting media, though
the aqueous and vitreous humors and the cornea are aUK> focus-
ing mechanisms.

In the actual human eye the focus must correspond with the
fovea of the retina if a distinct image is to be formed.

■MUBMd to coiMiM ot • iefi- a of leiUMi* (II In flgart), for tlio MUe or simpiiciiy,
thongh, of conrM, thto In not (trlctly accnnte.

It will appear that we may represent the eye as reduced to
the lens and the retina. The experiments referred to above
will convince the student that such is the case.

i-i^SU'3lfli'ii-^-"-.-i.

u;->A,-".^<^M^v^i

682

COMPARATIVE PHYSIOLOGY.

AOCX>MMODATZOM ,OF THB BTB.

Using the material already referred to, the student may
observe that, with the natural eye of the albino rabbit, its
lens (or better that of a bullock's eye, being larger), or a bi-
convex lens of glass, there is only one position of the instru*
ments and objects which will produce a perfectly distinct imago.
If cither the eye (retina), the lens, or the object be shifted, in-
stead of a distinct image, a blurred one, or simply diffusion-
circlea, appear.

A photographer must alter either the position of the object
or the position of his lens when the focus is not perfect. The
eye may be compared to a camera, and since the retina and
lens can not change position, either the shape of the lens must
change or the object assume a different position in space. As
a matter of fact, any one may observe that he can not see
objects distinctly within a certain limit of nearness to the eye,
known as the near point (punctumproximum); whilohe be-
comes conscious of no effect referable to the eye until objects
approach within about sixty-five to seventy yards. Beyond the
latter distance objects are seen clearly without any effort.

There are many ways in which we may be led to realize
these truths: 1. When one is reading a printed page it is only
the v<)ry few words to which the eyes are then specially di-
rected', that are seen clearly, the rest of the page appearing
blurred; and the same holds for the objects in any small room.
We speak of picking out an acquaintance in an audience or
crowd, which implies that each of the individuals composing
the throng is not distinctly seen at the same time. 2. If an ob-
server hold up a finger before his eyes, and direct his garxi in*x>
the distance (relax his accommodation), presently he will be-
hold a second shadowy finger beside the real one — i. e., he sees
doable; his eyes being accommodated for the distant objects,
can not adapt themselves at the same time for near ones.

In what does accommodation consist ? From experiments
it has been concluded that accommodation consists essentially
in an alteration of the convexity of the anterior surface of the
lens.

This change In the shape of the lens is accomplished as
follows : The lens is naturally very elastic and is kept in a par-
tially compressed condition by its capsule, to which is attached
the suspensory ligament which has a posterior attachment to

student may
no rabbit, its
ger), or a bi-
>f the instru-
istinot imago.
>e shifted, in-
ply diffusion-

I of the object
perfect. The
le retina and
the lens must
in space. As
B can not see
ess to the eye,
; while he be-

until objects
I. Beyond the
ly effort.

led to realize
page it is only
n specially di-
age appearing
ty small room,
in audience or
als composing
e. 2. If an ob-
ct his gaTiO in^o
tly he will be-
e — i. e., he sees
distant objects,
ear ones,
m experiments
sists essentially
•surface of the

tccomplished as
is kept in a par-
iiich is attached
r attachment to

VISION.

533

the choroid and ciliary processes. When the ciliary muscle,
which operates fi om a fixed point the comeo-sclerotic junction.

Fio. aM.-inn»tMtee mechanlfin of sccommodatlon {after FIck). Theje" '"^^

'olSlThe «Utl^ ^^daiiSl tto^iSTwrcondSimrof-the" eve (negative accom-
SStotionro? accomm^tion f ot long^atanceB); the right airfe. ihS for near ob-
jecta.

pulls upon the choroid, etc., it relaxes the suspensory ligament;
hence the lens, not being pressed upon in front as it is from
behind by the vitreous humor (invested by its hyaloid mem-
brane), is free to bulge and so increase its refractive power.
The nearer an object approaches the eye, the greater the diver-
gence of the rays of light proceeding from it, and hence the
necessity for greater focusing power in the lens.

If an animal be observed closely when looking from a remote
to a near object, it may be noticed that the eyes turn mward—
i.e., the visual axes converge and the pupils contract. These
are not, however, essential in the sense in which the changes
in the lens are ; for, as before stated, in the absence of the lens
distinct vision is quite impossible.

AZ>TERATIONS IN THE StZB OP THB PUPIL.

The pupil varies in sixe according as the iris is in a greater
or less degree active. All observers are agreed that the cuwu-
lar Ahera aroimd the pupillary margin are muscular, forming
the so-called sphincter of the iris; but great differences of opin-
ion still exist in regard to the r&diating fibers. It vi thought
by many that all the changes in the iris may be explained by
the elasticity >f its structure without aasuming the existence
of muscular fibers other than those of the sphincter ; thus a
contraction of the latter would result in diminution of the pu-

S34

COMPARATIVE PHYSIOLOGY.

pillary aperture, its relaxation to an enlargement, provided the
rest of the iris were highly elastic.

The conclusions in regard to the innervation of the iris rest
largely upon the residts of certain experiments which we shall
Brain above tneduRa

Optic centre-

Oeitlo-motor.i, ^

centre

Dilator etntre in
nudutla

Retina

IrU

Sj/mpothetic n«roe to
radiotinff/ibre*

Spinal cKIator centre

Fin «« — DiaffTiiiu to niuitrate innervaUon of the Irta. Dotted lino* Indicate general
■fMCtiom^"nMtlon(co^laUon). Cou«e of Impnliws indicated by arrows.

now briefly detail : 1. When the third nerve is divided, stimu-
lation of the optic nerve (or retina) does not cause contortion
of the pupil as usual. 2. When the optic nerve is divided, light
no longer cauws a contraction of the pupil, though stimulation
of the third nerve or its center in the anterior portion of the
floor of the aqueduct of Sylvius does bring about this result.
8. Section of the cervical sympathetic is followed by conti-ac-

irovided the

the iris rest
ich we shall

_ R etina

33^ <

nenwto
tret

« indicate general
ed by arrowe.

ivided, stimu-
le contraction
divided, light
h stimulation
ortion of tho
t this result
d by contrac-

VISION.

586

tion and stimulation of its peripheral end by dilatation of the
pupil.

From such experiments it has been concluded that — 1. The
optic is the afferent nerve and the third nerve the efferent nerve
concerned in iJie contraction of the pupil ; and that the center
in the brain is situated as indicated above, so that the act is or-
dinarily a reflex. 2. That the cervical sympathetic is the path
of the efferent impulses regulating the action of the radiating
fibers of the iris.

Its center has been located near that for the contraction of
the pupil, and it may be assumed to exert a tonic action over
the iris comparable to that of the vaso-motor center over the
blood-vessels.

The impulses may be traced through the cervical sympa-
thetic and its ganglia back to the first thoracic ganglion, and
thence to the spinal cord and brain. There may be subsidiary
centers in the cervical spinal cord.

It is to be remembered that, although the dilating center is
automatic in action, it may also act reflexly, or be modified by
unusual afferent impulses — as, e. g., the strong stimulation of
any sensory nerve which causes enlargement of the pupil
through inhibition of the center. To render the paths of
impulses affecting the iris somewhat clearer, it is well to bear
in mind the nervous supply of the part : 1. The third nerve,
through the ciliary (ophthalmic, lenticular) ganglion, supplies
short ciliary nerves to the iris, ciliary muscle, and choroid. 2.
The cervical sympathetic reaches the iris chiefly through the
long ciliary nerves and the ophthalmic division of the fifth.
8. There are sensory fibers from the fifth nerve; and, according
to some observers, also dilating fibers from this nerve inde-
pendent of the sympathetic, as well as those that may reach
the eye by the long ciliary nerves without entering the ciliary
ganglion. 4. The centers from which both the contracting and
dilating impulses proceed are situated near to each other in
the floor of the aqueduct of Sylvius. It is of practical im-
portance to remember the various circumstances under which
the pupil contracts and dilates.

Contraction (Jfyosw).— 1. Access of strong light to the
retina. 2. Associated contraction on accommodation for near
objects. 3. Similar associated contraction when the visual axes
converge, as in accommodation for near objects. 4. Reflex
stimulation of afferent nerves, as the nasal or ophthalmic divis-

fi86

COMPARATIVE PHYSIOLOGY.

ion of the fifth nerve. 5. During sleep. 6. Upon stimulation
of the optic or the third nerve, and the corpora quadrigemina
or adjacent parts of the brain. 7. Under the effects of certain
drugs, as physostigniin, morphia, etc.

DilatcUion (Mydriaaia). — 1. In darkness. 2. On stimulation
of the cervical sympathetic. 3. During asphyxia or dyspnoea.

4. By painful sensations from irritation of peripheral parts.

5. From the action of certain drugs, as atropin, etc. The
student may impress most of these facts upon his mind by
making the necessary observations, which can be readily done.

PftthologioaL — As sfaowing the importance of such connec-
tions, we may instance the fact that, in certain forms of nervous
disease (e. g., locomotor ataxia), the pupil contraota when the
eye is accommodated to near objects, but not to light (the
Argyll-Bobertson pupil). In other cases, owing to brain-dis-
ease, the pupils may be constantly dilated or the reverse ; or
one may be dilated and the other contracted.

Ooillip«ratiV0.— The iris varies in color in different groups of
animals, and even in individuals of the same group ; while the
color in early life is not always the permanent one.

In shape the pupil is elliptical in solipeds and most rumi-
mints. In the pig and dog it is circular, as also in the cat
when dilated : but when greatly contracted in the latter animal,
it may become a mere perpendicular slit.

The iris is covered posteriorly with a layer of pigment (uvea),
portions of which may project through the pupil into the an-
terior chamber, and constitute the "sootballs" (corpora nigra)
well seen in horses, and very suggestive of inflammatory
grovrths, though, of coursd, perfectly normal.

omoAZt mPBRFXionoifs of tbb btb.

Aiiioijiitciief of BefrMtiOll.— 1. We may speak of an eye in
which the refractive power is such that, unuer the limitations
referred to before (page 581), images are focused oi the retina,
as the cmrwM'upio eye. The latter is illustrated by Fig. 384.
In the upper figure, in which the eye is represented as passive
(negatively accommodated), parallel rays— i. e., rays from ob-
jects distant more than about seventy yards (according to some
writers much less) —are focused on the Tetiua ; but those from
objects near at ha\)d, the rays from which are divergent, are
focused liehind the retina. In the lower figure the lens is rep-

a aiimulation
D[uadrigemina
icts of certain

hi stimulation

or dyspnoea.

ipheral parts.

►in, etc. The

I his niuid by

I readily done.

such oonneo-

•ms of nervous

aots when the

to light (the

If to brain-disr

ae reverse ; or

jrent groups of

up ; while the

ae.

™d most rumi-

also in the cat

3 latter animal,

[>igment (uvea),

pil into the an-

/Dorpora nigra)

inflammatory

Btk of an eye in
r the limitations
I oji the retina,
ted by Fig. 384.
rated as passive
,, rmjrs from ob-
cording to some
bat those from
•e divergent, are
e the lens is rep-

VISION.

687

nisented as more bulging, from accommodation, as Buoh diver
irent ravs are properly focused.

2 In the myopic (near-sighted) eye the porallel rays cro^
within the vitreous humor, and diflusion-cucles be>ng formed
on the retina, the image of the object is nece«anly blurred.

" new " objects (after Landoia).

SO that an object must, in the case of such «i eye, be brought
unusually near, in order to be seen distinctiy-i. e., the near
point is abnormally near and the farpotnt also, for parallel

-/-?=-"::

Pi«. m-ABondUJe. of wfwction in • myopte V» (•"« tuM»y

rays can notbefocu«»d ; sothatobjecto must be near enough
for the rays from them that enter the eye lobe divergent

The myopic eye is usurily a long eye, and, ^oughjh^
mechanist; of a^mmodation may be nonnrf^t « notw

usually, the ciliary mu«»le being ^^^rfl^^^ZZT^r
of it. fibers, which may be either hypertrophiedor atroph>ed^«^
witii »me affected one way and others m the opposjto. More-

688

COMPARATIVE PHYSIOLOGY.

over, aiere is also generally, in bad oases. " spasm of accommo-
dation" (i. e., of the ciliary muscle), with oicreased ocular ten-
sion, etc. The remedies are, it»t of the accommodation mechan-
ism and the use of concave glasses.

8 The opposite defect is hypermetropia. Thefc«perm<rt«)pic
eve (Fiff 386), being too short, parallel rays are focused be-
Wnd theretina ; hence no distinct image of distant objects can

Fia. a85.-AiioiM«e« of wfMctton ta tin hypennetioplc ey« («fter Uadoto).

be formed, and they can only be seen clearly by the «"eo' con-
vex glasses, except by the strongest efltorte at acoommodatoon
When the eye is passive, no objects are seen distinctty beyond
a certain distance-i. e., the tuwrpoini is abnormally distant
(eight to eighty inches). The defect is to be remedied by the
use of convex glasses. .xl .j •_

4. Presbyopia, resulting from the preOtyoptc eye of the old, is
owing to defective focusing power, partly from diminished
ehisticity (and hence flattening) of the lens, but chiefly, proba-
bly to weakness of the ciliary muscle, so that the changes
required in the shape of the lens, that near objecte may be di^
tinctly seen, can not be made. The obvious remedy is to aid
the weakened refractive power by convex glasses. It is practi-
caUy important to bear in mind that, as soon as any of these
defecte in refractive power (though the same remark applies to
all ocular abnormalities) are recognized, the remedy should be
at once applied, otherwise corapUcations that may be to a large
extent irremediable may ensue.

TmUAL SaWBATIONB.

We have thus far considenjd merely what takes place in the
eye itself or the physical causes of vision, without reference to
those nervous changes which are essential to the perception of

»f acoommo-
i ocular ten-
ion meohan-

permefropto
f oouaed be-
lt objects can

rter Laadoli).

iie use of con-
iommodation.
incily beyond
•mally distant
nedied by the.

re of the old, is
n diminished
chiefly, iwoba-
; the changes
its mayhedis-
nedyis to aid
. It is practi-
8 any of these
lark applies to
ledy should be
ly be to a large

Ices place in the
tut reference to
e perception of

VISION.

589

an object It is true that an image of the object is formed on
the retina, but it would be a very crude conception of nervous
processes, indeed, to assume that anything rewsmbling that
image wei-e formed on the cells of the brain, not to speak of
the superposition of unages inconsistent with that clear mem-
ory of objects we retain. Before an object is " seen," not only
must there be a clear hnage formed on the retina, but impulses
generated in that nerve expansion must be conducted to the
brain, and louae in certain oelU there peculiar molecular condi-
tions, upon which the perception finally depends.

For the sake of clearness, we may speak of the changes

rn.m.

VM.)

— w). 1. S, S, rodi and conM k««i from In front; 4, 5, S, Mae view, i ne reei wiu
t clear from the preceding »gt«-

erii

640

COMPARATIVE PHYSIOLOGY.

effected in the retina aa aenaory impre$8ioM or impulw^ which,
when compkted by oonresponding change* in the bi»in, develop
into muattons, which ai« reprewmted psychically hjper^
tiotu; hence, though aU these have a natund connection, they
may for tiie moment be conridenjd wparately. It m as yet
beyond our power to explain how they are wdated to each
otiier except in the most general way, and the manner in which
a mental peroeption grows out of a physical alteration m the
molecules of the brain is at present entirely beyond human

comprehension. . . x ^i. * *i. «i»— /»#

f^ff^mm of th* BfltiBft.— There is no doubt that the flben ol
the optic nerves can not of tliemselves be directly affected by
liffht This may be experimentally demonstrated to one s self
S a variety of methods, of which the following is readily ca^
ried out: Look at the oirele (Fig. 8») on the left hand with the

tw.miiKttm

right eye, the left being dosed, and, with the page •bout twel^«
t«r flftwn inches distant, gradually approximate it to tte ^e.
when suddenly the cross will disappear, its image at that di^

optic nenre.

. i p iTOTiyt wi

««•<•'•**••*(«

VISION.

541

lUflM, which,
rain, develop
y hypereep-
lecUon, they
It is M yet
ited to each
ner in which
ration in the
jTond human

ttheflhenof
f aflected by
to one's self
is readily oar-
uuod with the

e about twelve
) it to the qre»
age at tbat dia-

r nuclear l«]r«r;/./>
e<elto; {.i.abenoT

tance having fallen on the blindapot, or the point of entrance
of the optic nerve. ... .. ._

It remains then, to determine what part of the retana ij
affected by Ught. The evidence that it it the layer, of rods and

frelTslvLing. It^^»'*-\*^*CowJ^ron
itoelf internal to these layers cast perceptMr> "^f^ows, the con-
cuLion that the rods and cones are the e««nt»l parts of the

sensorv oratan would be inevitable. .. j ^v »

Benswy w^jn ^ ^^^^^ ttiilillhtlwi.-It may be noticed that.

when a circular saw in a mill is rotated with extreme rapidity,

it seems to be at rest. ^_ . i. * iu«-«

If a sUck on flie at one end be rapidly moved about, there
seems to be a continuous flery circle.

If a top painted in sections with various colors be spun, the
different Llors can t.ot be distinguished but there U a color
,«iulting from the blending of tiie sensations from them aU,
which will be white if the spectral colors be employed.

When, on a dark night, a moving animal » iU«»>"«f^, Y_
a flash of lightaiing, it seems to be a* rest, though the attitude is
one we know to be appropriate for it during locomotion.

It becomes necessary to explam these and similAr phe-
nomena. Another ob«»rvatlon or two wUl furnish the data for

the solution. , .. . v

If ou awakening in the n'orning, when the eyes have been
weU rested and the retina is therefore not so readily fatigued,
one looks at the wVadow for a few seconds and then closes the
evea. he may j^reeive that the pictiure still remains visible as
tipontive ar-er-image; while, if a light be gased upon at night
and the eyes suddenly closed, an after-image of the light may

be observed. . ^ ,.

It thus appears, tiien, that the impression or sensation ovt-
lastB the stimulus in these cases, and this is tiie explanation
into which all the above-mentioned facts flt. When the fiery
point passing before the eyes m the case of the fire-brand stimu-
lates the same parts of the retina more f requentiy tium is oon-
Bistent with the time required for the previous impression ti)
fade, there is, of necessity, a continuous sensation, which is in-
terpreted by the mind as referable to one object In like mim-
ner, in tiie case of a moving object seen by an electiic flash, the
dumtion of the latter is so brief that the object Uluminated can
not make any appreciable change of position while it "iste ; a
second flash would show an alteration, another part of ttie

w m " " ' in

642

COMPARATIVE PHY8IOL0OV.

retina being Btimulated, op the original iinpreiwion having

faded, etc. .

In the caae of a top or (better wen) color disk, painted into
black and white iectons it may be observed that with a faint
light the different colon cease to appear distinct with a slower
rotation than when a bright light is used. The variation is
between about tV and A o' ■ second, according to the intensity
of the light used. Fusion is also readier with some colors than

others.

It is a remarkable fact that one can distinguish as readily
between the quantity of light emanating from 10 and 11 candles
as between 100 and 110.

The Yiioal Angle.— If two points be marked out with ink on
a sheet of white paper, so dose together that they can be just
distinguished 88 iv ■xt the distance Af 18 to 80 inches, then on
removing them e farther away they seem to merge into

one.

The principle involved may be stated thus: When the dis-
tance between two points is such that they subtend a less visual
angle than 60 seconds, they cease to be distinguished as two.
Fig. 391illuatrates the visual angle. It will be noticed that a
larger object at a greater d'aitanoe subtends the same visual
angle as a smaller one much nearer. The >i«e of the retinal

Fio. 8M.— The vimtl Mgle. The object at A" appcan no Umger than the one at A
(Le Conte).

image corresponding to 60 seconds is '004 mm. (4 it), and this
is about the diameter of a single rod or cone. It is not, how-
ever, true that when two cones are stimulated two objects are
inferred to exist in every case by the mind; for the retina va-
ries in difTerent parts very greatly in general sensibility and in
sensibility to color.

It is noticeable that visual discriminative power can be
greatly improved by culture, a remark whioh applies eapeeially
to colors. It seems altogether probable that the change is cen-
tral in the nerve-cells of the part or parts of the brain con-

V18I0N.

548

iwion having

, painted into
with a faint
with a slower
s variation ia
I the intensity
le colors than

ish as readily
md 11 candle*

it with ink on
»y can be just
iches, then on
to merge into

Wlieu the di»-
d a leas visual
lished as two.
noticed that a
) same visual
of the retinal

■ than the one at A

(4 It), and this
It is not, how-
two objects are
• the retina va-
isibilJty and in

power can be
ipliea eapeeaally
I change is cen-
the brain oon-

oemed, especially o: i ! m ,.'Hical region, where the cell processes
involved in vir'uo ure flniJ'y completed.

Gdlor-Yifift't. As we are aware by experience the range and
accuracy of color perception in man is very great, though vari-
able for different persons, a good deal being dependent on culti-
vation. However, there are also pronounced natural diiTer-
ences, some individuals being unable to differentiate between
certain primary colors as red and green, and so are " color-
blind." It is of course difficult to determine in how far the
lower animals can discriminate between colors; but in certain
groups, as the birds, it would seem to be reasonable to conclude
that their color-perceptions are highly developed.

It is further probable that in this group, and possibly some
others with the eyes placed more in the lateral than theant«rior
portion of the hc^J, the retinal area for the most distinct vision,
including that for colors ia larger than in man, at all events.

PffTOROLOOIOAi; AimOTB OF TXIION.

It is impossible to ignore entirely, in treating of the physi-
ology of the senses, the mind, or perceiving ego. ^^

By virtue of our mental constitution, we refer what we see
to the external world, though it is plain that all that we per-
ceive is made up of certain sensations. ^ . ^, . .

We recognise the " visual field " as that part of the outer
world within which alone our virion can act at any one time;
and this is, of course, smaller for one than for both eyes.

If one takM a lar<rfl "heet of paper and marks on its center
a spot on wV.. h o u or both eyes are fixed, by moving a point

up Sr down, to the right or the left, he may r*'J^l*^J*SS
of the visual field for a phine surface. The visual field for both

eyes measures about 180» in the horiiontal aendum; for one
eyeaboutl46»; and in the vertical meridian 100.

AftarJiiMMl, 0to.-Positive aftei-images have already been
referred to; but an entirely different """l*. OT^^S^/^^^^IT
tion of the retina, may follow when the eye is turned from the
object. If, after gaiing some seconds at the mm, one turns
awS or merely closes the eyes, he may see black suns. In
Uke manner, when one turns to a gray surface afterkeeping
the eyes fixed on a black spot on a white ground, he will see a
light spot. Such are termed negoHve after-images, and the«j
imty theiMdves be colored, as when one turns from a red to a

644

COMPAUATIVK PHY8I0L<K»Y.

white surface and neen the latter green,
lidjrcd ttM the results uf exhaustion.

They may be oon-

OO-ORDIIf ATIOlf OP TRB TWO BTBt IN Tinoir.

As a nutttor of fact, we are aware that an object may be
seen as one either witli a single eye or with both. For bi'
nocular vision it may be shown that
the images formed on the two retinas
must fall invariably on comtponding
points.

The position of the latter may be
gathered from Fig. 802. It will be no-
ticed that the malar side of one eye
corresponds to the nosol side of the
other, though upper always answers to
upper and lower to lower. This may
also be made evident if two saucers
(representing the fundus of each eye)
be laid over each other and marked off,
as in the figure.

That such corresponding points do

Via. m. -Diaciam to Hint- actually exist may be shown by tumiiiff
trato corrMpondIng point! ^i / .. . , ,. .

(after Foitor). £,s,Mt one eye so that the image shall not

^nu'ii oS?'.?i*'« '»U, as indicated in the figure. Only

trthX. %■!!;• itO'sg. now*nd tl»on. however, is a person to

uroi M« projactioiw of the be found who can voluntarily aooo.n-

retina of th« right {K) and u t .1. . i. . .. . ,/, . ,

the iefti^)e7e. itmaybv push this, but it occurs in all kmds of

tuSAi^^ X natural or induced squint, as in alcohol-

tKother "^ "^ •"''°' ^*°^ °^^« to partial paralysis of some
of the ocular muscles. We are thus
naturally led to consider the action of these muscles.

Oeolar XovOBailto.— Upon observing the movements of an
individual's eyes, the head being kept stationary, it may bo
noticed that (1) both eyes may oonvoige; (2) one diverge and
the other turn inward; (3) both move upward or downward;
(4) these movements may be accompanied by a certain degree
of rotation of the eyeball.

The eye can not be rotated around a horicontal axis without
combining this movement with others. To accomplish the
above movements it is obvious that certain muscles of the six
with which the eye is provided must work in harmony, both as

y nwy be onn-

or Tinoir.

object may be
mth. For bt-
be ahowa that
be two retinao
corresponding

latter may be
It will be no-
lo of onr eye
U side of the
vy* anawen to
er. This may
f two aaucera
I of each eye)
ad marked off,

ling points do
wn by turning
lage shall not

figure. Only
, is a person to
atarily aoco.n-
in all kinds of
t,asinaloohol-
■oljrsis of some

We are thus
slea.

cements of an
ry, it may bo
le diverge and
or downward;
certain degree

d axis without
ocomplish the
cles of the six
mony, both as

i-i-^Lji^I^l^-j^

•iUVfiSiSS:

..^...

IMAGE EVALUATION
TEST TARGET (MT-3)

1.0

1.1

111

lit

2.0

L25 ||I_U ii.6

— 6"

K-

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Sciences

Corporation

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ifi

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VISION.

645

to the direction and degree of the movement — i. e., the move-
ments of the eyes are a£Fected by very nice muscuhir co-ordina-
tions.

Fie. MS.— View of the two eyea and ralated parta (after Helmholta.)

Fig. 394 is meant to illustrate diagrommatically the move-
ments of the eyeball.

While the several recti muscles elevate or depress the eye,
and turn it inward or outward, and the oblique muscles rotate
it, the movements produced by the superior and inferior recti
always corrected by the assistance of the oblique muscles, since
the former tend of themselves to turn the eye somewhat in-
ward. In like manner the oblique muscles are corrected by
the recti. The following tabultur statement will express the
conditions of muscular contraction for the various movements
of the eye in man:

Straight
move-
ments.

EXevation Rectus superior and obliqaos in-
ferior.

Depression Beotus inferior and obliquus su-
perior.

Adduction to nasal side. . .Rectus intemns.
. Adduction to malar side.. .Rectus extemus.

546

Oblique
move-
ments.

COMPARATIVE PHYSIOLOGY. .

Blevation with adduction.. Rectus superior and intemus,

with obliquus inferior.
Depression with adduction.Rectu8 inferior and intemus,

with obliquus superior.
Elevation with abduction.. Rectus superior and extemus,

with obliquus inferior.
Depression with abduction.Rectu8 inferior and extemus,

with obliquus superior.

WTiat is the nervous mechanism by which these "aasoq-
ated" movements of the eyes are accomplished f It has been

found, experimental-
ly, that when different
parts of the corpo-
ra quadrigemina are
stimulated, certain
movements of the eyes
follow. Thus stimu-
lation of the right side
of the nates leads to
movements of both
eyes to the left, and
the reverse when the
opposite side is stimu-
lated ; also, stimula-
tion in the middle line
causes convergence
and downward move-
ment, etc., with the
corresponding move-
ments of the iris.
Since section of the
nates in the middle
line leads to move-
ments confined to the
Pio a»4 -Diagram intended to fllnrtrate action of eye of the same side,

■SS^£WiSlS«tS''^i.S:i^rtS the center wo«lda^

line linea the axes of movement. pear to be double.

However, it may be that the cells actually concerned do not lie
in the corpora quadrigemina, but below or outside of them. The
localization is as yet incomplete. In many groups of animals,
including the solipeds, ruminants, and Camivora, there is a
posterior rectus or retractor oculi by which the eye may be

»Y. .

erior and internus,

[uus inferior.

erior and intemns,

[UUB superior.

erior and eztemus,

[uus inferior.

erior and extemus,

luus superior.

uoh these "assoc^-
bed f It has been
nd, experimental-
that when different
ts of the oorpo-

quadrigemina are
nulated, certain
vements of the eyes
low. Thus stimu-
Lon of the right side
the nates leads to
tvements of both
» to the left, and

reverse when the
Mwite side is stimu-
ed ; also, stimula-
n in the middle line
uses convergence
id downward move-
ent, etc., with the
Responding move-
ents of the iris,
nee section of the
ites in the middle
le leads to move-
ents confined to the
ne of the same side,
le center would ap-
)ar to be double,
concerned do not lie
utside of them. The
y groups of animals,
^imivora, there is a
ich the eye may be

VISION.

Fib. W6.— PUigwunaitlc teeMwi of the «y of the haiw (C ta uf w u V «, opttcnerre:
b, eelerotic coat; e. choroid; d, retine; «, eomce; /, Ine: f/. A, eiliaiy Hnment and
p wceee B e of choroid re p reeeited ^» eepemted from it. the batter to dome ita Hni-
Ita; i, inaertioB of oiDair proeaaa t i on ciyatalUae lena; J, ciTttalliiie lena; k, lens
caosale; I, Tttneaa body; m, m, anterior and Materior Aaaben; o, thearctieal
inoieatlon of aqneona homor; p, p, tarsi (eyelids); q, V< flhroos membrane of ey«-
lida; r, elerator moaele of niiper eyelid ; «. «, orbMiuaria mnacle of Itds; t, t, afcin
of eyelids; «, coojonotiva; •, epidermic layer of the latter covering cornea; m,
poeterlor reetns mnscle; y, snpenor rectus; s, inferior rectos; w, Hbroiis sheath of
orbit (orbital membraiie).

drawn inward and thus protected the more effectually against
blows and obstaoles. It seems to be of special importance in
animals that feed with the head
down for long periods, as in the
ruminants, in which dasi it is
most highly developed.

The nuMvUa Ivkea is beUered
to exist only in man, the quadm*
mana, and certain of the lisard
tribe— L e., in animals in which
theazes of the eyeballs are parallel
to each other. Nevertheless, there
is no reason to doubt that the can*
tral part of the retina is more sensitive than the periphery or
that there is a central retinal sone for distinct vision in all
Twtebrates, thoo^ not so limited in all cases as in man.

Tio. aw.— DiS|fMn to ttlnstrate de-
cnssatioii of Ibera in the <ntk
of man (after nibf).

MIM

648

COMPARATIVE PHYSIOLOGY.

Irtimatiia Of tiM tUw tad Digtonoe of 014«eto.--The pro-
oesM. by which we form a judgment of the size and dwtanoe of

''^rwrh:raSe:^y^wn(pa«e542) thev^a^^
both with the size and the distance of an object Knowing
that two objects are at the same distance from the eye, we esti-
ml thatXone is krger than the other when the image one
To^B on the retina is larger, or when the visual a^te it sub-
tPT.ds is irreater than in the other case, and conversely. Thus.
St togTaTtwo persons ar^ at the distance of half a mile
^y,7one is judJTby us to be smaller than the oth<^t
wm be because the retinal image correspondmg to the object
telu^eTother things l«ing equal. But the subje^ i. more
complex than might be inferred from these -^tementa

Objects of a certain color seem nearer than others; also those
that are brighter, as in the case of mountains on a clear day.
^d J^t X^ all the quaUties of the image it»elf enter as
d^ toto r^nstruction of the judgment, but numerous mus-
fSSrslation.. The eyes accommodating and conve^ng for
near objects, from the law of association, give nse to the idea of
^^r^e^f 0^ habitually such Udces place wh^««r ob^te «e
viewed so that the subject becomes very complex. THat we
>d^im%ifectlyof the position of an object with b^e^e
LrSiJon attempting to stick a pin into a ^^^tam s,r^^
thread a needle, cork a small bottie, et«., when o^ejy*"^*^
8dlldity.-By the use of one eye alone we can form an idea
of Z^ve of a solid body ; though, in the case of such as a«»
yJ^conS^, this process is felt to be both laborious and im-

^^m the limit«d natu«» of the visual fleW^^ *°'Jf^
yision, it follows that we can not with one eye «»«l«»Uy ^
r^; all th. parts of a solid that is tum^ ^^^^^^^Z
rS practiJrone may learn t» define for himself what he

•^SSi f^g^* « «u^ following results from the c^W
tio^ immtozg, of two others, which answer t» the images f all-
inir on the right and on the left eye respectively. ___,,^
^iro^eTLt such fusion shall take Pj^-^tT^ 2J
images must fall on identical (corresponding) parts of the

'^- is well known, the pictim- used ^r jtereos«>pBs ^
diffeint views of the one object, as represented on a flat sur-

hjeott.— The pro-
e and distanoe of

inial angle Taries
>bjeot. Knowing
a the eye, we esti-
sn the image one
Bual angle it sub-
onvereely. Thus,
ce of half a mile
than the other, it
ling to the object
le subject is more
atementfl.
others; also those
18 on a dear day.
tage itself enter as
>ut numerous mus-
ind converging for
e rise to the idea of
en near objects are
iomplex. That we
Bt with but one eye
, certain small spot,
n one eye is closed,
e can form an idea
case of such as are
I laborious and im-

1 field for distinct
eye see equally dis-
i toward us. After
or himself what he

from the combinar
to the images f adl-

ively.

place, the respectiTe

iding) parts of the

or stereoscopes give
ented on a flat sur-

VISION.

649

face. These are thrown upon corresponding points of the retina
by the use either of prisms or mirrors, when the idea Of solidity
is produced. As to whether movements of the eyes (conver-
gence) are necessary for stereoscopic vision is disputed. It has

Fio. SW.-ninrtniteii blnrtcnlar Tlrion. If the trnncated pjrrMiiM, P, be looked at
with the head held Derpendlcularly oyer the fljnire, the Imaae formed in Uie right
eye when the left b clowid la Sgnred on the rlghvand that wonwhe" »• "£«»
eye is doaed la repreaented by the flpire in the midiUa. No anperiweition of theae
Iteniea will give P, yet by tLpytchU procrH thejr ai« combined into P, th« flgnie
aa It appeara to both eyea (after Bematein). *

been inferred, from the fact that objects appear solid during
an electric flash, the duration of which is far too short to per-
mit of movements of the ocular muscles, that such movements
are not essential. The truth seems to lie midway ; for while
simple flgures may not require them, the more complex do, or,
at all events, the judgment is very greatly assisted thereby. It
is of the utmost importance to bear in mind that all visual
judgments are the result of many processes, in which, not the
sense of vision alone, but others, are concerned; and the mutual
dependence of one sense on another is great, probably beyond
our powers to estimate. Reference has been made to this sub-
ject previously.

P&OTBOTXVB MBOBAMIBMS OF IBB BTIk

The eyelids have been appropriately compared to the shut-
ters of a window. They are, however, not impervious to light,
as any one may convince himself by noticing that he can locate
the position of a bright light with the eyes shut; also that a
sensitive person (child) will turn away (reflexly) from a light
when deeping if it be suddenly brought near the head. The
Meibomian glands, a modification of the sebaceous, secrete an
oily substance that seems to protect the lids i^inst the lachry-
mal fluid, and prevents the latter running over their edges as
oil would on the margms of a vessel. The lachrymal gland is

-, ^..^.^^..WiiiSN^-.' j>rilk I'SH

650

UOMPABATIVE PUYSIOLOOT.

not in structure unlike the parutid, the aeoretion of which its
own somewhat resembles.

The saltness of the tears, owing to abundance of sodium
chloride, is well known to all. The nervous mechanism of se*
oretion of tears is usually reflex, the stimulus coming from the
action of the air against the eyeball or from partial desiccation
owing to evaporation. When the eyeball itself, or the nose, is
irritated, the afferent nerves are the branches of the fifth, to
which also belong the efferent nerves. The latter include alsof
the cervical sympathetic. But it will, of course, be understood
that the alferent impulses may be derived through a large num-
ber of nerves, and that the secreting center may be acted upon
directly by the cerebrum (emotions). The excess of lachrymal
secretion is carried away by the na^al duct into which the lach-
rymal canals empty. While it is well known that closure of the
lids by the orbicularis muscle favors the removal of the fluid, the
method by which the latter is accomplished is not agreed upon.
Some believe that the closure of the lids forces the fluid on
through the tubes, when they suck in a fresh quantity ; others that
the orbicularis drives the fluid directly through the tubes, kept
open by muscular arrangements ; and there are several other
divergent opinions. The prevention of winking leads to irrita-
tion of the eye, which may assume a. serious character, so that

the obvious use of the secretion of tears
is to keep the eye both moist and clean.
Though rudimentary in man, there
is in all our domestic animals a third
eyelid (membrana nietitatu) which
may be made to sweep over the eye
and thus cleanse it. It is especially
well developed in those groups of
mammals that can not derive assist-
ance in wiping the eyes from their fore-
limbs, hence is found in perfection in
solipeds and ruminants. It is made up
of a flbro- cartilage, prismatic at its
base, and thus anteriorly where it is
covered by the conjunctiva. It is most
attached at the inner canthus of the
eye, from which region it can spread
over the whole globe anteriorly. The flbroH»rtilage is con-
tinued backward by a fatty cudiion which is loosely attached

Via. 888.— Laehiyiiwl canal*,
lachnrmai aac, and naaal
canal in man opened from
the fhmt (after Bappejr.).

ion of which ito

iance of sodium
neohaniBm of se-
ooming from the
lartial deaiocation
f , or Uie noae, is
of the fifth, to
atter include also
rae, be undenrtood
>ugh a large num-
nay be acted upon
cceas of lachrymal
to which the lach-
that domire of the
ral of the fluid, the
a not agreed upon,
oroes the fluid on
lantity ; others that
;h the tubes, kept
are several other
:ing leads to irrita-
character, so that
^e secretion of tears
>th moist and clean.
Btary in man, there
itio animals a third
nietitana) which
«reep over the eye
t. It is especially
1 those groups of
1 not derive assist-
)yes from their fore-
ad in perfection in
ants. It is made up
;e, prismatic at its
eriorly where it is
junctiva. It is most
ner canthus of the
igion it can spread
ro-cartilage is con-
. is loosely attached

VISION.

551

to all the ocular muscles. When the globe of the eye is with*
drawn by its muscles, the third eyelid is pushed out in a me-
chanical way with little or no direct assistance from muscles.

In this connection may also be mentioned the gland of
Harder, a yellowish red glandular structure situated about the
middle of the outer surface of the third eyelid, which furnishes
a thick unctuous secretion, also of a protective character. These
structures are all the more necessary, as in few animals is the
globe of the eye so well protected by bony walls as in man.

tPHOIAL UOMBUmtmOlffSi

CompantiTe.— It seems to be established that some anima)s
devoid of eyes, as certain myriopods, are able to perceive the
presence of light, even when tiie heat-rays are cut off. The most
rudimentary beginning of a visual apparatus appears to be a
mass of pigment with a nerve attached, as in certain worms ;
though it is questionable whether mere collections of pigment
without nerves may not in some instances represent still earlier
rudiments of our eyes.

The eye of the Ash is characterized by flatness of the cornea;
spherical form of the len8,'the anterior surface of which pro-
jecto far beyond the pupillary opening ; the presence of a pro-
cess of the choroid (proeesauafedciformia) ; and usually the ab-
sence of eyelids, the cornea being covered with transparent skin.

The eye of the bird, in some respects the most perfect ^ual
organ known, is of peculiar shape as a whole, presenting a large
posterior surface for retinal expansion ; a very convex cornea,
a highly developed lens, an extremely movable iris ; ^elids
and a nictitating membrane (third eyelid), which may be made
to cover the whole of the exposed part of the eye, and thus
shield screen-like from excess of light ; ossiflcations of the scle-
rotic ; a structure which is a peculiar modification of the
choroid, of which it is a sort of oflidioot and like it very vascular,
answering to the falciform process of the eye of the fltah and the
reptile. From its appearance it is termed thi^pecf en. Birds, on
account of a highly developed ciliary mua ^> ^jossess wonderful
powers of accommodation, rendered impoicU ui on account of
their rapid mode of pro g r e s s ion. They also deem to be able to
alter the size of the pupil at will. Their iris is composed of
striped muscular fibers.

A layer of fibrous tissue outside of the choroidal epithelium

.#<

669

COMPARATIVE PHYSIOLOGY.

forms the tapetum. It is most pronounced in the carnivom
and givee the glare to their eyee aa well Been in the oat tribe at
night It has been supposed to act as a reflector and thus
assist in vision in the same way as a pair of carriage lamps
light up the roadway.

Bvolnliai.— From the above brief aocQunt of the eye in dif-
ferent grades of animals, it will ap-
pear that its modifications answer to
differences in the environment

Adaptation is evident Darwin
believes this to have been efTeoted
partly by natural selection— i. e., the
■urvival of the animal in which the
form of eye appeared best adapted to
its needs— and partly by the use or
disuse of certain parts.

The latter is illustrated by the
blind fishes, insects, etc., of certain
caves, a' those of Kentucky; and it
Fi« wo -Bye of Boctamai bird is of extreme interest to note that
i?«'M?ir»; various grades of IransitiontoWMd
p.nectOTi; Ab.optfcnenre;^, complete blindneds are observable,
^cmi"^mll.ct' BW.iSS?i according to the degree of darkness
Hf'iKm&o'CK: in which the animal Uves, whether
trerne mobility of the iru. wholly within the cave or where
there is still some light A crab has been found witfi the eye-
stalk still present, but th« eye itself atrophied. Again, ani-
mals that burrow seem to be in process of losing their eyes,
through inflammation from obvious causes; and some of them,
as the moles, have the eye stiU existing, tiiough wdl-nigh or
wholly covered with skin. Internal parasites are often witii-
out eyes. It is not difficult to understand how one bu^ of prey,
with eves superior to tiiose of xi» fellows, would giun supremacy,
and, i^ periods of scarcity, survive and leave offspnng when

others would perish. v v-i. «i.a

It is, of course, impossible to t«we each st«p by which the
vertebrate eye has been developed from more ™dinientory
forms, though the data for such an attempt l»v»K^wy*?f""
mulated within the last few years; and it is not to be forgotten
Ouit even tiie vertebrate eye has many imperfections, so that
no doctrine of complete adaptation, according to the argument
from design as usually understood, can apply.

in the oamivoni
a the oat tribe at
ifleotor and thut
f carriage lampe

of the eye in dif-
limalB, it will ap-
oationi answer to
nvironment.
evident. Darwin
ve been effected
election— i. e., the
imal in which the
ed beat adapted to
tly by the use or
urtR.

lliutrated by the
la, etc., of certain
Kentucky; and it
nreat to note that
iranaition toward
B are oboerrable,
legree of darkness
nal lives, whether
le cave or where
lund with the eye-
tiied. Agaui, ani-
losing their eyes,
and some of them,
ough well-nigh or
ea are often with-
w one bird of prey,
Id gain supremacy,
ve offspring' when

step by which the
more rudimentary
have greatly aocu-
Qot to be forgotten
perfections, so that
g to the argument

VISION.

658

It is of great importance to recognise that what we really
see depends more upon the brain and the mind than the eye.
If any one will observe how frequent are his incipient errors
of vision speedily corrected, he will realise the truth of the

Bmnabove

--OofHeoJ emtrt

CetUrt In optit UMfamw

Omtrt In rtaton of- .
«i»rp- vaOriQimtna

BMna

Fis. 400.— Otaitniiii intended to lllnitrite the elabontlon of ylnul tin|mlM«, beslnnlnB
In ntina and culmlmtinK In the eerebiml cortex. Ooane of Impaleet It inaio*t«a
by arrowi. Knuwledfte of waMimj centen )■ not yet exact enough to pennit of
tfe eomtnctlon of a diantram, though donbtl«H eyentnally the central proeeMea
will be localiaed aa with vision. The httter remark H>pliM to the other teniea to
~ "irly the aame extent, posaibly qalte aa mnch.

above remark. Precisely the same data furnished by the eye
are in one mind worked up in virtue of past experience (edu-
cation) into an elaborate conception, while to another they an-
swer only to certain vague forms and colors. And herein lies
the great superiority of man's vision over that of all other
animals.

Within the limits of their mental vision do all creatures see.
Man has not the keen ocular discriminating poorer of the hawk;
he can neither see so far nor so dearly; nor has he the wide
field of vision of the gaselle; hut he has the mental resource
which enables him to make more out of the materials with
which his eyes famish him. It is by virtue of his higher cere-
bral development that he has added to his natural eyes others

,■'<

".!»,"?i««!

msr

COMPARATIVB PHTSIOLOOY.

in the mioroaoope and telescope, which none of Nature's fomu
can approacli.

PsthidOfiAftL— There may be ulceration uf the cornea, iu'
flammation of thia part, or various other dimrdem which lead
to opacity. The low vitality of this region, probably owing to
absence of blood-vessels, is evidenced by tho slowness with
which small tilcers heal. Opacity of the lens (cataract) when
complete caustm blindness, which can be ouly partially reme-
died by removal uf the former. Inflammations of any part of
the eye are serious, from possible adhesions, opacities, etc., fol-
lowing. Should such be accompanied by great excess of intra-
ocular tension, serious damage to the retina may result. Of
course, atrophy of the optic nerve (due to lesions in the brain,
etc.) is irremediable, and involves blindness. Inspection of the
internal parts of the eye (fundus oculi) often reveals the first
evidence of disease in remote parts as the kidneys.

From what has been said of the movements of the two eyes
in harmony, etc., the student might be led to infer that disease
of one organ, in consequence of an evident close connection of
the nervous mechanism of the eyes, would be likely to set up
a corresponding condition in the other unless speedily checked.
Buoh is the case, and is at once instructive and of great practi-
cal moment.

Paralysis of the various ocular muscles leads to squinting,
as already noticed.

Brtef Synopiii of the Fhyilologj of Yiiion.— All the other
parts of the eye may be said to exist for the retina, since all are
related to the formation of a dirtinct image on this nervous ex-
pansion. The principal refractive body is the crystalline lens.
The iris serves to regulate the quantity of light admitted to tha
eye, and to cut off too divergent rays. In order that objects at
different distances may be seen distinctly, the lens alters in
shape in response to the actions of the ciliary muscle on the
suspensory ligament, the anterior surface becoming more con-
vex. Accommodation is associated with convergence of the
visual axes and contraction of the pupil. The latter has circular
and radiating plain muscular fibers (striped in birds, that seem
to be able to alter the sixe of the pupil at will), governed by the
third, fifth, and sympathetic nerves. Contraction of the pupil
is a reflex act, the nervous center lying in the front part of the
floor of the aqueduct of Sylvius, while the action of the other
center (near this one) through the sympathetic nerve is tonic.

>f Nature*! fomu

»f the cornea, in-
nlera which lead
urobably owing to
■lowneM with
» (cataract) when
partially reine-
lu of any part of
opacitiea, etc., fol-
at exuees of intra-
a may result. Of
■ions in the brain.
Inspection of the
n reveals the first
neys.

its of the two eyes
o infer that disease
;lose connection of
be likely to set up
IS speedily cheeked,
and of great practi-

leads to squinting,

rion.— All the oiiher
retina, since all are
on this nervous ex-
bhe crjrstalline lens,
ight admitted to the
irder that objects at
■, the lens alters in
iliary muscle on the
>ecoming more con-
convergence of the
he latter has circular
d in birds, that seem
ill), governed by the
traction of the pupil
the front part of the
le action of the other
letic nerve is tonio.

VISION.

666

Accommodation through the ciliary muscle is governed by
a center situated in the hind part of the floor of the third ven-
tricle near the anterior bundles of the third nerve, which latter
is the medium of the change. When rays of light ure focused
anterior to the retina, the eye is myopic; when posterior to it,
liyperuietntpic.

The presbyopic eye is one in which the mechanism of accom-
modation is at fault, chiefly the ciliary muscle. The point of
entrance of the optic nerve (blind-spot) is insensible to light;
and visual impulses can be shown to originate in the layers of
rods and cones, probably through stimulation from chemical
changes effected by light acting on the retina. The sensation
outlasts the stimulus; hence positive after-images occur. Nega-
tive after-images occur in consequence of excessive stimulation
and exhaustion of the retina, or disorder of the chemical pro-
cesses that excite visual impulses. When stimuli succeed one
another with a certain degree of rapidity, sensation is continu.
ous. The eye can distinguish degrees of light within certain
limits, varying by about y^ of the total.

Objects become fused or are seen as one when the rays
from them falling on the retina approximate too closely on
that surface. The brain, as well as the eye itself, is concerned
in such discriminations, the former probably more tiiaa the
latter.

The macula lutea, and especially ihe fovea centralis, aro in
man the points of greatest retinal sensitiveness. When the
images of objects are thrown on these parts, they are seen with
complete distinctness; and it is to effect this result that the
movements of the two eyes in concert take place. An object is
seen as one when the position of the eyes (visual axes) is such
that the images formed fall on corresponding parts of the retina.
Binocular vision is necessary to supply the sensory data for the
idea of solidity. It is important to remember that, before an ob-
ject is "seen" at all, the sensory impreesions furnished by the
retina and conveyed inward by the optic nerve are elaborated in
the brain and brought under the cognizance of the perceiving
ego. We recognize many visual illusions and imperfections
of various kinds, the course of which it is difficult to locate
in any one part of the visual tract, such as are referred to
"irradiation," "contrast," etc. There may also be visual phe-
nomena that are purely subjective, and others that result from
suggestion rather than any definite sensory basis of retinal

556 COMPARATIVE PHYSIOLOGY.

images. Hence what one sees depends on his state of mind at

*^^Sapplies to appreciation of nse and distance also, though
in such cases we have the visual angle, certain ^^^^''Z
mente (muscular sense), the strain of accommodation etc., aa

guides.

B state of mind at

banco also, though
a muscular move-
imodation etc., as

HEARING.

As the end organ ol vision is protected both without and
within, so is the still more complicated end-prgan of the sense
of hearing more perfectly guarded against injury, bemg m-
closed within a membranous as well as bony covering and sur-
rounded by fluid, which must shield it from stimulation, except
through this medium.

Hearing proper, as distinguished from the mere recognition
of ia» to the tissues, can, in fact, only be attained through the
immilses conveyed to the auditory brain-centers, as originated
in tiie end-organ by the vibrations of the fluid with which It 18

It ^ be assumed that the student has made hunself famU-
iar witii the general anatomy of the ear. The essential points
in regard to sound are considered in the chapter on The
Voice: It wUl be remembered that what we term a musical
tone, as distinguished from a nois«, is characterised by the
regularity of vibrations of the air that reach the ear; and that
just as ethereal vibrations of a certain wave-length give nse to
the sensation of a particular color, so do aSnal vibrations of a
definite wave-length origuiate a certain tone. In each awe
must we take into account a physical cause for the physiological
effect, and these bear a very exact reUtionship to one another.

As will be seen later, whUe in aU animals that have a weU-
defined sense of hearing the process is essentiaUy such as we
have indicated above, the means leading up to the final straiu-
ktion of the end-organ are very various. At present we shall
consider the acoustic mechanism in mammals, witii special ref-
erence to man. There are in fact three seta of appamtas : (1)
one for collecting the aSrial vibrations; (2) one for teansmit-
ting them; and (3) one for receiving the impression throi^h a
fluid medium; in other words, an external, middle, and in-
ternal ear.

658

COMPARATIVE PHYSIOLOGY.

The external ear in man being practically immovable, owing
to the feeble development of its muscles, has, as compared \7ith

biiwch of tame.

such anunals as the horse or cow, but little use as a ooUecting
organ for the vibmtions of the air. The meatus or auditory
cSal may be regarded both as a conductor of vibrabOM and
Tprotective tTSTmiddle ear, especially the deUcate dnjm-
head, since it is provided with hairs externally m particular,
andwith ghmds that secrete a bitter substance of an unctuous

"* The Xaalmiia Tjmpvii is concavo-convex in form, w^
having attached to it the chain of bones shortly to be nofaced,
is wen adapted to lake up the vibrations ^^f^'^^l^^^
from the air; though it also enters into sympathetic viteation
when the bones of the head are the medium, as -rtrhen a tuning-
fork is held between the teeth. Ordinary stretehed membnmw
have a fundamental (self-tone, proper tone) tone of their own,
to which they respond more readily than to others.

■■

■If

HEARING. 569

nmovable, owing

If such held for the membrana tympani, it is evident that

s compared \7ith

certain tones would be heard better than others, and that when

■ • ■ «. ' ■• '

<^^^^

,plniUi:»,4,6,Mvityof
i; ». long hMidie of inal-

V''" ''■'■■/• ''^^'^'^-^ y

-It is here repreeented as
icMTltr; 18, BiMtaclUaii
bticDlar canal; lB,ezter-

V "^'' ' :"- '*'■■ J^

\ '.,' ^'""- .;."''' ■ '■'* _^r

W J!r

;'. '

meatas: IS, facial nerve;

\ ^^

tory nerve; SI, cochlear

use as a oollectinj?

meatus or auditory

withiii SftarfSStud ^iMdinnr). 1, dhrtSbd hMd of niallea«;'a^k; 8, handle,
with attachment of tendon oflenaor tynqianl: 4, divided tendon; 6,0, long handle

r of -vibratioiui and

the delicate drutn-

of nalleai: 7, outer radiating and inner dreolar fiber* of trmpanlc membrane; 8,
flbioas ring encircling membrana tvmpanl; a, 14, IS, dentated iben of Omber; 10;
11, poaterlor pocket connecting with malleaa; U, anterior pocket; 18, chorda qrm-
panl nerve.

lally in particular.

ace of an unctuous

the fundamental one was produced the result might be a sensa-

ivex in form, and

tion unpleasant from its intensity. This is partially obviated

Drily to be noticed.

by the damping e£Fect of the auditory oasioles, which also pre-

ommunicated to it

vent after-vibrations.

ipathetio vibration

Some suppose that what we denominate shrill or harsh

as When a tuning-

sounds are, in part at least, owing to the auditory meatus hav-

etched membranes

ing a oomsponding fundamental note of its own.

tone of their own,

The AvflitOfJ OMidas.— Though these small bones are con-

:■

others.

xMOted by perfect j<nntB, permittuig a certain amount of play

560

COMPARATIVE PHYSIOLOGY.

upon one another, experiment has shown that they vibrate in
i^ponse to the movements of the drum-head en maaae ; though
the stapes has by no means the range of movement of the hiui-
dle of the maUeus; in other words, there is low m amplitude,

Tf.« iML-Secttoii of MdltoTTonnm of horte (after ChwiTewi). A, »™Jm^ii^^
If, commeucement of wata tjmpuu.

but gain in intensity A ghmce at Pig. 404 wiU show that the
end attamed by this arrangement of membrane and bony levers,
which may be virtually reduced to one (as it is in Iji© frog, etc.),
is the transmission of the vibrations to the membrane of the
fenestra ovalis, through the stapes finally, and so to the fluids
within the internal ear. But it might be supposed that, for the
avoidance of shocks and the better adaptation of the apparatus

they vibrate in
masse; though
aent of the hau-
ls in amplitude,

«n). 3, ■uuiwj ji»u»y

s; O, muioid celli; B,
(dar ouwia; M, cochlea;

trill show that the
le and bony leyen,

ismiihefrogt«to')t
I membrane of the.
und so to the fluids
tposed that, for the
in of the apparatua

HEARING.

561

to its work, some regulative apparatxis, in the form of a nerv-
ous and muscular mechanism, would have been evolved in the

>rr

wMmIs, tympunm; Z'meinbnui* t]nniMaii:'B,'Bi»tacUati «»^; «•»«»**;'"
cells: 10, foimmen totandnm: 11, foramen oraie; 18, veatlbale; IS, cochlea; H,
ecala tympant; 15, icala Teetibnll; ID, aemicirenlar canala.
N B.— The ewia ao complicated an organ that it la almoat impoasible to gire a dia-
gimmmatlc represenution of It at once simple and onmpls*'",*,''^ ?£}?•
X comparison of the whole series of cnU is therefore deairaUe. tt is essential to
ondeistand how the end-oigan within the seala media la stimnlated.

higher groups of animals. Such is found in the tensor tym-
pani, laxator tympani, and stapedius muscles, as well as the
Eustachian tube.

MmdM of the Middle Bur.— The tensor tympani regulates
the degree of tension of the drum-head, and hence its ampli-
tude of vibration, having a damping effect, and thus preventing
the ill results of very loud sounds.

Ordinarily, this is, doubtless, a reflex act, in which the fifth
is usually the afferent nerve concerned. It is well-known that,
when we are aware that an explosion is about to take place, we
ai« not as much affected by it, which would seem to argue a
voluntary power of accommodation ; but of this we must speak
with caution.

According to some authorities the tooMxeor tympani is not a

562

COMPARATIVE PHYSIOLOGY.

muscle, but a supporting ligament for the malleus. The stape-
dius, however, has the important function of regulating the
movements of the stapes, so that it shall not be too violently
driven against the membrane covering the fenestra ovalis.

The two muscles, stapedius and tensor, suggest the accom-
modative mechanism of the iris. The motor nerve of the sta-
pedius is derived from the facial; of the tensor, from the tri-
geminus through the otic ganglion.

The ButaohUui Tube.— Manifestly, if the middle ear were
closed permanently, its air would gradually be absorbed. The
drum-head would be thrust in by atmospheric pressure, and
become useless for its vibrating function. The Eustachian
tube, by communicating with the throat, keeps the external and
internal pressure of the middle ear balanced. Whether this
canal is permaneutiy open, or only during swallowing, is as yet
undetei*mined.

Fio

, ««.— Diagmm inteBdcd to lUmtnte the procMMS of heiirinff (after IfndoW ■ AO,
exfenid auditory meatn*; T, tympanic "wi"**"*: «i,««^«! «• *5»2^fv2Sl
die oar: o. fenestra ovalta; r, feneetra rotni^; »f,,ecaja tympanl; ««. •«»»»••»•
bull; tveeUbnle; S,-ein\ex R utricle; i?, lymlclren to crtwe;r^Bajtochto
tube, long arrow Indicate* line of traction of tenww tympani; abort cnrred one
tbat of Stapedina.

One may satisfy himself that the middle ear and pharynx
communicate, by closing the nostrils and then distending the
upper air-passages by a forced expiratory effort, when a sense
of distention within the ears is experienced, owing to the rise
of atmospheric pressure in the tympanum.

HEARINO.

568

eiM. The gtape-
{ regulating the
be too violently
estra ovalis.
ggeat the accom-
nerve of the sta-
9or, from the tri-

middle ear were
e absorbed. The '
ric pressure, and
The Eustachian
I the external and
i. Whether this
dlowing, is as yet

ineCafterLMidola) AO,
lalTeaa; a, incns; P, mid-
tympani; at, icala vMtl-
rcanaU; rj?, Bnatachhm
inpltni; short enrred one

I ear and pharynx
len distending the
Fort, when a sense
, owing to the rise

Fia. 406.— Section throogh one of the coili of cochlea (after Chanveau). 8T, acala tym-
panl; 8V, acala vestlbnli; CC, cochlear canal (acala media); Co, organ of Corti;
Ji, membrane of Relaaner; b, membrana baailaria; bo, lamina apiralla oaaea; /,
membrana tectoria; 1, », roda of Corti; ne, cochlear nerve with ita ganglion, gi.

PathiOlogioal. — Inflammation of the tympanum may result
in adhesions of the small bones to other parts or to each other,

^ <5r»-^

Fio. 407.— I. Tranarerae aectlon of a tnm of cochlea. 11. Ampnlht of a aemlclrcniar
oanal and Ita crlata aconatica; op, auditory cella, one of which la a hahr-cell. III.
DiaRram <rf labyrinth of man. rV. Of bird. V. Of flah. (After Landola.)

COMPARATIVE PHYSIOLOGY.

na.40».

nwui labyftith and cochlea (after Huxley).

1.410.

Mccnle at alligator, mw«
', «ber cell*; «, nerve-llber
olniniiar auditory ceiii; A,

brita. . ._

auditory nerve In memora-

HEARING.

56S

or to occlusion of the Eustachian tube from excess of secretion,
cicatrices, etc., in consequence of which the relations of atmos-
pheric pressure become altered, the membrana tympani being
indrawn, and the whole series of conditions on which the nor-
mal transmission of vibrations depends disturbed, with the
natural result, partial deafness. The hardness of hearing ex-
perienced during a severe cold in the hettd (catarrh, etc.) is
owing in great part to the ooolusion of the Eustachian tube,
which may be either partial or complete.

By filling one or both of the ears external to the mem-
brana tympani with cotton-wool, one may satisfy himself how
essential for hearing is the vibratory mechanism, which is, of
course, under such circumstances inactive or nearly so; hence
the deafness.

When the middle ear is not functionally active, it is still
possible, so long as the auditory nerve is normal, to hear vibra-
tions of a body (as a tuning-fork) held against the head;
though, as would be expected, discrimination as to pitch is
very imperfect.

Auditory impulaea originate within the inner ear— that is
to say, in the vestibule and possibly the semicircular canals,
but especially in the cochletu It is to be remembered that the

Fis. 411.— Diagram intended to illuitrate relative position of variona parts of ear (after
Huxley). E, M, external auditory meatus; 3\, M, tympanic membrane; TV. tym-
panum; Mall, malleus; Ine, incus; Stp, stapes: F.o, fenestra avails; F.r, fenes-
tra rotunda; Eu, Eustachian tube; Jr. Z, membranous labyrinth, only one of the
semicircular canals and Its ampulla being represented; Sea. V, Sea. T, Sea. M,
scalM of cochlea, represented as straight (uncoiled).

666

COMPARATIVE PHYSIOLOGY.

whole of the end-organ concerned in hearing it bathed by endo-
lymph : and that the vibrationa of the latter are originated by
oorreaponding vibration* of the perilymph, which again it sent

i diamm of labrrinth (aftar Hint aod Mdlngw). TTpper flg-

Moenie; a,B, menibnuioat ooehlM; 4, cwmII* nanieiM; 6, teml-

Lower flsim: 1, atfleto; a, Meenle; 8,4,11, wnpnllv; 5,7,8.0,

adltoiT ■ " "

Tio. 411.-1

nn: 1, atricic;

CifCnlSr CftlUUI. Mvnor lunuv. J, Htciviv^ «, aHwuiv^ o,«,v, awimai^, w, f.i7. v,

•emiclreoliur canala; 10, Mdltoiy wn« (pMtly dUgmnnatle); 11. IS, IS, 14, 15, diS'
tribotion of bniMhw of narre to Taatlbol* and aemleUeolar canala,

into 08cillati(«i by the movements of the stapes against the
membrane covering the fenestra ovalis; so that the vibrations
thus set up- without the membranous labjrrinth are trans-
formed into similar ones within the vestibule and the scala
vestibuli, and end, after passing over the scala tympani, against
the membrane of the fenestra rotunda. The cochlear canal
may be regarded as the seat of the most important part of the

:■■

is bathed by endo-
are originated by
hioh again is sent

HEARING.

667

organ of hearing, and answers to the macula lutea of the eye
in many respects.

The function of the organ of Corti is unknown.

The structure of the ampullee of the semicircular canals,
and other parts of the labyrinth besides those specially con-

Fio. 41S.— DUtribntlon of cochlear nenre In iplral Umlm of utwo-lnferior part of
cochiM of rlsht ew (after Bappnr). 1, tmnk of cochlea nenre; 8, membranous
sone of aplral lamina; 8. tarmlnarexpanalon of cochlear nerve expoeed throiish-
ont by removal of rapenor plate of lamina ■piralli; 4, onflce of commanlcatlon
between icala tjrmpanl and tcala veetibnll.

sidered, with their peculiar haiiH^lls, suggests an auditory
function ; but what that may be is as yet quite undetermined.
It has been thought that the parts, other than the cochlea, are
concerned with the appreciation of noise, or perhaps the in-
tensity of sounds ; but this is a matter of pure speculation.

and BMIngei}. Upper IIk-
4. eanalie reonlwa; «.•«««]•

leoliur canaU.

e stapes against the
a that the vibrations
labyrinth are trans-
»bule and the scala
cala tympani, agunst
The cochlear canal
nportant part of the

▲uxnroRT smraATioNS, pbrobftions, amd

JUDOMBim.

We have thus far been concerned with the conduction of
the aSrial vibrations that are the physical cause of hearing ;
but before we can claim to have " heard " a word in the highest
sense, certain processes, some of them physiological and some
psychical, take place, as in the case of vision-; hence we may
speak of the aflbotion of the end-organ or of auditory impulses,
and of the processes by which these become, by the mediation
of the brain, auditory sensations, and when brought under the
cognizance of the mind as auditory perceptions and judg-
ments.

a j itertft W MD WHiiwweg-.-

ft68

COMPARATIVE PIIYSIOLOOV.

Aoditorj Jtidfmuits.— 8uoh are much mora fraquenUy trro-
neous than ore our vUiuil judgmenta, whether the direction or
the distance of the lound be considered. As in the cose of the
eye, the muscular sense, from accommodation of the ▼llwatory
mechanism, may assist our judgments, being aided by our
Htored post experiences (memory) according to the law of asso-
ciation. Sounds mn, however, always referred to the world
without us. The animals with movable ears greatly excel .Tian
in estimating the direction, if not the distance, of sounds. Tlere
on few physiological experiments more amusing thon tt.ose
performed on a person blindfolded, when attempting to deter-
mine either the distance or the direction of a sounding tuning-
fork, so gross are the errors made.

One who makes such observations on others may notice that
most persons move the ears slightly when attempting to make
the necessary discriminations, which of itself tends to show how
valuable mobility of these organs must be to those animals that
have it highly developed.

■PBOIAL OOMtDBRATIONf.

GompantiTe.— Among invertebrates steps of progressive de-
velopment can be traced. Thus, in certain of the jelly-flshes

we find an auditory vesicle (Fig.
414) inclosing fluid provided with
one or mora otoliths or calcareoxis
nodules and auditory cells with at-
tached cilia, the whole making up
an end-organ connected with the
auditory nerve. A not very dis-
similar arrangement of parts exists
in certain mollusks (Fig. 415). The
vesicle may lie on a ganglion of
the central nervous system. On
the other hand, the vesicle may be
open to the exterior, as in decapod
crustaceans ; and the otoliths be re-
placed by grains of sand from with-
out It is difficult to decide what

Fio. 4M.— Anditorr vMlcle of
onia {Carmarina) teen from I

■orfMe (pfter O. and R. Bert-

„ Br u. wia n. nor*- , ••.• » •

wigi. ifmA A', the andttpry the function of otoliths may be in
'i^'^nA^raWctm^ mammal. ; but there seems to be
tUX^S"'^ '^ litUe reason to doubt that they com-

IIKARINQ.

S69

frequently (
the direction or
[1 the case of the
of the vibratory
f aided by our
I the law of aaao-
ad to the world
reatly excel man
)fM)unda. TLere
iiing than tl-tose
tnpting to duter-
ounding tuning-

I may notice that
smpUng to make
tnda to show how
loee animal* that

ffl.

)f progrenive de-
>f the jelly-flshes
tory veeicle (Fig.
id provided with
iths or caloareoxu
tory oelLi with at-
nrhole making up
aneoted with the
A not very dis-
ent of parts ezista
n (Fig. 415). The
on a ganglion of
'ous system. On
he vesicle may be
rior, as in decapod
, the otoliths be re-
)f sand from with-
ilt to decide what
>toliths may be in
^ere seems to be
ubt that they com-

municate vii i-atlons in the invertebrates. When the oephal*
op«Kl molluBkB, with their highly developed nervous system,
are reached, we find a membranous and cartilaginous labyrinth.
Among mrtefyrates th«) different parts of the mammalian
ear are found in aJI stages of development. The outer ear may
be wholly vw^anting, as in the frog, or it may exist as a meatxu
only, as in b rds. The tym|»nic cavity is wanting in snakes.
Most fishes have u utricle and three ssmiciroular canals, but some

Pio. 415.— Andltorr veklcle of a heteropod mollnik (Pt*r«&aeheai)MtM CImi). JV.
•nditory nenre; Ot, otolith In fluid of vealcle; Wm, ciliated celli on Inner wall of
veeicle; Hi, Mdltonr celie; Cm, central cell*.

have only one ; and the lowest of this group have an ear not
greatly removed from the invertebrate type, as may be seen in
the lamprey, which has a saccule with auditory hairs and oto-
liths, in communication with two semicircular canals. Most
of the amphibia are without a membrana tympani. The frog
has (1) a membrana tympani communicating with the inner ear
by (2) a bony and cartilaginous lever (columella auri»\ and (8)
an inner ear consisting of three semicircular canals, a saccule
and utricle containing many otoliths, and a small dilatation of
the vestibule, which may indicate an undeveloped cochlea.
The membranous labyrinth is contained in a periotic capsule,
partly bony and partly cartilaginous, which is supplied with

670

COMPAEATIVB PHYSIOLOGY.

Fitt.

j'teffln'sK:ar^«ar.-!isw-"ir«^^ ^^sris

1, from goat; S, herriiig;
rp; 8, nj; », iWk; »,

O.C.

, In Kgioii of Wnd-bralji, to
i, hind-limin: N, •ndlwrjr
of cocUm: a. r, tecewM
m of •iidit«»7 nenre.

HEARINO.

571

perilymph. There is a fenestra oralis, but not a fenestra ro-
tunda, though the latter is present in reptiles. In crocodiles
and birds the cochlea is tubular, straight, and divided into a
Boala tympani and a scala vestibuli. The columella of lowe.'
forms still persists. In birds and mammals the bone back of
the ear is hollowed out to some extent and communicates with
the tympanum. Bxcept among the very lowest mammals
(Echidna), the ear is such as has been described in detail
already.

Xvolation.— The above brief description of the auditory organ
in different groups of the animal kingdom will suiflce to show
that there has been a progressive development or increasing
differentiation of structure, while the facts of physiology point
to a corresponding progress in function — in other words, there
has been an evolution. No doubt natural selection has played
a great part It has been suggested that this is illustrated by
cats, that can hear the high tones produced by mice, which
would be inaudible to most mammals ; and, as the very exist-
ence of such animals must depend on their detecting their prey,
it is possible to understand how this principle has iterated to
detennine even what cats shall survive. The author has noticed
that terrier dogs also have a very acute sense of hearing, and
they also kill rats, etc. But, unless it be denied that the im-
provement from use and the reveite can be inherited, this factor
must also be taken into the account

There seem to be great differences between hearing as it exists
in man and in lower forms. Birds, a&d at least some horses,
possibly some cats and dogs, like music, and give evidence of
the possession of a sense of rhythm, as evidenced by the conduct
of the steed of the soldier. On the other hand, some dogs seem to
greatly dislike music. Oertain animals that appear to be devoid
of true hearing, as spiders, are nevertheless sensitive to aSrial
vibrations ; whether by some special undiscovered organ or
through the general cutaneous or o&er kind of sensibility is
unknown. It also seems to be more than probable that some
groups of insects can hear sounds quite inaudible to us, though
by what organs is in great measure unknown. -

The so-called musical ear differs from the non-musical in
the ability to discriminate differences in pitch rather than in
quality; in fact, that one defective in the former power may
possess the latter in a high degree is a fact that has been some-
what lost sight of, both theoretically and practically. It does

. -MMWtWjmriB ft H i Wil W M

572

COMPARATIVE PHYSIOLOGY.

not at aU follow that one with UtUe capacity for tune may not
have the quaUflcations of ear requisite to ma -e a flrrt-rate elo-
cutionist Following custom, we have spoken as though certain
defects and their opposites depended on the ear, but m reality
we can not, in the case of man at aU events, afHrm that such la
the case; indeed, it seems, on the whole more likely that they
are cerebral or mental. Auditory discriminations seem to be
equally if not more susceptible of improvement by culture than
visual'ones, especially in the case of tiie young. i

A " good ear " seems to depend in no small degree on mem-
ory of sounds, tiiough the hitter may again have ite basiB in
the auditory end-organs or in the cerebral cortex, as concerned
in hearing. The nece«ity for the close connection between the
co-ordinations of the laryngeal apparatus in singing and speak-
ing and the ear might be inferred from the fact that many ex-
cellent musicians are tiiemselves unable to vocalise the music
they perfectiy appreciate.

Byiupiii of the PhyiioloKy of HMring— The ear can appre-
ciate differences in pitch, loudness, and quality of sounds,
though whether different parts of the inner ear are concerned in
these discriminations is unknown. Hearing is the result of a
series of processes, having their physical counterpart in aSri^
vibrations, which begin in the end-organ in the labyrinth and
terminate m the cerebral cortex. We recognize conducting
apparatus which is membranous, bony, and fluid. The auditory
nerve conveys tiie auditory impulses to tiie brain, though ex-
actty what terminal cells are concerned and how in originating
them must be regarded as undetermined. The essential part of
the organ of hearing is batiied by endolymph, and the princi-
pal part (in mammals) is within the cochlear canal. Man's
power to locate sounds is very imperfect. The auditory brain
center (or centers) has not been definitely located. OompMra-
tive anatomy and physiology point clearly to a progressive
development of the sense of hearing.

r tune may not
I a flnt-rate elo-
thougli certain
', but in reality
rm that such is
ikely that they
>n8 seem to be
by culture than

legiee on mem-
»ve its basis in
IX, as concerned
ion between the
ging and speak-
st that many ex-
caliie the music

le ear can appre-
Jity of soimds,
are concerned in
I the result of a
terpart in aBrial
le labyrinth and
'nize conducting
d. The auditory
train, though ex-
>w in originating
essential part of
1, and the princi-
tr canal. Man's
le auditory brain
ated. Oompara-
to a progressive

THE SENSES OP SMELL AND TASTE.

The nose internally may be divided into a respiratory and
an olfactory region. The latter, which corresponds, of course,
with the distribution of the olfactory nerve, embraces the upper
and part of the middle turbinated bone and the upper part of
the septum, all of which differ in microscopic structure from
the respiratory region. Among the ordinary cylindrical epi-
thelium of the olfactory region are found peculiar hairKsells
highly suggestive of those of the labyrinth of the ear, and

Flo. 418.— Farto eonoenwd in »imU (•fUr HinehfaM). I, idraetoijr gaaglioii and
nenre*; 9, braneli of naMd nerve, diatrilrated over the torbtawted bone*.

which are to be regarded as the end-organs of smell. If aromatic
bodies be held before the nose, and respiration suspended, they
will not be reoognised as such, and it is well known that sniff-

674

COMPARATIVE PHYSIOLOGY.

ing greatly assists the sense of smell. Again, if fluids, such as
eau de Cologne, be held in the nose, their aroma is not detected ;

and immediately after water has
been kept in the nostrils for a few
seconds, it may be noticed that
smell is greatly blunted. Such is
the case also when the mucous
membrane is much swollen from
a cold. There can be no doubt
that the presence of fluid in the
above cases is injurious lu the del-
icate hair<5ells, and that smell is
dependent upon the excitation of
these cells by extremely minute
particles emanating from aromatic
bodies.

When ammonia is held before

^ , the nose, a powerful sensation is

^'"•.4lV(K'l«llk«rwrolS experienced; but this is not smell

#__ \. .>nUhall«] mil of the *^ . . « .x< .« — .):

frog — a, epiaielW cell of the ,^_^,^^
olfMtory aria; 6. olfactory cell, proper,
illbri

oiractoryarea; o, o»«:«.r, «... r-r~M ^^ ^^ affection of Oldi-
Sf'f'S^.&t upKS75SS nary sensation, owing to rtimula-
of varicoM flbert. 8, olfactory ^q^ of the terminals Of the niui
ceiioftheep. ^^^^ It is possible that the audi-

tory nerve may also participate, though certainly not so as t»
produce a pure sensation of smelL

like the other sense-organs, that of smell is readily far
tigued ; and perhaps the satisfaction from smelling a bouquet
of mixed flowers is comparable to viewing the same, one scent
after anotiier being perceived, and no one remaining predomi-
nant. . 11 •
Our judgment of the position of bodies possessing smell is
less perfect even than for those emitting sounds: but we always
project our sensations into the outer world, never refemng the
object to the nose itself. Subjective sensations of smell are
rare in tiie normal subject, though common enough among
the diseased, as is complete or partial loss of smell. It has
been found that injury to the fifth nerve interferes with smell,
which is probably due to trophic changes in the olfactory

region. . .1. 1

Comparative.— The investigation of the senses m the lower
forms of life is extremely difficult, and in the lowest presents
almost insurmountable obstacles to the physiologist because

SENSES OP SMELL AND TASTE.

675

f fluids, such as
ia not detected;
after water has
ostrils for a few
t)e noticed that
iunted. Such is
en the mucous
;h swollen from
tn be no doubt
of fluid in the '
irious to the del-
nd that smell is
the excitation of
^tremely minute
ig from aromatic

ia is held before
rful sensation is
this is not smell
Section of ordi-
wingto stimula*
inals of the fifth
ible that the audi-
unly not so as to

»11 is readily fa-
nelling a bouquet
le same, one scent
maining predomi-

ossessing smell is
is; but we always
ever referring the
Hons of smell are
m enough among
of smell. It has
jrferes with smell,
I in the olfactory

lenses in the lower
be lowest presents
ysiologist because

their psychic life is so far removed from our own in terms of
which we must interpret, if at all.

The earliest form of olfactory organ appears to be a depres-
sion lined with special cells in connection with a nerve, which,
indeed, suggests the embryonic beginnings of the olfactory
organ in vertebrates, as an involution (pit) on the epithelium
of the head region. It would appear that we must believe that'
in some of the lower forms of invertebrates the senses of smell
and taste are blended, or possibly that a perception results
which is totally different from anything known to us. The
close relation of smell and taste, even in man, will be referred
to presently. There are, perhaps, greater individual differences
in sensitiveness of the nasal organ among mankind than of any
other of the sense-organs. Women usually have a much keener
peiception of odors than men. The sense of smell in the dog
is well known to be of extraordinary acuteness; but there are
not only great differences among the various breeds of dogs,
but among individuals of the same breeds; and this sense is
being constantly improved by a process of " artificial selection "
on the part of man, owing to the institution of field trials for •
setters and pointers, the best dogs for hunting (largely deter-
mined by the sense of smell) being used to breed from, to the
exclusion of the inferior in great part Our own power to
think in terms of smell is very feeble, and in this respect the
dog and kindred animals prabably have a world of their own
to no small extetit Their memory of smells is also immeasur-
ably better than our own. A dog has been known to detect an
old hat, the property of his master, that had been given away
two years before, as evidenced by his recovering it from a re-
mote place.

The importance of smell as a guide in the selection of food,
in detecting the presence of prey or of eneinies, etc., is very
obvious. By culture some persons have learned to distinguish
individuals by smell alone, like the dog, though to a less degree.

TABTB.

The tongue is provided with peculiar modifications of epi-
thelial cells, etc., known as papillae and taste-buds which may
be regarded as the end-organs of the glosso-pharyngeal and
lingual nerves; though that these all, especially the taste-buds,
are concerned with taste alone seems more than doubtful. In

fUmswawiMvif

576

COMPARATIVE PHYSIOLOGY.

certain animaU with rough tongues, the papillae, certain of
them at leaat, answer to the hairs of a brush for the cleansing
and general preservation of the coat of the animal in good con-
dition. We may, perhaps, speak of certain fundamental taste-
perceptions, such as sweet, bitter, acid, and saline. Certainly
the natun^ power of gustatory discrimination is considerable;

Fi«. 4«0.-P»plll» of tongue (after JSappey). 1. clrcnmvallato p«pHl»; 8, ftinglfotm
IM^lil*; l lUlfonn pojui"; «. g>»n4» at baae of tongue; 7, ton«U».

and. as in the case of tea-tasters, capable of extraordinary culti-
vation. All parts of the tongue are not equally sensitive, nor

•t j(»' W«-»"W»t-

te papUlK; 8, tangiform
r, tonsils.

ctraordinary culti-
lally aenntiye, nor

SENSES OF SMELL AND TASTE.

677

is tasteHMuaation confined entirely to the tongue. It can be
shown that the back edges and tip of the tongue, the soft palate,
the anterior pillars of the fauces, and a limited portion of the
back part of the hard palate, are concerned in tasting. Making
allowances for individual diflferences, it may be said that the
back of the tongue appreciates best bitter substances, the tip,
sweet ones, and the edges acids.

If any substance with a decided taste be placed upon the
tongue when wiped quite dry, it can not be tasted at all, show-
ing that solution is essential.

If a piece of apple, another of potato, and a third of onion,
be placed upon the tongue of a person blindfolded, and with
the nostrils closed, he will not be able to distinguish them,
showing that the senses of smell and of taste are related ; or,
perhaps, it may be said that much that we call tasting is in
large part smelling. When the electrodes from a battery are
placed on the tongue, a sensation of taste is aroused, described
differently by different persons; also when the tongue is quick-
ly tapped, showing that, though taste is usually the result of
chemical stimulation, it may be excited by such as are electrical
or mechanical.

But it is not to be forgotten that we have usually no pure
gustatory sensations, but that these are necessarily blended

Fia.4ai.

Fio. 411.— Hedinm-slsed elrcimiTallate papilla (after
Fie. 419.— Various kinds of p^Uto (aftiw Sappej). 1,
7, hemispherical papili«.

Fio: 4*11.

in^fbnn; 1,8,4,6, A, flUfOfm;

with those of common sensation, temperature, etc., and that our
judgments must, in the nature of the case, be based upon highly
VI

578 COMPARATIVE PHYSIOLOGY.

complex data, even leaving out of account other wnMi, «uoh as

vision. , * ii. u 1 »

The glosso-pharyngeal is the principal nerve for the back ol

the tongue, and for the tip the lingual ; or according to some

special fibers in this nerve, derived from the chord tympani.
It is worthy of note that temperature has much to do with

gustatory sensaUons, a very low or a very high temperature

Via. «B.-TMte-budi from tongue of »bWt (after BngehMim).

beinir fatal to nice discrimination, and, as would be expected, a
tem^mture not far tumoved from "body-heat" (40° C.) is the

most suitable. ,, ^ ^ _j. „

A certain amount of pressure is favorable to tastug, as any
one may easily determine by simply aUowing some solution of
quinine to rest on the tongue, and comparing the sensation with
that resulting when the same is rubbed into the organ ; hence
the importance of the movemente of the tongue in appreciating

the sapid qualities of food. ^

OoBVantiTe.— Among the lowest Umtm of life it is extremely
diiBcult to determine to what extent taste and smell east sepa-
rately or at all, as we can conceive of them. The differentia-
tion between ordinary tactile senribility and these senses has
nodoubt be«i very gradually effected. Obswrvatwrns on our
domestic animals show that their power of disorimmation by
taste as well as by smell is very pronounced, though their likes
and dislikes are so different from our own in many ui«««»<»^
At tiie same time we find tiiat tiiey often coincide, and it isn^
unlikely that a dog's power of discriminating between a good
beefiiteak and a poor one is quite equal if not superior to mwi s,
and certainly so if his sense of taste, as in tiie human subject, IS

develi^ in proportion to his smelling power.

r aetuM, such as

B for the back of
cording to some
ord tympani.
much to do with
igh temperature

'^ft^—

Bngetanaim).

uld be expected, a
A" (40° C.) is the

to tasting, as any
I some solution of
the sensation with
the organ ; hence
ue in appreciating

life it is extremely
i smell exist sepa-
, The differentla-
l these senses has
lerrations on our
discrimination by
though their likes
a many instances.
ncide,-anditi8not
g between a good
; superior to man's,
B human subject, is
Br.

THE OEREBRO-SPINAL SYSTEM OF NERVES.

L BPINAZi MBRVIIS.

These (thirty-one pairs), which leave the spinal cord through
the intervertebral foramina, are mixed nerves— i. e., their main
trunks consist of motor and sensory fibers. But before they
enter the spinal cord they separate into two groups, which are

Fia. 4M.— DIsgriin of roots of spinal nerve IllastratinK effects of section (after Dal-
ton). The dark regions indicate tlie degenerated parts.

known as the anterior or motor and the posterior or sensory
roots, which make connection with the anterior and posterior
gray horns respe. tively.

These facts ha\'e been established by a few simple but im-
portant physiologii-al experiments, which will now be briefly
described : 1. Stimulation of the peripheral end of a spinal
nerve gives rise to muscular movements ; while stimulation of
its central end causes pain. 2. Upon section of the anterior
root, stimulation of its central end gives negative results ; but
of its peripheral end causes muscular movements. 3. After
section of the posterior root, stimulation of the distal end is fol-
lowed by no sensory or motor effecte ; of its central end, by
sensory effects (pain).

These experiments show clearly that the anterior roots are
motor, the posterior sensory, and the main trunk of the nerve
made up of mixed motor and sensoty fibers.

S80

COMPARATIVE PHYSIOLOGY.

BlMptiOB.— It has been found that flometimea stimulation of
the peripheral end of the anterior root has given rise to pain,
an effect which disappears if the posterior root be cut. From
this it is inferred that certain sensory fibers turn up into the
anterior root a certain distance. Such are termed " recurrent
sensory fibers."

AiWttimiri iKptrimtnti.— 1. It is found that if the anterior
root be out, the fibers below the point of section degenerate,
while those above it do not 2. On the other hand, when the
posterior root is divided above the ganglion, the fibers toward
the cord degenerate, while those on either side of the ganglion
do not. From these experiment* it is inferred that the cells of
the posterior grnglion are essential to the nutrition of the sen-
sory fibers, and those of the anterior horn of the cord to the
motor fibers.

PtthologicMl. — Pathology teaches the same lesson, for it is
observed that, when there is disease of the anterior gray comua,
degeneration of motor tiben is almost sure to follow. These
cells, whether in the ganglion or the anterior horn, have been
termed "trophic." It is true, the funcfu^ns of the ganglia on
the posterior roots, other than those just indicated, are un-
known ; on the other hand, the cell'; of the anterior horn are
distinctly motor in function. To assumi), then, that the cells of
the ganglion are exclusively trophic, with the evidence now
before us, would be premature.

The view we have presented of the relation of the nervous
system makes all cells trophic in a certain sense ; and we think
the view that certain cells or certain fibers are exclusively tro-
phic must, as yet, be re(\'ar^ed as an open question.

It is important, hoi» r ar, to recogniro that certain connec-
tions between the parts of the nervous system, and indeed all
of the tissues, are essential for perfect "nutrition," if we are to
continue the use of that term at all.

tL TBB OBUUXIAL MIIRVSSL

These nerves have been divided into nerves of special sense,
motor, and mixed nerves.

The first class has already been considered, with the senses
to which they belong.

The physiology of the cranial nerves has been worked out
by means of sections and dinioo-pathological investigations.

' ^-««M«WMtt«MlM*dM«i«^«ailka

THE OKREBRO-SPINAL SYSTEM OF NK 'THS. 5g

« stimulation of
en rise to poiii,
t be out. From
urn up into the
•med " recurrent

kt if the anterior
tion degenerate,
hand, when the ^
be flbem toward
of the ganglion
. that the cellB of
ition of the sen-
the cord to the

I lesson, for it is
rior gray comua,
D follow. These
horn, have been
r the ganglia on
idicated, are un-
tnterior horn are
1, that the cells of
lie evidence now

n of the nenrous

le ; and we think

e exclurively tro-

tion.

A certain connec-

n, and indeed all

ition," if we are to

98 of special sense,

id, with the senses

I been worked oat
eal investigationB.

Speaking generally, » good knowledge of the anui< ,t\y of thew
nerves is a great stop toward the mastery of what is known of

•nuAliiM <MmJiincltvttm omHerm
Bnuklnm emUHiuilrum
potlUmm

(^rp-yjjigjjjoi.

n^nctklutcirtbrt

drlgtmhta f Cnu

iMdHUamri)*r«6tll<
oHonvatam }

jUtburta
jMtmtrtiuwuiUra

Obta .
data

runieuliu gracUli

Fia. 4ai.—Iiit«ided to thow MpeetollT the origlii of hnth deep tnd • nperflelal ennial
nervee (after Landoli). Roman cmumeten are nitvil tu indtcate the nerrea aa they
emetge, and Arabic llgntea their nuclei or deep origin.

their functions, and such will be assumed in this chapter, so that
the sbident may expect to find the treatment of the subject
somewhat condensed.

Tht ]lotoir4)eali or Thiid Herva.— With a deep origin in the
gray matter of the floor and roof of the aqueduct of Sylvius,
branches of distribution pass to the following muscles : 1. All
of the muscles attached to the eyeball, with the exception of the
external rectus and the superior oblique. 2. The levator pal-
pebrsB. 3. The circular muscle of the iris. 4. The ciliary
muscle. Both the latter branches reach the muscles by the
dliary nerves, as they pass from the lenticular (ciliary, ophthal-
mic) ganglion. The relation of the third nerve, as seen in the

p?'ft^^!WM<'--'wtirpw»

68S

COMPABATIVK PllYSIOLOOY.

changM of thn pupil with the movementi of the eyobelli, hu

already been noticed. . . ^t ■ .

Pathological— It followi that Motion or leilon of the third
nerve must give rlie to the following lymptonis : 1. Drooping
of the upper Ud (ptoela). 2. Fixed poalUon of the eye In the
outer angle of the orbit (luicltai). 8. Immobility, with the dila-
tation of the pupil (mydriails). 4. Low of accommodation.

TIm TrooUttt or fourth Jlerrt.— Thla nerve, arising In the
aqueduct of 8ylvlu«, panes to the superior oblique muscle.

Pathological.— hu&on of this nerve leads to peculiar changen.
Aa there Is double vision, some alteration must have occurred
in the usual position of the globe of the eye, though this Is not
easily seen on looking at a subject thus affected. The double
Image appears when the eyes are directed downward, and ap-
pears oblique and lower than that seen by the unaffected eye.

Th* Abduotor or lizth Vtrro.— Arising on the floor of the
fourth ventricle, It passes to the external rectus of the eyeball,
thus with the third and fourth nerve completing the innerva-
tion of the external ocular miucles (extrinsic muscles).

Pteffco/ogtca/.— Lesion of this nerve causes paralysis of the
above-mentioned muscle, and consequently Internal squint
(strabismus).

The TMial, Portia Dora, or Sofonth Honro.— It arises In a
gray nucleus in the floor of the fourth ventricle, and has an
extensive distribution to the miunles of the face, and may be
regaiiled, in fact, as the nerve of the facial muades, since It sup-
plies (1) the mtiablM of expreanon, as those of the forehead,
eyelids, nose, cheek, mouth, chin, outer ear, etc., and (8) certain
muselea of nuutieation, as the buooinator, posterior belly of the
digastric, the stylohyoid, and also (3) to the atapediua, with
branches to the soft palate and uvula.

Pathological.— It follows that paralysis of this nerve must
give rise to marked facial distortion, loss of expression, and
flattening of the features, as well as possibly some deficiency in
hearing, smelling, and swallowing. Mastication is difficult,
and the food not readily retained In the mouth. Speech Is
affected from paralysis of the lips, ete.

Secretory flbere proceed (1) to the parotold gland by the
superficial petrosal nerve, thence (2) to the otic ganglion, from
which the fibers pass by the aurioulo-temporal nerve to the
gland.

Ouetatory F«5era.— According to some, the chorda tympam

^UUliifa )MtyS>i«i**»«WW

THE CEREBBO-8P1NAL SYSTEM OF NERVES. 588

B eyebolli, ha*

m of the third
: 1. Drooping
the eye in the
, with the dila-
[iniodation.
, oriaing in the
le miuole.
culiarohangefl.
have occurred
ugh this is not
1. The double
iiward, and ap-
taffected eye.
the floor of the
of the eyeball,
Qg the innerrar
iscleR).

paralysis of the
internal squint

—It arises in a
cle, and has an
oe, and may be
les, since it sup-
f the forehead,
, and (2) certain
rior belly of the
stapedius, with

this nerve' must
expression, and
ne deficiency in
ion is difficult,
uth. Speech is

d gland by the
; ganglion, from
"bI nerve to the

chorda tympani

really supplies the fibers to the lingual nerve that are coiicemed
with taste.

It will thus be seen that the facial nerve has a great varioty
of important functions, and that paralysis may be more or loss
serious, according to the number of fibers involved.

Th« TrigMBinQi, TrillMial, or fifth ■«:▼•.— This nerve has
very extensive functions. It is the sensory nerve of the face :
but, as will be seen, it is peculiar, being a combination of the
motor and sensory ; or, in other wordH, has paths for both
afferent and efferent impulses. The motor and less extensive
division arises from a nucleus in the fioor of the fourth ventricle.
The sensory, much the larger, seems to have a very wide origin.
The nerve-fibers may be traced from the pons Varolii through
the medulla oblongata to the lower boundary of the olivary body
and to the posterior horn of the spinal cord. This origin sug-
gests a resemblance to a spinal nerve, the motor root coire-
■ponding to the anterior, and the sonnury to u posterior root,
the more so as there is a large ganglion connected AVith the
sensory part of the nerve within the brain-case.

Xlferent Fibers.— 1. Motor.— To certain muscles (1) of mas-
tication—temporal, maaaeter, pterygoid, mylohyoid, and the
anterior part of the digastric. 2. /Secretory.— To the lachrymal
gland of the ophthalmic division of this nerve. 8. Vaso-motor.
—Probably to the ocular vessels, those of the mucous mem-
brane of the cheek and gums, etc, 4. Trophic.— From the re-
sults ensuing on section of this nerve, it has been maintained
that special trophic fibers pass in it. We have discussed this
subject in an earlier chapter.

Afferent Fibers.— i. Sensory.— To the entire face. To par-
ticularize regions : 1. The whole of the skin of the face and
thatof the anterior surface of the external ear. 2. The external
auditory meatus. 3. The mucous lining of the cheeks, the fioor
of the mouth, and the anterior region of the tongue. 4. The
teeth and fiflriosteum of the jaws. 6. The lining membrane of
the entire nasal cavity. 6. The conjunctiva, globe of the eye,
and orbit. 7. ' The dura mater throughout.

Many of these afferent fibers are, of course, intimately con-
cerned with reflexes, as sneezing, winking, etc. Certain secre-
tory acts are often excited through this nerve, as lachrymation,
when the nasal mucous membrane is stimulated ; indeed, the
paths for afferent impulses giving rise to reflexes, including
secretion, are very numeroiis.

684

COMPARATIVE PHYSIOLOGl.

Gustatory impulses from the anterior end and lateral edges
of the tongue are conveyed by the lingual (gustatory) brajftch
of this nerve. Many are of opinion, however, that the flbew
of the chorda tympani, which afterward leave the hngual to

unite with ihe facial nerve, alone con-
vey such imprefBions. The subject
can not be regarded as quite settled.
Tactile sensibility in the tongue is very
pronounced, as we have all experi-
enced when a tooth, etc., has for some
reason presented on unusual surface
quality, and become a source of con-
stant offense to the tongue.

The ganglia of the fifth nerve, so
far as the functions of their cells are
concerned, are enigmatical at present.
They are doubtless in some sense tro-
phic at least. With each of these are
nerve connections (" roots " of the gan-
glia), which seem to contam different
kinds of fibers. These ganglia are
connected vrith the main nerve-centers
by both afferent and efferent nerves,
»nd also with the sympathetic nerves
themselves. Some r^ard the ganglia
as the representatives of the sympa-
thetic system within the cranium.

I. The Ciliary (Ophthalmic, Len-
ticular) Oanglion.—lta three roots
are : 1. From the branch of the third
nerve to the inferior oblique muscle
(motor root). 2. From the nasal
branch of the ophthalmic division of
the fifth. 8. From the carotid plexus
p,o7'4!«.-Unipoi.r ceU ftom of the sympathetic. The efferent
^twalK) "^r^.tt branches pass to the ins, »« derived
of rteath; T, Ahet bnmch- chiefly from the sympathetic, ana

l„g.tanodeofB«vier. ^^g^'^^t^tion of the pupil. There

are also vaso-motor fibers to the choroid, iris, and retina. The
afferent fibers are sensory, passing from the conjunctiva, ooiv

n. Tfte Naml or Sph^no-PaJatine Ganglicn.— The motor

KS«*«P««»*«»»«»«*-

d lateral edges
tatory) branch
that the fiben
the lingual to
srve, alone con-

The Bubjeot
s quite settled,
e tongue is very
ive all experi-
c, has for some
UDUBual surface
source of con-
igue.

) fifth nerve, so
f their cells are
tical at present,
some sense tro-
ach of these are
K>t8"of thegan-
ontain different
)se ganglia are
in nerve-centers
efferent nerves,
npalhetic nerves
gard the ganglia
s of the sympa-
ihe cranium.
^thalmic, Len-
-Its three roots
inch of the third
oblique muscle
BVom the nasal
ilmic division of
he carotid plexus

The efferent
iris, are derived
ympathetic, and
he pupil. There
and retina. The
conjunctiva, cor-

ton.— The motor

.yPistwM-'-tf"-^ ■: *^ap»^»*'*^^f*

THE CBREBBO-SPINAL SYSTEM OF NERVES. 586

root is derived from the facial through the great superficial
petrosal nerve; its sympathetic root from the carotid plexus.
Both together constitute the vidian nerve. It would seem that
afferent impulses from the nasal chambers pass through this
ganglion. The efferent paths are : 1. Motor to the levator pa-
lati and azygos uvuke. 2. Vaso-motor, derived from the sjrm-
pathetio. S. Secretory to the glands of the cheek, etc.

III. The Otic Ctanglion.—ItB roots are : 1. Motor, from the
third division. 2. Sensory, from the inferior division of the
fifth. 3. Sympathetic, from the plexus around the meningeal
artery. It makes communication with the chorda tympani and
seventh, and supplies the parotid gland with some fine fila-
ments. Motor fibers mixed with sensory ones pass to the tensor
tympani and tensor palati.

IV. The Submaxillary Oanglion.—Ita roots are: 1. Branch-
es of the chorda tympani, from which pass (a) secretory fibers to
the submaxill9«y and sublingual glands, (6) vaso-motor (dilator)
fibers to the vessels of the same glands. 2. The aympathetie,
derived from the superior cervical ganglion, passing to the sub-
maxillary gland. It is also thought to be the path of vaso-con-
striotor fibers to the gland. 3. The sensory, from the lingual
nerve, supplying th^ gland substance, its ducts, etc.

Pathological.— 1. The motor division of the nerve, when
the medium of efferent impulses, owing to central disorder, may
cause trismus (locked-jaw) from fontc tetanic action of the mus-
cles of mnstication supplied by this nerve. 3. Paralysis of the
same muscles may ensue from degeneration of the motor nuclei *
or prassnro on the nerve in its course. 3. Neuralgia of any of
the sensory branches may occur from a great variety of causes,
and often maps out very exactly the course and distribution of
the branches of the nerve. 4. Vaso-motor disturbances are not
infrequently associated with neuralgia. Blwdiing is an evi-
dence of the normal action of the vaso-motor fibers of the fifth
nerve. 5. A variety of trophic (metabolic) disturbances may
arise from disorder of this nerve, its nuclei of origin or ita gan-
glia, such as grayness and loss of hair (imperfect nutrition),
eruptions of the skin along the course of the nerves, etc. Atro-
phy of the face, on one or both sides, gradual and progressive,
may occur. Such affections as well as others, point in Uie most
forcible manner to the influence of the nervous system over the
metabolism of the body.

The CHoMmplittyiigwil or Viath Venr*.— This nerve, to-

ggg COMPARATIVE PHYSIOLOGY.

^♦v.« with the vajruB and spinal accessory, constitutes the
SS S^ or rate^^o. F?.nctionaUy, however, ihey are

'"'^Jht^^pharyngeal arises in the floor of the f oujh ven-
teicl ato^he^«««^'«' <^« ^»«^- It is a m«ed nerve
SeS«nt and afferent- flhe«.: ^-^"1^^^^
^tor flbci-9 to the middle constrictor of the Vi^'^^

tS:LS:^n?LteL^iln of the epiglottis St^ulaljon

TZ ^ons just mentioned gives rise reflexly to the move-

Ints oTfwaUowing and to reflex secretion ^^^ ^,

This nerve is also the special nerve of taste to the back of

*^'iK«uaogartric Vagui, er Tenth H«ry.-Most of the
fun^oxTS^SWhavTalready beenconsidered inprev«>«s

'^^S^me of the lower vertebrates (sharla) the nerve arises
bv a S of distinct roots, some of which remain separate
Sr^aSout This fact expUins ite peculiarities, anatomical
«.d£tionaI in the higher vertebrates. In these there have
W^:S.^tiiand wending, so ti«»t what seems to l«^
D^e is reaUy madeup of several distinct bundles of fibers,
manv of which leave the main trunk later. x_ i j»

^f imv be regarded as the iiiorf complicated nerve-tanmk m
the iXf ^dZdistribution of ite fibers is of the most ex^-
S^e^acter. Following omr ch^sification of efferent and

*^r^::S^which are motor to an extensive tract in

wdTtiie c^phagus, the stomach, and the intestine receive
^tXTZ^yS>m this source. By tiie laryngeal nerves,

^S^lSriX^-lly f«,m the spinal «--« -^t^:;:
cles of the Lirynx are innervated. The muscles of the ti«chej
bronchi, ete., are also suppUed by the pneumogasbnc. It is
proS thattx««^or fibers derived from <^« »y™^,*^
J^Tbranches of the vagus. The relations of tins nerve to
the heart and lungs have akeady been explained.

TAfferentmers.-It may be said that afferent impiJje.
from iS^flie legions to which efferent fibers are supplied pass

,.:,j|Mtl|li^»H«*i<>l8*''»*«**'*''**'*'**

constitutes the
wever, they are

the fourth ven-
mized nerve
bera, furnishing
pharynx, stylo-
2. AfferefU
from the hase
Eustachian tube,
Stimulation
dy to the move-
saliva,
te to the bade of

re.— Most of the
lered in previous

the nerve arises
remain separate
ities, anatomical
these there have
seems to be one
bundles of fibers,

d nerve-trunk in
if the most exten-
I of efferent and

extensive tract in

Bin muscles of the
intestine, receive
I laryngeal nerves,
ccessory, the mus-
ics of tiie tradbea,
umogastric. It is
} the sympafbetio
B of this nerve to
ned.

afferent impulses
are supplied pass

tHjg»«W>*W3«V/5'W*»ss«»--- •■/-■■

THB OBREBBO-SPINAL SYSTEM OF NERYEa 687

inward by the vagus. One of the widest tracts in the body
for afferent im] tlses giving rise to reflexes is connected with
the nerve-oentei-h by the branohes of this nerve, as evidenced by
the many well-known phenomena of this character referable to
the pharynx, larynx, Itmgs, stomach, etc., as vomiting, snees-
ing, coughing, etc. This nerve plays some important part in
secretion, no doubt, but what that is has not been as yet well
established.

Fattu)logieal.—&eotion of both vagi, as might be expected, '
leads to death, which may take place from a combination of
pathological changes, the factors in which vary a good deal
with the class of animals the subject of experiment Thus, the
heart in some animals (dog) beats with great rapidity and tends
to exhaust itself. In birds especially is taMy degeneration of
heart, stomach, intestines, etc., liable to follow.

Paralysis of the musdes of the larynx renders breathing
laborious. From loss of sensibility food accumulates in the
pharynx and finds its way into the larynx, favoring, if not
actually exciting, inflammation of the air-passeges.

But it is not to be forgotten that upon the views we advocate .
as to the constant influence of the nervous system over all parts
of the bodily metabolism, it is plain that after section of the
trunk of a nerve with fibers of such wide distribution and va-
ried functions the most profound changes in so-called nutrition
must be expected, as well as the more obvious functional de-
rangements; or, to put it otherwise, the results thai follow are
in themselves evidence of the strongest kind for the doctrine of
a constant neuro-metaboUc influence which we advocate. It
will not be forgotten that the depressor nerve, which exerts re-
flexly so important an influence over blood-pressure, is itsdf
derived from the vagus.

Tha Spliial Aaeaworj or EUvmlli V«rv«.— This nerve arises
from the medulla oblongata somewhat Uee back, and from the
spinal cor J in the region of the fifth to the seventh vertelwa.
Leaving the lateral columns, its fibers run upward between the
denticulate ligament and the posterior roots of the spinal nerve
to enter the cranial oavity, which as they issue from the cra-
nium subdivide into two bundles, one of which unites with the
vagus, while the other pursues an independent course to reach
the stemo-mastoid and trapedus muscles, to which they furnish
the motor supply; so that it may be considered functionaUy
equivalent to the anterior root of a spinal nerve. The portion

588

COMPAEATIVB PHYSIOLOGY.

Joining the vagus seems to supply a large part of the motor

fibers of that nerve. . „ « * ^i. v j

Pathologieal.—ToTde contraction of the flexors of the head

causes wry-neck, and when they are paralywd the head is drawn

to the BOtmd side.

The HypoglotMl or TwelfUi HenrB,— It arises from the low-
est part of the calamus scriptorius and perhaps from the olivary
body. The manner of its emergence between the anterior pyra-
mid and the olivary body, on a Une with the anterior spinal
roots, suggests that it corresponds to the latter; the more so as '
it is motor in function, though also containing some vaso-motor
fibers, in all probabiUty destined for the tongue. Such sensory
fibers as it may contain are derived from other sources (vagus,
trigeminus). It suppUes motor fibers to the tongue and the
muscles, attached to the hyoid bone.

Ptttftotogicoi.— Unilateral section of the nerve gives nse to
a corresponding lingual paralysis, so that when tlie tongue is
protruded it points to the injured side; when being drawn in,
tiie reverse. Speech, singing, deglutition, and taste may also
be abnormal, owing to the subject being unable to make the
usual co-ordinated movements of the tongue essential for these
acts.

RBX^TXOMS OP THH OBRHBRO-8PINA1. AWD STMPA-
T HimO ST8TBBI&

No division of the nervous system has been so misatisfao-
tory. because so out of rehition with other parts, as the sympa.
th^c. It was also desurable to attempt to coK>rdin»te the cere-
bml and spinal nerves in abetter fashion; and various attempts
in that direction have been made. Very recently a plan, hj
which the whole of the nerves issuing from the brain and eord
niay be brought into a unity of conception, has be^ IP^f^'^
ani though it would be premature to pronounce definitely as
yet upon the scheme, yet it does seem to be worth while to lay
ft befSe the student, as at all evente better than the i»lab^
impUed in the three divisions of the nerves which has been

**"£!to2?of the ckssiflcation of nerves into efferent and aflw-
ent, connected with the anterior and the posterior horns of «he
gray matter of the spinal cord, another division has ^^J^
poMd, vis., a division of nerve-flbers and their centers of origin

THE CBBEBRO-SPINAL SYSTEM OP NERVES. 689

t of the motor

)r8 of the head
e head is drawn

B from the low-
rom the olivary
e anterior pyra-
anterior spinal

the more so as
ome vaso-motor
, Such sensory

sources (vagus,
tongue and the

•ve gives rise to
a ihe tongue is
being drawn in,
taste may also
ble to make the
sential for these

AMD STIIPAr-

m so unsatisfao-
Is, as the sympar
ordinate the cere-
various attempte
%ntly a plan, by
le brain and eord
sbeen proposed;
mce definitely as
orth while to lay
lan the isolation
which has heen

flerent and afiFer-
irior horns of the
on has been pro-
■ oenten of origin

In the gray matter for the supply of the internal and the exter-
nal partdof the body— i. e., into splanchnic and somatic nerves.
The centers of origin of the splanchnic nerves are referred to
groups of cells in the gray matter of the cord around the cen-

Flo.«)7.

Fis. '

Fi8. «W.— Ganglion cell from •ympathetic jnngllon of frog; greatly magnUed, and
•howing both atiight and colled llbere (after Quain).

Fio.4«.-»nltlpolarMaigllonc«lto fromjmnpatlietic •?•»««;»' '^^'•ffliTJ^'"
fled (after Max SchnRse). a, cell freed from cauanle; ft. inclosed witUn a nu-
deated capanle. In both the proceaaea have been broken awajr.

tral canal; while the somatic nerves spring from the gray cor-
nua and supply the integument and the ordinary muscles of
locomotion, etc. The splanchnic nerves supply certain muscles
of respiration and deglutition, derived from the embryonic
lateral plates of the mesoblast; the somatic nerves, muscles
formed from the muscle-plates of the same region.

It is assumed that the segmentation of t^e vertebrate and
invertebrate animal is related; and that segmentation is pre-

690

COMPARATIVE PHYSIOLOGY.

served in the cranial region of the vertebrate, as shown by th^
nerves themselves.

The afferent fibers of both splanchnic and somatic nerves
pass into the spinal ganglion, situated in the nerve-root, which
may be regarded as stationary.

It is different with the anterior roots. Some of the fibers
are not connected with ganglia at all; others with ganglia not
fixed in position, but occurring at variable distances from the
central nervous system (these being the so-called sympathetic
ganglia): thus, the anterior root-fibers are divisible into two
groups, both of wh'oh are efferent, viz., ganglionated and non-
gangUonated. The gangUonated belong to tiie splanchnic syfr
tem, and have reUtively small fibers; the non-ganghonated
include botii somatic and splanchnic nerves, composing the
ordinary nerve-fibers of the voluntary striped muscles of le^
piration, deglutition, and locomotion.

It would appear that these now isolated gangha have been
themselves derived from a primitive ganglion mass situated on
the spinal nerves; so that tiie distinction usually made of gan-
glionated and non-ganglionated roots is not fundamental.

A spinal nerve is, then, formed of— 1. A posterior root, the
gangUon of which is stationary in position, and connected with
splanchnic and somatic nerves, both of which are afferent 2.
An anterior root, the ganglion of which is vagrant, and con-
nected with the efferent small-fibered splanchnic nerves.

Among tiie lower vertebrates both anterior and posterior
roots pass into Uie same stationary ganglion. Such is also tiie
case in the first two cervical nerves of the dog.

Does the above-mentioned plan of distribution, etc., hold for

the cranial nerves ? _*. j

Leaving out the nerves of special sense (olfactory, optic, ana
auditory), the other cranial nerves maybe thus divided: 1. A
foremost group of nerves, wholly efferent in man, vu., the
tiiird, fourth, motor division of the flf tii, the sixth, and seyento.
2. A hindmost group of nerves of mixed character, vi«., the
ninth, tenth, eleventh, and twelfth.

The nerves of the first group, since they have «><f **^
flbered, non-ganglionated motor nerves, and also small-fibered
sphmchnic efferent nerves, with vagrant ganglia (ganglion
oculomotorii, ganglion geniculatum, etc.), resemble a spinal
nerve in respect to tiieir anterior roots. They also resemble
spinal nerves as to their posterior roots, fbr at their exit from

■arfliiii'iu^tfiiii h'l^jClW

I shown by th^

somatic nerves
rve-root, 'which

e of the fibers
ith ganglia not
mces from the
ed sympathetic
isible into two
Dated and non-
splanchnic sys-
tn-ganglionated
composing the
musdes of ree-

iglia hare been
nass situated on
[y made of gan-
idamental.
sterior root, the
. connected with
ire afferent 2.
igrant, and con-
ic nerves.
>r and posterior
Such is also the

on, etc., hold for

ictory, optic, and
us divided: 1. A
1 man, viz., the
Eth, and seventh,
aracter, vis., the

have both large-
Oso small-ftbered
anglia (ganglion
isemble a spinal
ey also resemble
i their eixit from

THE CBEEBRO-SPINAL SYSTEM OP NERVES. 591

the brain they pass a ganglion corresponding to the stationary '
posterior ganglion of the posterior root of a spinal nerve.
These being, however, neither in root* nor ganglion functional,
are to be regarded as the pbylogenetically (ancestrally) degen-
erated remnants of what were once functional ganglia and
nerve-fibers; in other words, the afferent roots of these nerves
and their ganglia have degenerated.

The hindmost group of cranial nerves also answers to the
spinal nerves. They arise from nuclei of origin in the medulla
and in the cervical region of the spinal cord, directly continu-
ous with corresponding groups of nerve-cells in other parts of
the spinal cord; but in these nerves there is a scattering of the
components of the corresponding spinal nerves. Certain pecul-
iarities of these cranial nerves seem to become clearer if it be
assumed that, in the development of the vertebrate, degenera-
tion of some region once functional has occurred, in conse-
quence of which certain portions of nerves, etc., have disap-
peared or become functionless.

It is also to be remembered that a double segmentation ex-
ists in the body, viz., a somatic, represented by vertebrae and
their related muscles, and a splanchnic represented by visceral
and branchial clefts, and that these two have not followed the
same lines of development; so that in comparing spinal nerves
arranged in regard to somatic s^rments with cranial nerves,
the relations of the latter to the somatic muscles of the head
must be considered; in other words, like must be compared
with like.

THE VOICE.

It ii oonveaient to speak, in the oaie of man, of the ringing
voice and the speakiiig voice, though there is no fundamental
difference in their jj^roduotion. The voice of the lower animals
approximates the former rather than the hitter.

It is to be remembered that sound is an affection of the
nervous centers through the ear, as the result of aerial vibra-
tions.

We are now xo explain how such vibrations are caused by
the vocal mechanisms of animals and especially of man.

The tones of a piano or violin are demonstrably due to the
vibrations of the strings; of a clarionet to the vibration of its
reed. But, however musical tones may be produced, we distin-
guish in them differences in pitch, quantity, and qualify*

The pitch is dependent solely upon the number of vibrations
within a given time, as one second; the quantity or loudness
upon the amplitude of the vibrations, and the quality upon the
form of the vibnrtions. The first two scarcely require any fur-
ther notice: but it is rather important for our purpose to under^
stand clearly the nature of quality or timbre, which in a more
complex inatttir.

If a note be sounded near an open pano, it may be observed
that not only the string capable of giving out the correspond-
ing note passes into feeble vibration, but that several others
also respond. These latter produce the overtones or partials
which enter into notes and determine the quality by which one
instrument or one voice differs from another. In other words,
every tone is in reality compound, being composed of a fundar
mental tone and overtones. These vary in number and in rela-
tive strength with each form of instrument and each voice;
and it is now customary to explain the differences in quality of
voices solely in tiiis way; and this is, no doubt, correct in the

I, of the (ringing
no fundamental
B lower animalit

affection of the
of aerial vihra-

\B are oauied by
r of man.
rably due to the
I vibration of its
iuced, we diatin-
d quality,
ber of vibrationi
itity or loudnew
inality upon the
require any fur-
mrpoee to under*
which is a more

may be observed
t the correspond-
it several others
tones or partials
ity by which one
In other words,
posed of a fundar
mberand in rela-
and each voice;
Dces in quality of
bt, correct in the

THE VOICE.

598

What are the mechanisms by which voice is produced in
man ? Observation proves that the following are essential : 1.

Fia.4aBL

Fia.4M.

Fio. 4W.— liOngitiidiiial mcUoc of hnnutn Itlrjnx (•fter Sappoy). 1, yentrlcle of la^
ynx; S, ■operiOTTooal ooid; 8, Inferior vocal cord; 4, a^tenotd cartilage; 6 sec-
tion of arytepud mnacle; 8,8, Inferior portion of cavttjrof larynx; 7, section of
MMteriOTpart of cricoid cartilage; 8. aecllon of anterior part of same; 9, superior
border of ntcold caiillase; 10, lecUon of thyroid cartilage: 11.11. Biiperior pwtlon

5»roSW3iill;MW!lSi!i.!^ ^

Pio. MO.— Pofterior arpMt of mawlea of hnman larynx (after Sappey). 1. posterior
*'te^i™»** ""wcle; 8, 8, 4, dilterent fascicoll of arytenoid mwcle; 6, wyteno-
epigiottidean mnacle.

A certain amount of tension of the vocal cords (bands). 2. A
certain degree of approximation of their edges. 3. An expirsr
tory blast of air.

It will be noted that these are all conditions favorable to the
vibration of the vocal bands. The greater the tension the
higher the pitch; and the more occluded the glottic orifice the
more effective the expiratory blast of air.

The principle on which the vocal bands act may be illus-

K»4

COMPARATIVE PHYSIOLOGY.

tmted In the simplert way by a weU-known toy, constating of
!^ ela- "c bag tied upon a hollow .t«m of wood, aero, which
™bt"tn7a«.tretohed,and the vi»>«tio„ of which cu«hI
Z the air within the distended bag give, rise to the note.
' Sta «^ially important to recognl« the nature. extonl, and

Via. 4n

Fio. 481.— Utowl view j

toahow wirtt It covew; «. cricoid w^S"^' jJ-^Si^ w*SS3e«lco<«ytTOold
-^^Idrnwcle; I. Urtwml crieojoJ^^JSSi ninV-^Mi^w taryngt*!; «.

„. , _!,»rytenoldi

bnncliM, ** " ""
mpcriorli

ffom eztcTMl laryngeal.

sto; a portion U «lf"*»'~LH?3!r^iSiC. m obm>^^ branch to arjrte-

V'SiiftHISBIHSlBIIBlWI'WJ.y* I wPB^^Swir^

r, conRiBting of I

, aoroM which I

which caused
the note.
are,eztoDi,and

THE VOICE.

595

effect on the vocal bands of the movementa of the aiytenoid
cartilages. These are most roorked around a vertical axis, giv-
ing rise to an inward and outward movement of rotation, but

1. body of bToid boMi
loM moMte; 4. f;«*t of

' »• "isi

irieoMcarti-
roM moicler*, P'V"'"'
; 0, thyro-MytenoM mui-
Imm mdMle: 19, middle

mn. after ToniMlnt). a.
cUinofttyroidcwtlUige

^Srtcriorcrieo«i7t>nold

1 rabjwent mncoo* meja-
mhagesl bnuieh to uyte-
Syexit •ometlme* come*

Fid. 488.— DIagnmnMtIc Metton of luyns to lllnitnite action of l^MUHor erieo-anU
nold muiei* (after Landot*). In tnU and the two following flgorea the dotted
llnoa Indicate the new poaitlon of the parte owing to the action of the mneclee
concemMl.

there are also movements of less extent in all directions. It is
in fact through the movements of these cartilages to which the

Fis. 484.— Dlaarammatic tection of larynx to Ulnttrate action of Ari/tmuldeut pro-
prim mtuem (after Landoit).

nmmmmnsmmv*''

696

COMPAHATIVR PIIYSIOLOOY,

»i«. «J.-inMtmt«i •ctlon of thyKM»yUi>oM«iw !"»•«••.

Tocal bandi ai« attached poateriorly.that mort of the important
changes in the tension, approximation, eto^ of ttie latter are
produced. The lungs are to be regarded as the beUows furnish-
ing the necessary wind-power to set the vocal bands vibrating,
whUe the Urynx has respiratory as well as ^«»» '«n«^°?*' "
has been already learned. Assuming that the student has a
good knowledge of the general anatomy of the hirynx, we call
attention briefly to the following : ^ -j .

Widening of the glottie is effected by the orie<Htriftenotdeu$
voeHeu$ pulling outward the processus vocalis or attachment
jSrironSe vocal band, and a «mUar effect is produced
by the arytenoidem posticus acting alone w«„^r««.

Narrowing of the glottis is accomplished by *• «*^7/-
enoideus lateralis, and the following when actmg either singly
(except the arytenoideus posticus), or in oonceiV"- the sphinc-
ter of the larynx, vis., the thyro^rgtentndeus extemue, thyro-
arytenoideus intemus,thyr<HiryepigMtieus arytenotdeus pos-

"^msim of the vocal bands is brought about by the sphincter
group, and espedaUy by the external and internal thywMtfyte-

"" HSrTTtwplj.-The superior laryngeal contains the motor
fibers for the crico-thyroid (possibly also the ^'T^oideu. p«h
ticus) and also supplies the mucous jnembmne. The ijf«w
laryngeal supolies aU the other muscles. While both of these
n^rZ^ d^vod from the vagus, their fibers really belong U>
^eTin^««««ory. It is worthy of note that the entire group

IMMII II iiWHW

THE VOICK.

697

of iiiumsIm making up the iphinoter of the larynx is contraoted
when the inferior laryngeal is stimulated.

Snperior Ftee. Infmrlor Fwe.

Fw. 486.— CMtllaglnoM place* of Iha larynx of hon«, nuUnUiMd In their natural
poaltlon by tbe arttcnlar llgamentt (Ciwaveatt). a. orleoid eartllafe; b, b, aryte-
noid eartlkmw; e, body of tne tbyruld; c", <f, latMal platM of the tnyrold; <f, opi-
Slottla; «. body of tbe hv(iid:/, trachea. 1, cricoarytenoid artlcalatlon; S,capeale
f the crico-thyrold artlcniatlon; S, crieo-thyrotd membrane; 4, tbyro>byold mem-
brane; B, crico-tracbealii ligament.

Above the true vocal bands oomposed of elastic fibers lie the
soHsalled false vocal bands (cords) to be regarded as folds of the
mucous membrane which take no essential part in voice-produc-
tion. Between these two pairs of bands are the vtndridm of
Morg<tffni, which, as well as the adjacent parts, secrete mucus
and allow of the movements of both sets of bands and in so far
only assist in phonation.

The whole of the supra-laryngeal cavities, the trachea and
bronchial tubes, may be regarded as resonance-chambers, tho
former of which are of the most importance, so far as the
quality of the voice is concerned. There seems to be little
doubt that they have much to do with determining the differ-
ences by which one individuaFs voice at the same pitch differs
ftem another: nor is the view that they may have a slight in-
fluence on the pitch of the voice, or even its intensity, to be
ignored.

.: f f ^"^ji='^^fy^-'^""''fiss

'698

COMPARATIVE PHYSIOLOGY.

The epiglottis, in so far as it has any effect, in all prohability
modifies the voice in the direction oJqnj^^_^^^^^ ^^

the laryngeal muscles, owing to
pressure on nerves and conse-
quent narrowing of the glottic
opening, explains " roaring " in
the horse, in certain instancea
at all events.

Gompantivt.— Much more
is known of the sounds emanat-
ing from the lower animals
than of the mechanisms by
which they are produced. This
applies, of course, especially to
such sounds as are not pro-
duced by external parts of the
body, it being very difficult to
investigate these experimental-
ly or to observe the animal
closely enough when produc-
ing the various vocal effects
naturally.

AH our domestic mammal s
have a larynx, not as widely different from that of man as
might be supposed from the feeble range of their vocal powers.
T^re are structural differences in the htrynx of the domestic
animals, some of which are more readUy appreciated by the eye
than described. ,. . *

The false (superior) vocnl bands are rudimentary or wantr
ing in many mammals, including the horse, ass, etc.

In ruminants the hirynx is proportionately lU-developed;
the glottis is short, the vocal bands rudimenUu-y, and the ven-
tricles wanting. ,

The lamyx of the pig is peculiar in that the ventricles are
deep, though their opening is only a narrow slit ; there is^how-
ever a large membranous sac below the epiglottis, which,
acHngasaSonator, exphunsthe great intensity of the voice

of this animal. , , , j_ a'^

The actual behavior of the vocal bands has been studi^

experimentally in the dog when growling, barking, etc. And,

so far as it goes, this animal's mechanism of voioe-production

Fio. 487.-Po»tero-l»tena view «f the lar-
ynx of the horse (Otanvean). 1. epl-
Slottin; % arytenoid cwnj****' *

maacle; 5, crico-arytenolden* latera-
lie: 6, thyro-arytenoideua; 7. crico-
arytenotdenti poaticns: 8, cricp-thy-
roldeiw; 9, Uijameiit between the crl-
, ioid cartllkge'andftritrinaof trachea;
10 11. inlero-poeterior ejaremltlee of
crico-tbyrold cartilages.

■p^HpamenaFffii

THE VOICE.

599

all probability

, — Paralysis of
uscles, owing to
rves and conse-
ig of the glottic
18 "roaring "in
irtaiu instances

>. — ^Much more
sounds emanat-
lower animals ;
mechanisms by
produced. This
pse, especially to
IS are not pro-
nal parts of the
very difficult to
Be experimental-
rye the animal
1 when produc-
118 vocal effects

mestic mammals
that of man as

eir vocal powers,
of the domestic

wiated by the eye

nentary or want-
as, etc.

ely ill-developed;
,ary, and the ven-

the ventricles are
lit; there is, how-
spiglottis, which,
isityof the voice

has been studied
irking, etc. And,
[ voice-production

is not essentially different from that of man. Growling is the
result of a functional activity of the vocal mechanism, not un-
like that of man when singing a bass note; barking, of that
analogous to coughing or laughing, when the vocal bands are
rapidly approximated and separated.

The grunting of hogs and the lowing and bawling of homed
cattle are probably very similar in production, so far as the
larjmx is concerned, to the above. The cat has plainly very
great command over the larynx, and can produce a wide range
of tones. The peculiarities of the bray of the ass are owingto
voice production both during inspiration and expiration.

The quality of the voice of
most animals appears harsh to
our ears, owing probably to a
great preponderance of over-
tones, in conaequenne of an im-
perfect and unequal tension of
the vocal bands; but the influ-
ence of the supra-laryngeal cavi-
ties, often very large, must also be
taken into account.

In certain of the primates, and
especially in the howling mon-
keys, large cheek-pouches can be jfia. jiM.— l«wer Ihtbx (S^nx)_^
inflated with air from the larynx,
and so add to the intensity of the
note produced by the vocfd bands
that their voice may be heard for
miles. Song-birds produce their
notes, as may be seen, by exter-
nal movements low down at the bifurcation of the trachea
(syrinx). The notes are owing to the vibration of two folds of
the mucous membrane, which project into each bronchus, and
are r^^ulated in theur movements by muscles, the bronchial
rings in this region being correspondingly modified.

A large number of species of /Wie8 produce sounds and in
a variety of ways, in which the air-bladder, stomach, intestines,
etc., take part Most repHlM are voiceless, in the proper sense,
though there are few that can not produce a sort of hissing
sound, caused by the forcible emission of air through the upper
respiratory passages.

Frogs, as is well known, produce sounds of great variety in

crow (after G^nbanr). A, »een
from side; B, seen from in front.
a—/, mnscles concerned in move-
ments of lower larynx; g, mem-
bnma tympanlformls interna,
stretctitng from median surface of
either bionclms to a bony ridge
(pessnlns) which projects ^t the
angle of bif areation of trachea.

600

COMPARATIVE PHYSIOLOGY.

pitch. quaUty, and intensity, some species croaking so as to be
heard at the distance of at least a mUe. It is a matter of easy
observation that when frogs cioak the capacity of the mouth
cavity is greatly increased, owing to the distention of resonat-
ing sacs situated at each angle of the jaws. When tree-frogs
croak, thei* throats are greatly distended, apparently m suc-
cessive waves.

BPBOIAIi OOM8IDBIU,TXONB AMD SUBOSART. I

Svolntioa.— The very lowest forms, and in fact most inverte-
brate groups, seem' to be voiceless. Darwin has shown that
voice is, in a large number of groups, confined either entirely
to the male, or that it is so much more developed in hrai as to
become what he terms a " sexual character." There is abundant
evidence that males are chosen as mates by the females, among
birds especially, not alone for superiority in beauty of plumage,
but also for their song. Thus, by a process of natural selection
(sexual selection), the voice would tend to improve with the
lapse of time, if we admit heredity, which is an undeniable fact,
even among men— whole families for generations, as the Bachs,
having been musicians.

One can also understand why on these principles voice
should be especially developed in certain groups (birds), while
among others (mammals) form and strength should determine
sexual selection, the strongest winning in the contests for the
possession of the females, and so propagating tiieur species under
tiie more favorable cireumstanoe of choice of tiie most desira-
ble females. , , .1. 1 .

Pathology teaches that, when certain parts of the brain
(speech-centers) of man are injured by accident or disease Je
poww of speech may be lost From this it is evident ttiat the
vocal apparatus may be perfect and yet speech be wantmg; so
that it becomes comprehensible that the vocal powers of e.g.,
a dog, are so Umited, notwitiwtanding his comparatively highly
developed hwynx. He Ucks the energizing and directive ma-
chinery situated in the brain.

Some beUeve tiiat there was a period when man did not pos-
sess the power of speech at all; and many are convmoed ttat
the human race have undergone a gradual development m this
as in other respecte. CJertain it is that races differ sbU very
widely in capacity to express ideas by spoken words.

* BWiieii!JJWl'MI#li«iii- ' »

THE VOICB

601

ing 80 as to be
matter of easy
' of the mouth
ion of reBonat-
SThen tree-frogs
trently in suc-

ct most inverte-
las shown that
I either entirely
nL in him as to
lere is abundant
females, among
uty of plumage,
latural selection
iprove with the
undeniable fact,
ns^astheBachs,

principles voice
ps (birds), while
liould determine
contests for the
eir species under
the most desira-

ts of the brain
it or disease, the
evident that the
L be wanting; so
. powers of, e. g.,
[Muratively highly
ad directive ma-
man did not po«-
9 convinced fliat
rclopment in this
I differ stiU very
words.

We may regard the development of a race of speaking ani-
mals as dependent upon a corresponding advance in brain-
Btructuie, whether that was acquired by a sudden and pro-
nounced variation, or by gradual additions of increase in oer^
tain regions of the brain, or whether to the first there was then
added the second.

Apart from speech proper, there is a language of the face
and body generally, in which there is much that we share with
lower forms, especially lower mammalB. Darwin, noticing this
resemblance, regarded it as evidence strengthening the belief
that man is derived from lower forms. . Why should the forms
of facial expreasion associated so generally with certain emotions
among different races of men be so similar to each other and
to those which the lower animals employ, if there is not some
community of origin f This* is Darwin's query, and he con-
sidered, as has been stated, that the answer to be given was in
harmony with his views of man's origin, as based on an alto-
gether different sort of testimony.

The high functional development of the hand and arm in
man, and the use of these ports in writing, are suggestive.

gunmary. — The musical tones of the voice are caused by the
vibrations of the vocal bands, owing to the action on them of
an expiratory blast of air from the lungs. In order that the
bands may act effectively, they must be rendered tense and ap-
proximated, which is accomplished by the action of the laryn-
geal muscles, especially those attached to the arytenoid carti-
lages. We may speak of the respiratory glottis and the vocal-
izing glottis, according as we .consider the position and move-
ments of the vocal bands in respiration or in phonadon.

The pitch of the voice is determined by the length and the
tension of the vocal bands, and frequently both shortening and
increased tension are combined; perhaps we may say that al-
tered (not necessarily increased) tension and length arc always
combined.

Th^ quality of the voice depends chiefly upon the supra-
laryngeal cavities.

It is important to remember that in all phonation, in the
oasb si man at least, many parts combine to produce the result ;
so that voice-production is complex and variable in mechanism,
beyond what would be inf «rred from the apparent simplicity of
the mechanism involved; while the central nervous processes
are^ when comparison is made with phonation in lower ani-

602

COMPARATIVE PHYSIOLOGY.

mals, seen to be the most involved and important of the whole
—a fact which the results of disease of the brain are well calcu-
lated to impress, inasmuch as interruptions anywhere among a
class of cerebral connections, now known to be very extensive,
suffice to abolish voice, and especially speech-production.

Among mammals below man the vocal bands and laryngeal
and thoracic mechanism are very similar, but less perfectly
and complexly co-ordinated; so that their vocalization is more
limited in range, and their tones characterized by a quality
which to the human ear is less agreeable. Man's superiority as
a speaking animal is to.be traced chiefly to the special develop-
ment of his cerebrum, both generally and in certain definite
regions.

.-^^p-:~-~r,:.r^;ft .T ; \ ' ' •'> al7^^ ^t■'fe.^h;:^4 ■

t of the whole
are well calcu-
rhere among a
rery extensive,
duction.
and laryngeal
less perfectly
nation is more
1 by a quality
J superiority as
pecial develop-
sertain definite

CERTAIN TISSUES.

Prior to considering the subject of the next chapter, it may
be well to give a short account of certain tissues specially con-
cerned.

ComneotiTe TiMue.— This is the most widely distributed
tissue in the body, since it binds together all other forms of
tissue, and, in some of its many varieties, enters into the forma-
tion of every organ. As connective tissue proper, its ftmction
is subordinate; but when it becomes the aponeuroses of mua-

Fia. 480.— Fiben of tendon of man (RoUett).

cles, and especially tendons, by which, from its inextensibility,
the muscles are rendered effective in moving the levers (bones)
to which they are attached, its importance is more pronounced.
In structure, this fibrous tissue consists of bundlesof fine fibrils,
among which, especially in the younger stage, connective-tissue
cells may be found, and from which the fibers themselves are
formed.

'604

COMPARATIVE PHYSIOLOGY.

It is owing to differences in the shape and size of these cells
chiefly that the structural yariations of connective tissue in dif-
ferent regions of the body are due.

Fis. 440.— Loom network of connective tinue from man, in which an connective-tls-
rae oorpnaclM among the flben (Boilet). a, a, eapUUurr with blood<eU«.

ElMtle TiMRM.— This form of tissue is also of very wide distri-
bution and of great importance in the economy of a complicated
living organism that must constantly adapt itself to the stress
and strains of existence. In its purest form it occurs, e. g., in
the ligamentum nuclen of the ox, as a somewhat yellow, tough,
elastic structure easily flbriUated when boiled, but with diffi-
culty torn asunder when fresh. Under the microscope it ap-
pears as fibers with a very distinct outline and of varying size.
In the arteries, as already referred to, it forms a sort of elastic
membrane of the utmost importance in the functions of these
organs.

Bone^— In a long bone, as the femur, in the dried state, we
recognize a compact shaft and two ^ctremities of a more porous
nature, while the central portion of the former poresents a more
or less circular cavity, the medullary canal. By treatment
with hydrochloric acid abundance of lime salts may be ob-

of these cells
) tissue in dif-

I Me connective-tls<
blood-cell*.

erywidedistri-
! a complicated
If to the stress
Dcoura, e. g., in
yellow, tough,
but with diffi-
»o8Cope it ap-
f varying size,
b sort of elastic
ictions of these

dried state, we
' a more porous
iresents a more
By treatment
Its may be ob-

CBRTAIN TISSUES.

Fia.441.

Vm-HSt.

Fie. 441.— Fine elMtic flbem from peritoncam, 1 x 8B0 (KSlUker).
Fio. 448.— Lwger elMtlc Hbere (Hobln). ,^„ , . _.,...

Fie. 44S.— BlMtlc network (fenflfrtnted membrane) from middle coat of carotid of
horse, 1 » 8B0 (KSlllker).

Fie. 444.— Ijongltadinal MctloB of hmiMtiu. ihowing Haversian canala and lacnna,
1 X aoo (Sapper).

606

COMPARATIVE PHYSIOLOGY.

tiicau wd miuiIIodU uTtnsed in eonemtrlo ring*.

tained. A miotowwpio tnuuverw lection show» the TObrtance
of the ahaft to he penetrated by longiiudisal channeto (Havei^

F,„. 44«.-Boii*corpMclei md theJr ptoeeMM which flU the iMon. and cualicoU
(Rollett).

uttmm

!j.J ,1,,. *Tfl^

CERTAIN TISSUES.

60T

lian canals), while the intennediate space is occupied by crti-
ties (lacunae) connected with one another by very fine oauals

eetloii of TMcniM
li tnuwveiM canal.

the substance
mnels (Haver-

innK and canalicoU

Fio. 447.— Vertical aeotlon of artknlar cantlaoe iwting on bone, and showing cella
and capralea arranged in Utyera aa indicated hj nnmerala (Sappey).

(Fig. 444). A vertical cross • section exhibits the lamellae of
which it is made up and the vascular chann^ cut across
(Fig. 446).

All this is, however, only the fraiuework of osseous tissue.
If a bone from an animal freshly killed, without bleeding, be
examined, a very different state of things will be found. The
bone is heavier; its surface is covered with a closely adherent,
tough, fibrous structure, the periosteum : and its medullary
cavity filled with marrow. If the bone b^ broken across, its
section looks red, and blood flows from the surface. Investiga-
tion proves that the covering periosteum is a bed in which
blood'Vesaela and nerves ramify, and from which they enter

608

COMPARATIVK PnYSlOLOGY.

the opening* to be teen on the lurfaoe of the dead bone. Th«
Haveman canals are vaaoular channels, and the laounie filled
with bone corpuscles (Fig. 446). The nuurow in the extremi-
ties of the bone is of a red color in consequence of ito great vas-
cularity ; and in the young animal a simUar marrow fills the

meddlUuy canal, but Uter it is less vascuhir, and abounds in
fat Blood-vessels pass from it into the compaot tismie of the

bone. The
ftounsB filled
the extremi-
ito great VM-
row fllla the

CERTAIN TISSUES.

609

rtilage; b, conmet-
itting.

id abounds in
t tiamie of the

bone. The main artery, whence the othen are derived, for the
■haft of the bone, enters by the nutrient foramen on the sur-
face, and toward the center.

The bone-corpuscles (Fig. 446), answering to the connective-
tissue cells, are nutritive mid formative after a considerable
portion of the tissup has become the seat of the deposit of lime-
salts. Bone is a living tissue, though in a less degree than
most others; but it is only by bearing these relations in mind
that its function in the support of the soft parts of an animal,
and especially as constituting the essential levers of its locomo-
tive mechanism, can be understood.

OMTtilag*.— In the earliest stages of an animal's existence
the bones are represented by cartilage, and at all periods of its
existence this structure forms those elastic pads that, cover its
articular surfaces, and shield the bones and the entire animal
from imdue concussion. The kind of cartilage that covers the
extremities of the long bones, known as articular, is character-
ised by abundance of cells lying in a homogeneous bed or ma-
trix (Fig. 447).

Fibro-cartilage (Fig. 448) abounds in fibrous tissue, some
elastic fibers, characteristic cells, etc., and is found between the
bodies of the vertebrsa and in similar situations, as well as in the
epiglottis, the ear, etc.
8»

m/iimmmm

LOCOMOTION.

Tim entire locomotor ■yrt«m of tiaium U derived from the
embryonic mewblMt. Theee include the mu«jl«i, bone., certi-
bup^ind connective and ftbtoue ti-ue. ; and the timie. that
make up the va«ular .yntem or the motor apparatua for the
circuhitlon of the blood. Locomotion in the mammal i. effected
by the movement of certain bony levers while the equUlbrium
' of the body i« maintained.

The whole aeries of levera i»
bound together by muwdea,
tendons, ligamenta, etc., and
play over one another at cer-
tain points where they are in-
vested with cartilage, and
kept moist by a Mcretion from
the cells covering the syno-
vial membranes that form the
inner lining of joints.

Cartilage, a very low fonn
of tissue destitute of blood-
vessels, and hence badly re-
paired when lost by injury
or disease, forms a series of
smooth surfaces admirably
adapted for joints, and espe-
cially fitted to act as a series
of elastic buffers, and thus
prevent shocks. Bone, though
brittle in the dried state, possesses, when alive, a favorable de-
groe of elasticity, while sufBoiently rigid. Provision is made
by ito vascular periosteum and central marrow (in the case of
the long bones), as well as by the blood-supply derived from
thi) nutrient artery and its ramifications throughout the osseous

Fio. 461.

L<X:OMOTION.

611

Brived from the
lea, bone«, o«rti-
the tianiee that
iparatue for the
mmal i» effected
the equilibrium

is maintained,
ries of leren i*
ler by muaoles,
menta, etc., and
) another at oer-
here they are in-

cartilage, and
' a Mcretion from
rering the syno-
den that form the
1 of juinti.
a very low form
ititute of blood-
hence badly re-
i lost by injury
onus a series of
faces admirably
joints, and espe-
to act aa a aeries
luffers, and thus
iks. Bone, though
re, a favorable de-
>roviidon is made
ow (in the case of
»ply derived from
ighout the osseous

tissue, for abundant nourishment, growth, and repair after in-
jury.

We find In the body of mammals, including man, exam pies
of all three kinils of levers. It sometimes happenn that there
is an apparent saorittce of energy, the bent leverage not being
exemplified ; but on closer examination it will be seen that the
weight must either be moved with nice precision or through
large distances, and these objects can not be accomplished al-
ways by the arruugenients that would simply furnish the most
powerful lever. This is illustrated by the action of the bicep«
on the forearm.

It is to be remembered that, while the flexors and extensors
of a limb act in u certain degree the opposite of one another.

Fio. 48S.— Sktloton of d«er. The bonw In the estremitim of thia ' St neow»t of <iai»d-
nipedii are inclined very obliquely townrd each other and towk I y'.w acapniw and
lilac bone*. Thh nrrangement lncrea«e« the leverage of the muKular ayttem and
eonfen great rapidity on the moving partt. It angment* ehwtlelty, dininiihea
■hook, and Indirectly beget* continuity of movement, a, angle formed by femnr
with lllnm; ft, angle formed by tibia and flbula with femur: e, angle formed by
uhatampif with cannon-bone: «, angle formed by homemi with acapola: /, angle
formea by radiua and ulna with hnroema (Pettlgrew).

there is also, in all cases perhaps, a united action ; the one
set, however, preponderating over the other, and usually sev-
eral muscles, whether of the sam«; : / different c la s ses , act to-
gether.

Standing itself requires the exercise of a large nukiber of

612

COMPARATIVE, PHYSIOLOGY.

similar and antagonistio muscles so coK)rdinated that the line
of gravity fails within the area of the feet. An unconscious
animal falls, which is itself an evidence of the truth of the

above remarks. . ^ xi.

The following statements in regard to the ditecbon of the
line of gravity in man may prove useful : 1. That for the head
falls in front of the occipital articulation, as exemplified by the
nodding of the head in a drowsy pei-son occupying the sittmg
attitude. 2. That for the head and trunk together passes behind
a line joining the centers of the two hip-jomts, hence the uncor-
rected tendency of the erect body of man is to fall backward.
3. That for the head, trunk, and thighs falls behind the knee-
joints somewhat, which would also favor falling backward
(bending of the knees). 4. The line of gravity of the whole
body passes in front of a line joining the two ankle-jointe, so

4R<r

8*1«11

It I* 14

lit

'^s;iS5iiW«raffS®SE^aS

Thv B u. ll»how» the varions pMittona of both legs st the time when toe po«ie
^ImU elevated from the Bround, but behind the supported one; tihlrd group
ir^^b^U^bSStaSv^iO^^iiehau) lega .mnmewhen the .winging leg
i^^V^kS tSeSnioK? and the fourth iirSp</»). 1 »» V»'iK!'«"»iJ!L "•■^f
«hA Hr^hen theawhislnit lea lapropellef In advance of theiestbiK one. The
lettiw^ 6 aSdTlSdl^^eSngle. fSrmed by the bonea of the riglt leg when

enK' In m^lnga atep: the letter. m, n, and o. *• !»••«""• "»»SSl «? ^
SSt?5ot when the trontUrolHng over it; ff.Aow^

^k npon the left f oot (/) a. an azia; A, ahow. the routing forward of Uia lan
leg and foot npon the trunk (a) a. an axis.

that the body would tend, but for the contraction of the mus-
olesof the calves of the legs, to fall forward.

Taking these diffoi-ent facts into consideration explains the

L that the line

1 unconscious

truth of the

jfection of the
it for the head
iplified by tho
ing the sitting
passes behind
nee the uncor-
'all backward,
dnd the knee-
ing backward
r of the whole
inkle-joiute, so

1 1 1

r » atep, divided into
3 diffeient podtioiM
roond: feeond gnmp
ime when the pmte-
ted one; third gninp
«D the swinging leg
the poeitione daring
he letting one. The
f the right leg when
ions aasamed by the
ating forward of the
g forward of tbe^left

ion of the mus-
on explains the

LOCOMOTION.

618

various directions in which an individual, when erect, may fall
according as one or the other line (center) of gravity is dis-
placed for a long enough time.

Walking (man) implies the alternate movement of each leg
forward, pendulum-likci so that for a moment the entire body
must be supported on one foot When the right foot is lifted
or swung forward, the left must support the weight of the
body. It becomes oblique, the heel being raised, the toe still
resting on the ground ; and it is upon this as a fulcrum that
the body-weight is moved forward, when a similar action is
taken up by the opposite leg.

Xt follows that to prevent a fall there must be a leaning of
the body to one side, so that the line of gravity may pass through
each stationary foot; hence a person walking describes a series
of vertical curves with the head and of horizontal ones with the
body, the resulting total being complex.

Fiea. 4S4 and 480.— Showing the more or le«« perpendicnlar direction of the etrolse of
the wing in the flight of the bird (gull); how Uie wing is gradually extended as it
is elsTated («,/, a); bow it descends as a long lever nntilit aseomes the position
indicated by A; how it is flexed toward the termination -of the down-stroke, as
shown at A, ij, to convert it into a short lever (a, d) and prepare it for making the
Dp«tioke. Tno difference in the length of the wii^ dnring flexion and extension

~ is Indkated by the short and long levers o, A and «, d . The sadden conversion of
the wl^ from a long into a short lever at the end of the down-stroke is of great
importance, as it robs the wing of its momentam and prepares it for reversing its
movements (Pettigrew).

The peenliaritiee of the gait of different persojis are naturally
determined by their height, length of leg, and a variety of other
ftkctors, which are often inherited with great exactness. We
iustinotively adopt that gait which economizes energy, both
physical and mental.

Btmning difTers from walking, in that both feet are for a

-■■■ii'ff't'^lyTfii

614

COMPARATIVE PHYSIOLOGY.

Fias. 486 and 467 ehow that when the wingB^ are elevated («,f, ff) the body M\» M,
mdthrt when the winp. are depre*ef (A, i,j) the^body 6 e'e'JteJW- J^Kv^!
ihowi that the wlnm ii?e elevated a» »hort levcre («) nntU toward the temlnatlM
of me np^troke. wben they are gradually expanded (/. ^ to PWI*™ *em for
making fee dowi-rttoke. tig. 46? fhowa that the wlnge dewrad as long 'evwa
(Mantil toward the termination of the down-stroke, when they are sradnally
folded or flexed a,J) to rob them of . their momentom and prepare them for mrt-
IM the ip!iSAe.(tComp«e with Ftp. 4M and 488.) jBy thik mean, the iJrbe-
nSuiUiewlnm iBy)gfmm\yteimASuiag thedown-rtroke. while ttat above It
"■avoided during the np^rtroke. The concavo-convex f onn of the w1n«» «« the
forward toavel^ the body contributea to this reenlt. The wings Jt yM\ be ob-
iS^Sdact M a Mrachute Wh during the up and down atrokea. Wg. 487 ihiwa
SitKe^A^IdK»tation of the wTng. how It rotttej "PO" «i" • e««f • "•»•»
a radlua m, 6%, and upon a. c, 6 as a center, with a radius *, / (Pettigrew).

period of the cycle off the ground at the same time, owing to a
very enei^tic action of the foot acting as a fulcrum.

Jumping implies the propulsion of the body by the impulse
given by both feet at the same moment.

Hopping is the same act accomplished by the use of one

OompKntiv*.— Tbe movements of quadrupeds are naturally
very complicated, but have now been well worked out by the
use of instantaneous photography. Even the bird's flight is no
longw a wholly unsolved problem, but is fairly well under^
stood. The movements of centipedes and and other many-
legged mvertebratee are highly complicated, while their rapid
movements are to be aooounted for by the multiplicity of their
levers rather than the rapidity with which they are moved.

the body ftlli («):
vated(r). Fift.4M
lid tbe termiiuitlon

prepare them for
end as long levers
they are mdnally
Mre them for mak-
s means the air be-
irhlle that above it

the wings and tbe
ings Jt wUl be ob-
es. Slg. 4B7 sliowB
a, as a center, with
I (Pettigrew).

oae, owing to a

lun.

by the impulse

ihe uae of one

! are naturally
ced out by the
rd's flight is no
ly weU nnder-
1 other many-
die their rapid
plioityof their
ey are moved.

LOCOMOTION.

616

The length and flexibility of their bodies must also be taken
into account, rendering many legs necessary for support

The subject of locomotion is of such great importance in the
practice of comparative medicine that we shall now enter upon
it in somewhat more detail, especially as regards the horse.
This, of all our domestic animals, has become specialized as a
locon.oti\« mechanism. All the parts of his whole economy
have b«on coK)rdinated to that end ; and, except the horse be
viewed in this light, the significance of much in his nature

Fi«. «)e.-ChUlingham bnU (J9W SeoOetu). Shows powarfnl, ^vy body, md tte
mSlTnSremlQes adapted for land tnnsit. Also &ie flgnre^-8 moTemento made
l?a!e fStSSd UibTta walking and "»»«»%«.<• «'|nfJ|S*J,?5^
left anterior extremities: r, «, corres made by right and left ppstenor enremiues.
t£ rtStSw i^tha left liind foot move tqge^er to form ftw waved^l toe (y, •);
the IM fore and the right hind foot move together to form «».]»»'^J'toe,tv£.
The corves formed by tbe anterior («, n) and posterior (r, ») extremities form eU^pasa

iPettigrew).

will M missed. But, however well his other parts might be
suited to this purpose, unless the feet were adapted to rapid
movements and great and frequently repeated concussions, the
animal must soon braak down. As it is, under the unnaiural
conditions of our artificially constructed roads, faulty shoeing,
hounng, and feeding, lamenesses of the feet constitute a large
proportion of the cases that fall under thecare of the practitioner.
It may be well at the outset to give a little consideration to the
feet of the horse, in order to learn to what detent they are
adapted to natural conditions. The feet of all mammals illustrate
how the soft and yielding tissues^are oomlnned with the rigid,
to adapt to conditions of the surface over which they are re-
quited to move. In the camivora, beneath the outer tough skin
covering the sole, there is the fatty cushion protective to the
bones and more delicate soft parts ; while the daws, nails, etc

616

COMPARATIVE PHYSIOLOGY.

in which the toes end, are not only weapons of offense and de-
fense, but protective against injury from contact with bard sur-
faces, as well as directly helpful in locomotion. These princ
pies are admirably exemplified in the foot of solipeds.

The foot of the horse may be udd to consist of terminal
bones incased in soft structures adapted to shield the animal
from the effects of excessive ooncussiou aad for nutrition, the

Fm. 4M.

Fts.ieo.

Fio. 4S9.— Longltadinat median aectlon of foot. 1. •ntorior extensor of phalngMi,
or extensor pedis; 8, lateral extensor, or extensor Bnftraginls; S^Miiroto of BMta-
earpo-phato^geal articulation; 4. large meUrarpal bone; S. snperacial flexor or
phaiangeii, or perforatus; 6, deep flexor, or nerforana; 7, sheath; 8, buna; B, SMa-
moid iM^t mT ergot and fatty cushion of fctlcck; 11. cmclal llmment; M, short
semmold ligament; 18, flrst phalanx; 14, bursa; 15, swsond phdanx; 18, navlcu-
fan-bone; IT. plantar cushion; 18, third ^u^x; 19, pUintar surface of hoof; SO,
ieaaltlve or keratogenoos membrane of third nhalanx. . „ >vi t _ -*

Fro. «».— Horiaontal section of horse's foot. 1, front or toe of hoof; 2. Uilcknesa of
wall; 8, Umims; 4. Insertion of extensor nedls; fcpe pedis; 8, navicular bone; 7,
winos of OS pedis; 8, lateral cartihwc; », flexor pedis tendon; 10, planUr cushion;
11, inflexion of wall or *' bar "; 19,liamy frog.

whole being incased in a protective covering whidh in a state
of nature is constantly being worn away and renewed. He
hoof is the homologue of the nails and claws of othermammals,
and so may be regarded as a modification of the eindermis;
and thus viewed, its structure is at once more readily under-
stood and more interesting. To speak from an anatomical
standpoint, the foot of the horse is. made up of the terminal

M^ — .. - . .. . -,. ^.^

Sense and de-
ath hardsur-
Theae princ
leds.

I; of terminal
Id the animal
nutrition, the

f.«».

naor of phalangMi,
8, cnwnk of meta-
mpcncial flexor of
h', 8, bniM; S, mm-
llniiient; U,iihort
lUkUnx; 19, DAvica-
miface of hoof; SO,

oof; 2. thickneM of
, navicaiar bone; 7,
10, plantar cushion;

licih in a state
renewed. 13ie
thermammals,
the eindermis;
readily under-
an anatomical
f the terminal

LOCOMOTION.

617

iiM I

Fia. 461.

Fia.4eS.

Via. 481.— Lower face of home'e foot, hoof being rpmoved. 1, heel; S, coronary ciirh-
Ion; 8, branch of pbuttar cnahion; 4, median lacuna; S, lamina of the bare; «,
velvet tlaaue of aole. . ...... _.,._. j, .j j

Fio. 408.— LatemI view of hone's foot after removal of hoof. 1, periopHc ring, divided
br a narrow groove from coronary coshion, S, which Is contlnnoos with plantar -
cnahion, 4, and Joins vascular lamina, 8, through medlnm of white cone.

phalanx, the navicular bone, and the lower part of the second
phalanx; certain ligaments entering into the articulations ; the

IPIS.46S.

Fra. 464.

Via. 461.— Hoof Jnst ranoved from foot; side view, a, imter snrfMe of perlople, or
ooronarv fhw-bimd. with s«ne hairs passing throogh; a', outer surface of same
S^iISl«??artorfoot; o^» aecUouTtooafetoew^ll to showjto thlcta^^
to ruuarter of hoof; from b to fWmt U ontSde (or InsldeV toe. itam e tod tte
ootside (or Inside) heel; «, ftoc; /, bevel, or amter margin of^wall for reception of
eoronaiT cushion; g, keraphyUa, or hoinjr tamina. ^ .^ , ^ . .

Fio. 464.— Hoof , with outer portion of wall removed to show Ita interior, a, a, peri-
oirie, or earonary frog-band; b, cavity to upper put of wall for corooaiy cnsh-
1M5 «, upper or innw surfiMie of "bar"; d, vertfcal section of wall; rf' mjm, at
he^r«. hSlaontal section <rf ditto; /', homy lamtaMS of '• b« "; /", ditto of wall;
', lateral aspeet.of a tamaa; e^JipJKr* toner •;?«• of ho™! ~lei.*^|2«^j

Uon of hor^lMBfauB with the sole {ihe " white line »); i, toeetev at middl
toe; k, upper or inner snrfkee of horny ftag; J, frop«Uy,; »•, aivity correspond-
ing to a CSich of the firog; », ditto, -'" ^ '

iiay; m, cbyhj
body of frog.

618

COMPARATIVE PHYSIOLOGY.

terminatioiis of tbe common extensor and tho perforans ten-
dons ; the lateral cartilages ; a certain amount of connective
and fatty tissue ; the hoof-secreting mechanism, together with
the blood-vessels, nerves, lymphatics, etc., essential for all parts.

The relative size and position of parts may be gathered from
fhe accompanying cuts. The lateral cartilages belong to the
class known as flbro^sartihige, acting, no doubt, as perfect
buffers ; and as springs must be of no small assistance in loco-
motion. , ^ ^. .

The homy matter of the foot (hoof) owes ite formation to
the cells of a tissue bearing various names in different regions,

6, cella iNim lower surface, or dead horn of aoie.

but consisting of a basis of fibrous tissue abounding in blood-
vessels and nerves. The vessels from their arrangement have
detennined the names given to tiie formative tissue, such as
viUosities, villi, velvety tissue, vascular laminee, etc. It can not,
however, be too well borne in mind that these structiires are
after all, only modified corium (Fig. 871).

Just as the epie rmis, witii its numerous hky^n, anaes from
a modification of cells in the lower hiyers, resting on the vascu-
lar villi of the corium, so the hoof owes ito origin to a nmilar
aouice Thus from the velvety tissue is formed the sole and
frog ; from the periopUo ring, the periople; and from tiie coro-
nary cushion, the wall (see figures).

rforans ten-
\ ootmective
>gether with
for all parts,
kthered from
elong to the
i, as perfect
moe in loco-
formation to
rent regiona,

tenal from n to a
■; e, 0, commciice-
, «, jateial Uumna;
1, body of frog; I,

r surface of loto;

ling in blood-
igement have
issue, such as
le. It can not,
structures are

ra, arises from
onthevascu-
in toasimilar
1 the sole and
from the coro-

LOCOMOTION.

619

The arrangement of the horn-tubes, the homy laminsa (Figs.
467, 468), and the horn-cells is admirably adapted to form a
somewhat yielding yet very resisting structure.

Fio. 467.-HariioataI Motion of Jnnction of w»ll with iole of hoof, o, wall with lU
hom-tabea; b,b, homy lamlnn projecting from wall: c. «, horn-tube* formed by
terminal villi of vaMular lamtnn, the horn lurroundlng them and occupying the
■pace* between the homy Umina conititnting the "white line"; a, homy aole
with ita tube*.

Regarded from a mechanical point of view, for speed a
quadruped requires rather long limbs, co set on a somewhat
rigid trunk as to allow of a long as well as a rapidly repeated
stride, without undue concussion to either of the more rigid

c* o d* <r df d

Fio. 468.— Horisontal wetlon of wall and homy and TaacnUir laminn to ahow Innetion
of latter and laminelto. o. Inner portion of wall with lamina arlaing from it; 6,
vaacubtf lamina; «, homy lamina of average length; c', <f, unniually short laml-
nie; c",^', bunlnella on the side* of the homy lamina; d, vascnla lamina passing
between two horny ditto; d*, vascular Uimlna passing between three horny temr-
na; <t" latemi iaminella; «,«, arteries of vasentar lamina which have been in-
jected.

cortical parts. In the horse the fore-limbs are not attached to
the trunk by osseous connections, but the animal may be said
to be slung between its fore-limbs, all connections with the
trunk being Iqr soft parts, as musdes, tendons, and ligaments.

)

620

COMPARATIVE PHYSIOLOGY.

i?%

The advantages of nuch an ar-
rangement, to an animal in whidi
a great deal of forward-pitching
movement occura, in breaking
flhocka are evident. The length-
ened metatarsals and phalanges
are accompanied by a very per-
fect bracing of joints by liga-
ments and tendons below, while'
the shoulder is strengthened and
bound to the trunk by numerous
muscles, so that the whole, in
neatness, strength, and other
qualities required in a fleet ani-
mal, is, especially when taken in
connection with the feet, an ex-
ample of marvelous adaptation
to conditions to be constantly
met, aided in the wild species by
natural selection, and in our do-
mestic varieties by artificial se-
lection.

An examination of Fig. 470
will show the several levers
(bones) and the muscles acting on
them in one main movement of
the fore-limb.

The hind-limbfl are in all gaits
of the animal its main propellers,
and these are in bony connection
with the pelvis.

Fio. 4M.— Bxterml mnacleaof right mtMior
limb (Chauvean). 1. 1, long •bdnctor of
•nn: 1', Ita hameral iMtrtiaB: S. raper-
■pinattt* ; 8, labspliuitiu; V, iU tenoon
of insertion ; 4, ahort abdncUir of arm;
S. bicepa; 0. anterior bracbialia; 7, large
extenaor of forearm; 8, abort ertenaor
of forearm; g, anconena; 11, aatmior «z-
tanaor of metacarpui; 11', ita tendon; 13,
aponearoaia, aeparatlng that mnacie from
anterior brachialia; iC obltqne extensor
of metacarpna ; 14, anterior extenaor of .. .^ ^ . •. *_

phatauSu 14', Its principal tendon; IB. amall tendinooa branch It tnnii^ato
uSeSy extenB<Jr; li latwal extenaor of phalange;; W, Ita t«>>doai 17^brom
Smd It receives frSncarpna; 18, externiil flexor of metaM^na; 19, If ""tacar-
oal lendon; 90. lu snpracarpal tendon; Sl,,alnar portion of perforana; », tMHion
of perforana; )». its carpainigament; M, ita re-enfonlrg i^alugeal aheath; ff.
tendon of the perforans.

i»

ich it fnniahet to
wndon: 17, flbrom
m; 19. Its metMW-
rfonuia; M, tendon
laacMl ibeBth; tb.

LOCOMOTION.

621

It will not be forsroiten that in jointa the inaheathing carti-
lages (BometimeB others more or len free), the «ynovial fluid,
etc., all tend to diminish friction and lessen
concussion.

We shall now describe the principal gaits
of the horse in a somewhat synoptical way.
In each gait we have to consider the
relative position of the four limbs, the
duration of each phase in the move-
ment, the length of the stride, its
rate, etc. Much that applies to
the horse holds good, of course,
of other quadrupeds.

In every gait each leg passes
from a condition of flexion to
one of extension, the degree be-
ing dependent on the speed or,
more correctly, the effort of the
animal to attain high speed or
the reverse. When the foot
rests upon the
ground before
the limb is re-
moved, it de-
scribes the arc
of a circle, or os-
cillates like a
pendulum so that
the flexors and
extensors are
used alternately
more and less;
though in all
movements it is
likely that nei-

(MT orniet»ciu]Mu''or eptoondylo-metaearpiM; M, ther set is whoUv
ai. tendon of obliqne ezteneor; 89, large met*- —^y

Via. 470.— Internal Mpect of left »•
terior limb (Ohraveiiu). 1. pro-
longing Mrtilage of Mapal* ; 9,
Inner anrfnce of ecapola; S, eal)-

■polL, -, _
ecapuUiris; 4, adductor of fore-
arm, or Dortioa of caput mag-
nnm; 7, large exieuor of fore-
arm, other portion of capot mag-
num; 8, middle extensor, or ca-
put medium: i>. hnmaralis ezter-
nue, or ehart flexor of forearm;
10, eoTMoJinmeialia; 11, npper
extremity of hnmeme; It, co-
raco-radlalia, or flefor braehii;
IS, \^'.rit extremity of humema;
14. bracnial flwcia ; IB, antenor
exteneor of metacarpus, or ex-
ten«or metacarpi magnua ; Id,
belly and aponeurotic termina-
tion of flexor braehii; 17, ulna;
18, ninaris acceaeoriue, or oblique
flexor of metatwrpue; 19, intur-
nal flexor
radios; 1
carpal-bi

i^piiiient ; «(, inleinal radtmentary metao^^ bone:
extensor tendi

relaxed.

The

flexor tendons of foot ; 94, saspensonr

amal rudimentary metacarpal bone; 98, „^,^ ♦i.,.««.,i.v.l«

ion «rf foot-; 97, metacanM-phalangeal more thoroUgWy

sheath; 18, lateaal cartilages of foot; 99, podophylUs. musCular move-
ments are studied the more complex, so far as the use of muscles
is oonoemed, are they found to be, a fact which is illustrated
when even a single muscle is weakened or paralysed.

032

COMPARATIVE PHVSIOIiOUY.

Walking. — In this ftait the body reflta on diagonal feet alter-
nately with the two of the same side ; the center of gravity
being shifted to ono side, then returned to its original position,
to be moved next to the opposite side. In drawing heavy loads
the btjdy is supported on three limbs. The rate of movement in
one to two metrus per second.

AnbU.— In this mode of progrearion, most common in the

Fic. *n.-Movemcnrt (oMillittlon) of an extended Wnd-le« (Oolln). The Wp-Jptat
deMsiibe* the arc of a cirole, A B C, while Uie foot la «i we groniid, the llnea A D,
B D, and C D lepreaeDtiog the ohanglng axle of the huM-ieK.

giraffe and camel tribe, occasional in ruminants and solipeds,
the body is supported by the two legs on the same side, as in the
walk, but the two opposite legs are elevated simultane rasly and
not separately. In horses this gait is often termed pcusing, and
is frequently very fast. Only two strokes of the feet are heard
in this gait.

In racking the hind-leg leaves the ground sooner than the
corresponding fore-leg, hence four strokes of the feet' are heard.

The Trot.— The diagonal feet act together, two strokes of the
feet being hoard at each complete step. In the fast trot there
is an interval in which all four feet are in the air. The hind-
feet strike the ground in front of the fore-feet. The speed in

nii iiii »

>nal feet alter-
iter of gravity
gfinal position,
ig heavy loada
f movement in

[>mmon in the

LOCOMOTION.

69»

In). The hip>Joliit
nmd, the IIdm A D,

ts and Bolipeds,
i Bide, as in the
ttane rasly and
Bdjpactng, and
I feet are heard

M>ner than the
feet' are heard.
> strokes of the
fast trot there
lir. The hind-
The speed in

the fast trot may reach from eight to twelve metres per sec-
ond.

Tht GMlop.— The gallop may be regarded as a aeries of

ria ««.-MoT«nenU of fim-UmlM of hone (Colin). While one fpre-le| li deMribIng
the movemenu floured abore the other acta a* a «npport. While the right fore-
foot deaoribea the mo gh, the toft ahonlder deacribea the arc a' V e*. owing tothe
Impulie from eztenalon of the hind lea. The eenter of grarlty la advanced frpga
m to n, the left leg In one complete atop oocnpring the aUt poaltlona Indicated at
abed4/.

jumps in which the hind-legs talce the gre«ter part, though as
in all gaits the fore-legs are not only supporters but propellers.

Fm. 47S.— Varione poaittona of the liml^ in the trot (Colin).

In the perfect gallop only two strokes of the feet are heard; in
the canter or slow gallop four, in the ordinary gallop three.
According as the one or other hind-leg is extended farthest
behind the body the gallop is termed right-handed or loft-
handed.

094

COMPAftATlVR PHY810I;! OT.

In the foatMt gallop the length of w '-^ ni»'v amount to tU
to seven metres, and the Bpeetl to twel « t. »«eo metres per

aeoond. In auoh a rapid gait the contact of the one bind foot
produces a sound lengthened by the rapid impact of the fellow-
foot. The same applies to the fore-feet, hence only two sounds,
while in the other varieties of this gait the interval between the
impacts is sufBoient to allow of three, or it may be four sounds.

The accompanying plate, constructed by tlio help of instan-
taneous photography, illustrates the different positions of a
horse in the gallop.

Sloping shoulder-blades and well-bent stiHe-jointa are gener-
ally racogniied as of great importance to an animal intended
for high speed, and these are commonly to be met with in the

Pig. «r4.-V*rioiia po^tioM in tiM trot (OoUn).

fleetest of horses, dogs, and other quadrupeds (Fig. 488). It
may be seen that such an arrangement permits of a length-
ened stride being taken with ease, tends to reduce concussion,
and adds to beauty of form. To this must, in part at all events,
be attributed the grace of form and fleetness of the race-horse
and the greyhound, not to mention wild animals.

A horse for heavy-draught purposes requires great muscular
power, which in turn implies a strongly developed osseous sys-
tem; and in order that this may be attained some of those
principles on which sjleed depends must be subordinated to
those involved in strength. As is well known, the cart-horse
and race-horse, the mastiff and the greyhound, are opposites in
build and capacity for speed. However, between these extreme
forms there are many others of an intermediate character, as
the hunter, roadster, etc. When f unous race-horses are studied,

•.mount to six
;u metres per
one b ind foot
of ihe fellow-
y two sound*,
\ between the
) four sounds,
elp of instan-
ositlons of •

nts are gener-
mal intended
et with in the

mg. 4B2). It
I of A length-
toe concussion,
t at all events,
the raoe-horse

preat muscular
ed osseous sys-
lome of those
ibordinated to
the cart-horse
re opposites in
these extreme
e character, as
Bes are studied,

626

COMPABATIVE PHYSIOLOGY.

whUe the form of the animal generally agrees with what would
have been expected on mechanical principles it is a fact that
some of the fleetest horses that have ever run on the course have
not in all respects heen built in conformity with them. But
it is to be remembered that a vital mechanism differs from all
others in that the whole consists of parts dependent not only as
one portion of any machine is on the other, but that every part
is energized and directed by a governing nervous system ; that
every cell is being in a sense constantly renewed, so that the
comparison between any ordinary mechanism and the body of a
living animal holds only to a limited extent. Moreover, apart
from peculiarities in the muscles of animals, to which atten-
tion has been drawn (page 206), it is well to bear in mind that not
only every animal, but every tissue has its own functional indi-
viduality ; and to this especially (as exemplified in the most im-
portant of all the tissues, the nervous) must we attribute the
undoubted fact that the speed, endurar:oe, etc., of animals can
not be explained on mechanical principles alone— a truth to
which too little attention has hitherto been drawn. These
principles have, however, been unconsciously recognized prac-
tically, hence the great attention paid by breeders to using ani-
mals for stock purposes that have actually shown merit by their
performances.

Svolatioa.— It is noteworthy that with almost all quadru-
peds the gdlop is the natural method for rapid propulsion. In
all animals, either bred by man to attain great speed, as the
race-horse and greyhound, or those that have become so by the
process of natural selection, the entire conformation of the
body has been modified in hsomony with the changes that have
taken place in the l^fs and feet. This is seen in the greyhound
among domestic animals, and in the wild deer of the plain and
forest. Such instances illtistrate not only the principle of
natural selection as a whole, but the subordinate one of corre-
lated growth.

Any one observing the modes of locomotion of quadrupeds,
especially hoi-ses and dogs, will perceive the advantages of the
four-legged arrangement Not only is there a variety of modes
of progression, as walking, trotting, galloping, centering, the
alternations of which permit of rest to certain groups of mus-
cles, with their corresponding nervous connections, etc., but on
occasion some of these animals can progress Mrly well with
three legs. Sometimes it may also be noticed that a honn that

Ii what would
is a fact that
le course have
h them. But
ffers from all
at not only as
lat every part

system; that
1, so that the
[the body of a
oreover, apart

which atten-
mind that not
motional indi-
1 the most im-

attribute the
I animals can
ae — a truth to
rawn. These
cognized prao-
B to using ani-
merit by their

st all quadni-
ropulsion. In
; speed, as the
x>me so by the
nation of the
nges that have
the greyhound
I (he plain and
e principle of
e one of corre-

of quadrupeds,
antages of the
uiety of modes
cantering, the
groups of muR-
ns, etc., but on
urly wiell with
lat a honw that

LOCOMOTION.

627

prefers one gait, as pacing, for his easy, slow movements, will
break into a trot when pushed to a higher rate of speed.

Trotting can not be considered the natural gait for high
speed in the horse, yet, by a process of "artificial selection"
(by man) from horses that have shown capacity for great speed
by this mode of progression, strains of racers have been bred,
showing that even an acquired mode of locomotion may be
hereditary; while that galloping is the more natural mode of
locomotion of the horse is evident, among other things, by the
tendency of even the best trotting racers to break into a gallop
when unduly piished — an instAuce also of an hereditary tend^
ency of more ancient origin prevailing over one more recent.

The bipedal modes of progression of birds are naturally very
like those of man.

*. W*W . *»M*» < W - W. ' ■ * f' *^*f •'tf!* . ' * '^''*

■iMiii

INDEX.

Abductor or sixth nerre, 682.

Abnormal urine, 421.

Accelerator norres of heart, 268.

Accommodation of eye, 632.

Action of mammalian heart, 222.

Affections of retina, 640.

Afferent fibers, 683.

After-images, etc, 643.

Alimentary oanal of vertebrate,
831.

Allautois, 77.

Allantoic oavitj, 80.

Albumins, 146.
derived, 146.

Alterations in siie of pupil, 688.

Amble, «24.

Amnion, 78.

Amoeba, 18.

Amylolytic action of saliva, 297.

Animal body, 28.

Animal foods (table), 277.

Animal heat, 446.

Animals deprived of cerebrum, 482.

Anaemia, 117.

Anomalies of refraction, 686.

Apnoea, 396.

Apparatus used for stimulation of
muscle, 179.
for transmission of muscular move-
ments by tambours, 182.

Asphjrxia, respiration and circulation
fai,899.

Anditoijr ossMm, 6S9.

Auditory impulses, 666.
sensations, etc., 667.
Automatism, nervous system, 211.
Automatic functicms of spinal cord,
476.

Bacteria, 18.

Barking, 402.

Bawling, neighing, braying, 408.

Beat of the heart and its modifica-.

tions, 248.
Bell-animalcule, 21.
Bile, digestive action of, 808 .

salts, 802.

piftments, 802.
Biology, general, 1.

table, 4.
Blastodermic vesicle, 78.
Blood, 164.

cells, 168.

cells, decline, and death, 160.

chemical composition of, 160.

pressure, 22S-227.

flow, 227.
Bone, 604.
Botany, 4.
Brain, 481.

Capillaries, 264.
Carbon-dioiide of blood, 880.
Carbohydrates, 146.
Cardiac movements, 281.
tounds, 284.

';LiHlHfM^''l

680

COMPARATIVE PHYSIOLOGY.

Cartilage, 609.

Causes of the sounds of the heart, 236.

CeU, 6.

the male, 61.
Cellulose, 9.
Cerabellum, a08.
Cerebral cortex, 407.
Cerebro-spinal system of nerves, 680.
and sympathetio systems, relations
of, 688.
Certain tissues, 608.
Characteristics of proteids, general,
144.
of blood-flow, 226.
of secretion of different glands,
298.
Changes in muscle during contrac-
tion, 189.
produced in food in alimentary

canal, 864.
in circulation after birth, 129.
Chemical constitution of animal body,
142.
changes in muscle, 189.
composition of blood, 160.
Chemistry of unicellular plants, 9.
Chondrin, 146.
Chorion, 19.
Chronographs, 1*76.
Ciliary movements, 179.
(ophthalmic lenticular), ganglion,
684.
Circulation of blood, 214.
in mammal, 219,
under microacopc, 384.
in brain, 600.
Circumstances influencing character
of muscular anrt nervous activ-
ity, 199.
Classification of (inlmal kingdon:, 34.

of proteids, 146.
CI' "cal and pathological n blood,

167.
Coai^uUtion of blood, 168.

Coitus, 129.
Color-vision, 648.
Comparative re blood, 164, 172.
unstriped muscle, 202.
blood-pressure, 224.
cardiac pulsation, 240.
ciivulation, 244, 267.
digesUon, 280, 310, 867.
metabolism, 486.
diet, 438.

digestive juices, 298.
digestive organs, 324, 887.
bile, 803.

feeding experiments, 441.
fats and carbohydrates, 442.
animal heat, 446.
spinal cord, 477.
cerebral convolutions, 486.
muscular sense, 624.

vision, 686-561.

bearing, 568.

senses of smell and taste, 674, 678.

voice, 598.

locomotion, 614.

swallowing, 386.

vomiting, 840.

movements of lymph, 844.

respiration, 376, 898.

hiemoglobin, .389.

respiratory movements, 402.

respiration by skin, 412.

perspiration, 413.

expulsion of urine, 426.
Comparison of inspired and expired

air, 382.
Composition of serum, 181.

of corpuscles, 162.

of milk, 276.
Conclusions re unicellular plants, 10.

protoooccus, 12.

unicellular animals, 16.

nervous system, 212.

heart, 267.

salivary secretion, 314.

1, 164, 172.

202.

240.

», 867.

18.

24, 837.

ts, 441.
rates, 442.

ang, 486.
S4.

id taste, 674, 678.

iph, 844.
198.

Dents, 403.
n, 412.

e, 426.

)ired and expired

un, 181.

ellular plants, 10.

Is, 16.
212.

1, 314.

"I^

INDEX.

681

Condiments, 278.
('onnective tissue, 608.
Contractile tissues, 171.
('onnection of one part of brain witli

another, 491.
Construction of fat, 482.
Conditions under wliicii gases exist

in blond, 884.
Co-ordination of two eyes in vision,

644.
Cougliing, 401.
Corpuscles, 166.

action of the, 227.
Corpora quadrigemina, 606.
Corpus striatum and optic thalamus,

604.
Cranial nerves, 6S0.
Crying, 402.

Decussation, 471.

Defecation, 338.

Deglutition, 338.

Dentition of domestic animals (table),

290-296.
Development of embryo, 96.

of vascular system in vertebrates,
108.

of urogenital system, 112.
Dextrin, 146.
Diet, 487-489.

effects of gelatin in, 441.

effects oJ 'ialts, water, etc., 443.
Digestion of food, 274.
Digestive juices, 297.

acaon of bile, 808.

organs, movements of, 882.
Dioptrics of vision, 681.
Discoidal )ilBoenta, 88.
DonicsticatvvJ animals, 47.
nyspncs'ft, J596.

Effects of gelatin in diet, 441
I Efferent nervo-fibers, 683.
Entrance and exit of air, 870.

Elasticity of muscle, 189.

Elastin, 146.

Elastic tissues, 604.

Electrical phenomena of nmsclef 191.

organs, 197.
Bmbryologioal re digestion, 279.

brata, 610.

vision, 628.
Embryo, development of, 95.
Embryology, applied to evolution, 45.
Embryonic membrane of birds, 74.
Endocardiac pressure, 236.
Energy of animal oiaAy, 448.
Epiblast, 98.
Epithelium, 7.
Evolution, 42.

re reproduction, 98.

circulation, 268.

digestion, 368.

respiration, 404.

metabolism, 460.

spinal cord, 478.

brahi, 611.

vision, 66f^

hearing, fi71.

voice, 600.

iocomot'.on, 627.
Estimation of size, etc., of objects,

648.
Excretory function of skin, 411.
Excretion of perspiration, 412.

by the kidney, 416.
Experimental facts, 186.

)•« nervous system, 210.

digijstion. 806.

spinal nerves, 680.
Eustachian tube, 662.
Eye, accommodation of, 682.

optical imperfections of, 686.

)>roteotive mechanisms of, 649.

Fficial nerve, 681.

and laryngeal respiration, 874.
Pat, construction of, 482.

■•■I

682

OOMPARATIVE PHYSIOLOGY.

Fats, 145.

and carbohydrates, 443.
Fatigjie, 199.

Feeding experiments, 489.
Features of an arterial pulse tracing,

242.
Fertilization of oTum, 68.
Fibrin, 140, 164.
Faeces, 852.
FcBtal circulation, 120.

later stages of, 109.

membranes of mammals, 78.
Food, digestion of, 274.

stuffs, 274.
Foods, animal, Uble of, 277.

vegetable, table of, 277.
Foreign gases in respiration, 891.
Forced movements, 484.
Fossil and existing spedett, 46.
Fresh-vater polyps, 28.
Fungi, 10.

Functional variations, 204.
Functions of cerebral convolutions,
480.

of other portions of brain, 504.

Gastrula, 68.

Gastric juice, $".''9.

Gelatin, 140

Geographioal distribution, 40.

Globulins, 140.

Glosso-pbaryngeal or ninth nerve,

080.
Glycogen, 428.
uses of, 429.
Glycotiholic acid, 808.
Gout, 189.
Graafian follicle, 08.
Graphic method and study of muscle

physiology, 176.
Gustatory fibers, 082.

Heemoglobin and its derivatives, 380.
Hearing, 007.

Heart, 2<')1.

of various animals, 240, 246.

beat in cold-blooded animals, 200.

causation of beat of, 203.

influence of vagus nerve on, 808.

accelerator nerves of, 208.

in relation to blood-pressure, 260.
Hen's egg, 69.
Hiccough, 402.
History of blood-cells, 108.
Hydra, 26.
Hypoblast, 98.
Hypertrophy, 265.
Hypnotism, 002.
Hypoglossal or twelfth nerve, 088.

Impulse of heart, 282.
Influence of blood-supply, 199.

of temperature, 801.

of vagus nerve upon heart, 808.

of condition of blood in restpira-
tion, 898.

of respiration on circulation, 896.

of nervous 'system on metabolism,
458.
Inhibition of reflexes, 469.
Inorganic food-stuffs, 144, 274.
Inosit, 140.
Inorganic salts, 420.
Instincts, 48.
Investigation of heart -beat from

within, 288.
Intestinal movements, 887.
Irritability of muscle and nerve, 170.

Juices, digestive, 897.

Keratin, '140.

Lactose, 146.

Law of periodidty or rhythm in na-
ture, 87.

of habit, 41, 405.
of rhythm, 269.

'■M

, 246, 246.
id animalB, 2D0.
>f, 263.

nerve on, 868.
of, 268.
l-preBBure, 260.

8, 168.

rth nerve, 688.

(2.

apply, 199.

01.

ion heart, 268.

blood In respira-

drculation, 896.
a on metabolism,

sa, 469.
b, 144, 274.

heart -beat from

Its, 887.

le and nerve, 176.

»7.

or rhythm in na-

INDEX.

688

lesW'^frS*'**^

LawB of retinal Btimulation, 641.

Laughing, 401.

Living thingB, 3.

Living and Kfelcss matter, 82.

Lymphatic Byatem, 842.

Lymph and chyle, 848.

Locomotion, 610.

MaltoBe, 146.

Mammalian heart, 216, 222.
Man's place In animal kingdom, 86.
MedulU oblongata, 609.
Membrana tympani, 668.
MesobUst, 98.
MetadiBooidal placenta, 84.
Metabolism, 87, 428.

of Uver, 428.

of spleen, 429.

Influence of nervous system on,
462.

summary of, 468.
Metazoa, 6, 68.
Milk, oompooition of, 876.

sugar, 276.
Mimicry, 46.
Molds, 16.
Morphology of unicellular pUnts, 9.

of protoooGcus, 18.

of unicellular animals, 18.

applied to evolution, 46.
Motor ooull nerve, 681.
Movements of digestive organs, 388.

stomaoh, 886.

lymph, 844.
Mudn, 14S.
Mucor rauoedo, 17.
Mallerian duct, 115.
Multicellular organisms, 28.
Muscular contractioii, 186.
Muscle tone, 189.
MuBOttlar work, 198.
Muscles of respiration, 878.

of middle ear, 661.
Muscular sense, 684.

Nasal or spheno-palatine ganglion,

684.
Nature of act of secretion, 818.
Nerve-cells, 209.

supply (voice), 696.
Nervous mechanlBm, 184.

system, 808.

inhibition, 812.

system In rekition to heart, 249.

supply — digestion, 888.

system in relation to respiration,
898.
Nitrogen of blood, 889.
Nitrogenous metabolites, 147.

crystalline bodies, 420.

equilibrium, 440.
Non-nitrogenous metabolites, 147.

organic bodies, 420.
Non-crystalline bocUes, 146.
Notoohord, 99.
Nucleus, 6.
Nucleolus, 6.
Nuclear divtelon, 6.
Nuclein, 146.
Nutrition of ovum, 188.

Ocular movements, 644.
(Estrum, 121.

Optical imperfectiona of the eye, 686.
Origin of forms of Ufe, 42.

of spermatoiodn, 61.

of fowl's egg, 70.
Organic evolution reconsidered, 187.

food-stuffs, 144-874.
Otic mnglitm, 686.
Ovulltion, 180.
Ovum, 66.

or^n and development of, 67.

changes in, 68.
Ozy-hsemoglobin, 886.

Paleontolcspr, 46.
Pancreatic luice, 806.
Paraeitic oiganisms, 16.

684

COMPARATIVE PHYSIOLOGY.

Parturition, 128.
Pathological r« food^stuffa, 147.
muscle, 197.
circulation, 244, 266.
bile, 818.

Htomach, 880, 887.
lymphatics, 852.
feces, 804.
V digestion, 850.

respiration, 879, 401, 408.
skin, 411.
urine, 428.

expulsion of urine, 426.
metabolism, 43S, 448.
temperature, 440,
spinal cord, 471.
brain, SOS, SO<t.
muscular sense, 624.
.vision, 686, 584.
hearing, 668.
spinal nerves, 680.
third and other nerves, 682, 686,

687, 688.
voice, 608.
Peculiar respiratory movements, 401.
Peptones, 146.
Pendulum myograph, 184.
Perspiration, excretion of, 412.
Periods of gestation, 127.
Pflttger's monograph, 181.
Physiology of onicelluUr planto, 10.
of proteooocus, 12.
unicellular animals, 18.
nerres, 196.
Physiological aspects of development,
119.
research and ratKming, 148.
Placenta, 82.
discoidal, 88.
metadisooidal, 84,
aonary, 80.
diffuse, 80.
polyootyledonary, 80.
Simple, 00.

Placenta multiple, 90.

microscopic structure ot, 90,

Pneumogastric nervo, 686.
Polyps, 28.

Pressure, endocardiac, 286.
Pressure sensations, 622.
Proteids, general characteristics of,
144.

of milk, 276.
Proteus animalcule, IS. I

Proteooocus, 11.
ProtoKoa, 6, 68.
Protective and excretory function of !

sUn, 408.
Protective mechanism of the eye, 649.
Protoplasm, 8.
Proximate principles, 144.
Pulse, 241.

the venous, 244.
Psychological aspects of vision, 643.

Quantity and distribution of blood,

168.
of blood, influence on blood-press-

ure, 261.
of air respired, 878.

Reflex functions of the spinal oord,

466.
Regulation of temperature, 447.
Relations of cercbro-spin^l and sym-
pathetic symptoms, 6^.
Relative value of food-stuffs, 444.

time occupied by cardiac cycle, 2S7.
Removal of digested products from

die alimentary canal, 841.
Reproduction, 61.
Retinal stimulation, laws of, 541.
Respiratory system, 866.

rhythm, 879.

sounds, 81.
Respiration, muscles o^, 878.

faidal and laryngeal, 874.

t>pes of, 875.

in blood, 888.

lure ot, 90.
rro, 086.

10, 2a6.
, 622.
haraoterUtics of,

IS.

retory function of
m of the eye, 049.
IS, 144.

Its of vision, 643.
ibution of blood,

le on blood-press-

IS.

r the spinal cord,

lerature, 447.
w-spin^l and sym-
boms, oiiB.
ood-stoffs, 444.
cardiac cycle, 287.
«d products from
r canal, 841.

I, laws of, 041.
I, 8eo.

es of, 878.
geal, 874.

iMMtfpMi

iHlliHMiii«iiiiii.«ikllt

INDEX.

685

Respiration in tissues, 891.

Respiration and circulation in as-
phyxia, 899.
in mammal, 406.
by skin, 412.

Rigor mortis, 208.

Rhythm, 87.
law of, 269.

Rudimentary organs, 46.

Halts, 144, 276.

inorganic, 420.
Saliva, 297.

amylolytic action of, 297.
Scar-tissue, 189.
Serum, composition of, 161.
Secretion .as a physiological process,

of salivary glands, 811.

by stomach, 816, 821.

of bile and pancreatic juice, 816.

nature of the act, 818.

of urine, 421.
Secretory fibers, 082.
Segmentationand subsequentchanges,

64.
Self-digestion of digestive organs,

828.
Sense organs, 81.
Sexual selection, 48.
Separation of muscle firom central

nervous system, 201.
Semioirottlar canals, function of, 484.
Sighing, 409.
Soiaes, general remarks, 616.

of smell and taste, 078.
Skin as an organ of sense, 020.
Smell, 078.
Sleep, 001.
Sobbing, 402.
SoUdity, 048.
Soap, 146.
Sneering, 409.
Special considerations re muscle, 208.

drcttlation, 966.

Special considerations re digestion,
869.

metabolism, 460.

spinal cord, 477.

brain, 610.

vision, 661.

hearing, 668.

voice, 600.
Speclflu gravity of urine, 419.
Spermatosoa, 61.
Sphygmograph, 248.
Spinal cord, general, 461.

reflex functions of, 466.

as a conductor of impulses, 469.

automatic functions of, 476.

nerves, 679.

accessory, 687. ■
Sporangia, 17.
Starches, 147.

Study of metabolic processes, 486.
Submaxillary ganglion, 086.
Succus entericus, 807.
Sugars, 146.
Summary of biology, 9.

of evolution, 60.

of reproduction, 93.

development of the embryo, 186.

physiological research, etc., 162.

blood, 169.

muscle and nerve, 200.

circulation, 969.

blood-cells, 108.

digestion, 864.

respiration, 400.

perspiration, 418.

urine, 426.

metaboUsm, 468.

voice, 601.
Synoptical r« spinal cord, 479.

brain, 018.

skin, 020.

vision, 664.

hearing, 072.
Swallowing, 880.

gftaaaBe mwM»»^<i«.

686

COMPARATl V'K H1Y8IOLOOT.

Taotlte ■enilbinty, 528.

Tmiibour of Marey, 188.

Taste, B7B.

Teeth, 284.
■tructure and arrangement of the,
286.

Temperature, regulation of, 447.

Tetanliing key of Du Bols-Rcymond,
181.

Tetauio contraction, 187.

Tbermnl ohaiigoa In contracting mus-
cle, 19S.
itensations, 522.

Tiasues, 8.

Trigeminus, irifacial or fifth nerre,
688.

Trochlear or fourth nerve, 682.

Trot, 624.

Types of respiration, 875.

Unicellular plants, 9.

animals, 18.

with differentiaticn of structure, 21.
Unstrlped muscle, 202.
Urea, 147.

Urine considered physically an4cliem-
Ically, 419.

abnormal, 421.

Urine, secretion of, 491.
cipulslon of, 424.

Variations In onrdiac pulKStion, 289.

of average temperature, 446.
Vaso-motor nerves, 262.
Vegetfbln foods (Ubie), 277.
VeUi'iUy of blood and blood-prcs«-

uru, and.
Venous pulse, 244.
Vision, 626.

dioptrics of, 581.

psyohologloal aspects, 048.
Visual sensations, 588.

angle,, 642.
Voice, 598.
Vomiting, 889.
Vorticella, 21.

Walking, 628. •
Water, 448.
Wolffian duct, 116.
Work of the heart, 288.

Yeast, 9.

cells, 10.
Yawning, 402.

Zofilogy, 4.

THK END.

•i

421.

tc puUation, 289.
rnturc, 446.
262.

ble), 277.
and blood-proH-

i«o(.s, 648.
i88.

288.

•f

EaTABUSHSD BY EDWARD L. YOUMANS.

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" This handsome volume does great credit to its antbor and pnUishwB.
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evewieadier and scientific practitioner of ▼Wftoary medlotae, and wifl
b«of& sarviceto,e^fWf g»a* rtock and «f*»»l*»»Wf.*»»«2SS!Iii'.™i
It win take ita stand atoMside of the popular fwatiwa of HilHudand
KobeHMm, and on idl pnr^ sdentf flc matters will lead them. Ktther of
tiieae woritt. together^th Dr. Bllllnga's, »« make alftiost a omnp^
ttbrsn dn veterinary medicine"— Ws Jowmal iff Ompofottu Mtikku

uria ; or, Pus in the Urine,

AND ITB TREATMENT: Comprising *hf Dtapw«|" •»tPS?^fP*
of Acute and Oftronto tTrethritis. Prbrtatitia^l^tis. aW^ ft^
with Espedal Referwice to their Loojd Twatment. By Dr. Ro|mn
tTirfiiAiw, Profcasor of QenHo-tlrinaiy Wseaaea to ^ Vienna PoH-
kHnik. Translated, by pettriailMW by Dr. Wamw B. PtAtr, W. B.
0.8. (Eng.), Baltimore 1 8mo. Olotii, tl.OO.

N«w York: D. APPLBTQN 4 CO., 1, 8, # 6 Bond Street

Women

H. MAONAtinH-

Hftetrioa, Royal

edioine in Ire-

1 vol., 12II10,

tvowed iniaaion
to end, and can
intended. The
iable ftool^ of
laona tor treat-
s only with his
is compelled to
7er, and should
nrtainfaar. The
are nothing to

:s to the

rioal Sketch of
Earliest Am* to
8araeon,6rad-
>er cl tiie Royal
rg, Praaria, ete.,

•andpabUchsra.
Dnal, State, dty,
1 be atndtod by
idiofaie, and win
inddeikler. ^ . .
of HUHardand
hem. BMier of
noat a oomplete
trative JMMtu

is and T^reatmeot
tiL aiid ^eHtia,
By Dr. Bomk*
Qm Vienna Poli-
3. Vtiint,T.%.

nkd Street

A TREATISE ON THE PRACTICE OP MEDI-

OINE, for the Use of Stadento and Practitioners.

By B0BEBT8 BABTHOIX)W, M. A., M. D., LL. D.,
Praftisor of Hateris UaiOm and Oenena Thenpaatiw in the Jeffenon Medical Col-
lege of PhUadelphia ; racently Pnkmot ot the Fractloe of Medicine and of
Ciinioal Medldne in tlu Medical College of Ohio, in Cindnnati, etc, etc

F^ tdition, wind and «iUar9*d. ito. Oktk, |6.00 ; i^t^ or ha^f rumia, W.OO.

The Mme qaalitiee and ohaiacterietioe whieh have rendeired Om airthoi'e >' Trea-
ties on Materia Medics and Thenpentiei " so aooepUdde are equally manifeat in (hia.
It ia dear, oondenaed, and aoounte. The whole worii in brought up on a level with,
and ineofpontee, the ktaat aoquiatOona of medioal adenoe, and may be depended on
to ooBtain the moat raoent information op to the date of publication.

" Probably the oiowniiut ligature of the
woA belbra ui, and that whioh will make
it a Uvw^ with praetitioBSis of medi-
cine, ia its admiaable teaebhuf on the treat-
nMnt of dlMsae. Dr. Bartnolow haa no
ayoHMtlur with^the modem sofaool of thet^
uwticiri niUBsta, but poaaoMS a whols-
aome belief in the value and eOoacgr of
raaaeditti. He doss not fiiU to indicate,
however, tliat ths power of lesMdiai is
limited, that medlossre fbw indeed, and
thatrontiae sod rMUess nMAGatiensn
dsofnons. But throuduMrt the entire
tiemse hi oonneetton with esoh makdy
an laid down well-deftnad methods sad
tnie prfaidplea of trastmsnt. It may ba
mM i^kjaitia* tiist this p«t of the wwk
rests apcm tiwrooghly adintillo and jBW^
tioa niindite orth^npsufies. and 6 ex-
seotsahiamBatsidyjiMmer. nofotkon
the piaetiee of msiBsine with imob we
a^ aoquMnted wiR guide ths pnetttiiNier
fi aB the dsttdltof traataianlao waU as
ths one of whidt we are writing."— il«Mr>

** The woifc aa a whdo is poooBsr, in
that it is stMMKl with Ae iaSftvUhu^
orte.andio^^nis

that ths «a » e ri s«es
is based tsnsl,tiiat

isnadstslM
wUehAiswwfc

BMBtSOftiM

oonTtnfjiKss,
sad that tluMdtaat tils seaatodoas srs
aatiaeatly soaaid. It is not aa eUbofBle
tMaAw,Bdthariait a BSBual, hot hate-
wsgr bstswsa; it msy be eensl d s r aa a
thoaoai^ nasAu, tw t we rthy , si

ticsl guide for the general priiotitioner."—

^ It may be said of so imalt a book on
so km a eubjset, that it eaa be only a
aort of eompendinm w e<i«h m t tm m . But
tUseiitteinnwiBnotbeJuat For,wUle
the author iamasrerha the stt of oonden-
■atimi, it wni be found thst no assmtial
pointa have been omitted. Mention ia

't at hast of vmy aneqdvocst synuH
in the namtion of the signa of dls-
esss, snd duraoleristie ay mpt o ma are
hold wen up in the IhiagionBd in every
cess."— OCiMfoiMM Lamed and CtimU.

•* Dr. Bartholowis known tobsa very
dsar and expBdt writer, and tai thia woriic,
whieh ws take to be hie qperisi lUh-worit,
we sie viry suis Us many friend and sd-
mfawMwfllaotliediRsppoiBted. Wecsn
not isy mm than this witiioat sttempt-
ing to lUlow up the detaQs of tiie ]dsa,
duch, of eonrss, wmdd be uaelssa ia s
briefbookHioMee. We ein only atU that
we ftel eodUent the verdiot of the pro-
ftsrioB will plaee Dr. Baitholow'a * Pta»-
tioe* among ths atsadard tsifr-lnxte of
tind^y."— OmAmmM Oittttrta 0mltt.

** Ths bBok ia marked Iv sa abseaoe of
sB dlsdOiarion <tf tiie latest,ibie-apun tiieo-
ri« of pdats la palliolo|Rr ; hg the dear-
Bsss wnh wUdi pdata ui dJsgwsis sre
ststsd; brthsooadssBeMaadMng^auity
ofitssenensas; bnrtheabqndsiMeofthe

salhor's thsrspenne rasonmss; sad by
tiiooopioMnMif^its iUustntioas.*'— OUs
.MMwal Miitrdte

MmToikt D.AnPLBT(»r ftCK>.,I,S,*6BoBd8tnsi

I ^1

nm " f » , i . i » i» H M>

«wf"'^''*w5l|^^

A PRACTICAL TREATISE ON MATERIA

MEDIOA AND THEBAPEDT108.

By BOBERTS BARTHOLOW, M. A., M.D.,
PioftMor of Matuia Mfldlw and Tbanpentfc* in tha Jaffanon Ma«UaaI Collage, ato.

JV»«<NMaM- Umm^, Mlmfti, mud iHafitt <p " Tkt S«m

Fmm Pbivao* to Firra Eomoir.
" The appMrMioe of the aizth decennial reviiion of the * United Statee
PharniMopoeis' has impoaed on me the neoeaaity of preparing a new edi-
tion of this treatiae. I have aooordingly adapted the work to the oflBelal
■tandard, and have abo given to the whde of it a caiefal revirion, inow-
poratiag the more recent improvements in the adence and art of then-
pentiea. Many additions have heen made, and parte have been rewritten.
These additions and changes have added about one hnndred pages to the
body of the worlc, and increased apace has been secared in some |riaceaby
the omission of the references. In the new material, as in the oM, prac-
tical atility has been the mling principle, but the sdentiflc aq>eots of
therapeutics have not been sobordlnated to a atiUtarian empiricism. In
the new matter, as in the old, careiU consideration has been given to the
physiological action of remedies, which is regarded as the true basis of all
real progress in. therapeutical sdence; but, at the same time, I have not
been unroindfU of the oontributiona made by properly conducted clinical
observatimia.**

" fib is wanknownaas aaalraaatnaaot
of nwdioal adnMse, an amita ofaaarvor, a
good writer, a skilled praotitioDer, and an
S^nkMis, bold, thooA aoinallinaa ledc-
lew inveadgatoTv V& vimaA book wUl
noaivA Ae eordid weloemawMeh It de-
aervea, and wkidi the hononUa poM«<m
that he haa won Mititlaa Um to OamMid
«v it. ... Dr. Baithok>w*a traatiae haa
tha tnarib-aitd^frrait meift it if^ofjb-
ducHii)r diet aa wall as druffa. . . . *B»
woik doaa not ignoie or dqmdirta tbt
vahia of the em^^rtoal flnta of a wall-
gmonded sad laUoiua pioftfakiBBl «po>
HoiM. bat, aa flw aa poaaibk, to baaaa
tlw therapentioa] action ot ramadias inon
th&rpliyaWScal^^'to'"— ^***'**^

"After looMiw thronrii the woric,
moat leadm* will agree im tlw anthor.
iriioaa Iflog tnlolnf diowB Itaelf on aveiy

pace. Dr. BaiUioloWilikaaBoAerexM-
riaiMd teaehei^Profeiaor voo SekmS, ot
Vieina'-iddta out tha moat iaportaat
pbyioloetoal and th^npeutkal aeBaBa at
r, and glvaa tliam in a abort and

Jt domtatio mannar. Having

Ibrmed bia own coMdndoDa, be i^vea
them to tiia sabUc, widiont entering eo
ftdlv aa Wood iMo the wtnariman te on
wh&b they are ftmnded.'*— A«M«MeMr
{London).

*« We may admit, however, that Dr.
Bartbriow haa. to sfn^ «t»Mnc«S:
AAy eoMd witii the difBeolttn of Ua
daMliMU«^ and hie bwdc baa alao edter i
maittateeommaidit. RiBkuS^yoii^-
nal. 9y thia wa meMi that tt^aa Oo
randta of Hu authoi^e own stedy aad
obanrveChm, faiataad of a tttiaogna of the
eonten^ag atatemanta at Ut

New Yerii: P. APPLITOK * 00., 1, », * • Bowl Btiaet.

vxmr-iwmirmmms^'-

[ATBRIA

Uofl] Collage, ato.

•United StatM
ring a new edi-
'k to the oiBeial
revirion, iaew-
td art of tliera-
been rewritten,
vd pages to tbe
iionie places by
n the oU, prao-
■tlflc aqpeota of
Binpirioimi. In
sen giren to the
troe basis of all
time, I have not
tndooted olinioal

Hks SBoOer exM-
isorTon8ehmfl,ot
a moat inmntaiit
ipautkdsenaBBof
bam in a alwit sad
nsimar. HaviBi^
idnaknia, ha n^vas
idioat anteiing so
IM (anariineDta on

bowavar, Oiat Dr.
MkaitaiK,aiieocaB-

AOenMaaor Us
boiAbasalBo other'

IllslMfgalyaiil-
I that It givas tto
>B own mdf and
raeatalaRMitfthe
■ of hb pradaeas*

' l?!t "■'

A Text-Book on Surgery.

GENERAL, OPERATIVE, AND MEOHANIQAL

By JOHN A. WYBTH, M. D.,

PralMaor of Boifferr In tba New Torfc Poljrellnie; Boifaiw to Ifonnt Stnai Hoapltal, etc.

Prioa, bMlBsa, HMSt a4gi% f74)0|

18.00 1 half

mtM.

SOLD BY SUBSCRIPTION ONLY.

This work, eonaiatiag of eeTen hnodred and aixty-nlna pagaa, and containing
aaran hundred and aavantjr-ona Uluatrations, of whioh about iUty ara oolond, ia one
of the moat baautiAd and unique, and at tba aama time one of tbe moat complete,
worka on general aurgery aver publiabed.

It ia printed in clear, laiige type, on a anparior quality of paper, and the book,
huge without being bulky, is hi a aluqpe to be eaaily handled. The iUuatiationa an
aieontedwith eapeofaa raftrance tothaaocuate anatomy of the puta repieaented;
the rebitiona of bonaa, muadaa, nerrea, and veaaela to ai^aoent atruotura, ; and Itaies
of taudsion are taidioated in operationa about the Jdnta and artlonlationa, tiiw es-
pfadning and Amplifying thefa- deaeriptlona in the text The colored illueintions
which depict tbe more important opraationa, eapaohdly with raftranoe to the lai^
arteiiea, conatitute a novel and very important flsature of the work.

The following brief aynopaia will 09nvey an idea of the plan of the work :

Aa a pNHntoMnr to «ke eaaMaialioa of tka vaitoas epatatitu tba aatbor thoroufiihr «•-
waiaa tt a^maU wai of pien^ac Oo ^flktaat aatbaptle lontaal draailBta, HntWM, Mtunw,
*^%!^^!!^'' tta nMuAaiirftr teada«lag. with uHuMtad laatraetmna aa io tba maDiMr <7
gphrfag baadataa la tte igripua fcma amployeJ to dMwaat paito of the bed;

tbaallar-tNaliBMt of aaaaa.

' etb* aad aMontaei; tottraniMrta aad thidr

Mthtala,
; the Die and
bMDoatada tod

wooda and tba maaBar «f oloalBf ttu
tba variooa wvffiaX hawaa

<nnaMM,palibaad woaada,banM aad acaUa, ganana^ aad
tberawbhr SSSmA aadOAr anmvriatatmtaaliRJraa.
AmpaiMiaaa, wttb ftiU aad ■EnrtT daMa of tba mauMr a

toMtoMttadaamptoyad, enaaUtatoaa ta^ertaat riMptarte tb , ^ -^._

UMt an Mnintad ty eeteed anraitaaa sMda Itan dliwa nada«8 of ftaaen WioM ootta

^*ba

ito daMB of tba maanar of paHbnataf tbam, aad tba dif-
MlB#MtaBt riMptarte tbeboi*. AH tbe priaelral opeia-

J TIM vHBHiOII _

(HyanlMiy, mabaetomy. aad

----- . aanaiy
oa tba eya,aar, aad Inr

daal^wttb ia tlitt~ll«bt of the

Jawi; toaMn about tbe aaelt, tbyreotomjr!

advaaaad awgieai

w a due tban of atteatiea, aa do dafgnaMca
aad I ■'-

rf Om apiaa aad aaSi^ha, aadaSSSaaat taaton aad fwwtba.

This woik, written by an aooompUshed amgeon of wide M^erience, and fUly
abreast <tf the higheat attrinmonta hi auri^ knowledge and aidence, presents to
tba student aad pmetitianer a meaaa of aoqnaiatiag hbnaelf with modem anigery
aaitistaaghtaad pracdoad by a master of the art, aad will nuUe hfan to prepan
hhnself Ibr the iiMelHgent peifonnanoe of msny operations, and to treat many aur-
gloal Mces with wUah he may feel he k not aaOciently itunilhu*.

New Tork: D. APPLETON ds 00., 1, 8, & 6 Bond Strwt.

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Cooley's CyclopaBdia of Practical Receipts,

And ColUteml Inform.tlon in the Art., M»nulactu«», Profwlmw, and
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u a ComprohentWe Supplement to the PhanMcopcela, and General Book
of Reference for the Manufacturer, Tradewnan, Amateur, and Headt of
FamlUea. fiWA tdUiott. ReTtaed and partly rewritten by Rictubd \.
Traoii. Profeawr of Chemlrtry and Toxicology in the Royal Veterinary
College. Complete in two T0lumeli,8T0.1,Wpagea. With Illuitratlona.
Price, 19.00.
"The neat chawoteriatlo of thi. work it Ito general uaeftilnew. '» ©^J"!*;*

SjafUrtCl S^rS^lJhry'^iSid^^W ? £l««.r whtTt pur.
It is a *f''"*™'^" ■•T™*^-^^ 'i_ _,«!, J. If it la more eomprehenrive than lU

The Chemistry of Common Life.

By the Iftte Pwfeeaor Jaii» F. W. JonnewH. A new edition, re»taed and
enlMnd. and brought down to the Preeent Thne, by A«raoa Hnun
cZTm. A.. O.on., author of "Food: it. Souro*-, Con.Ut»«tj and
Uiea." mnMrmted with Maps and numeroua BngratlngB on Wood, in
one ToL, ISmo, SM paKM. Cloth, priee, $«.0O.
SmAST or Co«WT..-The Air we Bmthe; theWUor we »»»«*?«»*;'

we cSSS, the Plant we Rear; the Bread we It^; the »?«'-• Cook;tteBv.

•n«e. we Inftiae; theSweete we Extract; the LUjuor. we 7«"»f »5 "»• "•^•.

i?todSie In; the Potaon. we Heleet; the Odoftwo Enjoy; *« ««»•"'*• ^.

i;ke;tScolo; we Admire; What we Breathe ««» Bn«dje f«r ; What, How, and

^YnlL'Srtd^T^SriSlS^^

s:^:;'2?eirKS«;^^

the e^r had the mtportunity of etmraltiog ^"W*?*? Jiff 'J"?' LVonThtedeSi.
author contemplated.

D. APPLETON & CO., PubUshert,

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leceipts,

Profvwiom, and
nomy. Deaigncd
ind General Book
ur, and Headt of
I by RioRABO V.
Royal Veterinary
mth IlluitratioM.

neM. In covering
B«nie to have been
. Thta very corn-
letter what it pur-

dgment for spedat
prehenaive than hi
imltaorittpanoee
llluatnitloua of the
• exoellertt."— iVSmi

dition, reviled and

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nga on Wood. In

re Drink; the Boil
we Cook; the B»v-
lent; the Nareoti
the Smell* we Dia-
r; What, How, and
er.

nplk^y of itt etyle,
>£wton'a"Chainla-
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LWore hbdatfh,
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